path: root/src/runtime/c/sg/sqlite3Btree.c

/******************************************************************************
** This file is an amalgamation of many separate C source files from SQLite
** version 3.8.11.1.  By combining all the individual C code files into this 
** single large file, the entire code can be compiled as a single translation
** unit.  This allows many compilers to do optimizations that would not be
** possible if the files were compiled separately.  Performance improvements
** of 5% or more are commonly seen when SQLite is compiled as a single
** translation unit.
**
** This file is all you need to compile SQLite.  To use SQLite in other
** programs, you need this file and the "sqliteBtree.h" header file that defines
** the programming interface to the SQLite library.  (If you do not have 
** the "sqliteBtree.h" header file at hand, you will find a copy embedded within
** the text of this file.  Search for "Begin file sqliteBtree.h" to find the start
** of the embedded sqliteBtree.h header file.)
*/
#define SQLITE_CORE 1
#define SQLITE_AMALGAMATION 1
#ifndef SQLITE_PRIVATE
# define SQLITE_PRIVATE static
#endif
/************** Begin file sqliteInt.h ***************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the header file used to customize the compiler options for MSVC.
** This should be done first so that it can successfully prevent spurious
** compiler warnings due to subsequent content in this file and other files
** that are included by this file.
*/
/************** Include msvc.h in the middle of sqliteInt.h ******************/
/************** Begin file msvc.h ********************************************/
/*
** 2015 January 12
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains code that is specific to MSVC.
*/
#ifndef _MSVC_H_
#define _MSVC_H_

#if defined(_MSC_VER)
#pragma warning(disable : 4054)
#pragma warning(disable : 4055)
#pragma warning(disable : 4100)
#pragma warning(disable : 4127)
#pragma warning(disable : 4130)
#pragma warning(disable : 4152)
#pragma warning(disable : 4189)
#pragma warning(disable : 4206)
#pragma warning(disable : 4210)
#pragma warning(disable : 4232)
#pragma warning(disable : 4244)
#pragma warning(disable : 4305)
#pragma warning(disable : 4306)
#pragma warning(disable : 4702)
#pragma warning(disable : 4706)
#endif /* defined(_MSC_VER) */

#endif /* _MSVC_H_ */

/************** End of msvc.h ************************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/*
** Special setup for VxWorks
*/
/************** Include vxworks.h in the middle of sqliteInt.h ***************/
/************** Begin file vxworks.h *****************************************/
/*
** 2015-03-02
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains code that is specific to Wind River's VxWorks
*/
#if defined(__RTP__) || defined(_WRS_KERNEL)
/* This is VxWorks.  Set up things specially for that OS
*/
#include <vxWorks.h>
#include <pthread.h>  /* amalgamator: dontcache */
#define OS_VXWORKS 1
#define SQLITE_OS_OTHER 0
#define SQLITE_HOMEGROWN_RECURSIVE_MUTEX 1
#define SQLITE_ENABLE_LOCKING_STYLE 0
#define HAVE_UTIME 1
#else
/* This is not VxWorks. */
#define OS_VXWORKS 0
#endif /* defined(_WRS_KERNEL) */

/************** End of vxworks.h *********************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/*
** These #defines should enable >2GB file support on POSIX if the
** underlying operating system supports it.  If the OS lacks
** large file support, or if the OS is windows, these should be no-ops.
**
** Ticket #2739:  The _LARGEFILE_SOURCE macro must appear before any
** system #includes.  Hence, this block of code must be the very first
** code in all source files.
**
** Large file support can be disabled using the -DSQLITE_DISABLE_LFS switch
** on the compiler command line.  This is necessary if you are compiling
** on a recent machine (ex: Red Hat 7.2) but you want your code to work
** on an older machine (ex: Red Hat 6.0).  If you compile on Red Hat 7.2
** without this option, LFS is enable.  But LFS does not exist in the kernel
** in Red Hat 6.0, so the code won't work.  Hence, for maximum binary
** portability you should omit LFS.
**
** The previous paragraph was written in 2005.  (This paragraph is written
** on 2008-11-28.) These days, all Linux kernels support large files, so
** you should probably leave LFS enabled.  But some embedded platforms might
** lack LFS in which case the SQLITE_DISABLE_LFS macro might still be useful.
**
** Similar is true for Mac OS X.  LFS is only supported on Mac OS X 9 and later.
*/
#ifndef SQLITE_DISABLE_LFS
# define _LARGE_FILE       1
# ifndef _FILE_OFFSET_BITS
#   define _FILE_OFFSET_BITS 64
# endif
# define _LARGEFILE_SOURCE 1
#endif

/* What version of GCC is being used.  0 means GCC is not being used */
#ifdef __GNUC__
# define GCC_VERSION (__GNUC__*1000000+__GNUC_MINOR__*1000+__GNUC_PATCHLEVEL__)
#else
# define GCC_VERSION 0
#endif

/* Needed for various definitions... */
#if defined(__GNUC__) && !defined(_GNU_SOURCE)
# define _GNU_SOURCE
#endif

#if defined(__OpenBSD__) && !defined(_BSD_SOURCE)
# define _BSD_SOURCE
#endif

/*
** For MinGW, check to see if we can include the header file containing its
** version information, among other things.  Normally, this internal MinGW
** header file would [only] be included automatically by other MinGW header
** files; however, the contained version information is now required by this
** header file to work around binary compatibility issues (see below) and
** this is the only known way to reliably obtain it.  This entire #if block
** would be completely unnecessary if there was any other way of detecting
** MinGW via their preprocessor (e.g. if they customized their GCC to define
** some MinGW-specific macros).  When compiling for MinGW, either the
** _HAVE_MINGW_H or _HAVE__MINGW_H (note the extra underscore) macro must be
** defined; otherwise, detection of conditions specific to MinGW will be
** disabled.
*/
#if defined(_HAVE_MINGW_H)
# include "mingw.h"
#elif defined(_HAVE__MINGW_H)
# include "_mingw.h"
#endif

/*
** For MinGW version 4.x (and higher), check to see if the _USE_32BIT_TIME_T
** define is required to maintain binary compatibility with the MSVC runtime
** library in use (e.g. for Windows XP).
*/
#if !defined(_USE_32BIT_TIME_T) && !defined(_USE_64BIT_TIME_T) && \
    defined(_WIN32) && !defined(_WIN64) && \
    defined(__MINGW_MAJOR_VERSION) && __MINGW_MAJOR_VERSION >= 4 && \
    defined(__MSVCRT__)
# define _USE_32BIT_TIME_T
#endif

#include "sqlite3Btree.h"

#include <stdio.h>
#include <stdarg.h>     /* Needed for the definition of va_list */

/*
** Provide the ability to override linkage features of the interface.
*/
#ifndef SQLITE_EXTERN
# define SQLITE_EXTERN extern
#endif
#ifndef SQLITE_API
# define SQLITE_API
#endif
#ifndef SQLITE_CDECL
# define SQLITE_CDECL
#endif
#ifndef SQLITE_STDCALL
# define SQLITE_STDCALL
#endif

/*
** CAPI3REF: Compile-Time Library Version Numbers
**
** ^(The [SQLITE_VERSION] C preprocessor macro in the sqlite3.h header
** evaluates to a string literal that is the SQLite version in the
** format "X.Y.Z" where X is the major version number (always 3 for
** SQLite3) and Y is the minor version number and Z is the release number.)^
** ^(The [SQLITE_VERSION_NUMBER] C preprocessor macro resolves to an integer
** with the value (X*1000000 + Y*1000 + Z) where X, Y, and Z are the same
** numbers used in [SQLITE_VERSION].)^
** The SQLITE_VERSION_NUMBER for any given release of SQLite will also
** be larger than the release from which it is derived.  Either Y will
** be held constant and Z will be incremented or else Y will be incremented
** and Z will be reset to zero.
**
** Since version 3.6.18, SQLite source code has been stored in the
** <a href="http://www.fossil-scm.org/">Fossil configuration management
** system</a>.  ^The SQLITE_SOURCE_ID macro evaluates to
** a string which identifies a particular check-in of SQLite
** within its configuration management system.  ^The SQLITE_SOURCE_ID
** string contains the date and time of the check-in (UTC) and an SHA1
** hash of the entire source tree.
**
** See also: [sqlite3_libversion()],
** [sqlite3_libversion_number()], [sqlite3_sourceid()],
** [sqlite_version()] and [sqlite_source_id()].
*/
#define SQLITE_VERSION        "3.8.11.1"
#define SQLITE_VERSION_NUMBER 3008011
#define SQLITE_SOURCE_ID      "2015-07-29 20:00:57 cf538e2783e468bbc25e7cb2a9ee64d3e0e80b2f"

/*
** CAPI3REF: Device Characteristics
**
** The xDeviceCharacteristics method of the [sqlite3_io_methods]
** object returns an integer which is a vector of these
** bit values expressing I/O characteristics of the mass storage
** device that holds the file that the [sqlite3_io_methods]
** refers to.
**
** The SQLITE_IOCAP_ATOMIC property means that all writes of
** any size are atomic.  The SQLITE_IOCAP_ATOMICnnn values
** mean that writes of blocks that are nnn bytes in size and
** are aligned to an address which is an integer multiple of
** nnn are atomic.  The SQLITE_IOCAP_SAFE_APPEND value means
** that when data is appended to a file, the data is appended
** first then the size of the file is extended, never the other
** way around.  The SQLITE_IOCAP_SEQUENTIAL property means that
** information is written to disk in the same order as calls
** to xWrite().  The SQLITE_IOCAP_POWERSAFE_OVERWRITE property means that
** after reboot following a crash or power loss, the only bytes in a
** file that were written at the application level might have changed
** and that adjacent bytes, even bytes within the same sector are
** guaranteed to be unchanged.  The SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN
** flag indicate that a file cannot be deleted when open.  The
** SQLITE_IOCAP_IMMUTABLE flag indicates that the file is on
** read-only media and cannot be changed even by processes with
** elevated privileges.
*/
#define SQLITE_IOCAP_ATOMIC                 0x00000001
#define SQLITE_IOCAP_ATOMIC512              0x00000002
#define SQLITE_IOCAP_ATOMIC1K               0x00000004
#define SQLITE_IOCAP_ATOMIC2K               0x00000008
#define SQLITE_IOCAP_ATOMIC4K               0x00000010
#define SQLITE_IOCAP_ATOMIC8K               0x00000020
#define SQLITE_IOCAP_ATOMIC16K              0x00000040
#define SQLITE_IOCAP_ATOMIC32K              0x00000080
#define SQLITE_IOCAP_ATOMIC64K              0x00000100
#define SQLITE_IOCAP_SAFE_APPEND            0x00000200
#define SQLITE_IOCAP_SEQUENTIAL             0x00000400
#define SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN  0x00000800
#define SQLITE_IOCAP_POWERSAFE_OVERWRITE    0x00001000
#define SQLITE_IOCAP_IMMUTABLE              0x00002000

/*
** CAPI3REF: File Locking Levels
**
** SQLite uses one of these integer values as the second
** argument to calls it makes to the xLock() and xUnlock() methods
** of an [sqlite3_io_methods] object.
*/
#define SQLITE_LOCK_NONE          0
#define SQLITE_LOCK_SHARED        1
#define SQLITE_LOCK_RESERVED      2
#define SQLITE_LOCK_PENDING       3
#define SQLITE_LOCK_EXCLUSIVE     4

/*
** CAPI3REF: Synchronization Type Flags
**
** When SQLite invokes the xSync() method of an
** [sqlite3_io_methods] object it uses a combination of
** these integer values as the second argument.
**
** When the SQLITE_SYNC_DATAONLY flag is used, it means that the
** sync operation only needs to flush data to mass storage.  Inode
** information need not be flushed. If the lower four bits of the flag
** equal SQLITE_SYNC_NORMAL, that means to use normal fsync() semantics.
** If the lower four bits equal SQLITE_SYNC_FULL, that means
** to use Mac OS X style fullsync instead of fsync().
**
** Do not confuse the SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL flags
** with the [PRAGMA synchronous]=NORMAL and [PRAGMA synchronous]=FULL
** settings.  The [synchronous pragma] determines when calls to the
** xSync VFS method occur and applies uniformly across all platforms.
** The SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL flags determine how
** energetic or rigorous or forceful the sync operations are and
** only make a difference on Mac OSX for the default SQLite code.
** (Third-party VFS implementations might also make the distinction
** between SQLITE_SYNC_NORMAL and SQLITE_SYNC_FULL, but among the
** operating systems natively supported by SQLite, only Mac OSX
** cares about the difference.)
*/
#define SQLITE_SYNC_NORMAL        0x00002
#define SQLITE_SYNC_FULL          0x00003
#define SQLITE_SYNC_DATAONLY      0x00010

/*
** CAPI3REF: OS Interface Open File Handle
**
** An [sqlite3_file] object represents an open file in the 
** [sqlite3_vfs | OS interface layer].  Individual OS interface
** implementations will
** want to subclass this object by appending additional fields
** for their own use.  The pMethods entry is a pointer to an
** [sqlite3_io_methods] object that defines methods for performing
** I/O operations on the open file.
*/
typedef struct sqlite3_file sqlite3_file;
struct sqlite3_file {
  const struct sqlite3_io_methods *pMethods;  /* Methods for an open file */
};

/*
** CAPI3REF: OS Interface File Virtual Methods Object
**
** Every file opened by the [sqlite3_vfs.xOpen] method populates an
** [sqlite3_file] object (or, more commonly, a subclass of the
** [sqlite3_file] object) with a pointer to an instance of this object.
** This object defines the methods used to perform various operations
** against the open file represented by the [sqlite3_file] object.
**
** If the [sqlite3_vfs.xOpen] method sets the sqlite3_file.pMethods element 
** to a non-NULL pointer, then the sqlite3_io_methods.xClose method
** may be invoked even if the [sqlite3_vfs.xOpen] reported that it failed.  The
** only way to prevent a call to xClose following a failed [sqlite3_vfs.xOpen]
** is for the [sqlite3_vfs.xOpen] to set the sqlite3_file.pMethods element
** to NULL.
**
** The flags argument to xSync may be one of [SQLITE_SYNC_NORMAL] or
** [SQLITE_SYNC_FULL].  The first choice is the normal fsync().
** The second choice is a Mac OS X style fullsync.  The [SQLITE_SYNC_DATAONLY]
** flag may be ORed in to indicate that only the data of the file
** and not its inode needs to be synced.
**
** The integer values to xLock() and xUnlock() are one of
** <ul>
** <li> [SQLITE_LOCK_NONE],
** <li> [SQLITE_LOCK_SHARED],
** <li> [SQLITE_LOCK_RESERVED],
** <li> [SQLITE_LOCK_PENDING], or
** <li> [SQLITE_LOCK_EXCLUSIVE].
** </ul>
** xLock() increases the lock. xUnlock() decreases the lock.
** The xCheckReservedLock() method checks whether any database connection,
** either in this process or in some other process, is holding a RESERVED,
** PENDING, or EXCLUSIVE lock on the file.  It returns true
** if such a lock exists and false otherwise.
**
** The xFileControl() method is a generic interface that allows custom
** VFS implementations to directly control an open file using the
** [sqlite3_file_control()] interface.  The second "op" argument is an
** integer opcode.  The third argument is a generic pointer intended to
** point to a structure that may contain arguments or space in which to
** write return values.  Potential uses for xFileControl() might be
** functions to enable blocking locks with timeouts, to change the
** locking strategy (for example to use dot-file locks), to inquire
** about the status of a lock, or to break stale locks.  The SQLite
** core reserves all opcodes less than 100 for its own use.
** A [file control opcodes | list of opcodes] less than 100 is available.
** Applications that define a custom xFileControl method should use opcodes
** greater than 100 to avoid conflicts.  VFS implementations should
** return [SQLITE_NOTFOUND] for file control opcodes that they do not
** recognize.
**
** The xSectorSize() method returns the sector size of the
** device that underlies the file.  The sector size is the
** minimum write that can be performed without disturbing
** other bytes in the file.  The xDeviceCharacteristics()
** method returns a bit vector describing behaviors of the
** underlying device:
**
** <ul>
** <li> [SQLITE_IOCAP_ATOMIC]
** <li> [SQLITE_IOCAP_ATOMIC512]
** <li> [SQLITE_IOCAP_ATOMIC1K]
** <li> [SQLITE_IOCAP_ATOMIC2K]
** <li> [SQLITE_IOCAP_ATOMIC4K]
** <li> [SQLITE_IOCAP_ATOMIC8K]
** <li> [SQLITE_IOCAP_ATOMIC16K]
** <li> [SQLITE_IOCAP_ATOMIC32K]
** <li> [SQLITE_IOCAP_ATOMIC64K]
** <li> [SQLITE_IOCAP_SAFE_APPEND]
** <li> [SQLITE_IOCAP_SEQUENTIAL]
** </ul>
**
** The SQLITE_IOCAP_ATOMIC property means that all writes of
** any size are atomic.  The SQLITE_IOCAP_ATOMICnnn values
** mean that writes of blocks that are nnn bytes in size and
** are aligned to an address which is an integer multiple of
** nnn are atomic.  The SQLITE_IOCAP_SAFE_APPEND value means
** that when data is appended to a file, the data is appended
** first then the size of the file is extended, never the other
** way around.  The SQLITE_IOCAP_SEQUENTIAL property means that
** information is written to disk in the same order as calls
** to xWrite().
**
** If xRead() returns SQLITE_IOERR_SHORT_READ it must also fill
** in the unread portions of the buffer with zeros.  A VFS that
** fails to zero-fill short reads might seem to work.  However,
** failure to zero-fill short reads will eventually lead to
** database corruption.
*/
typedef struct sqlite3_io_methods sqlite3_io_methods;
struct sqlite3_io_methods {
  int iVersion;
  int (*xClose)(sqlite3_file*);
  int (*xRead)(sqlite3_file*, void*, int iAmt, sqlite3_int64 iOfst);
  int (*xWrite)(sqlite3_file*, const void*, int iAmt, sqlite3_int64 iOfst);
  int (*xTruncate)(sqlite3_file*, sqlite3_int64 size);
  int (*xSync)(sqlite3_file*, int flags);
  int (*xFileSize)(sqlite3_file*, sqlite3_int64 *pSize);
  int (*xLock)(sqlite3_file*, int);
  int (*xUnlock)(sqlite3_file*, int);
  int (*xCheckReservedLock)(sqlite3_file*, int *pResOut);
  int (*xFileControl)(sqlite3_file*, int op, void *pArg);
  int (*xSectorSize)(sqlite3_file*);
  int (*xDeviceCharacteristics)(sqlite3_file*);
  /* Methods above are valid for version 1 */
  int (*xShmMap)(sqlite3_file*, int iPg, int pgsz, int, void volatile**);
  int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
  void (*xShmBarrier)(sqlite3_file*);
  int (*xShmUnmap)(sqlite3_file*, int deleteFlag);
  /* Methods above are valid for version 2 */
  int (*xFetch)(sqlite3_file*, sqlite3_int64 iOfst, int iAmt, void **pp);
  int (*xUnfetch)(sqlite3_file*, sqlite3_int64 iOfst, void *p);
  /* Methods above are valid for version 3 */
  /* Additional methods may be added in future releases */
};

/*
** CAPI3REF: Standard File Control Opcodes
** KEYWORDS: {file control opcodes} {file control opcode}
**
** These integer constants are opcodes for the xFileControl method
** of the [sqlite3_io_methods] object and for the [sqlite3_file_control()]
** interface.
**
** <ul>
** <li>[[SQLITE_FCNTL_LOCKSTATE]]
** The [SQLITE_FCNTL_LOCKSTATE] opcode is used for debugging.  This
** opcode causes the xFileControl method to write the current state of
** the lock (one of [SQLITE_LOCK_NONE], [SQLITE_LOCK_SHARED],
** [SQLITE_LOCK_RESERVED], [SQLITE_LOCK_PENDING], or [SQLITE_LOCK_EXCLUSIVE])
** into an integer that the pArg argument points to. This capability
** is used during testing and is only available when the SQLITE_TEST
** compile-time option is used.
**
** <li>[[SQLITE_FCNTL_SIZE_HINT]]
** The [SQLITE_FCNTL_SIZE_HINT] opcode is used by SQLite to give the VFS
** layer a hint of how large the database file will grow to be during the
** current transaction.  This hint is not guaranteed to be accurate but it
** is often close.  The underlying VFS might choose to preallocate database
** file space based on this hint in order to help writes to the database
** file run faster.
**
** <li>[[SQLITE_FCNTL_CHUNK_SIZE]]
** The [SQLITE_FCNTL_CHUNK_SIZE] opcode is used to request that the VFS
** extends and truncates the database file in chunks of a size specified
** by the user. The fourth argument to [sqlite3_file_control()] should 
** point to an integer (type int) containing the new chunk-size to use
** for the nominated database. Allocating database file space in large
** chunks (say 1MB at a time), may reduce file-system fragmentation and
** improve performance on some systems.
**
** <li>[[SQLITE_FCNTL_FILE_POINTER]]
** The [SQLITE_FCNTL_FILE_POINTER] opcode is used to obtain a pointer
** to the [sqlite3_file] object associated with a particular database
** connection.  See the [sqlite3_file_control()] documentation for
** additional information.
**
** <li>[[SQLITE_FCNTL_SYNC_OMITTED]]
** No longer in use.
**
** <li>[[SQLITE_FCNTL_SYNC]]
** The [SQLITE_FCNTL_SYNC] opcode is generated internally by SQLite and
** sent to the VFS immediately before the xSync method is invoked on a
** database file descriptor. Or, if the xSync method is not invoked 
** because the user has configured SQLite with 
** [PRAGMA synchronous | PRAGMA synchronous=OFF] it is invoked in place 
** of the xSync method. In most cases, the pointer argument passed with
** this file-control is NULL. However, if the database file is being synced
** as part of a multi-database commit, the argument points to a nul-terminated
** string containing the transactions master-journal file name. VFSes that 
** do not need this signal should silently ignore this opcode. Applications 
** should not call [sqlite3_file_control()] with this opcode as doing so may 
** disrupt the operation of the specialized VFSes that do require it.  
**
** <li>[[SQLITE_FCNTL_COMMIT_PHASETWO]]
** The [SQLITE_FCNTL_COMMIT_PHASETWO] opcode is generated internally by SQLite
** and sent to the VFS after a transaction has been committed immediately
** but before the database is unlocked. VFSes that do not need this signal
** should silently ignore this opcode. Applications should not call
** [sqlite3_file_control()] with this opcode as doing so may disrupt the 
** operation of the specialized VFSes that do require it.  
**
** <li>[[SQLITE_FCNTL_WIN32_AV_RETRY]]
** ^The [SQLITE_FCNTL_WIN32_AV_RETRY] opcode is used to configure automatic
** retry counts and intervals for certain disk I/O operations for the
** windows [VFS] in order to provide robustness in the presence of
** anti-virus programs.  By default, the windows VFS will retry file read,
** file write, and file delete operations up to 10 times, with a delay
** of 25 milliseconds before the first retry and with the delay increasing
** by an additional 25 milliseconds with each subsequent retry.  This
** opcode allows these two values (10 retries and 25 milliseconds of delay)
** to be adjusted.  The values are changed for all database connections
** within the same process.  The argument is a pointer to an array of two
** integers where the first integer i the new retry count and the second
** integer is the delay.  If either integer is negative, then the setting
** is not changed but instead the prior value of that setting is written
** into the array entry, allowing the current retry settings to be
** interrogated.  The zDbName parameter is ignored.
**
** <li>[[SQLITE_FCNTL_PERSIST_WAL]]
** ^The [SQLITE_FCNTL_PERSIST_WAL] opcode is used to set or query the
** persistent [WAL | Write Ahead Log] setting.  By default, the auxiliary
** write ahead log and shared memory files used for transaction control
** are automatically deleted when the latest connection to the database
** closes.  Setting persistent WAL mode causes those files to persist after
** close.  Persisting the files is useful when other processes that do not
** have write permission on the directory containing the database file want
** to read the database file, as the WAL and shared memory files must exist
** in order for the database to be readable.  The fourth parameter to
** [sqlite3_file_control()] for this opcode should be a pointer to an integer.
** That integer is 0 to disable persistent WAL mode or 1 to enable persistent
** WAL mode.  If the integer is -1, then it is overwritten with the current
** WAL persistence setting.
**
** <li>[[SQLITE_FCNTL_POWERSAFE_OVERWRITE]]
** ^The [SQLITE_FCNTL_POWERSAFE_OVERWRITE] opcode is used to set or query the
** persistent "powersafe-overwrite" or "PSOW" setting.  The PSOW setting
** determines the [SQLITE_IOCAP_POWERSAFE_OVERWRITE] bit of the
** xDeviceCharacteristics methods. The fourth parameter to
** [sqlite3_file_control()] for this opcode should be a pointer to an integer.
** That integer is 0 to disable zero-damage mode or 1 to enable zero-damage
** mode.  If the integer is -1, then it is overwritten with the current
** zero-damage mode setting.
**
** <li>[[SQLITE_FCNTL_OVERWRITE]]
** ^The [SQLITE_FCNTL_OVERWRITE] opcode is invoked by SQLite after opening
** a write transaction to indicate that, unless it is rolled back for some
** reason, the entire database file will be overwritten by the current 
** transaction. This is used by VACUUM operations.
**
** <li>[[SQLITE_FCNTL_VFSNAME]]
** ^The [SQLITE_FCNTL_VFSNAME] opcode can be used to obtain the names of
** all [VFSes] in the VFS stack.  The names are of all VFS shims and the
** final bottom-level VFS are written into memory obtained from 
** [sqlite3_malloc()] and the result is stored in the char* variable
** that the fourth parameter of [sqlite3_file_control()] points to.
** The caller is responsible for freeing the memory when done.  As with
** all file-control actions, there is no guarantee that this will actually
** do anything.  Callers should initialize the char* variable to a NULL
** pointer in case this file-control is not implemented.  This file-control
** is intended for diagnostic use only.
**
** <li>[[SQLITE_FCNTL_PRAGMA]]
** ^Whenever a [PRAGMA] statement is parsed, an [SQLITE_FCNTL_PRAGMA] 
** file control is sent to the open [sqlite3_file] object corresponding
** to the database file to which the pragma statement refers. ^The argument
** to the [SQLITE_FCNTL_PRAGMA] file control is an array of
** pointers to strings (char**) in which the second element of the array
** is the name of the pragma and the third element is the argument to the
** pragma or NULL if the pragma has no argument.  ^The handler for an
** [SQLITE_FCNTL_PRAGMA] file control can optionally make the first element
** of the char** argument point to a string obtained from [sqlite3_mprintf()]
** or the equivalent and that string will become the result of the pragma or
** the error message if the pragma fails. ^If the
** [SQLITE_FCNTL_PRAGMA] file control returns [SQLITE_NOTFOUND], then normal 
** [PRAGMA] processing continues.  ^If the [SQLITE_FCNTL_PRAGMA]
** file control returns [SQLITE_OK], then the parser assumes that the
** VFS has handled the PRAGMA itself and the parser generates a no-op
** prepared statement if result string is NULL, or that returns a copy
** of the result string if the string is non-NULL.
** ^If the [SQLITE_FCNTL_PRAGMA] file control returns
** any result code other than [SQLITE_OK] or [SQLITE_NOTFOUND], that means
** that the VFS encountered an error while handling the [PRAGMA] and the
** compilation of the PRAGMA fails with an error.  ^The [SQLITE_FCNTL_PRAGMA]
** file control occurs at the beginning of pragma statement analysis and so
** it is able to override built-in [PRAGMA] statements.
**
** <li>[[SQLITE_FCNTL_BUSYHANDLER]]
** ^The [SQLITE_FCNTL_BUSYHANDLER]
** file-control may be invoked by SQLite on the database file handle
** shortly after it is opened in order to provide a custom VFS with access
** to the connections busy-handler callback. The argument is of type (void **)
** - an array of two (void *) values. The first (void *) actually points
** to a function of type (int (*)(void *)). In order to invoke the connections
** busy-handler, this function should be invoked with the second (void *) in
** the array as the only argument. If it returns non-zero, then the operation
** should be retried. If it returns zero, the custom VFS should abandon the
** current operation.
**
** <li>[[SQLITE_FCNTL_TEMPFILENAME]]
** ^Application can invoke the [SQLITE_FCNTL_TEMPFILENAME] file-control
** to have SQLite generate a
** temporary filename using the same algorithm that is followed to generate
** temporary filenames for TEMP tables and other internal uses.  The
** argument should be a char** which will be filled with the filename
** written into memory obtained from [sqlite3_malloc()].  The caller should
** invoke [sqlite3_free()] on the result to avoid a memory leak.
**
** <li>[[SQLITE_FCNTL_MMAP_SIZE]]
** The [SQLITE_FCNTL_MMAP_SIZE] file control is used to query or set the
** maximum number of bytes that will be used for memory-mapped I/O.
** The argument is a pointer to a value of type sqlite3_int64 that
** is an advisory maximum number of bytes in the file to memory map.  The
** pointer is overwritten with the old value.  The limit is not changed if
** the value originally pointed to is negative, and so the current limit 
** can be queried by passing in a pointer to a negative number.  This
** file-control is used internally to implement [PRAGMA mmap_size].
**
** <li>[[SQLITE_FCNTL_TRACE]]
** The [SQLITE_FCNTL_TRACE] file control provides advisory information
** to the VFS about what the higher layers of the SQLite stack are doing.
** This file control is used by some VFS activity tracing [shims].
** The argument is a zero-terminated string.  Higher layers in the
** SQLite stack may generate instances of this file control if
** the [SQLITE_USE_FCNTL_TRACE] compile-time option is enabled.
**
** <li>[[SQLITE_FCNTL_HAS_MOVED]]
** The [SQLITE_FCNTL_HAS_MOVED] file control interprets its argument as a
** pointer to an integer and it writes a boolean into that integer depending
** on whether or not the file has been renamed, moved, or deleted since it
** was first opened.
**
** <li>[[SQLITE_FCNTL_WIN32_SET_HANDLE]]
** The [SQLITE_FCNTL_WIN32_SET_HANDLE] opcode is used for debugging.  This
** opcode causes the xFileControl method to swap the file handle with the one
** pointed to by the pArg argument.  This capability is used during testing
** and only needs to be supported when SQLITE_TEST is defined.
**
** <li>[[SQLITE_FCNTL_WAL_BLOCK]]
** The [SQLITE_FCNTL_WAL_BLOCK] is a signal to the VFS layer that it might
** be advantageous to block on the next WAL lock if the lock is not immediately
** available.  The WAL subsystem issues this signal during rare
** circumstances in order to fix a problem with priority inversion.
** Applications should <em>not</em> use this file-control.
**
** <li>[[SQLITE_FCNTL_ZIPVFS]]
** The [SQLITE_FCNTL_ZIPVFS] opcode is implemented by zipvfs only. All other
** VFS should return SQLITE_NOTFOUND for this opcode.
**
** <li>[[SQLITE_FCNTL_RBU]]
** The [SQLITE_FCNTL_RBU] opcode is implemented by the special VFS used by
** the RBU extension only.  All other VFS should return SQLITE_NOTFOUND for
** this opcode.  
** </ul>
*/
#define SQLITE_FCNTL_LOCKSTATE               1
#define SQLITE_FCNTL_GET_LOCKPROXYFILE       2
#define SQLITE_FCNTL_SET_LOCKPROXYFILE       3
#define SQLITE_FCNTL_LAST_ERRNO              4
#define SQLITE_FCNTL_SIZE_HINT               5
#define SQLITE_FCNTL_CHUNK_SIZE              6
#define SQLITE_FCNTL_FILE_POINTER            7
#define SQLITE_FCNTL_SYNC_OMITTED            8
#define SQLITE_FCNTL_WIN32_AV_RETRY          9
#define SQLITE_FCNTL_PERSIST_WAL            10
#define SQLITE_FCNTL_OVERWRITE              11
#define SQLITE_FCNTL_VFSNAME                12
#define SQLITE_FCNTL_POWERSAFE_OVERWRITE    13
#define SQLITE_FCNTL_PRAGMA                 14
#define SQLITE_FCNTL_BUSYHANDLER            15
#define SQLITE_FCNTL_TEMPFILENAME           16
#define SQLITE_FCNTL_MMAP_SIZE              18
#define SQLITE_FCNTL_TRACE                  19
#define SQLITE_FCNTL_HAS_MOVED              20
#define SQLITE_FCNTL_SYNC                   21
#define SQLITE_FCNTL_COMMIT_PHASETWO        22
#define SQLITE_FCNTL_WIN32_SET_HANDLE       23
#define SQLITE_FCNTL_WAL_BLOCK              24
#define SQLITE_FCNTL_ZIPVFS                 25
#define SQLITE_FCNTL_RBU                    26

/*
** CAPI3REF: Mutex Handle
**
** The mutex module within SQLite defines [sqlite3_mutex] to be an
** abstract type for a mutex object.  The SQLite core never looks
** at the internal representation of an [sqlite3_mutex].  It only
** deals with pointers to the [sqlite3_mutex] object.
**
** Mutexes are created using [sqlite3_mutex_alloc()].
*/
typedef struct sqlite3_mutex sqlite3_mutex;

/*
** CAPI3REF: OS Interface Object
**
** An instance of the sqlite3_vfs object defines the interface between
** the SQLite core and the underlying operating system.  The "vfs"
** in the name of the object stands for "virtual file system".  See
** the [VFS | VFS documentation] for further information.
**
** The value of the iVersion field is initially 1 but may be larger in
** future versions of SQLite.  Additional fields may be appended to this
** object when the iVersion value is increased.  Note that the structure
** of the sqlite3_vfs object changes in the transaction between
** SQLite version 3.5.9 and 3.6.0 and yet the iVersion field was not
** modified.
**
** The szOsFile field is the size of the subclassed [sqlite3_file]
** structure used by this VFS.  mxPathname is the maximum length of
** a pathname in this VFS.
**
** Registered sqlite3_vfs objects are kept on a linked list formed by
** the pNext pointer.  The [sqlite3_vfs_register()] interface manages
** this list in a thread-safe way.  The [sqlite3_vfs_find()] interface
** searches the list.  Neither the application code nor the VFS
** implementation should use the pNext pointer.
**
** The pNext field is the only field in the sqlite3_vfs
** structure that SQLite will ever modify.  SQLite will only access
** or modify this field while holding a particular static mutex.
** The application should never modify anything within the sqlite3_vfs
** object once the object has been registered.
**
** The zName field holds the name of the VFS module.  The name must
** be unique across all VFS modules.
**
** [[sqlite3_vfs.xOpen]]
** ^SQLite guarantees that the zFilename parameter to xOpen
** is either a NULL pointer or string obtained
** from xFullPathname() with an optional suffix added.
** ^If a suffix is added to the zFilename parameter, it will
** consist of a single "-" character followed by no more than
** 11 alphanumeric and/or "-" characters.
** ^SQLite further guarantees that
** the string will be valid and unchanged until xClose() is
** called. Because of the previous sentence,
** the [sqlite3_file] can safely store a pointer to the
** filename if it needs to remember the filename for some reason.
** If the zFilename parameter to xOpen is a NULL pointer then xOpen
** must invent its own temporary name for the file.  ^Whenever the 
** xFilename parameter is NULL it will also be the case that the
** flags parameter will include [SQLITE_OPEN_DELETEONCLOSE].
**
** The flags argument to xOpen() includes all bits set in
** the flags argument to [sqlite3_open_v2()].  Or if [sqlite3_open()]
** or [sqlite3_open16()] is used, then flags includes at least
** [SQLITE_OPEN_READWRITE] | [SQLITE_OPEN_CREATE]. 
** If xOpen() opens a file read-only then it sets *pOutFlags to
** include [SQLITE_OPEN_READONLY].  Other bits in *pOutFlags may be set.
**
** ^(SQLite will also add one of the following flags to the xOpen()
** call, depending on the object being opened:
**
** <ul>
** <li>  [SQLITE_OPEN_MAIN_DB]
** <li>  [SQLITE_OPEN_MAIN_JOURNAL]
** <li>  [SQLITE_OPEN_TEMP_DB]
** <li>  [SQLITE_OPEN_TEMP_JOURNAL]
** <li>  [SQLITE_OPEN_TRANSIENT_DB]
** <li>  [SQLITE_OPEN_SUBJOURNAL]
** <li>  [SQLITE_OPEN_MASTER_JOURNAL]
** <li>  [SQLITE_OPEN_WAL]
** </ul>)^
**
** The file I/O implementation can use the object type flags to
** change the way it deals with files.  For example, an application
** that does not care about crash recovery or rollback might make
** the open of a journal file a no-op.  Writes to this journal would
** also be no-ops, and any attempt to read the journal would return
** SQLITE_IOERR.  Or the implementation might recognize that a database
** file will be doing page-aligned sector reads and writes in a random
** order and set up its I/O subsystem accordingly.
**
** SQLite might also add one of the following flags to the xOpen method:
**
** <ul>
** <li> [SQLITE_OPEN_DELETEONCLOSE]
** <li> [SQLITE_OPEN_EXCLUSIVE]
** </ul>
**
** The [SQLITE_OPEN_DELETEONCLOSE] flag means the file should be
** deleted when it is closed.  ^The [SQLITE_OPEN_DELETEONCLOSE]
** will be set for TEMP databases and their journals, transient
** databases, and subjournals.
**
** ^The [SQLITE_OPEN_EXCLUSIVE] flag is always used in conjunction
** with the [SQLITE_OPEN_CREATE] flag, which are both directly
** analogous to the O_EXCL and O_CREAT flags of the POSIX open()
** API.  The SQLITE_OPEN_EXCLUSIVE flag, when paired with the 
** SQLITE_OPEN_CREATE, is used to indicate that file should always
** be created, and that it is an error if it already exists.
** It is <i>not</i> used to indicate the file should be opened 
** for exclusive access.
**
** ^At least szOsFile bytes of memory are allocated by SQLite
** to hold the  [sqlite3_file] structure passed as the third
** argument to xOpen.  The xOpen method does not have to
** allocate the structure; it should just fill it in.  Note that
** the xOpen method must set the sqlite3_file.pMethods to either
** a valid [sqlite3_io_methods] object or to NULL.  xOpen must do
** this even if the open fails.  SQLite expects that the sqlite3_file.pMethods
** element will be valid after xOpen returns regardless of the success
** or failure of the xOpen call.
**
** [[sqlite3_vfs.xAccess]]
** ^The flags argument to xAccess() may be [SQLITE_ACCESS_EXISTS]
** to test for the existence of a file, or [SQLITE_ACCESS_READWRITE] to
** test whether a file is readable and writable, or [SQLITE_ACCESS_READ]
** to test whether a file is at least readable.   The file can be a
** directory.
**
** ^SQLite will always allocate at least mxPathname+1 bytes for the
** output buffer xFullPathname.  The exact size of the output buffer
** is also passed as a parameter to both  methods. If the output buffer
** is not large enough, [SQLITE_CANTOPEN] should be returned. Since this is
** handled as a fatal error by SQLite, vfs implementations should endeavor
** to prevent this by setting mxPathname to a sufficiently large value.
**
** The xRandomness(), xSleep(), xCurrentTime(), and xCurrentTimeInt64()
** interfaces are not strictly a part of the filesystem, but they are
** included in the VFS structure for completeness.
** The xRandomness() function attempts to return nBytes bytes
** of good-quality randomness into zOut.  The return value is
** the actual number of bytes of randomness obtained.
** The xSleep() method causes the calling thread to sleep for at
** least the number of microseconds given.  ^The xCurrentTime()
** method returns a Julian Day Number for the current date and time as
** a floating point value.
** ^The xCurrentTimeInt64() method returns, as an integer, the Julian
** Day Number multiplied by 86400000 (the number of milliseconds in 
** a 24-hour day).  
** ^SQLite will use the xCurrentTimeInt64() method to get the current
** date and time if that method is available (if iVersion is 2 or 
** greater and the function pointer is not NULL) and will fall back
** to xCurrentTime() if xCurrentTimeInt64() is unavailable.
**
** ^The xSetSystemCall(), xGetSystemCall(), and xNestSystemCall() interfaces
** are not used by the SQLite core.  These optional interfaces are provided
** by some VFSes to facilitate testing of the VFS code. By overriding 
** system calls with functions under its control, a test program can
** simulate faults and error conditions that would otherwise be difficult
** or impossible to induce.  The set of system calls that can be overridden
** varies from one VFS to another, and from one version of the same VFS to the
** next.  Applications that use these interfaces must be prepared for any
** or all of these interfaces to be NULL or for their behavior to change
** from one release to the next.  Applications must not attempt to access
** any of these methods if the iVersion of the VFS is less than 3.
*/
typedef struct sqlite3_vfs sqlite3_vfs;
typedef void (*sqlite3_syscall_ptr)(void);
struct sqlite3_vfs {
  int iVersion;            /* Structure version number (currently 3) */
  int szOsFile;            /* Size of subclassed sqlite3_file */
  int mxPathname;          /* Maximum file pathname length */
  sqlite3_vfs *pNext;      /* Next registered VFS */
  const char *zName;       /* Name of this virtual file system */
  void *pAppData;          /* Pointer to application-specific data */
  int (*xOpen)(sqlite3_vfs*, const char *zName, sqlite3_file*,
               int flags, int *pOutFlags);
  int (*xDelete)(sqlite3_vfs*, const char *zName, int syncDir);
  int (*xAccess)(sqlite3_vfs*, const char *zName, int flags, int *pResOut);
  int (*xFullPathname)(sqlite3_vfs*, const char *zName, int nOut, char *zOut);
  void *(*xDlOpen)(sqlite3_vfs*, const char *zFilename);
  void (*xDlError)(sqlite3_vfs*, int nByte, char *zErrMsg);
  void (*(*xDlSym)(sqlite3_vfs*,void*, const char *zSymbol))(void);
  void (*xDlClose)(sqlite3_vfs*, void*);
  int (*xRandomness)(sqlite3_vfs*, int nByte, char *zOut);
  int (*xSleep)(sqlite3_vfs*, int microseconds);
  int (*xCurrentTime)(sqlite3_vfs*, double*);
  int (*xGetLastError)(sqlite3_vfs*, int, char *);
  /*
  ** The methods above are in version 1 of the sqlite_vfs object
  ** definition.  Those that follow are added in version 2 or later
  */
  int (*xCurrentTimeInt64)(sqlite3_vfs*, sqlite3_int64*);
  /*
  ** The methods above are in versions 1 and 2 of the sqlite_vfs object.
  ** Those below are for version 3 and greater.
  */
  int (*xSetSystemCall)(sqlite3_vfs*, const char *zName, sqlite3_syscall_ptr);
  sqlite3_syscall_ptr (*xGetSystemCall)(sqlite3_vfs*, const char *zName);
  const char *(*xNextSystemCall)(sqlite3_vfs*, const char *zName);
  /*
  ** The methods above are in versions 1 through 3 of the sqlite_vfs object.
  ** New fields may be appended in figure versions.  The iVersion
  ** value will increment whenever this happens. 
  */
};

/*
** CAPI3REF: Flags for the xAccess VFS method
**
** These integer constants can be used as the third parameter to
** the xAccess method of an [sqlite3_vfs] object.  They determine
** what kind of permissions the xAccess method is looking for.
** With SQLITE_ACCESS_EXISTS, the xAccess method
** simply checks whether the file exists.
** With SQLITE_ACCESS_READWRITE, the xAccess method
** checks whether the named directory is both readable and writable
** (in other words, if files can be added, removed, and renamed within
** the directory).
** The SQLITE_ACCESS_READWRITE constant is currently used only by the
** [temp_store_directory pragma], though this could change in a future
** release of SQLite.
** With SQLITE_ACCESS_READ, the xAccess method
** checks whether the file is readable.  The SQLITE_ACCESS_READ constant is
** currently unused, though it might be used in a future release of
** SQLite.
*/
#define SQLITE_ACCESS_EXISTS    0
#define SQLITE_ACCESS_READWRITE 1   /* Used by PRAGMA temp_store_directory */
#define SQLITE_ACCESS_READ      2   /* Unused */

/*
** CAPI3REF: Flags for the xShmLock VFS method
**
** These integer constants define the various locking operations
** allowed by the xShmLock method of [sqlite3_io_methods].  The
** following are the only legal combinations of flags to the
** xShmLock method:
**
** <ul>
** <li>  SQLITE_SHM_LOCK | SQLITE_SHM_SHARED
** <li>  SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE
** <li>  SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED
** <li>  SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE
** </ul>
**
** When unlocking, the same SHARED or EXCLUSIVE flag must be supplied as
** was given on the corresponding lock.  
**
** The xShmLock method can transition between unlocked and SHARED or
** between unlocked and EXCLUSIVE.  It cannot transition between SHARED
** and EXCLUSIVE.
*/
#define SQLITE_SHM_UNLOCK       1
#define SQLITE_SHM_LOCK         2
#define SQLITE_SHM_SHARED       4
#define SQLITE_SHM_EXCLUSIVE    8

/*
** CAPI3REF: Maximum xShmLock index
**
** The xShmLock method on [sqlite3_io_methods] may use values
** between 0 and this upper bound as its "offset" argument.
** The SQLite core will never attempt to acquire or release a
** lock outside of this range
*/
#define SQLITE_SHM_NLOCK        8

SQLITE_PRIVATE int sqlite3_os_init(void);
SQLITE_PRIVATE int sqlite3_os_end(void);

/*
** CAPI3REF: Configuring The SQLite Library
**
** The sqlite3_config() interface is used to make global configuration
** changes to SQLite in order to tune SQLite to the specific needs of
** the application.  The default configuration is recommended for most
** applications and so this routine is usually not necessary.  It is
** provided to support rare applications with unusual needs.
**
** <b>The sqlite3_config() interface is not threadsafe. The application
** must ensure that no other SQLite interfaces are invoked by other
** threads while sqlite3_config() is running.</b>
**
** The sqlite3_config() interface
** may only be invoked prior to library initialization using
** [sqlite3BtreeInitialize()] or after shutdown by [sqlite3BtreeShutdown()].
** ^If sqlite3_config() is called after [sqlite3BtreeInitialize()] and before
** [sqlite3BtreeShutdown()] then it will return SQLITE_MISUSE.
** Note, however, that ^sqlite3_config() can be called as part of the
** implementation of an application-defined [sqlite3_os_init()].
**
** The first argument to sqlite3_config() is an integer
** [configuration option] that determines
** what property of SQLite is to be configured.  Subsequent arguments
** vary depending on the [configuration option]
** in the first argument.
**
** ^When a configuration option is set, sqlite3_config() returns [SQLITE_OK].
** ^If the option is unknown or SQLite is unable to set the option
** then this routine returns a non-zero [error code].
*/
SQLITE_PRIVATE int sqlite3_config(int, ...);

/*
** CAPI3REF: Memory Allocation Routines
**
** An instance of this object defines the interface between SQLite
** and low-level memory allocation routines.
**
** This object is used in only one place in the SQLite interface.
** A pointer to an instance of this object is the argument to
** [sqlite3_config()] when the configuration option is
** [SQLITE_CONFIG_MALLOC] or [SQLITE_CONFIG_GETMALLOC].  
** By creating an instance of this object
** and passing it to [sqlite3_config]([SQLITE_CONFIG_MALLOC])
** during configuration, an application can specify an alternative
** memory allocation subsystem for SQLite to use for all of its
** dynamic memory needs.
**
** Note that SQLite comes with several [built-in memory allocators]
** that are perfectly adequate for the overwhelming majority of applications
** and that this object is only useful to a tiny minority of applications
** with specialized memory allocation requirements.  This object is
** also used during testing of SQLite in order to specify an alternative
** memory allocator that simulates memory out-of-memory conditions in
** order to verify that SQLite recovers gracefully from such
** conditions.
**
** The xMalloc, xRealloc, and xFree methods must work like the
** malloc(), realloc() and free() functions from the standard C library.
** ^SQLite guarantees that the second argument to
** xRealloc is always a value returned by a prior call to xRoundup.
**
** xSize should return the allocated size of a memory allocation
** previously obtained from xMalloc or xRealloc.  The allocated size
** is always at least as big as the requested size but may be larger.
**
** The xRoundup method returns what would be the allocated size of
** a memory allocation given a particular requested size.  Most memory
** allocators round up memory allocations at least to the next multiple
** of 8.  Some allocators round up to a larger multiple or to a power of 2.
** Every memory allocation request coming in through [sqlite3_malloc()]
** or [sqlite3_realloc()] first calls xRoundup.  If xRoundup returns 0, 
** that causes the corresponding memory allocation to fail.
**
** The xInit method initializes the memory allocator.  For example,
** it might allocate any require mutexes or initialize internal data
** structures.  The xShutdown method is invoked (indirectly) by
** [sqlite3BtreeShutdown()] and should deallocate any resources acquired
** by xInit.  The pAppData pointer is used as the only parameter to
** xInit and xShutdown.
**
** SQLite holds the [SQLITE_MUTEX_STATIC_MASTER] mutex when it invokes
** the xInit method, so the xInit method need not be threadsafe.  The
** xShutdown method is only called from [sqlite3BtreeShutdown()] so it does
** not need to be threadsafe either.  For all other methods, SQLite
** holds the [SQLITE_MUTEX_STATIC_MEM] mutex as long as the
** [SQLITE_CONFIG_MEMSTATUS] configuration option is turned on (which
** it is by default) and so the methods are automatically serialized.
** However, if [SQLITE_CONFIG_MEMSTATUS] is disabled, then the other
** methods must be threadsafe or else make their own arrangements for
** serialization.
**
** SQLite will never invoke xInit() more than once without an intervening
** call to xShutdown().
*/
typedef struct sqlite3_mem_methods sqlite3_mem_methods;
struct sqlite3_mem_methods {
  void *(*xMalloc)(int);         /* Memory allocation function */
  void (*xFree)(void*);          /* Free a prior allocation */
  void *(*xRealloc)(void*,int);  /* Resize an allocation */
  int (*xSize)(void*);           /* Return the size of an allocation */
  int (*xRoundup)(int);          /* Round up request size to allocation size */
  int (*xInit)(void*);           /* Initialize the memory allocator */
  void (*xShutdown)(void*);      /* Deinitialize the memory allocator */
  void *pAppData;                /* Argument to xInit() and xShutdown() */
};

/*
** CAPI3REF: Configuration Options
** KEYWORDS: {configuration option}
**
** These constants are the available integer configuration options that
** can be passed as the first argument to the [sqlite3_config()] interface.
**
** New configuration options may be added in future releases of SQLite.
** Existing configuration options might be discontinued.  Applications
** should check the return code from [sqlite3_config()] to make sure that
** the call worked.  The [sqlite3_config()] interface will return a
** non-zero [error code] if a discontinued or unsupported configuration option
** is invoked.
**
** <dl>
** [[SQLITE_CONFIG_SINGLETHREAD]] <dt>SQLITE_CONFIG_SINGLETHREAD</dt>
** <dd>There are no arguments to this option.  ^This option sets the
** [threading mode] to Single-thread.  In other words, it disables
** all mutexing and puts SQLite into a mode where it can only be used
** by a single thread.   ^If SQLite is compiled with
** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
** it is not possible to change the [threading mode] from its default
** value of Single-thread and so [sqlite3_config()] will return 
** [SQLITE_ERROR] if called with the SQLITE_CONFIG_SINGLETHREAD
** configuration option.</dd>
**
** [[SQLITE_CONFIG_MULTITHREAD]] <dt>SQLITE_CONFIG_MULTITHREAD</dt>
** <dd>There are no arguments to this option.  ^This option sets the
** [threading mode] to Multi-thread.  In other words, it disables
** mutexing on [database connection] and [prepared statement] objects.
** The application is responsible for serializing access to
** [database connections] and [prepared statements].  But other mutexes
** are enabled so that SQLite will be safe to use in a multi-threaded
** environment as long as no two threads attempt to use the same
** [database connection] at the same time.  ^If SQLite is compiled with
** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
** it is not possible to set the Multi-thread [threading mode] and
** [sqlite3_config()] will return [SQLITE_ERROR] if called with the
** SQLITE_CONFIG_MULTITHREAD configuration option.</dd>
**
** [[SQLITE_CONFIG_SERIALIZED]] <dt>SQLITE_CONFIG_SERIALIZED</dt>
** <dd>There are no arguments to this option.  ^This option sets the
** [threading mode] to Serialized. In other words, this option enables
** all mutexes including the recursive
** mutexes on [database connection] and [prepared statement] objects.
** In this mode (which is the default when SQLite is compiled with
** [SQLITE_THREADSAFE=1]) the SQLite library will itself serialize access
** to [database connections] and [prepared statements] so that the
** application is free to use the same [database connection] or the
** same [prepared statement] in different threads at the same time.
** ^If SQLite is compiled with
** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
** it is not possible to set the Serialized [threading mode] and
** [sqlite3_config()] will return [SQLITE_ERROR] if called with the
** SQLITE_CONFIG_SERIALIZED configuration option.</dd>
**
** [[SQLITE_CONFIG_MALLOC]] <dt>SQLITE_CONFIG_MALLOC</dt>
** <dd> ^(The SQLITE_CONFIG_MALLOC option takes a single argument which is 
** a pointer to an instance of the [sqlite3_mem_methods] structure.
** The argument specifies
** alternative low-level memory allocation routines to be used in place of
** the memory allocation routines built into SQLite.)^ ^SQLite makes
** its own private copy of the content of the [sqlite3_mem_methods] structure
** before the [sqlite3_config()] call returns.</dd>
**
** [[SQLITE_CONFIG_GETMALLOC]] <dt>SQLITE_CONFIG_GETMALLOC</dt>
** <dd> ^(The SQLITE_CONFIG_GETMALLOC option takes a single argument which
** is a pointer to an instance of the [sqlite3_mem_methods] structure.
** The [sqlite3_mem_methods]
** structure is filled with the currently defined memory allocation routines.)^
** This option can be used to overload the default memory allocation
** routines with a wrapper that simulations memory allocation failure or
** tracks memory usage, for example. </dd>
**
** [[SQLITE_CONFIG_MEMSTATUS]] <dt>SQLITE_CONFIG_MEMSTATUS</dt>
** <dd> ^The SQLITE_CONFIG_MEMSTATUS option takes single argument of type int,
** interpreted as a boolean, which enables or disables the collection of
** memory allocation statistics. ^(When memory allocation statistics are
** disabled, the following SQLite interfaces become non-operational:
**   <ul>
**   <li> [sqlite3_memory_used()]
**   <li> [sqlite3_memory_highwater()]
**   <li> [sqlite3_soft_heap_limit64()]
**   <li> [sqlite3_status64()]
**   </ul>)^
** ^Memory allocation statistics are enabled by default unless SQLite is
** compiled with [SQLITE_DEFAULT_MEMSTATUS]=0 in which case memory
** allocation statistics are disabled by default.
** </dd>
**
** [[SQLITE_CONFIG_SCRATCH]] <dt>SQLITE_CONFIG_SCRATCH</dt>
** <dd> ^The SQLITE_CONFIG_SCRATCH option specifies a static memory buffer
** that SQLite can use for scratch memory.  ^(There are three arguments
** to SQLITE_CONFIG_SCRATCH:  A pointer an 8-byte
** aligned memory buffer from which the scratch allocations will be
** drawn, the size of each scratch allocation (sz),
** and the maximum number of scratch allocations (N).)^
** The first argument must be a pointer to an 8-byte aligned buffer
** of at least sz*N bytes of memory.
** ^SQLite will not use more than one scratch buffers per thread.
** ^SQLite will never request a scratch buffer that is more than 6
** times the database page size.
** ^If SQLite needs needs additional
** scratch memory beyond what is provided by this configuration option, then 
** [sqlite3_malloc()] will be used to obtain the memory needed.<p>
** ^When the application provides any amount of scratch memory using
** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
** [sqlite3_malloc|heap allocations].
** This can help [Robson proof|prevent memory allocation failures] due to heap
** fragmentation in low-memory embedded systems.
** </dd>
**
** [[SQLITE_CONFIG_PAGECACHE]] <dt>SQLITE_CONFIG_PAGECACHE</dt>
** <dd> ^The SQLITE_CONFIG_PAGECACHE option specifies a static memory buffer
** that SQLite can use for the database page cache with the default page
** cache implementation.  
** This configuration should not be used if an application-define page
** cache implementation is loaded using the [SQLITE_CONFIG_PCACHE2]
** configuration option.
** ^There are three arguments to SQLITE_CONFIG_PAGECACHE: A pointer to
** 8-byte aligned
** memory, the size of each page buffer (sz), and the number of pages (N).
** The sz argument should be the size of the largest database page
** (a power of two between 512 and 65536) plus some extra bytes for each
** page header.  ^The number of extra bytes needed by the page header
** can be determined using the [SQLITE_CONFIG_PCACHE_HDRSZ] option 
** to [sqlite3_config()].
** ^It is harmless, apart from the wasted memory,
** for the sz parameter to be larger than necessary.  The first
** argument should pointer to an 8-byte aligned block of memory that
** is at least sz*N bytes of memory, otherwise subsequent behavior is
** undefined.
** ^SQLite will use the memory provided by the first argument to satisfy its
** memory needs for the first N pages that it adds to cache.  ^If additional
** page cache memory is needed beyond what is provided by this option, then
** SQLite goes to [sqlite3_malloc()] for the additional storage space.</dd>
**
** [[SQLITE_CONFIG_HEAP]] <dt>SQLITE_CONFIG_HEAP</dt>
** <dd> ^The SQLITE_CONFIG_HEAP option specifies a static memory buffer 
** that SQLite will use for all of its dynamic memory allocation needs
** beyond those provided for by [SQLITE_CONFIG_SCRATCH] and
** [SQLITE_CONFIG_PAGECACHE].
** ^The SQLITE_CONFIG_HEAP option is only available if SQLite is compiled
** with either [SQLITE_ENABLE_MEMSYS3] or [SQLITE_ENABLE_MEMSYS5] and returns
** [SQLITE_ERROR] if invoked otherwise.
** ^There are three arguments to SQLITE_CONFIG_HEAP:
** An 8-byte aligned pointer to the memory,
** the number of bytes in the memory buffer, and the minimum allocation size.
** ^If the first pointer (the memory pointer) is NULL, then SQLite reverts
** to using its default memory allocator (the system malloc() implementation),
** undoing any prior invocation of [SQLITE_CONFIG_MALLOC].  ^If the
** memory pointer is not NULL then the alternative memory
** allocator is engaged to handle all of SQLites memory allocation needs.
** The first pointer (the memory pointer) must be aligned to an 8-byte
** boundary or subsequent behavior of SQLite will be undefined.
** The minimum allocation size is capped at 2**12. Reasonable values
** for the minimum allocation size are 2**5 through 2**8.</dd>
**
** [[SQLITE_CONFIG_MUTEX]] <dt>SQLITE_CONFIG_MUTEX</dt>
** <dd> ^(The SQLITE_CONFIG_MUTEX option takes a single argument which is a
** pointer to an instance of the [sqlite3_mutex_methods] structure.
** The argument specifies alternative low-level mutex routines to be used
** in place the mutex routines built into SQLite.)^  ^SQLite makes a copy of
** the content of the [sqlite3_mutex_methods] structure before the call to
** [sqlite3_config()] returns. ^If SQLite is compiled with
** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
** the entire mutexing subsystem is omitted from the build and hence calls to
** [sqlite3_config()] with the SQLITE_CONFIG_MUTEX configuration option will
** return [SQLITE_ERROR].</dd>
**
** [[SQLITE_CONFIG_GETMUTEX]] <dt>SQLITE_CONFIG_GETMUTEX</dt>
** <dd> ^(The SQLITE_CONFIG_GETMUTEX option takes a single argument which
** is a pointer to an instance of the [sqlite3_mutex_methods] structure.  The
** [sqlite3_mutex_methods]
** structure is filled with the currently defined mutex routines.)^
** This option can be used to overload the default mutex allocation
** routines with a wrapper used to track mutex usage for performance
** profiling or testing, for example.   ^If SQLite is compiled with
** the [SQLITE_THREADSAFE | SQLITE_THREADSAFE=0] compile-time option then
** the entire mutexing subsystem is omitted from the build and hence calls to
** [sqlite3_config()] with the SQLITE_CONFIG_GETMUTEX configuration option will
** return [SQLITE_ERROR].</dd>
**
** [[SQLITE_CONFIG_LOOKASIDE]] <dt>SQLITE_CONFIG_LOOKASIDE</dt>
** <dd> ^(The SQLITE_CONFIG_LOOKASIDE option takes two arguments that determine
** the default size of lookaside memory on each [database connection].
** The first argument is the
** size of each lookaside buffer slot and the second is the number of
** slots allocated to each database connection.)^  ^(SQLITE_CONFIG_LOOKASIDE
** sets the <i>default</i> lookaside size. The [SQLITE_DBCONFIG_LOOKASIDE]
** option to [sqlite3_db_config()] can be used to change the lookaside
** configuration on individual connections.)^ </dd>
**
** [[SQLITE_CONFIG_PCACHE2]] <dt>SQLITE_CONFIG_PCACHE2</dt>
** <dd> ^(The SQLITE_CONFIG_PCACHE2 option takes a single argument which is 
** a pointer to an [sqlite3_pcache_methods2] object.  This object specifies
** the interface to a custom page cache implementation.)^
** ^SQLite makes a copy of the [sqlite3_pcache_methods2] object.</dd>
**
** [[SQLITE_CONFIG_GETPCACHE2]] <dt>SQLITE_CONFIG_GETPCACHE2</dt>
** <dd> ^(The SQLITE_CONFIG_GETPCACHE2 option takes a single argument which
** is a pointer to an [sqlite3_pcache_methods2] object.  SQLite copies of
** the current page cache implementation into that object.)^ </dd>
**
** [[SQLITE_CONFIG_LOG]] <dt>SQLITE_CONFIG_LOG</dt>
** <dd> The SQLITE_CONFIG_LOG option is used to configure the SQLite
** global [error log].
** (^The SQLITE_CONFIG_LOG option takes two arguments: a pointer to a
** function with a call signature of void(*)(void*,int,const char*), 
** and a pointer to void. ^If the function pointer is not NULL, it is
** invoked by [sqlite3_log()] to process each logging event.  ^If the
** function pointer is NULL, the [sqlite3_log()] interface becomes a no-op.
** ^The void pointer that is the second argument to SQLITE_CONFIG_LOG is
** passed through as the first parameter to the application-defined logger
** function whenever that function is invoked.  ^The second parameter to
** the logger function is a copy of the first parameter to the corresponding
** [sqlite3_log()] call and is intended to be a [result code] or an
** [extended result code].  ^The third parameter passed to the logger is
** log message after formatting via [sqlite3_snprintf()].
** The SQLite logging interface is not reentrant; the logger function
** supplied by the application must not invoke any SQLite interface.
** In a multi-threaded application, the application-defined logger
** function must be threadsafe. </dd>
**
** [[SQLITE_CONFIG_URI]] <dt>SQLITE_CONFIG_URI
** <dd>^(The SQLITE_CONFIG_URI option takes a single argument of type int.
** If non-zero, then URI handling is globally enabled. If the parameter is zero,
** then URI handling is globally disabled.)^ ^If URI handling is globally
** enabled, all filenames passed to [sqlite3_open()], [sqlite3_open_v2()],
** [sqlite3_open16()] or
** specified as part of [ATTACH] commands are interpreted as URIs, regardless
** of whether or not the [SQLITE_OPEN_URI] flag is set when the database
** connection is opened. ^If it is globally disabled, filenames are
** only interpreted as URIs if the SQLITE_OPEN_URI flag is set when the
** database connection is opened. ^(By default, URI handling is globally
** disabled. The default value may be changed by compiling with the
** [SQLITE_USE_URI] symbol defined.)^
**
** [[SQLITE_CONFIG_COVERING_INDEX_SCAN]] <dt>SQLITE_CONFIG_COVERING_INDEX_SCAN
** <dd>^The SQLITE_CONFIG_COVERING_INDEX_SCAN option takes a single integer
** argument which is interpreted as a boolean in order to enable or disable
** the use of covering indices for full table scans in the query optimizer.
** ^The default setting is determined
** by the [SQLITE_ALLOW_COVERING_INDEX_SCAN] compile-time option, or is "on"
** if that compile-time option is omitted.
** The ability to disable the use of covering indices for full table scans
** is because some incorrectly coded legacy applications might malfunction
** when the optimization is enabled.  Providing the ability to
** disable the optimization allows the older, buggy application code to work
** without change even with newer versions of SQLite.
**
** [[SQLITE_CONFIG_PCACHE]] [[SQLITE_CONFIG_GETPCACHE]]
** <dt>SQLITE_CONFIG_PCACHE and SQLITE_CONFIG_GETPCACHE
** <dd> These options are obsolete and should not be used by new code.
** They are retained for backwards compatibility but are now no-ops.
** </dd>
**
** [[SQLITE_CONFIG_MMAP_SIZE]]
** <dt>SQLITE_CONFIG_MMAP_SIZE
** <dd>^SQLITE_CONFIG_MMAP_SIZE takes two 64-bit integer (sqlite3_int64) values
** that are the default mmap size limit (the default setting for
** [PRAGMA mmap_size]) and the maximum allowed mmap size limit.
** ^The default setting can be overridden by each database connection using
** either the [PRAGMA mmap_size] command, or by using the
** [SQLITE_FCNTL_MMAP_SIZE] file control.  ^(The maximum allowed mmap size
** will be silently truncated if necessary so that it does not exceed the
** compile-time maximum mmap size set by the
** [SQLITE_MAX_MMAP_SIZE] compile-time option.)^
** ^If either argument to this option is negative, then that argument is
** changed to its compile-time default.
**
** [[SQLITE_CONFIG_WIN32_HEAPSIZE]]
** <dt>SQLITE_CONFIG_WIN32_HEAPSIZE
** <dd>^The SQLITE_CONFIG_WIN32_HEAPSIZE option is only available if SQLite is
** compiled for Windows with the [SQLITE_WIN32_MALLOC] pre-processor macro
** defined. ^SQLITE_CONFIG_WIN32_HEAPSIZE takes a 32-bit unsigned integer value
** that specifies the maximum size of the created heap.
**
** [[SQLITE_CONFIG_PCACHE_HDRSZ]]
** <dt>SQLITE_CONFIG_PCACHE_HDRSZ
** <dd>^The SQLITE_CONFIG_PCACHE_HDRSZ option takes a single parameter which
** is a pointer to an integer and writes into that integer the number of extra
** bytes per page required for each page in [SQLITE_CONFIG_PAGECACHE].
** The amount of extra space required can change depending on the compiler,
** target platform, and SQLite version.
**
** [[SQLITE_CONFIG_PMASZ]]
** <dt>SQLITE_CONFIG_PMASZ
** <dd>^The SQLITE_CONFIG_PMASZ option takes a single parameter which
** is an unsigned integer and sets the "Minimum PMA Size" for the multithreaded
** sorter to that integer.  The default minimum PMA Size is set by the
** [SQLITE_SORTER_PMASZ] compile-time option.  New threads are launched
** to help with sort operations when multithreaded sorting
** is enabled (using the [PRAGMA threads] command) and the amount of content
** to be sorted exceeds the page size times the minimum of the
** [PRAGMA cache_size] setting and this value.
** </dl>
*/
#define SQLITE_CONFIG_SINGLETHREAD  1  /* nil */
#define SQLITE_CONFIG_MULTITHREAD   2  /* nil */
#define SQLITE_CONFIG_SERIALIZED    3  /* nil */
#define SQLITE_CONFIG_MALLOC        4  /* sqlite3_mem_methods* */
#define SQLITE_CONFIG_GETMALLOC     5  /* sqlite3_mem_methods* */
#define SQLITE_CONFIG_SCRATCH       6  /* void*, int sz, int N */
#define SQLITE_CONFIG_PAGECACHE     7  /* void*, int sz, int N */
#define SQLITE_CONFIG_HEAP          8  /* void*, int nByte, int min */
#define SQLITE_CONFIG_MEMSTATUS     9  /* boolean */
#define SQLITE_CONFIG_MUTEX        10  /* sqlite3_mutex_methods* */
#define SQLITE_CONFIG_GETMUTEX     11  /* sqlite3_mutex_methods* */
/* previously SQLITE_CONFIG_CHUNKALLOC 12 which is now unused. */ 
#define SQLITE_CONFIG_LOOKASIDE    13  /* int int */
#define SQLITE_CONFIG_PCACHE       14  /* no-op */
#define SQLITE_CONFIG_GETPCACHE    15  /* no-op */
#define SQLITE_CONFIG_LOG          16  /* xFunc, void* */
#define SQLITE_CONFIG_URI          17  /* int */
#define SQLITE_CONFIG_PCACHE2      18  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_GETPCACHE2   19  /* sqlite3_pcache_methods2* */
#define SQLITE_CONFIG_COVERING_INDEX_SCAN 20  /* int */
#define SQLITE_CONFIG_SQLLOG       21  /* xSqllog, void* */
#define SQLITE_CONFIG_MMAP_SIZE    22  /* sqlite3_int64, sqlite3_int64 */
#define SQLITE_CONFIG_WIN32_HEAPSIZE      23  /* int nByte */
#define SQLITE_CONFIG_PCACHE_HDRSZ        24  /* int *psz */
#define SQLITE_CONFIG_PMASZ               25  /* unsigned int szPma */

/*
** CAPI3REF: Formatted String Printing Functions
**
** These routines are work-alikes of the "printf()" family of functions
** from the standard C library.
** These routines understand most of the common K&R formatting options,
** plus some additional non-standard formats, detailed below.
** Note that some of the more obscure formatting options from recent
** C-library standards are omitted from this implementation.
**
** ^The sqlite3_mprintf() and sqlite3_vmprintf() routines write their
** results into memory obtained from [sqlite3_malloc()].
** The strings returned by these two routines should be
** released by [sqlite3_free()].  ^Both routines return a
** NULL pointer if [sqlite3_malloc()] is unable to allocate enough
** memory to hold the resulting string.
**
** ^(The sqlite3_snprintf() routine is similar to "snprintf()" from
** the standard C library.  The result is written into the
** buffer supplied as the second parameter whose size is given by
** the first parameter. Note that the order of the
** first two parameters is reversed from snprintf().)^  This is an
** historical accident that cannot be fixed without breaking
** backwards compatibility.  ^(Note also that sqlite3_snprintf()
** returns a pointer to its buffer instead of the number of
** characters actually written into the buffer.)^  We admit that
** the number of characters written would be a more useful return
** value but we cannot change the implementation of sqlite3_snprintf()
** now without breaking compatibility.
**
** ^As long as the buffer size is greater than zero, sqlite3_snprintf()
** guarantees that the buffer is always zero-terminated.  ^The first
** parameter "n" is the total size of the buffer, including space for
** the zero terminator.  So the longest string that can be completely
** written will be n-1 characters.
**
** ^The sqlite3_vsnprintf() routine is a varargs version of sqlite3_snprintf().
**
** These routines all implement some additional formatting
** options that are useful for constructing SQL statements.
** All of the usual printf() formatting options apply.  In addition, there
** is are "%q", "%Q", "%w" and "%z" options.
**
** ^(The %q option works like %s in that it substitutes a nul-terminated
** string from the argument list.  But %q also doubles every '\'' character.
** %q is designed for use inside a string literal.)^  By doubling each '\''
** character it escapes that character and allows it to be inserted into
** the string.
**
** For example, assume the string variable zText contains text as follows:
**
** <blockquote><pre>
**  char *zText = "It's a happy day!";
** </pre></blockquote>
**
** One can use this text in an SQL statement as follows:
**
** <blockquote><pre>
**  char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES('%q')", zText);
**  sqlite3_exec(db, zSQL, 0, 0, 0);
**  sqlite3_free(zSQL);
** </pre></blockquote>
**
** Because the %q format string is used, the '\'' character in zText
** is escaped and the SQL generated is as follows:
**
** <blockquote><pre>
**  INSERT INTO table1 VALUES('It''s a happy day!')
** </pre></blockquote>
**
** This is correct.  Had we used %s instead of %q, the generated SQL
** would have looked like this:
**
** <blockquote><pre>
**  INSERT INTO table1 VALUES('It's a happy day!');
** </pre></blockquote>
**
** This second example is an SQL syntax error.  As a general rule you should
** always use %q instead of %s when inserting text into a string literal.
**
** ^(The %Q option works like %q except it also adds single quotes around
** the outside of the total string.  Additionally, if the parameter in the
** argument list is a NULL pointer, %Q substitutes the text "NULL" (without
** single quotes).)^  So, for example, one could say:
**
** <blockquote><pre>
**  char *zSQL = sqlite3_mprintf("INSERT INTO table VALUES(%Q)", zText);
**  sqlite3_exec(db, zSQL, 0, 0, 0);
**  sqlite3_free(zSQL);
** </pre></blockquote>
**
** The code above will render a correct SQL statement in the zSQL
** variable even if the zText variable is a NULL pointer.
**
** ^(The "%w" formatting option is like "%q" except that it expects to
** be contained within double-quotes instead of single quotes, and it
** escapes the double-quote character instead of the single-quote
** character.)^  The "%w" formatting option is intended for safely inserting
** table and column names into a constructed SQL statement.
**
** ^(The "%z" formatting option works like "%s" but with the
** addition that after the string has been read and copied into
** the result, [sqlite3_free()] is called on the input string.)^
*/
SQLITE_PRIVATE char *sqlite3_mprintf(const char*,...);
SQLITE_PRIVATE char *sqlite3_vmprintf(const char*, va_list);
SQLITE_PRIVATE char *sqlite3_snprintf(int,char*,const char*, ...);
SQLITE_PRIVATE char *sqlite3_vsnprintf(int,char*,const char*, va_list);

/*
** CAPI3REF: Memory Allocation Subsystem
**
** The SQLite core uses these three routines for all of its own
** internal memory allocation needs. "Core" in the previous sentence
** does not include operating-system specific VFS implementation.  The
** Windows VFS uses native malloc() and free() for some operations.
**
** ^The sqlite3_malloc() routine returns a pointer to a block
** of memory at least N bytes in length, where N is the parameter.
** ^If sqlite3_malloc() is unable to obtain sufficient free
** memory, it returns a NULL pointer.  ^If the parameter N to
** sqlite3_malloc() is zero or negative then sqlite3_malloc() returns
** a NULL pointer.
**
** ^The sqlite3_malloc64(N) routine works just like
** sqlite3_malloc(N) except that N is an unsigned 64-bit integer instead
** of a signed 32-bit integer.
**
** ^Calling sqlite3_free() with a pointer previously returned
** by sqlite3_malloc() or sqlite3_realloc() releases that memory so
** that it might be reused.  ^The sqlite3_free() routine is
** a no-op if is called with a NULL pointer.  Passing a NULL pointer
** to sqlite3_free() is harmless.  After being freed, memory
** should neither be read nor written.  Even reading previously freed
** memory might result in a segmentation fault or other severe error.
** Memory corruption, a segmentation fault, or other severe error
** might result if sqlite3_free() is called with a non-NULL pointer that
** was not obtained from sqlite3_malloc() or sqlite3_realloc().
**
** ^The sqlite3_realloc(X,N) interface attempts to resize a
** prior memory allocation X to be at least N bytes.
** ^If the X parameter to sqlite3_realloc(X,N)
** is a NULL pointer then its behavior is identical to calling
** sqlite3_malloc(N).
** ^If the N parameter to sqlite3_realloc(X,N) is zero or
** negative then the behavior is exactly the same as calling
** sqlite3_free(X).
** ^sqlite3_realloc(X,N) returns a pointer to a memory allocation
** of at least N bytes in size or NULL if insufficient memory is available.
** ^If M is the size of the prior allocation, then min(N,M) bytes
** of the prior allocation are copied into the beginning of buffer returned
** by sqlite3_realloc(X,N) and the prior allocation is freed.
** ^If sqlite3_realloc(X,N) returns NULL and N is positive, then the
** prior allocation is not freed.
**
** ^The sqlite3_realloc64(X,N) interfaces works the same as
** sqlite3_realloc(X,N) except that N is a 64-bit unsigned integer instead
** of a 32-bit signed integer.
**
** ^The memory returned by sqlite3_malloc(), sqlite3_realloc(),
** sqlite3_malloc64(), and sqlite3_realloc64()
** is always aligned to at least an 8 byte boundary, or to a
** 4 byte boundary if the [SQLITE_4_BYTE_ALIGNED_MALLOC] compile-time
** option is used.
**
** In SQLite version 3.5.0 and 3.5.1, it was possible to define
** the SQLITE_OMIT_MEMORY_ALLOCATION which would cause the built-in
** implementation of these routines to be omitted.  That capability
** is no longer provided.  Only built-in memory allocators can be used.
**
** Prior to SQLite version 3.7.10, the Windows OS interface layer called
** the system malloc() and free() directly when converting
** filenames between the UTF-8 encoding used by SQLite
** and whatever filename encoding is used by the particular Windows
** installation.  Memory allocation errors were detected, but
** they were reported back as [SQLITE_CANTOPEN] or
** [SQLITE_IOERR] rather than [SQLITE_NOMEM].
**
** The pointer arguments to [sqlite3_free()] and [sqlite3_realloc()]
** must be either NULL or else pointers obtained from a prior
** invocation of [sqlite3_malloc()] or [sqlite3_realloc()] that have
** not yet been released.
**
** The application must not read or write any part of
** a block of memory after it has been released using
** [sqlite3_free()] or [sqlite3_realloc()].
*/
SQLITE_PRIVATE void *sqlite3_malloc(int);
SQLITE_PRIVATE void *sqlite3_malloc64(sqlite3_uint64);
SQLITE_PRIVATE void *sqlite3_realloc(void*, int);
SQLITE_PRIVATE void *sqlite3_realloc64(void*, sqlite3_uint64);
SQLITE_PRIVATE void sqlite3_free(void*);

/*
** CAPI3REF: Run-Time Limit Categories
** KEYWORDS: {limit category} {*limit categories}
**
** These constants define various performance limits
** that can be lowered at run-time using [sqlite3_limit()].
** The synopsis of the meanings of the various limits is shown below.
** Additional information is available at [limits | Limits in SQLite].
**
** <dl>
** [[SQLITE_LIMIT_LENGTH]] ^(<dt>SQLITE_LIMIT_LENGTH</dt>
** <dd>The maximum size of any string or BLOB or table row, in bytes.<dd>)^
**
** [[SQLITE_LIMIT_SQL_LENGTH]] ^(<dt>SQLITE_LIMIT_SQL_LENGTH</dt>
** <dd>The maximum length of an SQL statement, in bytes.</dd>)^
**
** [[SQLITE_LIMIT_COLUMN]] ^(<dt>SQLITE_LIMIT_COLUMN</dt>
** <dd>The maximum number of columns in a table definition or in the
** result set of a [SELECT] or the maximum number of columns in an index
** or in an ORDER BY or GROUP BY clause.</dd>)^
**
** [[SQLITE_LIMIT_EXPR_DEPTH]] ^(<dt>SQLITE_LIMIT_EXPR_DEPTH</dt>
** <dd>The maximum depth of the parse tree on any expression.</dd>)^
**
** [[SQLITE_LIMIT_COMPOUND_SELECT]] ^(<dt>SQLITE_LIMIT_COMPOUND_SELECT</dt>
** <dd>The maximum number of terms in a compound SELECT statement.</dd>)^
**
** [[SQLITE_LIMIT_VDBE_OP]] ^(<dt>SQLITE_LIMIT_VDBE_OP</dt>
** <dd>The maximum number of instructions in a virtual machine program
** used to implement an SQL statement.  This limit is not currently
** enforced, though that might be added in some future release of
** SQLite.</dd>)^
**
** [[SQLITE_LIMIT_FUNCTION_ARG]] ^(<dt>SQLITE_LIMIT_FUNCTION_ARG</dt>
** <dd>The maximum number of arguments on a function.</dd>)^
**
** [[SQLITE_LIMIT_ATTACHED]] ^(<dt>SQLITE_LIMIT_ATTACHED</dt>
** <dd>The maximum number of [ATTACH | attached databases].)^</dd>
**
** [[SQLITE_LIMIT_LIKE_PATTERN_LENGTH]]
** ^(<dt>SQLITE_LIMIT_LIKE_PATTERN_LENGTH</dt>
** <dd>The maximum length of the pattern argument to the [LIKE] or
** [GLOB] operators.</dd>)^
**
** [[SQLITE_LIMIT_VARIABLE_NUMBER]]
** ^(<dt>SQLITE_LIMIT_VARIABLE_NUMBER</dt>
** <dd>The maximum index number of any [parameter] in an SQL statement.)^
**
** [[SQLITE_LIMIT_TRIGGER_DEPTH]] ^(<dt>SQLITE_LIMIT_TRIGGER_DEPTH</dt>
** <dd>The maximum depth of recursion for triggers.</dd>)^
**
** [[SQLITE_LIMIT_WORKER_THREADS]] ^(<dt>SQLITE_LIMIT_WORKER_THREADS</dt>
** <dd>The maximum number of auxiliary worker threads that a single
** [prepared statement] may start.</dd>)^
** </dl>
*/
#define SQLITE_LIMIT_LENGTH                    0
#define SQLITE_LIMIT_SQL_LENGTH                1
#define SQLITE_LIMIT_COLUMN                    2
#define SQLITE_LIMIT_EXPR_DEPTH                3
#define SQLITE_LIMIT_COMPOUND_SELECT           4
#define SQLITE_LIMIT_VDBE_OP                   5
#define SQLITE_LIMIT_FUNCTION_ARG              6
#define SQLITE_LIMIT_ATTACHED                  7
#define SQLITE_LIMIT_LIKE_PATTERN_LENGTH       8
#define SQLITE_LIMIT_VARIABLE_NUMBER           9
#define SQLITE_LIMIT_TRIGGER_DEPTH            10
#define SQLITE_LIMIT_WORKER_THREADS           11

/*
** CAPI3REF: Name Of The Folder Holding Temporary Files
**
** ^(If this global variable is made to point to a string which is
** the name of a folder (a.k.a. directory), then all temporary files
** created by SQLite when using a built-in [sqlite3_vfs | VFS]
** will be placed in that directory.)^  ^If this variable
** is a NULL pointer, then SQLite performs a search for an appropriate
** temporary file directory.
**
** Applications are strongly discouraged from using this global variable.
** It is required to set a temporary folder on Windows Runtime (WinRT).
** But for all other platforms, it is highly recommended that applications
** neither read nor write this variable.  This global variable is a relic
** that exists for backwards compatibility of legacy applications and should
** be avoided in new projects.
**
** It is not safe to read or modify this variable in more than one
** thread at a time.  It is not safe to read or modify this variable
** if a [database connection] is being used at the same time in a separate
** thread.
** It is intended that this variable be set once
** as part of process initialization and before any SQLite interface
** routines have been called and that this variable remain unchanged
** thereafter.
**
** ^The [temp_store_directory pragma] may modify this variable and cause
** it to point to memory obtained from [sqlite3_malloc].  ^Furthermore,
** the [temp_store_directory pragma] always assumes that any string
** that this variable points to is held in memory obtained from 
** [sqlite3_malloc] and the pragma may attempt to free that memory
** using [sqlite3_free].
** Hence, if this variable is modified directly, either it should be
** made NULL or made to point to memory obtained from [sqlite3_malloc]
** or else the use of the [temp_store_directory pragma] should be avoided.
** Except when requested by the [temp_store_directory pragma], SQLite
** does not free the memory that sqlite3_temp_directory points to.  If
** the application wants that memory to be freed, it must do
** so itself, taking care to only do so after all [database connection]
** objects have been destroyed.
**
** <b>Note to Windows Runtime users:</b>  The temporary directory must be set
** prior to calling [sqlite3_open] or [sqlite3_open_v2].  Otherwise, various
** features that require the use of temporary files may fail.  Here is an
** example of how to do this using C++ with the Windows Runtime:
**
** <blockquote><pre>
** LPCWSTR zPath = Windows::Storage::ApplicationData::Current->
** &nbsp;     TemporaryFolder->Path->Data();
** char zPathBuf&#91;MAX_PATH + 1&#93;;
** memset(zPathBuf, 0, sizeof(zPathBuf));
** WideCharToMultiByte(CP_UTF8, 0, zPath, -1, zPathBuf, sizeof(zPathBuf),
** &nbsp;     NULL, NULL);
** sqlite3_temp_directory = sqlite3_mprintf("%s", zPathBuf);
** </pre></blockquote>
*/
SQLITE_PRIVATE char *sqlite3_temp_directory;

/*
** CAPI3REF: Virtual File System Objects
**
** A virtual filesystem (VFS) is an [sqlite3_vfs] object
** that SQLite uses to interact
** with the underlying operating system.  Most SQLite builds come with a
** single default VFS that is appropriate for the host computer.
** New VFSes can be registered and existing VFSes can be unregistered.
** The following interfaces are provided.
**
** ^The sqlite3_vfs_find() interface returns a pointer to a VFS given its name.
** ^Names are case sensitive.
** ^Names are zero-terminated UTF-8 strings.
** ^If there is no match, a NULL pointer is returned.
** ^If zVfsName is NULL then the default VFS is returned.
**
** ^New VFSes are registered with sqlite3_vfs_register().
** ^Each new VFS becomes the default VFS if the makeDflt flag is set.
** ^The same VFS can be registered multiple times without injury.
** ^To make an existing VFS into the default VFS, register it again
** with the makeDflt flag set.  If two different VFSes with the
** same name are registered, the behavior is undefined.  If a
** VFS is registered with a name that is NULL or an empty string,
** then the behavior is undefined.
**
*/
SQLITE_PRIVATE sqlite3_vfs *sqlite3_vfs_find(const char *zVfsName);
SQLITE_PRIVATE int sqlite3_vfs_register(sqlite3_vfs*, int makeDflt);

/*
** CAPI3REF: Mutexes
**
** The SQLite core uses these routines for thread
** synchronization. Though they are intended for internal
** use by SQLite, code that links against SQLite is
** permitted to use any of these routines.
**
** The SQLite source code contains multiple implementations
** of these mutex routines.  An appropriate implementation
** is selected automatically at compile-time.  The following
** implementations are available in the SQLite core:
**
** <ul>
** <li>   SQLITE_MUTEX_PTHREADS
** <li>   SQLITE_MUTEX_W32
** <li>   SQLITE_MUTEX_NOOP
** </ul>
**
** The SQLITE_MUTEX_NOOP implementation is a set of routines
** that does no real locking and is appropriate for use in
** a single-threaded application.  The SQLITE_MUTEX_PTHREADS and
** SQLITE_MUTEX_W32 implementations are appropriate for use on Unix
** and Windows.
**
** If SQLite is compiled with the SQLITE_MUTEX_APPDEF preprocessor
** macro defined (with "-DSQLITE_MUTEX_APPDEF=1"), then no mutex
** implementation is included with the library. In this case the
** application must supply a custom mutex implementation using the
** [SQLITE_CONFIG_MUTEX] option of the sqlite3_config() function
** before calling sqlite3BtreeInitialize() or any other public sqlite3_
** function that calls sqlite3BtreeInitialize().
**
** ^The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it. ^The sqlite3_mutex_alloc()
** routine returns NULL if it is unable to allocate the requested
** mutex.  The argument to sqlite3_mutex_alloc() must one of these
** integer constants:
**
** <ul>
** <li>  SQLITE_MUTEX_FAST
** <li>  SQLITE_MUTEX_RECURSIVE
** <li>  SQLITE_MUTEX_STATIC_MASTER
** <li>  SQLITE_MUTEX_STATIC_MEM
** <li>  SQLITE_MUTEX_STATIC_OPEN
** <li>  SQLITE_MUTEX_STATIC_PRNG
** <li>  SQLITE_MUTEX_STATIC_LRU
** <li>  SQLITE_MUTEX_STATIC_PMEM
** <li>  SQLITE_MUTEX_STATIC_APP1
** <li>  SQLITE_MUTEX_STATIC_APP2
** <li>  SQLITE_MUTEX_STATIC_APP3
** <li>  SQLITE_MUTEX_STATIC_VFS1
** <li>  SQLITE_MUTEX_STATIC_VFS2
** <li>  SQLITE_MUTEX_STATIC_VFS3
** </ul>
**
** ^The first two constants (SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE)
** cause sqlite3_mutex_alloc() to create
** a new mutex.  ^The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
** The mutex implementation does not need to make a distinction
** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to.  SQLite will only request a recursive mutex in
** cases where it really needs one.  If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** ^The other allowed parameters to sqlite3_mutex_alloc() (anything other
** than SQLITE_MUTEX_FAST and SQLITE_MUTEX_RECURSIVE) each return
** a pointer to a static preexisting mutex.  ^Nine static mutexes are
** used by the current version of SQLite.  Future versions of SQLite
** may add additional static mutexes.  Static mutexes are for internal
** use by SQLite only.  Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** ^Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
** returns a different mutex on every call.  ^For the static
** mutex types, the same mutex is returned on every call that has
** the same type number.
**
** ^The sqlite3_mutex_free() routine deallocates a previously
** allocated dynamic mutex.  Attempting to deallocate a static
** mutex results in undefined behavior.
**
** ^The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  ^If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  ^The sqlite3_mutex_try() interface returns [SQLITE_OK]
** upon successful entry.  ^(Mutexes created using
** SQLITE_MUTEX_RECURSIVE can be entered multiple times by the same thread.
** In such cases, the
** mutex must be exited an equal number of times before another thread
** can enter.)^  If the same thread tries to enter any mutex other
** than an SQLITE_MUTEX_RECURSIVE more than once, the behavior is undefined.
**
** ^(Some systems (for example, Windows 95) do not support the operation
** implemented by sqlite3_mutex_try().  On those systems, sqlite3_mutex_try()
** will always return SQLITE_BUSY. The SQLite core only ever uses
** sqlite3_mutex_try() as an optimization so this is acceptable 
** behavior.)^
**
** ^The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.   The behavior
** is undefined if the mutex is not currently entered by the
** calling thread or is not currently allocated.
**
** ^If the argument to sqlite3_mutex_enter(), sqlite3_mutex_try(), or
** sqlite3_mutex_leave() is a NULL pointer, then all three routines
** behave as no-ops.
**
** See also: [sqlite3_mutex_held()] and [sqlite3_mutex_notheld()].
*/
SQLITE_PRIVATE sqlite3_mutex *sqlite3_mutex_alloc(int);
SQLITE_PRIVATE void sqlite3_mutex_free(sqlite3_mutex*);
SQLITE_PRIVATE void sqlite3_mutex_enter(sqlite3_mutex*);
SQLITE_PRIVATE int sqlite3_mutex_try(sqlite3_mutex*);
SQLITE_PRIVATE void sqlite3_mutex_leave(sqlite3_mutex*);

/*
** CAPI3REF: Mutex Methods Object
**
** An instance of this structure defines the low-level routines
** used to allocate and use mutexes.
**
** Usually, the default mutex implementations provided by SQLite are
** sufficient, however the application has the option of substituting a custom
** implementation for specialized deployments or systems for which SQLite
** does not provide a suitable implementation. In this case, the application
** creates and populates an instance of this structure to pass
** to sqlite3_config() along with the [SQLITE_CONFIG_MUTEX] option.
** Additionally, an instance of this structure can be used as an
** output variable when querying the system for the current mutex
** implementation, using the [SQLITE_CONFIG_GETMUTEX] option.
**
** ^The xMutexInit method defined by this structure is invoked as
** part of system initialization by the sqlite3BtreeInitialize() function.
** ^The xMutexInit routine is called by SQLite exactly once for each
** effective call to [sqlite3BtreeInitialize()].
**
** ^The xMutexEnd method defined by this structure is invoked as
** part of system shutdown by the sqlite3BtreeShutdown() function. The
** implementation of this method is expected to release all outstanding
** resources obtained by the mutex methods implementation, especially
** those obtained by the xMutexInit method.  ^The xMutexEnd()
** interface is invoked exactly once for each call to [sqlite3BtreeShutdown()].
**
** ^(The remaining seven methods defined by this structure (xMutexAlloc,
** xMutexFree, xMutexEnter, xMutexTry, xMutexLeave, xMutexHeld and
** xMutexNotheld) implement the following interfaces (respectively):
**
** <ul>
**   <li>  [sqlite3_mutex_alloc()] </li>
**   <li>  [sqlite3_mutex_free()] </li>
**   <li>  [sqlite3_mutex_enter()] </li>
**   <li>  [sqlite3_mutex_try()] </li>
**   <li>  [sqlite3_mutex_leave()] </li>
**   <li>  [sqlite3_mutex_held()] </li>
**   <li>  [sqlite3_mutex_notheld()] </li>
** </ul>)^
**
** The only difference is that the public sqlite3_XXX functions enumerated
** above silently ignore any invocations that pass a NULL pointer instead
** of a valid mutex handle. The implementations of the methods defined
** by this structure are not required to handle this case, the results
** of passing a NULL pointer instead of a valid mutex handle are undefined
** (i.e. it is acceptable to provide an implementation that segfaults if
** it is passed a NULL pointer).
**
** The xMutexInit() method must be threadsafe.  It must be harmless to
** invoke xMutexInit() multiple times within the same process and without
** intervening calls to xMutexEnd().  Second and subsequent calls to
** xMutexInit() must be no-ops.
**
** xMutexInit() must not use SQLite memory allocation ([sqlite3_malloc()]
** and its associates).  Similarly, xMutexAlloc() must not use SQLite memory
** allocation for a static mutex.  ^However xMutexAlloc() may use SQLite
** memory allocation for a fast or recursive mutex.
**
** ^SQLite will invoke the xMutexEnd() method when [sqlite3BtreeShutdown()] is
** called, but only if the prior call to xMutexInit returned SQLITE_OK.
** If xMutexInit fails in any way, it is expected to clean up after itself
** prior to returning.
*/
typedef struct sqlite3_mutex_methods sqlite3_mutex_methods;
struct sqlite3_mutex_methods {
  int (*xMutexInit)(void);
  int (*xMutexEnd)(void);
  sqlite3_mutex *(*xMutexAlloc)(int);
  void (*xMutexFree)(sqlite3_mutex *);
  void (*xMutexEnter)(sqlite3_mutex *);
  int (*xMutexTry)(sqlite3_mutex *);
  void (*xMutexLeave)(sqlite3_mutex *);
  int (*xMutexHeld)(sqlite3_mutex *);
  int (*xMutexNotheld)(sqlite3_mutex *);
};

/*
** CAPI3REF: Mutex Types
**
** The [sqlite3_mutex_alloc()] interface takes a single argument
** which is one of these integer constants.
**
** The set of static mutexes may change from one SQLite release to the
** next.  Applications that override the built-in mutex logic must be
** prepared to accommodate additional static mutexes.
*/
#define SQLITE_MUTEX_FAST             0
#define SQLITE_MUTEX_RECURSIVE        1
#define SQLITE_MUTEX_STATIC_MASTER    2
#define SQLITE_MUTEX_STATIC_MEM       3  /* sqlite3_malloc() */
#define SQLITE_MUTEX_STATIC_MEM2      4  /* NOT USED */
#define SQLITE_MUTEX_STATIC_OPEN      4  /* sqlite3BtreeOpen() */
#define SQLITE_MUTEX_STATIC_PRNG      5  /* sqlite3_random() */
#define SQLITE_MUTEX_STATIC_LRU       6  /* lru page list */
#define SQLITE_MUTEX_STATIC_LRU2      7  /* NOT USED */
#define SQLITE_MUTEX_STATIC_PMEM      7  /* sqlite3PageMalloc() */
#define SQLITE_MUTEX_STATIC_APP1      8  /* For use by application */
#define SQLITE_MUTEX_STATIC_APP2      9  /* For use by application */
#define SQLITE_MUTEX_STATIC_APP3     10  /* For use by application */
#define SQLITE_MUTEX_STATIC_VFS1     11  /* For use by built-in VFS */
#define SQLITE_MUTEX_STATIC_VFS2     12  /* For use by extension VFS */
#define SQLITE_MUTEX_STATIC_VFS3     13  /* For use by application VFS */

/*
** CAPI3REF: Status Parameters
** KEYWORDS: {status parameters}
**
** These integer constants designate various run-time status parameters
** that can be returned by [sqlite3_status()].
**
** <dl>
** [[SQLITE_STATUS_MEMORY_USED]] ^(<dt>SQLITE_STATUS_MEMORY_USED</dt>
** <dd>This parameter is the current amount of memory checked out
** using [sqlite3_malloc()], either directly or indirectly.  The
** figure includes calls made to [sqlite3_malloc()] by the application
** and internal memory usage by the SQLite library.  Scratch memory
** controlled by [SQLITE_CONFIG_SCRATCH] and auxiliary page-cache
** memory controlled by [SQLITE_CONFIG_PAGECACHE] is not included in
** this parameter.  The amount returned is the sum of the allocation
** sizes as reported by the xSize method in [sqlite3_mem_methods].</dd>)^
**
** [[SQLITE_STATUS_MALLOC_SIZE]] ^(<dt>SQLITE_STATUS_MALLOC_SIZE</dt>
** <dd>This parameter records the largest memory allocation request
** handed to [sqlite3_malloc()] or [sqlite3_realloc()] (or their
** internal equivalents).  Only the value returned in the
** *pHighwater parameter to [sqlite3_status()] is of interest.  
** The value written into the *pCurrent parameter is undefined.</dd>)^
**
** [[SQLITE_STATUS_MALLOC_COUNT]] ^(<dt>SQLITE_STATUS_MALLOC_COUNT</dt>
** <dd>This parameter records the number of separate memory allocations
** currently checked out.</dd>)^
**
** [[SQLITE_STATUS_PAGECACHE_USED]] ^(<dt>SQLITE_STATUS_PAGECACHE_USED</dt>
** <dd>This parameter returns the number of pages used out of the
** [pagecache memory allocator] that was configured using 
** [SQLITE_CONFIG_PAGECACHE].  The
** value returned is in pages, not in bytes.</dd>)^
**
** [[SQLITE_STATUS_PAGECACHE_OVERFLOW]] 
** ^(<dt>SQLITE_STATUS_PAGECACHE_OVERFLOW</dt>
** <dd>This parameter returns the number of bytes of page cache
** allocation which could not be satisfied by the [SQLITE_CONFIG_PAGECACHE]
** buffer and where forced to overflow to [sqlite3_malloc()].  The
** returned value includes allocations that overflowed because they
** where too large (they were larger than the "sz" parameter to
** [SQLITE_CONFIG_PAGECACHE]) and allocations that overflowed because
** no space was left in the page cache.</dd>)^
**
** [[SQLITE_STATUS_PAGECACHE_SIZE]] ^(<dt>SQLITE_STATUS_PAGECACHE_SIZE</dt>
** <dd>This parameter records the largest memory allocation request
** handed to [pagecache memory allocator].  Only the value returned in the
** *pHighwater parameter to [sqlite3_status()] is of interest.  
** The value written into the *pCurrent parameter is undefined.</dd>)^
**
** [[SQLITE_STATUS_SCRATCH_USED]] ^(<dt>SQLITE_STATUS_SCRATCH_USED</dt>
** <dd>This parameter returns the number of allocations used out of the
** [scratch memory allocator] configured using
** [SQLITE_CONFIG_SCRATCH].  The value returned is in allocations, not
** in bytes.  Since a single thread may only have one scratch allocation
** outstanding at time, this parameter also reports the number of threads
** using scratch memory at the same time.</dd>)^
**
** [[SQLITE_STATUS_SCRATCH_OVERFLOW]] ^(<dt>SQLITE_STATUS_SCRATCH_OVERFLOW</dt>
** <dd>This parameter returns the number of bytes of scratch memory
** allocation which could not be satisfied by the [SQLITE_CONFIG_SCRATCH]
** buffer and where forced to overflow to [sqlite3_malloc()].  The values
** returned include overflows because the requested allocation was too
** larger (that is, because the requested allocation was larger than the
** "sz" parameter to [SQLITE_CONFIG_SCRATCH]) and because no scratch buffer
** slots were available.
** </dd>)^
**
** [[SQLITE_STATUS_SCRATCH_SIZE]] ^(<dt>SQLITE_STATUS_SCRATCH_SIZE</dt>
** <dd>This parameter records the largest memory allocation request
** handed to [scratch memory allocator].  Only the value returned in the
** *pHighwater parameter to [sqlite3_status()] is of interest.  
** The value written into the *pCurrent parameter is undefined.</dd>)^
**
** [[SQLITE_STATUS_PARSER_STACK]] ^(<dt>SQLITE_STATUS_PARSER_STACK</dt>
** <dd>This parameter records the deepest parser stack.  It is only
** meaningful if SQLite is compiled with [YYTRACKMAXSTACKDEPTH].</dd>)^
** </dl>
**
** New status parameters may be added from time to time.
*/
#define SQLITE_STATUS_MEMORY_USED          0
#define SQLITE_STATUS_PAGECACHE_USED       1
#define SQLITE_STATUS_PAGECACHE_OVERFLOW   2
#define SQLITE_STATUS_SCRATCH_USED         3
#define SQLITE_STATUS_SCRATCH_OVERFLOW     4
#define SQLITE_STATUS_MALLOC_SIZE          5
#define SQLITE_STATUS_PARSER_STACK         6
#define SQLITE_STATUS_PAGECACHE_SIZE       7
#define SQLITE_STATUS_SCRATCH_SIZE         8
#define SQLITE_STATUS_MALLOC_COUNT         9

/*
** CAPI3REF: Status Parameters for database connections
** KEYWORDS: {SQLITE_DBSTATUS options}
**
** These constants are the available integer "verbs" that can be passed as
** the second argument to the [sqlite3_db_status()] interface.
**
** New verbs may be added in future releases of SQLite. Existing verbs
** might be discontinued. Applications should check the return code from
** [sqlite3_db_status()] to make sure that the call worked.
** The [sqlite3_db_status()] interface will return a non-zero error code
** if a discontinued or unsupported verb is invoked.
**
** <dl>
** [[SQLITE_DBSTATUS_LOOKASIDE_USED]] ^(<dt>SQLITE_DBSTATUS_LOOKASIDE_USED</dt>
** <dd>This parameter returns the number of lookaside memory slots currently
** checked out.</dd>)^
**
** [[SQLITE_DBSTATUS_LOOKASIDE_HIT]] ^(<dt>SQLITE_DBSTATUS_LOOKASIDE_HIT</dt>
** <dd>This parameter returns the number malloc attempts that were 
** satisfied using lookaside memory. Only the high-water value is meaningful;
** the current value is always zero.)^
**
** [[SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE]]
** ^(<dt>SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE</dt>
** <dd>This parameter returns the number malloc attempts that might have
** been satisfied using lookaside memory but failed due to the amount of
** memory requested being larger than the lookaside slot size.
** Only the high-water value is meaningful;
** the current value is always zero.)^
**
** [[SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL]]
** ^(<dt>SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL</dt>
** <dd>This parameter returns the number malloc attempts that might have
** been satisfied using lookaside memory but failed due to all lookaside
** memory already being in use.
** Only the high-water value is meaningful;
** the current value is always zero.)^
**
** [[SQLITE_DBSTATUS_CACHE_USED]] ^(<dt>SQLITE_DBSTATUS_CACHE_USED</dt>
** <dd>This parameter returns the approximate number of bytes of heap
** memory used by all pager caches associated with the database connection.)^
** ^The highwater mark associated with SQLITE_DBSTATUS_CACHE_USED is always 0.
**
** [[SQLITE_DBSTATUS_SCHEMA_USED]] ^(<dt>SQLITE_DBSTATUS_SCHEMA_USED</dt>
** <dd>This parameter returns the approximate number of bytes of heap
** memory used to store the schema for all databases associated
** with the connection - main, temp, and any [ATTACH]-ed databases.)^ 
** ^The full amount of memory used by the schemas is reported, even if the
** schema memory is shared with other database connections due to
** [shared cache mode] being enabled.
** ^The highwater mark associated with SQLITE_DBSTATUS_SCHEMA_USED is always 0.
**
** [[SQLITE_DBSTATUS_STMT_USED]] ^(<dt>SQLITE_DBSTATUS_STMT_USED</dt>
** <dd>This parameter returns the approximate number of bytes of heap
** and lookaside memory used by all prepared statements associated with
** the database connection.)^
** ^The highwater mark associated with SQLITE_DBSTATUS_STMT_USED is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_CACHE_HIT]] ^(<dt>SQLITE_DBSTATUS_CACHE_HIT</dt>
** <dd>This parameter returns the number of pager cache hits that have
** occurred.)^ ^The highwater mark associated with SQLITE_DBSTATUS_CACHE_HIT 
** is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_CACHE_MISS]] ^(<dt>SQLITE_DBSTATUS_CACHE_MISS</dt>
** <dd>This parameter returns the number of pager cache misses that have
** occurred.)^ ^The highwater mark associated with SQLITE_DBSTATUS_CACHE_MISS 
** is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_CACHE_WRITE]] ^(<dt>SQLITE_DBSTATUS_CACHE_WRITE</dt>
** <dd>This parameter returns the number of dirty cache entries that have
** been written to disk. Specifically, the number of pages written to the
** wal file in wal mode databases, or the number of pages written to the
** database file in rollback mode databases. Any pages written as part of
** transaction rollback or database recovery operations are not included.
** If an IO or other error occurs while writing a page to disk, the effect
** on subsequent SQLITE_DBSTATUS_CACHE_WRITE requests is undefined.)^ ^The
** highwater mark associated with SQLITE_DBSTATUS_CACHE_WRITE is always 0.
** </dd>
**
** [[SQLITE_DBSTATUS_DEFERRED_FKS]] ^(<dt>SQLITE_DBSTATUS_DEFERRED_FKS</dt>
** <dd>This parameter returns zero for the current value if and only if
** all foreign key constraints (deferred or immediate) have been
** resolved.)^  ^The highwater mark is always 0.
** </dd>
** </dl>
*/
#define SQLITE_DBSTATUS_LOOKASIDE_USED       0
#define SQLITE_DBSTATUS_CACHE_USED           1
#define SQLITE_DBSTATUS_SCHEMA_USED          2
#define SQLITE_DBSTATUS_STMT_USED            3
#define SQLITE_DBSTATUS_LOOKASIDE_HIT        4
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_SIZE  5
#define SQLITE_DBSTATUS_LOOKASIDE_MISS_FULL  6
#define SQLITE_DBSTATUS_CACHE_HIT            7
#define SQLITE_DBSTATUS_CACHE_MISS           8
#define SQLITE_DBSTATUS_CACHE_WRITE          9
#define SQLITE_DBSTATUS_DEFERRED_FKS        10
#define SQLITE_DBSTATUS_MAX                 10   /* Largest defined DBSTATUS */

/*
** CAPI3REF: Checkpoint Mode Values
** KEYWORDS: {checkpoint mode}
**
** These constants define all valid values for the "checkpoint mode" passed
** as the third parameter to the [sqlite3_wal_checkpoint_v2()] interface.
** See the [sqlite3_wal_checkpoint_v2()] documentation for details on the
** meaning of each of these checkpoint modes.
*/
#define SQLITE_CHECKPOINT_PASSIVE  0  /* Do as much as possible w/o blocking */
#define SQLITE_CHECKPOINT_FULL     1  /* Wait for writers, then checkpoint */
#define SQLITE_CHECKPOINT_RESTART  2  /* Like FULL but wait for for readers */
#define SQLITE_CHECKPOINT_TRUNCATE 3  /* Like RESTART but also truncate WAL */

/*
** CAPI3REF: Custom Page Cache Object
**
** The sqlite3_pcache type is opaque.  It is implemented by
** the pluggable module.  The SQLite core has no knowledge of
** its size or internal structure and never deals with the
** sqlite3_pcache object except by holding and passing pointers
** to the object.
**
** See [sqlite3_pcache_methods2] for additional information.
*/
typedef struct sqlite3_pcache sqlite3_pcache;

/*
** CAPI3REF: Custom Page Cache Object
**
** The sqlite3_pcache_page object represents a single page in the
** page cache.  The page cache will allocate instances of this
** object.  Various methods of the page cache use pointers to instances
** of this object as parameters or as their return value.
**
** See [sqlite3_pcache_methods2] for additional information.
*/
typedef struct sqlite3_pcache_page sqlite3_pcache_page;
struct sqlite3_pcache_page {
  void *pBuf;        /* The content of the page */
  void *pExtra;      /* Extra information associated with the page */
};

/*
** CAPI3REF: Application Defined Page Cache.
** KEYWORDS: {page cache}
**
** ^(The [sqlite3_config]([SQLITE_CONFIG_PCACHE2], ...) interface can
** register an alternative page cache implementation by passing in an 
** instance of the sqlite3_pcache_methods2 structure.)^
** In many applications, most of the heap memory allocated by 
** SQLite is used for the page cache.
** By implementing a 
** custom page cache using this API, an application can better control
** the amount of memory consumed by SQLite, the way in which 
** that memory is allocated and released, and the policies used to 
** determine exactly which parts of a database file are cached and for 
** how long.
**
** The alternative page cache mechanism is an
** extreme measure that is only needed by the most demanding applications.
** The built-in page cache is recommended for most uses.
**
** ^(The contents of the sqlite3_pcache_methods2 structure are copied to an
** internal buffer by SQLite within the call to [sqlite3_config].  Hence
** the application may discard the parameter after the call to
** [sqlite3_config()] returns.)^
**
** [[the xInit() page cache method]]
** ^(The xInit() method is called once for each effective 
** call to [sqlite3BtreeInitialize()])^
** (usually only once during the lifetime of the process). ^(The xInit()
** method is passed a copy of the sqlite3_pcache_methods2.pArg value.)^
** The intent of the xInit() method is to set up global data structures 
** required by the custom page cache implementation. 
** ^(If the xInit() method is NULL, then the 
** built-in default page cache is used instead of the application defined
** page cache.)^
**
** [[the xShutdown() page cache method]]
** ^The xShutdown() method is called by [sqlite3BtreeShutdown()].
** It can be used to clean up 
** any outstanding resources before process shutdown, if required.
** ^The xShutdown() method may be NULL.
**
** ^SQLite automatically serializes calls to the xInit method,
** so the xInit method need not be threadsafe.  ^The
** xShutdown method is only called from [sqlite3BtreeShutdown()] so it does
** not need to be threadsafe either.  All other methods must be threadsafe
** in multithreaded applications.
**
** ^SQLite will never invoke xInit() more than once without an intervening
** call to xShutdown().
**
** [[the xCreate() page cache methods]]
** ^SQLite invokes the xCreate() method to construct a new cache instance.
** SQLite will typically create one cache instance for each open database file,
** though this is not guaranteed. ^The
** first parameter, szPage, is the size in bytes of the pages that must
** be allocated by the cache.  ^szPage will always a power of two.  ^The
** second parameter szExtra is a number of bytes of extra storage 
** associated with each page cache entry.  ^The szExtra parameter will
** a number less than 250.  SQLite will use the
** extra szExtra bytes on each page to store metadata about the underlying
** database page on disk.  The value passed into szExtra depends
** on the SQLite version, the target platform, and how SQLite was compiled.
** ^The third argument to xCreate(), bPurgeable, is true if the cache being
** created will be used to cache database pages of a file stored on disk, or
** false if it is used for an in-memory database. The cache implementation
** does not have to do anything special based with the value of bPurgeable;
** it is purely advisory.  ^On a cache where bPurgeable is false, SQLite will
** never invoke xUnpin() except to deliberately delete a page.
** ^In other words, calls to xUnpin() on a cache with bPurgeable set to
** false will always have the "discard" flag set to true.  
** ^Hence, a cache created with bPurgeable false will
** never contain any unpinned pages.
**
** [[the xCachesize() page cache method]]
** ^(The xCachesize() method may be called at any time by SQLite to set the
** suggested maximum cache-size (number of pages stored by) the cache
** instance passed as the first argument. This is the value configured using
** the SQLite "[PRAGMA cache_size]" command.)^  As with the bPurgeable
** parameter, the implementation is not required to do anything with this
** value; it is advisory only.
**
** [[the xPagecount() page cache methods]]
** The xPagecount() method must return the number of pages currently
** stored in the cache, both pinned and unpinned.
** 
** [[the xFetch() page cache methods]]
** The xFetch() method locates a page in the cache and returns a pointer to 
** an sqlite3_pcache_page object associated with that page, or a NULL pointer.
** The pBuf element of the returned sqlite3_pcache_page object will be a
** pointer to a buffer of szPage bytes used to store the content of a 
** single database page.  The pExtra element of sqlite3_pcache_page will be
** a pointer to the szExtra bytes of extra storage that SQLite has requested
** for each entry in the page cache.
**
** The page to be fetched is determined by the key. ^The minimum key value
** is 1.  After it has been retrieved using xFetch, the page is considered
** to be "pinned".
**
** If the requested page is already in the page cache, then the page cache
** implementation must return a pointer to the page buffer with its content
** intact.  If the requested page is not already in the cache, then the
** cache implementation should use the value of the createFlag
** parameter to help it determined what action to take:
**
** <table border=1 width=85% align=center>
** <tr><th> createFlag <th> Behavior when page is not already in cache
** <tr><td> 0 <td> Do not allocate a new page.  Return NULL.
** <tr><td> 1 <td> Allocate a new page if it easy and convenient to do so.
**                 Otherwise return NULL.
** <tr><td> 2 <td> Make every effort to allocate a new page.  Only return
**                 NULL if allocating a new page is effectively impossible.
** </table>
**
** ^(SQLite will normally invoke xFetch() with a createFlag of 0 or 1.  SQLite
** will only use a createFlag of 2 after a prior call with a createFlag of 1
** failed.)^  In between the to xFetch() calls, SQLite may
** attempt to unpin one or more cache pages by spilling the content of
** pinned pages to disk and synching the operating system disk cache.
**
** [[the xUnpin() page cache method]]
** ^xUnpin() is called by SQLite with a pointer to a currently pinned page
** as its second argument.  If the third parameter, discard, is non-zero,
** then the page must be evicted from the cache.
** ^If the discard parameter is
** zero, then the page may be discarded or retained at the discretion of
** page cache implementation. ^The page cache implementation
** may choose to evict unpinned pages at any time.
**
** The cache must not perform any reference counting. A single 
** call to xUnpin() unpins the page regardless of the number of prior calls 
** to xFetch().
**
** [[the xRekey() page cache methods]]
** The xRekey() method is used to change the key value associated with the
** page passed as the second argument. If the cache
** previously contains an entry associated with newKey, it must be
** discarded. ^Any prior cache entry associated with newKey is guaranteed not
** to be pinned.
**
** When SQLite calls the xTruncate() method, the cache must discard all
** existing cache entries with page numbers (keys) greater than or equal
** to the value of the iLimit parameter passed to xTruncate(). If any
** of these pages are pinned, they are implicitly unpinned, meaning that
** they can be safely discarded.
**
** [[the xDestroy() page cache method]]
** ^The xDestroy() method is used to delete a cache allocated by xCreate().
** All resources associated with the specified cache should be freed. ^After
** calling the xDestroy() method, SQLite considers the [sqlite3_pcache*]
** handle invalid, and will not use it with any other sqlite3_pcache_methods2
** functions.
**
** [[the xShrink() page cache method]]
** ^SQLite invokes the xShrink() method when it wants the page cache to
** free up as much of heap memory as possible.  The page cache implementation
** is not obligated to free any memory, but well-behaved implementations should
** do their best.
*/
typedef struct sqlite3_pcache_methods2 sqlite3_pcache_methods2;
struct sqlite3_pcache_methods2 {
  int iVersion;
  void *pArg;
  int (*xInit)(void*);
  void (*xShutdown)(void*);
  sqlite3_pcache *(*xCreate)(int szPage, int szExtra, int bPurgeable);
  void (*xCachesize)(sqlite3_pcache*, int nCachesize);
  int (*xPagecount)(sqlite3_pcache*);
  sqlite3_pcache_page *(*xFetch)(sqlite3_pcache*, unsigned key, int createFlag);
  void (*xUnpin)(sqlite3_pcache*, sqlite3_pcache_page*, int discard);
  void (*xRekey)(sqlite3_pcache*, sqlite3_pcache_page*, 
      unsigned oldKey, unsigned newKey);
  void (*xTruncate)(sqlite3_pcache*, unsigned iLimit);
  void (*xDestroy)(sqlite3_pcache*);
  void (*xShrink)(sqlite3_pcache*);
};

/*
** CAPI3REF: Online Backup Object
**
** The sqlite3_backup object records state information about an ongoing
** online backup operation.  ^The sqlite3_backup object is created by
** a call to [sqlite3_backup_init()] and is destroyed by a call to
** [sqlite3_backup_finish()].
**
** See Also: [Using the SQLite Online Backup API]
*/
typedef struct sqlite3_backup sqlite3_backup;

/*
** CAPI3REF: Error Logging Interface
**
** ^The [sqlite3_log()] interface writes a message into the [error log]
** established by the [SQLITE_CONFIG_LOG] option to [sqlite3_config()].
** ^If logging is enabled, the zFormat string and subsequent arguments are
** used with [sqlite3_snprintf()] to generate the final output string.
**
** The sqlite3_log() interface is intended for use by extensions such as
** virtual tables, collating functions, and SQL functions.  While there is
** nothing to prevent an application from calling sqlite3_log(), doing so
** is considered bad form.
**
** The zFormat string must not be NULL.
**
** To avoid deadlocks and other threading problems, the sqlite3_log() routine
** will not use dynamically allocated memory.  The log message is stored in
** a fixed-length buffer on the stack.  If the log message is longer than
** a few hundred characters, it will be truncated to the length of the
** buffer.
*/
SQLITE_PRIVATE void sqlite3_log(int iErrCode, const char *zFormat, ...);

/*
** CAPI3REF: Text Encodings
**
** These constant define integer codes that represent the various
** text encodings supported by SQLite.
*/
#define SQLITE_UTF8           1    /* IMP: R-37514-35566 */
#define SQLITE_UTF16LE        2    /* IMP: R-03371-37637 */
#define SQLITE_UTF16BE        3    /* IMP: R-51971-34154 */
#define SQLITE_UTF16          4    /* Use native byte order */
#define SQLITE_ANY            5    /* Deprecated */
#define SQLITE_UTF16_ALIGNED  8    /* sqlite3_create_collation only */

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
*/
#ifdef _HAVE_SQLITE_CONFIG_H
#include "config.h"
#endif

/************** Include sqliteLimit.h in the middle of sqliteInt.h ***********/
/************** Begin file sqliteLimit.h *************************************/
/*
** 2007 May 7
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** 
** This file defines various limits of what SQLite can process.
*/

/*
** The maximum length of a TEXT or BLOB in bytes.   This also
** limits the size of a row in a table or index.
**
** The hard limit is the ability of a 32-bit signed integer
** to count the size: 2^31-1 or 2147483647.
*/
#ifndef SQLITE_MAX_LENGTH
# define SQLITE_MAX_LENGTH 1000000000
#endif

/*
** This is the maximum number of
**
**    * Columns in a table
**    * Columns in an index
**    * Columns in a view
**    * Terms in the SET clause of an UPDATE statement
**    * Terms in the result set of a SELECT statement
**    * Terms in the GROUP BY or ORDER BY clauses of a SELECT statement.
**    * Terms in the VALUES clause of an INSERT statement
**
** The hard upper limit here is 32676.  Most database people will
** tell you that in a well-normalized database, you usually should
** not have more than a dozen or so columns in any table.  And if
** that is the case, there is no point in having more than a few
** dozen values in any of the other situations described above.
*/
#ifndef SQLITE_MAX_COLUMN
# define SQLITE_MAX_COLUMN 2000
#endif

/*
** The maximum length of a single SQL statement in bytes.
**
** It used to be the case that setting this value to zero would
** turn the limit off.  That is no longer true.  It is not possible
** to turn this limit off.
*/
#ifndef SQLITE_MAX_SQL_LENGTH
# define SQLITE_MAX_SQL_LENGTH 1000000000
#endif

/*
** The maximum depth of an expression tree. This is limited to 
** some extent by SQLITE_MAX_SQL_LENGTH. But sometime you might 
** want to place more severe limits on the complexity of an 
** expression.
**
** A value of 0 used to mean that the limit was not enforced.
** But that is no longer true.  The limit is now strictly enforced
** at all times.
*/
#ifndef SQLITE_MAX_EXPR_DEPTH
# define SQLITE_MAX_EXPR_DEPTH 1000
#endif

/*
** The maximum number of terms in a compound SELECT statement.
** The code generator for compound SELECT statements does one
** level of recursion for each term.  A stack overflow can result
** if the number of terms is too large.  In practice, most SQL
** never has more than 3 or 4 terms.  Use a value of 0 to disable
** any limit on the number of terms in a compount SELECT.
*/
#ifndef SQLITE_MAX_COMPOUND_SELECT
# define SQLITE_MAX_COMPOUND_SELECT 500
#endif

/*
** The maximum number of opcodes in a VDBE program.
** Not currently enforced.
*/
#ifndef SQLITE_MAX_VDBE_OP
# define SQLITE_MAX_VDBE_OP 25000
#endif

/*
** The maximum number of arguments to an SQL function.
*/
#ifndef SQLITE_MAX_FUNCTION_ARG
# define SQLITE_MAX_FUNCTION_ARG 127
#endif

/*
** The suggested maximum number of in-memory pages to use for
** the main database table and for temporary tables.
**
** IMPLEMENTATION-OF: R-31093-59126 The default suggested cache size
** is 2000 pages.
** IMPLEMENTATION-OF: R-48205-43578 The default suggested cache size can be
** altered using the SQLITE_DEFAULT_CACHE_SIZE compile-time options.
*/
#ifndef SQLITE_DEFAULT_CACHE_SIZE
# define SQLITE_DEFAULT_CACHE_SIZE  2000
#endif

/*
** The default number of frames to accumulate in the log file before
** checkpointing the database in WAL mode.
*/
#ifndef SQLITE_DEFAULT_WAL_AUTOCHECKPOINT
# define SQLITE_DEFAULT_WAL_AUTOCHECKPOINT  1000
#endif

/*
** The maximum number of attached databases.  This must be between 0
** and 62.  The upper bound on 62 is because a 64-bit integer bitmap
** is used internally to track attached databases.
*/
#ifndef SQLITE_MAX_ATTACHED
# define SQLITE_MAX_ATTACHED 10
#endif


/*
** The maximum value of a ?nnn wildcard that the parser will accept.
*/
#ifndef SQLITE_MAX_VARIABLE_NUMBER
# define SQLITE_MAX_VARIABLE_NUMBER 999
#endif

/* Maximum page size.  The upper bound on this value is 65536.  This a limit
** imposed by the use of 16-bit offsets within each page.
**
** Earlier versions of SQLite allowed the user to change this value at
** compile time. This is no longer permitted, on the grounds that it creates
** a library that is technically incompatible with an SQLite library 
** compiled with a different limit. If a process operating on a database 
** with a page-size of 65536 bytes crashes, then an instance of SQLite 
** compiled with the default page-size limit will not be able to rollback 
** the aborted transaction. This could lead to database corruption.
*/
#ifdef SQLITE_MAX_PAGE_SIZE
# undef SQLITE_MAX_PAGE_SIZE
#endif
#define SQLITE_MAX_PAGE_SIZE 65536


/*
** The default size of a database page.
*/
#ifndef SQLITE_DEFAULT_PAGE_SIZE
# define SQLITE_DEFAULT_PAGE_SIZE 1024
#endif
#if SQLITE_DEFAULT_PAGE_SIZE>SQLITE_MAX_PAGE_SIZE
# undef SQLITE_DEFAULT_PAGE_SIZE
# define SQLITE_DEFAULT_PAGE_SIZE SQLITE_MAX_PAGE_SIZE
#endif

/*
** Ordinarily, if no value is explicitly provided, SQLite creates databases
** with page size SQLITE_DEFAULT_PAGE_SIZE. However, based on certain
** device characteristics (sector-size and atomic write() support),
** SQLite may choose a larger value. This constant is the maximum value
** SQLite will choose on its own.
*/
#ifndef SQLITE_MAX_DEFAULT_PAGE_SIZE
# define SQLITE_MAX_DEFAULT_PAGE_SIZE 8192
#endif
#if SQLITE_MAX_DEFAULT_PAGE_SIZE>SQLITE_MAX_PAGE_SIZE
# undef SQLITE_MAX_DEFAULT_PAGE_SIZE
# define SQLITE_MAX_DEFAULT_PAGE_SIZE SQLITE_MAX_PAGE_SIZE
#endif


/*
** Maximum number of pages in one database file.
**
** This is really just the default value for the max_page_count pragma.
** This value can be lowered (or raised) at run-time using that the
** max_page_count macro.
*/
#ifndef SQLITE_MAX_PAGE_COUNT
# define SQLITE_MAX_PAGE_COUNT 1073741823
#endif

/*
** Maximum length (in bytes) of the pattern in a LIKE or GLOB
** operator.
*/
#ifndef SQLITE_MAX_LIKE_PATTERN_LENGTH
# define SQLITE_MAX_LIKE_PATTERN_LENGTH 50000
#endif

/*
** Maximum depth of recursion for triggers.
**
** A value of 1 means that a trigger program will not be able to itself
** fire any triggers. A value of 0 means that no trigger programs at all 
** may be executed.
*/
#ifndef SQLITE_MAX_TRIGGER_DEPTH
# define SQLITE_MAX_TRIGGER_DEPTH 1000
#endif

/************** End of sqliteLimit.h *****************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/* Disable nuisance warnings on Borland compilers */
#if defined(__BORLANDC__)
#pragma warn -rch /* unreachable code */
#pragma warn -ccc /* Condition is always true or false */
#pragma warn -aus /* Assigned value is never used */
#pragma warn -csu /* Comparing signed and unsigned */
#pragma warn -spa /* Suspicious pointer arithmetic */
#endif

/*
** Include standard header files as necessary
*/
#ifdef HAVE_STDINT_H
#include <stdint.h>
#endif
#ifdef HAVE_INTTYPES_H
#include <inttypes.h>
#endif

/*
** The following macros are used to cast pointers to integers and
** integers to pointers.  The way you do this varies from one compiler
** to the next, so we have developed the following set of #if statements
** to generate appropriate macros for a wide range of compilers.
**
** The correct "ANSI" way to do this is to use the intptr_t type. 
** Unfortunately, that typedef is not available on all compilers, or
** if it is available, it requires an #include of specific headers
** that vary from one machine to the next.
**
** Ticket #3860:  The llvm-gcc-4.2 compiler from Apple chokes on
** the ((void*)&((char*)0)[X]) construct.  But MSVC chokes on ((void*)(X)).
** So we have to define the macros in different ways depending on the
** compiler.
*/
#if defined(__PTRDIFF_TYPE__)  /* This case should work for GCC */
# define SQLITE_INT_TO_PTR(X)  ((void*)(__PTRDIFF_TYPE__)(X))
# define SQLITE_PTR_TO_INT(X)  ((int)(__PTRDIFF_TYPE__)(X))
#elif !defined(__GNUC__)       /* Works for compilers other than LLVM */
# define SQLITE_INT_TO_PTR(X)  ((void*)&((char*)0)[X])
# define SQLITE_PTR_TO_INT(X)  ((int)(((char*)X)-(char*)0))
#elif defined(HAVE_STDINT_H)   /* Use this case if we have ANSI headers */
# define SQLITE_INT_TO_PTR(X)  ((void*)(intptr_t)(X))
# define SQLITE_PTR_TO_INT(X)  ((int)(intptr_t)(X))
#else                          /* Generates a warning - but it always works */
# define SQLITE_INT_TO_PTR(X)  ((void*)(X))
# define SQLITE_PTR_TO_INT(X)  ((int)(X))
#endif

/*
** A macro to hint to the compiler that a function should not be
** inlined.
*/
#if defined(__GNUC__)
#  define SQLITE_NOINLINE  __attribute__((noinline))
#elif defined(_MSC_VER) && _MSC_VER>=1310
#  define SQLITE_NOINLINE  __declspec(noinline)
#else
#  define SQLITE_NOINLINE
#endif

/*
** Make sure that the compiler intrinsics we desire are enabled when
** compiling with an appropriate version of MSVC unless prevented by
** the SQLITE_DISABLE_INTRINSIC define.
*/
#if !defined(SQLITE_DISABLE_INTRINSIC)
#  if defined(_MSC_VER) && _MSC_VER>=1300
#    if !defined(_WIN32_WCE)
#      include <intrin.h>
#      pragma intrinsic(_byteswap_ushort)
#      pragma intrinsic(_byteswap_ulong)
#      pragma intrinsic(_ReadWriteBarrier)
#    else
#      include <cmnintrin.h>
#    endif
#  endif
#endif

/*
** Powersafe overwrite is on by default.  But can be turned off using
** the -DSQLITE_POWERSAFE_OVERWRITE=0 command-line option.
*/
#ifndef SQLITE_POWERSAFE_OVERWRITE
# define SQLITE_POWERSAFE_OVERWRITE 1
#endif

/*
** EVIDENCE-OF: R-25715-37072 Memory allocation statistics are enabled by
** default unless SQLite is compiled with SQLITE_DEFAULT_MEMSTATUS=0 in
** which case memory allocation statistics are disabled by default.
*/
#if !defined(SQLITE_DEFAULT_MEMSTATUS)
# define SQLITE_DEFAULT_MEMSTATUS 1
#endif

/*
** Exactly one of the following macros must be defined in order to
** specify which memory allocation subsystem to use.
**
**     SQLITE_SYSTEM_MALLOC          // Use normal system malloc()
**     SQLITE_WIN32_MALLOC           // Use Win32 native heap API
**     SQLITE_ZERO_MALLOC            // Use a stub allocator that always fails
**     SQLITE_MEMDEBUG               // Debugging version of system malloc()
**
** On Windows, if the SQLITE_WIN32_MALLOC_VALIDATE macro is defined and the
** assert() macro is enabled, each call into the Win32 native heap subsystem
** will cause HeapValidate to be called.  If heap validation should fail, an
** assertion will be triggered.
**
** If none of the above are defined, then set SQLITE_SYSTEM_MALLOC as
** the default.
*/
#if defined(SQLITE_SYSTEM_MALLOC) \
  + defined(SQLITE_WIN32_MALLOC) \
  + defined(SQLITE_ZERO_MALLOC) \
  + defined(SQLITE_MEMDEBUG)>1
# error "Two or more of the following compile-time configuration options\
 are defined but at most one is allowed:\
 SQLITE_SYSTEM_MALLOC, SQLITE_WIN32_MALLOC, SQLITE_MEMDEBUG,\
 SQLITE_ZERO_MALLOC"
#endif
#if defined(SQLITE_SYSTEM_MALLOC) \
  + defined(SQLITE_WIN32_MALLOC) \
  + defined(SQLITE_ZERO_MALLOC) \
  + defined(SQLITE_MEMDEBUG)==0
# define SQLITE_SYSTEM_MALLOC 1
#endif

/*
** We need to define _XOPEN_SOURCE as follows in order to enable
** recursive mutexes on most Unix systems and fchmod() on OpenBSD.
** But _XOPEN_SOURCE define causes problems for Mac OS X, so omit
** it.
*/
#if !defined(_XOPEN_SOURCE) && !defined(__DARWIN__) && !defined(__APPLE__)
#  define _XOPEN_SOURCE 600
#endif

/*
** NDEBUG and SQLITE_DEBUG are opposites.  It should always be true that
** defined(NDEBUG)==!defined(SQLITE_DEBUG).  If this is not currently true,
** make it true by defining or undefining NDEBUG.
**
** Setting NDEBUG makes the code smaller and faster by disabling the
** assert() statements in the code.  So we want the default action
** to be for NDEBUG to be set and NDEBUG to be undefined only if SQLITE_DEBUG
** is set.  Thus NDEBUG becomes an opt-in rather than an opt-out
** feature.
*/
#if !defined(NDEBUG) && !defined(SQLITE_DEBUG) 
# define NDEBUG 1
#endif
#if defined(NDEBUG) && defined(SQLITE_DEBUG)
# undef NDEBUG
#endif

/*
** The testcase() macro is used to aid in coverage testing.  When 
** doing coverage testing, the condition inside the argument to
** testcase() must be evaluated both true and false in order to
** get full branch coverage.  The testcase() macro is inserted
** to help ensure adequate test coverage in places where simple
** condition/decision coverage is inadequate.  For example, testcase()
** can be used to make sure boundary values are tested.  For
** bitmask tests, testcase() can be used to make sure each bit
** is significant and used at least once.  On switch statements
** where multiple cases go to the same block of code, testcase()
** can insure that all cases are evaluated.
**
*/
#ifdef SQLITE_COVERAGE_TEST
SQLITE_PRIVATE   void sqlite3Coverage(int);
# define testcase(X)  if( X ){ sqlite3Coverage(__LINE__); }
#else
# define testcase(X)
#endif

/*
** The TESTONLY macro is used to enclose variable declarations or
** other bits of code that are needed to support the arguments
** within testcase() and assert() macros.
*/
#if !defined(NDEBUG) || defined(SQLITE_COVERAGE_TEST)
# define TESTONLY(X)  X
#else
# define TESTONLY(X)
#endif

/*
** Sometimes we need a small amount of code such as a variable initialization
** to setup for a later assert() statement.  We do not want this code to
** appear when assert() is disabled.  The following macro is therefore
** used to contain that setup code.  The "VVA" acronym stands for
** "Verification, Validation, and Accreditation".  In other words, the
** code within VVA_ONLY() will only run during verification processes.
*/
#ifndef NDEBUG
# define VVA_ONLY(X)  X
#else
# define VVA_ONLY(X)
#endif

/*
** The ALWAYS and NEVER macros surround boolean expressions which 
** are intended to always be true or false, respectively.  Such
** expressions could be omitted from the code completely.  But they
** are included in a few cases in order to enhance the resilience
** of SQLite to unexpected behavior - to make the code "self-healing"
** or "ductile" rather than being "brittle" and crashing at the first
** hint of unplanned behavior.
**
** In other words, ALWAYS and NEVER are added for defensive code.
**
** When doing coverage testing ALWAYS and NEVER are hard-coded to
** be true and false so that the unreachable code they specify will
** not be counted as untested code.
*/
#if defined(SQLITE_COVERAGE_TEST)
# define ALWAYS(X)      (1)
# define NEVER(X)       (0)
#elif !defined(NDEBUG)
# define ALWAYS(X)      ((X)?1:(assert(0),0))
# define NEVER(X)       ((X)?(assert(0),1):0)
#else
# define ALWAYS(X)      (X)
# define NEVER(X)       (X)
#endif

/*
** Declarations used for tracing the operating system interfaces.
*/
#if defined(SQLITE_FORCE_OS_TRACE) || defined(SQLITE_TEST) || \
    (defined(SQLITE_DEBUG) && SQLITE_OS_WIN)
  extern int sqlite3OSTrace;
# define OSTRACE(X)          if( sqlite3OSTrace ) sqlite3DebugPrintf X
# define SQLITE_HAVE_OS_TRACE
#else
# define OSTRACE(X)
# undef  SQLITE_HAVE_OS_TRACE
#endif

/*
** Is the sqlite3ErrName() function needed in the build?  Currently,
** it is needed by "mutex_w32.c" (when debugging), "os_win.c" (when
** OSTRACE is enabled), and by several "test*.c" files (which are
** compiled using SQLITE_TEST).
*/
#if defined(SQLITE_HAVE_OS_TRACE) || defined(SQLITE_TEST) || \
    (defined(SQLITE_DEBUG) && SQLITE_OS_WIN)
# define SQLITE_NEED_ERR_NAME
#else
# undef  SQLITE_NEED_ERR_NAME
#endif

/*
** The macro unlikely() is a hint that surrounds a boolean
** expression that is usually false.  Macro likely() surrounds
** a boolean expression that is usually true.  These hints could,
** in theory, be used by the compiler to generate better code, but
** currently they are just comments for human readers.
*/
#define likely(X)    (X)
#define unlikely(X)  (X)

#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <stddef.h>

/*
** The "file format" number is an integer that is incremented whenever
** the VDBE-level file format changes.  The following macros define the
** the default file format for new databases and the maximum file format
** that the library can read.
*/
#define SQLITE_MAX_FILE_FORMAT 4
#ifndef SQLITE_DEFAULT_FILE_FORMAT
# define SQLITE_DEFAULT_FILE_FORMAT 4
#endif

/*
** The default initial allocation for the pagecache when using separate
** pagecaches for each database connection.  A positive number is the
** number of pages.  A negative number N translations means that a buffer
** of -1024*N bytes is allocated and used for as many pages as it will hold.
*/
#ifndef SQLITE_DEFAULT_PCACHE_INITSZ
# define SQLITE_DEFAULT_PCACHE_INITSZ 100
#endif

/*
** GCC does not define the offsetof() macro so we'll have to do it
** ourselves.
*/
#ifndef offsetof
#define offsetof(STRUCTURE,FIELD) ((int)((char*)&((STRUCTURE*)0)->FIELD))
#endif

/*
** Macros to compute minimum and maximum of two numbers.
*/
#define MIN(A,B) ((A)<(B)?(A):(B))
#define MAX(A,B) ((A)>(B)?(A):(B))

/*
** Swap two objects of type TYPE.
*/
#define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}

/*
** SQLITE_MAX_U32 is a u64 constant that is the maximum u64 value
** that can be stored in a u32 without loss of data.  The value
** is 0x00000000ffffffff.  But because of quirks of some compilers, we
** have to specify the value in the less intuitive manner shown:
*/
#define SQLITE_MAX_U32  ((((u64)1)<<32)-1)

/*
** Set the SQLITE_PTRSIZE macro to the number of bytes in a pointer
*/
#ifndef SQLITE_PTRSIZE
# if defined(__SIZEOF_POINTER__)
#   define SQLITE_PTRSIZE __SIZEOF_POINTER__
# elif defined(i386)     || defined(__i386__)   || defined(_M_IX86) ||    \
       defined(_M_ARM)   || defined(__arm__)    || defined(__x86)
#   define SQLITE_PTRSIZE 4
# else
#   define SQLITE_PTRSIZE 8
# endif
#endif

/*
** Constants for the largest and smallest possible 64-bit signed integers.
** These macros are designed to work correctly on both 32-bit and 64-bit
** compilers.
*/
#define LARGEST_INT64  (0xffffffff|(((i64)0x7fffffff)<<32))
#define SMALLEST_INT64 (((i64)-1) - LARGEST_INT64)

/* 
** Round up a number to the next larger multiple of 8.  This is used
** to force 8-byte alignment on 64-bit architectures.
*/
#define ROUND8(x)     (((x)+7)&~7)

/*
** Round down to the nearest multiple of 8
*/
#define ROUNDDOWN8(x) ((x)&~7)

/*
** Disable MMAP on platforms where it is known to not work
*/
#if defined(__OpenBSD__) || defined(__QNXNTO__)
# undef SQLITE_MAX_MMAP_SIZE
# define SQLITE_MAX_MMAP_SIZE 0
#endif

/*
** Default maximum size of memory used by memory-mapped I/O in the VFS
*/
#ifdef __APPLE__
# include <TargetConditionals.h>
# if TARGET_OS_IPHONE
#   undef SQLITE_MAX_MMAP_SIZE
#   define SQLITE_MAX_MMAP_SIZE 0
# endif
#endif
#ifndef SQLITE_MAX_MMAP_SIZE
# if defined(__linux__) \
  || defined(_WIN32) \
  || (defined(__APPLE__) && defined(__MACH__)) \
  || defined(__sun) \
  || defined(__FreeBSD__) \
  || defined(__DragonFly__)
#   define SQLITE_MAX_MMAP_SIZE 0x7fff0000  /* 2147418112 */
# else
#   define SQLITE_MAX_MMAP_SIZE 0
# endif
# define SQLITE_MAX_MMAP_SIZE_xc 1 /* exclude from ctime.c */
#endif

/*
** The default MMAP_SIZE is zero on all platforms.  Or, even if a larger
** default MMAP_SIZE is specified at compile-time, make sure that it does
** not exceed the maximum mmap size.
*/
#ifndef SQLITE_DEFAULT_MMAP_SIZE
# define SQLITE_DEFAULT_MMAP_SIZE 0
# define SQLITE_DEFAULT_MMAP_SIZE_xc 1  /* Exclude from ctime.c */
#endif
#if SQLITE_DEFAULT_MMAP_SIZE>SQLITE_MAX_MMAP_SIZE
# undef SQLITE_DEFAULT_MMAP_SIZE
# define SQLITE_DEFAULT_MMAP_SIZE SQLITE_MAX_MMAP_SIZE
#endif

/*
** An instance of the following structure is used to store the busy-handler
** callback for a given sqlite handle. 
**
** The sqlite.busyHandler member of the sqlite struct contains the busy
** callback for the database handle. Each pager opened via the sqlite
** handle is passed a pointer to sqlite.busyHandler. The busy-handler
** callback is currently invoked only from within pager.c.
*/
typedef struct BusyHandler BusyHandler;
struct BusyHandler {
  int (*xFunc)(void *,int);  /* The busy callback */
  void *pArg;                /* First arg to busy callback */
  int nBusy;                 /* Incremented with each busy call */
};

/*
** The root-page of the master database table.
*/
#define MASTER_ROOT       1

/*
** A convenience macro that returns the number of elements in
** an array.
*/
#define ArraySize(X)    ((int)(sizeof(X)/sizeof(X[0])))

/*
** When SQLITE_OMIT_WSD is defined, it means that the target platform does
** not support Writable Static Data (WSD) such as global and static variables.
** All variables must either be on the stack or dynamically allocated from
** the heap.  When WSD is unsupported, the variable declarations scattered
** throughout the SQLite code must become constants instead.  The SQLITE_WSD
** macro is used for this purpose.  And instead of referencing the variable
** directly, we use its constant as a key to lookup the run-time allocated
** buffer that holds real variable.  The constant is also the initializer
** for the run-time allocated buffer.
**
** In the usual case where WSD is supported, the SQLITE_WSD and GLOBAL
** macros become no-ops and have zero performance impact.
*/
#ifdef SQLITE_OMIT_WSD
  #define SQLITE_WSD const
  #define GLOBAL(t,v) (*(t*)sqlite3_wsd_find((void*)&(v), sizeof(v)))
  #define sqlite3GlobalConfig GLOBAL(struct Sqlite3Config, sqlite3Config)
SQLITE_PRIVATE   int sqlite3_wsd_init(int N, int J);
SQLITE_PRIVATE   void *sqlite3_wsd_find(void *K, int L);
#else
  #define SQLITE_WSD 
  #define GLOBAL(t,v) v
  #define sqlite3GlobalConfig sqlite3Config
#endif

/*
** The following macros are used to suppress compiler warnings and to
** make it clear to human readers when a function parameter is deliberately 
** left unused within the body of a function. This usually happens when
** a function is called via a function pointer. For example the 
** implementation of an SQL aggregate step callback may not use the
** parameter indicating the number of arguments passed to the aggregate,
** if it knows that this is enforced elsewhere.
**
** When a function parameter is not used at all within the body of a function,
** it is generally named "NotUsed" or "NotUsed2" to make things even clearer.
** However, these macros may also be used to suppress warnings related to
** parameters that may or may not be used depending on compilation options.
** For example those parameters only used in assert() statements. In these
** cases the parameters are named as per the usual conventions.
*/
#define UNUSED_PARAMETER(x) (void)(x)
#define UNUSED_PARAMETER2(x,y) UNUSED_PARAMETER(x),UNUSED_PARAMETER(y)

typedef struct Bitvec Bitvec;
typedef struct CollSeq CollSeq;
typedef struct PrintfArguments PrintfArguments;
typedef struct Savepoint Savepoint;
typedef struct StrAccum StrAccum;

/************** Include pager.h in the middle of sqliteInt.h *****************/
/************** Begin file pager.h *******************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** Default maximum size for persistent journal files. A negative 
** value means no limit. This value may be overridden using the 
** sqlite3PagerJournalSizeLimit() API. See also "PRAGMA journal_size_limit".
*/
#ifndef SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT
  #define SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT -1
#endif

/*
** The type used to represent a page number.  The first page in a file
** is called page 1.  0 is used to represent "not a page".
*/
typedef u32 Pgno;

/*
** Each open file is managed by a separate instance of the "Pager" structure.
*/
typedef struct Pager Pager;

/*
** Handle type for pages.
*/
typedef struct PgHdr DbPage;

/*
** Page number PAGER_MJ_PGNO is never used in an SQLite database (it is
** reserved for working around a windows/posix incompatibility). It is
** used in the journal to signify that the remainder of the journal file 
** is devoted to storing a master journal name - there are no more pages to
** roll back. See comments for function writeMasterJournal() in pager.c 
** for details.
*/
#define PAGER_MJ_PGNO(x) ((Pgno)((PENDING_BYTE/((x)->pageSize))+1))

/*
** Allowed values for the flags parameter to sqlite3PagerOpen().
**
** NOTE: These values must match the corresponding BTREE_ values in btree.h.
*/
#define PAGER_OMIT_JOURNAL  0x0001    /* Do not use a rollback journal */
#define PAGER_MEMORY        0x0002    /* In-memory database */

/*
** Valid values for the second argument to sqlite3PagerLockingMode().
*/
#define PAGER_LOCKINGMODE_QUERY      -1
#define PAGER_LOCKINGMODE_NORMAL      0
#define PAGER_LOCKINGMODE_EXCLUSIVE   1

/*
** Numeric constants that encode the journalmode.  
*/
#define PAGER_JOURNALMODE_QUERY     (-1)  /* Query the value of journalmode */
#define PAGER_JOURNALMODE_DELETE      0   /* Commit by deleting journal file */
#define PAGER_JOURNALMODE_PERSIST     1   /* Commit by zeroing journal header */
#define PAGER_JOURNALMODE_OFF         2   /* Journal omitted.  */
#define PAGER_JOURNALMODE_TRUNCATE    3   /* Commit by truncating journal */
#define PAGER_JOURNALMODE_MEMORY      4   /* In-memory journal file */
#define PAGER_JOURNALMODE_WAL         5   /* Use write-ahead logging */

/*
** Flags that make up the mask passed to sqlite3PagerAcquire().
*/
#define PAGER_GET_NOCONTENT     0x01  /* Do not load data from disk */
#define PAGER_GET_READONLY      0x02  /* Read-only page is acceptable */

/*
** Flags for sqlite3PagerSetFlags()
*/
#define PAGER_SYNCHRONOUS_OFF       0x01  /* PRAGMA synchronous=OFF */
#define PAGER_SYNCHRONOUS_NORMAL    0x02  /* PRAGMA synchronous=NORMAL */
#define PAGER_SYNCHRONOUS_FULL      0x03  /* PRAGMA synchronous=FULL */
#define PAGER_SYNCHRONOUS_MASK      0x03  /* Mask for three values above */
#define PAGER_FULLFSYNC             0x04  /* PRAGMA fullfsync=ON */
#define PAGER_CKPT_FULLFSYNC        0x08  /* PRAGMA checkpoint_fullfsync=ON */
#define PAGER_CACHESPILL            0x10  /* PRAGMA cache_spill=ON */
#define PAGER_FLAGS_MASK            0x1c  /* All above except SYNCHRONOUS */

/*
** The remainder of this file contains the declarations of the functions
** that make up the Pager sub-system API. See source code comments for 
** a detailed description of each routine.
*/

/* Open and close a Pager connection. */ 
SQLITE_PRIVATE int sqlite3PagerOpen(
  sqlite3_vfs*,
  Pager **ppPager,
  const char*,
  int,
  int,
  int,
  void(*)(DbPage*)
);
SQLITE_PRIVATE int sqlite3PagerClose(Pager *pPager);
SQLITE_PRIVATE int sqlite3PagerReadFileheader(Pager*, int, unsigned char*);

/* Functions used to configure a Pager object. */
SQLITE_PRIVATE void sqlite3PagerSetBusyhandler(Pager*, int(*)(void *), void *);
SQLITE_PRIVATE int sqlite3PagerSetPagesize(Pager*, u32*, int);
#ifdef SQLITE_HAS_CODEC
SQLITE_PRIVATE void sqlite3PagerAlignReserve(Pager*,Pager*);
#endif
SQLITE_PRIVATE int sqlite3PagerMaxPageCount(Pager*, int);
SQLITE_PRIVATE void sqlite3PagerSetCachesize(Pager*, int);
SQLITE_PRIVATE void sqlite3PagerSetMmapLimit(Pager *, sqlite3_int64);
SQLITE_PRIVATE void sqlite3PagerSetFlags(Pager*,unsigned);
#if 0
SQLITE_PRIVATE int sqlite3PagerLockingMode(Pager *, int);
SQLITE_PRIVATE int sqlite3PagerSetJournalMode(Pager *, int);
SQLITE_PRIVATE int sqlite3PagerGetJournalMode(Pager*);
SQLITE_PRIVATE int sqlite3PagerOkToChangeJournalMode(Pager*);
SQLITE_PRIVATE i64 sqlite3PagerJournalSizeLimit(Pager *, i64);
#endif

/* Functions used to obtain and release page references. */ 
SQLITE_PRIVATE int sqlite3PagerAcquire(Pager *pPager, Pgno pgno, DbPage **ppPage, int clrFlag);
#define sqlite3PagerGet(A,B,C) sqlite3PagerAcquire(A,B,C,0)
SQLITE_PRIVATE DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno);
SQLITE_PRIVATE void sqlite3PagerRef(DbPage*);
SQLITE_PRIVATE void sqlite3PagerUnref(DbPage*);
SQLITE_PRIVATE void sqlite3PagerUnrefNotNull(DbPage*);

/* Operations on page references. */
SQLITE_PRIVATE int sqlite3PagerWrite(DbPage*);
SQLITE_PRIVATE void sqlite3PagerDontWrite(DbPage*);
SQLITE_PRIVATE int sqlite3PagerMovepage(Pager*,DbPage*,Pgno,int);
SQLITE_PRIVATE int sqlite3PagerPageRefcount(DbPage*);
SQLITE_PRIVATE void *sqlite3PagerGetData(DbPage *); 
SQLITE_PRIVATE void *sqlite3PagerGetExtra(DbPage *); 

/* Functions used to manage pager transactions and savepoints. */
SQLITE_PRIVATE void sqlite3PagerPagecount(Pager*, int*);
SQLITE_PRIVATE int sqlite3PagerBegin(Pager*, int exFlag, int);
SQLITE_PRIVATE int sqlite3PagerCommitPhaseOne(Pager*,const char *zMaster, int);
SQLITE_PRIVATE int sqlite3PagerExclusiveLock(Pager*);
SQLITE_PRIVATE int sqlite3PagerSync(Pager *pPager, const char *zMaster);
SQLITE_PRIVATE int sqlite3PagerCommitPhaseTwo(Pager*);
SQLITE_PRIVATE int sqlite3PagerRollback(Pager*);
SQLITE_PRIVATE int sqlite3PagerOpenSavepoint(Pager *pPager, int n);
SQLITE_PRIVATE int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint);
SQLITE_PRIVATE int sqlite3PagerSharedLock(Pager *pPager);

#ifndef SQLITE_OMIT_WAL
SQLITE_PRIVATE   int sqlite3PagerCheckpoint(Pager *pPager, int, int*, int*);
SQLITE_PRIVATE   int sqlite3PagerWalSupported(Pager *pPager);
#if 0
SQLITE_PRIVATE   int sqlite3PagerWalCallback(Pager *pPager);
#endif
SQLITE_PRIVATE   int sqlite3PagerOpenWal(Pager *pPager, int *pisOpen);
#if 0
SQLITE_PRIVATE   int sqlite3PagerCloseWal(Pager *pPager);
#endif
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
SQLITE_PRIVATE   int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */
SQLITE_PRIVATE u8 sqlite3PagerIsreadonly(Pager*);
SQLITE_PRIVATE u32 sqlite3PagerDataVersion(Pager*);
#ifdef SQLITE_DEBUG
SQLITE_PRIVATE   int sqlite3PagerRefcount(Pager*);
#endif
#if 0
SQLITE_PRIVATE int sqlite3PagerMemUsed(Pager*);
#endif
SQLITE_PRIVATE const char *sqlite3PagerFilename(Pager*, int);
SQLITE_PRIVATE const sqlite3_vfs *sqlite3PagerVfs(Pager*);
#ifdef SQLITE_DIRECT_OVERFLOW_READ
SQLITE_PRIVATE sqlite3_file *sqlite3PagerFile(Pager*);
#endif
SQLITE_PRIVATE const char *sqlite3PagerJournalname(Pager*);
SQLITE_PRIVATE int sqlite3PagerNosync(Pager*);
SQLITE_PRIVATE void *sqlite3PagerTempSpace(Pager*);
#if 0
SQLITE_PRIVATE void sqlite3PagerCacheStat(Pager *, int, int, int *);
SQLITE_PRIVATE void sqlite3PagerClearCache(Pager *);
#endif
SQLITE_PRIVATE int sqlite3SectorSize(sqlite3_file *);

/* Functions used to truncate the database file. */
SQLITE_PRIVATE void sqlite3PagerTruncateImage(Pager*,Pgno);

SQLITE_PRIVATE void sqlite3PagerRekey(DbPage*, Pgno, u16);

#if defined(SQLITE_HAS_CODEC) && !defined(SQLITE_OMIT_WAL)
SQLITE_PRIVATE void *sqlite3PagerCodec(DbPage *);
#endif

/* Functions to support testing and debugging. */
#if !defined(NDEBUG) || defined(SQLITE_TEST)
SQLITE_PRIVATE   Pgno sqlite3PagerPagenumber(DbPage*);
SQLITE_PRIVATE   int sqlite3PagerIswriteable(DbPage*);
#endif
#ifdef SQLITE_TEST
SQLITE_PRIVATE   int *sqlite3PagerStats(Pager*);
SQLITE_PRIVATE   void sqlite3PagerRefdump(Pager*);
  void disable_simulated_io_errors(void);
  void enable_simulated_io_errors(void);
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

#endif /* _PAGER_H_ */

/************** End of pager.h ***********************************************/
/************** Continuing where we left off in sqliteInt.h ******************/
/************** Include pcache.h in the middle of sqliteInt.h ****************/
/************** Begin file pcache.h ******************************************/
/*
** 2008 August 05
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem. 
*/

#ifndef _PCACHE_H_

typedef struct PgHdr PgHdr;
typedef struct PCache PCache;

/*
** Every page in the cache is controlled by an instance of the following
** structure.
*/
struct PgHdr {
  sqlite3_pcache_page *pPage;    /* Pcache object page handle */
  void *pData;                   /* Page data */
  void *pExtra;                  /* Extra content */
  PgHdr *pDirty;                 /* Transient list of dirty pages */
  Pager *pPager;                 /* The pager this page is part of */
  Pgno pgno;                     /* Page number for this page */
#ifdef SQLITE_CHECK_PAGES
  u32 pageHash;                  /* Hash of page content */
#endif
  u16 flags;                     /* PGHDR flags defined below */

  /**********************************************************************
  ** Elements above are public.  All that follows is private to pcache.c
  ** and should not be accessed by other modules.
  */
  i16 nRef;                      /* Number of users of this page */
  PCache *pCache;                /* Cache that owns this page */

  PgHdr *pDirtyNext;             /* Next element in list of dirty pages */
  PgHdr *pDirtyPrev;             /* Previous element in list of dirty pages */
};

/* Bit values for PgHdr.flags */
#define PGHDR_CLEAN           0x001  /* Page not on the PCache.pDirty list */
#define PGHDR_DIRTY           0x002  /* Page is on the PCache.pDirty list */
#define PGHDR_WRITEABLE       0x004  /* Journaled and ready to modify */
#define PGHDR_NEED_SYNC       0x008  /* Fsync the rollback journal before
                                     ** writing this page to the database */
#define PGHDR_NEED_READ       0x010  /* Content is unread */
#define PGHDR_DONT_WRITE      0x020  /* Do not write content to disk */
#define PGHDR_MMAP            0x040  /* This is an mmap page object */

/* Initialize and shutdown the page cache subsystem */
SQLITE_PRIVATE int sqlite3PcacheInitialize(void);
SQLITE_PRIVATE void sqlite3PcacheShutdown(void);

/* Page cache buffer management:
** These routines implement SQLITE_CONFIG_PAGECACHE.
*/
SQLITE_PRIVATE void sqlite3PCacheBufferSetup(void *, int sz, int n);

/* Create a new pager cache.
** Under memory stress, invoke xStress to try to make pages clean.
** Only clean and unpinned pages can be reclaimed.
*/
SQLITE_PRIVATE int sqlite3PcacheOpen(
  int szPage,                    /* Size of every page */
  int szExtra,                   /* Extra space associated with each page */
  int bPurgeable,                /* True if pages are on backing store */
  int (*xStress)(void*, PgHdr*), /* Call to try to make pages clean */
  void *pStress,                 /* Argument to xStress */
  PCache *pToInit                /* Preallocated space for the PCache */
);

/* Modify the page-size after the cache has been created. */
SQLITE_PRIVATE int sqlite3PcacheSetPageSize(PCache *, int);

/* Return the size in bytes of a PCache object.  Used to preallocate
** storage space.
*/
SQLITE_PRIVATE int sqlite3PcacheSize(void);

/* One release per successful fetch.  Page is pinned until released.
** Reference counted. 
*/
SQLITE_PRIVATE sqlite3_pcache_page *sqlite3PcacheFetch(PCache*, Pgno, int createFlag);
SQLITE_PRIVATE int sqlite3PcacheFetchStress(PCache*, Pgno, sqlite3_pcache_page**);
SQLITE_PRIVATE PgHdr *sqlite3PcacheFetchFinish(PCache*, Pgno, sqlite3_pcache_page *pPage);
SQLITE_PRIVATE void sqlite3PcacheRelease(PgHdr*);

SQLITE_PRIVATE void sqlite3PcacheDrop(PgHdr*);         /* Remove page from cache */
SQLITE_PRIVATE void sqlite3PcacheMakeDirty(PgHdr*);    /* Make sure page is marked dirty */
SQLITE_PRIVATE void sqlite3PcacheMakeClean(PgHdr*);    /* Mark a single page as clean */
SQLITE_PRIVATE void sqlite3PcacheCleanAll(PCache*);    /* Mark all dirty list pages as clean */

/* Change a page number.  Used by incr-vacuum. */
SQLITE_PRIVATE void sqlite3PcacheMove(PgHdr*, Pgno);

/* Remove all pages with pgno>x.  Reset the cache if x==0 */
SQLITE_PRIVATE void sqlite3PcacheTruncate(PCache*, Pgno x);

/* Get a list of all dirty pages in the cache, sorted by page number */
SQLITE_PRIVATE PgHdr *sqlite3PcacheDirtyList(PCache*);

/* Reset and close the cache object */
SQLITE_PRIVATE void sqlite3PcacheClose(PCache*);

/* Clear flags from pages of the page cache */
SQLITE_PRIVATE void sqlite3PcacheClearSyncFlags(PCache *);

/* Discard the contents of the cache */
SQLITE_PRIVATE void sqlite3PcacheClear(PCache*);

/* Return the total number of outstanding page references */
SQLITE_PRIVATE int sqlite3PcacheRefCount(PCache*);

/* Increment the reference count of an existing page */
SQLITE_PRIVATE void sqlite3PcacheRef(PgHdr*);

SQLITE_PRIVATE int sqlite3PcachePageRefcount(PgHdr*);

#ifdef SQLITE_TEST
/* Return the total number of pages stored in the cache */
SQLITE_PRIVATE int sqlite3PcachePagecount(PCache*);
#endif

#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
/* Iterate through all dirty pages currently stored in the cache. This
** interface is only available if SQLITE_CHECK_PAGES is defined when the 
** library is built.
*/
SQLITE_PRIVATE void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *));
#endif

/* Set and get the suggested cache-size for the specified pager-cache.
**
** If no global maximum is configured, then the system attempts to limit
** the total number of pages cached by purgeable pager-caches to the sum
** of the suggested cache-sizes.
*/
SQLITE_PRIVATE void sqlite3PcacheSetCachesize(PCache *, int);
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3PcacheGetCachesize(PCache *);
#endif

#if 0
/* Free up as much memory as possible from the page cache */
SQLITE_PRIVATE void sqlite3PcacheShrink(PCache*);
#endif

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/* Try to return memory used by the pcache module to the main memory heap */
SQLITE_PRIVATE int sqlite3PcacheReleaseMemory(int);
#endif

#ifdef SQLITE_TEST
SQLITE_PRIVATE void sqlite3PcacheStats(int*,int*,int*,int*);
#endif

SQLITE_PRIVATE void sqlite3PCacheSetDefault(void);

/* Return the header size */
SQLITE_PRIVATE int sqlite3HeaderSizePcache(void);
SQLITE_PRIVATE int sqlite3HeaderSizePcache1(void);

#endif /* _PCACHE_H_ */

/************** End of pcache.h **********************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/************** Include os.h in the middle of sqliteInt.h ********************/
/************** Begin file os.h **********************************************/
/*
** 2001 September 16
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This header file (together with is companion C source-code file
** "os.c") attempt to abstract the underlying operating system so that
** the SQLite library will work on both POSIX and windows systems.
**
** This header file is #include-ed by sqliteInt.h and thus ends up
** being included by every source file.
*/
#ifndef _SQLITE_OS_H_
#define _SQLITE_OS_H_

/*
** Attempt to automatically detect the operating system and setup the
** necessary pre-processor macros for it.
*/
/************** Include os_setup.h in the middle of os.h *********************/
/************** Begin file os_setup.h ****************************************/
/*
** 2013 November 25
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains pre-processor directives related to operating system
** detection and/or setup.
*/
#ifndef _OS_SETUP_H_
#define _OS_SETUP_H_

/*
** Figure out if we are dealing with Unix, Windows, or some other operating
** system.
**
** After the following block of preprocess macros, all of SQLITE_OS_UNIX,
** SQLITE_OS_WIN, and SQLITE_OS_OTHER will defined to either 1 or 0.  One of
** the three will be 1.  The other two will be 0.
*/
#if defined(SQLITE_OS_OTHER)
#  if SQLITE_OS_OTHER==1
#    undef SQLITE_OS_UNIX
#    define SQLITE_OS_UNIX 0
#    undef SQLITE_OS_WIN
#    define SQLITE_OS_WIN 0
#  else
#    undef SQLITE_OS_OTHER
#  endif
#endif
#if !defined(SQLITE_OS_UNIX) && !defined(SQLITE_OS_OTHER)
#  define SQLITE_OS_OTHER 0
#  ifndef SQLITE_OS_WIN
#    if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || \
        defined(__MINGW32__) || defined(__BORLANDC__)
#      define SQLITE_OS_WIN 1
#      define SQLITE_OS_UNIX 0
#    else
#      define SQLITE_OS_WIN 0
#      define SQLITE_OS_UNIX 1
#    endif
#  else
#    define SQLITE_OS_UNIX 0
#  endif
#else
#  ifndef SQLITE_OS_WIN
#    define SQLITE_OS_WIN 0
#  endif
#endif

#endif /* _OS_SETUP_H_ */

/************** End of os_setup.h ********************************************/
/************** Continuing where we left off in os.h *************************/

/* If the SET_FULLSYNC macro is not defined above, then make it
** a no-op
*/
#ifndef SET_FULLSYNC
# define SET_FULLSYNC(x,y)
#endif

/*
** The default size of a disk sector
*/
#ifndef SQLITE_DEFAULT_SECTOR_SIZE
# define SQLITE_DEFAULT_SECTOR_SIZE 4096
#endif

/*
** Temporary files are named starting with this prefix followed by 16 random
** alphanumeric characters, and no file extension. They are stored in the
** OS's standard temporary file directory, and are deleted prior to exit.
** If sqlite is being embedded in another program, you may wish to change the
** prefix to reflect your program's name, so that if your program exits
** prematurely, old temporary files can be easily identified. This can be done
** using -DSQLITE_TEMP_FILE_PREFIX=myprefix_ on the compiler command line.
**
** 2006-10-31:  The default prefix used to be "sqlite_".  But then
** Mcafee started using SQLite in their anti-virus product and it
** started putting files with the "sqlite" name in the c:/temp folder.
** This annoyed many windows users.  Those users would then do a 
** Google search for "sqlite", find the telephone numbers of the
** developers and call to wake them up at night and complain.
** For this reason, the default name prefix is changed to be "sqlite" 
** spelled backwards.  So the temp files are still identified, but
** anybody smart enough to figure out the code is also likely smart
** enough to know that calling the developer will not help get rid
** of the file.
*/
#ifndef SQLITE_TEMP_FILE_PREFIX
# define SQLITE_TEMP_FILE_PREFIX "etilqs_"
#endif

/*
** The following values may be passed as the second argument to
** sqlite3OsLock(). The various locks exhibit the following semantics:
**
** SHARED:    Any number of processes may hold a SHARED lock simultaneously.
** RESERVED:  A single process may hold a RESERVED lock on a file at
**            any time. Other processes may hold and obtain new SHARED locks.
** PENDING:   A single process may hold a PENDING lock on a file at
**            any one time. Existing SHARED locks may persist, but no new
**            SHARED locks may be obtained by other processes.
** EXCLUSIVE: An EXCLUSIVE lock precludes all other locks.
**
** PENDING_LOCK may not be passed directly to sqlite3OsLock(). Instead, a
** process that requests an EXCLUSIVE lock may actually obtain a PENDING
** lock. This can be upgraded to an EXCLUSIVE lock by a subsequent call to
** sqlite3OsLock().
*/
#define NO_LOCK         0
#define SHARED_LOCK     1
#define RESERVED_LOCK   2
#define PENDING_LOCK    3
#define EXCLUSIVE_LOCK  4

/*
** File Locking Notes:  (Mostly about windows but also some info for Unix)
**
** We cannot use LockFileEx() or UnlockFileEx() on Win95/98/ME because
** those functions are not available.  So we use only LockFile() and
** UnlockFile().
**
** LockFile() prevents not just writing but also reading by other processes.
** A SHARED_LOCK is obtained by locking a single randomly-chosen 
** byte out of a specific range of bytes. The lock byte is obtained at 
** random so two separate readers can probably access the file at the 
** same time, unless they are unlucky and choose the same lock byte.
** An EXCLUSIVE_LOCK is obtained by locking all bytes in the range.
** There can only be one writer.  A RESERVED_LOCK is obtained by locking
** a single byte of the file that is designated as the reserved lock byte.
** A PENDING_LOCK is obtained by locking a designated byte different from
** the RESERVED_LOCK byte.
**
** On WinNT/2K/XP systems, LockFileEx() and UnlockFileEx() are available,
** which means we can use reader/writer locks.  When reader/writer locks
** are used, the lock is placed on the same range of bytes that is used
** for probabilistic locking in Win95/98/ME.  Hence, the locking scheme
** will support two or more Win95 readers or two or more WinNT readers.
** But a single Win95 reader will lock out all WinNT readers and a single
** WinNT reader will lock out all other Win95 readers.
**
** The following #defines specify the range of bytes used for locking.
** SHARED_SIZE is the number of bytes available in the pool from which
** a random byte is selected for a shared lock.  The pool of bytes for
** shared locks begins at SHARED_FIRST. 
**
** The same locking strategy and
** byte ranges are used for Unix.  This leaves open the possibility of having
** clients on win95, winNT, and unix all talking to the same shared file
** and all locking correctly.  To do so would require that samba (or whatever
** tool is being used for file sharing) implements locks correctly between
** windows and unix.  I'm guessing that isn't likely to happen, but by
** using the same locking range we are at least open to the possibility.
**
** Locking in windows is manditory.  For this reason, we cannot store
** actual data in the bytes used for locking.  The pager never allocates
** the pages involved in locking therefore.  SHARED_SIZE is selected so
** that all locks will fit on a single page even at the minimum page size.
** PENDING_BYTE defines the beginning of the locks.  By default PENDING_BYTE
** is set high so that we don't have to allocate an unused page except
** for very large databases.  But one should test the page skipping logic 
** by setting PENDING_BYTE low and running the entire regression suite.
**
** Changing the value of PENDING_BYTE results in a subtly incompatible
** file format.  Depending on how it is changed, you might not notice
** the incompatibility right away, even running a full regression test.
** The default location of PENDING_BYTE is the first byte past the
** 1GB boundary.
**
*/
#ifdef SQLITE_OMIT_WSD
# define PENDING_BYTE     (0x40000000)
#else
# define PENDING_BYTE      sqlite3PendingByte
#endif
#define RESERVED_BYTE     (PENDING_BYTE+1)
#define SHARED_FIRST      (PENDING_BYTE+2)
#define SHARED_SIZE       510

/*
** Wrapper around OS specific sqlite3_os_init() function.
*/
SQLITE_PRIVATE int sqlite3OsInit(void);

/* 
** Functions for accessing sqlite3_file methods 
*/
SQLITE_PRIVATE int sqlite3OsClose(sqlite3_file*);
SQLITE_PRIVATE int sqlite3OsRead(sqlite3_file*, void*, int amt, i64 offset);
SQLITE_PRIVATE int sqlite3OsWrite(sqlite3_file*, const void*, int amt, i64 offset);
SQLITE_PRIVATE int sqlite3OsTruncate(sqlite3_file*, i64 size);
SQLITE_PRIVATE int sqlite3OsSync(sqlite3_file*, int);
SQLITE_PRIVATE int sqlite3OsFileSize(sqlite3_file*, i64 *pSize);
SQLITE_PRIVATE int sqlite3OsLock(sqlite3_file*, int);
SQLITE_PRIVATE int sqlite3OsUnlock(sqlite3_file*, int);
SQLITE_PRIVATE int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut);
SQLITE_PRIVATE int sqlite3OsFileControl(sqlite3_file*,int,void*);
SQLITE_PRIVATE void sqlite3OsFileControlHint(sqlite3_file*,int,void*);
#define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
SQLITE_PRIVATE int sqlite3OsSectorSize(sqlite3_file *id);
SQLITE_PRIVATE int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
SQLITE_PRIVATE int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);
SQLITE_PRIVATE int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
SQLITE_PRIVATE void sqlite3OsShmBarrier(sqlite3_file *id);
SQLITE_PRIVATE int sqlite3OsShmUnmap(sqlite3_file *id, int);
SQLITE_PRIVATE int sqlite3OsFetch(sqlite3_file *id, i64, int, void **);
SQLITE_PRIVATE int sqlite3OsUnfetch(sqlite3_file *, i64, void *);


/* 
** Functions for accessing sqlite3_vfs methods 
*/
SQLITE_PRIVATE int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
SQLITE_PRIVATE int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
SQLITE_PRIVATE int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);
SQLITE_PRIVATE int sqlite3OsFullPathname(sqlite3_vfs *, const char *, int, char *);
SQLITE_PRIVATE int sqlite3OsRandomness(sqlite3_vfs *, int, char *);
SQLITE_PRIVATE int sqlite3OsSleep(sqlite3_vfs *, int);

#endif /* _SQLITE_OS_H_ */

/************** End of os.h **************************************************/
/************** Continuing where we left off in sqliteInt.h ******************/
/************** Include mutex.h in the middle of sqliteInt.h *****************/
/************** Begin file mutex.h *******************************************/
/*
** 2007 August 28
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains the common header for all mutex implementations.
** The sqliteInt.h header #includes this file so that it is available
** to all source files.  We break it out in an effort to keep the code
** better organized.
**
** NOTE:  source files should *not* #include this header file directly.
** Source files should #include the sqliteInt.h file and let that file
** include this one indirectly.
*/


/*
** Figure out what version of the code to use.  The choices are
**
**   SQLITE_MUTEX_OMIT         No mutex logic.  Not even stubs.  The
**                             mutexes implementation cannot be overridden
**                             at start-time.
**
**   SQLITE_MUTEX_NOOP         For single-threaded applications.  No
**                             mutual exclusion is provided.  But this
**                             implementation can be overridden at
**                             start-time.
**
**   SQLITE_MUTEX_PTHREADS     For multi-threaded applications on Unix.
**
**   SQLITE_MUTEX_W32          For multi-threaded applications on Win32.
*/
#if !SQLITE_THREADSAFE
# define SQLITE_MUTEX_OMIT
#endif
#if SQLITE_THREADSAFE && !defined(SQLITE_MUTEX_NOOP)
#  if SQLITE_OS_UNIX
#    define SQLITE_MUTEX_PTHREADS
#  elif SQLITE_OS_WIN
#    define SQLITE_MUTEX_W32
#  else
#    define SQLITE_MUTEX_NOOP
#  endif
#endif

#ifdef SQLITE_MUTEX_OMIT
/*
** If this is a no-op implementation, implement everything as macros.
*/
#define sqlite3_mutex_alloc(X)    ((sqlite3_mutex*)8)
#define sqlite3_mutex_free(X)
#define sqlite3_mutex_enter(X)    
#define sqlite3_mutex_try(X)      SQLITE_OK
#define sqlite3_mutex_leave(X)    
#define sqlite3_mutex_held(X)     ((void)(X),1)
#define sqlite3_mutex_notheld(X)  ((void)(X),1)
#define sqlite3MutexAlloc(X)      ((sqlite3_mutex*)8)
#define sqlite3MutexInit()        SQLITE_OK
#define sqlite3MutexEnd()
#define MUTEX_LOGIC(X)
#else
#define MUTEX_LOGIC(X)            X
#endif /* defined(SQLITE_MUTEX_OMIT) */

/************** End of mutex.h ***********************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/*
** The number of different kinds of things that can be limited
** using the sqlite3_limit() interface.
*/
#define SQLITE_N_LIMIT (SQLITE_LIMIT_WORKER_THREADS+1)

/*
** Possible values for the sqlite.magic field.
** The numbers are obtained at random and have no special meaning, other
** than being distinct from one another.
*/
#define SQLITE_MAGIC_OPEN     0xa029a697  /* Database is open */
#define SQLITE_MAGIC_CLOSED   0x9f3c2d33  /* Database is closed */
#define SQLITE_MAGIC_SICK     0x4b771290  /* Error and awaiting close */
#define SQLITE_MAGIC_BUSY     0xf03b7906  /* Database currently in use */
#define SQLITE_MAGIC_ERROR    0xb5357930  /* An SQLITE_MISUSE error occurred */
#define SQLITE_MAGIC_ZOMBIE   0x64cffc7f  /* Close with last statement close */

/*
** The SQLITE_*_BKPT macros are substitutes for the error codes with
** the same name but without the _BKPT suffix.  These macros invoke
** routines that report the line-number on which the error originated
** using sqlite3_log().  The routines also provide a convenient place
** to set a debugger breakpoint.
*/
SQLITE_PRIVATE int sqlite3CorruptError(int);
SQLITE_PRIVATE int sqlite3MisuseError(int);
SQLITE_PRIVATE int sqlite3CantopenError(int);
#define SQLITE_CORRUPT_BKPT sqlite3CorruptError(__LINE__)
#define SQLITE_MISUSE_BKPT sqlite3MisuseError(__LINE__)
#define SQLITE_CANTOPEN_BKPT sqlite3CantopenError(__LINE__)

#include <ctype.h>

# define sqlite3Toupper(x)   toupper((unsigned char)(x))
# define sqlite3Isspace(x)   isspace((unsigned char)(x))
# define sqlite3Isalnum(x)   isalnum((unsigned char)(x))
# define sqlite3Isalpha(x)   isalpha((unsigned char)(x))
# define sqlite3Isdigit(x)   isdigit((unsigned char)(x))
# define sqlite3Isxdigit(x)  isxdigit((unsigned char)(x))
# define sqlite3Tolower(x)   tolower((unsigned char)(x))

/*
** Internal function prototypes
*/
SQLITE_PRIVATE int sqlite3Strlen30(const char*);

SQLITE_PRIVATE int sqlite3MallocInit(void);
SQLITE_PRIVATE void sqlite3MallocEnd(void);
SQLITE_PRIVATE void *sqlite3Malloc(u64);
SQLITE_PRIVATE void *sqlite3MallocZero(u64);
SQLITE_PRIVATE void *sqlite3DbMallocZero(Btree*, u64);
SQLITE_PRIVATE void *sqlite3DbMallocRaw(Btree*, u64);
SQLITE_PRIVATE void *sqlite3Realloc(void*, u64);
SQLITE_PRIVATE void *sqlite3DbReallocOrFree(Btree*, void *, u64);
SQLITE_PRIVATE void *sqlite3DbRealloc(Btree*, void *, u64);
SQLITE_PRIVATE void sqlite3DbFree(Btree*, void*);
SQLITE_PRIVATE int sqlite3MallocSize(void*);
SQLITE_PRIVATE int sqlite3DbMallocSize(Btree*, void*);
SQLITE_PRIVATE void *sqlite3ScratchMalloc(int);
SQLITE_PRIVATE void sqlite3ScratchFree(void*);
SQLITE_PRIVATE void *sqlite3PageMalloc(int);
SQLITE_PRIVATE void sqlite3PageFree(void*);
SQLITE_PRIVATE void sqlite3MemSetDefault(void);
SQLITE_PRIVATE int sqlite3HeapNearlyFull(void);

/*
** On systems with ample stack space and that support alloca(), make
** use of alloca() to obtain space for large automatic objects.  By default,
** obtain space from malloc().
**
** The alloca() routine never returns NULL.  This will cause code paths
** that deal with sqlite3StackAlloc() failures to be unreachable.
*/
#ifdef SQLITE_USE_ALLOCA
# define sqlite3StackAllocRaw(D,N)   alloca(N)
# define sqlite3StackAllocZero(D,N)  memset(alloca(N), 0, N)
# define sqlite3StackFree(D,P)       
#else
# define sqlite3StackAllocRaw(D,N)   sqlite3DbMallocRaw(D,N)
# define sqlite3StackAllocZero(D,N)  sqlite3DbMallocZero(D,N)
# define sqlite3StackFree(D,P)       sqlite3DbFree(D,P)
#endif

#ifndef SQLITE_MUTEX_OMIT
SQLITE_PRIVATE   sqlite3_mutex_methods const *sqlite3DefaultMutex(void);
SQLITE_PRIVATE   sqlite3_mutex_methods const *sqlite3NoopMutex(void);
SQLITE_PRIVATE   sqlite3_mutex *sqlite3MutexAlloc(int);
SQLITE_PRIVATE   int sqlite3MutexInit(void);
SQLITE_PRIVATE   int sqlite3MutexEnd(void);
#endif
#if !defined(SQLITE_MUTEX_OMIT) && !defined(SQLITE_MUTEX_NOOP)
SQLITE_PRIVATE   void sqlite3MemoryBarrier(void);
#else
# define sqlite3MemoryBarrier()
#endif

#ifndef SQLITE_OMIT_FLOATING_POINT
SQLITE_PRIVATE   int sqlite3IsNaN(double);
#else
# define sqlite3IsNaN(X)  0
#endif

/*
** An instance of the following structure holds information about SQL
** functions arguments that are the parameters to the printf() function.
*/
struct PrintfArguments {
  int nArg;                /* Total number of arguments */
  int nUsed;               /* Number of arguments used so far */
  Mem **apArg;   /* The argument values */
};

#define SQLITE_PRINTF_INTERNAL 0x01
#define SQLITE_PRINTF_SQLFUNC  0x02

SQLITE_PRIVATE void sqlite3StrAccumInit(StrAccum*, Btree* pBtree, char*, int, int);
SQLITE_PRIVATE void sqlite3StrAccumAppend(StrAccum*,const char*,int);
SQLITE_PRIVATE void sqlite3AppendChar(StrAccum*,int,char);
SQLITE_PRIVATE char *sqlite3StrAccumFinish(StrAccum*);
SQLITE_PRIVATE void sqlite3StrAccumReset(StrAccum*);

SQLITE_PRIVATE int sqlite3SafetyCheckSickOrOk(Btree*);

SQLITE_PRIVATE int sqlite3InvokeBusyHandler(BusyHandler*);

SQLITE_PRIVATE void sqlite3BackupRestart(sqlite3_backup *);
SQLITE_PRIVATE void sqlite3BackupUpdate(sqlite3_backup *, Pgno, const u8 *);

typedef int (*RecordCompare)(int,const void*,UnpackedRecord*);

#define SQLITE_RecoveryMode   0x00010000  /* Ignore schema errors */
#define SQLITE_CellSizeCk     0x10000000  /* Check btree cell sizes on load */

/*
** The following are used as the second parameter to sqlite3Savepoint(),
** and as the P1 argument to the OP_Savepoint instruction.
*/
#define SAVEPOINT_BEGIN      0
#define SAVEPOINT_RELEASE    1
#define SAVEPOINT_ROLLBACK   2

/*
** A "Collating Sequence" is defined by an instance of the following
** structure. Conceptually, a collating sequence consists of a name and
** a comparison routine that defines the order of that sequence.
**
** If CollSeq.xCmp is NULL, it means that the
** collating sequence is undefined.  Indices built on an undefined
** collating sequence may not be read or written.
*/
struct CollSeq {
  char *zName;          /* Name of the collating sequence, UTF-8 encoded */
  u8 enc;               /* Text encoding handled by xCmp() */
  void *pUser;          /* First argument to xCmp() */
  int (*xCmp)(void*,int, const void*, int, const void*);
  void (*xDel)(void*);  /* Destructor for pUser */
};

/*
** An instance of the following structure is passed as the first
** argument to sqlite3VdbeKeyCompare and is used to control the 
** comparison of the two index keys.
**
** Note that aSortOrder[] and aColl[] have nField+1 slots.  There
** are nField slots for the columns of an index then one extra slot
** for the rowid at the end.
*/
struct KeyInfo {
  u32 nRef;           /* Number of references to this KeyInfo object */
  u8 enc;             /* Text encoding - one of the SQLITE_UTF* values */
  u16 nField;         /* Number of key columns in the index */
  u16 nXField;        /* Number of columns beyond the key columns */
  Btree *pBtree;      /* The database connection */
  u8 *aSortOrder;     /* Sort order for each column. */
  CollSeq *aColl[1];  /* Collating sequence for each term of the key */
};

/*
** An objected used to accumulate the text of a string where we
** do not necessarily know how big the string will be in the end.
*/
struct StrAccum {
  Btree *pBtree;       /* Optional database for lookaside.  Can be NULL */
  char *zBase;         /* A base allocation.  Not from malloc. */
  char *zText;         /* The string collected so far */
  int  nChar;          /* Length of the string so far */
  int  nAlloc;         /* Amount of space allocated in zText */
  int  mxAlloc;        /* Maximum allowed allocation.  0 for no malloc usage */
  u8   accError;       /* STRACCUM_NOMEM or STRACCUM_TOOBIG */
};
#define STRACCUM_NOMEM   1
#define STRACCUM_TOOBIG  2

/************** Include btreeInt.h in the middle of sqliteInt.h **************/
/************** Begin file btreeInt.h ****************************************/
/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements an external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
**
** The basic idea is that each page of the file contains N database
** entries and N+1 pointers to subpages.
**
**   ----------------------------------------------------------------
**   |  Ptr(0) | Key(0) | Ptr(1) | Key(1) | ... | Key(N-1) | Ptr(N) |
**   ----------------------------------------------------------------
**
** All of the keys on the page that Ptr(0) points to have values less
** than Key(0).  All of the keys on page Ptr(1) and its subpages have
** values greater than Key(0) and less than Key(1).  All of the keys
** on Ptr(N) and its subpages have values greater than Key(N-1).  And
** so forth.
**
** Finding a particular key requires reading O(log(M)) pages from the 
** disk where M is the number of entries in the tree.
**
** In this implementation, a single file can hold one or more separate 
** BTrees.  Each BTree is identified by the index of its root page.  The
** key and data for any entry are combined to form the "payload".  A
** fixed amount of payload can be carried directly on the database
** page.  If the payload is larger than the preset amount then surplus
** bytes are stored on overflow pages.  The payload for an entry
** and the preceding pointer are combined to form a "Cell".  Each 
** page has a small header which contains the Ptr(N) pointer and other
** information such as the size of key and data.
**
** FORMAT DETAILS
**
** The file is divided into pages.  The first page is called page 1,
** the second is page 2, and so forth.  A page number of zero indicates
** "no such page".  The page size can be any power of 2 between 512 and 65536.
** Each page can be either a btree page, a freelist page, an overflow
** page, or a pointer-map page.
**
** The first page is always a btree page.  The first 100 bytes of the first
** page contain a special header (the "file header") that describes the file.
** The format of the file header is as follows:
**
**   OFFSET   SIZE    DESCRIPTION
**      0      16     Header string: "SQLite format 3\000"
**     16       2     Page size in bytes.  (1 means 65536)
**     18       1     File format write version
**     19       1     File format read version
**     20       1     Bytes of unused space at the end of each page
**     21       1     Max embedded payload fraction (must be 64)
**     22       1     Min embedded payload fraction (must be 32)
**     23       1     Min leaf payload fraction (must be 32)
**     24       4     File change counter
**     28       4     Reserved for future use
**     32       4     First freelist page
**     36       4     Number of freelist pages in the file
**     40      60     15 4-byte meta values passed to higher layers
**
**     40       4     Schema cookie
**     44       4     File format of schema layer
**     48       4     Size of page cache
**     52       4     Largest root-page (auto/incr_vacuum)
**     56       4     1=UTF-8 2=UTF16le 3=UTF16be
**     60       4     User version
**     64       4     Incremental vacuum mode
**     68       4     Application-ID
**     72      20     unused
**     92       4     The version-valid-for number
**     96       4     SQLITE_VERSION_NUMBER
**
** All of the integer values are big-endian (most significant byte first).
**
** The file change counter is incremented when the database is changed
** This counter allows other processes to know when the file has changed
** and thus when they need to flush their cache.
**
** The max embedded payload fraction is the amount of the total usable
** space in a page that can be consumed by a single cell for standard
** B-tree (non-LEAFDATA) tables.  A value of 255 means 100%.  The default
** is to limit the maximum cell size so that at least 4 cells will fit
** on one page.  Thus the default max embedded payload fraction is 64.
**
** If the payload for a cell is larger than the max payload, then extra
** payload is spilled to overflow pages.  Once an overflow page is allocated,
** as many bytes as possible are moved into the overflow pages without letting
** the cell size drop below the min embedded payload fraction.
**
** The min leaf payload fraction is like the min embedded payload fraction
** except that it applies to leaf nodes in a LEAFDATA tree.  The maximum
** payload fraction for a LEAFDATA tree is always 100% (or 255) and it
** not specified in the header.
**
** Each btree pages is divided into three sections:  The header, the
** cell pointer array, and the cell content area.  Page 1 also has a 100-byte
** file header that occurs before the page header.
**
**      |----------------|
**      | file header    |   100 bytes.  Page 1 only.
**      |----------------|
**      | page header    |   8 bytes for leaves.  12 bytes for interior nodes
**      |----------------|
**      | cell pointer   |   |  2 bytes per cell.  Sorted order.
**      | array          |   |  Grows downward
**      |                |   v
**      |----------------|
**      | unallocated    |
**      | space          |
**      |----------------|   ^  Grows upwards
**      | cell content   |   |  Arbitrary order interspersed with freeblocks.
**      | area           |   |  and free space fragments.
**      |----------------|
**
** The page headers looks like this:
**
**   OFFSET   SIZE     DESCRIPTION
**      0       1      Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf
**      1       2      byte offset to the first freeblock
**      3       2      number of cells on this page
**      5       2      first byte of the cell content area
**      7       1      number of fragmented free bytes
**      8       4      Right child (the Ptr(N) value).  Omitted on leaves.
**
** The flags define the format of this btree page.  The leaf flag means that
** this page has no children.  The zerodata flag means that this page carries
** only keys and no data.  The intkey flag means that the key is an integer
** which is stored in the key size entry of the cell header rather than in
** the payload area.
**
** The cell pointer array begins on the first byte after the page header.
** The cell pointer array contains zero or more 2-byte numbers which are
** offsets from the beginning of the page to the cell content in the cell
** content area.  The cell pointers occur in sorted order.  The system strives
** to keep free space after the last cell pointer so that new cells can
** be easily added without having to defragment the page.
**
** Cell content is stored at the very end of the page and grows toward the
** beginning of the page.
**
** Unused space within the cell content area is collected into a linked list of
** freeblocks.  Each freeblock is at least 4 bytes in size.  The byte offset
** to the first freeblock is given in the header.  Freeblocks occur in
** increasing order.  Because a freeblock must be at least 4 bytes in size,
** any group of 3 or fewer unused bytes in the cell content area cannot
** exist on the freeblock chain.  A group of 3 or fewer free bytes is called
** a fragment.  The total number of bytes in all fragments is recorded.
** in the page header at offset 7.
**
**    SIZE    DESCRIPTION
**      2     Byte offset of the next freeblock
**      2     Bytes in this freeblock
**
** Cells are of variable length.  Cells are stored in the cell content area at
** the end of the page.  Pointers to the cells are in the cell pointer array
** that immediately follows the page header.  Cells is not necessarily
** contiguous or in order, but cell pointers are contiguous and in order.
**
** Cell content makes use of variable length integers.  A variable
** length integer is 1 to 9 bytes where the lower 7 bits of each 
** byte are used.  The integer consists of all bytes that have bit 8 set and
** the first byte with bit 8 clear.  The most significant byte of the integer
** appears first.  A variable-length integer may not be more than 9 bytes long.
** As a special case, all 8 bytes of the 9th byte are used as data.  This
** allows a 64-bit integer to be encoded in 9 bytes.
**
**    0x00                      becomes  0x00000000
**    0x7f                      becomes  0x0000007f
**    0x81 0x00                 becomes  0x00000080
**    0x82 0x00                 becomes  0x00000100
**    0x80 0x7f                 becomes  0x0000007f
**    0x8a 0x91 0xd1 0xac 0x78  becomes  0x12345678
**    0x81 0x81 0x81 0x81 0x01  becomes  0x10204081
**
** Variable length integers are used for rowids and to hold the number of
** bytes of key and data in a btree cell.
**
** The content of a cell looks like this:
**
**    SIZE    DESCRIPTION
**      4     Page number of the left child. Omitted if leaf flag is set.
**     var    Number of bytes of data. Omitted if the zerodata flag is set.
**     var    Number of bytes of key. Or the key itself if intkey flag is set.
**      *     Payload
**      4     First page of the overflow chain.  Omitted if no overflow
**
** Overflow pages form a linked list.  Each page except the last is completely
** filled with data (pagesize - 4 bytes).  The last page can have as little
** as 1 byte of data.
**
**    SIZE    DESCRIPTION
**      4     Page number of next overflow page
**      *     Data
**
** Freelist pages come in two subtypes: trunk pages and leaf pages.  The
** file header points to the first in a linked list of trunk page.  Each trunk
** page points to multiple leaf pages.  The content of a leaf page is
** unspecified.  A trunk page looks like this:
**
**    SIZE    DESCRIPTION
**      4     Page number of next trunk page
**      4     Number of leaf pointers on this page
**      *     zero or more pages numbers of leaves
*/
/* #include "sqliteInt.h" */


/* The following value is the maximum cell size assuming a maximum page
** size give above.
*/
#define MX_CELL_SIZE(pBt)  ((int)(pBt->pageSize-8))

/* The maximum number of cells on a single page of the database.  This
** assumes a minimum cell size of 6 bytes  (4 bytes for the cell itself
** plus 2 bytes for the index to the cell in the page header).  Such
** small cells will be rare, but they are possible.
*/
#define MX_CELL(pBt) ((pBt->pageSize-8)/6)

/* Forward declarations */
typedef struct MemPage MemPage;
typedef struct BtLock BtLock;
typedef struct CellInfo CellInfo;

/*
** This is a magic string that appears at the beginning of every
** SQLite database in order to identify the file as a real database.
**
** You can change this value at compile-time by specifying a
** -DSQLITE_FILE_HEADER="..." on the compiler command-line.  The
** header must be exactly 16 bytes including the zero-terminator so
** the string itself should be 15 characters long.  If you change
** the header, then your custom library will not be able to read 
** databases generated by the standard tools and the standard tools
** will not be able to read databases created by your custom library.
*/
#ifndef SQLITE_FILE_HEADER /* 123456789 123456 */
#  define SQLITE_FILE_HEADER "SQLite Btree v3"
                             
#endif

/*
** Page type flags.  An ORed combination of these flags appear as the
** first byte of on-disk image of every BTree page.
*/
#define PTF_INTKEY    0x01
#define PTF_ZERODATA  0x02
#define PTF_LEAFDATA  0x04
#define PTF_LEAF      0x08

/*
** As each page of the file is loaded into memory, an instance of the following
** structure is appended and initialized to zero.  This structure stores
** information about the page that is decoded from the raw file page.
**
** The pParent field points back to the parent page.  This allows us to
** walk up the BTree from any leaf to the root.  Care must be taken to
** unref() the parent page pointer when this page is no longer referenced.
** The pageDestructor() routine handles that chore.
**
** Access to all fields of this structure is controlled by the mutex
** stored in MemPage.pBt->mutex.
*/
struct MemPage {
  u8 isInit;           /* True if previously initialized. MUST BE FIRST! */
  u8 nOverflow;        /* Number of overflow cell bodies in aCell[] */
  u8 intKey;           /* True if table b-trees.  False for index b-trees */
  u8 intKeyLeaf;       /* True if the leaf of an intKey table */
  u8 noPayload;        /* True if internal intKey page (thus w/o data) */
  u8 leaf;             /* True if a leaf page */
  u8 hdrOffset;        /* 100 for page 1.  0 otherwise */
  u8 childPtrSize;     /* 0 if leaf==1.  4 if leaf==0 */
  u8 max1bytePayload;  /* min(maxLocal,127) */
  u8 bBusy;            /* Prevent endless loops on corrupt database files */
  u16 maxLocal;        /* Copy of BtShared.maxLocal or BtShared.maxLeaf */
  u16 minLocal;        /* Copy of BtShared.minLocal or BtShared.minLeaf */
  u16 cellOffset;      /* Index in aData of first cell pointer */
  u16 nFree;           /* Number of free bytes on the page */
  u16 nCell;           /* Number of cells on this page, local and ovfl */
  u16 maskPage;        /* Mask for page offset */
  u16 aiOvfl[5];       /* Insert the i-th overflow cell before the aiOvfl-th
                       ** non-overflow cell */
  u8 *apOvfl[5];       /* Pointers to the body of overflow cells */
  BtShared *pBt;       /* Pointer to BtShared that this page is part of */
  u8 *aData;           /* Pointer to disk image of the page data */
  u8 *aDataEnd;        /* One byte past the end of usable data */
  u8 *aCellIdx;        /* The cell index area */
  u8 *aDataOfst;       /* Same as aData for leaves.  aData+4 for interior */
  DbPage *pDbPage;     /* Pager page handle */
  u16 (*xCellSize)(MemPage*,u8*);             /* cellSizePtr method */
  void (*xParseCell)(MemPage*,u8*,CellInfo*); /* btreeParseCell method */
  Pgno pgno;           /* Page number for this page */
};

/*
** The in-memory image of a disk page has the auxiliary information appended
** to the end.  EXTRA_SIZE is the number of bytes of space needed to hold
** that extra information.
*/
#define EXTRA_SIZE sizeof(MemPage)

/*
** A linked list of the following structures is stored at BtShared.pLock.
** Locks are added (or upgraded from READ_LOCK to WRITE_LOCK) when a cursor 
** is opened on the table with root page BtShared.iTable. Locks are removed
** from this list when a transaction is committed or rolled back, or when
** a btree handle is closed.
*/
struct BtLock {
  Btree *pBtree;        /* Btree handle holding this lock */
  Pgno iTable;          /* Root page of table */
  u8 eLock;             /* READ_LOCK or WRITE_LOCK */
  BtLock *pNext;        /* Next in BtShared.pLock list */
};

/* Candidate values for BtLock.eLock */
#define READ_LOCK     1
#define WRITE_LOCK    2

/* A Btree handle
**
** A database connection contains a pointer to an instance of
** this object for every database file that it has open.  This structure
** is opaque to the database connection.  The database connection cannot
** see the internals of this structure and only deals with pointers to
** this structure.
**
** For some database files, the same underlying database cache might be 
** shared between multiple connections.  In that case, each connection
** has it own instance of this object.  But each instance of this object
** points to the same BtShared object.  The database cache and the
** schema associated with the database file are all contained within
** the BtShared object.
**
** All fields in this structure are accessed under sqlite3.mutex.
** The pBt pointer itself may not be changed while there exists cursors 
** in the referenced BtShared that point back to this Btree since those
** cursors have to go through this Btree to find their BtShared and
** they often do so without holding sqlite3.mutex.
*/
struct Btree {
  sqlite3_mutex *mutex;         /* Connection mutex */
  int flags;                    /* Miscellaneous flags */
  i64 szMmap;                   /* Default mmap_size setting */
  u8 enc;                       /* Text encoding */
  u8 mallocFailed;              /* True if we have seen a malloc failure */
  u32 magic;                    /* Magic number for detect library misuse */
  int nVdbeRead;                /* Number of active VDBEs that read or write */
  BusyHandler busyHandler;      /* Busy callback */
  int nSavepoint;               /* Number of non-transaction savepoints */
  int *pnBytesFreed;            /* If not NULL, increment this in DbFree() */
  BtShared *pBt;     /* Sharable content of this btree */
  u8 inTrans;        /* TRANS_NONE, TRANS_READ or TRANS_WRITE */
  u8 sharable;       /* True if we can share pBt with another db */
  u8 locked;         /* True if db currently has pBt locked */
  u8 hasIncrblobCur; /* True if there are one or more Incrblob cursors */
  int wantToLock;    /* Number of nested calls to sqlite3BtreeEnter() */
  int nBackup;       /* Number of backup operations reading this btree */
  u32 iDataVersion;  /* Combines with pBt->pPager->iDataVersion */
  Btree *pNext;      /* List of other sharable Btrees from the same db */
  Btree *pPrev;      /* Back pointer of the same list */
#ifndef SQLITE_OMIT_SHARED_CACHE
  BtLock lock;       /* Object used to lock page 1 */
#endif
};

/*
** Btree.inTrans may take one of the following values.
**
** If the shared-data extension is enabled, there may be multiple users
** of the Btree structure. At most one of these may open a write transaction,
** but any number may have active read transactions.
*/
#define TRANS_NONE  0
#define TRANS_READ  1
#define TRANS_WRITE 2

/*
** An instance of this object represents a single database file.
** 
** A single database file can be in use at the same time by two
** or more database connections.  When two or more connections are
** sharing the same database file, each connection has it own
** private Btree object for the file and each of those Btrees points
** to this one BtShared object.  BtShared.nRef is the number of
** connections currently sharing this database file.
**
** Fields in this structure are accessed under the BtShared.mutex
** mutex, except for nRef and pNext which are accessed under the
** global SQLITE_MUTEX_STATIC_MASTER mutex.  The pPager field
** may not be modified once it is initially set as long as nRef>0.
** The pSchema field may be set once under BtShared.mutex and
** thereafter is unchanged as long as nRef>0.
**
** isPending:
**
**   If a BtShared client fails to obtain a write-lock on a database
**   table (because there exists one or more read-locks on the table),
**   the shared-cache enters 'pending-lock' state and isPending is
**   set to true.
**
**   The shared-cache leaves the 'pending lock' state when either of
**   the following occur:
**
**     1) The current writer (BtShared.pWriter) concludes its transaction, OR
**     2) The number of locks held by other connections drops to zero.
**
**   while in the 'pending-lock' state, no connection may start a new
**   transaction.
**
**   This feature is included to help prevent writer-starvation.
*/
struct BtShared {
  Pager *pPager;        /* The page cache */
  Btree *pBt;          /* Database connection currently using this Btree */
  BtCursor *pCursor;    /* A list of all open cursors */
  MemPage *pPage1;      /* First page of the database */
  u8 openFlags;         /* Flags to sqlite3BtreeOpen() */
#ifndef SQLITE_OMIT_AUTOVACUUM
  u8 autoVacuum;        /* True if auto-vacuum is enabled */
  u8 incrVacuum;        /* True if incr-vacuum is enabled */
  u8 bDoTruncate;       /* True to truncate db on commit */
#endif
  u8 inTransaction;     /* Transaction state */
  u8 max1bytePayload;   /* Maximum first byte of cell for a 1-byte payload */
#ifdef SQLITE_HAS_CODEC
  u8 optimalReserve;    /* Desired amount of reserved space per page */
#endif
  u16 btsFlags;         /* Boolean parameters.  See BTS_* macros below */
  u16 maxLocal;         /* Maximum local payload in non-LEAFDATA tables */
  u16 minLocal;         /* Minimum local payload in non-LEAFDATA tables */
  u16 maxLeaf;          /* Maximum local payload in a LEAFDATA table */
  u16 minLeaf;          /* Minimum local payload in a LEAFDATA table */
  u32 pageSize;         /* Total number of bytes on a page */
  u32 file_format;      /* File Format */
  u32 usableSize;       /* Number of usable bytes on each page */
  int nTransaction;     /* Number of open transactions (read + write) */
  u32 nPage;            /* Number of pages in the database */
  void *pSchema;        /* Pointer to space allocated by sqlite3BtreeSchema() */
  void (*xFreeSchema)(void*);  /* Destructor for BtShared.pSchema */
  sqlite3_mutex *mutex; /* Non-recursive mutex required to access this object */
  Bitvec *pHasContent;  /* Set of pages moved to free-list this transaction */
#ifndef SQLITE_OMIT_SHARED_CACHE
  int nRef;             /* Number of references to this structure */
  BtShared *pNext;      /* Next on a list of sharable BtShared structs */
  BtLock *pLock;        /* List of locks held on this shared-btree struct */
  Btree *pWriter;       /* Btree with currently open write transaction */
#endif
  u8 *pTmpSpace;        /* Temp space sufficient to hold a single cell */
};

/*
** Allowed values for BtShared.btsFlags
*/
#define BTS_READ_ONLY        0x0001   /* Underlying file is readonly */
#define BTS_PAGESIZE_FIXED   0x0002   /* Page size can no longer be changed */
#define BTS_SECURE_DELETE    0x0004   /* PRAGMA secure_delete is enabled */
#define BTS_INITIALLY_EMPTY  0x0008   /* Database was empty at trans start */
#define BTS_NO_WAL           0x0010   /* Do not open write-ahead-log files */
#define BTS_EXCLUSIVE        0x0020   /* pWriter has an exclusive lock */
#define BTS_PENDING          0x0040   /* Waiting for read-locks to clear */

/*
** An instance of the following structure is used to hold information
** about a cell.  The parseCellPtr() function fills in this structure
** based on information extract from the raw disk page.
*/
struct CellInfo {
  i64 nKey;      /* The key for INTKEY tables, or nPayload otherwise */
  u8 *pPayload;  /* Pointer to the start of payload */
  u32 nPayload;  /* Bytes of payload */
  u16 nLocal;    /* Amount of payload held locally, not on overflow */
  u16 iOverflow; /* Offset to overflow page number.  Zero if no overflow */
  u16 nSize;     /* Size of the cell content on the main b-tree page */
};

/*
** Maximum depth of an SQLite B-Tree structure. Any B-Tree deeper than
** this will be declared corrupt. This value is calculated based on a
** maximum database size of 2^31 pages a minimum fanout of 2 for a
** root-node and 3 for all other internal nodes.
**
** If a tree that appears to be taller than this is encountered, it is
** assumed that the database is corrupt.
*/
#define BTCURSOR_MAX_DEPTH 20

/*
** A cursor is a pointer to a particular entry within a particular
** b-tree within a database file.
**
** The entry is identified by its MemPage and the index in
** MemPage.aCell[] of the entry.
**
** A single database file can be shared by two more database connections,
** but cursors cannot be shared.  Each cursor is associated with a
** particular database connection identified BtCursor.pBtree.db.
**
** Fields in this structure are accessed under the BtShared.mutex
** found at self->pBt->mutex. 
**
** skipNext meaning:
**    eState==SKIPNEXT && skipNext>0:  Next sqlite3BtreeNext() is no-op.
**    eState==SKIPNEXT && skipNext<0:  Next sqlite3BtreePrevious() is no-op.
**    eState==FAULT:                   Cursor fault with skipNext as error code.
*/
struct BtCursor {
  Btree *pBtree;            /* The Btree to which this cursor belongs */
  BtShared *pBt;            /* The BtShared this cursor points to */
  BtCursor *pNext;          /* Forms a linked list of all cursors */
  Pgno *aOverflow;          /* Cache of overflow page locations */
  CellInfo info;            /* A parse of the cell we are pointing at */
  i64 nKey;                 /* Size of pKey, or last integer key */
  void *pKey;               /* Saved key that was cursor last known position */
  Pgno pgnoRoot;            /* The root page of this tree */
  int nOvflAlloc;           /* Allocated size of aOverflow[] array */
  int skipNext;    /* Prev() is noop if negative. Next() is noop if positive.
                   ** Error code if eState==CURSOR_FAULT */
  u8 curFlags;              /* zero or more BTCF_* flags defined below */
  u8 curPagerFlags;         /* Flags to send to sqlite3PagerAcquire() */
  u8 eState;                /* One of the CURSOR_XXX constants (see below) */
  u8 hints;                 /* As configured by CursorSetHints() */
  i8 iPage;                 /* Index of current page in apPage */
  u8 curIntKey;             /* Value of apPage[0]->intKey */
  struct KeyInfo *pKeyInfo; /* Argument passed to comparison function */
  void *padding1;           /* Make object size a multiple of 16 */
  u16 aiIdx[BTCURSOR_MAX_DEPTH];        /* Current index in apPage[i] */
  MemPage *apPage[BTCURSOR_MAX_DEPTH];  /* Pages from root to current page */
};

/*
** Legal values for BtCursor.curFlags
*/
#define BTCF_WriteFlag    0x01   /* True if a write cursor */
#define BTCF_ValidNKey    0x02   /* True if info.nKey is valid */
#define BTCF_ValidOvfl    0x04   /* True if aOverflow is valid */
#define BTCF_AtLast       0x08   /* Cursor is pointing ot the last entry */
#define BTCF_Incrblob     0x10   /* True if an incremental I/O handle */
#define BTCF_Multiple     0x20   /* Maybe another cursor on the same btree */

/*
** Potential values for BtCursor.eState.
**
** CURSOR_INVALID:
**   Cursor does not point to a valid entry. This can happen (for example) 
**   because the table is empty or because BtreeCursorFirst() has not been
**   called.
**
** CURSOR_VALID:
**   Cursor points to a valid entry. getPayload() etc. may be called.
**
** CURSOR_SKIPNEXT:
**   Cursor is valid except that the Cursor.skipNext field is non-zero
**   indicating that the next sqlite3BtreeNext() or sqlite3BtreePrevious()
**   operation should be a no-op.
**
** CURSOR_REQUIRESEEK:
**   The table that this cursor was opened on still exists, but has been 
**   modified since the cursor was last used. The cursor position is saved
**   in variables BtCursor.pKey and BtCursor.nKey. When a cursor is in 
**   this state, restoreCursorPosition() can be called to attempt to
**   seek the cursor to the saved position.
**
** CURSOR_FAULT:
**   An unrecoverable error (an I/O error or a malloc failure) has occurred
**   on a different connection that shares the BtShared cache with this
**   cursor.  The error has left the cache in an inconsistent state.
**   Do nothing else with this cursor.  Any attempt to use the cursor
**   should return the error code stored in BtCursor.skipNext
*/
#define CURSOR_INVALID           0
#define CURSOR_VALID             1
#define CURSOR_SKIPNEXT          2
#define CURSOR_REQUIRESEEK       3
#define CURSOR_FAULT             4

/* 
** The database page the PENDING_BYTE occupies. This page is never used.
*/
# define PENDING_BYTE_PAGE(pBt) PAGER_MJ_PGNO(pBt)

/*
** These macros define the location of the pointer-map entry for a 
** database page. The first argument to each is the number of usable
** bytes on each page of the database (often 1024). The second is the
** page number to look up in the pointer map.
**
** PTRMAP_PAGENO returns the database page number of the pointer-map
** page that stores the required pointer. PTRMAP_PTROFFSET returns
** the offset of the requested map entry.
**
** If the pgno argument passed to PTRMAP_PAGENO is a pointer-map page,
** then pgno is returned. So (pgno==PTRMAP_PAGENO(pgsz, pgno)) can be
** used to test if pgno is a pointer-map page. PTRMAP_ISPAGE implements
** this test.
*/
#define PTRMAP_PAGENO(pBt, pgno) ptrmapPageno(pBt, pgno)
#define PTRMAP_PTROFFSET(pgptrmap, pgno) (5*(pgno-pgptrmap-1))
#define PTRMAP_ISPAGE(pBt, pgno) (PTRMAP_PAGENO((pBt),(pgno))==(pgno))

/*
** The pointer map is a lookup table that identifies the parent page for
** each child page in the database file.  The parent page is the page that
** contains a pointer to the child.  Every page in the database contains
** 0 or 1 parent pages.  (In this context 'database page' refers
** to any page that is not part of the pointer map itself.)  Each pointer map
** entry consists of a single byte 'type' and a 4 byte parent page number.
** The PTRMAP_XXX identifiers below are the valid types.
**
** The purpose of the pointer map is to facility moving pages from one
** position in the file to another as part of autovacuum.  When a page
** is moved, the pointer in its parent must be updated to point to the
** new location.  The pointer map is used to locate the parent page quickly.
**
** PTRMAP_ROOTPAGE: The database page is a root-page. The page-number is not
**                  used in this case.
**
** PTRMAP_FREEPAGE: The database page is an unused (free) page. The page-number 
**                  is not used in this case.
**
** PTRMAP_OVERFLOW1: The database page is the first page in a list of 
**                   overflow pages. The page number identifies the page that
**                   contains the cell with a pointer to this overflow page.
**
** PTRMAP_OVERFLOW2: The database page is the second or later page in a list of
**                   overflow pages. The page-number identifies the previous
**                   page in the overflow page list.
**
** PTRMAP_BTREE: The database page is a non-root btree page. The page number
**               identifies the parent page in the btree.
*/
#define PTRMAP_ROOTPAGE 1
#define PTRMAP_FREEPAGE 2
#define PTRMAP_OVERFLOW1 3
#define PTRMAP_OVERFLOW2 4
#define PTRMAP_BTREE 5

/* A bunch of assert() statements to check the transaction state variables
** of handle p (type Btree*) are internally consistent.
*/
#define btreeIntegrity(p) \
  assert( p->pBt->inTransaction!=TRANS_NONE || p->pBt->nTransaction==0 ); \
  assert( p->pBt->inTransaction>=p->inTrans ); 


/*
** The ISAUTOVACUUM macro is used within balance_nonroot() to determine
** if the database supports auto-vacuum or not. Because it is used
** within an expression that is an argument to another macro 
** (sqliteMallocRaw), it is not possible to use conditional compilation.
** So, this macro is defined instead.
*/
#ifndef SQLITE_OMIT_AUTOVACUUM
#define ISAUTOVACUUM (pBt->autoVacuum)
#else
#define ISAUTOVACUUM 0
#endif


/*
** This structure is passed around through all the sanity checking routines
** in order to keep track of some global state information.
**
** The aRef[] array is allocated so that there is 1 bit for each page in
** the database. As the integrity-check proceeds, for each page used in
** the database the corresponding bit is set. This allows integrity-check to 
** detect pages that are used twice and orphaned pages (both of which 
** indicate corruption).
*/
typedef struct IntegrityCk IntegrityCk;
struct IntegrityCk {
  BtShared *pBt;    /* The tree being checked out */
  Pager *pPager;    /* The associated pager.  Also accessible by pBt->pPager */
  u8 *aPgRef;       /* 1 bit per page in the db (see above) */
  Pgno nPage;       /* Number of pages in the database */
  int mxErr;        /* Stop accumulating errors when this reaches zero */
  int nErr;         /* Number of messages written to zErrMsg so far */
  int mallocFailed; /* A memory allocation error has occurred */
  const char *zPfx; /* Error message prefix */
  int v1, v2;       /* Values for up to two %d fields in zPfx */
  StrAccum errMsg;  /* Accumulate the error message text here */
  u32 *heap;        /* Min-heap used for analyzing cell coverage */
};

/*
** Routines to read or write a two- and four-byte big-endian integer values.
*/
#define get2byte(x)   ((x)[0]<<8 | (x)[1])
#define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v))
#define get4byte sqlite3Get4byte
#define put4byte sqlite3Put4byte

/*
** get2byteAligned(), unlike get2byte(), requires that its argument point to a
** two-byte aligned address.  get2bytea() is only used for accessing the
** cell addresses in a btree header.
*/
#if SQLITE_BYTEORDER==4321
# define get2byteAligned(x)  (*(u16*)(x))
#elif SQLITE_BYTEORDER==1234 && !defined(SQLITE_DISABLE_INTRINSIC) \
    && GCC_VERSION>=4008000
# define get2byteAligned(x)  __builtin_bswap16(*(u16*)(x))
#elif SQLITE_BYTEORDER==1234 && !defined(SQLITE_DISABLE_INTRINSIC) \
    && defined(_MSC_VER) && _MSC_VER>=1300
# define get2byteAligned(x)  _byteswap_ushort(*(u16*)(x))
#else
# define get2byteAligned(x)  ((x)[0]<<8 | (x)[1])
#endif

#ifndef SQLITE_OMIT_INCRBLOB
SQLITE_PRIVATE   int sqlite3VdbeMemExpandBlob(Mem *);
  #define ExpandBlob(P) (((P)->flags&MEM_Zero)?sqlite3VdbeMemExpandBlob(P):0)
#else
  #define sqlite3VdbeMemExpandBlob(x) SQLITE_OK
  #define ExpandBlob(P) SQLITE_OK
#endif

SQLITE_PRIVATE int sqlite3HeaderSizeBtree(void);

SQLITE_PRIVATE void sqlite3VdbeRecordUnpack(KeyInfo*,int,const void*,UnpackedRecord*);
SQLITE_PRIVATE UnpackedRecord *sqlite3VdbeAllocUnpackedRecord(KeyInfo *, char *, int, char **);

typedef int (*RecordCompare)(int,const void*,UnpackedRecord*);
SQLITE_PRIVATE RecordCompare sqlite3VdbeFindCompare(UnpackedRecord*);

/************** End of btreeInt.h ********************************************/
/************** Continuing where we left off in sqliteInt.h ******************/

/*
** Structure containing global configuration data for the SQLite library.
**
** This structure also contains some state information.
*/
struct Sqlite3Config {
  int bMemstat;                     /* True to enable memory status */
  int bCoreMutex;                   /* True to enable core mutexing */
  int bFullMutex;                   /* True to enable full mutexing */
  int bOpenUri;                     /* True to interpret filenames as URIs */
  int bUseCis;                      /* Use covering indices for full-scans */
  int mxStrlen;                     /* Maximum string length */
  int neverCorrupt;                 /* Database is always well-formed */
  int szLookaside;                  /* Default lookaside buffer size */
  int nLookaside;                   /* Default lookaside buffer count */
  sqlite3_mem_methods m;            /* Low-level memory allocation interface */
  sqlite3_mutex_methods mutex;      /* Low-level mutex interface */
  sqlite3_pcache_methods2 pcache2;  /* Low-level page-cache interface */
  void *pHeap;                      /* Heap storage space */
  int nHeap;                        /* Size of pHeap[] */
  int mnReq, mxReq;                 /* Min and max heap requests sizes */
  sqlite3_int64 szMmap;             /* mmap() space per open file */
  sqlite3_int64 mxMmap;             /* Maximum value for szMmap */
  void *pScratch;                   /* Scratch memory */
  int szScratch;                    /* Size of each scratch buffer */
  int nScratch;                     /* Number of scratch buffers */
  void *pPage;                      /* Page cache memory */
  int szPage;                       /* Size of each page in pPage[] */
  int nPage;                        /* Number of pages in pPage[] */
  int mxParserStack;                /* maximum depth of the parser stack */
  int sharedCacheEnabled;           /* true if shared-cache mode enabled */
  u32 szPma;                        /* Maximum Sorter PMA size */
  /* The above might be initialized to non-zero.  The following need to always
  ** initially be zero, however. */
  int isInit;                       /* True after initialization has finished */
  int inProgress;                   /* True while initialization in progress */
  int isMutexInit;                  /* True after mutexes are initialized */
  int isMallocInit;                 /* True after malloc is initialized */
  int isPCacheInit;                 /* True after malloc is initialized */
  int nRefInitMutex;                /* Number of users of pInitMutex */
  sqlite3_mutex *pInitMutex;        /* Mutex used by sqlite3BtreeInitialize() */
  void (*xLog)(void*,int,const char*); /* Function for logging */
  void *pLogArg;                       /* First argument to xLog() */
#ifdef SQLITE_VDBE_COVERAGE
  /* The following callback (if not NULL) is invoked on every VDBE branch
  ** operation.  Set the callback using SQLITE_TESTCTRL_VDBE_COVERAGE.
  */
  void (*xVdbeBranch)(void*,int iSrcLine,u8 eThis,u8 eMx);  /* Callback */
  void *pVdbeBranchArg;                                     /* 1st argument */
#endif
  int bLocaltimeFault;              /* True to fail localtime() calls */
};

#ifndef SQLITE_AMALGAMATION
SQLITE_PRIVATE SQLITE_WSD struct Sqlite3Config sqlite3Config;
#ifndef SQLITE_OMIT_WSD
SQLITE_PRIVATE int sqlite3PendingByte;
#endif
#endif

#if (defined(i386)     || defined(__i386__)   || defined(_M_IX86) ||    \
     defined(__x86_64) || defined(__x86_64__) || defined(_M_X64)  ||    \
     defined(_M_AMD64) || defined(_M_ARM)     || defined(__x86)   ||    \
     defined(__arm__)) && !defined(SQLITE_RUNTIME_BYTEORDER)
# define SQLITE_BYTEORDER    1234
# define SQLITE_BIGENDIAN    0
# define SQLITE_LITTLEENDIAN 1
# define SQLITE_UTF16NATIVE  SQLITE_UTF16LE
#endif
#if (defined(sparc)    || defined(__ppc__))  \
    && !defined(SQLITE_RUNTIME_BYTEORDER)
# define SQLITE_BYTEORDER    4321
# define SQLITE_BIGENDIAN    1
# define SQLITE_LITTLEENDIAN 0
# define SQLITE_UTF16NATIVE  SQLITE_UTF16BE
#endif
#if !defined(SQLITE_BYTEORDER)
# define SQLITE_BYTEORDER    0     /* 0 means "unknown at compile-time" */
# define SQLITE_BIGENDIAN    (*(char *)(&sqlite3one)==0)
# define SQLITE_LITTLEENDIAN (*(char *)(&sqlite3one)==1)
# define SQLITE_UTF16NATIVE  (SQLITE_BIGENDIAN?SQLITE_UTF16BE:SQLITE_UTF16LE)
#endif

#ifdef SQLITE_ENABLE_ATOMIC_WRITE
SQLITE_PRIVATE   int sqlite3JournalOpen(sqlite3_vfs *, const char *, sqlite3_file *, int, int);
SQLITE_PRIVATE   int sqlite3JournalSize(sqlite3_vfs *);
SQLITE_PRIVATE   int sqlite3JournalCreate(sqlite3_file *);
SQLITE_PRIVATE   int sqlite3JournalExists(sqlite3_file *p);
#else
  #define sqlite3JournalSize(pVfs) ((pVfs)->szOsFile)
  #define sqlite3JournalExists(p) 1
#endif

SQLITE_PRIVATE void sqlite3MemJournalOpen(sqlite3_file *);
SQLITE_PRIVATE int sqlite3MemJournalSize(void);
SQLITE_PRIVATE int sqlite3IsMemJournal(sqlite3_file *);

#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY
SQLITE_PRIVATE   void sqlite3ConnectionBlocked(Btree*, Btree*);
SQLITE_PRIVATE   void sqlite3ConnectionUnlocked(Btree *db);
SQLITE_PRIVATE   void sqlite3ConnectionClosed(Btree *db);
#else
  #define sqlite3ConnectionBlocked(x,y)
  #define sqlite3ConnectionUnlocked(x)
  #define sqlite3ConnectionClosed(x)
#endif

/*
** If the SQLITE_ENABLE IOTRACE exists then the global variable
** sqlite3IoTrace is a pointer to a printf-like routine used to
** print I/O tracing messages. 
*/
#ifdef SQLITE_ENABLE_IOTRACE
# define IOTRACE(A)  if( sqlite3IoTrace ){ sqlite3IoTrace A; }
SQLITE_PRIVATE   void sqlite3VdbeIOTraceSql(Vdbe*);
SQLITE_API SQLITE_EXTERN void (SQLITE_CDECL *sqlite3IoTrace)(const char*,...);
#else
# define IOTRACE(A)
# define sqlite3VdbeIOTraceSql(X)
#endif

SQLITE_PRIVATE Bitvec *sqlite3BitvecCreate(u32);
SQLITE_PRIVATE int sqlite3BitvecTest(Bitvec*, u32);
SQLITE_PRIVATE int sqlite3BitvecTestNotNull(Bitvec*, u32);
SQLITE_PRIVATE int sqlite3BitvecSet(Bitvec*, u32);
SQLITE_PRIVATE void sqlite3BitvecClear(Bitvec*, u32, void*);
SQLITE_PRIVATE void sqlite3BitvecDestroy(Bitvec*);
SQLITE_PRIVATE u32 sqlite3BitvecSize(Bitvec*);

SQLITE_PRIVATE const void *sqlite3ValueText(Mem*, u8);

/*
** These routines are available for the mem2.c debugging memory allocator
** only.  They are used to verify that different "types" of memory
** allocations are properly tracked by the system.
**
** sqlite3MemdebugSetType() sets the "type" of an allocation to one of
** the MEMTYPE_* macros defined below.  The type must be a bitmask with
** a single bit set.
**
** sqlite3MemdebugHasType() returns true if any of the bits in its second
** argument match the type set by the previous sqlite3MemdebugSetType().
** sqlite3MemdebugHasType() is intended for use inside assert() statements.
**
** sqlite3MemdebugNoType() returns true if none of the bits in its second
** argument match the type set by the previous sqlite3MemdebugSetType().
**
** Perhaps the most important point is the difference between MEMTYPE_HEAP
** and MEMTYPE_LOOKASIDE.  If an allocation is MEMTYPE_LOOKASIDE, that means
** it might have been allocated by lookaside, except the allocation was
** too large or lookaside was already full.  It is important to verify
** that allocations that might have been satisfied by lookaside are not
** passed back to non-lookaside free() routines.  Asserts such as the
** example above are placed on the non-lookaside free() routines to verify
** this constraint. 
**
** All of this is no-op for a production build.  It only comes into
** play when the SQLITE_MEMDEBUG compile-time option is used.
*/
#ifdef SQLITE_MEMDEBUG
SQLITE_PRIVATE   void sqlite3MemdebugSetType(void*,u8);
SQLITE_PRIVATE   int sqlite3MemdebugHasType(void*,u8);
SQLITE_PRIVATE   int sqlite3MemdebugNoType(void*,u8);
#else
# define sqlite3MemdebugSetType(X,Y)  /* no-op */
# define sqlite3MemdebugHasType(X,Y)  1
# define sqlite3MemdebugNoType(X,Y)   1
#endif
#define MEMTYPE_HEAP       0x01  /* General heap allocations */
#define MEMTYPE_LOOKASIDE  0x02  /* Heap that might have been lookaside */
#define MEMTYPE_SCRATCH    0x04  /* Scratch allocations */
#define MEMTYPE_PCACHE     0x08  /* Page cache allocations */


SQLITE_PRIVATE i64 sqlite3VdbeIntValue(Mem*);
SQLITE_PRIVATE double sqlite3VdbeRealValue(Mem*);

SQLITE_PRIVATE int sqlite3VdbeRecordCompareWithSkip(int, const void *, UnpackedRecord *, int);

#endif /* _SQLITEINT_H_ */

/************** End of sqliteInt.h *******************************************/
/************** Begin file global.c ******************************************/
/*
** 2008 June 13
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains definitions of global variables and constants.
*/
/* #include "sqliteInt.h" */

/* EVIDENCE-OF: R-02982-34736 In order to maintain full backwards
** compatibility for legacy applications, the URI filename capability is
** disabled by default.
**
** EVIDENCE-OF: R-38799-08373 URI filenames can be enabled or disabled
** using the SQLITE_USE_URI=1 or SQLITE_USE_URI=0 compile-time options.
**
** EVIDENCE-OF: R-43642-56306 By default, URI handling is globally
** disabled. The default value may be changed by compiling with the
** SQLITE_USE_URI symbol defined.
*/
#ifndef SQLITE_USE_URI
# define  SQLITE_USE_URI 0
#endif

/* EVIDENCE-OF: R-38720-18127 The default setting is determined by the
** SQLITE_ALLOW_COVERING_INDEX_SCAN compile-time option, or is "on" if
** that compile-time option is omitted.
*/
#ifndef SQLITE_ALLOW_COVERING_INDEX_SCAN
# define SQLITE_ALLOW_COVERING_INDEX_SCAN 1
#endif

/* The minimum PMA size is set to this value multiplied by the database
** page size in bytes.
*/
#ifndef SQLITE_SORTER_PMASZ
# define SQLITE_SORTER_PMASZ 250
#endif

/*
** The following singleton contains the global configuration for
** the SQLite library.
*/
SQLITE_PRIVATE SQLITE_WSD struct Sqlite3Config sqlite3Config = {
   SQLITE_DEFAULT_MEMSTATUS,  /* bMemstat */
   1,                         /* bCoreMutex */
   SQLITE_THREADSAFE==1,      /* bFullMutex */
   SQLITE_USE_URI,            /* bOpenUri */
   SQLITE_ALLOW_COVERING_INDEX_SCAN,   /* bUseCis */
   0x7ffffffe,                /* mxStrlen */
   0,                         /* neverCorrupt */
   128,                       /* szLookaside */
   500,                       /* nLookaside */
   {0,0,0,0,0,0,0,0},         /* m */
   {0,0,0,0,0,0,0,0,0},       /* mutex */
   {0,0,0,0,0,0,0,0,0,0,0,0,0},/* pcache2 */
   (void*)0,                  /* pHeap */
   0,                         /* nHeap */
   0, 0,                      /* mnHeap, mxHeap */
   SQLITE_DEFAULT_MMAP_SIZE,  /* szMmap */
   SQLITE_MAX_MMAP_SIZE,      /* mxMmap */
   (void*)0,                  /* pScratch */
   0,                         /* szScratch */
   0,                         /* nScratch */
   (void*)0,                  /* pPage */
   0,                         /* szPage */
   SQLITE_DEFAULT_PCACHE_INITSZ, /* nPage */
   0,                         /* mxParserStack */
   0,                         /* sharedCacheEnabled */
   SQLITE_SORTER_PMASZ,       /* szPma */
   /* All the rest should always be initialized to zero */
   0,                         /* isInit */
   0,                         /* inProgress */
   0,                         /* isMutexInit */
   0,                         /* isMallocInit */
   0,                         /* isPCacheInit */
   0,                         /* nRefInitMutex */
   0,                         /* pInitMutex */
   0,                         /* xLog */
   0,                         /* pLogArg */
#ifdef SQLITE_VDBE_COVERAGE
   0,                         /* xVdbeBranch */
   0,                         /* pVbeBranchArg */
#endif
   0                          /* bLocaltimeFault */
};

/*
** The value of the "pending" byte must be 0x40000000 (1 byte past the
** 1-gibabyte boundary) in a compatible database.  SQLite never uses
** the database page that contains the pending byte.  It never attempts
** to read or write that page.  The pending byte page is set assign
** for use by the VFS layers as space for managing file locks.
**
** During testing, it is often desirable to move the pending byte to
** a different position in the file.  This allows code that has to
** deal with the pending byte to run on files that are much smaller
** than 1 GiB.  The sqlite3_test_control() interface can be used to
** move the pending byte.
**
** IMPORTANT:  Changing the pending byte to any value other than
** 0x40000000 results in an incompatible database file format!
** Changing the pending byte during operation will result in undefined
** and incorrect behavior.
*/
#ifndef SQLITE_OMIT_WSD
SQLITE_PRIVATE int sqlite3PendingByte = 0x40000000;
#endif

/************** End of global.c **********************************************/
/************** Begin file status.c ******************************************/
/*
** 2008 June 18
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This module implements the sqlite3_status() interface and related
** functionality.
*/
/* #include "sqliteInt.h" */

/*
** Variables in which to record status information.
*/
typedef struct sqlite3StatType sqlite3StatType;
static SQLITE_WSD struct sqlite3StatType {
#if SQLITE_PTRSIZE>4
  sqlite3_int64 nowValue[10];         /* Current value */
  sqlite3_int64 mxValue[10];          /* Maximum value */
#else
  u32 nowValue[10];                   /* Current value */
  u32 mxValue[10];                    /* Maximum value */
#endif
} sqlite3Stat = { {0,}, {0,} };

#ifndef NDEBUG
/*
** Elements of sqlite3Stat[] are protected by either the memory allocator
** mutex, or by the pcache1 mutex.  The following array determines which.
*/
static const char statMutex[] = {
  0,  /* SQLITE_STATUS_MEMORY_USED */
  1,  /* SQLITE_STATUS_PAGECACHE_USED */
  1,  /* SQLITE_STATUS_PAGECACHE_OVERFLOW */
  0,  /* SQLITE_STATUS_SCRATCH_USED */
  0,  /* SQLITE_STATUS_SCRATCH_OVERFLOW */
  0,  /* SQLITE_STATUS_MALLOC_SIZE */
  0,  /* SQLITE_STATUS_PARSER_STACK */
  1,  /* SQLITE_STATUS_PAGECACHE_SIZE */
  0,  /* SQLITE_STATUS_SCRATCH_SIZE */
  0,  /* SQLITE_STATUS_MALLOC_COUNT */
};
#endif

/* The "wsdStat" macro will resolve to the status information
** state vector.  If writable static data is unsupported on the target,
** we have to locate the state vector at run-time.  In the more common
** case where writable static data is supported, wsdStat can refer directly
** to the "sqlite3Stat" state vector declared above.
*/
#ifdef SQLITE_OMIT_WSD
# define wsdStatInit  sqlite3StatType *x = &GLOBAL(sqlite3StatType,sqlite3Stat)
# define wsdStat x[0]
#else
# define wsdStatInit
# define wsdStat sqlite3Stat
#endif

/*
** Return the current value of a status parameter.  The caller must
** be holding the appropriate mutex.
*/
SQLITE_PRIVATE sqlite3_int64 sqlite3StatusValue(int op){
  wsdStatInit;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  return wsdStat.nowValue[op];
}


/*
** Add N to the value of a status record.  The caller must hold the
** appropriate mutex.  (Locking is checked by assert()).
**
** The StatusUp() routine can accept positive or negative values for N.
** The value of N is added to the current status value and the high-water
** mark is adjusted if necessary.
**
** The StatusDown() routine lowers the current value by N.  The highwater
** mark is unchanged.  N must be non-negative for StatusDown().
*/
SQLITE_PRIVATE void sqlite3StatusUp(int op, int N){
  wsdStatInit;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  wsdStat.nowValue[op] += N;
  if( wsdStat.nowValue[op]>wsdStat.mxValue[op] ){
    wsdStat.mxValue[op] = wsdStat.nowValue[op];
  }
}
SQLITE_PRIVATE void sqlite3StatusDown(int op, int N){
  wsdStatInit;
  assert( N>=0 );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  wsdStat.nowValue[op] -= N;
}

/*
** Set the value of a status to X.  The highwater mark is adjusted if
** necessary.  The caller must hold the appropriate mutex.
*/
SQLITE_PRIVATE void sqlite3StatusSet(int op, int X){
  wsdStatInit;
  assert( op>=0 && op<ArraySize(wsdStat.nowValue) );
  assert( op>=0 && op<ArraySize(statMutex) );
  assert( sqlite3_mutex_held(statMutex[op] ? sqlite3Pcache1Mutex()
                                           : sqlite3MallocMutex()) );
  wsdStat.nowValue[op] = X;
  if( wsdStat.nowValue[op]>wsdStat.mxValue[op] ){
    wsdStat.mxValue[op] = wsdStat.nowValue[op];
  }
}

/************** End of status.c **********************************************/
/************** Begin file os.c **********************************************/
/*
** 2005 November 29
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains OS interface code that is common to all
** architectures.
*/
#define _SQLITE_OS_C_ 1
/* #include "sqliteInt.h" */
#undef _SQLITE_OS_C_

/*
** The default SQLite sqlite3_vfs implementations do not allocate
** memory (actually, os_unix.c allocates a small amount of memory
** from within OsOpen()), but some third-party implementations may.
** So we test the effects of a malloc() failing and the sqlite3OsXXX()
** function returning SQLITE_IOERR_NOMEM using the DO_OS_MALLOC_TEST macro.
**
** The following functions are instrumented for malloc() failure 
** testing:
**
**     sqlite3OsRead()
**     sqlite3OsWrite()
**     sqlite3OsSync()
**     sqlite3OsFileSize()
**     sqlite3OsLock()
**     sqlite3OsCheckReservedLock()
**     sqlite3OsFileControl()
**     sqlite3OsShmMap()
**     sqlite3OsOpen()
**     sqlite3OsDelete()
**     sqlite3OsAccess()
**     sqlite3OsFullPathname()
**
*/
#if defined(SQLITE_TEST)
SQLITE_PRIVATE int sqlite3_memdebug_vfs_oom_test = 1;
  #define DO_OS_MALLOC_TEST(x)                                       \
  if (sqlite3_memdebug_vfs_oom_test && (!x || !sqlite3IsMemJournal(x))) {  \
    void *pTstAlloc = sqlite3Malloc(10);                             \
    if (!pTstAlloc) return SQLITE_IOERR_NOMEM;                       \
    sqlite3_free(pTstAlloc);                                         \
  }
#else
  #define DO_OS_MALLOC_TEST(x)
#endif

/*
** The following routines are convenience wrappers around methods
** of the sqlite3_file object.  This is mostly just syntactic sugar. All
** of this would be completely automatic if SQLite were coded using
** C++ instead of plain old C.
*/
SQLITE_PRIVATE int sqlite3OsClose(sqlite3_file *pId){
  int rc = SQLITE_OK;
  if( pId->pMethods ){
    rc = pId->pMethods->xClose(pId);
    pId->pMethods = 0;
  }
  return rc;
}
SQLITE_PRIVATE int sqlite3OsRead(sqlite3_file *id, void *pBuf, int amt, i64 offset){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xRead(id, pBuf, amt, offset);
}
SQLITE_PRIVATE int sqlite3OsWrite(sqlite3_file *id, const void *pBuf, int amt, i64 offset){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xWrite(id, pBuf, amt, offset);
}
SQLITE_PRIVATE int sqlite3OsTruncate(sqlite3_file *id, i64 size){
  return id->pMethods->xTruncate(id, size);
}
SQLITE_PRIVATE int sqlite3OsSync(sqlite3_file *id, int flags){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xSync(id, flags);
}
SQLITE_PRIVATE int sqlite3OsFileSize(sqlite3_file *id, i64 *pSize){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xFileSize(id, pSize);
}
SQLITE_PRIVATE int sqlite3OsLock(sqlite3_file *id, int lockType){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xLock(id, lockType);
}
SQLITE_PRIVATE int sqlite3OsUnlock(sqlite3_file *id, int lockType){
  return id->pMethods->xUnlock(id, lockType);
}
SQLITE_PRIVATE int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xCheckReservedLock(id, pResOut);
}

/*
** Use sqlite3OsFileControl() when we are doing something that might fail
** and we need to know about the failures.  Use sqlite3OsFileControlHint()
** when simply tossing information over the wall to the VFS and we do not
** really care if the VFS receives and understands the information since it
** is only a hint and can be safely ignored.  The sqlite3OsFileControlHint()
** routine has no return value since the return value would be meaningless.
*/
SQLITE_PRIVATE int sqlite3OsFileControl(sqlite3_file *id, int op, void *pArg){
#ifdef SQLITE_TEST
  if( op!=SQLITE_FCNTL_COMMIT_PHASETWO ){
    /* Faults are not injected into COMMIT_PHASETWO because, assuming SQLite
    ** is using a regular VFS, it is called after the corresponding 
    ** transaction has been committed. Injecting a fault at this point 
    ** confuses the test scripts - the COMMIT comand returns SQLITE_NOMEM
    ** but the transaction is committed anyway.
    **
    ** The core must call OsFileControl() though, not OsFileControlHint(),
    ** as if a custom VFS (e.g. zipvfs) returns an error here, it probably
    ** means the commit really has failed and an error should be returned
    ** to the user.  */
    DO_OS_MALLOC_TEST(id);
  }
#endif
  return id->pMethods->xFileControl(id, op, pArg);
}
SQLITE_PRIVATE void sqlite3OsFileControlHint(sqlite3_file *id, int op, void *pArg){
  (void)id->pMethods->xFileControl(id, op, pArg);
}

SQLITE_PRIVATE int sqlite3OsSectorSize(sqlite3_file *id){
  int (*xSectorSize)(sqlite3_file*) = id->pMethods->xSectorSize;
  return (xSectorSize ? xSectorSize(id) : SQLITE_DEFAULT_SECTOR_SIZE);
}
SQLITE_PRIVATE int sqlite3OsDeviceCharacteristics(sqlite3_file *id){
  return id->pMethods->xDeviceCharacteristics(id);
}
SQLITE_PRIVATE int sqlite3OsShmLock(sqlite3_file *id, int offset, int n, int flags){
  return id->pMethods->xShmLock(id, offset, n, flags);
}
SQLITE_PRIVATE void sqlite3OsShmBarrier(sqlite3_file *id){
  id->pMethods->xShmBarrier(id);
}
SQLITE_PRIVATE int sqlite3OsShmUnmap(sqlite3_file *id, int deleteFlag){
  return id->pMethods->xShmUnmap(id, deleteFlag);
}
SQLITE_PRIVATE int sqlite3OsShmMap(
  sqlite3_file *id,               /* Database file handle */
  int iPage,
  int pgsz,
  int bExtend,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Pointer to mapping */
){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xShmMap(id, iPage, pgsz, bExtend, pp);
}

#if SQLITE_MAX_MMAP_SIZE>0
/* The real implementation of xFetch and xUnfetch */
SQLITE_PRIVATE int sqlite3OsFetch(sqlite3_file *id, i64 iOff, int iAmt, void **pp){
  DO_OS_MALLOC_TEST(id);
  return id->pMethods->xFetch(id, iOff, iAmt, pp);
}
SQLITE_PRIVATE int sqlite3OsUnfetch(sqlite3_file *id, i64 iOff, void *p){
  return id->pMethods->xUnfetch(id, iOff, p);
}
#else
/* No-op stubs to use when memory-mapped I/O is disabled */
SQLITE_PRIVATE int sqlite3OsFetch(sqlite3_file *id, i64 iOff, int iAmt, void **pp){
  *pp = 0;
  return SQLITE_OK;
}
SQLITE_PRIVATE int sqlite3OsUnfetch(sqlite3_file *id, i64 iOff, void *p){
  return SQLITE_OK;
}
#endif

/*
** The next group of routines are convenience wrappers around the
** VFS methods.
*/
SQLITE_PRIVATE int sqlite3OsOpen(
  sqlite3_vfs *pVfs, 
  const char *zPath, 
  sqlite3_file *pFile, 
  int flags, 
  int *pFlagsOut
){
  int rc;
  DO_OS_MALLOC_TEST(0);
  /* 0x87f7f is a mask of SQLITE_OPEN_ flags that are valid to be passed
  ** down into the VFS layer.  Some SQLITE_OPEN_ flags (for example,
  ** SQLITE_OPEN_FULLMUTEX or SQLITE_OPEN_SHAREDCACHE) are blocked before
  ** reaching the VFS. */
  rc = pVfs->xOpen(pVfs, zPath, pFile, flags & 0x87f7f, pFlagsOut);
  assert( rc==SQLITE_OK || pFile->pMethods==0 );
  return rc;
}
SQLITE_PRIVATE int sqlite3OsDelete(sqlite3_vfs *pVfs, const char *zPath, int dirSync){
  DO_OS_MALLOC_TEST(0);
  assert( dirSync==0 || dirSync==1 );
  return pVfs->xDelete(pVfs, zPath, dirSync);
}
SQLITE_PRIVATE int sqlite3OsAccess(
  sqlite3_vfs *pVfs, 
  const char *zPath, 
  int flags, 
  int *pResOut
){
  DO_OS_MALLOC_TEST(0);
  return pVfs->xAccess(pVfs, zPath, flags, pResOut);
}
SQLITE_PRIVATE int sqlite3OsFullPathname(
  sqlite3_vfs *pVfs, 
  const char *zPath, 
  int nPathOut, 
  char *zPathOut
){
  DO_OS_MALLOC_TEST(0);
  zPathOut[0] = 0;
  return pVfs->xFullPathname(pVfs, zPath, nPathOut, zPathOut);
}
SQLITE_PRIVATE int sqlite3OsRandomness(sqlite3_vfs *pVfs, int nByte, char *zBufOut){
  return pVfs->xRandomness(pVfs, nByte, zBufOut);
}
SQLITE_PRIVATE int sqlite3OsSleep(sqlite3_vfs *pVfs, int nMicro){
  return pVfs->xSleep(pVfs, nMicro);
}

/*
** This function is a wrapper around the OS specific implementation of
** sqlite3_os_init(). The purpose of the wrapper is to provide the
** ability to simulate a malloc failure, so that the handling of an
** error in sqlite3_os_init() by the upper layers can be tested.
*/
SQLITE_PRIVATE int sqlite3OsInit(void){
  void *p = sqlite3_malloc(10);
  if( p==0 ) return SQLITE_NOMEM;
  sqlite3_free(p);
  return sqlite3_os_init();
}

/*
** The list of all registered VFS implementations.
*/
static sqlite3_vfs * SQLITE_WSD vfsList = 0;
#define vfsList GLOBAL(sqlite3_vfs *, vfsList)

/*
** Locate a VFS by name.  If no name is given, simply return the
** first VFS on the list.
*/
SQLITE_PRIVATE sqlite3_vfs *sqlite3_vfs_find(const char *zVfs){
  sqlite3_vfs *pVfs = 0;
#if SQLITE_THREADSAFE
  sqlite3_mutex *mutex;
#endif
#ifndef SQLITE_OMIT_AUTOINIT
  int rc = sqlite3BtreeInitialize();
  if( rc ) return 0;
#endif
#if SQLITE_THREADSAFE
  mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
#endif
  sqlite3_mutex_enter(mutex);
  for(pVfs = vfsList; pVfs; pVfs=pVfs->pNext){
    if( zVfs==0 ) break;
    if( strcmp(zVfs, pVfs->zName)==0 ) break;
  }
  sqlite3_mutex_leave(mutex);
  return pVfs;
}

/*
** Unlink a VFS from the linked list
*/
static void vfsUnlink(sqlite3_vfs *pVfs){
  assert( sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER)) );
  if( pVfs==0 ){
    /* No-op */
  }else if( vfsList==pVfs ){
    vfsList = pVfs->pNext;
  }else if( vfsList ){
    sqlite3_vfs *p = vfsList;
    while( p->pNext && p->pNext!=pVfs ){
      p = p->pNext;
    }
    if( p->pNext==pVfs ){
      p->pNext = pVfs->pNext;
    }
  }
}

/*
** Register a VFS with the system.  It is harmless to register the same
** VFS multiple times.  The new VFS becomes the default if makeDflt is
** true.
*/
SQLITE_PRIVATE int sqlite3_vfs_register(sqlite3_vfs *pVfs, int makeDflt){
  MUTEX_LOGIC(sqlite3_mutex *mutex;)
#ifndef SQLITE_OMIT_AUTOINIT
  int rc = sqlite3BtreeInitialize();
  if( rc ) return rc;
#endif
#ifdef SQLITE_ENABLE_API_ARMOR
  if( pVfs==0 ) return SQLITE_MISUSE_BKPT;
#endif

  MUTEX_LOGIC( mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER); )
  sqlite3_mutex_enter(mutex);
  vfsUnlink(pVfs);
  if( makeDflt || vfsList==0 ){
    pVfs->pNext = vfsList;
    vfsList = pVfs;
  }else{
    pVfs->pNext = vfsList->pNext;
    vfsList->pNext = pVfs;
  }
  assert(vfsList);
  sqlite3_mutex_leave(mutex);
  return SQLITE_OK;
}

/************** End of os.c **************************************************/
/************** Begin file mem1.c ********************************************/
/*
** 2007 August 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains low-level memory allocation drivers for when
** SQLite will use the standard C-library malloc/realloc/free interface
** to obtain the memory it needs.
**
** This file contains implementations of the low-level memory allocation
** routines specified in the sqlite3_mem_methods object.  The content of
** this file is only used if SQLITE_SYSTEM_MALLOC is defined.  The
** SQLITE_SYSTEM_MALLOC macro is defined automatically if neither the
** SQLITE_MEMDEBUG nor the SQLITE_WIN32_MALLOC macros are defined.  The
** default configuration is to use memory allocation routines in this
** file.
**
** C-preprocessor macro summary:
**
**    HAVE_MALLOC_USABLE_SIZE     The configure script sets this symbol if
**                                the malloc_usable_size() interface exists
**                                on the target platform.  Or, this symbol
**                                can be set manually, if desired.
**                                If an equivalent interface exists by
**                                a different name, using a separate -D
**                                option to rename it.
**
**    SQLITE_WITHOUT_ZONEMALLOC   Some older macs lack support for the zone
**                                memory allocator.  Set this symbol to enable
**                                building on older macs.
**
**    SQLITE_WITHOUT_MSIZE        Set this symbol to disable the use of
**                                _msize() on windows systems.  This might
**                                be necessary when compiling for Delphi,
**                                for example.
*/
/* #include "sqliteInt.h" */

/*
** This version of the memory allocator is the default.  It is
** used when no other memory allocator is specified using compile-time
** macros.
*/
#ifdef SQLITE_SYSTEM_MALLOC
#if defined(__APPLE__) && !defined(SQLITE_WITHOUT_ZONEMALLOC)

/*
** Use the zone allocator available on apple products unless the
** SQLITE_WITHOUT_ZONEMALLOC symbol is defined.
*/
#include <sys/sysctl.h>
#include <malloc/malloc.h>
#include <libkern/OSAtomic.h>
static malloc_zone_t* _sqliteZone_;
#define SQLITE_MALLOC(x) malloc_zone_malloc(_sqliteZone_, (x))
#define SQLITE_FREE(x) malloc_zone_free(_sqliteZone_, (x));
#define SQLITE_REALLOC(x,y) malloc_zone_realloc(_sqliteZone_, (x), (y))
#define SQLITE_MALLOCSIZE(x) \
        (_sqliteZone_ ? _sqliteZone_->size(_sqliteZone_,x) : malloc_size(x))

#else /* if not __APPLE__ */

/*
** Use standard C library malloc and free on non-Apple systems.  
** Also used by Apple systems if SQLITE_WITHOUT_ZONEMALLOC is defined.
*/
#define SQLITE_MALLOC(x)             malloc(x)
#define SQLITE_FREE(x)               free(x)
#define SQLITE_REALLOC(x,y)          realloc((x),(y))

/*
** The malloc.h header file is needed for malloc_usable_size() function
** on some systems (e.g. Linux).
*/
#if HAVE_MALLOC_H && HAVE_MALLOC_USABLE_SIZE
#  define SQLITE_USE_MALLOC_H 1
#  define SQLITE_USE_MALLOC_USABLE_SIZE 1
/*
** The MSVCRT has malloc_usable_size(), but it is called _msize().  The
** use of _msize() is automatic, but can be disabled by compiling with
** -DSQLITE_WITHOUT_MSIZE.  Using the _msize() function also requires
** the malloc.h header file.
*/
#elif defined(_MSC_VER) && !defined(SQLITE_WITHOUT_MSIZE)
#  define SQLITE_USE_MALLOC_H
#  define SQLITE_USE_MSIZE
#endif

/*
** Include the malloc.h header file, if necessary.  Also set define macro
** SQLITE_MALLOCSIZE to the appropriate function name, which is _msize()
** for MSVC and malloc_usable_size() for most other systems (e.g. Linux).
** The memory size function can always be overridden manually by defining
** the macro SQLITE_MALLOCSIZE to the desired function name.
*/
#if defined(SQLITE_USE_MALLOC_H)
#  include <malloc.h>
#  if defined(SQLITE_USE_MALLOC_USABLE_SIZE)
#    if !defined(SQLITE_MALLOCSIZE)
#      define SQLITE_MALLOCSIZE(x)   malloc_usable_size(x)
#    endif
#  elif defined(SQLITE_USE_MSIZE)
#    if !defined(SQLITE_MALLOCSIZE)
#      define SQLITE_MALLOCSIZE      _msize
#    endif
#  endif
#endif /* defined(SQLITE_USE_MALLOC_H) */

#endif /* __APPLE__ or not __APPLE__ */

/*
** Like malloc(), but remember the size of the allocation
** so that we can find it later using sqlite3MemSize().
**
** For this low-level routine, we are guaranteed that nByte>0 because
** cases of nByte<=0 will be intercepted and dealt with by higher level
** routines.
*/
static void *sqlite3MemMalloc(int nByte){
#ifdef SQLITE_MALLOCSIZE
  void *p = SQLITE_MALLOC( nByte );
  if( p==0 ){
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes of memory", nByte);
  }
  return p;
#else
  sqlite3_int64 *p;
  assert( nByte>0 );
  nByte = ROUND8(nByte);
  p = SQLITE_MALLOC( nByte+8 );
  if( p ){
    p[0] = nByte;
    p++;
  }else{
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM, "failed to allocate %u bytes of memory", nByte);
  }
  return (void *)p;
#endif
}

/*
** Like free() but works for allocations obtained from sqlite3MemMalloc()
** or sqlite3MemRealloc().
**
** For this low-level routine, we already know that pPrior!=0 since
** cases where pPrior==0 will have been intecepted and dealt with
** by higher-level routines.
*/
static void sqlite3MemFree(void *pPrior){
#ifdef SQLITE_MALLOCSIZE
  SQLITE_FREE(pPrior);
#else
  sqlite3_int64 *p = (sqlite3_int64*)pPrior;
  assert( pPrior!=0 );
  p--;
  SQLITE_FREE(p);
#endif
}

/*
** Report the allocated size of a prior return from xMalloc()
** or xRealloc().
*/
static int sqlite3MemSize(void *pPrior){
#ifdef SQLITE_MALLOCSIZE
  return pPrior ? (int)SQLITE_MALLOCSIZE(pPrior) : 0;
#else
  sqlite3_int64 *p;
  if( pPrior==0 ) return 0;
  p = (sqlite3_int64*)pPrior;
  p--;
  return (int)p[0];
#endif
}

/*
** Like realloc().  Resize an allocation previously obtained from
** sqlite3MemMalloc().
**
** For this low-level interface, we know that pPrior!=0.  Cases where
** pPrior==0 while have been intercepted by higher-level routine and
** redirected to xMalloc.  Similarly, we know that nByte>0 because
** cases where nByte<=0 will have been intercepted by higher-level
** routines and redirected to xFree.
*/
static void *sqlite3MemRealloc(void *pPrior, int nByte){
#ifdef SQLITE_MALLOCSIZE
  void *p = SQLITE_REALLOC(pPrior, nByte);
  if( p==0 ){
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM,
      "failed memory resize %u to %u bytes",
      SQLITE_MALLOCSIZE(pPrior), nByte);
  }
  return p;
#else
  sqlite3_int64 *p = (sqlite3_int64*)pPrior;
  assert( pPrior!=0 && nByte>0 );
  assert( nByte==ROUND8(nByte) ); /* EV: R-46199-30249 */
  p--;
  p = SQLITE_REALLOC(p, nByte+8 );
  if( p ){
    p[0] = nByte;
    p++;
  }else{
    testcase( sqlite3GlobalConfig.xLog!=0 );
    sqlite3_log(SQLITE_NOMEM,
      "failed memory resize %u to %u bytes",
      sqlite3MemSize(pPrior), nByte);
  }
  return (void*)p;
#endif
}

/*
** Round up a request size to the next valid allocation size.
*/
static int sqlite3MemRoundup(int n){
  return ROUND8(n);
}

/*
** Initialize this module.
*/
static int sqlite3MemInit(void *NotUsed){
#if defined(__APPLE__) && !defined(SQLITE_WITHOUT_ZONEMALLOC)
  int cpuCount;
  size_t len;
  if( _sqliteZone_ ){
    return SQLITE_OK;
  }
  len = sizeof(cpuCount);
  /* One usually wants to use hw.acctivecpu for MT decisions, but not here */
  sysctlbyname("hw.ncpu", &cpuCount, &len, NULL, 0);
  if( cpuCount>1 ){
    /* defer MT decisions to system malloc */
    _sqliteZone_ = malloc_default_zone();
  }else{
    /* only 1 core, use our own zone to contention over global locks, 
    ** e.g. we have our own dedicated locks */
    bool success;
    malloc_zone_t* newzone = malloc_create_zone(4096, 0);
    malloc_set_zone_name(newzone, "Sqlite_Heap");
    do{
      success = OSAtomicCompareAndSwapPtrBarrier(NULL, newzone, 
                                 (void * volatile *)&_sqliteZone_);
    }while(!_sqliteZone_);
    if( !success ){
      /* somebody registered a zone first */
      malloc_destroy_zone(newzone);
    }
  }
#endif
  UNUSED_PARAMETER(NotUsed);
  return SQLITE_OK;
}

/*
** Deinitialize this module.
*/
static void sqlite3MemShutdown(void *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  return;
}

/*
** This routine is the only routine in this file with external linkage.
**
** Populate the low-level memory allocation function pointers in
** sqlite3GlobalConfig.m with pointers to the routines in this file.
*/
SQLITE_PRIVATE void sqlite3MemSetDefault(void){
  static const sqlite3_mem_methods defaultMethods = {
     sqlite3MemMalloc,
     sqlite3MemFree,
     sqlite3MemRealloc,
     sqlite3MemSize,
     sqlite3MemRoundup,
     sqlite3MemInit,
     sqlite3MemShutdown,
     0
  };
  sqlite3_config(SQLITE_CONFIG_MALLOC, &defaultMethods);
}

#endif /* SQLITE_SYSTEM_MALLOC */

/************** End of mem1.c ************************************************/
/************** Begin file mutex.c *******************************************/
/*
** 2007 August 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes.
**
** This file contains code that is common across all mutex implementations.
*/
/* #include "sqliteInt.h" */

#if defined(SQLITE_DEBUG) && !defined(SQLITE_MUTEX_OMIT)
/*
** For debugging purposes, record when the mutex subsystem is initialized
** and uninitialized so that we can assert() if there is an attempt to
** allocate a mutex while the system is uninitialized.
*/
static SQLITE_WSD int mutexIsInit = 0;
#endif /* SQLITE_DEBUG && !defined(SQLITE_MUTEX_OMIT) */


#ifndef SQLITE_MUTEX_OMIT
/*
** Initialize the mutex system.
*/
SQLITE_PRIVATE int sqlite3MutexInit(void){ 
  int rc = SQLITE_OK;
  if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
    /* If the xMutexAlloc method has not been set, then the user did not
    ** install a mutex implementation via sqlite3_config() prior to 
    ** sqlite3BtreeInitialize() being called. This block copies pointers to
    ** the default implementation into the sqlite3GlobalConfig structure.
    */
    sqlite3_mutex_methods const *pFrom;
    sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;

    if( sqlite3GlobalConfig.bCoreMutex ){
      pFrom = sqlite3DefaultMutex();
    }else{
      pFrom = sqlite3NoopMutex();
    }
    pTo->xMutexInit = pFrom->xMutexInit;
    pTo->xMutexEnd = pFrom->xMutexEnd;
    pTo->xMutexFree = pFrom->xMutexFree;
    pTo->xMutexEnter = pFrom->xMutexEnter;
    pTo->xMutexTry = pFrom->xMutexTry;
    pTo->xMutexLeave = pFrom->xMutexLeave;
    pTo->xMutexHeld = pFrom->xMutexHeld;
    pTo->xMutexNotheld = pFrom->xMutexNotheld;
    sqlite3MemoryBarrier();
    pTo->xMutexAlloc = pFrom->xMutexAlloc;
  }
  assert( sqlite3GlobalConfig.mutex.xMutexInit );
  rc = sqlite3GlobalConfig.mutex.xMutexInit();

#ifdef SQLITE_DEBUG
  GLOBAL(int, mutexIsInit) = 1;
#endif

  return rc;
}

/*
** Shutdown the mutex system. This call frees resources allocated by
** sqlite3MutexInit().
*/
SQLITE_PRIVATE int sqlite3MutexEnd(void){
  int rc = SQLITE_OK;
  if( sqlite3GlobalConfig.mutex.xMutexEnd ){
    rc = sqlite3GlobalConfig.mutex.xMutexEnd();
  }

#ifdef SQLITE_DEBUG
  GLOBAL(int, mutexIsInit) = 0;
#endif

  return rc;
}

/*
** Retrieve a pointer to a static mutex or allocate a new dynamic one.
*/
SQLITE_PRIVATE sqlite3_mutex *sqlite3_mutex_alloc(int id){
#ifndef SQLITE_OMIT_AUTOINIT
  if( id<=SQLITE_MUTEX_RECURSIVE && sqlite3BtreeInitialize() ) return 0;
  if( id>SQLITE_MUTEX_RECURSIVE && sqlite3MutexInit() ) return 0;
#endif
  assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
  return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
}

SQLITE_PRIVATE sqlite3_mutex *sqlite3MutexAlloc(int id){
  if( !sqlite3GlobalConfig.bCoreMutex ){
    return 0;
  }
  assert( GLOBAL(int, mutexIsInit) );
  assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
  return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
}

/*
** Free a dynamic mutex.
*/
SQLITE_PRIVATE void sqlite3_mutex_free(sqlite3_mutex *p){
  if( p ){
    assert( sqlite3GlobalConfig.mutex.xMutexFree );
    sqlite3GlobalConfig.mutex.xMutexFree(p);
  }
}

/*
** Obtain the mutex p. If some other thread already has the mutex, block
** until it can be obtained.
*/
SQLITE_PRIVATE void sqlite3_mutex_enter(sqlite3_mutex *p){
  if( p ){
    assert( sqlite3GlobalConfig.mutex.xMutexEnter );
    sqlite3GlobalConfig.mutex.xMutexEnter(p);
  }
}

/*
** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
*/
SQLITE_PRIVATE int sqlite3_mutex_try(sqlite3_mutex *p){
  int rc = SQLITE_OK;
  if( p ){
    assert( sqlite3GlobalConfig.mutex.xMutexTry );
    return sqlite3GlobalConfig.mutex.xMutexTry(p);
  }
  return rc;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was previously
** entered by the same thread.  The behavior is undefined if the mutex 
** is not currently entered. If a NULL pointer is passed as an argument
** this function is a no-op.
*/
SQLITE_PRIVATE void sqlite3_mutex_leave(sqlite3_mutex *p){
  if( p ){
    assert( sqlite3GlobalConfig.mutex.xMutexLeave );
    sqlite3GlobalConfig.mutex.xMutexLeave(p);
  }
}

#ifndef NDEBUG
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use inside assert() statements.
*/
SQLITE_PRIVATE int sqlite3_mutex_held(sqlite3_mutex *p){
  assert( p==0 || sqlite3GlobalConfig.mutex.xMutexHeld );
  return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
}
SQLITE_PRIVATE int sqlite3_mutex_notheld(sqlite3_mutex *p){
  assert( p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld );
  return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
}
#endif

#endif /* !defined(SQLITE_MUTEX_OMIT) */

/************** End of mutex.c ***********************************************/
/************** Begin file mutex_noop.c **************************************/
/*
** 2008 October 07
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes.
**
** This implementation in this file does not provide any mutual
** exclusion and is thus suitable for use only in applications
** that use SQLite in a single thread.  The routines defined
** here are place-holders.  Applications can substitute working
** mutex routines at start-time using the
**
**     sqlite3_config(SQLITE_CONFIG_MUTEX,...)
**
** interface.
**
** If compiled with SQLITE_DEBUG, then additional logic is inserted
** that does error checking on mutexes to make sure they are being
** called correctly.
*/
/* #include "sqliteInt.h" */

#ifndef SQLITE_MUTEX_OMIT

#ifndef SQLITE_DEBUG
/*
** Stub routines for all mutex methods.
**
** This routines provide no mutual exclusion or error checking.
*/
static int noopMutexInit(void){ return SQLITE_OK; }
static int noopMutexEnd(void){ return SQLITE_OK; }
static sqlite3_mutex *noopMutexAlloc(int id){ 
  UNUSED_PARAMETER(id);
  return (sqlite3_mutex*)8; 
}
static void noopMutexFree(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
static void noopMutexEnter(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
static int noopMutexTry(sqlite3_mutex *p){
  UNUSED_PARAMETER(p);
  return SQLITE_OK;
}
static void noopMutexLeave(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }

SQLITE_PRIVATE sqlite3_mutex_methods const *sqlite3NoopMutex(void){
  static const sqlite3_mutex_methods sMutex = {
    noopMutexInit,
    noopMutexEnd,
    noopMutexAlloc,
    noopMutexFree,
    noopMutexEnter,
    noopMutexTry,
    noopMutexLeave,

    0,
    0,
  };

  return &sMutex;
}
#endif /* !SQLITE_DEBUG */

#ifdef SQLITE_DEBUG
/*
** In this implementation, error checking is provided for testing
** and debugging purposes.  The mutexes still do not provide any
** mutual exclusion.
*/

/*
** The mutex object
*/
typedef struct sqlite3_debug_mutex {
  int id;     /* The mutex type */
  int cnt;    /* Number of entries without a matching leave */
} sqlite3_debug_mutex;

/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use inside assert() statements.
*/
static int debugMutexHeld(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  return p==0 || p->cnt>0;
}
static int debugMutexNotheld(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  return p==0 || p->cnt==0;
}

/*
** Initialize and deinitialize the mutex subsystem.
*/
static int debugMutexInit(void){ return SQLITE_OK; }
static int debugMutexEnd(void){ return SQLITE_OK; }

/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated. 
*/
static sqlite3_mutex *debugMutexAlloc(int id){
  static sqlite3_debug_mutex aStatic[SQLITE_MUTEX_STATIC_VFS3 - 1];
  sqlite3_debug_mutex *pNew = 0;
  switch( id ){
    case SQLITE_MUTEX_FAST:
    case SQLITE_MUTEX_RECURSIVE: {
      pNew = sqlite3Malloc(sizeof(*pNew));
      if( pNew ){
        pNew->id = id;
        pNew->cnt = 0;
      }
      break;
    }
    default: {
#ifdef SQLITE_ENABLE_API_ARMOR
      if( id-2<0 || id-2>=ArraySize(aStatic) ){
        (void)SQLITE_MISUSE_BKPT;
        return 0;
      }
#endif
      pNew = &aStatic[id-2];
      pNew->id = id;
      break;
    }
  }
  return (sqlite3_mutex*)pNew;
}

/*
** This routine deallocates a previously allocated mutex.
*/
static void debugMutexFree(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  assert( p->cnt==0 );
  if( p->id==SQLITE_MUTEX_RECURSIVE || p->id==SQLITE_MUTEX_FAST ){
    sqlite3_free(p);
  }else{
#ifdef SQLITE_ENABLE_API_ARMOR
    (void)SQLITE_MISUSE_BKPT;
#endif
  }
}

/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
static void debugMutexEnter(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
  p->cnt++;
}
static int debugMutexTry(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
  p->cnt++;
  return SQLITE_OK;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
static void debugMutexLeave(sqlite3_mutex *pX){
  sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  assert( debugMutexHeld(pX) );
  p->cnt--;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
}

SQLITE_PRIVATE sqlite3_mutex_methods const *sqlite3NoopMutex(void){
  static const sqlite3_mutex_methods sMutex = {
    debugMutexInit,
    debugMutexEnd,
    debugMutexAlloc,
    debugMutexFree,
    debugMutexEnter,
    debugMutexTry,
    debugMutexLeave,

    debugMutexHeld,
    debugMutexNotheld
  };

  return &sMutex;
}
#endif /* SQLITE_DEBUG */

/*
** If compiled with SQLITE_MUTEX_NOOP, then the no-op mutex implementation
** is used regardless of the run-time threadsafety setting.
*/
#ifdef SQLITE_MUTEX_NOOP
SQLITE_PRIVATE sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
  return sqlite3NoopMutex();
}
#endif /* defined(SQLITE_MUTEX_NOOP) */
#endif /* !defined(SQLITE_MUTEX_OMIT) */

/************** End of mutex_noop.c ******************************************/
/************** Begin file mutex_unix.c **************************************/
/*
** 2007 August 28
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes for pthreads
*/
/* #include "sqliteInt.h" */

/*
** The code in this file is only used if we are compiling threadsafe
** under unix with pthreads.
**
** Note that this implementation requires a version of pthreads that
** supports recursive mutexes.
*/
#ifdef SQLITE_MUTEX_PTHREADS

#include <pthread.h>

/*
** The sqlite3_mutex.id, sqlite3_mutex.nRef, and sqlite3_mutex.owner fields
** are necessary under two condidtions:  (1) Debug builds and (2) using
** home-grown mutexes.  Encapsulate these conditions into a single #define.
*/
#if defined(SQLITE_DEBUG) || defined(SQLITE_HOMEGROWN_RECURSIVE_MUTEX)
# define SQLITE_MUTEX_NREF 1
#else
# define SQLITE_MUTEX_NREF 0
#endif

/*
** Each recursive mutex is an instance of the following structure.
*/
struct sqlite3_mutex {
  pthread_mutex_t mutex;     /* Mutex controlling the lock */
#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)
  int id;                    /* Mutex type */
#endif
#if SQLITE_MUTEX_NREF
  volatile int nRef;         /* Number of entrances */
  volatile pthread_t owner;  /* Thread that is within this mutex */
  int trace;                 /* True to trace changes */
#endif
};
#if SQLITE_MUTEX_NREF
#define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, 0, 0, (pthread_t)0, 0 }
#else
#define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER }
#endif

/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside assert() statements.  On some platforms,
** there might be race conditions that can cause these routines to
** deliver incorrect results.  In particular, if pthread_equal() is
** not an atomic operation, then these routines might delivery
** incorrect results.  On most platforms, pthread_equal() is a 
** comparison of two integers and is therefore atomic.  But we are
** told that HPUX is not such a platform.  If so, then these routines
** will not always work correctly on HPUX.
**
** On those platforms where pthread_equal() is not atomic, SQLite
** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
** make sure no assert() statements are evaluated and hence these
** routines are never called.
*/
#if !defined(NDEBUG) || defined(SQLITE_DEBUG)
static int pthreadMutexHeld(sqlite3_mutex *p){
  return (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
}
static int pthreadMutexNotheld(sqlite3_mutex *p){
  return p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
}
#endif

/*
** Try to provide a memory barrier operation, needed for initialization
** and also for the implementation of xShmBarrier in the VFS in cases
** where SQLite is compiled without mutexes.
*/
SQLITE_PRIVATE void sqlite3MemoryBarrier(void){
#if defined(SQLITE_MEMORY_BARRIER)
  SQLITE_MEMORY_BARRIER;
#elif defined(__GNUC__) && GCC_VERSION>=4001000
  __sync_synchronize();
#endif
}

/*
** Initialize and deinitialize the mutex subsystem.
*/
static int pthreadMutexInit(void){ return SQLITE_OK; }
static int pthreadMutexEnd(void){ return SQLITE_OK; }

/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated.  SQLite
** will unwind its stack and return an error.  The argument
** to sqlite3_mutex_alloc() is one of these integer constants:
**
** <ul>
** <li>  SQLITE_MUTEX_FAST
** <li>  SQLITE_MUTEX_RECURSIVE
** <li>  SQLITE_MUTEX_STATIC_MASTER
** <li>  SQLITE_MUTEX_STATIC_MEM
** <li>  SQLITE_MUTEX_STATIC_OPEN
** <li>  SQLITE_MUTEX_STATIC_PRNG
** <li>  SQLITE_MUTEX_STATIC_LRU
** <li>  SQLITE_MUTEX_STATIC_PMEM
** <li>  SQLITE_MUTEX_STATIC_APP1
** <li>  SQLITE_MUTEX_STATIC_APP2
** <li>  SQLITE_MUTEX_STATIC_APP3
** <li>  SQLITE_MUTEX_STATIC_VFS1
** <li>  SQLITE_MUTEX_STATIC_VFS2
** <li>  SQLITE_MUTEX_STATIC_VFS3
** </ul>
**
** The first two constants cause sqlite3_mutex_alloc() to create
** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
** The mutex implementation does not need to make a distinction
** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to.  But SQLite will only request a recursive mutex in
** cases where it really needs one.  If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** The other allowed parameters to sqlite3_mutex_alloc() each return
** a pointer to a static preexisting mutex.  Six static mutexes are
** used by the current version of SQLite.  Future versions of SQLite
** may add additional static mutexes.  Static mutexes are for internal
** use by SQLite only.  Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
** returns a different mutex on every call.  But for the static 
** mutex types, the same mutex is returned on every call that has
** the same type number.
*/
static sqlite3_mutex *pthreadMutexAlloc(int iType){
  static sqlite3_mutex staticMutexes[] = {
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER,
    SQLITE3_MUTEX_INITIALIZER
  };
  sqlite3_mutex *p;
  switch( iType ){
    case SQLITE_MUTEX_RECURSIVE: {
      p = sqlite3MallocZero( sizeof(*p) );
      if( p ){
#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
        /* If recursive mutexes are not available, we will have to
        ** build our own.  See below. */
        pthread_mutex_init(&p->mutex, 0);
#else
        /* Use a recursive mutex if it is available */
        pthread_mutexattr_t recursiveAttr;
        pthread_mutexattr_init(&recursiveAttr);
        pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
        pthread_mutex_init(&p->mutex, &recursiveAttr);
        pthread_mutexattr_destroy(&recursiveAttr);
#endif
      }
      break;
    }
    case SQLITE_MUTEX_FAST: {
      p = sqlite3MallocZero( sizeof(*p) );
      if( p ){
        pthread_mutex_init(&p->mutex, 0);
      }
      break;
    }
    default: {
#ifdef SQLITE_ENABLE_API_ARMOR
      if( iType-2<0 || iType-2>=ArraySize(staticMutexes) ){
        (void)SQLITE_MISUSE_BKPT;
        return 0;
      }
#endif
      p = &staticMutexes[iType-2];
      break;
    }
  }
#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)
  if( p ) p->id = iType;
#endif
  return p;
}


/*
** This routine deallocates a previously
** allocated mutex.  SQLite is careful to deallocate every
** mutex that it allocates.
*/
static void pthreadMutexFree(sqlite3_mutex *p){
  assert( p->nRef==0 );
#if SQLITE_ENABLE_API_ARMOR
  if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE )
#endif
  {
    pthread_mutex_destroy(&p->mutex);
    sqlite3_free(p);
  }
#ifdef SQLITE_ENABLE_API_ARMOR
  else{
    (void)SQLITE_MISUSE_BKPT;
  }
#endif
}

/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
static void pthreadMutexEnter(sqlite3_mutex *p){
  assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
  /* If recursive mutexes are not available, then we have to grow
  ** our own.  This implementation assumes that pthread_equal()
  ** is atomic - that it cannot be deceived into thinking self
  ** and p->owner are equal if p->owner changes between two values
  ** that are not equal to self while the comparison is taking place.
  ** This implementation also assumes a coherent cache - that 
  ** separate processes cannot read different values from the same
  ** address at the same time.  If either of these two conditions
  ** are not met, then the mutexes will fail and problems will result.
  */
  {
    pthread_t self = pthread_self();
    if( p->nRef>0 && pthread_equal(p->owner, self) ){
      p->nRef++;
    }else{
      pthread_mutex_lock(&p->mutex);
      assert( p->nRef==0 );
      p->owner = self;
      p->nRef = 1;
    }
  }
#else
  /* Use the built-in recursive mutexes if they are available.
  */
  pthread_mutex_lock(&p->mutex);
#if SQLITE_MUTEX_NREF
  assert( p->nRef>0 || p->owner==0 );
  p->owner = pthread_self();
  p->nRef++;
#endif
#endif

#ifdef SQLITE_DEBUG
  if( p->trace ){
    printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
  }
#endif
}
static int pthreadMutexTry(sqlite3_mutex *p){
  int rc;
  assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
  /* If recursive mutexes are not available, then we have to grow
  ** our own.  This implementation assumes that pthread_equal()
  ** is atomic - that it cannot be deceived into thinking self
  ** and p->owner are equal if p->owner changes between two values
  ** that are not equal to self while the comparison is taking place.
  ** This implementation also assumes a coherent cache - that 
  ** separate processes cannot read different values from the same
  ** address at the same time.  If either of these two conditions
  ** are not met, then the mutexes will fail and problems will result.
  */
  {
    pthread_t self = pthread_self();
    if( p->nRef>0 && pthread_equal(p->owner, self) ){
      p->nRef++;
      rc = SQLITE_OK;
    }else if( pthread_mutex_trylock(&p->mutex)==0 ){
      assert( p->nRef==0 );
      p->owner = self;
      p->nRef = 1;
      rc = SQLITE_OK;
    }else{
      rc = SQLITE_BUSY;
    }
  }
#else
  /* Use the built-in recursive mutexes if they are available.
  */
  if( pthread_mutex_trylock(&p->mutex)==0 ){
#if SQLITE_MUTEX_NREF
    p->owner = pthread_self();
    p->nRef++;
#endif
    rc = SQLITE_OK;
  }else{
    rc = SQLITE_BUSY;
  }
#endif

#ifdef SQLITE_DEBUG
  if( rc==SQLITE_OK && p->trace ){
    printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
  }
#endif
  return rc;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
static void pthreadMutexLeave(sqlite3_mutex *p){
  assert( pthreadMutexHeld(p) );
#if SQLITE_MUTEX_NREF
  p->nRef--;
  if( p->nRef==0 ) p->owner = 0;
#endif
  assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );

#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
  if( p->nRef==0 ){
    pthread_mutex_unlock(&p->mutex);
  }
#else
  pthread_mutex_unlock(&p->mutex);
#endif

#ifdef SQLITE_DEBUG
  if( p->trace ){
    printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
  }
#endif
}

SQLITE_PRIVATE sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
  static const sqlite3_mutex_methods sMutex = {
    pthreadMutexInit,
    pthreadMutexEnd,
    pthreadMutexAlloc,
    pthreadMutexFree,
    pthreadMutexEnter,
    pthreadMutexTry,
    pthreadMutexLeave,
#ifdef SQLITE_DEBUG
    pthreadMutexHeld,
    pthreadMutexNotheld
#else
    0,
    0
#endif
  };

  return &sMutex;
}

#endif /* SQLITE_MUTEX_PTHREADS */

/************** End of mutex_unix.c ******************************************/
/************** Begin file mutex_w32.c ***************************************/
/*
** 2007 August 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes for Win32.
*/
/* #include "sqliteInt.h" */

#if SQLITE_OS_WIN
/*
** Include code that is common to all os_*.c files
*/
/************** Include os_common.h in the middle of mutex_w32.c *************/
/************** Begin file os_common.h ***************************************/
/*
** 2004 May 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains macros and a little bit of code that is common to
** all of the platform-specific files (os_*.c) and is #included into those
** files.
**
** This file should be #included by the os_*.c files only.  It is not a
** general purpose header file.
*/
#ifndef _OS_COMMON_H_
#define _OS_COMMON_H_

/*
** At least two bugs have slipped in because we changed the MEMORY_DEBUG
** macro to SQLITE_DEBUG and some older makefiles have not yet made the
** switch.  The following code should catch this problem at compile-time.
*/
#ifdef MEMORY_DEBUG
# error "The MEMORY_DEBUG macro is obsolete.  Use SQLITE_DEBUG instead."
#endif

/*
** Macros for performance tracing.  Normally turned off.  Only works
** on i486 hardware.
*/
#ifdef SQLITE_PERFORMANCE_TRACE

/* 
** hwtime.h contains inline assembler code for implementing 
** high-performance timing routines.
*/
#include "hwtime.h"

static sqlite_uint64 g_start;
static sqlite_uint64 g_elapsed;
#define TIMER_START       g_start=sqlite3Hwtime()
#define TIMER_END         g_elapsed=sqlite3Hwtime()-g_start
#define TIMER_ELAPSED     g_elapsed
#else
#define TIMER_START
#define TIMER_END
#define TIMER_ELAPSED     ((sqlite_uint64)0)
#endif

/*
** If we compile with the SQLITE_TEST macro set, then the following block
** of code will give us the ability to simulate a disk I/O error.  This
** is used for testing the I/O recovery logic.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_io_error_hit = 0;            /* Total number of I/O Errors */
SQLITE_PRIVATE int sqlite3_io_error_hardhit = 0;        /* Number of non-benign errors */
SQLITE_PRIVATE int sqlite3_io_error_pending = 0;        /* Count down to first I/O error */
SQLITE_PRIVATE int sqlite3_io_error_persist = 0;        /* True if I/O errors persist */
SQLITE_PRIVATE int sqlite3_io_error_benign = 0;         /* True if errors are benign */
SQLITE_PRIVATE int sqlite3_diskfull_pending = 0;
SQLITE_PRIVATE int sqlite3_diskfull = 0;
#define SimulateIOErrorBenign(X) sqlite3_io_error_benign=(X)
#define SimulateIOError(CODE)  \
  if( (sqlite3_io_error_persist && sqlite3_io_error_hit) \
       || sqlite3_io_error_pending-- == 1 )  \
              { local_ioerr(); CODE; }
static void local_ioerr(){
  IOTRACE(("IOERR\n"));
  sqlite3_io_error_hit++;
  if( !sqlite3_io_error_benign ) sqlite3_io_error_hardhit++;
}
#define SimulateDiskfullError(CODE) \
   if( sqlite3_diskfull_pending ){ \
     if( sqlite3_diskfull_pending == 1 ){ \
       local_ioerr(); \
       sqlite3_diskfull = 1; \
       sqlite3_io_error_hit = 1; \
       CODE; \
     }else{ \
       sqlite3_diskfull_pending--; \
     } \
   }
#else
#define SimulateIOErrorBenign(X)
#define SimulateIOError(A)
#define SimulateDiskfullError(A)
#endif

/*
** When testing, keep a count of the number of open files.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_open_file_count = 0;
#define OpenCounter(X)  sqlite3_open_file_count+=(X)
#else
#define OpenCounter(X)
#endif

#endif /* !defined(_OS_COMMON_H_) */

/************** End of os_common.h *******************************************/
/************** Continuing where we left off in mutex_w32.c ******************/

/*
** Include the header file for the Windows VFS.
*/
/************** Include os_win.h in the middle of mutex_w32.c ****************/
/************** Begin file os_win.h ******************************************/
/*
** 2013 November 25
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains code that is specific to Windows.
*/
#ifndef _OS_WIN_H_
#define _OS_WIN_H_

/*
** Include the primary Windows SDK header file.
*/
#include "windows.h"

#ifdef __CYGWIN__
# include <sys/cygwin.h>
# include <errno.h> /* amalgamator: dontcache */
#endif

/*
** Determine if we are dealing with Windows NT.
**
** We ought to be able to determine if we are compiling for Windows 9x or
** Windows NT using the _WIN32_WINNT macro as follows:
**
** #if defined(_WIN32_WINNT)
** # define SQLITE_OS_WINNT 1
** #else
** # define SQLITE_OS_WINNT 0
** #endif
**
** However, Visual Studio 2005 does not set _WIN32_WINNT by default, as
** it ought to, so the above test does not work.  We'll just assume that
** everything is Windows NT unless the programmer explicitly says otherwise
** by setting SQLITE_OS_WINNT to 0.
*/
#if SQLITE_OS_WIN && !defined(SQLITE_OS_WINNT)
# define SQLITE_OS_WINNT 1
#endif

/*
** Determine if we are dealing with Windows CE - which has a much reduced
** API.
*/
#if defined(_WIN32_WCE)
# define SQLITE_OS_WINCE 1
#else
# define SQLITE_OS_WINCE 0
#endif

/*
** Determine if we are dealing with WinRT, which provides only a subset of
** the full Win32 API.
*/
#if !defined(SQLITE_OS_WINRT)
# define SQLITE_OS_WINRT 0
#endif

/*
** For WinCE, some API function parameters do not appear to be declared as
** volatile.
*/
#if SQLITE_OS_WINCE
# define SQLITE_WIN32_VOLATILE
#else
# define SQLITE_WIN32_VOLATILE volatile
#endif

/*
** For some Windows sub-platforms, the _beginthreadex() / _endthreadex()
** functions are not available (e.g. those not using MSVC, Cygwin, etc).
*/
#if SQLITE_OS_WIN && !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && \
    SQLITE_THREADSAFE>0 && !defined(__CYGWIN__)
# define SQLITE_OS_WIN_THREADS 1
#else
# define SQLITE_OS_WIN_THREADS 0
#endif

#endif /* _OS_WIN_H_ */

/************** End of os_win.h **********************************************/
/************** Continuing where we left off in mutex_w32.c ******************/
#endif

/*
** The code in this file is only used if we are compiling multithreaded
** on a Win32 system.
*/
#ifdef SQLITE_MUTEX_W32

/*
** Each recursive mutex is an instance of the following structure.
*/
struct sqlite3_mutex {
  CRITICAL_SECTION mutex;    /* Mutex controlling the lock */
  int id;                    /* Mutex type */
#ifdef SQLITE_DEBUG
  volatile int nRef;         /* Number of enterances */
  volatile DWORD owner;      /* Thread holding this mutex */
  volatile int trace;        /* True to trace changes */
#endif
};

/*
** These are the initializer values used when declaring a "static" mutex
** on Win32.  It should be noted that all mutexes require initialization
** on the Win32 platform.
*/
#define SQLITE_W32_MUTEX_INITIALIZER { 0 }

#ifdef SQLITE_DEBUG
#define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0, \
                                    0L, (DWORD)0, 0 }
#else
#define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0 }
#endif

#ifdef SQLITE_DEBUG
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside assert() statements.
*/
static int winMutexHeld(sqlite3_mutex *p){
  return p->nRef!=0 && p->owner==GetCurrentThreadId();
}

static int winMutexNotheld2(sqlite3_mutex *p, DWORD tid){
  return p->nRef==0 || p->owner!=tid;
}

static int winMutexNotheld(sqlite3_mutex *p){
  DWORD tid = GetCurrentThreadId();
  return winMutexNotheld2(p, tid);
}
#endif

/*
** Try to provide a memory barrier operation, needed for initialization
** and also for the xShmBarrier method of the VFS in cases when SQLite is
** compiled without mutexes (SQLITE_THREADSAFE=0).
*/
SQLITE_PRIVATE void sqlite3MemoryBarrier(void){
#if defined(SQLITE_MEMORY_BARRIER)
  SQLITE_MEMORY_BARRIER;
#elif defined(__GNUC__)
  __sync_synchronize();
#elif !defined(SQLITE_DISABLE_INTRINSIC) && \
      defined(_MSC_VER) && _MSC_VER>=1300
  _ReadWriteBarrier();
#elif defined(MemoryBarrier)
  MemoryBarrier();
#endif
}

/*
** Initialize and deinitialize the mutex subsystem.
*/
static sqlite3_mutex winMutex_staticMutexes[] = {
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER,
  SQLITE3_MUTEX_INITIALIZER
};

static int winMutex_isInit = 0;
static int winMutex_isNt = -1; /* <0 means "need to query" */

/* As the winMutexInit() and winMutexEnd() functions are called as part
** of the sqlite3BtreeInitialize() and sqlite3BtreeShutdown() processing, the
** "interlocked" magic used here is probably not strictly necessary.
*/
static LONG SQLITE_WIN32_VOLATILE winMutex_lock = 0;

SQLITE_PRIVATE int sqlite3_win32_is_nt(void); /* os_win.c */
SQLITE_PRIVATE void sqlite3_win32_sleep(DWORD milliseconds); /* os_win.c */

static int winMutexInit(void){
  /* The first to increment to 1 does actual initialization */
  if( InterlockedCompareExchange(&winMutex_lock, 1, 0)==0 ){
    int i;
    for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
#if SQLITE_OS_WINRT
      InitializeCriticalSectionEx(&winMutex_staticMutexes[i].mutex, 0, 0);
#else
      InitializeCriticalSection(&winMutex_staticMutexes[i].mutex);
#endif
    }
    winMutex_isInit = 1;
  }else{
    /* Another thread is (in the process of) initializing the static
    ** mutexes */
    while( !winMutex_isInit ){
      sqlite3_win32_sleep(1);
    }
  }
  return SQLITE_OK;
}

static int winMutexEnd(void){
  /* The first to decrement to 0 does actual shutdown
  ** (which should be the last to shutdown.) */
  if( InterlockedCompareExchange(&winMutex_lock, 0, 1)==1 ){
    if( winMutex_isInit==1 ){
      int i;
      for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
        DeleteCriticalSection(&winMutex_staticMutexes[i].mutex);
      }
      winMutex_isInit = 0;
    }
  }
  return SQLITE_OK;
}

/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it.  If it returns NULL
** that means that a mutex could not be allocated.  SQLite
** will unwind its stack and return an error.  The argument
** to sqlite3_mutex_alloc() is one of these integer constants:
**
** <ul>
** <li>  SQLITE_MUTEX_FAST
** <li>  SQLITE_MUTEX_RECURSIVE
** <li>  SQLITE_MUTEX_STATIC_MASTER
** <li>  SQLITE_MUTEX_STATIC_MEM
** <li>  SQLITE_MUTEX_STATIC_OPEN
** <li>  SQLITE_MUTEX_STATIC_PRNG
** <li>  SQLITE_MUTEX_STATIC_LRU
** <li>  SQLITE_MUTEX_STATIC_PMEM
** <li>  SQLITE_MUTEX_STATIC_APP1
** <li>  SQLITE_MUTEX_STATIC_APP2
** <li>  SQLITE_MUTEX_STATIC_APP3
** <li>  SQLITE_MUTEX_STATIC_VFS1
** <li>  SQLITE_MUTEX_STATIC_VFS2
** <li>  SQLITE_MUTEX_STATIC_VFS3
** </ul>
**
** The first two constants cause sqlite3_mutex_alloc() to create
** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
** The mutex implementation does not need to make a distinction
** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to.  But SQLite will only request a recursive mutex in
** cases where it really needs one.  If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** The other allowed parameters to sqlite3_mutex_alloc() each return
** a pointer to a static preexisting mutex.  Six static mutexes are
** used by the current version of SQLite.  Future versions of SQLite
** may add additional static mutexes.  Static mutexes are for internal
** use by SQLite only.  Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
** returns a different mutex on every call.  But for the static
** mutex types, the same mutex is returned on every call that has
** the same type number.
*/
static sqlite3_mutex *winMutexAlloc(int iType){
  sqlite3_mutex *p;

  switch( iType ){
    case SQLITE_MUTEX_FAST:
    case SQLITE_MUTEX_RECURSIVE: {
      p = sqlite3MallocZero( sizeof(*p) );
      if( p ){
        p->id = iType;
#ifdef SQLITE_DEBUG
#ifdef SQLITE_WIN32_MUTEX_TRACE_DYNAMIC
        p->trace = 1;
#endif
#endif
#if SQLITE_OS_WINRT
        InitializeCriticalSectionEx(&p->mutex, 0, 0);
#else
        InitializeCriticalSection(&p->mutex);
#endif
      }
      break;
    }
    default: {
#ifdef SQLITE_ENABLE_API_ARMOR
      if( iType-2<0 || iType-2>=ArraySize(winMutex_staticMutexes) ){
        (void)SQLITE_MISUSE_BKPT;
        return 0;
      }
#endif
      p = &winMutex_staticMutexes[iType-2];
      p->id = iType;
#ifdef SQLITE_DEBUG
#ifdef SQLITE_WIN32_MUTEX_TRACE_STATIC
      p->trace = 1;
#endif
#endif
      break;
    }
  }
  return p;
}


/*
** This routine deallocates a previously
** allocated mutex.  SQLite is careful to deallocate every
** mutex that it allocates.
*/
static void winMutexFree(sqlite3_mutex *p){
  assert( p );
  assert( p->nRef==0 && p->owner==0 );
  if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE ){
    DeleteCriticalSection(&p->mutex);
    sqlite3_free(p);
  }else{
#ifdef SQLITE_ENABLE_API_ARMOR
    (void)SQLITE_MISUSE_BKPT;
#endif
  }
}

/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex.  If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread.  In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter.  If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
static void winMutexEnter(sqlite3_mutex *p){
#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  DWORD tid = GetCurrentThreadId();
#endif
#ifdef SQLITE_DEBUG
  assert( p );
  assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
#else
  assert( p );
#endif
  assert( winMutex_isInit==1 );
  EnterCriticalSection(&p->mutex);
#ifdef SQLITE_DEBUG
  assert( p->nRef>0 || p->owner==0 );
  p->owner = tid;
  p->nRef++;
  if( p->trace ){
    OSTRACE(("ENTER-MUTEX tid=%lu, mutex=%p (%d), nRef=%d\n",
             tid, p, p->trace, p->nRef));
  }
#endif
}

static int winMutexTry(sqlite3_mutex *p){
#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  DWORD tid = GetCurrentThreadId();
#endif
  int rc = SQLITE_BUSY;
  assert( p );
  assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
  /*
  ** The sqlite3_mutex_try() routine is very rarely used, and when it
  ** is used it is merely an optimization.  So it is OK for it to always
  ** fail.
  **
  ** The TryEnterCriticalSection() interface is only available on WinNT.
  ** And some windows compilers complain if you try to use it without
  ** first doing some #defines that prevent SQLite from building on Win98.
  ** For that reason, we will omit this optimization for now.  See
  ** ticket #2685.
  */
#if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0400
  assert( winMutex_isInit==1 );
  assert( winMutex_isNt>=-1 && winMutex_isNt<=1 );
  if( winMutex_isNt<0 ){
    winMutex_isNt = sqlite3_win32_is_nt();
  }
  assert( winMutex_isNt==0 || winMutex_isNt==1 );
  if( winMutex_isNt && TryEnterCriticalSection(&p->mutex) ){
#ifdef SQLITE_DEBUG
    p->owner = tid;
    p->nRef++;
#endif
    rc = SQLITE_OK;
  }
#else
  UNUSED_PARAMETER(p);
#endif
#ifdef SQLITE_DEBUG
  if( p->trace ){
    OSTRACE(("TRY-MUTEX tid=%lu, mutex=%p (%d), owner=%lu, nRef=%d, rc=%s\n",
             tid, p, p->trace, p->owner, p->nRef, sqlite3ErrName(rc)));
  }
#endif
  return rc;
}

/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread.  The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated.  SQLite will never do either.
*/
static void winMutexLeave(sqlite3_mutex *p){
#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  DWORD tid = GetCurrentThreadId();
#endif
  assert( p );
#ifdef SQLITE_DEBUG
  assert( p->nRef>0 );
  assert( p->owner==tid );
  p->nRef--;
  if( p->nRef==0 ) p->owner = 0;
  assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
#endif
  assert( winMutex_isInit==1 );
  LeaveCriticalSection(&p->mutex);
#ifdef SQLITE_DEBUG
  if( p->trace ){
    OSTRACE(("LEAVE-MUTEX tid=%lu, mutex=%p (%d), nRef=%d\n",
             tid, p, p->trace, p->nRef));
  }
#endif
}

SQLITE_PRIVATE sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
  static const sqlite3_mutex_methods sMutex = {
    winMutexInit,
    winMutexEnd,
    winMutexAlloc,
    winMutexFree,
    winMutexEnter,
    winMutexTry,
    winMutexLeave,
#ifdef SQLITE_DEBUG
    winMutexHeld,
    winMutexNotheld
#else
    0,
    0
#endif
  };
  return &sMutex;
}

#endif /* SQLITE_MUTEX_W32 */

/************** End of mutex_w32.c *******************************************/
/************** Begin file malloc.c ******************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** Memory allocation functions used throughout sqlite.
*/
/* #include "sqliteInt.h" */
/* #include <stdarg.h> */

/*
** Attempt to release up to n bytes of non-essential memory currently
** held by SQLite. An example of non-essential memory is memory used to
** cache database pages that are not currently in use.
*/
SQLITE_PRIVATE int sqlite3_release_memory(int n){
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
  return sqlite3PcacheReleaseMemory(n);
#else
  /* IMPLEMENTATION-OF: R-34391-24921 The sqlite3_release_memory() routine
  ** is a no-op returning zero if SQLite is not compiled with
  ** SQLITE_ENABLE_MEMORY_MANAGEMENT. */
  UNUSED_PARAMETER(n);
  return 0;
#endif
}

/*
** An instance of the following object records the location of
** each unused scratch buffer.
*/
typedef struct ScratchFreeslot {
  struct ScratchFreeslot *pNext;   /* Next unused scratch buffer */
} ScratchFreeslot;

/*
** State information local to the memory allocation subsystem.
*/
static SQLITE_WSD struct Mem0Global {
  sqlite3_mutex *mutex;         /* Mutex to serialize access */
  sqlite3_int64 alarmThreshold; /* The soft heap limit */

  /*
  ** Pointers to the end of sqlite3GlobalConfig.pScratch memory
  ** (so that a range test can be used to determine if an allocation
  ** being freed came from pScratch) and a pointer to the list of
  ** unused scratch allocations.
  */
  void *pScratchEnd;
  ScratchFreeslot *pScratchFree;
  u32 nScratchFree;

  /*
  ** True if heap is nearly "full" where "full" is defined by the
  ** sqlite3_soft_heap_limit() setting.
  */
  int nearlyFull;
} mem0 = { 0, 0, 0, 0, 0, 0 };

#define mem0 GLOBAL(struct Mem0Global, mem0)

#ifndef NDEBUG
/*
** Return the memory allocator mutex. sqlite3_status() needs it.
*/
SQLITE_PRIVATE sqlite3_mutex *sqlite3MallocMutex(void){
  return mem0.mutex;
}
#endif

/*
** Initialize the memory allocation subsystem.
*/
SQLITE_PRIVATE int sqlite3MallocInit(void){
  int rc;
  if( sqlite3GlobalConfig.m.xMalloc==0 ){
    sqlite3MemSetDefault();
  }
  memset(&mem0, 0, sizeof(mem0));
  if( sqlite3GlobalConfig.bCoreMutex ){
    mem0.mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MEM);
  }
  if( sqlite3GlobalConfig.pScratch && sqlite3GlobalConfig.szScratch>=100
      && sqlite3GlobalConfig.nScratch>0 ){
    int i, n, sz;
    ScratchFreeslot *pSlot;
    sz = ROUNDDOWN8(sqlite3GlobalConfig.szScratch);
    sqlite3GlobalConfig.szScratch = sz;
    pSlot = (ScratchFreeslot*)sqlite3GlobalConfig.pScratch;
    n = sqlite3GlobalConfig.nScratch;
    mem0.pScratchFree = pSlot;
    mem0.nScratchFree = n;
    for(i=0; i<n-1; i++){
      pSlot->pNext = (ScratchFreeslot*)(sz+(char*)pSlot);
      pSlot = pSlot->pNext;
    }
    pSlot->pNext = 0;
    mem0.pScratchEnd = (void*)&pSlot[1];
  }else{
    mem0.pScratchEnd = 0;
    sqlite3GlobalConfig.pScratch = 0;
    sqlite3GlobalConfig.szScratch = 0;
    sqlite3GlobalConfig.nScratch = 0;
  }
  if( sqlite3GlobalConfig.pPage==0 || sqlite3GlobalConfig.szPage<512
      || sqlite3GlobalConfig.nPage<=0 ){
    sqlite3GlobalConfig.pPage = 0;
    sqlite3GlobalConfig.szPage = 0;
  }
  rc = sqlite3GlobalConfig.m.xInit(sqlite3GlobalConfig.m.pAppData);
  if( rc!=SQLITE_OK ) memset(&mem0, 0, sizeof(mem0));
  return rc;
}

/*
** Return true if the heap is currently under memory pressure - in other
** words if the amount of heap used is close to the limit set by
** sqlite3_soft_heap_limit().
*/
SQLITE_PRIVATE int sqlite3HeapNearlyFull(void){
  return mem0.nearlyFull;
}

/*
** Deinitialize the memory allocation subsystem.
*/
SQLITE_PRIVATE void sqlite3MallocEnd(void){
  if( sqlite3GlobalConfig.m.xShutdown ){
    sqlite3GlobalConfig.m.xShutdown(sqlite3GlobalConfig.m.pAppData);
  }
  memset(&mem0, 0, sizeof(mem0));
}

/*
** Trigger the alarm 
*/
static void sqlite3MallocAlarm(int nByte){
  if( mem0.alarmThreshold<=0 ) return;
  sqlite3_mutex_leave(mem0.mutex);
  sqlite3_release_memory(nByte);
  sqlite3_mutex_enter(mem0.mutex);
}

/*
** Do a memory allocation with statistics and alarms.  Assume the
** lock is already held.
*/
static int mallocWithAlarm(int n, void **pp){
  int nFull;
  void *p;
  assert( sqlite3_mutex_held(mem0.mutex) );
  nFull = sqlite3GlobalConfig.m.xRoundup(n);
  sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, n);
  if( mem0.alarmThreshold>0 ){
    sqlite3_int64 nUsed = sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED);
    if( nUsed >= mem0.alarmThreshold - nFull ){
      mem0.nearlyFull = 1;
      sqlite3MallocAlarm(nFull);
    }else{
      mem0.nearlyFull = 0;
    }
  }
  p = sqlite3GlobalConfig.m.xMalloc(nFull);
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
  if( p==0 && mem0.alarmThreshold>0 ){
    sqlite3MallocAlarm(nFull);
    p = sqlite3GlobalConfig.m.xMalloc(nFull);
  }
#endif
  if( p ){
    nFull = sqlite3MallocSize(p);
    sqlite3StatusUp(SQLITE_STATUS_MEMORY_USED, nFull);
    sqlite3StatusUp(SQLITE_STATUS_MALLOC_COUNT, 1);
  }
  *pp = p;
  return nFull;
}

/*
** Allocate memory.  This routine is like sqlite3_malloc() except that it
** assumes the memory subsystem has already been initialized.
*/
SQLITE_PRIVATE void *sqlite3Malloc(u64 n){
  void *p;
  if( n==0 || n>=0x7fffff00 ){
    /* A memory allocation of a number of bytes which is near the maximum
    ** signed integer value might cause an integer overflow inside of the
    ** xMalloc().  Hence we limit the maximum size to 0x7fffff00, giving
    ** 255 bytes of overhead.  SQLite itself will never use anything near
    ** this amount.  The only way to reach the limit is with sqlite3_malloc() */
    p = 0;
  }else if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    mallocWithAlarm((int)n, &p);
    sqlite3_mutex_leave(mem0.mutex);
  }else{
    p = sqlite3GlobalConfig.m.xMalloc((int)n);
  }
  assert( EIGHT_BYTE_ALIGNMENT(p) );  /* IMP: R-11148-40995 */
  return p;
}

/*
** This version of the memory allocation is for use by the application.
** First make sure the memory subsystem is initialized, then do the
** allocation.
*/
SQLITE_PRIVATE void *sqlite3_malloc(int n){
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  return n<=0 ? 0 : sqlite3Malloc(n);
}
SQLITE_PRIVATE void *sqlite3_malloc64(sqlite3_uint64 n){
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  return sqlite3Malloc(n);
}

/*
** Each thread may only have a single outstanding allocation from
** xScratchMalloc().  We verify this constraint in the single-threaded
** case by setting scratchAllocOut to 1 when an allocation
** is outstanding clearing it when the allocation is freed.
*/
#if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
static int scratchAllocOut = 0;
#endif


/*
** Allocate memory that is to be used and released right away.
** This routine is similar to alloca() in that it is not intended
** for situations where the memory might be held long-term.  This
** routine is intended to get memory to old large transient data
** structures that would not normally fit on the stack of an
** embedded processor.
*/
SQLITE_PRIVATE void *sqlite3ScratchMalloc(int n){
  void *p;
  assert( n>0 );

  sqlite3_mutex_enter(mem0.mutex);
  sqlite3StatusSet(SQLITE_STATUS_SCRATCH_SIZE, n);
  if( mem0.nScratchFree && sqlite3GlobalConfig.szScratch>=n ){
    p = mem0.pScratchFree;
    mem0.pScratchFree = mem0.pScratchFree->pNext;
    mem0.nScratchFree--;
    sqlite3StatusUp(SQLITE_STATUS_SCRATCH_USED, 1);
    sqlite3_mutex_leave(mem0.mutex);
  }else{
    sqlite3_mutex_leave(mem0.mutex);
    p = sqlite3Malloc(n);
    if( sqlite3GlobalConfig.bMemstat && p ){
      sqlite3_mutex_enter(mem0.mutex);
      sqlite3StatusUp(SQLITE_STATUS_SCRATCH_OVERFLOW, sqlite3MallocSize(p));
      sqlite3_mutex_leave(mem0.mutex);
    }
    sqlite3MemdebugSetType(p, MEMTYPE_SCRATCH);
  }
  assert( sqlite3_mutex_notheld(mem0.mutex) );


#if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
  /* EVIDENCE-OF: R-12970-05880 SQLite will not use more than one scratch
  ** buffers per thread.
  **
  ** This can only be checked in single-threaded mode.
  */
  assert( scratchAllocOut==0 );
  if( p ) scratchAllocOut++;
#endif

  return p;
}
SQLITE_PRIVATE void sqlite3ScratchFree(void *p){
  if( p ){

#if SQLITE_THREADSAFE==0 && !defined(NDEBUG)
    /* Verify that no more than two scratch allocation per thread
    ** is outstanding at one time.  (This is only checked in the
    ** single-threaded case since checking in the multi-threaded case
    ** would be much more complicated.) */
    assert( scratchAllocOut>=1 && scratchAllocOut<=2 );
    scratchAllocOut--;
#endif

    if( p>=sqlite3GlobalConfig.pScratch && p<mem0.pScratchEnd ){
      /* Release memory from the SQLITE_CONFIG_SCRATCH allocation */
      ScratchFreeslot *pSlot;
      pSlot = (ScratchFreeslot*)p;
      sqlite3_mutex_enter(mem0.mutex);
      pSlot->pNext = mem0.pScratchFree;
      mem0.pScratchFree = pSlot;
      mem0.nScratchFree++;
      assert( mem0.nScratchFree <= (u32)sqlite3GlobalConfig.nScratch );
      sqlite3StatusDown(SQLITE_STATUS_SCRATCH_USED, 1);
      sqlite3_mutex_leave(mem0.mutex);
    }else{
      /* Release memory back to the heap */
      assert( sqlite3MemdebugHasType(p, MEMTYPE_SCRATCH) );
      assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_SCRATCH) );
      sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
      if( sqlite3GlobalConfig.bMemstat ){
        int iSize = sqlite3MallocSize(p);
        sqlite3_mutex_enter(mem0.mutex);
        sqlite3StatusDown(SQLITE_STATUS_SCRATCH_OVERFLOW, iSize);
        sqlite3StatusDown(SQLITE_STATUS_MEMORY_USED, iSize);
        sqlite3StatusDown(SQLITE_STATUS_MALLOC_COUNT, 1);
        sqlite3GlobalConfig.m.xFree(p);
        sqlite3_mutex_leave(mem0.mutex);
      }else{
        sqlite3GlobalConfig.m.xFree(p);
      }
    }
  }
}

/*
** Return the size of a memory allocation previously obtained from
** sqlite3Malloc() or sqlite3_malloc().
*/
SQLITE_PRIVATE int sqlite3MallocSize(void *p){
  assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
  return sqlite3GlobalConfig.m.xSize(p);
}
SQLITE_PRIVATE int sqlite3DbMallocSize(Btree *pBtree, void *p){
  if( pBtree==0 ){
#if SQLITE_DEBUG
    assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_HEAP) );
    assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
#endif
    return sqlite3GlobalConfig.m.xSize(p);
  }else{
    assert( sqlite3_mutex_held(pBtree->mutex) );
    return 0;
  }
}

/*
** Free memory previously obtained from sqlite3Malloc().
*/
SQLITE_PRIVATE void sqlite3_free(void *p){
  if( p==0 ) return;  /* IMP: R-49053-54554 */
  assert( sqlite3MemdebugHasType(p, MEMTYPE_HEAP) );
  assert( sqlite3MemdebugNoType(p, (u8)~MEMTYPE_HEAP) );
  if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusDown(SQLITE_STATUS_MEMORY_USED, sqlite3MallocSize(p));
    sqlite3StatusDown(SQLITE_STATUS_MALLOC_COUNT, 1);
    sqlite3GlobalConfig.m.xFree(p);
    sqlite3_mutex_leave(mem0.mutex);
  }else{
    sqlite3GlobalConfig.m.xFree(p);
  }
}

/*
** Add the size of memory allocation "p" to the count in
** *db->pnBytesFreed.
*/
static SQLITE_NOINLINE void measureAllocationSize(Btree *pBtree, void *p){
  *pBtree->pnBytesFreed += sqlite3DbMallocSize(pBtree,p);
}

/*
** Free memory that might be associated with a particular database
** connection.
*/
SQLITE_PRIVATE void sqlite3DbFree(Btree *pBtree, void *p){
  assert( pBTree==0 || sqlite3_mutex_held(pTree->mutex) );
  if( p==0 ) return;
  if( pBtree ){
    if( pBtree->pnBytesFreed ){
      measureAllocationSize(pBtree, p);
      return;
    }
  }
  assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
  assert( sqlite3MemdebugNoType(p, (u8)~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
  assert( pBtree!=0 || sqlite3MemdebugNoType(p, MEMTYPE_LOOKASIDE) );
  sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
  sqlite3_free(p);
}

/*
** Change the size of an existing memory allocation
*/
SQLITE_PRIVATE void *sqlite3Realloc(void *pOld, u64 nBytes){
  int nOld, nNew, nDiff;
  void *pNew;
  assert( sqlite3MemdebugHasType(pOld, MEMTYPE_HEAP) );
  assert( sqlite3MemdebugNoType(pOld, (u8)~MEMTYPE_HEAP) );
  if( pOld==0 ){
    return sqlite3Malloc(nBytes); /* IMP: R-04300-56712 */
  }
  if( nBytes==0 ){
    sqlite3_free(pOld); /* IMP: R-26507-47431 */
    return 0;
  }
  if( nBytes>=0x7fffff00 ){
    /* The 0x7ffff00 limit term is explained in comments on sqlite3Malloc() */
    return 0;
  }
  nOld = sqlite3MallocSize(pOld);
  /* IMPLEMENTATION-OF: R-46199-30249 SQLite guarantees that the second
  ** argument to xRealloc is always a value returned by a prior call to
  ** xRoundup. */
  nNew = sqlite3GlobalConfig.m.xRoundup((int)nBytes);
  if( nOld==nNew ){
    pNew = pOld;
  }else if( sqlite3GlobalConfig.bMemstat ){
    sqlite3_mutex_enter(mem0.mutex);
    sqlite3StatusSet(SQLITE_STATUS_MALLOC_SIZE, (int)nBytes);
    nDiff = nNew - nOld;
    if( sqlite3StatusValue(SQLITE_STATUS_MEMORY_USED) >= 
          mem0.alarmThreshold-nDiff ){
      sqlite3MallocAlarm(nDiff);
    }
    pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
    if( pNew==0 && mem0.alarmThreshold>0 ){
      sqlite3MallocAlarm((int)nBytes);
      pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
    }
    if( pNew ){
      nNew = sqlite3MallocSize(pNew);
      sqlite3StatusUp(SQLITE_STATUS_MEMORY_USED, nNew-nOld);
    }
    sqlite3_mutex_leave(mem0.mutex);
  }else{
    pNew = sqlite3GlobalConfig.m.xRealloc(pOld, nNew);
  }
  assert( EIGHT_BYTE_ALIGNMENT(pNew) ); /* IMP: R-11148-40995 */
  return pNew;
}

/*
** The public interface to sqlite3Realloc.  Make sure that the memory
** subsystem is initialized prior to invoking sqliteRealloc.
*/
SQLITE_PRIVATE void *sqlite3_realloc(void *pOld, int n){
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  if( n<0 ) n = 0;  /* IMP: R-26507-47431 */
  return sqlite3Realloc(pOld, n);
}
SQLITE_PRIVATE void *sqlite3_realloc64(void *pOld, sqlite3_uint64 n){
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  return sqlite3Realloc(pOld, n);
}


/*
** Allocate and zero memory.
*/ 
SQLITE_PRIVATE void *sqlite3MallocZero(u64 n){
  void *p = sqlite3Malloc(n);
  if( p ){
    memset(p, 0, (size_t)n);
  }
  return p;
}

/*
** Allocate and zero memory.  If the allocation fails, make
** the mallocFailed flag in the connection pointer.
*/
SQLITE_PRIVATE void *sqlite3DbMallocZero(Btree *pBtree, u64 n){
  void *p = sqlite3DbMallocRaw(pBtree, n);
  if( p ){
    memset(p, 0, (size_t)n);
  }
  return p;
}

/*
** Allocate and zero memory.  If the allocation fails, make
** the mallocFailed flag in the connection pointer.
**
** If pBtree!=0 and pBtree->mallocFailed is true (indicating a prior malloc
** failure on the same database connection) then always return 0.
** Hence for a particular database connection, once malloc starts
** failing, it fails consistently until mallocFailed is reset.
** This is an important assumption.  There are many places in the
** code that do things like this:
**
**         int *a = (int*)sqlite3DbMallocRaw(pBtree, 100);
**         int *b = (int*)sqlite3DbMallocRaw(pBtree, 200);
**         if( b ) a[10] = 9;
**
** In other words, if a subsequent malloc (ex: "b") worked, it is assumed
** that all prior mallocs (ex: "a") worked too.
*/
SQLITE_PRIVATE void *sqlite3DbMallocRaw(Btree *pBtree, u64 n){
  void *p;
  assert( pBtree==0 || sqlite3_mutex_held(pBtree->mutex) );
  assert( pBtree==0 || pBtree->pnBytesFreed==0 );
  if( pBtree && pBtree->mallocFailed ){
    return 0;
  }
  p = sqlite3Malloc(n);
  if( !p && pBtree ){
    pBtree->mallocFailed = 1;
  }
  sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
  return p;
}

/*
** Resize the block of memory pointed to by p to n bytes. If the
** resize fails, set the mallocFailed flag in the connection object.
*/
SQLITE_PRIVATE void *sqlite3DbRealloc(Btree *pBtree, void *p, u64 n){
  void *pNew = 0;
  assert( pBtree!=0 );
  assert( sqlite3_mutex_held(pBtree->mutex) );
  if( pBtree->mallocFailed==0 ){
    if( p==0 ){
      return sqlite3DbMallocRaw(pBtree, n);
    }
    assert( sqlite3MemdebugHasType(p, (MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
    assert( sqlite3MemdebugNoType(p, (u8)~(MEMTYPE_LOOKASIDE|MEMTYPE_HEAP)) );
    sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
    pNew = sqlite3_realloc64(p, n);
    if( !pNew ){
      pBtree->mallocFailed = 1;
    }
    sqlite3MemdebugSetType(pNew, MEMTYPE_HEAP);
  }
  return pNew;
}

/*
** Attempt to reallocate p.  If the reallocation fails, then free p
** and set the mallocFailed flag in the database connection.
*/
SQLITE_PRIVATE void *sqlite3DbReallocOrFree(Btree *pBtree, void *p, u64 n){
  void *pNew;
  pNew = sqlite3DbRealloc(pBtree, p, n);
  if( !pNew ){
    sqlite3DbFree(pBtree, p);
  }
  return pNew;
}

/*
** Make a copy of a string in memory obtained from sqliteMalloc(). These 
** functions call sqlite3MallocRaw() directly instead of sqliteMalloc(). This
** is because when memory debugging is turned on, these two functions are 
** called via macros that record the current file and line number in the
** ThreadData structure.
*/
char *sqlite3DbStrDup(Btree *pBtree, const char *z){
  char *zNew;
  size_t n;
  if( z==0 ){
    return 0;
  }
  n = sqlite3Strlen30(z) + 1;
  assert( (n&0x7fffffff)==n );
  zNew = sqlite3DbMallocRaw(pBtree, (int)n);
  if( zNew ){
    memcpy(zNew, z, n);
  }
  return zNew;
}

/************** End of malloc.c **********************************************/
/************** Begin file printf.c ******************************************/
/*
** The "printf" code that follows dates from the 1980's.  It is in
** the public domain. 
**
**************************************************************************
**
** This file contains code for a set of "printf"-like routines.  These
** routines format strings much like the printf() from the standard C
** library, though the implementation here has enhancements to support
** SQLite.
*/
/* #include "sqliteInt.h" */

/*
** Conversion types fall into various categories as defined by the
** following enumeration.
*/
#define etRADIX       1 /* Integer types.  %d, %x, %o, and so forth */
#define etFLOAT       2 /* Floating point.  %f */
#define etEXP         3 /* Exponentional notation. %e and %E */
#define etGENERIC     4 /* Floating or exponential, depending on exponent. %g */
#define etSIZE        5 /* Return number of characters processed so far. %n */
#define etSTRING      6 /* Strings. %s */
#define etDYNSTRING   7 /* Dynamically allocated strings. %z */
#define etPERCENT     8 /* Percent symbol. %% */
#define etCHARX       9 /* Characters. %c */
/* The rest are extensions, not normally found in printf() */
#define etSQLESCAPE  10 /* Strings with '\'' doubled.  %q */
#define etSQLESCAPE2 11 /* Strings with '\'' doubled and enclosed in '',
                          NULL pointers replaced by SQL NULL.  %Q */
#define etPOINTER    14 /* The %p conversion */
#define etSQLESCAPE3 15 /* %w -> Strings with '\"' doubled */
#define etORDINAL    16 /* %r -> 1st, 2nd, 3rd, 4th, etc.  English only */

#define etINVALID     0 /* Any unrecognized conversion type */


/*
** An "etByte" is an 8-bit unsigned value.
*/
typedef unsigned char etByte;

/*
** Each builtin conversion character (ex: the 'd' in "%d") is described
** by an instance of the following structure
*/
typedef struct et_info {   /* Information about each format field */
  char fmttype;            /* The format field code letter */
  etByte base;             /* The base for radix conversion */
  etByte flags;            /* One or more of FLAG_ constants below */
  etByte type;             /* Conversion paradigm */
  etByte charset;          /* Offset into aDigits[] of the digits string */
  etByte prefix;           /* Offset into aPrefix[] of the prefix string */
} et_info;

/*
** Allowed values for et_info.flags
*/
#define FLAG_SIGNED  1     /* True if the value to convert is signed */
#define FLAG_INTERN  2     /* True if for internal use only */
#define FLAG_STRING  4     /* Allow infinity precision */


/*
** The following table is searched linearly, so it is good to put the
** most frequently used conversion types first.
*/
static const char aDigits[] = "0123456789ABCDEF0123456789abcdef";
static const char aPrefix[] = "-x0\000X0";
static const et_info fmtinfo[] = {
  {  'd', 10, 1, etRADIX,      0,  0 },
  {  's',  0, 4, etSTRING,     0,  0 },
  {  'g',  0, 1, etGENERIC,    30, 0 },
  {  'z',  0, 4, etDYNSTRING,  0,  0 },
  {  'q',  0, 4, etSQLESCAPE,  0,  0 },
  {  'Q',  0, 4, etSQLESCAPE2, 0,  0 },
  {  'w',  0, 4, etSQLESCAPE3, 0,  0 },
  {  'c',  0, 0, etCHARX,      0,  0 },
  {  'o',  8, 0, etRADIX,      0,  2 },
  {  'u', 10, 0, etRADIX,      0,  0 },
  {  'x', 16, 0, etRADIX,      16, 1 },
  {  'X', 16, 0, etRADIX,      0,  4 },
#ifndef SQLITE_OMIT_FLOATING_POINT
  {  'f',  0, 1, etFLOAT,      0,  0 },
  {  'e',  0, 1, etEXP,        30, 0 },
  {  'E',  0, 1, etEXP,        14, 0 },
  {  'G',  0, 1, etGENERIC,    14, 0 },
#endif
  {  'i', 10, 1, etRADIX,      0,  0 },
  {  'n',  0, 0, etSIZE,       0,  0 },
  {  '%',  0, 0, etPERCENT,    0,  0 },
  {  'p', 16, 0, etPOINTER,    0,  1 },

/* All the rest have the FLAG_INTERN bit set and are thus for internal
** use only */
  {  'r', 10, 3, etORDINAL,    0,  0 },
};

/*
** If SQLITE_OMIT_FLOATING_POINT is defined, then none of the floating point
** conversions will work.
*/
#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** "*val" is a double such that 0.1 <= *val < 10.0
** Return the ascii code for the leading digit of *val, then
** multiply "*val" by 10.0 to renormalize.
**
** Example:
**     input:     *val = 3.14159
**     output:    *val = 1.4159    function return = '3'
**
** The counter *cnt is incremented each time.  After counter exceeds
** 16 (the number of significant digits in a 64-bit float) '0' is
** always returned.
*/
static char et_getdigit(LONGDOUBLE_TYPE *val, int *cnt){
  int digit;
  LONGDOUBLE_TYPE d;
  if( (*cnt)<=0 ) return '0';
  (*cnt)--;
  digit = (int)*val;
  d = digit;
  digit += '0';
  *val = (*val - d)*10.0;
  return (char)digit;
}
#endif /* SQLITE_OMIT_FLOATING_POINT */

/*
** Set the StrAccum object to an error mode.
*/
static void setStrAccumError(StrAccum *p, u8 eError){
  assert( eError==STRACCUM_NOMEM || eError==STRACCUM_TOOBIG );
  p->accError = eError;
  p->nAlloc = 0;
}

/*
** Extra argument values from a PrintfArguments object
*/
static sqlite3_int64 getIntArg(PrintfArguments *p){
  if( p->nArg<=p->nUsed ) return 0;
  return sqlite3VdbeIntValue((Mem*)p->apArg[p->nUsed++]);
}
static double getDoubleArg(PrintfArguments *p){
  if( p->nArg<=p->nUsed ) return 0.0;
  return sqlite3VdbeRealValue((Mem*)p->apArg[p->nUsed++]);
}
static char *getTextArg(PrintfArguments *p){
  if( p->nArg<=p->nUsed ) return 0;
  return (char*)sqlite3ValueText(p->apArg[p->nUsed++], SQLITE_UTF8);
}


/*
** On machines with a small stack size, you can redefine the
** SQLITE_PRINT_BUF_SIZE to be something smaller, if desired.
*/
#ifndef SQLITE_PRINT_BUF_SIZE
# define SQLITE_PRINT_BUF_SIZE 70
#endif
#define etBUFSIZE SQLITE_PRINT_BUF_SIZE  /* Size of the output buffer */

/*
** Render a string given by "fmt" into the StrAccum object.
*/
SQLITE_PRIVATE void sqlite3VXPrintf(
  StrAccum *pAccum,          /* Accumulate results here */
  u32 bFlags,                /* SQLITE_PRINTF_* flags */
  const char *fmt,           /* Format string */
  va_list ap                 /* arguments */
){
  int c;                     /* Next character in the format string */
  char *bufpt;               /* Pointer to the conversion buffer */
  int precision;             /* Precision of the current field */
  int length;                /* Length of the field */
  int idx;                   /* A general purpose loop counter */
  int width;                 /* Width of the current field */
  etByte flag_leftjustify;   /* True if "-" flag is present */
  etByte flag_plussign;      /* True if "+" flag is present */
  etByte flag_blanksign;     /* True if " " flag is present */
  etByte flag_alternateform; /* True if "#" flag is present */
  etByte flag_altform2;      /* True if "!" flag is present */
  etByte flag_zeropad;       /* True if field width constant starts with zero */
  etByte flag_long;          /* True if "l" flag is present */
  etByte flag_longlong;      /* True if the "ll" flag is present */
  etByte done;               /* Loop termination flag */
  etByte xtype = 0;          /* Conversion paradigm */
  u8 bArgList;               /* True for SQLITE_PRINTF_SQLFUNC */
  u8 useIntern;              /* Ok to use internal conversions (ex: %T) */
  char prefix;               /* Prefix character.  "+" or "-" or " " or '\0'. */
  sqlite_uint64 longvalue;   /* Value for integer types */
  LONGDOUBLE_TYPE realvalue; /* Value for real types */
  const et_info *infop;      /* Pointer to the appropriate info structure */
  char *zOut;                /* Rendering buffer */
  int nOut;                  /* Size of the rendering buffer */
  char *zExtra = 0;          /* Malloced memory used by some conversion */
#ifndef SQLITE_OMIT_FLOATING_POINT
  int  exp, e2;              /* exponent of real numbers */
  int nsd;                   /* Number of significant digits returned */
  double rounder;            /* Used for rounding floating point values */
  etByte flag_dp;            /* True if decimal point should be shown */
  etByte flag_rtz;           /* True if trailing zeros should be removed */
#endif
  PrintfArguments *pArgList = 0; /* Arguments for SQLITE_PRINTF_SQLFUNC */
  char buf[etBUFSIZE];       /* Conversion buffer */

  bufpt = 0;
  if( bFlags ){
    if( (bArgList = (bFlags & SQLITE_PRINTF_SQLFUNC))!=0 ){
      pArgList = va_arg(ap, PrintfArguments*);
    }
    useIntern = bFlags & SQLITE_PRINTF_INTERNAL;
  }else{
    bArgList = useIntern = 0;
  }
  for(; (c=(*fmt))!=0; ++fmt){
    if( c!='%' ){
      bufpt = (char *)fmt;
#if HAVE_STRCHRNUL
      fmt = strchrnul(fmt, '%');
#else
      do{ fmt++; }while( *fmt && *fmt != '%' );
#endif
      sqlite3StrAccumAppend(pAccum, bufpt, (int)(fmt - bufpt));
      if( *fmt==0 ) break;
    }
    if( (c=(*++fmt))==0 ){
      sqlite3StrAccumAppend(pAccum, "%", 1);
      break;
    }
    /* Find out what flags are present */
    flag_leftjustify = flag_plussign = flag_blanksign = 
     flag_alternateform = flag_altform2 = flag_zeropad = 0;
    done = 0;
    do{
      switch( c ){
        case '-':   flag_leftjustify = 1;     break;
        case '+':   flag_plussign = 1;        break;
        case ' ':   flag_blanksign = 1;       break;
        case '#':   flag_alternateform = 1;   break;
        case '!':   flag_altform2 = 1;        break;
        case '0':   flag_zeropad = 1;         break;
        default:    done = 1;                 break;
      }
    }while( !done && (c=(*++fmt))!=0 );
    /* Get the field width */
    if( c=='*' ){
      if( bArgList ){
        width = (int)getIntArg(pArgList);
      }else{
        width = va_arg(ap,int);
      }
      if( width<0 ){
        flag_leftjustify = 1;
        width = width >= -2147483647 ? -width : 0;
      }
      c = *++fmt;
    }else{
      unsigned wx = 0;
      while( c>='0' && c<='9' ){
        wx = wx*10 + c - '0';
        c = *++fmt;
      }
      testcase( wx>0x7fffffff );
      width = wx & 0x7fffffff;
    }

    /* Get the precision */
    if( c=='.' ){
      c = *++fmt;
      if( c=='*' ){
        if( bArgList ){
          precision = (int)getIntArg(pArgList);
        }else{
          precision = va_arg(ap,int);
        }
        c = *++fmt;
        if( precision<0 ){
          precision = precision >= -2147483647 ? -precision : -1;
        }
      }else{
        unsigned px = 0;
        while( c>='0' && c<='9' ){
          px = px*10 + c - '0';
          c = *++fmt;
        }
        testcase( px>0x7fffffff );
        precision = px & 0x7fffffff;
      }
    }else{
      precision = -1;
    }
    /* Get the conversion type modifier */
    if( c=='l' ){
      flag_long = 1;
      c = *++fmt;
      if( c=='l' ){
        flag_longlong = 1;
        c = *++fmt;
      }else{
        flag_longlong = 0;
      }
    }else{
      flag_long = flag_longlong = 0;
    }
    /* Fetch the info entry for the field */
    infop = &fmtinfo[0];
    xtype = etINVALID;
    for(idx=0; idx<ArraySize(fmtinfo); idx++){
      if( c==fmtinfo[idx].fmttype ){
        infop = &fmtinfo[idx];
        if( useIntern || (infop->flags & FLAG_INTERN)==0 ){
          xtype = infop->type;
        }else{
          return;
        }
        break;
      }
    }

    /*
    ** At this point, variables are initialized as follows:
    **
    **   flag_alternateform          TRUE if a '#' is present.
    **   flag_altform2               TRUE if a '!' is present.
    **   flag_plussign               TRUE if a '+' is present.
    **   flag_leftjustify            TRUE if a '-' is present or if the
    **                               field width was negative.
    **   flag_zeropad                TRUE if the width began with 0.
    **   flag_long                   TRUE if the letter 'l' (ell) prefixed
    **                               the conversion character.
    **   flag_longlong               TRUE if the letter 'll' (ell ell) prefixed
    **                               the conversion character.
    **   flag_blanksign              TRUE if a ' ' is present.
    **   width                       The specified field width.  This is
    **                               always non-negative.  Zero is the default.
    **   precision                   The specified precision.  The default
    **                               is -1.
    **   xtype                       The class of the conversion.
    **   infop                       Pointer to the appropriate info struct.
    */
    switch( xtype ){
      case etPOINTER:
        flag_longlong = sizeof(char*)==sizeof(i64);
        flag_long = sizeof(char*)==sizeof(long int);
        /* Fall through into the next case */
      case etORDINAL:
      case etRADIX:
        if( infop->flags & FLAG_SIGNED ){
          i64 v;
          if( bArgList ){
            v = getIntArg(pArgList);
          }else if( flag_longlong ){
            v = va_arg(ap,i64);
          }else if( flag_long ){
            v = va_arg(ap,long int);
          }else{
            v = va_arg(ap,int);
          }
          if( v<0 ){
            if( v==SMALLEST_INT64 ){
              longvalue = ((u64)1)<<63;
            }else{
              longvalue = -v;
            }
            prefix = '-';
          }else{
            longvalue = v;
            if( flag_plussign )        prefix = '+';
            else if( flag_blanksign )  prefix = ' ';
            else                       prefix = 0;
          }
        }else{
          if( bArgList ){
            longvalue = (u64)getIntArg(pArgList);
          }else if( flag_longlong ){
            longvalue = va_arg(ap,u64);
          }else if( flag_long ){
            longvalue = va_arg(ap,unsigned long int);
          }else{
            longvalue = va_arg(ap,unsigned int);
          }
          prefix = 0;
        }
        if( longvalue==0 ) flag_alternateform = 0;
        if( flag_zeropad && precision<width-(prefix!=0) ){
          precision = width-(prefix!=0);
        }
        if( precision<etBUFSIZE-10 ){
          nOut = etBUFSIZE;
          zOut = buf;
        }else{
          nOut = precision + 10;
          zOut = zExtra = sqlite3Malloc( nOut );
          if( zOut==0 ){
            setStrAccumError(pAccum, STRACCUM_NOMEM);
            return;
          }
        }
        bufpt = &zOut[nOut-1];
        if( xtype==etORDINAL ){
          static const char zOrd[] = "thstndrd";
          int x = (int)(longvalue % 10);
          if( x>=4 || (longvalue/10)%10==1 ){
            x = 0;
          }
          *(--bufpt) = zOrd[x*2+1];
          *(--bufpt) = zOrd[x*2];
        }
        {
          const char *cset = &aDigits[infop->charset];
          u8 base = infop->base;
          do{                                           /* Convert to ascii */
            *(--bufpt) = cset[longvalue%base];
            longvalue = longvalue/base;
          }while( longvalue>0 );
        }
        length = (int)(&zOut[nOut-1]-bufpt);
        for(idx=precision-length; idx>0; idx--){
          *(--bufpt) = '0';                             /* Zero pad */
        }
        if( prefix ) *(--bufpt) = prefix;               /* Add sign */
        if( flag_alternateform && infop->prefix ){      /* Add "0" or "0x" */
          const char *pre;
          char x;
          pre = &aPrefix[infop->prefix];
          for(; (x=(*pre))!=0; pre++) *(--bufpt) = x;
        }
        length = (int)(&zOut[nOut-1]-bufpt);
        break;
      case etFLOAT:
      case etEXP:
      case etGENERIC:
        if( bArgList ){
          realvalue = getDoubleArg(pArgList);
        }else{
          realvalue = va_arg(ap,double);
        }
#ifdef SQLITE_OMIT_FLOATING_POINT
        length = 0;
#else
        if( precision<0 ) precision = 6;         /* Set default precision */
        if( realvalue<0.0 ){
          realvalue = -realvalue;
          prefix = '-';
        }else{
          if( flag_plussign )          prefix = '+';
          else if( flag_blanksign )    prefix = ' ';
          else                         prefix = 0;
        }
        if( xtype==etGENERIC && precision>0 ) precision--;
        testcase( precision>0xfff );
        for(idx=precision&0xfff, rounder=0.5; idx>0; idx--, rounder*=0.1){}
        if( xtype==etFLOAT ) realvalue += rounder;
        /* Normalize realvalue to within 10.0 > realvalue >= 1.0 */
        exp = 0;
        if( sqlite3IsNaN((double)realvalue) ){
          bufpt = "NaN";
          length = 3;
          break;
        }
        if( realvalue>0.0 ){
          LONGDOUBLE_TYPE scale = 1.0;
          while( realvalue>=1e100*scale && exp<=350 ){ scale *= 1e100;exp+=100;}
          while( realvalue>=1e10*scale && exp<=350 ){ scale *= 1e10; exp+=10; }
          while( realvalue>=10.0*scale && exp<=350 ){ scale *= 10.0; exp++; }
          realvalue /= scale;
          while( realvalue<1e-8 ){ realvalue *= 1e8; exp-=8; }
          while( realvalue<1.0 ){ realvalue *= 10.0; exp--; }
          if( exp>350 ){
            bufpt = buf;
            buf[0] = prefix;
            memcpy(buf+(prefix!=0),"Inf",4);
            length = 3+(prefix!=0);
            break;
          }
        }
        bufpt = buf;
        /*
        ** If the field type is etGENERIC, then convert to either etEXP
        ** or etFLOAT, as appropriate.
        */
        if( xtype!=etFLOAT ){
          realvalue += rounder;
          if( realvalue>=10.0 ){ realvalue *= 0.1; exp++; }
        }
        if( xtype==etGENERIC ){
          flag_rtz = !flag_alternateform;
          if( exp<-4 || exp>precision ){
            xtype = etEXP;
          }else{
            precision = precision - exp;
            xtype = etFLOAT;
          }
        }else{
          flag_rtz = flag_altform2;
        }
        if( xtype==etEXP ){
          e2 = 0;
        }else{
          e2 = exp;
        }
        if( MAX(e2,0)+(i64)precision+(i64)width > etBUFSIZE - 15 ){
          bufpt = zExtra 
              = sqlite3Malloc( MAX(e2,0)+(i64)precision+(i64)width+15 );
          if( bufpt==0 ){
            setStrAccumError(pAccum, STRACCUM_NOMEM);
            return;
          }
        }
        zOut = bufpt;
        nsd = 16 + flag_altform2*10;
        flag_dp = (precision>0 ?1:0) | flag_alternateform | flag_altform2;
        /* The sign in front of the number */
        if( prefix ){
          *(bufpt++) = prefix;
        }
        /* Digits prior to the decimal point */
        if( e2<0 ){
          *(bufpt++) = '0';
        }else{
          for(; e2>=0; e2--){
            *(bufpt++) = et_getdigit(&realvalue,&nsd);
          }
        }
        /* The decimal point */
        if( flag_dp ){
          *(bufpt++) = '.';
        }
        /* "0" digits after the decimal point but before the first
        ** significant digit of the number */
        for(e2++; e2<0; precision--, e2++){
          assert( precision>0 );
          *(bufpt++) = '0';
        }
        /* Significant digits after the decimal point */
        while( (precision--)>0 ){
          *(bufpt++) = et_getdigit(&realvalue,&nsd);
        }
        /* Remove trailing zeros and the "." if no digits follow the "." */
        if( flag_rtz && flag_dp ){
          while( bufpt[-1]=='0' ) *(--bufpt) = 0;
          assert( bufpt>zOut );
          if( bufpt[-1]=='.' ){
            if( flag_altform2 ){
              *(bufpt++) = '0';
            }else{
              *(--bufpt) = 0;
            }
          }
        }
        /* Add the "eNNN" suffix */
        if( xtype==etEXP ){
          *(bufpt++) = aDigits[infop->charset];
          if( exp<0 ){
            *(bufpt++) = '-'; exp = -exp;
          }else{
            *(bufpt++) = '+';
          }
          if( exp>=100 ){
            *(bufpt++) = (char)((exp/100)+'0');        /* 100's digit */
            exp %= 100;
          }
          *(bufpt++) = (char)(exp/10+'0');             /* 10's digit */
          *(bufpt++) = (char)(exp%10+'0');             /* 1's digit */
        }
        *bufpt = 0;

        /* The converted number is in buf[] and zero terminated. Output it.
        ** Note that the number is in the usual order, not reversed as with
        ** integer conversions. */
        length = (int)(bufpt-zOut);
        bufpt = zOut;

        /* Special case:  Add leading zeros if the flag_zeropad flag is
        ** set and we are not left justified */
        if( flag_zeropad && !flag_leftjustify && length < width){
          int i;
          int nPad = width - length;
          for(i=width; i>=nPad; i--){
            bufpt[i] = bufpt[i-nPad];
          }
          i = prefix!=0;
          while( nPad-- ) bufpt[i++] = '0';
          length = width;
        }
#endif /* !defined(SQLITE_OMIT_FLOATING_POINT) */
        break;
      case etSIZE:
        if( !bArgList ){
          *(va_arg(ap,int*)) = pAccum->nChar;
        }
        length = width = 0;
        break;
      case etPERCENT:
        buf[0] = '%';
        bufpt = buf;
        length = 1;
        break;
      case etCHARX:
        if( bArgList ){
          bufpt = getTextArg(pArgList);
          c = bufpt ? bufpt[0] : 0;
        }else{
          c = va_arg(ap,int);
        }
        if( precision>1 ){
          width -= precision-1;
          if( width>1 && !flag_leftjustify ){
            sqlite3AppendChar(pAccum, width-1, ' ');
            width = 0;
          }
          sqlite3AppendChar(pAccum, precision-1, c);
        }
        length = 1;
        buf[0] = c;
        bufpt = buf;
        break;
      case etSTRING:
      case etDYNSTRING:
        if( bArgList ){
          bufpt = getTextArg(pArgList);
          xtype = etSTRING;
        }else{
          bufpt = va_arg(ap,char*);
        }
        if( bufpt==0 ){
          bufpt = "";
        }else if( xtype==etDYNSTRING ){
          zExtra = bufpt;
        }
        if( precision>=0 ){
          for(length=0; length<precision && bufpt[length]; length++){}
        }else{
          length = sqlite3Strlen30(bufpt);
        }
        break;
      case etSQLESCAPE:           /* Escape ' characters */
      case etSQLESCAPE2:          /* Escape ' and enclose in '...' */
      case etSQLESCAPE3: {        /* Escape " characters */
        int i, j, k, n, isnull;
        int needQuote;
        char ch;
        char q = ((xtype==etSQLESCAPE3)?'"':'\'');   /* Quote character */
        char *escarg;

        if( bArgList ){
          escarg = getTextArg(pArgList);
        }else{
          escarg = va_arg(ap,char*);
        }
        isnull = escarg==0;
        if( isnull ) escarg = (xtype==etSQLESCAPE2 ? "NULL" : "(NULL)");
        k = precision;
        for(i=n=0; k!=0 && (ch=escarg[i])!=0; i++, k--){
          if( ch==q )  n++;
        }
        needQuote = !isnull && xtype==etSQLESCAPE2;
        n += i + 3;
        if( n>etBUFSIZE ){
          bufpt = zExtra = sqlite3Malloc( n );
          if( bufpt==0 ){
            setStrAccumError(pAccum, STRACCUM_NOMEM);
            return;
          }
        }else{
          bufpt = buf;
        }
        j = 0;
        if( needQuote ) bufpt[j++] = q;
        k = i;
        for(i=0; i<k; i++){
          bufpt[j++] = ch = escarg[i];
          if( ch==q ) bufpt[j++] = ch;
        }
        if( needQuote ) bufpt[j++] = q;
        bufpt[j] = 0;
        length = j;
        /* The precision in %q and %Q means how many input characters to
        ** consume, not the length of the output...
        ** if( precision>=0 && precision<length ) length = precision; */
        break;
      }
      default: {
        assert( xtype==etINVALID );
        return;
      }
    }/* End switch over the format type */
    /*
    ** The text of the conversion is pointed to by "bufpt" and is
    ** "length" characters long.  The field width is "width".  Do
    ** the output.
    */
    width -= length;
    if( width>0 && !flag_leftjustify ) sqlite3AppendChar(pAccum, width, ' ');
    sqlite3StrAccumAppend(pAccum, bufpt, length);
    if( width>0 && flag_leftjustify ) sqlite3AppendChar(pAccum, width, ' ');

    if( zExtra ){
      sqlite3_free(zExtra);
      zExtra = 0;
    }
  }/* End for loop over the format string */
} /* End of function */

/*
** Enlarge the memory allocation on a StrAccum object so that it is
** able to accept at least N more bytes of text.
**
** Return the number of bytes of text that StrAccum is able to accept
** after the attempted enlargement.  The value returned might be zero.
*/
static int sqlite3StrAccumEnlarge(StrAccum *p, int N){
  char *zNew;
  assert( p->nChar+(i64)N >= p->nAlloc ); /* Only called if really needed */
  if( p->accError ){
    testcase(p->accError==STRACCUM_TOOBIG);
    testcase(p->accError==STRACCUM_NOMEM);
    return 0;
  }
  if( p->mxAlloc==0 ){
    N = p->nAlloc - p->nChar - 1;
    setStrAccumError(p, STRACCUM_TOOBIG);
    return N;
  }else{
    char *zOld = (p->zText==p->zBase ? 0 : p->zText);
    i64 szNew = p->nChar;
    szNew += N + 1;
    if( szNew+p->nChar<=p->mxAlloc ){
      /* Force exponential buffer size growth as long as it does not overflow,
      ** to avoid having to call this routine too often */
      szNew += p->nChar;
    }
    if( szNew > p->mxAlloc ){
      sqlite3StrAccumReset(p);
      setStrAccumError(p, STRACCUM_TOOBIG);
      return 0;
    }else{
      p->nAlloc = (int)szNew;
    }
    if( p->pBtree ){
      zNew = sqlite3DbRealloc(p->pBtree, zOld, p->nAlloc);
    }else{
      zNew = sqlite3_realloc64(zOld, p->nAlloc);
    }
    if( zNew ){
      assert( p->zText!=0 || p->nChar==0 );
      if( zOld==0 && p->nChar>0 ) memcpy(zNew, p->zText, p->nChar);
      p->zText = zNew;
      p->nAlloc = sqlite3DbMallocSize(p->pBtree, zNew);
    }else{
      sqlite3StrAccumReset(p);
      setStrAccumError(p, STRACCUM_NOMEM);
      return 0;
    }
  }
  return N;
}

/*
** Append N copies of character c to the given string buffer.
*/
SQLITE_PRIVATE void sqlite3AppendChar(StrAccum *p, int N, char c){
  testcase( p->nChar + (i64)N > 0x7fffffff );
  if( p->nChar+(i64)N >= p->nAlloc && (N = sqlite3StrAccumEnlarge(p, N))<=0 ){
    return;
  }
  while( (N--)>0 ) p->zText[p->nChar++] = c;
}

/*
** The StrAccum "p" is not large enough to accept N new bytes of z[].
** So enlarge if first, then do the append.
**
** This is a helper routine to sqlite3StrAccumAppend() that does special-case
** work (enlarging the buffer) using tail recursion, so that the
** sqlite3StrAccumAppend() routine can use fast calling semantics.
*/
static void SQLITE_NOINLINE enlargeAndAppend(StrAccum *p, const char *z, int N){
  N = sqlite3StrAccumEnlarge(p, N);
  if( N>0 ){
    memcpy(&p->zText[p->nChar], z, N);
    p->nChar += N;
  }
}

/*
** Append N bytes of text from z to the StrAccum object.  Increase the
** size of the memory allocation for StrAccum if necessary.
*/
SQLITE_PRIVATE void sqlite3StrAccumAppend(StrAccum *p, const char *z, int N){
  assert( z!=0 || N==0 );
  assert( p->zText!=0 || p->nChar==0 || p->accError );
  assert( N>=0 );
  assert( p->accError==0 || p->nAlloc==0 );
  if( p->nChar+N >= p->nAlloc ){
    enlargeAndAppend(p,z,N);
  }else{
    assert( p->zText );
    p->nChar += N;
    memcpy(&p->zText[p->nChar-N], z, N);
  }
}

/*
** Finish off a string by making sure it is zero-terminated.
** Return a pointer to the resulting string.  Return a NULL
** pointer if any kind of error was encountered.
*/
SQLITE_PRIVATE char *sqlite3StrAccumFinish(StrAccum *p){
  if( p->zText ){
    p->zText[p->nChar] = 0;
    if( p->mxAlloc>0 && p->zText==p->zBase ){
      p->zText = sqlite3DbMallocRaw(p->pBtree, p->nChar+1 );
      if( p->zText ){
        memcpy(p->zText, p->zBase, p->nChar+1);
      }else{
        setStrAccumError(p, STRACCUM_NOMEM);
      }
    }
  }
  return p->zText;
}

/*
** Reset an StrAccum string.  Reclaim all malloced memory.
*/
SQLITE_PRIVATE void sqlite3StrAccumReset(StrAccum *p){
  if( p->zText!=p->zBase ){
    sqlite3DbFree(p->pBtree, p->zText);
  }
  p->zText = 0;
}

/*
** Initialize a string accumulator.
**
** p:     The accumulator to be initialized.
** db:    Pointer to a database connection.  May be NULL.  Lookaside
**        memory is used if not NULL. db->mallocFailed is set appropriately
**        when not NULL.
** zBase: An initial buffer.  May be NULL in which case the initial buffer
**        is malloced.
** n:     Size of zBase in bytes.  If total space requirements never exceed
**        n then no memory allocations ever occur.
** mx:    Maximum number of bytes to accumulate.  If mx==0 then no memory
**        allocations will ever occur.
*/
SQLITE_PRIVATE void sqlite3StrAccumInit(StrAccum *p, Btree* pBtree, char *zBase, int n, int mx){
  p->zText = p->zBase = zBase;
  p->pBtree = pBtree;
  p->nChar = 0;
  p->nAlloc = n;
  p->mxAlloc = mx;
  p->accError = 0;
}

/*
** Print into memory obtained from sqlite3_malloc().  Omit the internal
** %-conversion extensions.
*/
SQLITE_PRIVATE char *sqlite3_vmprintf(const char *zFormat, va_list ap){
  char *z;
  char zBase[SQLITE_PRINT_BUF_SIZE];
  StrAccum acc;

#ifdef SQLITE_ENABLE_API_ARMOR  
  if( zFormat==0 ){
    (void)SQLITE_MISUSE_BKPT;
    return 0;
  }
#endif
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  sqlite3StrAccumInit(&acc, 0, zBase, sizeof(zBase), SQLITE_MAX_LENGTH);
  sqlite3VXPrintf(&acc, 0, zFormat, ap);
  z = sqlite3StrAccumFinish(&acc);
  return z;
}

/*
** Print into memory obtained from sqlite3_malloc()().  Omit the internal
** %-conversion extensions.
*/
SQLITE_PRIVATE char *sqlite3_mprintf(const char *zFormat, ...){
  va_list ap;
  char *z;
#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return 0;
#endif
  va_start(ap, zFormat);
  z = sqlite3_vmprintf(zFormat, ap);
  va_end(ap);
  return z;
}

/*
** sqlite3_snprintf() works like snprintf() except that it ignores the
** current locale settings.  This is important for SQLite because we
** are not able to use a "," as the decimal point in place of "." as
** specified by some locales.
**
** Oops:  The first two arguments of sqlite3_snprintf() are backwards
** from the snprintf() standard.  Unfortunately, it is too late to change
** this without breaking compatibility, so we just have to live with the
** mistake.
**
** sqlite3_vsnprintf() is the varargs version.
*/
SQLITE_PRIVATE char *sqlite3_vsnprintf(int n, char *zBuf, const char *zFormat, va_list ap){
  StrAccum acc;
  if( n<=0 ) return zBuf;
#ifdef SQLITE_ENABLE_API_ARMOR
  if( zBuf==0 || zFormat==0 ) {
    (void)SQLITE_MISUSE_BKPT;
    if( zBuf ) zBuf[0] = 0;
    return zBuf;
  }
#endif
  sqlite3StrAccumInit(&acc, 0, zBuf, n, 0);
  sqlite3VXPrintf(&acc, 0, zFormat, ap);
  return sqlite3StrAccumFinish(&acc);
}
SQLITE_PRIVATE char *sqlite3_snprintf(int n, char *zBuf, const char *zFormat, ...){
  char *z;
  va_list ap;
  va_start(ap,zFormat);
  z = sqlite3_vsnprintf(n, zBuf, zFormat, ap);
  va_end(ap);
  return z;
}

/*
** This is the routine that actually formats the sqlite3_log() message.
** We house it in a separate routine from sqlite3_log() to avoid using
** stack space on small-stack systems when logging is disabled.
**
** sqlite3_log() must render into a static buffer.  It cannot dynamically
** allocate memory because it might be called while the memory allocator
** mutex is held.
**
** sqlite3VXPrintf() might ask for *temporary* memory allocations for
** certain format characters (%q) or for very large precisions or widths.
** Care must be taken that any sqlite3_log() calls that occur while the
** memory mutex is held do not use these mechanisms.
*/
static void renderLogMsg(int iErrCode, const char *zFormat, va_list ap){
  StrAccum acc;                          /* String accumulator */
  char zMsg[SQLITE_PRINT_BUF_SIZE*3];    /* Complete log message */

  sqlite3StrAccumInit(&acc, 0, zMsg, sizeof(zMsg), 0);
  sqlite3VXPrintf(&acc, 0, zFormat, ap);
  sqlite3GlobalConfig.xLog(sqlite3GlobalConfig.pLogArg, iErrCode,
                           sqlite3StrAccumFinish(&acc));
}

/*
** Format and write a message to the log if logging is enabled.
*/
SQLITE_PRIVATE void sqlite3_log(int iErrCode, const char *zFormat, ...){
  va_list ap;                             /* Vararg list */
  if( sqlite3GlobalConfig.xLog ){
    va_start(ap, zFormat);
    renderLogMsg(iErrCode, zFormat, ap);
    va_end(ap);
  }
}

#if defined(SQLITE_DEBUG) || defined(SQLITE_HAVE_OS_TRACE)
/*
** A version of printf() that understands %lld.  Used for debugging.
** The printf() built into some versions of windows does not understand %lld
** and segfaults if you give it a long long int.
*/
SQLITE_PRIVATE void sqlite3DebugPrintf(const char *zFormat, ...){
  va_list ap;
  StrAccum acc;
  char zBuf[500];
  sqlite3StrAccumInit(&acc, 0, zBuf, sizeof(zBuf), 0);
  va_start(ap,zFormat);
  sqlite3VXPrintf(&acc, 0, zFormat, ap);
  va_end(ap);
  sqlite3StrAccumFinish(&acc);
  fprintf(stdout,"%s", zBuf);
  fflush(stdout);
}
#endif


/*
** variable-argument wrapper around sqlite3VXPrintf().  The bFlags argument
** can contain the bit SQLITE_PRINTF_INTERNAL enable internal formats.
*/
SQLITE_PRIVATE void sqlite3XPrintf(StrAccum *p, u32 bFlags, const char *zFormat, ...){
  va_list ap;
  va_start(ap,zFormat);
  sqlite3VXPrintf(p, bFlags, zFormat, ap);
  va_end(ap);
}

/************** End of printf.c **********************************************/
/************** Begin file random.c ******************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains code to implement a pseudo-random number
** generator (PRNG) for SQLite.
**
** Random numbers are used by some of the database backends in order
** to generate random integer keys for tables or random filenames.
*/
/* #include "sqliteInt.h" */


/* All threads share a single random number generator.
** This structure is the current state of the generator.
*/
static SQLITE_WSD struct sqlite3PrngType {
  unsigned char isInit;          /* True if initialized */
  unsigned char i, j;            /* State variables */
  unsigned char s[256];          /* State variables */
} sqlite3Prng;

/*
** Return N random bytes.
*/
SQLITE_PRIVATE void sqlite3_randomness(int N, void *pBuf){
  unsigned char t;
  unsigned char *zBuf = pBuf;

  /* The "wsdPrng" macro will resolve to the pseudo-random number generator
  ** state vector.  If writable static data is unsupported on the target,
  ** we have to locate the state vector at run-time.  In the more common
  ** case where writable static data is supported, wsdPrng can refer directly
  ** to the "sqlite3Prng" state vector declared above.
  */
#ifdef SQLITE_OMIT_WSD
  struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng);
# define wsdPrng p[0]
#else
# define wsdPrng sqlite3Prng
#endif

#if SQLITE_THREADSAFE
  sqlite3_mutex *mutex;
#endif

#ifndef SQLITE_OMIT_AUTOINIT
  if( sqlite3BtreeInitialize() ) return;
#endif

#if SQLITE_THREADSAFE
  mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG);
#endif

  sqlite3_mutex_enter(mutex);
  if( N<=0 || pBuf==0 ){
    wsdPrng.isInit = 0;
    sqlite3_mutex_leave(mutex);
    return;
  }

  /* Initialize the state of the random number generator once,
  ** the first time this routine is called.  The seed value does
  ** not need to contain a lot of randomness since we are not
  ** trying to do secure encryption or anything like that...
  **
  ** Nothing in this file or anywhere else in SQLite does any kind of
  ** encryption.  The RC4 algorithm is being used as a PRNG (pseudo-random
  ** number generator) not as an encryption device.
  */
  if( !wsdPrng.isInit ){
    int i;
    char k[256];
    wsdPrng.j = 0;
    wsdPrng.i = 0;
    sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
    for(i=0; i<256; i++){
      wsdPrng.s[i] = (u8)i;
    }
    for(i=0; i<256; i++){
      wsdPrng.j += wsdPrng.s[i] + k[i];
      t = wsdPrng.s[wsdPrng.j];
      wsdPrng.s[wsdPrng.j] = wsdPrng.s[i];
      wsdPrng.s[i] = t;
    }
    wsdPrng.isInit = 1;
  }

  assert( N>0 );
  do{
    wsdPrng.i++;
    t = wsdPrng.s[wsdPrng.i];
    wsdPrng.j += t;
    wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j];
    wsdPrng.s[wsdPrng.j] = t;
    t += wsdPrng.s[wsdPrng.i];
    *(zBuf++) = wsdPrng.s[t];
  }while( --N );
  sqlite3_mutex_leave(mutex);
}

/************** End of random.c **********************************************/
/************** Begin file util.c ********************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
*/
/* #include "sqliteInt.h" */
/* #include <stdarg.h> */
#if HAVE_ISNAN || SQLITE_HAVE_ISNAN
# include <math.h>
#endif

/*
** Routine needed to support the testcase() macro.
*/
#ifdef SQLITE_COVERAGE_TEST
SQLITE_PRIVATE void sqlite3Coverage(int x){
  static unsigned dummy = 0;
  dummy += (unsigned)x;
}
#endif

#ifndef SQLITE_OMIT_FLOATING_POINT
/*
** Return true if the floating point value is Not a Number (NaN).
**
** Use the math library isnan() function if compiled with SQLITE_HAVE_ISNAN.
** Otherwise, we have our own implementation that works on most systems.
*/
SQLITE_PRIVATE int sqlite3IsNaN(double x){
  int rc;   /* The value return */
#if !SQLITE_HAVE_ISNAN && !HAVE_ISNAN
  /*
  ** Systems that support the isnan() library function should probably
  ** make use of it by compiling with -DSQLITE_HAVE_ISNAN.  But we have
  ** found that many systems do not have a working isnan() function so
  ** this implementation is provided as an alternative.
  **
  ** This NaN test sometimes fails if compiled on GCC with -ffast-math.
  ** On the other hand, the use of -ffast-math comes with the following
  ** warning:
  **
  **      This option [-ffast-math] should never be turned on by any
  **      -O option since it can result in incorrect output for programs
  **      which depend on an exact implementation of IEEE or ISO 
  **      rules/specifications for math functions.
  **
  ** Under MSVC, this NaN test may fail if compiled with a floating-
  ** point precision mode other than /fp:precise.  From the MSDN 
  ** documentation:
  **
  **      The compiler [with /fp:precise] will properly handle comparisons 
  **      involving NaN. For example, x != x evaluates to true if x is NaN 
  **      ...
  */
#ifdef __FAST_MATH__
# error SQLite will not work correctly with the -ffast-math option of GCC.
#endif
  volatile double y = x;
  volatile double z = y;
  rc = (y!=z);
#else  /* if HAVE_ISNAN */
  rc = isnan(x);
#endif /* HAVE_ISNAN */
  testcase( rc );
  return rc;
}
#endif /* SQLITE_OMIT_FLOATING_POINT */

/*
** Compute a string length that is limited to what can be stored in
** lower 30 bits of a 32-bit signed integer.
**
** The value returned will never be negative.  Nor will it ever be greater
** than the actual length of the string.  For very long strings (greater
** than 1GiB) the value returned might be less than the true string length.
*/
SQLITE_PRIVATE int sqlite3Strlen30(const char *z){
  if( z==0 ) return 0;
  return 0x3fffffff & (int)strlen(z);
}

/*
** The string z[] is an text representation of a real number.
** Convert this string to a double and write it into *pResult.
**
** The string z[] is length bytes in length (bytes, not characters) and
** uses the encoding enc.  The string is not necessarily zero-terminated.
**
** Return TRUE if the result is a valid real number (or integer) and FALSE
** if the string is empty or contains extraneous text.  Valid numbers
** are in one of these formats:
**
**    [+-]digits[E[+-]digits]
**    [+-]digits.[digits][E[+-]digits]
**    [+-].digits[E[+-]digits]
**
** Leading and trailing whitespace is ignored for the purpose of determining
** validity.
**
** If some prefix of the input string is a valid number, this routine
** returns FALSE but it still converts the prefix and writes the result
** into *pResult.
*/
SQLITE_PRIVATE int sqlite3AtoF(const char *z, double *pResult, int length, u8 enc){
#ifndef SQLITE_OMIT_FLOATING_POINT
  int incr;
  const char *zEnd = z + length;
  /* sign * significand * (10 ^ (esign * exponent)) */
  int sign = 1;    /* sign of significand */
  i64 s = 0;       /* significand */
  int d = 0;       /* adjust exponent for shifting decimal point */
  int esign = 1;   /* sign of exponent */
  int e = 0;       /* exponent */
  int eValid = 1;  /* True exponent is either not used or is well-formed */
  double result;
  int nDigits = 0;
  int nonNum = 0;

  assert( enc==SQLITE_UTF8 || enc==SQLITE_UTF16LE || enc==SQLITE_UTF16BE );
  *pResult = 0.0;   /* Default return value, in case of an error */

  if( enc==SQLITE_UTF8 ){
    incr = 1;
  }else{
    int i;
    incr = 2;
    assert( SQLITE_UTF16LE==2 && SQLITE_UTF16BE==3 );
    for(i=3-enc; i<length && z[i]==0; i+=2){}
    nonNum = i<length;
    zEnd = z+i+enc-3;
    z += (enc&1);
  }

  /* skip leading spaces */
  while( z<zEnd && sqlite3Isspace(*z) ) z+=incr;
  if( z>=zEnd ) return 0;

  /* get sign of significand */
  if( *z=='-' ){
    sign = -1;
    z+=incr;
  }else if( *z=='+' ){
    z+=incr;
  }

  /* skip leading zeroes */
  while( z<zEnd && z[0]=='0' ) z+=incr, nDigits++;

  /* copy max significant digits to significand */
  while( z<zEnd && sqlite3Isdigit(*z) && s<((LARGEST_INT64-9)/10) ){
    s = s*10 + (*z - '0');
    z+=incr, nDigits++;
  }

  /* skip non-significant significand digits
  ** (increase exponent by d to shift decimal left) */
  while( z<zEnd && sqlite3Isdigit(*z) ) z+=incr, nDigits++, d++;
  if( z>=zEnd ) goto do_atof_calc;

  /* if decimal point is present */
  if( *z=='.' ){
    z+=incr;
    /* copy digits from after decimal to significand
    ** (decrease exponent by d to shift decimal right) */
    while( z<zEnd && sqlite3Isdigit(*z) && s<((LARGEST_INT64-9)/10) ){
      s = s*10 + (*z - '0');
      z+=incr, nDigits++, d--;
    }
    /* skip non-significant digits */
    while( z<zEnd && sqlite3Isdigit(*z) ) z+=incr, nDigits++;
  }
  if( z>=zEnd ) goto do_atof_calc;

  /* if exponent is present */
  if( *z=='e' || *z=='E' ){
    z+=incr;
    eValid = 0;
    if( z>=zEnd ) goto do_atof_calc;
    /* get sign of exponent */
    if( *z=='-' ){
      esign = -1;
      z+=incr;
    }else if( *z=='+' ){
      z+=incr;
    }
    /* copy digits to exponent */
    while( z<zEnd && sqlite3Isdigit(*z) ){
      e = e<10000 ? (e*10 + (*z - '0')) : 10000;
      z+=incr;
      eValid = 1;
    }
  }

  /* skip trailing spaces */
  if( nDigits && eValid ){
    while( z<zEnd && sqlite3Isspace(*z) ) z+=incr;
  }

do_atof_calc:
  /* adjust exponent by d, and update sign */
  e = (e*esign) + d;
  if( e<0 ) {
    esign = -1;
    e *= -1;
  } else {
    esign = 1;
  }

  /* if 0 significand */
  if( !s ) {
    /* In the IEEE 754 standard, zero is signed.
    ** Add the sign if we've seen at least one digit */
    result = (sign<0 && nDigits) ? -(double)0 : (double)0;
  } else {
    /* attempt to reduce exponent */
    if( esign>0 ){
      while( s<(LARGEST_INT64/10) && e>0 ) e--,s*=10;
    }else{
      while( !(s%10) && e>0 ) e--,s/=10;
    }

    /* adjust the sign of significand */
    s = sign<0 ? -s : s;

    /* if exponent, scale significand as appropriate
    ** and store in result. */
    if( e ){
      LONGDOUBLE_TYPE scale = 1.0;
      /* attempt to handle extremely small/large numbers better */
      if( e>307 && e<342 ){
        while( e%308 ) { scale *= 1.0e+1; e -= 1; }
        if( esign<0 ){
          result = s / scale;
          result /= 1.0e+308;
        }else{
          result = s * scale;
          result *= 1.0e+308;
        }
      }else if( e>=342 ){
        if( esign<0 ){
          result = 0.0*s;
        }else{
          result = 1e308*1e308*s;  /* Infinity */
        }
      }else{
        /* 1.0e+22 is the largest power of 10 than can be 
        ** represented exactly. */
        while( e%22 ) { scale *= 1.0e+1; e -= 1; }
        while( e>0 ) { scale *= 1.0e+22; e -= 22; }
        if( esign<0 ){
          result = s / scale;
        }else{
          result = s * scale;
        }
      }
    } else {
      result = (double)s;
    }
  }

  /* store the result */
  *pResult = result;

  /* return true if number and no extra non-whitespace chracters after */
  return z>=zEnd && nDigits>0 && eValid && nonNum==0;
#else
  return !sqlite3Atoi64(z, pResult, length, enc);
#endif /* SQLITE_OMIT_FLOATING_POINT */
}

/*
** Compare the 19-character string zNum against the text representation
** value 2^63:  9223372036854775808.  Return negative, zero, or positive
** if zNum is less than, equal to, or greater than the string.
** Note that zNum must contain exactly 19 characters.
**
** Unlike memcmp() this routine is guaranteed to return the difference
** in the values of the last digit if the only difference is in the
** last digit.  So, for example,
**
**      compare2pow63("9223372036854775800", 1)
**
** will return -8.
*/
static int compare2pow63(const char *zNum, int incr){
  int c = 0;
  int i;
                    /* 012345678901234567 */
  const char *pow63 = "922337203685477580";
  for(i=0; c==0 && i<18; i++){
    c = (zNum[i*incr]-pow63[i])*10;
  }
  if( c==0 ){
    c = zNum[18*incr] - '8';
    testcase( c==(-1) );
    testcase( c==0 );
    testcase( c==(+1) );
  }
  return c;
}

/*
** Convert zNum to a 64-bit signed integer.  zNum must be decimal. This
** routine does *not* accept hexadecimal notation.
**
** If the zNum value is representable as a 64-bit twos-complement 
** integer, then write that value into *pNum and return 0.
**
** If zNum is exactly 9223372036854775808, return 2.  This special
** case is broken out because while 9223372036854775808 cannot be a 
** signed 64-bit integer, its negative -9223372036854775808 can be.
**
** If zNum is too big for a 64-bit integer and is not
** 9223372036854775808  or if zNum contains any non-numeric text,
** then return 1.
**
** length is the number of bytes in the string (bytes, not characters).
** The string is not necessarily zero-terminated.  The encoding is
** given by enc.
*/
SQLITE_PRIVATE int sqlite3Atoi64(const char *zNum, i64 *pNum, int length, u8 enc){
  int incr;
  u64 u = 0;
  int neg = 0; /* assume positive */
  int i;
  int c = 0;
  int nonNum = 0;
  const char *zStart;
  const char *zEnd = zNum + length;
  assert( enc==SQLITE_UTF8 || enc==SQLITE_UTF16LE || enc==SQLITE_UTF16BE );
  if( enc==SQLITE_UTF8 ){
    incr = 1;
  }else{
    incr = 2;
    assert( SQLITE_UTF16LE==2 && SQLITE_UTF16BE==3 );
    for(i=3-enc; i<length && zNum[i]==0; i+=2){}
    nonNum = i<length;
    zEnd = zNum+i+enc-3;
    zNum += (enc&1);
  }
  while( zNum<zEnd && sqlite3Isspace(*zNum) ) zNum+=incr;
  if( zNum<zEnd ){
    if( *zNum=='-' ){
      neg = 1;
      zNum+=incr;
    }else if( *zNum=='+' ){
      zNum+=incr;
    }
  }
  zStart = zNum;
  while( zNum<zEnd && zNum[0]=='0' ){ zNum+=incr; } /* Skip leading zeros. */
  for(i=0; &zNum[i]<zEnd && (c=zNum[i])>='0' && c<='9'; i+=incr){
    u = u*10 + c - '0';
  }
  if( u>LARGEST_INT64 ){
    *pNum = neg ? SMALLEST_INT64 : LARGEST_INT64;
  }else if( neg ){
    *pNum = -(i64)u;
  }else{
    *pNum = (i64)u;
  }
  testcase( i==18 );
  testcase( i==19 );
  testcase( i==20 );
  if( (c!=0 && &zNum[i]<zEnd) || (i==0 && zStart==zNum) || i>19*incr || nonNum ){
    /* zNum is empty or contains non-numeric text or is longer
    ** than 19 digits (thus guaranteeing that it is too large) */
    return 1;
  }else if( i<19*incr ){
    /* Less than 19 digits, so we know that it fits in 64 bits */
    assert( u<=LARGEST_INT64 );
    return 0;
  }else{
    /* zNum is a 19-digit numbers.  Compare it against 9223372036854775808. */
    c = compare2pow63(zNum, incr);
    if( c<0 ){
      /* zNum is less than 9223372036854775808 so it fits */
      assert( u<=LARGEST_INT64 );
      return 0;
    }else if( c>0 ){
      /* zNum is greater than 9223372036854775808 so it overflows */
      return 1;
    }else{
      /* zNum is exactly 9223372036854775808.  Fits if negative.  The
      ** special case 2 overflow if positive */
      assert( u-1==LARGEST_INT64 );
      return neg ? 0 : 2;
    }
  }
}

/*
** The variable-length integer encoding is as follows:
**
** KEY:
**         A = 0xxxxxxx    7 bits of data and one flag bit
**         B = 1xxxxxxx    7 bits of data and one flag bit
**         C = xxxxxxxx    8 bits of data
**
**  7 bits - A
** 14 bits - BA
** 21 bits - BBA
** 28 bits - BBBA
** 35 bits - BBBBA
** 42 bits - BBBBBA
** 49 bits - BBBBBBA
** 56 bits - BBBBBBBA
** 64 bits - BBBBBBBBC
*/

/*
** Write a 64-bit variable-length integer to memory starting at p[0].
** The length of data write will be between 1 and 9 bytes.  The number
** of bytes written is returned.
**
** A variable-length integer consists of the lower 7 bits of each byte
** for all bytes that have the 8th bit set and one byte with the 8th
** bit clear.  Except, if we get to the 9th byte, it stores the full
** 8 bits and is the last byte.
*/
static int SQLITE_NOINLINE putVarint64(unsigned char *p, u64 v){
  int i, j, n;
  u8 buf[10];
  if( v & (((u64)0xff000000)<<32) ){
    p[8] = (u8)v;
    v >>= 8;
    for(i=7; i>=0; i--){
      p[i] = (u8)((v & 0x7f) | 0x80);
      v >>= 7;
    }
    return 9;
  }    
  n = 0;
  do{
    buf[n++] = (u8)((v & 0x7f) | 0x80);
    v >>= 7;
  }while( v!=0 );
  buf[0] &= 0x7f;
  assert( n<=9 );
  for(i=0, j=n-1; j>=0; j--, i++){
    p[i] = buf[j];
  }
  return n;
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreePutVarint(unsigned char *p, u64 v){
  if( v<=0x7f ){
    p[0] = v&0x7f;
    return 1;
  }
  if( v<=0x3fff ){
    p[0] = ((v>>7)&0x7f)|0x80;
    p[1] = v&0x7f;
    return 2;
  }
  return putVarint64(p,v);
}

/*
** Bitmasks used by sqlite3GetVarint().  These precomputed constants
** are defined here rather than simply putting the constant expressions
** inline in order to work around bugs in the RVT compiler.
**
** SLOT_2_0     A mask for  (0x7f<<14) | 0x7f
**
** SLOT_4_2_0   A mask for  (0x7f<<28) | SLOT_2_0
*/
#define SLOT_2_0     0x001fc07f
#define SLOT_4_2_0   0xf01fc07f


/*
** Read a 64-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
*/
SQLITE_API u8 SQLITE_STDCALL sqlite3BtreeGetVarint(const unsigned char *p, u64 *v){
  u32 a,b,s;

  a = *p;
  /* a: p0 (unmasked) */
  if (!(a&0x80))
  {
    *v = a;
    return 1;
  }

  p++;
  b = *p;
  /* b: p1 (unmasked) */
  if (!(b&0x80))
  {
    a &= 0x7f;
    a = a<<7;
    a |= b;
    *v = a;
    return 2;
  }

  /* Verify that constants are precomputed correctly */
  assert( SLOT_2_0 == ((0x7f<<14) | (0x7f)) );
  assert( SLOT_4_2_0 == ((0xfU<<28) | (0x7f<<14) | (0x7f)) );

  p++;
  a = a<<14;
  a |= *p;
  /* a: p0<<14 | p2 (unmasked) */
  if (!(a&0x80))
  {
    a &= SLOT_2_0;
    b &= 0x7f;
    b = b<<7;
    a |= b;
    *v = a;
    return 3;
  }

  /* CSE1 from below */
  a &= SLOT_2_0;
  p++;
  b = b<<14;
  b |= *p;
  /* b: p1<<14 | p3 (unmasked) */
  if (!(b&0x80))
  {
    b &= SLOT_2_0;
    /* moved CSE1 up */
    /* a &= (0x7f<<14)|(0x7f); */
    a = a<<7;
    a |= b;
    *v = a;
    return 4;
  }

  /* a: p0<<14 | p2 (masked) */
  /* b: p1<<14 | p3 (unmasked) */
  /* 1:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked) */
  /* moved CSE1 up */
  /* a &= (0x7f<<14)|(0x7f); */
  b &= SLOT_2_0;
  s = a;
  /* s: p0<<14 | p2 (masked) */

  p++;
  a = a<<14;
  a |= *p;
  /* a: p0<<28 | p2<<14 | p4 (unmasked) */
  if (!(a&0x80))
  {
    /* we can skip these cause they were (effectively) done above in calc'ing s */
    /* a &= (0x7f<<28)|(0x7f<<14)|(0x7f); */
    /* b &= (0x7f<<14)|(0x7f); */
    b = b<<7;
    a |= b;
    s = s>>18;
    *v = ((u64)s)<<32 | a;
    return 5;
  }

  /* 2:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked) */
  s = s<<7;
  s |= b;
  /* s: p0<<21 | p1<<14 | p2<<7 | p3 (masked) */

  p++;
  b = b<<14;
  b |= *p;
  /* b: p1<<28 | p3<<14 | p5 (unmasked) */
  if (!(b&0x80))
  {
    /* we can skip this cause it was (effectively) done above in calc'ing s */
    /* b &= (0x7f<<28)|(0x7f<<14)|(0x7f); */
    a &= SLOT_2_0;
    a = a<<7;
    a |= b;
    s = s>>18;
    *v = ((u64)s)<<32 | a;
    return 6;
  }

  p++;
  a = a<<14;
  a |= *p;
  /* a: p2<<28 | p4<<14 | p6 (unmasked) */
  if (!(a&0x80))
  {
    a &= SLOT_4_2_0;
    b &= SLOT_2_0;
    b = b<<7;
    a |= b;
    s = s>>11;
    *v = ((u64)s)<<32 | a;
    return 7;
  }

  /* CSE2 from below */
  a &= SLOT_2_0;
  p++;
  b = b<<14;
  b |= *p;
  /* b: p3<<28 | p5<<14 | p7 (unmasked) */
  if (!(b&0x80))
  {
    b &= SLOT_4_2_0;
    /* moved CSE2 up */
    /* a &= (0x7f<<14)|(0x7f); */
    a = a<<7;
    a |= b;
    s = s>>4;
    *v = ((u64)s)<<32 | a;
    return 8;
  }

  p++;
  a = a<<15;
  a |= *p;
  /* a: p4<<29 | p6<<15 | p8 (unmasked) */

  /* moved CSE2 up */
  /* a &= (0x7f<<29)|(0x7f<<15)|(0xff); */
  b &= SLOT_2_0;
  b = b<<8;
  a |= b;

  s = s<<4;
  b = p[-4];
  b &= 0x7f;
  b = b>>3;
  s |= b;

  *v = ((u64)s)<<32 | a;

  return 9;
}

/*
** Read a 32-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
**
** If the varint stored in p[0] is larger than can fit in a 32-bit unsigned
** integer, then set *v to 0xffffffff.
**
** A MACRO version, getVarint32, is provided which inlines the 
** single-byte case.  All code should use the MACRO version as 
** this function assumes the single-byte case has already been handled.
*/
SQLITE_API u8 SQLITE_STDCALL sqlite3BtreeGetVarint32(const unsigned char *p, u32 *v){
  u32 a,b;

  /* The 1-byte case.  Overwhelmingly the most common.  Handled inline
  ** by the getVarin32() macro */
  a = *p;
  /* a: p0 (unmasked) */
#ifndef getVarint32
  if (!(a&0x80))
  {
    /* Values between 0 and 127 */
    *v = a;
    return 1;
  }
#endif

  /* The 2-byte case */
  p++;
  b = *p;
  /* b: p1 (unmasked) */
  if (!(b&0x80))
  {
    /* Values between 128 and 16383 */
    a &= 0x7f;
    a = a<<7;
    *v = a | b;
    return 2;
  }

  /* The 3-byte case */
  p++;
  a = a<<14;
  a |= *p;
  /* a: p0<<14 | p2 (unmasked) */
  if (!(a&0x80))
  {
    /* Values between 16384 and 2097151 */
    a &= (0x7f<<14)|(0x7f);
    b &= 0x7f;
    b = b<<7;
    *v = a | b;
    return 3;
  }

  /* A 32-bit varint is used to store size information in btrees.
  ** Objects are rarely larger than 2MiB limit of a 3-byte varint.
  ** A 3-byte varint is sufficient, for example, to record the size
  ** of a 1048569-byte BLOB or string.
  **
  ** We only unroll the first 1-, 2-, and 3- byte cases.  The very
  ** rare larger cases can be handled by the slower 64-bit varint
  ** routine.
  */
#if 1
  {
    u64 v64;
    u8 n;

    p -= 2;
    n = sqlite3BtreeGetVarint(p, &v64);
    assert( n>3 && n<=9 );
    if( (v64 & SQLITE_MAX_U32)!=v64 ){
      *v = 0xffffffff;
    }else{
      *v = (u32)v64;
    }
    return n;
  }

#else
  /* For following code (kept for historical record only) shows an
  ** unrolling for the 3- and 4-byte varint cases.  This code is
  ** slightly faster, but it is also larger and much harder to test.
  */
  p++;
  b = b<<14;
  b |= *p;
  /* b: p1<<14 | p3 (unmasked) */
  if (!(b&0x80))
  {
    /* Values between 2097152 and 268435455 */
    b &= (0x7f<<14)|(0x7f);
    a &= (0x7f<<14)|(0x7f);
    a = a<<7;
    *v = a | b;
    return 4;
  }

  p++;
  a = a<<14;
  a |= *p;
  /* a: p0<<28 | p2<<14 | p4 (unmasked) */
  if (!(a&0x80))
  {
    /* Values  between 268435456 and 34359738367 */
    a &= SLOT_4_2_0;
    b &= SLOT_4_2_0;
    b = b<<7;
    *v = a | b;
    return 5;
  }

  /* We can only reach this point when reading a corrupt database
  ** file.  In that case we are not in any hurry.  Use the (relatively
  ** slow) general-purpose sqlite3BtreeGetVarint() routine to extract the
  ** value. */
  {
    u64 v64;
    u8 n;

    p -= 4;
    n = sqlite3BtreeGetVarint(p, &v64);
    assert( n>5 && n<=9 );
    *v = (u32)v64;
    return n;
  }
#endif
}

/*
** Return the number of bytes that will be needed to store the given
** 64-bit integer.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeVarintLen(u64 v){
  int i;
  for(i=1; (v >>= 7)!=0; i++){ assert( i<9 ); }
  return i;
}


/*
** Read or write a four-byte big-endian integer value.
*/
SQLITE_PRIVATE u32 sqlite3Get4byte(const u8 *p){
#if SQLITE_BYTEORDER==4321
  u32 x;
  memcpy(&x,p,4);
  return x;
#elif SQLITE_BYTEORDER==1234 && !defined(SQLITE_DISABLE_INTRINSIC) \
    && defined(__GNUC__) && GCC_VERSION>=4003000
  u32 x;
  memcpy(&x,p,4);
  return __builtin_bswap32(x);
#elif SQLITE_BYTEORDER==1234 && !defined(SQLITE_DISABLE_INTRINSIC) \
    && defined(_MSC_VER) && _MSC_VER>=1300
  u32 x;
  memcpy(&x,p,4);
  return _byteswap_ulong(x);
#else
  testcase( p[0]&0x80 );
  return ((unsigned)p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3];
#endif
}
SQLITE_PRIVATE void sqlite3Put4byte(unsigned char *p, u32 v){
#if SQLITE_BYTEORDER==4321
  memcpy(p,&v,4);
#elif SQLITE_BYTEORDER==1234 && defined(__GNUC__) && GCC_VERSION>=4003000
  u32 x = __builtin_bswap32(v);
  memcpy(p,&x,4);
#elif SQLITE_BYTEORDER==1234 && defined(_MSC_VER) && _MSC_VER>=1300
  u32 x = _byteswap_ulong(v);
  memcpy(p,&x,4);
#else
  p[0] = (u8)(v>>24);
  p[1] = (u8)(v>>16);
  p[2] = (u8)(v>>8);
  p[3] = (u8)v;
#endif
}

/*
** Log an error that is an API call on a connection pointer that should
** not have been used.  The "type" of connection pointer is given as the
** argument.  The zType is a word like "NULL" or "closed" or "invalid".
*/
static void logBadConnection(const char *zType){
  sqlite3_log(SQLITE_MISUSE, 
     "API call with %s database connection pointer",
     zType
  );
}

SQLITE_PRIVATE int sqlite3SafetyCheckSickOrOk(Btree *pBtree){
  u32 magic;
  magic = pBtree->magic;
  if( magic!=SQLITE_MAGIC_SICK &&
      magic!=SQLITE_MAGIC_OPEN &&
      magic!=SQLITE_MAGIC_BUSY ){
    testcase( sqlite3GlobalConfig.xLog!=0 );
    logBadConnection("invalid");
    return 0;
  }else{
    return 1;
  }
}

/*
** Compute the absolute value of a 32-bit signed integer, of possible.  Or 
** if the integer has a value of -2147483648, return +2147483647
*/
SQLITE_PRIVATE int sqlite3AbsInt32(int x){
  if( x>=0 ) return x;
  if( x==(int)0x80000000 ) return 0x7fffffff;
  return -x;
}

/************** End of util.c ************************************************/
/************** Begin file os_unix.c *****************************************/
/*
** 2004 May 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains the VFS implementation for unix-like operating systems
** include Linux, MacOSX, *BSD, QNX, VxWorks, AIX, HPUX, and others.
**
** There are actually several different VFS implementations in this file.
** The differences are in the way that file locking is done.  The default
** implementation uses Posix Advisory Locks.  Alternative implementations
** use flock(), dot-files, various proprietary locking schemas, or simply
** skip locking all together.
**
** This source file is organized into divisions where the logic for various
** subfunctions is contained within the appropriate division.  PLEASE
** KEEP THE STRUCTURE OF THIS FILE INTACT.  New code should be placed
** in the correct division and should be clearly labeled.
**
** The layout of divisions is as follows:
**
**   *  General-purpose declarations and utility functions.
**   *  Unique file ID logic used by VxWorks.
**   *  Various locking primitive implementations (all except proxy locking):
**      + for Posix Advisory Locks
**      + for no-op locks
**      + for dot-file locks
**      + for flock() locking
**      + for named semaphore locks (VxWorks only)
**      + for AFP filesystem locks (MacOSX only)
**   *  sqlite3_file methods not associated with locking.
**   *  Definitions of sqlite3_io_methods objects for all locking
**      methods plus "finder" functions for each locking method.
**   *  sqlite3_vfs method implementations.
**   *  Locking primitives for the proxy uber-locking-method. (MacOSX only)
**   *  Definitions of sqlite3_vfs objects for all locking methods
**      plus implementations of sqlite3_os_init() and sqlite3_os_end().
*/
/* #include "sqliteInt.h" */
#if SQLITE_OS_UNIX              /* This file is used on unix only */

/*
** There are various methods for file locking used for concurrency
** control:
**
**   1. POSIX locking (the default),
**   2. No locking,
**   3. Dot-file locking,
**   4. flock() locking,
**   5. AFP locking (OSX only),
**   6. Named POSIX semaphores (VXWorks only),
**   7. proxy locking. (OSX only)
**
** Styles 4, 5, and 7 are only available of SQLITE_ENABLE_LOCKING_STYLE
** is defined to 1.  The SQLITE_ENABLE_LOCKING_STYLE also enables automatic
** selection of the appropriate locking style based on the filesystem
** where the database is located.  
*/
#if !defined(SQLITE_ENABLE_LOCKING_STYLE)
#  if defined(__APPLE__)
#    define SQLITE_ENABLE_LOCKING_STYLE 1
#  else
#    define SQLITE_ENABLE_LOCKING_STYLE 0
#  endif
#endif

/*
** standard include files.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>
#include <errno.h>
#if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
# include <sys/mman.h>
#endif

#if SQLITE_ENABLE_LOCKING_STYLE
# include <sys/ioctl.h>
# include <sys/file.h>
# include <sys/param.h>
#endif /* SQLITE_ENABLE_LOCKING_STYLE */

#if defined(__APPLE__) && ((__MAC_OS_X_VERSION_MIN_REQUIRED > 1050) || \
                           (__IPHONE_OS_VERSION_MIN_REQUIRED > 2000))
#  if (!defined(TARGET_OS_EMBEDDED) || (TARGET_OS_EMBEDDED==0)) \
       && (!defined(TARGET_IPHONE_SIMULATOR) || (TARGET_IPHONE_SIMULATOR==0))
#    define HAVE_GETHOSTUUID 1
#  else
#    warning "gethostuuid() is disabled."
#  endif
#endif


#if OS_VXWORKS
/* # include <sys/ioctl.h> */
# include <semaphore.h>
# include <limits.h>
#endif /* OS_VXWORKS */

#if defined(__APPLE__) || SQLITE_ENABLE_LOCKING_STYLE
# include <sys/mount.h>
#endif

#ifdef HAVE_UTIME
# include <utime.h>
#endif

/*
** Allowed values of unixFile.fsFlags
*/
#define SQLITE_FSFLAGS_IS_MSDOS     0x1

/*
** If we are to be thread-safe, include the pthreads header and define
** the SQLITE_UNIX_THREADS macro.
*/
#if SQLITE_THREADSAFE
/* # include <pthread.h> */
# define SQLITE_UNIX_THREADS 1
#endif

/*
** Default permissions when creating a new file
*/
#ifndef SQLITE_DEFAULT_FILE_PERMISSIONS
# define SQLITE_DEFAULT_FILE_PERMISSIONS 0644
#endif

/*
** Default permissions when creating auto proxy dir
*/
#ifndef SQLITE_DEFAULT_PROXYDIR_PERMISSIONS
# define SQLITE_DEFAULT_PROXYDIR_PERMISSIONS 0755
#endif

/*
** Maximum supported path-length.
*/
#define MAX_PATHNAME 512

/* Always cast the getpid() return type for compatibility with
** kernel modules in VxWorks. */
#define osGetpid(X) (pid_t)getpid()

/*
** Only set the lastErrno if the error code is a real error and not 
** a normal expected return code of SQLITE_BUSY or SQLITE_OK
*/
#define IS_LOCK_ERROR(x)  ((x != SQLITE_OK) && (x != SQLITE_BUSY))

/* Forward references */
typedef struct unixShm unixShm;               /* Connection shared memory */
typedef struct unixShmNode unixShmNode;       /* Shared memory instance */
typedef struct unixInodeInfo unixInodeInfo;   /* An i-node */
typedef struct UnixUnusedFd UnixUnusedFd;     /* An unused file descriptor */

/*
** Sometimes, after a file handle is closed by SQLite, the file descriptor
** cannot be closed immediately. In these cases, instances of the following
** structure are used to store the file descriptor while waiting for an
** opportunity to either close or reuse it.
*/
struct UnixUnusedFd {
  int fd;                   /* File descriptor to close */
  int flags;                /* Flags this file descriptor was opened with */
  UnixUnusedFd *pNext;      /* Next unused file descriptor on same file */
};

/*
** The unixFile structure is subclass of sqlite3_file specific to the unix
** VFS implementations.
*/
typedef struct unixFile unixFile;
struct unixFile {
  sqlite3_io_methods const *pMethod;  /* Always the first entry */
  sqlite3_vfs *pVfs;                  /* The VFS that created this unixFile */
  unixInodeInfo *pInode;              /* Info about locks on this inode */
  int h;                              /* The file descriptor */
  unsigned char eFileLock;            /* The type of lock held on this fd */
  unsigned short int ctrlFlags;       /* Behavioral bits.  UNIXFILE_* flags */
  int lastErrno;                      /* The unix errno from last I/O error */
  void *lockingContext;               /* Locking style specific state */
  UnixUnusedFd *pUnused;              /* Pre-allocated UnixUnusedFd */
  const char *zPath;                  /* Name of the file */
  unixShm *pShm;                      /* Shared memory segment information */
  int szChunk;                        /* Configured by FCNTL_CHUNK_SIZE */
#if SQLITE_MAX_MMAP_SIZE>0
  int nFetchOut;                      /* Number of outstanding xFetch refs */
  sqlite3_int64 mmapSize;             /* Usable size of mapping at pMapRegion */
  sqlite3_int64 mmapSizeActual;       /* Actual size of mapping at pMapRegion */
  sqlite3_int64 mmapSizeMax;          /* Configured FCNTL_MMAP_SIZE value */
  void *pMapRegion;                   /* Memory mapped region */
#endif
#ifdef __QNXNTO__
  int sectorSize;                     /* Device sector size */
  int deviceCharacteristics;          /* Precomputed device characteristics */
#endif
#if SQLITE_ENABLE_LOCKING_STYLE
  int openFlags;                      /* The flags specified at open() */
#endif
#if SQLITE_ENABLE_LOCKING_STYLE || defined(__APPLE__)
  unsigned fsFlags;                   /* cached details from statfs() */
#endif
#if OS_VXWORKS
  struct vxworksFileId *pId;          /* Unique file ID */
#endif
#ifdef SQLITE_DEBUG
  /* The next group of variables are used to track whether or not the
  ** transaction counter in bytes 24-27 of database files are updated
  ** whenever any part of the database changes.  An assertion fault will
  ** occur if a file is updated without also updating the transaction
  ** counter.  This test is made to avoid new problems similar to the
  ** one described by ticket #3584. 
  */
  unsigned char transCntrChng;   /* True if the transaction counter changed */
  unsigned char dbUpdate;        /* True if any part of database file changed */
  unsigned char inNormalWrite;   /* True if in a normal write operation */

#endif

#ifdef SQLITE_TEST
  /* In test mode, increase the size of this structure a bit so that 
  ** it is larger than the struct CrashFile defined in test6.c.
  */
  char aPadding[32];
#endif
};

/* This variable holds the process id (pid) from when the xRandomness()
** method was called.  If xOpen() is called from a different process id,
** indicating that a fork() has occurred, the PRNG will be reset.
*/
static pid_t randomnessPid = 0;

/*
** Allowed values for the unixFile.ctrlFlags bitmask:
*/
#define UNIXFILE_EXCL        0x01     /* Connections from one process only */
#define UNIXFILE_RDONLY      0x02     /* Connection is read only */
#define UNIXFILE_PERSIST_WAL 0x04     /* Persistent WAL mode */
#ifndef SQLITE_DISABLE_DIRSYNC
# define UNIXFILE_DIRSYNC    0x08     /* Directory sync needed */
#else
# define UNIXFILE_DIRSYNC    0x00
#endif
#define UNIXFILE_PSOW        0x10     /* SQLITE_IOCAP_POWERSAFE_OVERWRITE */
#define UNIXFILE_DELETE      0x20     /* Delete on close */
#define UNIXFILE_URI         0x40     /* Filename might have query parameters */
#define UNIXFILE_NOLOCK      0x80     /* Do no file locking */
#define UNIXFILE_WARNED    0x0100     /* verifyDbFile() warnings issued */
#define UNIXFILE_BLOCK     0x0200     /* Next SHM lock might block */

/*
** Include code that is common to all os_*.c files
*/
/************** Include os_common.h in the middle of os_unix.c ***************/
/************** Begin file os_common.h ***************************************/
/*
** 2004 May 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains macros and a little bit of code that is common to
** all of the platform-specific files (os_*.c) and is #included into those
** files.
**
** This file should be #included by the os_*.c files only.  It is not a
** general purpose header file.
*/
#ifndef _OS_COMMON_H_
#define _OS_COMMON_H_

/*
** At least two bugs have slipped in because we changed the MEMORY_DEBUG
** macro to SQLITE_DEBUG and some older makefiles have not yet made the
** switch.  The following code should catch this problem at compile-time.
*/
#ifdef MEMORY_DEBUG
# error "The MEMORY_DEBUG macro is obsolete.  Use SQLITE_DEBUG instead."
#endif

/*
** Macros for performance tracing.  Normally turned off.  Only works
** on i486 hardware.
*/
#ifdef SQLITE_PERFORMANCE_TRACE

/* 
** hwtime.h contains inline assembler code for implementing 
** high-performance timing routines.
*/
/* #include "hwtime.h" */

static sqlite_uint64 g_start;
static sqlite_uint64 g_elapsed;
#define TIMER_START       g_start=sqlite3Hwtime()
#define TIMER_END         g_elapsed=sqlite3Hwtime()-g_start
#define TIMER_ELAPSED     g_elapsed
#else
#define TIMER_START
#define TIMER_END
#define TIMER_ELAPSED     ((sqlite_uint64)0)
#endif

/*
** If we compile with the SQLITE_TEST macro set, then the following block
** of code will give us the ability to simulate a disk I/O error.  This
** is used for testing the I/O recovery logic.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_io_error_hit = 0;            /* Total number of I/O Errors */
SQLITE_PRIVATE int sqlite3_io_error_hardhit = 0;        /* Number of non-benign errors */
SQLITE_PRIVATE int sqlite3_io_error_pending = 0;        /* Count down to first I/O error */
SQLITE_PRIVATE int sqlite3_io_error_persist = 0;        /* True if I/O errors persist */
SQLITE_PRIVATE int sqlite3_io_error_benign = 0;         /* True if errors are benign */
SQLITE_PRIVATE int sqlite3_diskfull_pending = 0;
SQLITE_PRIVATE int sqlite3_diskfull = 0;
#define SimulateIOErrorBenign(X) sqlite3_io_error_benign=(X)
#define SimulateIOError(CODE)  \
  if( (sqlite3_io_error_persist && sqlite3_io_error_hit) \
       || sqlite3_io_error_pending-- == 1 )  \
              { local_ioerr(); CODE; }
static void local_ioerr(){
  IOTRACE(("IOERR\n"));
  sqlite3_io_error_hit++;
  if( !sqlite3_io_error_benign ) sqlite3_io_error_hardhit++;
}
#define SimulateDiskfullError(CODE) \
   if( sqlite3_diskfull_pending ){ \
     if( sqlite3_diskfull_pending == 1 ){ \
       local_ioerr(); \
       sqlite3_diskfull = 1; \
       sqlite3_io_error_hit = 1; \
       CODE; \
     }else{ \
       sqlite3_diskfull_pending--; \
     } \
   }
#else
#define SimulateIOErrorBenign(X)
#define SimulateIOError(A)
#define SimulateDiskfullError(A)
#endif

/*
** When testing, keep a count of the number of open files.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_open_file_count = 0;
#define OpenCounter(X)  sqlite3_open_file_count+=(X)
#else
#define OpenCounter(X)
#endif

#endif /* !defined(_OS_COMMON_H_) */

/************** End of os_common.h *******************************************/
/************** Continuing where we left off in os_unix.c ********************/

/*
** Define various macros that are missing from some systems.
*/
#ifndef O_LARGEFILE
# define O_LARGEFILE 0
#endif
#ifdef SQLITE_DISABLE_LFS
# undef O_LARGEFILE
# define O_LARGEFILE 0
#endif
#ifndef O_NOFOLLOW
# define O_NOFOLLOW 0
#endif
#ifndef O_BINARY
# define O_BINARY 0
#endif

/*
** The threadid macro resolves to the thread-id or to 0.  Used for
** testing and debugging only.
*/
#if SQLITE_THREADSAFE
#define threadid pthread_self()
#else
#define threadid 0
#endif

/*
** HAVE_MREMAP defaults to true on Linux and false everywhere else.
*/
#if !defined(HAVE_MREMAP)
# if defined(__linux__) && defined(_GNU_SOURCE)
#  define HAVE_MREMAP 1
# else
#  define HAVE_MREMAP 0
# endif
#endif

/*
** Explicitly call the 64-bit version of lseek() on Android. Otherwise, lseek()
** is the 32-bit version, even if _FILE_OFFSET_BITS=64 is defined.
*/
#ifdef __ANDROID__
# define lseek lseek64
#endif

/*
** Different Unix systems declare open() in different ways.  Same use
** open(const char*,int,mode_t).  Others use open(const char*,int,...).
** The difference is important when using a pointer to the function.
**
** The safest way to deal with the problem is to always use this wrapper
** which always has the same well-defined interface.
*/
static int posixOpen(const char *zFile, int flags, int mode){
  return open(zFile, flags, mode);
}

/*
** On some systems, calls to fchown() will trigger a message in a security
** log if they come from non-root processes.  So avoid calling fchown() if
** we are not running as root.
*/
static int posixFchown(int fd, uid_t uid, gid_t gid){
#if OS_VXWORKS
  return 0;
#else
  return geteuid() ? 0 : fchown(fd,uid,gid);
#endif
}

/* Forward reference */
static int openDirectory(const char*, int*);
static int unixGetpagesize(void);

/*
** Many system calls are accessed through pointer-to-functions so that
** they may be overridden at runtime to facilitate fault injection during
** testing and sandboxing.  The following array holds the names and pointers
** to all overrideable system calls.
*/
static struct unix_syscall {
  const char *zName;            /* Name of the system call */
  sqlite3_syscall_ptr pCurrent; /* Current value of the system call */
  sqlite3_syscall_ptr pDefault; /* Default value */
} aSyscall[] = {
  { "open",         (sqlite3_syscall_ptr)posixOpen,  0  },
#define osOpen      ((int(*)(const char*,int,int))aSyscall[0].pCurrent)

  { "close",        (sqlite3_syscall_ptr)close,      0  },
#define osClose     ((int(*)(int))aSyscall[1].pCurrent)

  { "access",       (sqlite3_syscall_ptr)access,     0  },
#define osAccess    ((int(*)(const char*,int))aSyscall[2].pCurrent)

  { "getcwd",       (sqlite3_syscall_ptr)getcwd,     0  },
#define osGetcwd    ((char*(*)(char*,size_t))aSyscall[3].pCurrent)

  { "stat",         (sqlite3_syscall_ptr)stat,       0  },
#define osStat      ((int(*)(const char*,struct stat*))aSyscall[4].pCurrent)

/*
** The DJGPP compiler environment looks mostly like Unix, but it
** lacks the fcntl() system call.  So redefine fcntl() to be something
** that always succeeds.  This means that locking does not occur under
** DJGPP.  But it is DOS - what did you expect?
*/
#ifdef __DJGPP__
  { "fstat",        0,                 0  },
#define osFstat(a,b,c)    0
#else     
  { "fstat",        (sqlite3_syscall_ptr)fstat,      0  },
#define osFstat     ((int(*)(int,struct stat*))aSyscall[5].pCurrent)
#endif

  { "ftruncate",    (sqlite3_syscall_ptr)ftruncate,  0  },
#define osFtruncate ((int(*)(int,off_t))aSyscall[6].pCurrent)

  { "fcntl",        (sqlite3_syscall_ptr)fcntl,      0  },
#define osFcntl     ((int(*)(int,int,...))aSyscall[7].pCurrent)

  { "read",         (sqlite3_syscall_ptr)read,       0  },
#define osRead      ((ssize_t(*)(int,void*,size_t))aSyscall[8].pCurrent)

#if defined(USE_PREAD) || SQLITE_ENABLE_LOCKING_STYLE
  { "pread",        (sqlite3_syscall_ptr)pread,      0  },
#else
  { "pread",        (sqlite3_syscall_ptr)0,          0  },
#endif
#define osPread     ((ssize_t(*)(int,void*,size_t,off_t))aSyscall[9].pCurrent)

#if defined(USE_PREAD64)
  { "pread64",      (sqlite3_syscall_ptr)pread64,    0  },
#else
  { "pread64",      (sqlite3_syscall_ptr)0,          0  },
#endif
#define osPread64   ((ssize_t(*)(int,void*,size_t,off_t))aSyscall[10].pCurrent)

  { "write",        (sqlite3_syscall_ptr)write,      0  },
#define osWrite     ((ssize_t(*)(int,const void*,size_t))aSyscall[11].pCurrent)

#if defined(USE_PREAD) || SQLITE_ENABLE_LOCKING_STYLE
  { "pwrite",       (sqlite3_syscall_ptr)pwrite,     0  },
#else
  { "pwrite",       (sqlite3_syscall_ptr)0,          0  },
#endif
#define osPwrite    ((ssize_t(*)(int,const void*,size_t,off_t))\
                    aSyscall[12].pCurrent)

#if defined(USE_PREAD64)
  { "pwrite64",     (sqlite3_syscall_ptr)pwrite64,   0  },
#else
  { "pwrite64",     (sqlite3_syscall_ptr)0,          0  },
#endif
#define osPwrite64  ((ssize_t(*)(int,const void*,size_t,off_t))\
                    aSyscall[13].pCurrent)

  { "fchmod",       (sqlite3_syscall_ptr)fchmod,     0  },
#define osFchmod    ((int(*)(int,mode_t))aSyscall[14].pCurrent)

#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
  { "fallocate",    (sqlite3_syscall_ptr)posix_fallocate,  0 },
#else
  { "fallocate",    (sqlite3_syscall_ptr)0,                0 },
#endif
#define osFallocate ((int(*)(int,off_t,off_t))aSyscall[15].pCurrent)

  { "unlink",       (sqlite3_syscall_ptr)unlink,           0 },
#define osUnlink    ((int(*)(const char*))aSyscall[16].pCurrent)

  { "openDirectory",    (sqlite3_syscall_ptr)openDirectory,      0 },
#define osOpenDirectory ((int(*)(const char*,int*))aSyscall[17].pCurrent)

  { "mkdir",        (sqlite3_syscall_ptr)mkdir,           0 },
#define osMkdir     ((int(*)(const char*,mode_t))aSyscall[18].pCurrent)

  { "rmdir",        (sqlite3_syscall_ptr)rmdir,           0 },
#define osRmdir     ((int(*)(const char*))aSyscall[19].pCurrent)

  { "fchown",       (sqlite3_syscall_ptr)posixFchown,     0 },
#define osFchown    ((int(*)(int,uid_t,gid_t))aSyscall[20].pCurrent)

#if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
  { "mmap",       (sqlite3_syscall_ptr)mmap,     0 },
#define osMmap ((void*(*)(void*,size_t,int,int,int,off_t))aSyscall[21].pCurrent)

  { "munmap",       (sqlite3_syscall_ptr)munmap,          0 },
#define osMunmap ((void*(*)(void*,size_t))aSyscall[22].pCurrent)

#if HAVE_MREMAP
  { "mremap",       (sqlite3_syscall_ptr)mremap,          0 },
#else
  { "mremap",       (sqlite3_syscall_ptr)0,               0 },
#endif
#define osMremap ((void*(*)(void*,size_t,size_t,int,...))aSyscall[23].pCurrent)
  { "getpagesize",  (sqlite3_syscall_ptr)unixGetpagesize, 0 },
#define osGetpagesize ((int(*)(void))aSyscall[24].pCurrent)

#endif

}; /* End of the overrideable system calls */

/*
** This is the xSetSystemCall() method of sqlite3_vfs for all of the
** "unix" VFSes.  Return SQLITE_OK opon successfully updating the
** system call pointer, or SQLITE_NOTFOUND if there is no configurable
** system call named zName.
*/
static int unixSetSystemCall(
  sqlite3_vfs *pNotUsed,        /* The VFS pointer.  Not used */
  const char *zName,            /* Name of system call to override */
  sqlite3_syscall_ptr pNewFunc  /* Pointer to new system call value */
){
  unsigned int i;
  int rc = SQLITE_NOTFOUND;

  UNUSED_PARAMETER(pNotUsed);
  if( zName==0 ){
    /* If no zName is given, restore all system calls to their default
    ** settings and return NULL
    */
    rc = SQLITE_OK;
    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
      if( aSyscall[i].pDefault ){
        aSyscall[i].pCurrent = aSyscall[i].pDefault;
      }
    }
  }else{
    /* If zName is specified, operate on only the one system call
    ** specified.
    */
    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
      if( strcmp(zName, aSyscall[i].zName)==0 ){
        if( aSyscall[i].pDefault==0 ){
          aSyscall[i].pDefault = aSyscall[i].pCurrent;
        }
        rc = SQLITE_OK;
        if( pNewFunc==0 ) pNewFunc = aSyscall[i].pDefault;
        aSyscall[i].pCurrent = pNewFunc;
        break;
      }
    }
  }
  return rc;
}

/*
** Return the value of a system call.  Return NULL if zName is not a
** recognized system call name.  NULL is also returned if the system call
** is currently undefined.
*/
static sqlite3_syscall_ptr unixGetSystemCall(
  sqlite3_vfs *pNotUsed,
  const char *zName
){
  unsigned int i;

  UNUSED_PARAMETER(pNotUsed);
  for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
    if( strcmp(zName, aSyscall[i].zName)==0 ) return aSyscall[i].pCurrent;
  }
  return 0;
}

/*
** Return the name of the first system call after zName.  If zName==NULL
** then return the name of the first system call.  Return NULL if zName
** is the last system call or if zName is not the name of a valid
** system call.
*/
static const char *unixNextSystemCall(sqlite3_vfs *p, const char *zName){
  int i = -1;

  UNUSED_PARAMETER(p);
  if( zName ){
    for(i=0; i<ArraySize(aSyscall)-1; i++){
      if( strcmp(zName, aSyscall[i].zName)==0 ) break;
    }
  }
  for(i++; i<ArraySize(aSyscall); i++){
    if( aSyscall[i].pCurrent!=0 ) return aSyscall[i].zName;
  }
  return 0;
}

/*
** Do not accept any file descriptor less than this value, in order to avoid
** opening database file using file descriptors that are commonly used for 
** standard input, output, and error.
*/
#ifndef SQLITE_MINIMUM_FILE_DESCRIPTOR
# define SQLITE_MINIMUM_FILE_DESCRIPTOR 3
#endif

/*
** Invoke open().  Do so multiple times, until it either succeeds or
** fails for some reason other than EINTR.
**
** If the file creation mode "m" is 0 then set it to the default for
** SQLite.  The default is SQLITE_DEFAULT_FILE_PERMISSIONS (normally
** 0644) as modified by the system umask.  If m is not 0, then
** make the file creation mode be exactly m ignoring the umask.
**
** The m parameter will be non-zero only when creating -wal, -journal,
** and -shm files.  We want those files to have *exactly* the same
** permissions as their original database, unadulterated by the umask.
** In that way, if a database file is -rw-rw-rw or -rw-rw-r-, and a
** transaction crashes and leaves behind hot journals, then any
** process that is able to write to the database will also be able to
** recover the hot journals.
*/
static int robust_open(const char *z, int f, mode_t m){
  int fd;
  mode_t m2 = m ? m : SQLITE_DEFAULT_FILE_PERMISSIONS;
  while(1){
#if defined(O_CLOEXEC)
    fd = osOpen(z,f|O_CLOEXEC,m2);
#else
    fd = osOpen(z,f,m2);
#endif
    if( fd<0 ){
      if( errno==EINTR ) continue;
      break;
    }
    if( fd>=SQLITE_MINIMUM_FILE_DESCRIPTOR ) break;
    osClose(fd);
//    sqlite3_log(SQLITE_WARNING, 
//                "attempt to open \"%s\" as file descriptor %d", z, fd);
    fd = -1;
    if( osOpen("/dev/null", f, m)<0 ) break;
  }
  if( fd>=0 ){
    if( m!=0 ){
      struct stat statbuf;
      if( osFstat(fd, &statbuf)==0 
       && statbuf.st_size==0
       && (statbuf.st_mode&0777)!=m 
      ){
        osFchmod(fd, m);
      }
    }
#if defined(FD_CLOEXEC) && (!defined(O_CLOEXEC) || O_CLOEXEC==0)
    osFcntl(fd, F_SETFD, osFcntl(fd, F_GETFD, 0) | FD_CLOEXEC);
#endif
  }
  return fd;
}

/*
** Helper functions to obtain and relinquish the global mutex. The
** global mutex is used to protect the unixInodeInfo and
** vxworksFileId objects used by this file, all of which may be 
** shared by multiple threads.
**
** Function unixMutexHeld() is used to assert() that the global mutex 
** is held when required. This function is only used as part of assert() 
** statements. e.g.
**
**   unixEnterMutex()
**     assert( unixMutexHeld() );
**   unixEnterLeave()
*/
static void unixEnterMutex(void){
  sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}
static void unixLeaveMutex(void){
  sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}

#ifndef NDEBUG
static int unixMutexHeld(void) {
  return sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}
#endif



#ifdef SQLITE_HAVE_OS_TRACE
/*
** Helper function for printing out trace information from debugging
** binaries. This returns the string representation of the supplied
** integer lock-type.
*/
static const char *azFileLock(int eFileLock){
  switch( eFileLock ){
    case NO_LOCK: return "NONE";
    case SHARED_LOCK: return "SHARED";
    case RESERVED_LOCK: return "RESERVED";
    case PENDING_LOCK: return "PENDING";
    case EXCLUSIVE_LOCK: return "EXCLUSIVE";
  }
  return "ERROR";
}
#endif

#ifdef SQLITE_LOCK_TRACE
/*
** Print out information about all locking operations.
**
** This routine is used for troubleshooting locks on multithreaded
** platforms.  Enable by compiling with the -DSQLITE_LOCK_TRACE
** command-line option on the compiler.  This code is normally
** turned off.
*/
static int lockTrace(int fd, int op, struct flock *p){
  char *zOpName, *zType;
  int s;
  int savedErrno;
  if( op==F_GETLK ){
    zOpName = "GETLK";
  }else if( op==F_SETLK ){
    zOpName = "SETLK";
  }else{
    s = osFcntl(fd, op, p);
    sqlite3DebugPrintf("fcntl unknown %d %d %d\n", fd, op, s);
    return s;
  }
  if( p->l_type==F_RDLCK ){
    zType = "RDLCK";
  }else if( p->l_type==F_WRLCK ){
    zType = "WRLCK";
  }else if( p->l_type==F_UNLCK ){
    zType = "UNLCK";
  }else{
    assert( 0 );
  }
  assert( p->l_whence==SEEK_SET );
  s = osFcntl(fd, op, p);
  savedErrno = errno;
  sqlite3DebugPrintf("fcntl %d %d %s %s %d %d %d %d\n",
     threadid, fd, zOpName, zType, (int)p->l_start, (int)p->l_len,
     (int)p->l_pid, s);
  if( s==(-1) && op==F_SETLK && (p->l_type==F_RDLCK || p->l_type==F_WRLCK) ){
    struct flock l2;
    l2 = *p;
    osFcntl(fd, F_GETLK, &l2);
    if( l2.l_type==F_RDLCK ){
      zType = "RDLCK";
    }else if( l2.l_type==F_WRLCK ){
      zType = "WRLCK";
    }else if( l2.l_type==F_UNLCK ){
      zType = "UNLCK";
    }else{
      assert( 0 );
    }
    sqlite3DebugPrintf("fcntl-failure-reason: %s %d %d %d\n",
       zType, (int)l2.l_start, (int)l2.l_len, (int)l2.l_pid);
  }
  errno = savedErrno;
  return s;
}
#undef osFcntl
#define osFcntl lockTrace
#endif /* SQLITE_LOCK_TRACE */

/*
** Retry ftruncate() calls that fail due to EINTR
**
** All calls to ftruncate() within this file should be made through
** this wrapper.  On the Android platform, bypassing the logic below
** could lead to a corrupt database.
*/
static int robust_ftruncate(int h, sqlite3_int64 sz){
  int rc;
#ifdef __ANDROID__
  /* On Android, ftruncate() always uses 32-bit offsets, even if 
  ** _FILE_OFFSET_BITS=64 is defined. This means it is unsafe to attempt to
  ** truncate a file to any size larger than 2GiB. Silently ignore any
  ** such attempts.  */
  if( sz>(sqlite3_int64)0x7FFFFFFF ){
    rc = SQLITE_OK;
  }else
#endif
  do{ rc = osFtruncate(h,sz); }while( rc<0 && errno==EINTR );
  return rc;
}

/*
** This routine translates a standard POSIX errno code into something
** useful to the clients of the sqlite3 functions.  Specifically, it is
** intended to translate a variety of "try again" errors into SQLITE_BUSY
** and a variety of "please close the file descriptor NOW" errors into 
** SQLITE_IOERR
** 
** Errors during initialization of locks, or file system support for locks,
** should handle ENOLCK, ENOTSUP, EOPNOTSUPP separately.
*/
static int sqliteErrorFromPosixError(int posixError, int sqliteIOErr) {
  switch (posixError) {
#if 0
  /* At one point this code was not commented out. In theory, this branch
  ** should never be hit, as this function should only be called after
  ** a locking-related function (i.e. fcntl()) has returned non-zero with
  ** the value of errno as the first argument. Since a system call has failed,
  ** errno should be non-zero.
  **
  ** Despite this, if errno really is zero, we still don't want to return
  ** SQLITE_OK. The system call failed, and *some* SQLite error should be
  ** propagated back to the caller. Commenting this branch out means errno==0
  ** will be handled by the "default:" case below.
  */
  case 0: 
    return SQLITE_OK;
#endif

  case EAGAIN:
  case ETIMEDOUT:
  case EBUSY:
  case EINTR:
  case ENOLCK:  
    /* random NFS retry error, unless during file system support 
     * introspection, in which it actually means what it says */
    return SQLITE_BUSY;
    
  case EACCES: 
    /* EACCES is like EAGAIN during locking operations, but not any other time*/
    if( (sqliteIOErr == SQLITE_IOERR_LOCK) || 
        (sqliteIOErr == SQLITE_IOERR_UNLOCK) || 
        (sqliteIOErr == SQLITE_IOERR_RDLOCK) ||
        (sqliteIOErr == SQLITE_IOERR_CHECKRESERVEDLOCK) ){
      return SQLITE_BUSY;
    }
    /* else fall through */
  case EPERM: 
    return SQLITE_PERM;
    
#if EOPNOTSUPP!=ENOTSUP
  case EOPNOTSUPP: 
    /* something went terribly awry, unless during file system support 
     * introspection, in which it actually means what it says */
#endif
#ifdef ENOTSUP
  case ENOTSUP: 
    /* invalid fd, unless during file system support introspection, in which 
     * it actually means what it says */
#endif
  case EIO:
  case EBADF:
  case EINVAL:
  case ENOTCONN:
  case ENODEV:
  case ENXIO:
  case ENOENT:
#ifdef ESTALE                     /* ESTALE is not defined on Interix systems */
  case ESTALE:
#endif
  case ENOSYS:
    /* these should force the client to close the file and reconnect */
    
  default: 
    return sqliteIOErr;
  }
}


/******************************************************************************
****************** Begin Unique File ID Utility Used By VxWorks ***************
**
** On most versions of unix, we can get a unique ID for a file by concatenating
** the device number and the inode number.  But this does not work on VxWorks.
** On VxWorks, a unique file id must be based on the canonical filename.
**
** A pointer to an instance of the following structure can be used as a
** unique file ID in VxWorks.  Each instance of this structure contains
** a copy of the canonical filename.  There is also a reference count.  
** The structure is reclaimed when the number of pointers to it drops to
** zero.
**
** There are never very many files open at one time and lookups are not
** a performance-critical path, so it is sufficient to put these
** structures on a linked list.
*/
struct vxworksFileId {
  struct vxworksFileId *pNext;  /* Next in a list of them all */
  int nRef;                     /* Number of references to this one */
  int nName;                    /* Length of the zCanonicalName[] string */
  char *zCanonicalName;         /* Canonical filename */
};

#if OS_VXWORKS
/* 
** All unique filenames are held on a linked list headed by this
** variable:
*/
static struct vxworksFileId *vxworksFileList = 0;

/*
** Simplify a filename into its canonical form
** by making the following changes:
**
**  * removing any trailing and duplicate /
**  * convert /./ into just /
**  * convert /A/../ where A is any simple name into just /
**
** Changes are made in-place.  Return the new name length.
**
** The original filename is in z[0..n-1].  Return the number of
** characters in the simplified name.
*/
static int vxworksSimplifyName(char *z, int n){
  int i, j;
  while( n>1 && z[n-1]=='/' ){ n--; }
  for(i=j=0; i<n; i++){
    if( z[i]=='/' ){
      if( z[i+1]=='/' ) continue;
      if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
        i += 1;
        continue;
      }
      if( z[i+1]=='.' && i+3<n && z[i+2]=='.' && z[i+3]=='/' ){
        while( j>0 && z[j-1]!='/' ){ j--; }
        if( j>0 ){ j--; }
        i += 2;
        continue;
      }
    }
    z[j++] = z[i];
  }
  z[j] = 0;
  return j;
}

/*
** Find a unique file ID for the given absolute pathname.  Return
** a pointer to the vxworksFileId object.  This pointer is the unique
** file ID.
**
** The nRef field of the vxworksFileId object is incremented before
** the object is returned.  A new vxworksFileId object is created
** and added to the global list if necessary.
**
** If a memory allocation error occurs, return NULL.
*/
static struct vxworksFileId *vxworksFindFileId(const char *zAbsoluteName){
  struct vxworksFileId *pNew;         /* search key and new file ID */
  struct vxworksFileId *pCandidate;   /* For looping over existing file IDs */
  int n;                              /* Length of zAbsoluteName string */

  assert( zAbsoluteName[0]=='/' );
  n = (int)strlen(zAbsoluteName);
  pNew = sqlite3_malloc64( sizeof(*pNew) + (n+1) );
  if( pNew==0 ) return 0;
  pNew->zCanonicalName = (char*)&pNew[1];
  memcpy(pNew->zCanonicalName, zAbsoluteName, n+1);
  n = vxworksSimplifyName(pNew->zCanonicalName, n);

  /* Search for an existing entry that matching the canonical name.
  ** If found, increment the reference count and return a pointer to
  ** the existing file ID.
  */
  unixEnterMutex();
  for(pCandidate=vxworksFileList; pCandidate; pCandidate=pCandidate->pNext){
    if( pCandidate->nName==n 
     && memcmp(pCandidate->zCanonicalName, pNew->zCanonicalName, n)==0
    ){
       sqlite3_free(pNew);
       pCandidate->nRef++;
       unixLeaveMutex();
       return pCandidate;
    }
  }

  /* No match was found.  We will make a new file ID */
  pNew->nRef = 1;
  pNew->nName = n;
  pNew->pNext = vxworksFileList;
  vxworksFileList = pNew;
  unixLeaveMutex();
  return pNew;
}

/*
** Decrement the reference count on a vxworksFileId object.  Free
** the object when the reference count reaches zero.
*/
static void vxworksReleaseFileId(struct vxworksFileId *pId){
  unixEnterMutex();
  assert( pId->nRef>0 );
  pId->nRef--;
  if( pId->nRef==0 ){
    struct vxworksFileId **pp;
    for(pp=&vxworksFileList; *pp && *pp!=pId; pp = &((*pp)->pNext)){}
    assert( *pp==pId );
    *pp = pId->pNext;
    sqlite3_free(pId);
  }
  unixLeaveMutex();
}
#endif /* OS_VXWORKS */
/*************** End of Unique File ID Utility Used By VxWorks ****************
******************************************************************************/


/******************************************************************************
*************************** Posix Advisory Locking ****************************
**
** POSIX advisory locks are broken by design.  ANSI STD 1003.1 (1996)
** section 6.5.2.2 lines 483 through 490 specify that when a process
** sets or clears a lock, that operation overrides any prior locks set
** by the same process.  It does not explicitly say so, but this implies
** that it overrides locks set by the same process using a different
** file descriptor.  Consider this test case:
**
**       int fd1 = open("./file1", O_RDWR|O_CREAT, 0644);
**       int fd2 = open("./file2", O_RDWR|O_CREAT, 0644);
**
** Suppose ./file1 and ./file2 are really the same file (because
** one is a hard or symbolic link to the other) then if you set
** an exclusive lock on fd1, then try to get an exclusive lock
** on fd2, it works.  I would have expected the second lock to
** fail since there was already a lock on the file due to fd1.
** But not so.  Since both locks came from the same process, the
** second overrides the first, even though they were on different
** file descriptors opened on different file names.
**
** This means that we cannot use POSIX locks to synchronize file access
** among competing threads of the same process.  POSIX locks will work fine
** to synchronize access for threads in separate processes, but not
** threads within the same process.
**
** To work around the problem, SQLite has to manage file locks internally
** on its own.  Whenever a new database is opened, we have to find the
** specific inode of the database file (the inode is determined by the
** st_dev and st_ino fields of the stat structure that fstat() fills in)
** and check for locks already existing on that inode.  When locks are
** created or removed, we have to look at our own internal record of the
** locks to see if another thread has previously set a lock on that same
** inode.
**
** (Aside: The use of inode numbers as unique IDs does not work on VxWorks.
** For VxWorks, we have to use the alternative unique ID system based on
** canonical filename and implemented in the previous division.)
**
** The sqlite3_file structure for POSIX is no longer just an integer file
** descriptor.  It is now a structure that holds the integer file
** descriptor and a pointer to a structure that describes the internal
** locks on the corresponding inode.  There is one locking structure
** per inode, so if the same inode is opened twice, both unixFile structures
** point to the same locking structure.  The locking structure keeps
** a reference count (so we will know when to delete it) and a "cnt"
** field that tells us its internal lock status.  cnt==0 means the
** file is unlocked.  cnt==-1 means the file has an exclusive lock.
** cnt>0 means there are cnt shared locks on the file.
**
** Any attempt to lock or unlock a file first checks the locking
** structure.  The fcntl() system call is only invoked to set a 
** POSIX lock if the internal lock structure transitions between
** a locked and an unlocked state.
**
** But wait:  there are yet more problems with POSIX advisory locks.
**
** If you close a file descriptor that points to a file that has locks,
** all locks on that file that are owned by the current process are
** released.  To work around this problem, each unixInodeInfo object
** maintains a count of the number of pending locks on tha inode.
** When an attempt is made to close an unixFile, if there are
** other unixFile open on the same inode that are holding locks, the call
** to close() the file descriptor is deferred until all of the locks clear.
** The unixInodeInfo structure keeps a list of file descriptors that need to
** be closed and that list is walked (and cleared) when the last lock
** clears.
**
** Yet another problem:  LinuxThreads do not play well with posix locks.
**
** Many older versions of linux use the LinuxThreads library which is
** not posix compliant.  Under LinuxThreads, a lock created by thread
** A cannot be modified or overridden by a different thread B.
** Only thread A can modify the lock.  Locking behavior is correct
** if the appliation uses the newer Native Posix Thread Library (NPTL)
** on linux - with NPTL a lock created by thread A can override locks
** in thread B.  But there is no way to know at compile-time which
** threading library is being used.  So there is no way to know at
** compile-time whether or not thread A can override locks on thread B.
** One has to do a run-time check to discover the behavior of the
** current process.
**
** SQLite used to support LinuxThreads.  But support for LinuxThreads
** was dropped beginning with version 3.7.0.  SQLite will still work with
** LinuxThreads provided that (1) there is no more than one connection 
** per database file in the same process and (2) database connections
** do not move across threads.
*/

/*
** An instance of the following structure serves as the key used
** to locate a particular unixInodeInfo object.
*/
struct unixFileId {
  dev_t dev;                  /* Device number */
#if OS_VXWORKS
  struct vxworksFileId *pId;  /* Unique file ID for vxworks. */
#else
  ino_t ino;                  /* Inode number */
#endif
};

/*
** An instance of the following structure is allocated for each open
** inode.  Or, on LinuxThreads, there is one of these structures for
** each inode opened by each thread.
**
** A single inode can have multiple file descriptors, so each unixFile
** structure contains a pointer to an instance of this object and this
** object keeps a count of the number of unixFile pointing to it.
*/
struct unixInodeInfo {
  struct unixFileId fileId;       /* The lookup key */
  int nShared;                    /* Number of SHARED locks held */
  unsigned char eFileLock;        /* One of SHARED_LOCK, RESERVED_LOCK etc. */
  unsigned char bProcessLock;     /* An exclusive process lock is held */
  int nRef;                       /* Number of pointers to this structure */
  unixShmNode *pShmNode;          /* Shared memory associated with this inode */
  int nLock;                      /* Number of outstanding file locks */
  UnixUnusedFd *pUnused;          /* Unused file descriptors to close */
  unixInodeInfo *pNext;           /* List of all unixInodeInfo objects */
  unixInodeInfo *pPrev;           /*    .... doubly linked */
#if SQLITE_ENABLE_LOCKING_STYLE
  unsigned long long sharedByte;  /* for AFP simulated shared lock */
#endif
#if OS_VXWORKS
  sem_t *pSem;                    /* Named POSIX semaphore */
  char aSemName[MAX_PATHNAME+2];  /* Name of that semaphore */
#endif
};

/*
** A lists of all unixInodeInfo objects.
*/
static unixInodeInfo *inodeList = 0;

/*
**
** This function - unixLogError_x(), is only ever called via the macro
** unixLogError().
**
** It is invoked after an error occurs in an OS function and errno has been
** set. It logs a message using sqlite3_log() containing the current value of
** errno and, if possible, the human-readable equivalent from strerror() or
** strerror_r().
**
** The first argument passed to the macro should be the error code that
** will be returned to SQLite (e.g. SQLITE_IOERR_DELETE, SQLITE_CANTOPEN). 
** The two subsequent arguments should be the name of the OS function that
** failed (e.g. "unlink", "open") and the associated file-system path,
** if any.
*/
#define unixLogError(a,b,c)     unixLogErrorAtLine(a,b,c,__LINE__)
static int unixLogErrorAtLine(
  int errcode,                    /* SQLite error code */
  const char *zFunc,              /* Name of OS function that failed */
  const char *zPath,              /* File path associated with error */
  int iLine                       /* Source line number where error occurred */
){
  char *zErr;                     /* Message from strerror() or equivalent */
  int iErrno = errno;             /* Saved syscall error number */

  /* If this is not a threadsafe build (SQLITE_THREADSAFE==0), then use
  ** the strerror() function to obtain the human-readable error message
  ** equivalent to errno. Otherwise, use strerror_r().
  */ 
#if SQLITE_THREADSAFE && defined(HAVE_STRERROR_R)
  char aErr[80];
  memset(aErr, 0, sizeof(aErr));
  zErr = aErr;

  /* If STRERROR_R_CHAR_P (set by autoconf scripts) or __USE_GNU is defined,
  ** assume that the system provides the GNU version of strerror_r() that
  ** returns a pointer to a buffer containing the error message. That pointer 
  ** may point to aErr[], or it may point to some static storage somewhere. 
  ** Otherwise, assume that the system provides the POSIX version of 
  ** strerror_r(), which always writes an error message into aErr[].
  **
  ** If the code incorrectly assumes that it is the POSIX version that is
  ** available, the error message will often be an empty string. Not a
  ** huge problem. Incorrectly concluding that the GNU version is available 
  ** could lead to a segfault though.
  */
#if defined(STRERROR_R_CHAR_P) || defined(__USE_GNU)
  zErr = 
# endif
  strerror_r(iErrno, aErr, sizeof(aErr)-1);

#elif SQLITE_THREADSAFE
  /* This is a threadsafe build, but strerror_r() is not available. */
  zErr = "";
#else
  /* Non-threadsafe build, use strerror(). */
  zErr = strerror(iErrno);
#endif

  if( zPath==0 ) zPath = "";
  sqlite3_log(errcode,
      "os_unix.c:%d: (%d) %s(%s) - %s",
      iLine, iErrno, zFunc, zPath, zErr
  );

  return errcode;
}

/*
** Close a file descriptor.
**
** We assume that close() almost always works, since it is only in a
** very sick application or on a very sick platform that it might fail.
** If it does fail, simply leak the file descriptor, but do log the
** error.
**
** Note that it is not safe to retry close() after EINTR since the
** file descriptor might have already been reused by another thread.
** So we don't even try to recover from an EINTR.  Just log the error
** and move on.
*/
static void robust_close(unixFile *pFile, int h, int lineno){
  if( osClose(h) ){
    unixLogErrorAtLine(SQLITE_IOERR_CLOSE, "close",
                       pFile ? pFile->zPath : 0, lineno);
  }
}

/*
** Set the pFile->lastErrno.  Do this in a subroutine as that provides
** a convenient place to set a breakpoint.
*/
static void storeLastErrno(unixFile *pFile, int error){
  pFile->lastErrno = error;
}

/*
** Close all file descriptors accumuated in the unixInodeInfo->pUnused list.
*/ 
static void closePendingFds(unixFile *pFile){
  unixInodeInfo *pInode = pFile->pInode;
  UnixUnusedFd *p;
  UnixUnusedFd *pNext;
  for(p=pInode->pUnused; p; p=pNext){
    pNext = p->pNext;
    robust_close(pFile, p->fd, __LINE__);
    sqlite3_free(p);
  }
  pInode->pUnused = 0;
}

/*
** Release a unixInodeInfo structure previously allocated by findInodeInfo().
**
** The mutex entered using the unixEnterMutex() function must be held
** when this function is called.
*/
static void releaseInodeInfo(unixFile *pFile){
  unixInodeInfo *pInode = pFile->pInode;
  assert( unixMutexHeld() );
  if( ALWAYS(pInode) ){
    pInode->nRef--;
    if( pInode->nRef==0 ){
      assert( pInode->pShmNode==0 );
      closePendingFds(pFile);
      if( pInode->pPrev ){
        assert( pInode->pPrev->pNext==pInode );
        pInode->pPrev->pNext = pInode->pNext;
      }else{
        assert( inodeList==pInode );
        inodeList = pInode->pNext;
      }
      if( pInode->pNext ){
        assert( pInode->pNext->pPrev==pInode );
        pInode->pNext->pPrev = pInode->pPrev;
      }
      sqlite3_free(pInode);
    }
  }
}

/*
** Given a file descriptor, locate the unixInodeInfo object that
** describes that file descriptor.  Create a new one if necessary.  The
** return value might be uninitialized if an error occurs.
**
** The mutex entered using the unixEnterMutex() function must be held
** when this function is called.
**
** Return an appropriate error code.
*/
static int findInodeInfo(
  unixFile *pFile,               /* Unix file with file desc used in the key */
  unixInodeInfo **ppInode        /* Return the unixInodeInfo object here */
){
  int rc;                        /* System call return code */
  int fd;                        /* The file descriptor for pFile */
  struct unixFileId fileId;      /* Lookup key for the unixInodeInfo */
  struct stat statbuf;           /* Low-level file information */
  unixInodeInfo *pInode = 0;     /* Candidate unixInodeInfo object */

  assert( unixMutexHeld() );

  /* Get low-level information about the file that we can used to
  ** create a unique name for the file.
  */
  fd = pFile->h;
  rc = osFstat(fd, &statbuf);
  if( rc!=0 ){
    storeLastErrno(pFile, errno);
#ifdef EOVERFLOW
    if( pFile->lastErrno==EOVERFLOW ) return SQLITE_NOLFS;
#endif
    return SQLITE_IOERR;
  }

#ifdef __APPLE__
  /* On OS X on an msdos filesystem, the inode number is reported
  ** incorrectly for zero-size files.  See ticket #3260.  To work
  ** around this problem (we consider it a bug in OS X, not SQLite)
  ** we always increase the file size to 1 by writing a single byte
  ** prior to accessing the inode number.  The one byte written is
  ** an ASCII 'S' character which also happens to be the first byte
  ** in the header of every SQLite database.  In this way, if there
  ** is a race condition such that another thread has already populated
  ** the first page of the database, no damage is done.
  */
  if( statbuf.st_size==0 && (pFile->fsFlags & SQLITE_FSFLAGS_IS_MSDOS)!=0 ){
    do{ rc = osWrite(fd, "S", 1); }while( rc<0 && errno==EINTR );
    if( rc!=1 ){
      storeLastErrno(pFile, errno);
      return SQLITE_IOERR;
    }
    rc = osFstat(fd, &statbuf);
    if( rc!=0 ){
      storeLastErrno(pFile, errno);
      return SQLITE_IOERR;
    }
  }
#endif

  memset(&fileId, 0, sizeof(fileId));
  fileId.dev = statbuf.st_dev;
#if OS_VXWORKS
  fileId.pId = pFile->pId;
#else
  fileId.ino = statbuf.st_ino;
#endif
  pInode = inodeList;
  while( pInode && memcmp(&fileId, &pInode->fileId, sizeof(fileId)) ){
    pInode = pInode->pNext;
  }
  if( pInode==0 ){
    pInode = sqlite3_malloc64( sizeof(*pInode) );
    if( pInode==0 ){
      return SQLITE_NOMEM;
    }
    memset(pInode, 0, sizeof(*pInode));
    memcpy(&pInode->fileId, &fileId, sizeof(fileId));
    pInode->nRef = 1;
    pInode->pNext = inodeList;
    pInode->pPrev = 0;
    if( inodeList ) inodeList->pPrev = pInode;
    inodeList = pInode;
  }else{
    pInode->nRef++;
  }
  *ppInode = pInode;
  return SQLITE_OK;
}

/*
** Return TRUE if pFile has been renamed or unlinked since it was first opened.
*/
static int fileHasMoved(unixFile *pFile){
#if OS_VXWORKS
  return pFile->pInode!=0 && pFile->pId!=pFile->pInode->fileId.pId;
#else
  struct stat buf;
  return pFile->pInode!=0 &&
      (osStat(pFile->zPath, &buf)!=0 || buf.st_ino!=pFile->pInode->fileId.ino);
#endif
}


/*
** Check a unixFile that is a database.  Verify the following:
**
** (1) There is exactly one hard link on the file
** (2) The file is not a symbolic link
** (3) The file has not been renamed or unlinked
**
** Issue sqlite3_log(SQLITE_WARNING,...) messages if anything is not right.
*/
static void verifyDbFile(unixFile *pFile){
  struct stat buf;
  int rc;
  if( pFile->ctrlFlags & UNIXFILE_WARNED ){
    /* One or more of the following warnings have already been issued.  Do not
    ** repeat them so as not to clutter the error log */
    return;
  }
  rc = osFstat(pFile->h, &buf);
  if( rc!=0 ){
//    sqlite3_log(SQLITE_WARNING, "cannot fstat db file %s", pFile->zPath);
    pFile->ctrlFlags |= UNIXFILE_WARNED;
    return;
  }
  if( buf.st_nlink==0 && (pFile->ctrlFlags & UNIXFILE_DELETE)==0 ){
//    sqlite3_log(SQLITE_WARNING, "file unlinked while open: %s", pFile->zPath);
    pFile->ctrlFlags |= UNIXFILE_WARNED;
    return;
  }
  if( buf.st_nlink>1 ){
//    sqlite3_log(SQLITE_WARNING, "multiple links to file: %s", pFile->zPath);
    pFile->ctrlFlags |= UNIXFILE_WARNED;
    return;
  }
  if( fileHasMoved(pFile) ){
//    sqlite3_log(SQLITE_WARNING, "file renamed while open: %s", pFile->zPath);
    pFile->ctrlFlags |= UNIXFILE_WARNED;
    return;
  }
}


/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
*/
static int unixCheckReservedLock(sqlite3_file *id, int *pResOut){
  int rc = SQLITE_OK;
  int reserved = 0;
  unixFile *pFile = (unixFile*)id;

  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );

  assert( pFile );
  unixEnterMutex(); /* Because pFile->pInode is shared across threads */

  /* Check if a thread in this process holds such a lock */
  if( pFile->pInode->eFileLock>SHARED_LOCK ){
    reserved = 1;
  }

  /* Otherwise see if some other process holds it.
  */
#ifndef __DJGPP__
  if( !reserved && !pFile->pInode->bProcessLock ){
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = RESERVED_BYTE;
    lock.l_len = 1;
    lock.l_type = F_WRLCK;
    if( osFcntl(pFile->h, F_GETLK, &lock) ){
      rc = SQLITE_IOERR_CHECKRESERVEDLOCK;
      storeLastErrno(pFile, errno);
    } else if( lock.l_type!=F_UNLCK ){
      reserved = 1;
    }
  }
#endif
  
  unixLeaveMutex();
  OSTRACE(("TEST WR-LOCK %d %d %d (unix)\n", pFile->h, rc, reserved));

  *pResOut = reserved;
  return rc;
}

/*
** Attempt to set a system-lock on the file pFile.  The lock is 
** described by pLock.
**
** If the pFile was opened read/write from unix-excl, then the only lock
** ever obtained is an exclusive lock, and it is obtained exactly once
** the first time any lock is attempted.  All subsequent system locking
** operations become no-ops.  Locking operations still happen internally,
** in order to coordinate access between separate database connections
** within this process, but all of that is handled in memory and the
** operating system does not participate.
**
** This function is a pass-through to fcntl(F_SETLK) if pFile is using
** any VFS other than "unix-excl" or if pFile is opened on "unix-excl"
** and is read-only.
**
** Zero is returned if the call completes successfully, or -1 if a call
** to fcntl() fails. In this case, errno is set appropriately (by fcntl()).
*/
static int unixFileLock(unixFile *pFile, struct flock *pLock){
  int rc;
  unixInodeInfo *pInode = pFile->pInode;
  assert( unixMutexHeld() );
  assert( pInode!=0 );
  if( ((pFile->ctrlFlags & UNIXFILE_EXCL)!=0 || pInode->bProcessLock)
   && ((pFile->ctrlFlags & UNIXFILE_RDONLY)==0)
  ){
    if( pInode->bProcessLock==0 ){
      struct flock lock;
      assert( pInode->nLock==0 );
      lock.l_whence = SEEK_SET;
      lock.l_start = SHARED_FIRST;
      lock.l_len = SHARED_SIZE;
      lock.l_type = F_WRLCK;
      rc = osFcntl(pFile->h, F_SETLK, &lock);
      if( rc<0 ) return rc;
      pInode->bProcessLock = 1;
      pInode->nLock++;
    }else{
      rc = 0;
    }
  }else{
    rc = osFcntl(pFile->h, F_SETLK, pLock);
  }
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
*/
static int unixLock(sqlite3_file *id, int eFileLock){
  /* The following describes the implementation of the various locks and
  ** lock transitions in terms of the POSIX advisory shared and exclusive
  ** lock primitives (called read-locks and write-locks below, to avoid
  ** confusion with SQLite lock names). The algorithms are complicated
  ** slightly in order to be compatible with windows systems simultaneously
  ** accessing the same database file, in case that is ever required.
  **
  ** Symbols defined in os.h indentify the 'pending byte' and the 'reserved
  ** byte', each single bytes at well known offsets, and the 'shared byte
  ** range', a range of 510 bytes at a well known offset.
  **
  ** To obtain a SHARED lock, a read-lock is obtained on the 'pending
  ** byte'.  If this is successful, a random byte from the 'shared byte
  ** range' is read-locked and the lock on the 'pending byte' released.
  **
  ** A process may only obtain a RESERVED lock after it has a SHARED lock.
  ** A RESERVED lock is implemented by grabbing a write-lock on the
  ** 'reserved byte'. 
  **
  ** A process may only obtain a PENDING lock after it has obtained a
  ** SHARED lock. A PENDING lock is implemented by obtaining a write-lock
  ** on the 'pending byte'. This ensures that no new SHARED locks can be
  ** obtained, but existing SHARED locks are allowed to persist. A process
  ** does not have to obtain a RESERVED lock on the way to a PENDING lock.
  ** This property is used by the algorithm for rolling back a journal file
  ** after a crash.
  **
  ** An EXCLUSIVE lock, obtained after a PENDING lock is held, is
  ** implemented by obtaining a write-lock on the entire 'shared byte
  ** range'. Since all other locks require a read-lock on one of the bytes
  ** within this range, this ensures that no other locks are held on the
  ** database. 
  **
  ** The reason a single byte cannot be used instead of the 'shared byte
  ** range' is that some versions of windows do not support read-locks. By
  ** locking a random byte from a range, concurrent SHARED locks may exist
  ** even if the locking primitive used is always a write-lock.
  */
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;
  unixInodeInfo *pInode;
  struct flock lock;
  int tErrno = 0;

  assert( pFile );
  OSTRACE(("LOCK    %d %s was %s(%s,%d) pid=%d (unix)\n", pFile->h,
      azFileLock(eFileLock), azFileLock(pFile->eFileLock),
      azFileLock(pFile->pInode->eFileLock), pFile->pInode->nShared,
      osGetpid(0)));

  /* If there is already a lock of this type or more restrictive on the
  ** unixFile, do nothing. Don't use the end_lock: exit path, as
  ** unixEnterMutex() hasn't been called yet.
  */
  if( pFile->eFileLock>=eFileLock ){
    OSTRACE(("LOCK    %d %s ok (already held) (unix)\n", pFile->h,
            azFileLock(eFileLock)));
    return SQLITE_OK;
  }

  /* Make sure the locking sequence is correct.
  **  (1) We never move from unlocked to anything higher than shared lock.
  **  (2) SQLite never explicitly requests a pendig lock.
  **  (3) A shared lock is always held when a reserve lock is requested.
  */
  assert( pFile->eFileLock!=NO_LOCK || eFileLock==SHARED_LOCK );
  assert( eFileLock!=PENDING_LOCK );
  assert( eFileLock!=RESERVED_LOCK || pFile->eFileLock==SHARED_LOCK );

  /* This mutex is needed because pFile->pInode is shared across threads
  */
  unixEnterMutex();
  pInode = pFile->pInode;

  /* If some thread using this PID has a lock via a different unixFile*
  ** handle that precludes the requested lock, return BUSY.
  */
  if( (pFile->eFileLock!=pInode->eFileLock && 
          (pInode->eFileLock>=PENDING_LOCK || eFileLock>SHARED_LOCK))
  ){
    rc = SQLITE_BUSY;
    goto end_lock;
  }

  /* If a SHARED lock is requested, and some thread using this PID already
  ** has a SHARED or RESERVED lock, then increment reference counts and
  ** return SQLITE_OK.
  */
  if( eFileLock==SHARED_LOCK && 
      (pInode->eFileLock==SHARED_LOCK || pInode->eFileLock==RESERVED_LOCK) ){
    assert( eFileLock==SHARED_LOCK );
    assert( pFile->eFileLock==0 );
    assert( pInode->nShared>0 );
    pFile->eFileLock = SHARED_LOCK;
    pInode->nShared++;
    pInode->nLock++;
    goto end_lock;
  }


  /* A PENDING lock is needed before acquiring a SHARED lock and before
  ** acquiring an EXCLUSIVE lock.  For the SHARED lock, the PENDING will
  ** be released.
  */
  lock.l_len = 1L;
  lock.l_whence = SEEK_SET;
  if( eFileLock==SHARED_LOCK 
      || (eFileLock==EXCLUSIVE_LOCK && pFile->eFileLock<PENDING_LOCK)
  ){
    lock.l_type = (eFileLock==SHARED_LOCK?F_RDLCK:F_WRLCK);
    lock.l_start = PENDING_BYTE;
    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
      goto end_lock;
    }
  }


  /* If control gets to this point, then actually go ahead and make
  ** operating system calls for the specified lock.
  */
  if( eFileLock==SHARED_LOCK ){
    assert( pInode->nShared==0 );
    assert( pInode->eFileLock==0 );
    assert( rc==SQLITE_OK );

    /* Now get the read-lock */
    lock.l_start = SHARED_FIRST;
    lock.l_len = SHARED_SIZE;
    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
    }

    /* Drop the temporary PENDING lock */
    lock.l_start = PENDING_BYTE;
    lock.l_len = 1L;
    lock.l_type = F_UNLCK;
    if( unixFileLock(pFile, &lock) && rc==SQLITE_OK ){
      /* This could happen with a network mount */
      tErrno = errno;
      rc = SQLITE_IOERR_UNLOCK; 
    }

    if( rc ){
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
      goto end_lock;
    }else{
      pFile->eFileLock = SHARED_LOCK;
      pInode->nLock++;
      pInode->nShared = 1;
    }
  }else if( eFileLock==EXCLUSIVE_LOCK && pInode->nShared>1 ){
    /* We are trying for an exclusive lock but another thread in this
    ** same process is still holding a shared lock. */
    rc = SQLITE_BUSY;
  }else{
    /* The request was for a RESERVED or EXCLUSIVE lock.  It is
    ** assumed that there is a SHARED or greater lock on the file
    ** already.
    */
    assert( 0!=pFile->eFileLock );
    lock.l_type = F_WRLCK;

    assert( eFileLock==RESERVED_LOCK || eFileLock==EXCLUSIVE_LOCK );
    if( eFileLock==RESERVED_LOCK ){
      lock.l_start = RESERVED_BYTE;
      lock.l_len = 1L;
    }else{
      lock.l_start = SHARED_FIRST;
      lock.l_len = SHARED_SIZE;
    }

    if( unixFileLock(pFile, &lock) ){
      tErrno = errno;
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( rc!=SQLITE_BUSY ){
        storeLastErrno(pFile, tErrno);
      }
    }
  }
  

#ifdef SQLITE_DEBUG
  /* Set up the transaction-counter change checking flags when
  ** transitioning from a SHARED to a RESERVED lock.  The change
  ** from SHARED to RESERVED marks the beginning of a normal
  ** write operation (not a hot journal rollback).
  */
  if( rc==SQLITE_OK
   && pFile->eFileLock<=SHARED_LOCK
   && eFileLock==RESERVED_LOCK
  ){
    pFile->transCntrChng = 0;
    pFile->dbUpdate = 0;
    pFile->inNormalWrite = 1;
  }
#endif


  if( rc==SQLITE_OK ){
    pFile->eFileLock = eFileLock;
    pInode->eFileLock = eFileLock;
  }else if( eFileLock==EXCLUSIVE_LOCK ){
    pFile->eFileLock = PENDING_LOCK;
    pInode->eFileLock = PENDING_LOCK;
  }

end_lock:
  unixLeaveMutex();
  OSTRACE(("LOCK    %d %s %s (unix)\n", pFile->h, azFileLock(eFileLock), 
      rc==SQLITE_OK ? "ok" : "failed"));
  return rc;
}

/*
** Add the file descriptor used by file handle pFile to the corresponding
** pUnused list.
*/
static void setPendingFd(unixFile *pFile){
  unixInodeInfo *pInode = pFile->pInode;
  UnixUnusedFd *p = pFile->pUnused;
  p->pNext = pInode->pUnused;
  pInode->pUnused = p;
  pFile->h = -1;
  pFile->pUnused = 0;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
** 
** If handleNFSUnlock is true, then on downgrading an EXCLUSIVE_LOCK to SHARED
** the byte range is divided into 2 parts and the first part is unlocked then
** set to a read lock, then the other part is simply unlocked.  This works 
** around a bug in BSD NFS lockd (also seen on MacOSX 10.3+) that fails to 
** remove the write lock on a region when a read lock is set.
*/
static int posixUnlock(sqlite3_file *id, int eFileLock, int handleNFSUnlock){
  unixFile *pFile = (unixFile*)id;
  unixInodeInfo *pInode;
  struct flock lock;
  int rc = SQLITE_OK;

  assert( pFile );
  OSTRACE(("UNLOCK  %d %d was %d(%d,%d) pid=%d (unix)\n", pFile->h, eFileLock,
      pFile->eFileLock, pFile->pInode->eFileLock, pFile->pInode->nShared,
      osGetpid(0)));

  assert( eFileLock<=SHARED_LOCK );
  if( pFile->eFileLock<=eFileLock ){
    return SQLITE_OK;
  }
  unixEnterMutex();
  pInode = pFile->pInode;
  assert( pInode->nShared!=0 );
  if( pFile->eFileLock>SHARED_LOCK ){
    assert( pInode->eFileLock==pFile->eFileLock );

#ifdef SQLITE_DEBUG
    /* When reducing a lock such that other processes can start
    ** reading the database file again, make sure that the
    ** transaction counter was updated if any part of the database
    ** file changed.  If the transaction counter is not updated,
    ** other connections to the same file might not realize that
    ** the file has changed and hence might not know to flush their
    ** cache.  The use of a stale cache can lead to database corruption.
    */
    pFile->inNormalWrite = 0;
#endif

    /* downgrading to a shared lock on NFS involves clearing the write lock
    ** before establishing the readlock - to avoid a race condition we downgrade
    ** the lock in 2 blocks, so that part of the range will be covered by a 
    ** write lock until the rest is covered by a read lock:
    **  1:   [WWWWW]
    **  2:   [....W]
    **  3:   [RRRRW]
    **  4:   [RRRR.]
    */
    if( eFileLock==SHARED_LOCK ){
#if !defined(__APPLE__) || !SQLITE_ENABLE_LOCKING_STYLE
      (void)handleNFSUnlock;
      assert( handleNFSUnlock==0 );
#endif
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
      if( handleNFSUnlock ){
        int tErrno;               /* Error code from system call errors */
        off_t divSize = SHARED_SIZE - 1;
        
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
        lock.l_type = F_RDLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_RDLOCK);
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST+divSize;
        lock.l_len = SHARED_SIZE-divSize;
        if( unixFileLock(pFile, &lock)==(-1) ){
          tErrno = errno;
          rc = SQLITE_IOERR_UNLOCK;
          if( IS_LOCK_ERROR(rc) ){
            storeLastErrno(pFile, tErrno);
          }
          goto end_unlock;
        }
      }else
#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
      {
        lock.l_type = F_RDLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = SHARED_FIRST;
        lock.l_len = SHARED_SIZE;
        if( unixFileLock(pFile, &lock) ){
          /* In theory, the call to unixFileLock() cannot fail because another
          ** process is holding an incompatible lock. If it does, this 
          ** indicates that the other process is not following the locking
          ** protocol. If this happens, return SQLITE_IOERR_RDLOCK. Returning
          ** SQLITE_BUSY would confuse the upper layer (in practice it causes 
          ** an assert to fail). */ 
          rc = SQLITE_IOERR_RDLOCK;
          storeLastErrno(pFile, errno);
          goto end_unlock;
        }
      }
    }
    lock.l_type = F_UNLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = PENDING_BYTE;
    lock.l_len = 2L;  assert( PENDING_BYTE+1==RESERVED_BYTE );
    if( unixFileLock(pFile, &lock)==0 ){
      pInode->eFileLock = SHARED_LOCK;
    }else{
      rc = SQLITE_IOERR_UNLOCK;
      storeLastErrno(pFile, errno);
      goto end_unlock;
    }
  }
  if( eFileLock==NO_LOCK ){
    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
    */
    pInode->nShared--;
    if( pInode->nShared==0 ){
      lock.l_type = F_UNLCK;
      lock.l_whence = SEEK_SET;
      lock.l_start = lock.l_len = 0L;
      if( unixFileLock(pFile, &lock)==0 ){
        pInode->eFileLock = NO_LOCK;
      }else{
        rc = SQLITE_IOERR_UNLOCK;
        storeLastErrno(pFile, errno);
        pInode->eFileLock = NO_LOCK;
        pFile->eFileLock = NO_LOCK;
      }
    }

    /* Decrement the count of locks against this same file.  When the
    ** count reaches zero, close any other file descriptors whose close
    ** was deferred because of outstanding locks.
    */
    pInode->nLock--;
    assert( pInode->nLock>=0 );
    if( pInode->nLock==0 ){
      closePendingFds(pFile);
    }
  }

end_unlock:
  unixLeaveMutex();
  if( rc==SQLITE_OK ) pFile->eFileLock = eFileLock;
  return rc;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
*/
static int unixUnlock(sqlite3_file *id, int eFileLock){
#if SQLITE_MAX_MMAP_SIZE>0
  assert( eFileLock==SHARED_LOCK || ((unixFile *)id)->nFetchOut==0 );
#endif
  return posixUnlock(id, eFileLock, 0);
}

#if SQLITE_MAX_MMAP_SIZE>0
static int unixMapfile(unixFile *pFd, i64 nByte);
static void unixUnmapfile(unixFile *pFd);
#endif

/*
** This function performs the parts of the "close file" operation 
** common to all locking schemes. It closes the directory and file
** handles, if they are valid, and sets all fields of the unixFile
** structure to 0.
**
** It is *not* necessary to hold the mutex when this routine is called,
** even on VxWorks.  A mutex will be acquired on VxWorks by the
** vxworksReleaseFileId() routine.
*/
static int closeUnixFile(sqlite3_file *id){
  unixFile *pFile = (unixFile*)id;
#if SQLITE_MAX_MMAP_SIZE>0
  unixUnmapfile(pFile);
#endif
  if( pFile->h>=0 ){
    robust_close(pFile, pFile->h, __LINE__);
    pFile->h = -1;
  }
#if OS_VXWORKS
  if( pFile->pId ){
    if( pFile->ctrlFlags & UNIXFILE_DELETE ){
      osUnlink(pFile->pId->zCanonicalName);
    }
    vxworksReleaseFileId(pFile->pId);
    pFile->pId = 0;
  }
#endif
#ifdef SQLITE_UNLINK_AFTER_CLOSE
  if( pFile->ctrlFlags & UNIXFILE_DELETE ){
    osUnlink(pFile->zPath);
    sqlite3_free(*(char**)&pFile->zPath);
    pFile->zPath = 0;
  }
#endif
  OSTRACE(("CLOSE   %-3d\n", pFile->h));
  OpenCounter(-1);
  sqlite3_free(pFile->pUnused);
  memset(pFile, 0, sizeof(unixFile));
  return SQLITE_OK;
}

/*
** Close a file.
*/
static int unixClose(sqlite3_file *id){
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile *)id;
  verifyDbFile(pFile);
  unixUnlock(id, NO_LOCK);
  unixEnterMutex();

  /* unixFile.pInode is always valid here. Otherwise, a different close
  ** routine (e.g. nolockClose()) would be called instead.
  */
  assert( pFile->pInode->nLock>0 || pFile->pInode->bProcessLock==0 );
  if( ALWAYS(pFile->pInode) && pFile->pInode->nLock ){
    /* If there are outstanding locks, do not actually close the file just
    ** yet because that would clear those locks.  Instead, add the file
    ** descriptor to pInode->pUnused list.  It will be automatically closed 
    ** when the last lock is cleared.
    */
    setPendingFd(pFile);
  }
  releaseInodeInfo(pFile);
  rc = closeUnixFile(id);
  unixLeaveMutex();
  return rc;
}

/************** End of the posix advisory lock implementation *****************
******************************************************************************/

/******************************************************************************
****************************** No-op Locking **********************************
**
** Of the various locking implementations available, this is by far the
** simplest:  locking is ignored.  No attempt is made to lock the database
** file for reading or writing.
**
** This locking mode is appropriate for use on read-only databases
** (ex: databases that are burned into CD-ROM, for example.)  It can
** also be used if the application employs some external mechanism to
** prevent simultaneous access of the same database by two or more
** database connections.  But there is a serious risk of database
** corruption if this locking mode is used in situations where multiple
** database connections are accessing the same database file at the same
** time and one or more of those connections are writing.
*/

static int nolockCheckReservedLock(sqlite3_file *NotUsed, int *pResOut){
  UNUSED_PARAMETER(NotUsed);
  *pResOut = 0;
  return SQLITE_OK;
}
static int nolockLock(sqlite3_file *NotUsed, int NotUsed2){
  UNUSED_PARAMETER2(NotUsed, NotUsed2);
  return SQLITE_OK;
}
static int nolockUnlock(sqlite3_file *NotUsed, int NotUsed2){
  UNUSED_PARAMETER2(NotUsed, NotUsed2);
  return SQLITE_OK;
}

/*
** Close the file.
*/
static int nolockClose(sqlite3_file *id) {
  return closeUnixFile(id);
}

/******************* End of the no-op lock implementation *********************
******************************************************************************/

/******************************************************************************
************************* Begin dot-file Locking ******************************
**
** The dotfile locking implementation uses the existence of separate lock
** files (really a directory) to control access to the database.  This works
** on just about every filesystem imaginable.  But there are serious downsides:
**
**    (1)  There is zero concurrency.  A single reader blocks all other
**         connections from reading or writing the database.
**
**    (2)  An application crash or power loss can leave stale lock files
**         sitting around that need to be cleared manually.
**
** Nevertheless, a dotlock is an appropriate locking mode for use if no
** other locking strategy is available.
**
** Dotfile locking works by creating a subdirectory in the same directory as
** the database and with the same name but with a ".lock" extension added.
** The existence of a lock directory implies an EXCLUSIVE lock.  All other
** lock types (SHARED, RESERVED, PENDING) are mapped into EXCLUSIVE.
*/

/*
** The file suffix added to the data base filename in order to create the
** lock directory.
*/
#define DOTLOCK_SUFFIX ".lock"

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
**
** In dotfile locking, either a lock exists or it does not.  So in this
** variation of CheckReservedLock(), *pResOut is set to true if any lock
** is held on the file and false if the file is unlocked.
*/
static int dotlockCheckReservedLock(sqlite3_file *id, int *pResOut) {
  int rc = SQLITE_OK;
  int reserved = 0;
  unixFile *pFile = (unixFile*)id;

  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
  
  assert( pFile );

  /* Check if a thread in this process holds such a lock */
  if( pFile->eFileLock>SHARED_LOCK ){
    /* Either this connection or some other connection in the same process
    ** holds a lock on the file.  No need to check further. */
    reserved = 1;
  }else{
    /* The lock is held if and only if the lockfile exists */
    const char *zLockFile = (const char*)pFile->lockingContext;
    reserved = osAccess(zLockFile, 0)==0;
  }
  OSTRACE(("TEST WR-LOCK %d %d %d (dotlock)\n", pFile->h, rc, reserved));
  *pResOut = reserved;
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
**
** With dotfile locking, we really only support state (4): EXCLUSIVE.
** But we track the other locking levels internally.
*/
static int dotlockLock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  char *zLockFile = (char *)pFile->lockingContext;
  int rc = SQLITE_OK;


  /* If we have any lock, then the lock file already exists.  All we have
  ** to do is adjust our internal record of the lock level.
  */
  if( pFile->eFileLock > NO_LOCK ){
    pFile->eFileLock = eFileLock;
    /* Always update the timestamp on the old file */
#ifdef HAVE_UTIME
    utime(zLockFile, NULL);
#else
    utimes(zLockFile, NULL);
#endif
    return SQLITE_OK;
  }
  
  /* grab an exclusive lock */
  rc = osMkdir(zLockFile, 0777);
  if( rc<0 ){
    /* failed to open/create the lock directory */
    int tErrno = errno;
    if( EEXIST == tErrno ){
      rc = SQLITE_BUSY;
    } else {
      rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
      if( IS_LOCK_ERROR(rc) ){
        storeLastErrno(pFile, tErrno);
      }
    }
    return rc;
  } 
  
  /* got it, set the type and return ok */
  pFile->eFileLock = eFileLock;
  return rc;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
**
** When the locking level reaches NO_LOCK, delete the lock file.
*/
static int dotlockUnlock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  char *zLockFile = (char *)pFile->lockingContext;
  int rc;

  assert( pFile );
  OSTRACE(("UNLOCK  %d %d was %d pid=%d (dotlock)\n", pFile->h, eFileLock,
           pFile->eFileLock, osGetpid(0)));
  assert( eFileLock<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->eFileLock==eFileLock ){
    return SQLITE_OK;
  }

  /* To downgrade to shared, simply update our internal notion of the
  ** lock state.  No need to mess with the file on disk.
  */
  if( eFileLock==SHARED_LOCK ){
    pFile->eFileLock = SHARED_LOCK;
    return SQLITE_OK;
  }
  
  /* To fully unlock the database, delete the lock file */
  assert( eFileLock==NO_LOCK );
  rc = osRmdir(zLockFile);
  if( rc<0 && errno==ENOTDIR ) rc = osUnlink(zLockFile);
  if( rc<0 ){
    int tErrno = errno;
    rc = 0;
    if( ENOENT != tErrno ){
      rc = SQLITE_IOERR_UNLOCK;
    }
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

/*
** Close a file.  Make sure the lock has been released before closing.
*/
static int dotlockClose(sqlite3_file *id) {
  int rc = SQLITE_OK;
  if( id ){
    unixFile *pFile = (unixFile*)id;
    dotlockUnlock(id, NO_LOCK);
    sqlite3_free(pFile->lockingContext);
    rc = closeUnixFile(id);
  }
  return rc;
}
/****************** End of the dot-file lock implementation *******************
******************************************************************************/

/******************************************************************************
************************** Begin flock Locking ********************************
**
** Use the flock() system call to do file locking.
**
** flock() locking is like dot-file locking in that the various
** fine-grain locking levels supported by SQLite are collapsed into
** a single exclusive lock.  In other words, SHARED, RESERVED, and
** PENDING locks are the same thing as an EXCLUSIVE lock.  SQLite
** still works when you do this, but concurrency is reduced since
** only a single process can be reading the database at a time.
**
** Omit this section if SQLITE_ENABLE_LOCKING_STYLE is turned off
*/
#if SQLITE_ENABLE_LOCKING_STYLE

/*
** Retry flock() calls that fail with EINTR
*/
#ifdef EINTR
static int robust_flock(int fd, int op){
  int rc;
  do{ rc = flock(fd,op); }while( rc<0 && errno==EINTR );
  return rc;
}
#else
# define robust_flock(a,b) flock(a,b)
#endif
     

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
*/
static int flockCheckReservedLock(sqlite3_file *id, int *pResOut){
  int rc = SQLITE_OK;
  int reserved = 0;
  unixFile *pFile = (unixFile*)id;
  
  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
  
  assert( pFile );
  
  /* Check if a thread in this process holds such a lock */
  if( pFile->eFileLock>SHARED_LOCK ){
    reserved = 1;
  }
  
  /* Otherwise see if some other process holds it. */
  if( !reserved ){
    /* attempt to get the lock */
    int lrc = robust_flock(pFile->h, LOCK_EX | LOCK_NB);
    if( !lrc ){
      /* got the lock, unlock it */
      lrc = robust_flock(pFile->h, LOCK_UN);
      if ( lrc ) {
        int tErrno = errno;
        /* unlock failed with an error */
        lrc = SQLITE_IOERR_UNLOCK; 
        if( IS_LOCK_ERROR(lrc) ){
          storeLastErrno(pFile, tErrno);
          rc = lrc;
        }
      }
    } else {
      int tErrno = errno;
      reserved = 1;
      /* someone else might have it reserved */
      lrc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK); 
      if( IS_LOCK_ERROR(lrc) ){
        storeLastErrno(pFile, tErrno);
        rc = lrc;
      }
    }
  }
  OSTRACE(("TEST WR-LOCK %d %d %d (flock)\n", pFile->h, rc, reserved));

#ifdef SQLITE_IGNORE_FLOCK_LOCK_ERRORS
  if( (rc & SQLITE_IOERR) == SQLITE_IOERR ){
    rc = SQLITE_OK;
    reserved=1;
  }
#endif /* SQLITE_IGNORE_FLOCK_LOCK_ERRORS */
  *pResOut = reserved;
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** flock() only really support EXCLUSIVE locks.  We track intermediate
** lock states in the sqlite3_file structure, but all locks SHARED or
** above are really EXCLUSIVE locks and exclude all other processes from
** access the file.
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
*/
static int flockLock(sqlite3_file *id, int eFileLock) {
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;

  assert( pFile );

  /* if we already have a lock, it is exclusive.  
  ** Just adjust level and punt on outta here. */
  if (pFile->eFileLock > NO_LOCK) {
    pFile->eFileLock = eFileLock;
    return SQLITE_OK;
  }
  
  /* grab an exclusive lock */
  
  if (robust_flock(pFile->h, LOCK_EX | LOCK_NB)) {
    int tErrno = errno;
    /* didn't get, must be busy */
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_LOCK);
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
  } else {
    /* got it, set the type and return ok */
    pFile->eFileLock = eFileLock;
  }
  OSTRACE(("LOCK    %d %s %s (flock)\n", pFile->h, azFileLock(eFileLock), 
           rc==SQLITE_OK ? "ok" : "failed"));
#ifdef SQLITE_IGNORE_FLOCK_LOCK_ERRORS
  if( (rc & SQLITE_IOERR) == SQLITE_IOERR ){
    rc = SQLITE_BUSY;
  }
#endif /* SQLITE_IGNORE_FLOCK_LOCK_ERRORS */
  return rc;
}


/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
*/
static int flockUnlock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  
  assert( pFile );
  OSTRACE(("UNLOCK  %d %d was %d pid=%d (flock)\n", pFile->h, eFileLock,
           pFile->eFileLock, osGetpid(0)));
  assert( eFileLock<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->eFileLock==eFileLock ){
    return SQLITE_OK;
  }
  
  /* shared can just be set because we always have an exclusive */
  if (eFileLock==SHARED_LOCK) {
    pFile->eFileLock = eFileLock;
    return SQLITE_OK;
  }
  
  /* no, really, unlock. */
  if( robust_flock(pFile->h, LOCK_UN) ){
#ifdef SQLITE_IGNORE_FLOCK_LOCK_ERRORS
    return SQLITE_OK;
#endif /* SQLITE_IGNORE_FLOCK_LOCK_ERRORS */
    return SQLITE_IOERR_UNLOCK;
  }else{
    pFile->eFileLock = NO_LOCK;
    return SQLITE_OK;
  }
}

/*
** Close a file.
*/
static int flockClose(sqlite3_file *id) {
  int rc = SQLITE_OK;
  if( id ){
    flockUnlock(id, NO_LOCK);
    rc = closeUnixFile(id);
  }
  return rc;
}

#endif /* SQLITE_ENABLE_LOCKING_STYLE && !OS_VXWORK */

/******************* End of the flock lock implementation *********************
******************************************************************************/

/******************************************************************************
************************ Begin Named Semaphore Locking ************************
**
** Named semaphore locking is only supported on VxWorks.
**
** Semaphore locking is like dot-lock and flock in that it really only
** supports EXCLUSIVE locking.  Only a single process can read or write
** the database file at a time.  This reduces potential concurrency, but
** makes the lock implementation much easier.
*/
#if OS_VXWORKS

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
*/
static int semXCheckReservedLock(sqlite3_file *id, int *pResOut) {
  int rc = SQLITE_OK;
  int reserved = 0;
  unixFile *pFile = (unixFile*)id;

  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
  
  assert( pFile );

  /* Check if a thread in this process holds such a lock */
  if( pFile->eFileLock>SHARED_LOCK ){
    reserved = 1;
  }
  
  /* Otherwise see if some other process holds it. */
  if( !reserved ){
    sem_t *pSem = pFile->pInode->pSem;

    if( sem_trywait(pSem)==-1 ){
      int tErrno = errno;
      if( EAGAIN != tErrno ){
        rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_CHECKRESERVEDLOCK);
        storeLastErrno(pFile, tErrno);
      } else {
        /* someone else has the lock when we are in NO_LOCK */
        reserved = (pFile->eFileLock < SHARED_LOCK);
      }
    }else{
      /* we could have it if we want it */
      sem_post(pSem);
    }
  }
  OSTRACE(("TEST WR-LOCK %d %d %d (sem)\n", pFile->h, rc, reserved));

  *pResOut = reserved;
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** Semaphore locks only really support EXCLUSIVE locks.  We track intermediate
** lock states in the sqlite3_file structure, but all locks SHARED or
** above are really EXCLUSIVE locks and exclude all other processes from
** access the file.
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
*/
static int semXLock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  sem_t *pSem = pFile->pInode->pSem;
  int rc = SQLITE_OK;

  /* if we already have a lock, it is exclusive.  
  ** Just adjust level and punt on outta here. */
  if (pFile->eFileLock > NO_LOCK) {
    pFile->eFileLock = eFileLock;
    rc = SQLITE_OK;
    goto sem_end_lock;
  }
  
  /* lock semaphore now but bail out when already locked. */
  if( sem_trywait(pSem)==-1 ){
    rc = SQLITE_BUSY;
    goto sem_end_lock;
  }

  /* got it, set the type and return ok */
  pFile->eFileLock = eFileLock;

 sem_end_lock:
  return rc;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
*/
static int semXUnlock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  sem_t *pSem = pFile->pInode->pSem;

  assert( pFile );
  assert( pSem );
  OSTRACE(("UNLOCK  %d %d was %d pid=%d (sem)\n", pFile->h, eFileLock,
           pFile->eFileLock, osGetpid(0)));
  assert( eFileLock<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->eFileLock==eFileLock ){
    return SQLITE_OK;
  }
  
  /* shared can just be set because we always have an exclusive */
  if (eFileLock==SHARED_LOCK) {
    pFile->eFileLock = eFileLock;
    return SQLITE_OK;
  }
  
  /* no, really unlock. */
  if ( sem_post(pSem)==-1 ) {
    int rc, tErrno = errno;
    rc = sqliteErrorFromPosixError(tErrno, SQLITE_IOERR_UNLOCK);
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc; 
  }
  pFile->eFileLock = NO_LOCK;
  return SQLITE_OK;
}

/*
 ** Close a file.
 */
static int semXClose(sqlite3_file *id) {
  if( id ){
    unixFile *pFile = (unixFile*)id;
    semXUnlock(id, NO_LOCK);
    assert( pFile );
    unixEnterMutex();
    releaseInodeInfo(pFile);
    unixLeaveMutex();
    closeUnixFile(id);
  }
  return SQLITE_OK;
}

#endif /* OS_VXWORKS */
/*
** Named semaphore locking is only available on VxWorks.
**
*************** End of the named semaphore lock implementation ****************
******************************************************************************/


/******************************************************************************
*************************** Begin AFP Locking *********************************
**
** AFP is the Apple Filing Protocol.  AFP is a network filesystem found
** on Apple Macintosh computers - both OS9 and OSX.
**
** Third-party implementations of AFP are available.  But this code here
** only works on OSX.
*/

#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
/*
** The afpLockingContext structure contains all afp lock specific state
*/
typedef struct afpLockingContext afpLockingContext;
struct afpLockingContext {
  int reserved;
  const char *dbPath;             /* Name of the open file */
};

struct ByteRangeLockPB2
{
  unsigned long long offset;        /* offset to first byte to lock */
  unsigned long long length;        /* nbr of bytes to lock */
  unsigned long long retRangeStart; /* nbr of 1st byte locked if successful */
  unsigned char unLockFlag;         /* 1 = unlock, 0 = lock */
  unsigned char startEndFlag;       /* 1=rel to end of fork, 0=rel to start */
  int fd;                           /* file desc to assoc this lock with */
};

#define afpfsByteRangeLock2FSCTL        _IOWR('z', 23, struct ByteRangeLockPB2)

/*
** This is a utility for setting or clearing a bit-range lock on an
** AFP filesystem.
** 
** Return SQLITE_OK on success, SQLITE_BUSY on failure.
*/
static int afpSetLock(
  const char *path,              /* Name of the file to be locked or unlocked */
  unixFile *pFile,               /* Open file descriptor on path */
  unsigned long long offset,     /* First byte to be locked */
  unsigned long long length,     /* Number of bytes to lock */
  int setLockFlag                /* True to set lock.  False to clear lock */
){
  struct ByteRangeLockPB2 pb;
  int err;
  
  pb.unLockFlag = setLockFlag ? 0 : 1;
  pb.startEndFlag = 0;
  pb.offset = offset;
  pb.length = length; 
  pb.fd = pFile->h;
  
  OSTRACE(("AFPSETLOCK [%s] for %d%s in range %llx:%llx\n", 
    (setLockFlag?"ON":"OFF"), pFile->h, (pb.fd==-1?"[testval-1]":""),
    offset, length));
  err = fsctl(path, afpfsByteRangeLock2FSCTL, &pb, 0);
  if ( err==-1 ) {
    int rc;
    int tErrno = errno;
    OSTRACE(("AFPSETLOCK failed to fsctl() '%s' %d %s\n",
             path, tErrno, strerror(tErrno)));
#ifdef SQLITE_IGNORE_AFP_LOCK_ERRORS
    rc = SQLITE_BUSY;
#else
    rc = sqliteErrorFromPosixError(tErrno,
                    setLockFlag ? SQLITE_IOERR_LOCK : SQLITE_IOERR_UNLOCK);
#endif /* SQLITE_IGNORE_AFP_LOCK_ERRORS */
    if( IS_LOCK_ERROR(rc) ){
      storeLastErrno(pFile, tErrno);
    }
    return rc;
  } else {
    return SQLITE_OK;
  }
}

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
*/
static int afpCheckReservedLock(sqlite3_file *id, int *pResOut){
  int rc = SQLITE_OK;
  int reserved = 0;
  unixFile *pFile = (unixFile*)id;
  afpLockingContext *context;
  
  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
  
  assert( pFile );
  context = (afpLockingContext *) pFile->lockingContext;
  if( context->reserved ){
    *pResOut = 1;
    return SQLITE_OK;
  }
  unixEnterMutex(); /* Because pFile->pInode is shared across threads */
  
  /* Check if a thread in this process holds such a lock */
  if( pFile->pInode->eFileLock>SHARED_LOCK ){
    reserved = 1;
  }
  
  /* Otherwise see if some other process holds it.
   */
  if( !reserved ){
    /* lock the RESERVED byte */
    int lrc = afpSetLock(context->dbPath, pFile, RESERVED_BYTE, 1,1);  
    if( SQLITE_OK==lrc ){
      /* if we succeeded in taking the reserved lock, unlock it to restore
      ** the original state */
      lrc = afpSetLock(context->dbPath, pFile, RESERVED_BYTE, 1, 0);
    } else {
      /* if we failed to get the lock then someone else must have it */
      reserved = 1;
    }
    if( IS_LOCK_ERROR(lrc) ){
      rc=lrc;
    }
  }
  
  unixLeaveMutex();
  OSTRACE(("TEST WR-LOCK %d %d %d (afp)\n", pFile->h, rc, reserved));
  
  *pResOut = reserved;
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
*/
static int afpLock(sqlite3_file *id, int eFileLock){
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;
  unixInodeInfo *pInode = pFile->pInode;
  afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
  
  assert( pFile );
  OSTRACE(("LOCK    %d %s was %s(%s,%d) pid=%d (afp)\n", pFile->h,
           azFileLock(eFileLock), azFileLock(pFile->eFileLock),
           azFileLock(pInode->eFileLock), pInode->nShared , osGetpid(0)));

  /* If there is already a lock of this type or more restrictive on the
  ** unixFile, do nothing. Don't use the afp_end_lock: exit path, as
  ** unixEnterMutex() hasn't been called yet.
  */
  if( pFile->eFileLock>=eFileLock ){
    OSTRACE(("LOCK    %d %s ok (already held) (afp)\n", pFile->h,
           azFileLock(eFileLock)));
    return SQLITE_OK;
  }

  /* Make sure the locking sequence is correct
  **  (1) We never move from unlocked to anything higher than shared lock.
  **  (2) SQLite never explicitly requests a pendig lock.
  **  (3) A shared lock is always held when a reserve lock is requested.
  */
  assert( pFile->eFileLock!=NO_LOCK || eFileLock==SHARED_LOCK );
  assert( eFileLock!=PENDING_LOCK );
  assert( eFileLock!=RESERVED_LOCK || pFile->eFileLock==SHARED_LOCK );
  
  /* This mutex is needed because pFile->pInode is shared across threads
  */
  unixEnterMutex();
  pInode = pFile->pInode;

  /* If some thread using this PID has a lock via a different unixFile*
  ** handle that precludes the requested lock, return BUSY.
  */
  if( (pFile->eFileLock!=pInode->eFileLock && 
       (pInode->eFileLock>=PENDING_LOCK || eFileLock>SHARED_LOCK))
     ){
    rc = SQLITE_BUSY;
    goto afp_end_lock;
  }
  
  /* If a SHARED lock is requested, and some thread using this PID already
  ** has a SHARED or RESERVED lock, then increment reference counts and
  ** return SQLITE_OK.
  */
  if( eFileLock==SHARED_LOCK && 
     (pInode->eFileLock==SHARED_LOCK || pInode->eFileLock==RESERVED_LOCK) ){
    assert( eFileLock==SHARED_LOCK );
    assert( pFile->eFileLock==0 );
    assert( pInode->nShared>0 );
    pFile->eFileLock = SHARED_LOCK;
    pInode->nShared++;
    pInode->nLock++;
    goto afp_end_lock;
  }
    
  /* A PENDING lock is needed before acquiring a SHARED lock and before
  ** acquiring an EXCLUSIVE lock.  For the SHARED lock, the PENDING will
  ** be released.
  */
  if( eFileLock==SHARED_LOCK 
      || (eFileLock==EXCLUSIVE_LOCK && pFile->eFileLock<PENDING_LOCK)
  ){
    int failed;
    failed = afpSetLock(context->dbPath, pFile, PENDING_BYTE, 1, 1);
    if (failed) {
      rc = failed;
      goto afp_end_lock;
    }
  }
  
  /* If control gets to this point, then actually go ahead and make
  ** operating system calls for the specified lock.
  */
  if( eFileLock==SHARED_LOCK ){
    int lrc1, lrc2, lrc1Errno = 0;
    long lk, mask;
    
    assert( pInode->nShared==0 );
    assert( pInode->eFileLock==0 );
        
    mask = (sizeof(long)==8) ? LARGEST_INT64 : 0x7fffffff;
    /* Now get the read-lock SHARED_LOCK */
    /* note that the quality of the randomness doesn't matter that much */
    lk = random(); 
    pInode->sharedByte = (lk & mask)%(SHARED_SIZE - 1);
    lrc1 = afpSetLock(context->dbPath, pFile, 
          SHARED_FIRST+pInode->sharedByte, 1, 1);
    if( IS_LOCK_ERROR(lrc1) ){
      lrc1Errno = pFile->lastErrno;
    }
    /* Drop the temporary PENDING lock */
    lrc2 = afpSetLock(context->dbPath, pFile, PENDING_BYTE, 1, 0);
    
    if( IS_LOCK_ERROR(lrc1) ) {
      storeLastErrno(pFile, lrc1Errno);
      rc = lrc1;
      goto afp_end_lock;
    } else if( IS_LOCK_ERROR(lrc2) ){
      rc = lrc2;
      goto afp_end_lock;
    } else if( lrc1 != SQLITE_OK ) {
      rc = lrc1;
    } else {
      pFile->eFileLock = SHARED_LOCK;
      pInode->nLock++;
      pInode->nShared = 1;
    }
  }else if( eFileLock==EXCLUSIVE_LOCK && pInode->nShared>1 ){
    /* We are trying for an exclusive lock but another thread in this
     ** same process is still holding a shared lock. */
    rc = SQLITE_BUSY;
  }else{
    /* The request was for a RESERVED or EXCLUSIVE lock.  It is
    ** assumed that there is a SHARED or greater lock on the file
    ** already.
    */
    int failed = 0;
    assert( 0!=pFile->eFileLock );
    if (eFileLock >= RESERVED_LOCK && pFile->eFileLock < RESERVED_LOCK) {
        /* Acquire a RESERVED lock */
        failed = afpSetLock(context->dbPath, pFile, RESERVED_BYTE, 1,1);
      if( !failed ){
        context->reserved = 1;
      }
    }
    if (!failed && eFileLock == EXCLUSIVE_LOCK) {
      /* Acquire an EXCLUSIVE lock */
        
      /* Remove the shared lock before trying the range.  we'll need to 
      ** reestablish the shared lock if we can't get the  afpUnlock
      */
      if( !(failed = afpSetLock(context->dbPath, pFile, SHARED_FIRST +
                         pInode->sharedByte, 1, 0)) ){
        int failed2 = SQLITE_OK;
        /* now attemmpt to get the exclusive lock range */
        failed = afpSetLock(context->dbPath, pFile, SHARED_FIRST, 
                               SHARED_SIZE, 1);
        if( failed && (failed2 = afpSetLock(context->dbPath, pFile, 
                       SHARED_FIRST + pInode->sharedByte, 1, 1)) ){
          /* Can't reestablish the shared lock.  Sqlite can't deal, this is
          ** a critical I/O error
          */
          rc = ((failed & SQLITE_IOERR) == SQLITE_IOERR) ? failed2 : 
               SQLITE_IOERR_LOCK;
          goto afp_end_lock;
        } 
      }else{
        rc = failed; 
      }
    }
    if( failed ){
      rc = failed;
    }
  }
  
  if( rc==SQLITE_OK ){
    pFile->eFileLock = eFileLock;
    pInode->eFileLock = eFileLock;
  }else if( eFileLock==EXCLUSIVE_LOCK ){
    pFile->eFileLock = PENDING_LOCK;
    pInode->eFileLock = PENDING_LOCK;
  }
  
afp_end_lock:
  unixLeaveMutex();
  OSTRACE(("LOCK    %d %s %s (afp)\n", pFile->h, azFileLock(eFileLock), 
         rc==SQLITE_OK ? "ok" : "failed"));
  return rc;
}

/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
*/
static int afpUnlock(sqlite3_file *id, int eFileLock) {
  int rc = SQLITE_OK;
  unixFile *pFile = (unixFile*)id;
  unixInodeInfo *pInode;
  afpLockingContext *context = (afpLockingContext *) pFile->lockingContext;
  int skipShared = 0;
#ifdef SQLITE_TEST
  int h = pFile->h;
#endif

  assert( pFile );
  OSTRACE(("UNLOCK  %d %d was %d(%d,%d) pid=%d (afp)\n", pFile->h, eFileLock,
           pFile->eFileLock, pFile->pInode->eFileLock, pFile->pInode->nShared,
           osGetpid(0)));

  assert( eFileLock<=SHARED_LOCK );
  if( pFile->eFileLock<=eFileLock ){
    return SQLITE_OK;
  }
  unixEnterMutex();
  pInode = pFile->pInode;
  assert( pInode->nShared!=0 );
  if( pFile->eFileLock>SHARED_LOCK ){
    assert( pInode->eFileLock==pFile->eFileLock );
    SimulateIOErrorBenign(1);
    SimulateIOError( h=(-1) )
    SimulateIOErrorBenign(0);
    
#ifdef SQLITE_DEBUG
    /* When reducing a lock such that other processes can start
    ** reading the database file again, make sure that the
    ** transaction counter was updated if any part of the database
    ** file changed.  If the transaction counter is not updated,
    ** other connections to the same file might not realize that
    ** the file has changed and hence might not know to flush their
    ** cache.  The use of a stale cache can lead to database corruption.
    */
    assert( pFile->inNormalWrite==0
           || pFile->dbUpdate==0
           || pFile->transCntrChng==1 );
    pFile->inNormalWrite = 0;
#endif
    
    if( pFile->eFileLock==EXCLUSIVE_LOCK ){
      rc = afpSetLock(context->dbPath, pFile, SHARED_FIRST, SHARED_SIZE, 0);
      if( rc==SQLITE_OK && (eFileLock==SHARED_LOCK || pInode->nShared>1) ){
        /* only re-establish the shared lock if necessary */
        int sharedLockByte = SHARED_FIRST+pInode->sharedByte;
        rc = afpSetLock(context->dbPath, pFile, sharedLockByte, 1, 1);
      } else {
        skipShared = 1;
      }
    }
    if( rc==SQLITE_OK && pFile->eFileLock>=PENDING_LOCK ){
      rc = afpSetLock(context->dbPath, pFile, PENDING_BYTE, 1, 0);
    } 
    if( rc==SQLITE_OK && pFile->eFileLock>=RESERVED_LOCK && context->reserved ){
      rc = afpSetLock(context->dbPath, pFile, RESERVED_BYTE, 1, 0);
      if( !rc ){ 
        context->reserved = 0; 
      }
    }
    if( rc==SQLITE_OK && (eFileLock==SHARED_LOCK || pInode->nShared>1)){
      pInode->eFileLock = SHARED_LOCK;
    }
  }
  if( rc==SQLITE_OK && eFileLock==NO_LOCK ){

    /* Decrement the shared lock counter.  Release the lock using an
    ** OS call only when all threads in this same process have released
    ** the lock.
    */
    unsigned long long sharedLockByte = SHARED_FIRST+pInode->sharedByte;
    pInode->nShared--;
    if( pInode->nShared==0 ){
      SimulateIOErrorBenign(1);
      SimulateIOError( h=(-1) )
      SimulateIOErrorBenign(0);
      if( !skipShared ){
        rc = afpSetLock(context->dbPath, pFile, sharedLockByte, 1, 0);
      }
      if( !rc ){
        pInode->eFileLock = NO_LOCK;
        pFile->eFileLock = NO_LOCK;
      }
    }
    if( rc==SQLITE_OK ){
      pInode->nLock--;
      assert( pInode->nLock>=0 );
      if( pInode->nLock==0 ){
        closePendingFds(pFile);
      }
    }
  }
  
  unixLeaveMutex();
  if( rc==SQLITE_OK ) pFile->eFileLock = eFileLock;
  return rc;
}

/*
** Close a file & cleanup AFP specific locking context 
*/
static int afpClose(sqlite3_file *id) {
  int rc = SQLITE_OK;
  if( id ){
    unixFile *pFile = (unixFile*)id;
    afpUnlock(id, NO_LOCK);
    unixEnterMutex();
    if( pFile->pInode && pFile->pInode->nLock ){
      /* If there are outstanding locks, do not actually close the file just
      ** yet because that would clear those locks.  Instead, add the file
      ** descriptor to pInode->aPending.  It will be automatically closed when
      ** the last lock is cleared.
      */
      setPendingFd(pFile);
    }
    releaseInodeInfo(pFile);
    sqlite3_free(pFile->lockingContext);
    rc = closeUnixFile(id);
    unixLeaveMutex();
  }
  return rc;
}

#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
/*
** The code above is the AFP lock implementation.  The code is specific
** to MacOSX and does not work on other unix platforms.  No alternative
** is available.  If you don't compile for a mac, then the "unix-afp"
** VFS is not available.
**
********************* End of the AFP lock implementation **********************
******************************************************************************/

/******************************************************************************
*************************** Begin NFS Locking ********************************/

#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
/*
 ** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
 ** must be either NO_LOCK or SHARED_LOCK.
 **
 ** If the locking level of the file descriptor is already at or below
 ** the requested locking level, this routine is a no-op.
 */
static int nfsUnlock(sqlite3_file *id, int eFileLock){
  return posixUnlock(id, eFileLock, 1);
}

#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
/*
** The code above is the NFS lock implementation.  The code is specific
** to MacOSX and does not work on other unix platforms.  No alternative
** is available.  
**
********************* End of the NFS lock implementation **********************
******************************************************************************/

/******************************************************************************
**************** Non-locking sqlite3_file methods *****************************
**
** The next division contains implementations for all methods of the 
** sqlite3_file object other than the locking methods.  The locking
** methods were defined in divisions above (one locking method per
** division).  Those methods that are common to all locking modes
** are gather together into this division.
*/

/*
** Seek to the offset passed as the second argument, then read cnt 
** bytes into pBuf. Return the number of bytes actually read.
**
** NB:  If you define USE_PREAD or USE_PREAD64, then it might also
** be necessary to define _XOPEN_SOURCE to be 500.  This varies from
** one system to another.  Since SQLite does not define USE_PREAD
** in any form by default, we will not attempt to define _XOPEN_SOURCE.
** See tickets #2741 and #2681.
**
** To avoid stomping the errno value on a failed read the lastErrno value
** is set before returning.
*/
static int seekAndRead(unixFile *id, sqlite3_int64 offset, void *pBuf, int cnt){
  int got;
  int prior = 0;
#if (!defined(USE_PREAD) && !defined(USE_PREAD64))
  i64 newOffset;
#endif
  TIMER_START;
  assert( cnt==(cnt&0x1ffff) );
  assert( id->h>2 );
  do{
#if defined(USE_PREAD)
    got = osPread(id->h, pBuf, cnt, offset);
    SimulateIOError( got = -1 );
#elif defined(USE_PREAD64)
    got = osPread64(id->h, pBuf, cnt, offset);
    SimulateIOError( got = -1 );
#else
    newOffset = lseek(id->h, offset, SEEK_SET);
    SimulateIOError( newOffset-- );
    if( newOffset!=offset ){
      if( newOffset == -1 ){
        storeLastErrno((unixFile*)id, errno);
      }else{
        storeLastErrno((unixFile*)id, 0);
      }
      return -1;
    }
    got = osRead(id->h, pBuf, cnt);
#endif
    if( got==cnt ) break;
    if( got<0 ){
      if( errno==EINTR ){ got = 1; continue; }
      prior = 0;
      storeLastErrno((unixFile*)id,  errno);
      break;
    }else if( got>0 ){
      cnt -= got;
      offset += got;
      prior += got;
      pBuf = (void*)(got + (char*)pBuf);
    }
  }while( got>0 );
  TIMER_END;
  OSTRACE(("READ    %-3d %5d %7lld %llu\n",
            id->h, got+prior, offset-prior, TIMER_ELAPSED));
  return got+prior;
}

/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
static int unixRead(
  sqlite3_file *id, 
  void *pBuf, 
  int amt,
  sqlite3_int64 offset
){
  unixFile *pFile = (unixFile *)id;
  int got;
  assert( id );
  assert( offset>=0 );
  assert( amt>0 );

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */
#if 0
  assert( pFile->pUnused==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 
  );
#endif

#if SQLITE_MAX_MMAP_SIZE>0
  /* Deal with as much of this read request as possible by transfering
  ** data from the memory mapping using memcpy().  */
  if( offset<pFile->mmapSize ){
    if( offset+amt <= pFile->mmapSize ){
      memcpy(pBuf, &((u8 *)(pFile->pMapRegion))[offset], amt);
      return SQLITE_OK;
    }else{
      int nCopy = pFile->mmapSize - offset;
      memcpy(pBuf, &((u8 *)(pFile->pMapRegion))[offset], nCopy);
      pBuf = &((u8 *)pBuf)[nCopy];
      amt -= nCopy;
      offset += nCopy;
    }
  }
#endif

  got = seekAndRead(pFile, offset, pBuf, amt);
  if( got==amt ){
    return SQLITE_OK;
  }else if( got<0 ){
    /* lastErrno set by seekAndRead */
    return SQLITE_IOERR_READ;
  }else{
    storeLastErrno(pFile, 0);   /* not a system error */
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[got], 0, amt-got);
    return SQLITE_IOERR_SHORT_READ;
  }
}

/*
** Attempt to seek the file-descriptor passed as the first argument to
** absolute offset iOff, then attempt to write nBuf bytes of data from
** pBuf to it. If an error occurs, return -1 and set *piErrno. Otherwise, 
** return the actual number of bytes written (which may be less than
** nBuf).
*/
static int seekAndWriteFd(
  int fd,                         /* File descriptor to write to */
  i64 iOff,                       /* File offset to begin writing at */
  const void *pBuf,               /* Copy data from this buffer to the file */
  int nBuf,                       /* Size of buffer pBuf in bytes */
  int *piErrno                    /* OUT: Error number if error occurs */
){
  int rc = 0;                     /* Value returned by system call */

  assert( nBuf==(nBuf&0x1ffff) );
  assert( fd>2 );
  nBuf &= 0x1ffff;
  TIMER_START;

#if defined(USE_PREAD)
  do{ rc = (int)osPwrite(fd, pBuf, nBuf, iOff); }while( rc<0 && errno==EINTR );
#elif defined(USE_PREAD64)
  do{ rc = (int)osPwrite64(fd, pBuf, nBuf, iOff);}while( rc<0 && errno==EINTR);
#else
  do{
    i64 iSeek = lseek(fd, iOff, SEEK_SET);
    SimulateIOError( iSeek-- );

    if( iSeek!=iOff ){
      if( piErrno ) *piErrno = (iSeek==-1 ? errno : 0);
      return -1;
    }
    rc = osWrite(fd, pBuf, nBuf);
  }while( rc<0 && errno==EINTR );
#endif

  TIMER_END;
  OSTRACE(("WRITE   %-3d %5d %7lld %llu\n", fd, rc, iOff, TIMER_ELAPSED));

  if( rc<0 && piErrno ) *piErrno = errno;
  return rc;
}


/*
** Seek to the offset in id->offset then read cnt bytes into pBuf.
** Return the number of bytes actually read.  Update the offset.
**
** To avoid stomping the errno value on a failed write the lastErrno value
** is set before returning.
*/
static int seekAndWrite(unixFile *id, i64 offset, const void *pBuf, int cnt){
  return seekAndWriteFd(id->h, offset, pBuf, cnt, &id->lastErrno);
}


/*
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
static int unixWrite(
  sqlite3_file *id, 
  const void *pBuf, 
  int amt,
  sqlite3_int64 offset 
){
  unixFile *pFile = (unixFile*)id;
  int wrote = 0;
  assert( id );
  assert( amt>0 );

  /* If this is a database file (not a journal, master-journal or temp
  ** file), the bytes in the locking range should never be read or written. */
#if 0
  assert( pFile->pUnused==0
       || offset>=PENDING_BYTE+512
       || offset+amt<=PENDING_BYTE 
  );
#endif

#ifdef SQLITE_DEBUG
  /* If we are doing a normal write to a database file (as opposed to
  ** doing a hot-journal rollback or a write to some file other than a
  ** normal database file) then record the fact that the database
  ** has changed.  If the transaction counter is modified, record that
  ** fact too.
  */
  if( pFile->inNormalWrite ){
    pFile->dbUpdate = 1;  /* The database has been modified */
    if( offset<=24 && offset+amt>=27 ){
      int rc;
      char oldCntr[4];
      SimulateIOErrorBenign(1);
      rc = seekAndRead(pFile, 24, oldCntr, 4);
      SimulateIOErrorBenign(0);
      if( rc!=4 || memcmp(oldCntr, &((char*)pBuf)[24-offset], 4)!=0 ){
        pFile->transCntrChng = 1;  /* The transaction counter has changed */
      }
    }
  }
#endif

#if SQLITE_MAX_MMAP_SIZE>0
  /* Deal with as much of this write request as possible by transfering
  ** data from the memory mapping using memcpy().  */
  if( offset<pFile->mmapSize ){
    if( offset+amt <= pFile->mmapSize ){
      memcpy(&((u8 *)(pFile->pMapRegion))[offset], pBuf, amt);
      return SQLITE_OK;
    }else{
      int nCopy = pFile->mmapSize - offset;
      memcpy(&((u8 *)(pFile->pMapRegion))[offset], pBuf, nCopy);
      pBuf = &((u8 *)pBuf)[nCopy];
      amt -= nCopy;
      offset += nCopy;
    }
  }
#endif
 
  while( (wrote = seekAndWrite(pFile, offset, pBuf, amt))<amt && wrote>0 ){
    amt -= wrote;
    offset += wrote;
    pBuf = &((char*)pBuf)[wrote];
  }
  SimulateIOError(( wrote=(-1), amt=1 ));
  SimulateDiskfullError(( wrote=0, amt=1 ));

  if( amt>wrote ){
    if( wrote<0 && pFile->lastErrno!=ENOSPC ){
      /* lastErrno set by seekAndWrite */
      return SQLITE_IOERR_WRITE;
    }else{
      storeLastErrno(pFile, 0); /* not a system error */
      return SQLITE_FULL;
    }
  }

  return SQLITE_OK;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occurring at the right times.
*/
SQLITE_PRIVATE int sqlite3_sync_count = 0;
SQLITE_PRIVATE int sqlite3_fullsync_count = 0;
#endif

/*
** We do not trust systems to provide a working fdatasync().  Some do.
** Others do no.  To be safe, we will stick with the (slightly slower)
** fsync(). If you know that your system does support fdatasync() correctly,
** then simply compile with -Dfdatasync=fdatasync or -DHAVE_FDATASYNC
*/
#if !defined(fdatasync) && !HAVE_FDATASYNC
# define fdatasync fsync
#endif

/*
** Define HAVE_FULLFSYNC to 0 or 1 depending on whether or not
** the F_FULLFSYNC macro is defined.  F_FULLFSYNC is currently
** only available on Mac OS X.  But that could change.
*/
#ifdef F_FULLFSYNC
# define HAVE_FULLFSYNC 1
#else
# define HAVE_FULLFSYNC 0
#endif


/*
** The fsync() system call does not work as advertised on many
** unix systems.  The following procedure is an attempt to make
** it work better.
**
** The SQLITE_NO_SYNC macro disables all fsync()s.  This is useful
** for testing when we want to run through the test suite quickly.
** You are strongly advised *not* to deploy with SQLITE_NO_SYNC
** enabled, however, since with SQLITE_NO_SYNC enabled, an OS crash
** or power failure will likely corrupt the database file.
**
** SQLite sets the dataOnly flag if the size of the file is unchanged.
** The idea behind dataOnly is that it should only write the file content
** to disk, not the inode.  We only set dataOnly if the file size is 
** unchanged since the file size is part of the inode.  However, 
** Ted Ts'o tells us that fdatasync() will also write the inode if the
** file size has changed.  The only real difference between fdatasync()
** and fsync(), Ted tells us, is that fdatasync() will not flush the
** inode if the mtime or owner or other inode attributes have changed.
** We only care about the file size, not the other file attributes, so
** as far as SQLite is concerned, an fdatasync() is always adequate.
** So, we always use fdatasync() if it is available, regardless of
** the value of the dataOnly flag.
*/
static int full_fsync(int fd, int fullSync, int dataOnly){
  int rc;

  /* The following "ifdef/elif/else/" block has the same structure as
  ** the one below. It is replicated here solely to avoid cluttering 
  ** up the real code with the UNUSED_PARAMETER() macros.
  */
#ifdef SQLITE_NO_SYNC
  UNUSED_PARAMETER(fd);
  UNUSED_PARAMETER(fullSync);
  UNUSED_PARAMETER(dataOnly);
#elif HAVE_FULLFSYNC
  UNUSED_PARAMETER(dataOnly);
#else
  UNUSED_PARAMETER(fullSync);
  UNUSED_PARAMETER(dataOnly);
#endif

  /* Record the number of times that we do a normal fsync() and 
  ** FULLSYNC.  This is used during testing to verify that this procedure
  ** gets called with the correct arguments.
  */
#ifdef SQLITE_TEST
  if( fullSync ) sqlite3_fullsync_count++;
  sqlite3_sync_count++;
#endif

  /* If we compiled with the SQLITE_NO_SYNC flag, then syncing is a
  ** no-op
  */
#ifdef SQLITE_NO_SYNC
  rc = SQLITE_OK;
#elif HAVE_FULLFSYNC
  if( fullSync ){
    rc = osFcntl(fd, F_FULLFSYNC, 0);
  }else{
    rc = 1;
  }
  /* If the FULLFSYNC failed, fall back to attempting an fsync().
  ** It shouldn't be possible for fullfsync to fail on the local 
  ** file system (on OSX), so failure indicates that FULLFSYNC
  ** isn't supported for this file system. So, attempt an fsync 
  ** and (for now) ignore the overhead of a superfluous fcntl call.  
  ** It'd be better to detect fullfsync support once and avoid 
  ** the fcntl call every time sync is called.
  */
  if( rc ) rc = fsync(fd);

#elif defined(__APPLE__)
  /* fdatasync() on HFS+ doesn't yet flush the file size if it changed correctly
  ** so currently we default to the macro that redefines fdatasync to fsync
  */
  rc = fsync(fd);
#else 
  rc = fdatasync(fd);
#if OS_VXWORKS
  if( rc==-1 && errno==ENOTSUP ){
    rc = fsync(fd);
  }
#endif /* OS_VXWORKS */
#endif /* ifdef SQLITE_NO_SYNC elif HAVE_FULLFSYNC */

  if( OS_VXWORKS && rc!= -1 ){
    rc = 0;
  }
  return rc;
}

/*
** Open a file descriptor to the directory containing file zFilename.
** If successful, *pFd is set to the opened file descriptor and
** SQLITE_OK is returned. If an error occurs, either SQLITE_NOMEM
** or SQLITE_CANTOPEN is returned and *pFd is set to an undefined
** value.
**
** The directory file descriptor is used for only one thing - to
** fsync() a directory to make sure file creation and deletion events
** are flushed to disk.  Such fsyncs are not needed on newer
** journaling filesystems, but are required on older filesystems.
**
** This routine can be overridden using the xSetSysCall interface.
** The ability to override this routine was added in support of the
** chromium sandbox.  Opening a directory is a security risk (we are
** told) so making it overrideable allows the chromium sandbox to
** replace this routine with a harmless no-op.  To make this routine
** a no-op, replace it with a stub that returns SQLITE_OK but leaves
** *pFd set to a negative number.
**
** If SQLITE_OK is returned, the caller is responsible for closing
** the file descriptor *pFd using close().
*/
static int openDirectory(const char *zFilename, int *pFd){
  int ii;
  int fd = -1;
  char zDirname[MAX_PATHNAME+1];

  sqlite3_snprintf(MAX_PATHNAME, zDirname, "%s", zFilename);
  for(ii=(int)strlen(zDirname); ii>1 && zDirname[ii]!='/'; ii--);
  if( ii>0 ){
    zDirname[ii] = '\0';
    fd = robust_open(zDirname, O_RDONLY|O_BINARY, 0);
    if( fd>=0 ){
      OSTRACE(("OPENDIR %-3d %s\n", fd, zDirname));
    }
  }
  *pFd = fd;
  return (fd>=0?SQLITE_OK:unixLogError(SQLITE_CANTOPEN_BKPT, "open", zDirname));
}

/*
** Make sure all writes to a particular file are committed to disk.
**
** If dataOnly==0 then both the file itself and its metadata (file
** size, access time, etc) are synced.  If dataOnly!=0 then only the
** file data is synced.
**
** Under Unix, also make sure that the directory entry for the file
** has been created by fsync-ing the directory that contains the file.
** If we do not do this and we encounter a power failure, the directory
** entry for the journal might not exist after we reboot.  The next
** SQLite to access the file will not know that the journal exists (because
** the directory entry for the journal was never created) and the transaction
** will not roll back - possibly leading to database corruption.
*/
static int unixSync(sqlite3_file *id, int flags){
  int rc;
  unixFile *pFile = (unixFile*)id;

  int isDataOnly = (flags&SQLITE_SYNC_DATAONLY);
  int isFullsync = (flags&0x0F)==SQLITE_SYNC_FULL;

  /* Check that one of SQLITE_SYNC_NORMAL or FULL was passed */
  assert((flags&0x0F)==SQLITE_SYNC_NORMAL
      || (flags&0x0F)==SQLITE_SYNC_FULL
  );

  /* Unix cannot, but some systems may return SQLITE_FULL from here. This
  ** line is to test that doing so does not cause any problems.
  */
  SimulateDiskfullError( return SQLITE_FULL );

  assert( pFile );
  OSTRACE(("SYNC    %-3d\n", pFile->h));
  rc = full_fsync(pFile->h, isFullsync, isDataOnly);
  SimulateIOError( rc=1 );
  if( rc ){
    storeLastErrno(pFile, errno);
    return unixLogError(SQLITE_IOERR_FSYNC, "full_fsync", pFile->zPath);
  }

  /* Also fsync the directory containing the file if the DIRSYNC flag
  ** is set.  This is a one-time occurrence.  Many systems (examples: AIX)
  ** are unable to fsync a directory, so ignore errors on the fsync.
  */
  if( pFile->ctrlFlags & UNIXFILE_DIRSYNC ){
    int dirfd;
    OSTRACE(("DIRSYNC %s (have_fullfsync=%d fullsync=%d)\n", pFile->zPath,
            HAVE_FULLFSYNC, isFullsync));
    rc = osOpenDirectory(pFile->zPath, &dirfd);
    if( rc==SQLITE_OK && dirfd>=0 ){
      full_fsync(dirfd, 0, 0);
      robust_close(pFile, dirfd, __LINE__);
    }else if( rc==SQLITE_CANTOPEN ){
      rc = SQLITE_OK;
    }
    pFile->ctrlFlags &= ~UNIXFILE_DIRSYNC;
  }
  return rc;
}

/*
** Truncate an open file to a specified size
*/
static int unixTruncate(sqlite3_file *id, i64 nByte){
  unixFile *pFile = (unixFile *)id;
  int rc;
  assert( pFile );
  SimulateIOError( return SQLITE_IOERR_TRUNCATE );

  /* If the user has configured a chunk-size for this file, truncate the
  ** file so that it consists of an integer number of chunks (i.e. the
  ** actual file size after the operation may be larger than the requested
  ** size).
  */
  if( pFile->szChunk>0 ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  rc = robust_ftruncate(pFile->h, nByte);
  if( rc ){
    storeLastErrno(pFile, errno);
    return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
  }else{
#ifdef SQLITE_DEBUG
    /* If we are doing a normal write to a database file (as opposed to
    ** doing a hot-journal rollback or a write to some file other than a
    ** normal database file) and we truncate the file to zero length,
    ** that effectively updates the change counter.  This might happen
    ** when restoring a database using the backup API from a zero-length
    ** source.
    */
    if( pFile->inNormalWrite && nByte==0 ){
      pFile->transCntrChng = 1;
    }
#endif

#if SQLITE_MAX_MMAP_SIZE>0
    /* If the file was just truncated to a size smaller than the currently
    ** mapped region, reduce the effective mapping size as well. SQLite will
    ** use read() and write() to access data beyond this point from now on.  
    */
    if( nByte<pFile->mmapSize ){
      pFile->mmapSize = nByte;
    }
#endif

    return SQLITE_OK;
  }
}

/*
** Determine the current size of a file in bytes
*/
static int unixFileSize(sqlite3_file *id, i64 *pSize){
  int rc;
  struct stat buf;
  assert( id );
  rc = osFstat(((unixFile*)id)->h, &buf);
  SimulateIOError( rc=1 );
  if( rc!=0 ){
    storeLastErrno((unixFile*)id, errno);
    return SQLITE_IOERR_FSTAT;
  }
  *pSize = buf.st_size;

  /* When opening a zero-size database, the findInodeInfo() procedure
  ** writes a single byte into that file in order to work around a bug
  ** in the OS-X msdos filesystem.  In order to avoid problems with upper
  ** layers, we need to report this file size as zero even though it is
  ** really 1.   Ticket #3260.
  */
  if( *pSize==1 ) *pSize = 0;


  return SQLITE_OK;
}

#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
/*
** Handler for proxy-locking file-control verbs.  Defined below in the
** proxying locking division.
*/
static int proxyFileControl(sqlite3_file*,int,void*);
#endif

/* 
** This function is called to handle the SQLITE_FCNTL_SIZE_HINT 
** file-control operation.  Enlarge the database to nBytes in size
** (rounded up to the next chunk-size).  If the database is already
** nBytes or larger, this routine is a no-op.
*/
static int fcntlSizeHint(unixFile *pFile, i64 nByte){
  if( pFile->szChunk>0 ){
    i64 nSize;                    /* Required file size */
    struct stat buf;              /* Used to hold return values of fstat() */
   
    if( osFstat(pFile->h, &buf) ){
      return SQLITE_IOERR_FSTAT;
    }

    nSize = ((nByte+pFile->szChunk-1) / pFile->szChunk) * pFile->szChunk;
    if( nSize>(i64)buf.st_size ){

#if defined(HAVE_POSIX_FALLOCATE) && HAVE_POSIX_FALLOCATE
      /* The code below is handling the return value of osFallocate() 
      ** correctly. posix_fallocate() is defined to "returns zero on success, 
      ** or an error number on  failure". See the manpage for details. */
      int err;
      do{
        err = osFallocate(pFile->h, buf.st_size, nSize-buf.st_size);
      }while( err==EINTR );
      if( err ) return SQLITE_IOERR_WRITE;
#else
      /* If the OS does not have posix_fallocate(), fake it. Write a 
      ** single byte to the last byte in each block that falls entirely
      ** within the extended region. Then, if required, a single byte
      ** at offset (nSize-1), to set the size of the file correctly.
      ** This is a similar technique to that used by glibc on systems
      ** that do not have a real fallocate() call.
      */
      int nBlk = buf.st_blksize;  /* File-system block size */
      int nWrite = 0;             /* Number of bytes written by seekAndWrite */
      i64 iWrite;                 /* Next offset to write to */

      iWrite = ((buf.st_size + 2*nBlk - 1)/nBlk)*nBlk-1;
      assert( iWrite>=buf.st_size );
      assert( (iWrite/nBlk)==((buf.st_size+nBlk-1)/nBlk) );
      assert( ((iWrite+1)%nBlk)==0 );
      for(/*no-op*/; iWrite<nSize; iWrite+=nBlk ){
        nWrite = seekAndWrite(pFile, iWrite, "", 1);
        if( nWrite!=1 ) return SQLITE_IOERR_WRITE;
      }
      if( nWrite==0 || (nSize%nBlk) ){
        nWrite = seekAndWrite(pFile, nSize-1, "", 1);
        if( nWrite!=1 ) return SQLITE_IOERR_WRITE;
      }
#endif
    }
  }

#if SQLITE_MAX_MMAP_SIZE>0
  if( pFile->mmapSizeMax>0 && nByte>pFile->mmapSize ){
    int rc;
    if( pFile->szChunk<=0 ){
      if( robust_ftruncate(pFile->h, nByte) ){
        storeLastErrno(pFile, errno);
        return unixLogError(SQLITE_IOERR_TRUNCATE, "ftruncate", pFile->zPath);
      }
    }

    rc = unixMapfile(pFile, nByte);
    return rc;
  }
#endif

  return SQLITE_OK;
}

/*
** If *pArg is initially negative then this is a query.  Set *pArg to
** 1 or 0 depending on whether or not bit mask of pFile->ctrlFlags is set.
**
** If *pArg is 0 or 1, then clear or set the mask bit of pFile->ctrlFlags.
*/
static void unixModeBit(unixFile *pFile, unsigned char mask, int *pArg){
  if( *pArg<0 ){
    *pArg = (pFile->ctrlFlags & mask)!=0;
  }else if( (*pArg)==0 ){
    pFile->ctrlFlags &= ~mask;
  }else{
    pFile->ctrlFlags |= mask;
  }
}

/* Forward declaration */
static int unixGetTempname(int nBuf, char *zBuf);

/*
** Information and control of an open file handle.
*/
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  unixFile *pFile = (unixFile*)id;
  switch( op ){
    case SQLITE_FCNTL_WAL_BLOCK: {
      /* pFile->ctrlFlags |= UNIXFILE_BLOCK; // Deferred feature */
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = pFile->eFileLock;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_LAST_ERRNO: {
      *(int*)pArg = pFile->lastErrno;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      pFile->szChunk = *(int *)pArg;
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SIZE_HINT: {
      int rc;
      SimulateIOErrorBenign(1);
      rc = fcntlSizeHint(pFile, *(i64 *)pArg);
      SimulateIOErrorBenign(0);
      return rc;
    }
    case SQLITE_FCNTL_PERSIST_WAL: {
      unixModeBit(pFile, UNIXFILE_PERSIST_WAL, (int*)pArg);
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_POWERSAFE_OVERWRITE: {
      unixModeBit(pFile, UNIXFILE_PSOW, (int*)pArg);
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_VFSNAME: {
      *(char**)pArg = sqlite3_mprintf("%s", pFile->pVfs->zName);
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_TEMPFILENAME: {
      char *zTFile = sqlite3_malloc64( pFile->pVfs->mxPathname );
      if( zTFile ){
        unixGetTempname(pFile->pVfs->mxPathname, zTFile);
        *(char**)pArg = zTFile;
      }
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_HAS_MOVED: {
      *(int*)pArg = fileHasMoved(pFile);
      return SQLITE_OK;
    }
#if SQLITE_MAX_MMAP_SIZE>0
    case SQLITE_FCNTL_MMAP_SIZE: {
      i64 newLimit = *(i64*)pArg;
      int rc = SQLITE_OK;
      if( newLimit>sqlite3GlobalConfig.mxMmap ){
        newLimit = sqlite3GlobalConfig.mxMmap;
      }
      *(i64*)pArg = pFile->mmapSizeMax;
      if( newLimit>=0 && newLimit!=pFile->mmapSizeMax && pFile->nFetchOut==0 ){
        pFile->mmapSizeMax = newLimit;
        if( pFile->mmapSize>0 ){
          unixUnmapfile(pFile);
          rc = unixMapfile(pFile, -1);
        }
      }
      return rc;
    }
#endif
#ifdef SQLITE_DEBUG
    /* The pager calls this method to signal that it has done
    ** a rollback and that the database is therefore unchanged and
    ** it hence it is OK for the transaction change counter to be
    ** unchanged.
    */
    case SQLITE_FCNTL_DB_UNCHANGED: {
      ((unixFile*)id)->dbUpdate = 0;
      return SQLITE_OK;
    }
#endif
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    case SQLITE_FCNTL_SET_LOCKPROXYFILE:
    case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
      return proxyFileControl(id,op,pArg);
    }
#endif /* SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__) */
  }
  return SQLITE_NOTFOUND;
}

/*
** Return the sector size in bytes of the underlying block device for
** the specified file. This is almost always 512 bytes, but may be
** larger for some devices.
**
** SQLite code assumes this function cannot fail. It also assumes that
** if two files are created in the same file-system directory (i.e.
** a database and its journal file) that the sector size will be the
** same for both.
*/
#ifndef __QNXNTO__ 
static int unixSectorSize(sqlite3_file *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  return SQLITE_DEFAULT_SECTOR_SIZE;
}
#endif

/*
** The following version of unixSectorSize() is optimized for QNX.
*/
#ifdef __QNXNTO__
#include <sys/dcmd_blk.h>
#include <sys/statvfs.h>
static int unixSectorSize(sqlite3_file *id){
  unixFile *pFile = (unixFile*)id;
  if( pFile->sectorSize == 0 ){
    struct statvfs fsInfo;
       
    /* Set defaults for non-supported filesystems */
    pFile->sectorSize = SQLITE_DEFAULT_SECTOR_SIZE;
    pFile->deviceCharacteristics = 0;
    if( fstatvfs(pFile->h, &fsInfo) == -1 ) {
      return pFile->sectorSize;
    }

    if( !strcmp(fsInfo.f_basetype, "tmp") ) {
      pFile->sectorSize = fsInfo.f_bsize;
      pFile->deviceCharacteristics =
        SQLITE_IOCAP_ATOMIC4K |       /* All ram filesystem writes are atomic */
        SQLITE_IOCAP_SAFE_APPEND |    /* growing the file does not occur until
                                      ** the write succeeds */
        SQLITE_IOCAP_SEQUENTIAL |     /* The ram filesystem has no write behind
                                      ** so it is ordered */
        0;
    }else if( strstr(fsInfo.f_basetype, "etfs") ){
      pFile->sectorSize = fsInfo.f_bsize;
      pFile->deviceCharacteristics =
        /* etfs cluster size writes are atomic */
        (pFile->sectorSize / 512 * SQLITE_IOCAP_ATOMIC512) |
        SQLITE_IOCAP_SAFE_APPEND |    /* growing the file does not occur until
                                      ** the write succeeds */
        SQLITE_IOCAP_SEQUENTIAL |     /* The ram filesystem has no write behind
                                      ** so it is ordered */
        0;
    }else if( !strcmp(fsInfo.f_basetype, "qnx6") ){
      pFile->sectorSize = fsInfo.f_bsize;
      pFile->deviceCharacteristics =
        SQLITE_IOCAP_ATOMIC |         /* All filesystem writes are atomic */
        SQLITE_IOCAP_SAFE_APPEND |    /* growing the file does not occur until
                                      ** the write succeeds */
        SQLITE_IOCAP_SEQUENTIAL |     /* The ram filesystem has no write behind
                                      ** so it is ordered */
        0;
    }else if( !strcmp(fsInfo.f_basetype, "qnx4") ){
      pFile->sectorSize = fsInfo.f_bsize;
      pFile->deviceCharacteristics =
        /* full bitset of atomics from max sector size and smaller */
        ((pFile->sectorSize / 512 * SQLITE_IOCAP_ATOMIC512) << 1) - 2 |
        SQLITE_IOCAP_SEQUENTIAL |     /* The ram filesystem has no write behind
                                      ** so it is ordered */
        0;
    }else if( strstr(fsInfo.f_basetype, "dos") ){
      pFile->sectorSize = fsInfo.f_bsize;
      pFile->deviceCharacteristics =
        /* full bitset of atomics from max sector size and smaller */
        ((pFile->sectorSize / 512 * SQLITE_IOCAP_ATOMIC512) << 1) - 2 |
        SQLITE_IOCAP_SEQUENTIAL |     /* The ram filesystem has no write behind
                                      ** so it is ordered */
        0;
    }else{
      pFile->deviceCharacteristics =
        SQLITE_IOCAP_ATOMIC512 |      /* blocks are atomic */
        SQLITE_IOCAP_SAFE_APPEND |    /* growing the file does not occur until
                                      ** the write succeeds */
        0;
    }
  }
  /* Last chance verification.  If the sector size isn't a multiple of 512
  ** then it isn't valid.*/
  if( pFile->sectorSize % 512 != 0 ){
    pFile->deviceCharacteristics = 0;
    pFile->sectorSize = SQLITE_DEFAULT_SECTOR_SIZE;
  }
  return pFile->sectorSize;
}
#endif /* __QNXNTO__ */

/*
** Return the device characteristics for the file.
**
** This VFS is set up to return SQLITE_IOCAP_POWERSAFE_OVERWRITE by default.
** However, that choice is controversial since technically the underlying
** file system does not always provide powersafe overwrites.  (In other
** words, after a power-loss event, parts of the file that were never
** written might end up being altered.)  However, non-PSOW behavior is very,
** very rare.  And asserting PSOW makes a large reduction in the amount
** of required I/O for journaling, since a lot of padding is eliminated.
**  Hence, while POWERSAFE_OVERWRITE is on by default, there is a file-control
** available to turn it off and URI query parameter available to turn it off.
*/
static int unixDeviceCharacteristics(sqlite3_file *id){
  unixFile *p = (unixFile*)id;
  int rc = 0;
#ifdef __QNXNTO__
  if( p->sectorSize==0 ) unixSectorSize(id);
  rc = p->deviceCharacteristics;
#endif
  if( p->ctrlFlags & UNIXFILE_PSOW ){
    rc |= SQLITE_IOCAP_POWERSAFE_OVERWRITE;
  }
  return rc;
}

#if !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0

/*
** Return the system page size.
**
** This function should not be called directly by other code in this file. 
** Instead, it should be called via macro osGetpagesize().
*/
static int unixGetpagesize(void){
#if OS_VXWORKS
  return 1024;
#elif defined(_BSD_SOURCE)
  return getpagesize();
#else
  return (int)sysconf(_SC_PAGESIZE);
#endif
}

#endif /* !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0 */

#ifndef SQLITE_OMIT_WAL

/*
** Object used to represent an shared memory buffer.  
**
** When multiple threads all reference the same wal-index, each thread
** has its own unixShm object, but they all point to a single instance
** of this unixShmNode object.  In other words, each wal-index is opened
** only once per process.
**
** Each unixShmNode object is connected to a single unixInodeInfo object.
** We could coalesce this object into unixInodeInfo, but that would mean
** every open file that does not use shared memory (in other words, most
** open files) would have to carry around this extra information.  So
** the unixInodeInfo object contains a pointer to this unixShmNode object
** and the unixShmNode object is created only when needed.
**
** unixMutexHeld() must be true when creating or destroying
** this object or while reading or writing the following fields:
**
**      nRef
**
** The following fields are read-only after the object is created:
** 
**      fid
**      zFilename
**
** Either unixShmNode.mutex must be held or unixShmNode.nRef==0 and
** unixMutexHeld() is true when reading or writing any other field
** in this structure.
*/
struct unixShmNode {
  unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
  sqlite3_mutex *mutex;      /* Mutex to access this object */
  char *zFilename;           /* Name of the mmapped file */
  int h;                     /* Open file descriptor */
  int szRegion;              /* Size of shared-memory regions */
  u16 nRegion;               /* Size of array apRegion */
  u8 isReadonly;             /* True if read-only */
  char **apRegion;           /* Array of mapped shared-memory regions */
  int nRef;                  /* Number of unixShm objects pointing to this */
  unixShm *pFirst;           /* All unixShm objects pointing to this */
#ifdef SQLITE_DEBUG
  u8 exclMask;               /* Mask of exclusive locks held */
  u8 sharedMask;             /* Mask of shared locks held */
  u8 nextShmId;              /* Next available unixShm.id value */
#endif
};

/*
** Structure used internally by this VFS to record the state of an
** open shared memory connection.
**
** The following fields are initialized when this object is created and
** are read-only thereafter:
**
**    unixShm.pFile
**    unixShm.id
**
** All other fields are read/write.  The unixShm.pFile->mutex must be held
** while accessing any read/write fields.
*/
struct unixShm {
  unixShmNode *pShmNode;     /* The underlying unixShmNode object */
  unixShm *pNext;            /* Next unixShm with the same unixShmNode */
  u8 hasMutex;               /* True if holding the unixShmNode mutex */
  u8 id;                     /* Id of this connection within its unixShmNode */
  u16 sharedMask;            /* Mask of shared locks held */
  u16 exclMask;              /* Mask of exclusive locks held */
};

/*
** Constants used for locking
*/
#define UNIX_SHM_BASE   ((22+SQLITE_SHM_NLOCK)*4)         /* first lock byte */
#define UNIX_SHM_DMS    (UNIX_SHM_BASE+SQLITE_SHM_NLOCK)  /* deadman switch */

/*
** Apply posix advisory locks for all bytes from ofst through ofst+n-1.
**
** Locks block if the mask is exactly UNIX_SHM_C and are non-blocking
** otherwise.
*/
static int unixShmSystemLock(
  unixFile *pFile,       /* Open connection to the WAL file */
  int lockType,          /* F_UNLCK, F_RDLCK, or F_WRLCK */
  int ofst,              /* First byte of the locking range */
  int n                  /* Number of bytes to lock */
){
  unixShmNode *pShmNode; /* Apply locks to this open shared-memory segment */
  struct flock f;        /* The posix advisory locking structure */
  int rc = SQLITE_OK;    /* Result code form fcntl() */

  /* Access to the unixShmNode object is serialized by the caller */
  pShmNode = pFile->pInode->pShmNode;
  assert( sqlite3_mutex_held(pShmNode->mutex) || pShmNode->nRef==0 );

  /* Shared locks never span more than one byte */
  assert( n==1 || lockType!=F_RDLCK );

  /* Locks are within range */
  assert( n>=1 && n<SQLITE_SHM_NLOCK );

  if( pShmNode->h>=0 ){
    int lkType;
    /* Initialize the locking parameters */
    memset(&f, 0, sizeof(f));
    f.l_type = lockType;
    f.l_whence = SEEK_SET;
    f.l_start = ofst;
    f.l_len = n;

    lkType = (pFile->ctrlFlags & UNIXFILE_BLOCK)!=0 ? F_SETLKW : F_SETLK;
    rc = osFcntl(pShmNode->h, lkType, &f);
    rc = (rc!=(-1)) ? SQLITE_OK : SQLITE_BUSY;
    pFile->ctrlFlags &= ~UNIXFILE_BLOCK;
  }

  /* Update the global lock state and do debug tracing */
#ifdef SQLITE_DEBUG
  { u16 mask;
  OSTRACE(("SHM-LOCK "));
  mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst);
  if( rc==SQLITE_OK ){
    if( lockType==F_UNLCK ){
      OSTRACE(("unlock %d ok", ofst));
      pShmNode->exclMask &= ~mask;
      pShmNode->sharedMask &= ~mask;
    }else if( lockType==F_RDLCK ){
      OSTRACE(("read-lock %d ok", ofst));
      pShmNode->exclMask &= ~mask;
      pShmNode->sharedMask |= mask;
    }else{
      assert( lockType==F_WRLCK );
      OSTRACE(("write-lock %d ok", ofst));
      pShmNode->exclMask |= mask;
      pShmNode->sharedMask &= ~mask;
    }
  }else{
    if( lockType==F_UNLCK ){
      OSTRACE(("unlock %d failed", ofst));
    }else if( lockType==F_RDLCK ){
      OSTRACE(("read-lock failed"));
    }else{
      assert( lockType==F_WRLCK );
      OSTRACE(("write-lock %d failed", ofst));
    }
  }
  OSTRACE((" - afterwards %03x,%03x\n",
           pShmNode->sharedMask, pShmNode->exclMask));
  }
#endif

  return rc;        
}

/*
** Return the minimum number of 32KB shm regions that should be mapped at
** a time, assuming that each mapping must be an integer multiple of the
** current system page-size.
**
** Usually, this is 1. The exception seems to be systems that are configured
** to use 64KB pages - in this case each mapping must cover at least two
** shm regions.
*/
static int unixShmRegionPerMap(void){
  int shmsz = 32*1024;            /* SHM region size */
  int pgsz = osGetpagesize();   /* System page size */
  assert( ((pgsz-1)&pgsz)==0 );   /* Page size must be a power of 2 */
  if( pgsz<shmsz ) return 1;
  return pgsz/shmsz;
}

/*
** Purge the unixShmNodeList list of all entries with unixShmNode.nRef==0.
**
** This is not a VFS shared-memory method; it is a utility function called
** by VFS shared-memory methods.
*/
static void unixShmPurge(unixFile *pFd){
  unixShmNode *p = pFd->pInode->pShmNode;
  assert( unixMutexHeld() );
  if( p && p->nRef==0 ){
    int nShmPerMap = unixShmRegionPerMap();
    int i;
    assert( p->pInode==pFd->pInode );
    sqlite3_mutex_free(p->mutex);
    for(i=0; i<p->nRegion; i+=nShmPerMap){
      if( p->h>=0 ){
        osMunmap(p->apRegion[i], p->szRegion);
      }else{
        sqlite3_free(p->apRegion[i]);
      }
    }
    sqlite3_free(p->apRegion);
    if( p->h>=0 ){
      robust_close(pFd, p->h, __LINE__);
      p->h = -1;
    }
    p->pInode->pShmNode = 0;
    sqlite3_free(p);
  }
}

/*
** Open a shared-memory area associated with open database file pDbFd.  
** This particular implementation uses mmapped files.
**
** The file used to implement shared-memory is in the same directory
** as the open database file and has the same name as the open database
** file with the "-shm" suffix added.  For example, if the database file
** is "/home/user1/config.db" then the file that is created and mmapped
** for shared memory will be called "/home/user1/config.db-shm".  
**
** Another approach to is to use files in /dev/shm or /dev/tmp or an
** some other tmpfs mount. But if a file in a different directory
** from the database file is used, then differing access permissions
** or a chroot() might cause two different processes on the same
** database to end up using different files for shared memory - 
** meaning that their memory would not really be shared - resulting
** in database corruption.  Nevertheless, this tmpfs file usage
** can be enabled at compile-time using -DSQLITE_SHM_DIRECTORY="/dev/shm"
** or the equivalent.  The use of the SQLITE_SHM_DIRECTORY compile-time
** option results in an incompatible build of SQLite;  builds of SQLite
** that with differing SQLITE_SHM_DIRECTORY settings attempt to use the
** same database file at the same time, database corruption will likely
** result. The SQLITE_SHM_DIRECTORY compile-time option is considered
** "unsupported" and may go away in a future SQLite release.
**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
** the file must be truncated to zero length or have its header cleared.
**
** If the original database file (pDbFd) is using the "unix-excl" VFS
** that means that an exclusive lock is held on the database file and
** that no other processes are able to read or write the database.  In
** that case, we do not really need shared memory.  No shared memory
** file is created.  The shared memory will be simulated with heap memory.
*/
static int unixOpenSharedMemory(unixFile *pDbFd){
  struct unixShm *p = 0;          /* The connection to be opened */
  struct unixShmNode *pShmNode;   /* The underlying mmapped file */
  int rc;                         /* Result code */
  unixInodeInfo *pInode;          /* The inode of fd */
  char *zShmFilename;             /* Name of the file used for SHM */
  int nShmFilename;               /* Size of the SHM filename in bytes */

  /* Allocate space for the new unixShm object. */
  p = sqlite3_malloc64( sizeof(*p) );
  if( p==0 ) return SQLITE_NOMEM;
  memset(p, 0, sizeof(*p));
  assert( pDbFd->pShm==0 );

  /* Check to see if a unixShmNode object already exists. Reuse an existing
  ** one if present. Create a new one if necessary.
  */
  unixEnterMutex();
  pInode = pDbFd->pInode;
  pShmNode = pInode->pShmNode;
  if( pShmNode==0 ){
    struct stat sStat;                 /* fstat() info for database file */
#ifndef SQLITE_SHM_DIRECTORY
    const char *zBasePath = pDbFd->zPath;
#endif

    /* Call fstat() to figure out the permissions on the database file. If
    ** a new *-shm file is created, an attempt will be made to create it
    ** with the same permissions.
    */
    if( osFstat(pDbFd->h, &sStat) && pInode->bProcessLock==0 ){
      rc = SQLITE_IOERR_FSTAT;
      goto shm_open_err;
    }

#ifdef SQLITE_SHM_DIRECTORY
    nShmFilename = sizeof(SQLITE_SHM_DIRECTORY) + 31;
#else
    nShmFilename = 6 + (int)strlen(zBasePath);
#endif
    pShmNode = sqlite3_malloc64( sizeof(*pShmNode) + nShmFilename );
    if( pShmNode==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    memset(pShmNode, 0, sizeof(*pShmNode)+nShmFilename);
    zShmFilename = pShmNode->zFilename = (char*)&pShmNode[1];
#ifdef SQLITE_SHM_DIRECTORY
    sqlite3_snprintf(nShmFilename, zShmFilename, 
                     SQLITE_SHM_DIRECTORY "/sqlite-shm-%x-%x",
                     (u32)sStat.st_ino, (u32)sStat.st_dev);
#else
    sqlite3_snprintf(nShmFilename, zShmFilename, "%s-shm", zBasePath);
#endif
    pShmNode->h = -1;
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    if( pInode->bProcessLock==0 ){
      int openFlags = O_RDWR | O_CREAT;
      pShmNode->h = robust_open(zShmFilename, openFlags, (sStat.st_mode&0777));
      if( pShmNode->h<0 ){
        rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zShmFilename);
        goto shm_open_err;
      }

      /* If this process is running as root, make sure that the SHM file
      ** is owned by the same user that owns the original database.  Otherwise,
      ** the original owner will not be able to connect.
      */
      osFchown(pShmNode->h, sStat.st_uid, sStat.st_gid);
  
      /* Check to see if another process is holding the dead-man switch.
      ** If not, truncate the file to zero length. 
      */
      rc = SQLITE_OK;
      if( unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){
        if( robust_ftruncate(pShmNode->h, 0) ){
          rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename);
        }
      }
      if( rc==SQLITE_OK ){
        rc = unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, 1);
      }
      if( rc ) goto shm_open_err;
    }
  }

  /* Make the new connection a child of the unixShmNode */
  p->pShmNode = pShmNode;
#ifdef SQLITE_DEBUG
  p->id = pShmNode->nextShmId++;
#endif
  pShmNode->nRef++;
  pDbFd->pShm = p;
  unixLeaveMutex();

  /* The reference count on pShmNode has already been incremented under
  ** the cover of the unixEnterMutex() mutex and the pointer from the
  ** new (struct unixShm) object to the pShmNode has been set. All that is
  ** left to do is to link the new object into the linked list starting
  ** at pShmNode->pFirst. This must be done while holding the pShmNode->mutex 
  ** mutex.
  */
  sqlite3_mutex_enter(pShmNode->mutex);
  p->pNext = pShmNode->pFirst;
  pShmNode->pFirst = p;
  sqlite3_mutex_leave(pShmNode->mutex);
  return SQLITE_OK;

  /* Jump here on any error */
shm_open_err:
  unixShmPurge(pDbFd);       /* This call frees pShmNode if required */
  sqlite3_free(p);
  unixLeaveMutex();
  return rc;
}

/*
** This function is called to obtain a pointer to region iRegion of the 
** shared-memory associated with the database file fd. Shared-memory regions 
** are numbered starting from zero. Each shared-memory region is szRegion 
** bytes in size.
**
** If an error occurs, an error code is returned and *pp is set to NULL.
**
** Otherwise, if the bExtend parameter is 0 and the requested shared-memory
** region has not been allocated (by any client, including one running in a
** separate process), then *pp is set to NULL and SQLITE_OK returned. If 
** bExtend is non-zero and the requested shared-memory region has not yet 
** been allocated, it is allocated by this function.
**
** If the shared-memory region has already been allocated or is allocated by
** this call as described above, then it is mapped into this processes 
** address space (if it is not already), *pp is set to point to the mapped 
** memory and SQLITE_OK returned.
*/
static int unixShmMap(
  sqlite3_file *fd,               /* Handle open on database file */
  int iRegion,                    /* Region to retrieve */
  int szRegion,                   /* Size of regions */
  int bExtend,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  unixFile *pDbFd = (unixFile*)fd;
  unixShm *p;
  unixShmNode *pShmNode;
  int rc = SQLITE_OK;
  int nShmPerMap = unixShmRegionPerMap();
  int nReqRegion;

  /* If the shared-memory file has not yet been opened, open it now. */
  if( pDbFd->pShm==0 ){
    rc = unixOpenSharedMemory(pDbFd);
    if( rc!=SQLITE_OK ) return rc;
  }

  p = pDbFd->pShm;
  pShmNode = p->pShmNode;
  sqlite3_mutex_enter(pShmNode->mutex);
  assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );
  assert( pShmNode->pInode==pDbFd->pInode );
  assert( pShmNode->h>=0 || pDbFd->pInode->bProcessLock==1 );
  assert( pShmNode->h<0 || pDbFd->pInode->bProcessLock==0 );

  /* Minimum number of regions required to be mapped. */
  nReqRegion = ((iRegion+nShmPerMap) / nShmPerMap) * nShmPerMap;

  if( pShmNode->nRegion<nReqRegion ){
    char **apNew;                      /* New apRegion[] array */
    int nByte = nReqRegion*szRegion;   /* Minimum required file size */
    struct stat sStat;                 /* Used by fstat() */

    pShmNode->szRegion = szRegion;

    if( pShmNode->h>=0 ){
      /* The requested region is not mapped into this processes address space.
      ** Check to see if it has been allocated (i.e. if the wal-index file is
      ** large enough to contain the requested region).
      */
      if( osFstat(pShmNode->h, &sStat) ){
        rc = SQLITE_IOERR_SHMSIZE;
        goto shmpage_out;
      }
  
      if( sStat.st_size<nByte ){
        /* The requested memory region does not exist. If bExtend is set to
        ** false, exit early. *pp will be set to NULL and SQLITE_OK returned.
        */
        if( !bExtend ){
          goto shmpage_out;
        }

        /* Alternatively, if bExtend is true, extend the file. Do this by
        ** writing a single byte to the end of each (OS) page being
        ** allocated or extended. Technically, we need only write to the
        ** last page in order to extend the file. But writing to all new
        ** pages forces the OS to allocate them immediately, which reduces
        ** the chances of SIGBUS while accessing the mapped region later on.
        */
        else{
          static const int pgsz = 4096;
          int iPg;

          /* Write to the last byte of each newly allocated or extended page */
          assert( (nByte % pgsz)==0 );
          for(iPg=(sStat.st_size/pgsz); iPg<(nByte/pgsz); iPg++){
            if( seekAndWriteFd(pShmNode->h, iPg*pgsz + pgsz-1, "", 1, 0)!=1 ){
              const char *zFile = pShmNode->zFilename;
              rc = unixLogError(SQLITE_IOERR_SHMSIZE, "write", zFile);
              goto shmpage_out;
            }
          }
        }
      }
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (char **)sqlite3_realloc(
        pShmNode->apRegion, nReqRegion*sizeof(char *)
    );
    if( !apNew ){
      rc = SQLITE_IOERR_NOMEM;
      goto shmpage_out;
    }
    pShmNode->apRegion = apNew;
    while( pShmNode->nRegion<nReqRegion ){
      int nMap = szRegion*nShmPerMap;
      int i;
      void *pMem;
      if( pShmNode->h>=0 ){
        pMem = osMmap(0, nMap,
            pShmNode->isReadonly ? PROT_READ : PROT_READ|PROT_WRITE, 
            MAP_SHARED, pShmNode->h, szRegion*(i64)pShmNode->nRegion
        );
        if( pMem==MAP_FAILED ){
          rc = unixLogError(SQLITE_IOERR_SHMMAP, "mmap", pShmNode->zFilename);
          goto shmpage_out;
        }
      }else{
        pMem = sqlite3_malloc64(szRegion);
        if( pMem==0 ){
          rc = SQLITE_NOMEM;
          goto shmpage_out;
        }
        memset(pMem, 0, szRegion);
      }

      for(i=0; i<nShmPerMap; i++){
        pShmNode->apRegion[pShmNode->nRegion+i] = &((char*)pMem)[szRegion*i];
      }
      pShmNode->nRegion += nShmPerMap;
    }
  }

shmpage_out:
  if( pShmNode->nRegion>iRegion ){
    *pp = pShmNode->apRegion[iRegion];
  }else{
    *pp = 0;
  }
  if( pShmNode->isReadonly && rc==SQLITE_OK ) rc = SQLITE_READONLY;
  sqlite3_mutex_leave(pShmNode->mutex);
  return rc;
}

/*
** Change the lock state for a shared-memory segment.
**
** Note that the relationship between SHAREd and EXCLUSIVE locks is a little
** different here than in posix.  In xShmLock(), one can go from unlocked
** to shared and back or from unlocked to exclusive and back.  But one may
** not go from shared to exclusive or from exclusive to shared.
*/
static int unixShmLock(
  sqlite3_file *fd,          /* Database file holding the shared memory */
  int ofst,                  /* First lock to acquire or release */
  int n,                     /* Number of locks to acquire or release */
  int flags                  /* What to do with the lock */
){
  unixFile *pDbFd = (unixFile*)fd;      /* Connection holding shared memory */
  unixShm *p = pDbFd->pShm;             /* The shared memory being locked */
  unixShm *pX;                          /* For looping over all siblings */
  unixShmNode *pShmNode = p->pShmNode;  /* The underlying file iNode */
  int rc = SQLITE_OK;                   /* Result code */
  u16 mask;                             /* Mask of locks to take or release */

  assert( pShmNode==pDbFd->pInode->pShmNode );
  assert( pShmNode->pInode==pDbFd->pInode );
  assert( ofst>=0 && ofst+n<=SQLITE_SHM_NLOCK );
  assert( n>=1 );
  assert( flags==(SQLITE_SHM_LOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE) );
  assert( n==1 || (flags & SQLITE_SHM_EXCLUSIVE)!=0 );
  assert( pShmNode->h>=0 || pDbFd->pInode->bProcessLock==1 );
  assert( pShmNode->h<0 || pDbFd->pInode->bProcessLock==0 );

  mask = (1<<(ofst+n)) - (1<<ofst);
  assert( n>1 || mask==(1<<ofst) );
  sqlite3_mutex_enter(pShmNode->mutex);
  if( flags & SQLITE_SHM_UNLOCK ){
    u16 allMask = 0; /* Mask of locks held by siblings */

    /* See if any siblings hold this same lock */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( pX==p ) continue;
      assert( (pX->exclMask & (p->exclMask|p->sharedMask))==0 );
      allMask |= pX->sharedMask;
    }

    /* Unlock the system-level locks */
    if( (mask & allMask)==0 ){
      rc = unixShmSystemLock(pDbFd, F_UNLCK, ofst+UNIX_SHM_BASE, n);
    }else{
      rc = SQLITE_OK;
    }

    /* Undo the local locks */
    if( rc==SQLITE_OK ){
      p->exclMask &= ~mask;
      p->sharedMask &= ~mask;
    } 
  }else if( flags & SQLITE_SHM_SHARED ){
    u16 allShared = 0;  /* Union of locks held by connections other than "p" */

    /* Find out which shared locks are already held by sibling connections.
    ** If any sibling already holds an exclusive lock, go ahead and return
    ** SQLITE_BUSY.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
      allShared |= pX->sharedMask;
    }

    /* Get shared locks at the system level, if necessary */
    if( rc==SQLITE_OK ){
      if( (allShared & mask)==0 ){
        rc = unixShmSystemLock(pDbFd, F_RDLCK, ofst+UNIX_SHM_BASE, n);
      }else{
        rc = SQLITE_OK;
      }
    }

    /* Get the local shared locks */
    if( rc==SQLITE_OK ){
      p->sharedMask |= mask;
    }
  }else{
    /* Make sure no sibling connections hold locks that will block this
    ** lock.  If any do, return SQLITE_BUSY right away.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 || (pX->sharedMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
    }
  
    /* Get the exclusive locks at the system level.  Then if successful
    ** also mark the local connection as being locked.
    */
    if( rc==SQLITE_OK ){
      rc = unixShmSystemLock(pDbFd, F_WRLCK, ofst+UNIX_SHM_BASE, n);
      if( rc==SQLITE_OK ){
        assert( (p->sharedMask & mask)==0 );
        p->exclMask |= mask;
      }
    }
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  OSTRACE(("SHM-LOCK shmid-%d, pid-%d got %03x,%03x\n",
           p->id, osGetpid(0), p->sharedMask, p->exclMask));
  return rc;
}

/*
** Implement a memory barrier or memory fence on shared memory.  
**
** All loads and stores begun before the barrier must complete before
** any load or store begun after the barrier.
*/
static void unixShmBarrier(
  sqlite3_file *fd                /* Database file holding the shared memory */
){
  UNUSED_PARAMETER(fd);
  sqlite3MemoryBarrier();         /* compiler-defined memory barrier */
  unixEnterMutex();               /* Also mutex, for redundancy */
  unixLeaveMutex();
}

/*
** Close a connection to shared-memory.  Delete the underlying 
** storage if deleteFlag is true.
**
** If there is no shared memory associated with the connection then this
** routine is a harmless no-op.
*/
static int unixShmUnmap(
  sqlite3_file *fd,               /* The underlying database file */
  int deleteFlag                  /* Delete shared-memory if true */
){
  unixShm *p;                     /* The connection to be closed */
  unixShmNode *pShmNode;          /* The underlying shared-memory file */
  unixShm **pp;                   /* For looping over sibling connections */
  unixFile *pDbFd;                /* The underlying database file */

  pDbFd = (unixFile*)fd;
  p = pDbFd->pShm;
  if( p==0 ) return SQLITE_OK;
  pShmNode = p->pShmNode;

  assert( pShmNode==pDbFd->pInode->pShmNode );
  assert( pShmNode->pInode==pDbFd->pInode );

  /* Remove connection p from the set of connections associated
  ** with pShmNode */
  sqlite3_mutex_enter(pShmNode->mutex);
  for(pp=&pShmNode->pFirst; (*pp)!=p; pp = &(*pp)->pNext){}
  *pp = p->pNext;

  /* Free the connection p */
  sqlite3_free(p);
  pDbFd->pShm = 0;
  sqlite3_mutex_leave(pShmNode->mutex);

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  unixEnterMutex();
  assert( pShmNode->nRef>0 );
  pShmNode->nRef--;
  if( pShmNode->nRef==0 ){
    if( deleteFlag && pShmNode->h>=0 ){
      osUnlink(pShmNode->zFilename);
    }
    unixShmPurge(pDbFd);
  }
  unixLeaveMutex();

  return SQLITE_OK;
}


#else
# define unixShmMap     0
# define unixShmLock    0
# define unixShmBarrier 0
# define unixShmUnmap   0
#endif /* #ifndef SQLITE_OMIT_WAL */

#if SQLITE_MAX_MMAP_SIZE>0
/*
** If it is currently memory mapped, unmap file pFd.
*/
static void unixUnmapfile(unixFile *pFd){
  assert( pFd->nFetchOut==0 );
  if( pFd->pMapRegion ){
    osMunmap(pFd->pMapRegion, pFd->mmapSizeActual);
    pFd->pMapRegion = 0;
    pFd->mmapSize = 0;
    pFd->mmapSizeActual = 0;
  }
}

/*
** Attempt to set the size of the memory mapping maintained by file 
** descriptor pFd to nNew bytes. Any existing mapping is discarded.
**
** If successful, this function sets the following variables:
**
**       unixFile.pMapRegion
**       unixFile.mmapSize
**       unixFile.mmapSizeActual
**
** If unsuccessful, an error message is logged via sqlite3_log() and
** the three variables above are zeroed. In this case SQLite should
** continue accessing the database using the xRead() and xWrite()
** methods.
*/
static void unixRemapfile(
  unixFile *pFd,                  /* File descriptor object */
  i64 nNew                        /* Required mapping size */
){
  const char *zErr = "mmap";
  int h = pFd->h;                      /* File descriptor open on db file */
  u8 *pOrig = (u8 *)pFd->pMapRegion;   /* Pointer to current file mapping */
  i64 nOrig = pFd->mmapSizeActual;     /* Size of pOrig region in bytes */
  u8 *pNew = 0;                        /* Location of new mapping */
  int flags = PROT_READ;               /* Flags to pass to mmap() */

  assert( pFd->nFetchOut==0 );
  assert( nNew>pFd->mmapSize );
  assert( nNew<=pFd->mmapSizeMax );
  assert( nNew>0 );
  assert( pFd->mmapSizeActual>=pFd->mmapSize );
  assert( MAP_FAILED!=0 );

  if( (pFd->ctrlFlags & UNIXFILE_RDONLY)==0 ) flags |= PROT_WRITE;

  if( pOrig ){
#if HAVE_MREMAP
    i64 nReuse = pFd->mmapSize;
#else
    const int szSyspage = osGetpagesize();
    i64 nReuse = (pFd->mmapSize & ~(szSyspage-1));
#endif
    u8 *pReq = &pOrig[nReuse];

    /* Unmap any pages of the existing mapping that cannot be reused. */
    if( nReuse!=nOrig ){
      osMunmap(pReq, nOrig-nReuse);
    }

#if HAVE_MREMAP
    pNew = osMremap(pOrig, nReuse, nNew, MREMAP_MAYMOVE);
    zErr = "mremap";
#else
    pNew = osMmap(pReq, nNew-nReuse, flags, MAP_SHARED, h, nReuse);
    if( pNew!=MAP_FAILED ){
      if( pNew!=pReq ){
        osMunmap(pNew, nNew - nReuse);
        pNew = 0;
      }else{
        pNew = pOrig;
      }
    }
#endif

    /* The attempt to extend the existing mapping failed. Free it. */
    if( pNew==MAP_FAILED || pNew==0 ){
      osMunmap(pOrig, nReuse);
    }
  }

  /* If pNew is still NULL, try to create an entirely new mapping. */
  if( pNew==0 ){
    pNew = osMmap(0, nNew, flags, MAP_SHARED, h, 0);
  }

  if( pNew==MAP_FAILED ){
    pNew = 0;
    nNew = 0;
    unixLogError(SQLITE_OK, zErr, pFd->zPath);

    /* If the mmap() above failed, assume that all subsequent mmap() calls
    ** will probably fail too. Fall back to using xRead/xWrite exclusively
    ** in this case.  */
    pFd->mmapSizeMax = 0;
  }
  pFd->pMapRegion = (void *)pNew;
  pFd->mmapSize = pFd->mmapSizeActual = nNew;
}

/*
** Memory map or remap the file opened by file-descriptor pFd (if the file
** is already mapped, the existing mapping is replaced by the new). Or, if 
** there already exists a mapping for this file, and there are still 
** outstanding xFetch() references to it, this function is a no-op.
**
** If parameter nByte is non-negative, then it is the requested size of 
** the mapping to create. Otherwise, if nByte is less than zero, then the 
** requested size is the size of the file on disk. The actual size of the
** created mapping is either the requested size or the value configured 
** using SQLITE_FCNTL_MMAP_LIMIT, whichever is smaller.
**
** SQLITE_OK is returned if no error occurs (even if the mapping is not
** recreated as a result of outstanding references) or an SQLite error
** code otherwise.
*/
static int unixMapfile(unixFile *pFd, i64 nByte){
  i64 nMap = nByte;
  int rc;

  assert( nMap>=0 || pFd->nFetchOut==0 );
  if( pFd->nFetchOut>0 ) return SQLITE_OK;

  if( nMap<0 ){
    struct stat statbuf;          /* Low-level file information */
    rc = osFstat(pFd->h, &statbuf);
    if( rc!=SQLITE_OK ){
      return SQLITE_IOERR_FSTAT;
    }
    nMap = statbuf.st_size;
  }
  if( nMap>pFd->mmapSizeMax ){
    nMap = pFd->mmapSizeMax;
  }

  if( nMap!=pFd->mmapSize ){
    if( nMap>0 ){
      unixRemapfile(pFd, nMap);
    }else{
      unixUnmapfile(pFd);
    }
  }

  return SQLITE_OK;
}
#endif /* SQLITE_MAX_MMAP_SIZE>0 */

/*
** If possible, return a pointer to a mapping of file fd starting at offset
** iOff. The mapping must be valid for at least nAmt bytes.
**
** If such a pointer can be obtained, store it in *pp and return SQLITE_OK.
** Or, if one cannot but no error occurs, set *pp to 0 and return SQLITE_OK.
** Finally, if an error does occur, return an SQLite error code. The final
** value of *pp is undefined in this case.
**
** If this function does return a pointer, the caller must eventually 
** release the reference by calling unixUnfetch().
*/
static int unixFetch(sqlite3_file *fd, i64 iOff, int nAmt, void **pp){
#if SQLITE_MAX_MMAP_SIZE>0
  unixFile *pFd = (unixFile *)fd;   /* The underlying database file */
#endif
  *pp = 0;

#if SQLITE_MAX_MMAP_SIZE>0
  if( pFd->mmapSizeMax>0 ){
    if( pFd->pMapRegion==0 ){
      int rc = unixMapfile(pFd, -1);
      if( rc!=SQLITE_OK ) return rc;
    }
    if( pFd->mmapSize >= iOff+nAmt ){
      *pp = &((u8 *)pFd->pMapRegion)[iOff];
      pFd->nFetchOut++;
    }
  }
#endif
  return SQLITE_OK;
}

/*
** If the third argument is non-NULL, then this function releases a 
** reference obtained by an earlier call to unixFetch(). The second
** argument passed to this function must be the same as the corresponding
** argument that was passed to the unixFetch() invocation. 
**
** Or, if the third argument is NULL, then this function is being called 
** to inform the VFS layer that, according to POSIX, any existing mapping 
** may now be invalid and should be unmapped.
*/
static int unixUnfetch(sqlite3_file *fd, i64 iOff, void *p){
#if SQLITE_MAX_MMAP_SIZE>0
  unixFile *pFd = (unixFile *)fd;   /* The underlying database file */
  UNUSED_PARAMETER(iOff);

  /* If p==0 (unmap the entire file) then there must be no outstanding 
  ** xFetch references. Or, if p!=0 (meaning it is an xFetch reference),
  ** then there must be at least one outstanding.  */
  assert( (p==0)==(pFd->nFetchOut==0) );

  /* If p!=0, it must match the iOff value. */
  assert( p==0 || p==&((u8 *)pFd->pMapRegion)[iOff] );

  if( p ){
    pFd->nFetchOut--;
  }else{
    unixUnmapfile(pFd);
  }

  assert( pFd->nFetchOut>=0 );
#else
  UNUSED_PARAMETER(fd);
  UNUSED_PARAMETER(p);
  UNUSED_PARAMETER(iOff);
#endif
  return SQLITE_OK;
}

/*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/

/*
** This division contains definitions of sqlite3_io_methods objects that
** implement various file locking strategies.  It also contains definitions
** of "finder" functions.  A finder-function is used to locate the appropriate
** sqlite3_io_methods object for a particular database file.  The pAppData
** field of the sqlite3_vfs VFS objects are initialized to be pointers to
** the correct finder-function for that VFS.
**
** Most finder functions return a pointer to a fixed sqlite3_io_methods
** object.  The only interesting finder-function is autolockIoFinder, which
** looks at the filesystem type and tries to guess the best locking
** strategy from that.
**
** For finder-function F, two objects are created:
**
**    (1) The real finder-function named "FImpt()".
**
**    (2) A constant pointer to this function named just "F".
**
**
** A pointer to the F pointer is used as the pAppData value for VFS
** objects.  We have to do this instead of letting pAppData point
** directly at the finder-function since C90 rules prevent a void*
** from be cast into a function pointer.
**
**
** Each instance of this macro generates two objects:
**
**   *  A constant sqlite3_io_methods object call METHOD that has locking
**      methods CLOSE, LOCK, UNLOCK, CKRESLOCK.
**
**   *  An I/O method finder function called FINDER that returns a pointer
**      to the METHOD object in the previous bullet.
*/
#define IOMETHODS(FINDER,METHOD,VERSION,CLOSE,LOCK,UNLOCK,CKLOCK,SHMMAP)     \
static const sqlite3_io_methods METHOD = {                                   \
   VERSION,                    /* iVersion */                                \
   CLOSE,                      /* xClose */                                  \
   unixRead,                   /* xRead */                                   \
   unixWrite,                  /* xWrite */                                  \
   unixTruncate,               /* xTruncate */                               \
   unixSync,                   /* xSync */                                   \
   unixFileSize,               /* xFileSize */                               \
   LOCK,                       /* xLock */                                   \
   UNLOCK,                     /* xUnlock */                                 \
   CKLOCK,                     /* xCheckReservedLock */                      \
   unixFileControl,            /* xFileControl */                            \
   unixSectorSize,             /* xSectorSize */                             \
   unixDeviceCharacteristics,  /* xDeviceCapabilities */                     \
   SHMMAP,                     /* xShmMap */                                 \
   unixShmLock,                /* xShmLock */                                \
   unixShmBarrier,             /* xShmBarrier */                             \
   unixShmUnmap,               /* xShmUnmap */                               \
   unixFetch,                  /* xFetch */                                  \
   unixUnfetch,                /* xUnfetch */                                \
};                                                                           \
static const sqlite3_io_methods *FINDER##Impl(const char *z, unixFile *p){   \
  UNUSED_PARAMETER(z); UNUSED_PARAMETER(p);                                  \
  return &METHOD;                                                            \
}                                                                            \
static const sqlite3_io_methods *(*const FINDER)(const char*,unixFile *p)    \
    = FINDER##Impl;

/*
** Here are all of the sqlite3_io_methods objects for each of the
** locking strategies.  Functions that return pointers to these methods
** are also created.
*/
IOMETHODS(
  posixIoFinder,            /* Finder function name */
  posixIoMethods,           /* sqlite3_io_methods object name */
  3,                        /* shared memory and mmap are enabled */
  unixClose,                /* xClose method */
  unixLock,                 /* xLock method */
  unixUnlock,               /* xUnlock method */
  unixCheckReservedLock,    /* xCheckReservedLock method */
  unixShmMap                /* xShmMap method */
)
IOMETHODS(
  nolockIoFinder,           /* Finder function name */
  nolockIoMethods,          /* sqlite3_io_methods object name */
  3,                        /* shared memory is disabled */
  nolockClose,              /* xClose method */
  nolockLock,               /* xLock method */
  nolockUnlock,             /* xUnlock method */
  nolockCheckReservedLock,  /* xCheckReservedLock method */
  0                         /* xShmMap method */
)
IOMETHODS(
  dotlockIoFinder,          /* Finder function name */
  dotlockIoMethods,         /* sqlite3_io_methods object name */
  1,                        /* shared memory is disabled */
  dotlockClose,             /* xClose method */
  dotlockLock,              /* xLock method */
  dotlockUnlock,            /* xUnlock method */
  dotlockCheckReservedLock, /* xCheckReservedLock method */
  0                         /* xShmMap method */
)

#if SQLITE_ENABLE_LOCKING_STYLE
IOMETHODS(
  flockIoFinder,            /* Finder function name */
  flockIoMethods,           /* sqlite3_io_methods object name */
  1,                        /* shared memory is disabled */
  flockClose,               /* xClose method */
  flockLock,                /* xLock method */
  flockUnlock,              /* xUnlock method */
  flockCheckReservedLock,   /* xCheckReservedLock method */
  0                         /* xShmMap method */
)
#endif

#if OS_VXWORKS
IOMETHODS(
  semIoFinder,              /* Finder function name */
  semIoMethods,             /* sqlite3_io_methods object name */
  1,                        /* shared memory is disabled */
  semXClose,                /* xClose method */
  semXLock,                 /* xLock method */
  semXUnlock,               /* xUnlock method */
  semXCheckReservedLock,    /* xCheckReservedLock method */
  0                         /* xShmMap method */
)
#endif

#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
IOMETHODS(
  afpIoFinder,              /* Finder function name */
  afpIoMethods,             /* sqlite3_io_methods object name */
  1,                        /* shared memory is disabled */
  afpClose,                 /* xClose method */
  afpLock,                  /* xLock method */
  afpUnlock,                /* xUnlock method */
  afpCheckReservedLock,     /* xCheckReservedLock method */
  0                         /* xShmMap method */
)
#endif

/*
** The proxy locking method is a "super-method" in the sense that it
** opens secondary file descriptors for the conch and lock files and
** it uses proxy, dot-file, AFP, and flock() locking methods on those
** secondary files.  For this reason, the division that implements
** proxy locking is located much further down in the file.  But we need
** to go ahead and define the sqlite3_io_methods and finder function
** for proxy locking here.  So we forward declare the I/O methods.
*/
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
static int proxyClose(sqlite3_file*);
static int proxyLock(sqlite3_file*, int);
static int proxyUnlock(sqlite3_file*, int);
static int proxyCheckReservedLock(sqlite3_file*, int*);
IOMETHODS(
  proxyIoFinder,            /* Finder function name */
  proxyIoMethods,           /* sqlite3_io_methods object name */
  1,                        /* shared memory is disabled */
  proxyClose,               /* xClose method */
  proxyLock,                /* xLock method */
  proxyUnlock,              /* xUnlock method */
  proxyCheckReservedLock,   /* xCheckReservedLock method */
  0                         /* xShmMap method */
)
#endif

/* nfs lockd on OSX 10.3+ doesn't clear write locks when a read lock is set */
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
IOMETHODS(
  nfsIoFinder,               /* Finder function name */
  nfsIoMethods,              /* sqlite3_io_methods object name */
  1,                         /* shared memory is disabled */
  unixClose,                 /* xClose method */
  unixLock,                  /* xLock method */
  nfsUnlock,                 /* xUnlock method */
  unixCheckReservedLock,     /* xCheckReservedLock method */
  0                          /* xShmMap method */
)
#endif

#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
/* 
** This "finder" function attempts to determine the best locking strategy 
** for the database file "filePath".  It then returns the sqlite3_io_methods
** object that implements that strategy.
**
** This is for MacOSX only.
*/
static const sqlite3_io_methods *autolockIoFinderImpl(
  const char *filePath,    /* name of the database file */
  unixFile *pNew           /* open file object for the database file */
){
  static const struct Mapping {
    const char *zFilesystem;              /* Filesystem type name */
    const sqlite3_io_methods *pMethods;   /* Appropriate locking method */
  } aMap[] = {
    { "hfs",    &posixIoMethods },
    { "ufs",    &posixIoMethods },
    { "afpfs",  &afpIoMethods },
    { "smbfs",  &afpIoMethods },
    { "webdav", &nolockIoMethods },
    { 0, 0 }
  };
  int i;
  struct statfs fsInfo;
  struct flock lockInfo;

  if( !filePath ){
    /* If filePath==NULL that means we are dealing with a transient file
    ** that does not need to be locked. */
    return &nolockIoMethods;
  }
  if( statfs(filePath, &fsInfo) != -1 ){
    if( fsInfo.f_flags & MNT_RDONLY ){
      return &nolockIoMethods;
    }
    for(i=0; aMap[i].zFilesystem; i++){
      if( strcmp(fsInfo.f_fstypename, aMap[i].zFilesystem)==0 ){
        return aMap[i].pMethods;
      }
    }
  }

  /* Default case. Handles, amongst others, "nfs".
  ** Test byte-range lock using fcntl(). If the call succeeds, 
  ** assume that the file-system supports POSIX style locks. 
  */
  lockInfo.l_len = 1;
  lockInfo.l_start = 0;
  lockInfo.l_whence = SEEK_SET;
  lockInfo.l_type = F_RDLCK;
  if( osFcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
    if( strcmp(fsInfo.f_fstypename, "nfs")==0 ){
      return &nfsIoMethods;
    } else {
      return &posixIoMethods;
    }
  }else{
    return &dotlockIoMethods;
  }
}
static const sqlite3_io_methods 
  *(*const autolockIoFinder)(const char*,unixFile*) = autolockIoFinderImpl;

#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */

#if OS_VXWORKS
/*
** This "finder" function for VxWorks checks to see if posix advisory
** locking works.  If it does, then that is what is used.  If it does not
** work, then fallback to named semaphore locking.
*/
static const sqlite3_io_methods *vxworksIoFinderImpl(
  const char *filePath,    /* name of the database file */
  unixFile *pNew           /* the open file object */
){
  struct flock lockInfo;

  if( !filePath ){
    /* If filePath==NULL that means we are dealing with a transient file
    ** that does not need to be locked. */
    return &nolockIoMethods;
  }

  /* Test if fcntl() is supported and use POSIX style locks.
  ** Otherwise fall back to the named semaphore method.
  */
  lockInfo.l_len = 1;
  lockInfo.l_start = 0;
  lockInfo.l_whence = SEEK_SET;
  lockInfo.l_type = F_RDLCK;
  if( osFcntl(pNew->h, F_GETLK, &lockInfo)!=-1 ) {
    return &posixIoMethods;
  }else{
    return &semIoMethods;
  }
}
static const sqlite3_io_methods 
  *(*const vxworksIoFinder)(const char*,unixFile*) = vxworksIoFinderImpl;

#endif /* OS_VXWORKS */

/*
** An abstract type for a pointer to an IO method finder function:
*/
typedef const sqlite3_io_methods *(*finder_type)(const char*,unixFile*);


/****************************************************************************
**************************** sqlite3_vfs methods ****************************
**
** This division contains the implementation of methods on the
** sqlite3_vfs object.
*/

/*
** Initialize the contents of the unixFile structure pointed to by pId.
*/
static int fillInUnixFile(
  sqlite3_vfs *pVfs,      /* Pointer to vfs object */
  int h,                  /* Open file descriptor of file being opened */
  sqlite3_file *pId,      /* Write to the unixFile structure here */
  const char *zFilename,  /* Name of the file being opened */
  int ctrlFlags           /* Zero or more UNIXFILE_* values */
){
  const sqlite3_io_methods *pLockingStyle;
  unixFile *pNew = (unixFile *)pId;
  int rc = SQLITE_OK;

  assert( pNew->pInode==NULL );

  /* Usually the path zFilename should not be a relative pathname. The
  ** exception is when opening the proxy "conch" file in builds that
  ** include the special Apple locking styles.
  */
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
  assert( zFilename==0 || zFilename[0]=='/' 
    || pVfs->pAppData==(void*)&autolockIoFinder );
#else
  assert( zFilename==0 || zFilename[0]=='/' );
#endif

  /* No locking occurs in temporary files */
  assert( zFilename!=0 || (ctrlFlags & UNIXFILE_NOLOCK)!=0 );

  OSTRACE(("OPEN    %-3d %s\n", h, zFilename));
  pNew->h = h;
  pNew->pVfs = pVfs;
  pNew->zPath = zFilename;
  pNew->ctrlFlags = (u8)ctrlFlags;
#if SQLITE_MAX_MMAP_SIZE>0
  pNew->mmapSizeMax = sqlite3GlobalConfig.szMmap;
#endif
  if( SQLITE_POWERSAFE_OVERWRITE ){
    pNew->ctrlFlags |= UNIXFILE_PSOW;
  }
  if( strcmp(pVfs->zName,"unix-excl")==0 ){
    pNew->ctrlFlags |= UNIXFILE_EXCL;
  }

#if OS_VXWORKS
  pNew->pId = vxworksFindFileId(zFilename);
  if( pNew->pId==0 ){
    ctrlFlags |= UNIXFILE_NOLOCK;
    rc = SQLITE_NOMEM;
  }
#endif

  if( ctrlFlags & UNIXFILE_NOLOCK ){
    pLockingStyle = &nolockIoMethods;
  }else{
    pLockingStyle = (**(finder_type*)pVfs->pAppData)(zFilename, pNew);
#if SQLITE_ENABLE_LOCKING_STYLE
    /* Cache zFilename in the locking context (AFP and dotlock override) for
    ** proxyLock activation is possible (remote proxy is based on db name)
    ** zFilename remains valid until file is closed, to support */
    pNew->lockingContext = (void*)zFilename;
#endif
  }

  if( pLockingStyle == &posixIoMethods
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE
    || pLockingStyle == &nfsIoMethods
#endif
  ){
    unixEnterMutex();
    rc = findInodeInfo(pNew, &pNew->pInode);
    if( rc!=SQLITE_OK ){
      /* If an error occurred in findInodeInfo(), close the file descriptor
      ** immediately, before releasing the mutex. findInodeInfo() may fail
      ** in two scenarios:
      **
      **   (a) A call to fstat() failed.
      **   (b) A malloc failed.
      **
      ** Scenario (b) may only occur if the process is holding no other
      ** file descriptors open on the same file. If there were other file
      ** descriptors on this file, then no malloc would be required by
      ** findInodeInfo(). If this is the case, it is quite safe to close
      ** handle h - as it is guaranteed that no posix locks will be released
      ** by doing so.
      **
      ** If scenario (a) caused the error then things are not so safe. The
      ** implicit assumption here is that if fstat() fails, things are in
      ** such bad shape that dropping a lock or two doesn't matter much.
      */
      robust_close(pNew, h, __LINE__);
      h = -1;
    }
    unixLeaveMutex();
  }

#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
  else if( pLockingStyle == &afpIoMethods ){
    /* AFP locking uses the file path so it needs to be included in
    ** the afpLockingContext.
    */
    afpLockingContext *pCtx;
    pNew->lockingContext = pCtx = sqlite3_malloc64( sizeof(*pCtx) );
    if( pCtx==0 ){
      rc = SQLITE_NOMEM;
    }else{
      /* NB: zFilename exists and remains valid until the file is closed
      ** according to requirement F11141.  So we do not need to make a
      ** copy of the filename. */
      pCtx->dbPath = zFilename;
      pCtx->reserved = 0;
      srandomdev();
      unixEnterMutex();
      rc = findInodeInfo(pNew, &pNew->pInode);
      if( rc!=SQLITE_OK ){
        sqlite3_free(pNew->lockingContext);
        robust_close(pNew, h, __LINE__);
        h = -1;
      }
      unixLeaveMutex();        
    }
  }
#endif

  else if( pLockingStyle == &dotlockIoMethods ){
    /* Dotfile locking uses the file path so it needs to be included in
    ** the dotlockLockingContext 
    */
    char *zLockFile;
    int nFilename;
    assert( zFilename!=0 );
    nFilename = (int)strlen(zFilename) + 6;
    zLockFile = (char *)sqlite3_malloc64(nFilename);
    if( zLockFile==0 ){
      rc = SQLITE_NOMEM;
    }else{
      sqlite3_snprintf(nFilename, zLockFile, "%s" DOTLOCK_SUFFIX, zFilename);
    }
    pNew->lockingContext = zLockFile;
  }

#if OS_VXWORKS
  else if( pLockingStyle == &semIoMethods ){
    /* Named semaphore locking uses the file path so it needs to be
    ** included in the semLockingContext
    */
    unixEnterMutex();
    rc = findInodeInfo(pNew, &pNew->pInode);
    if( (rc==SQLITE_OK) && (pNew->pInode->pSem==NULL) ){
      char *zSemName = pNew->pInode->aSemName;
      int n;
      sqlite3_snprintf(MAX_PATHNAME, zSemName, "/%s.sem",
                       pNew->pId->zCanonicalName);
      for( n=1; zSemName[n]; n++ )
        if( zSemName[n]=='/' ) zSemName[n] = '_';
      pNew->pInode->pSem = sem_open(zSemName, O_CREAT, 0666, 1);
      if( pNew->pInode->pSem == SEM_FAILED ){
        rc = SQLITE_NOMEM;
        pNew->pInode->aSemName[0] = '\0';
      }
    }
    unixLeaveMutex();
  }
#endif
  
  storeLastErrno(pNew, 0);
#if OS_VXWORKS
  if( rc!=SQLITE_OK ){
    if( h>=0 ) robust_close(pNew, h, __LINE__);
    h = -1;
    osUnlink(zFilename);
    pNew->ctrlFlags |= UNIXFILE_DELETE;
  }
#endif
  if( rc!=SQLITE_OK ){
    if( h>=0 ) robust_close(pNew, h, __LINE__);
  }else{
    pNew->pMethod = pLockingStyle;
    OpenCounter(+1);
    verifyDbFile(pNew);
  }
  return rc;
}

/*
** Return the name of a directory in which to put temporary files.
** If no suitable temporary file directory can be found, return NULL.
*/
static const char *unixTempFileDir(void){
  static const char *azDirs[] = {
     0,
     0,
     0,
     "/var/tmp",
     "/usr/tmp",
     "/tmp",
     0        /* List terminator */
  };
  unsigned int i;
  struct stat buf;
  const char *zDir = 0;

  azDirs[0] = sqlite3_temp_directory;
  if( !azDirs[1] ) azDirs[1] = getenv("SQLITE_TMPDIR");
  if( !azDirs[2] ) azDirs[2] = getenv("TMPDIR");
  for(i=0; i<sizeof(azDirs)/sizeof(azDirs[0]); zDir=azDirs[i++]){
    if( zDir==0 ) continue;
    if( osStat(zDir, &buf) ) continue;
    if( !S_ISDIR(buf.st_mode) ) continue;
    if( osAccess(zDir, 07) ) continue;
    break;
  }
  return zDir;
}

/*
** Create a temporary file name in zBuf.  zBuf must be allocated
** by the calling process and must be big enough to hold at least
** pVfs->mxPathname bytes.
*/
static int unixGetTempname(int nBuf, char *zBuf){
  static const unsigned char zChars[] =
    "abcdefghijklmnopqrstuvwxyz"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "0123456789";
  unsigned int i, j;
  const char *zDir;

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing. 
  */
  SimulateIOError( return SQLITE_IOERR );

  zDir = unixTempFileDir();
  if( zDir==0 ) zDir = ".";

  /* Check that the output buffer is large enough for the temporary file 
  ** name. If it is not, return SQLITE_ERROR.
  */
  if( (strlen(zDir) + strlen(SQLITE_TEMP_FILE_PREFIX) + 18) >= (size_t)nBuf ){
    return SQLITE_ERROR;
  }

  do{
    sqlite3_snprintf(nBuf-18, zBuf, "%s/"SQLITE_TEMP_FILE_PREFIX, zDir);
    j = (int)strlen(zBuf);
    sqlite3_randomness(15, &zBuf[j]);
    for(i=0; i<15; i++, j++){
      zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
    }
    zBuf[j] = 0;
    zBuf[j+1] = 0;
  }while( osAccess(zBuf,0)==0 );
  return SQLITE_OK;
}

#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
/*
** Routine to transform a unixFile into a proxy-locking unixFile.
** Implementation in the proxy-lock division, but used by unixOpen()
** if SQLITE_PREFER_PROXY_LOCKING is defined.
*/
static int proxyTransformUnixFile(unixFile*, const char*);
#endif

/*
** Search for an unused file descriptor that was opened on the database 
** file (not a journal or master-journal file) identified by pathname
** zPath with SQLITE_OPEN_XXX flags matching those passed as the second
** argument to this function.
**
** Such a file descriptor may exist if a database connection was closed
** but the associated file descriptor could not be closed because some
** other file descriptor open on the same file is holding a file-lock.
** Refer to comments in the unixClose() function and the lengthy comment
** describing "Posix Advisory Locking" at the start of this file for 
** further details. Also, ticket #4018.
**
** If a suitable file descriptor is found, then it is returned. If no
** such file descriptor is located, -1 is returned.
*/
static UnixUnusedFd *findReusableFd(const char *zPath, int flags){
  UnixUnusedFd *pUnused = 0;

  /* Do not search for an unused file descriptor on vxworks. Not because
  ** vxworks would not benefit from the change (it might, we're not sure),
  ** but because no way to test it is currently available. It is better 
  ** not to risk breaking vxworks support for the sake of such an obscure 
  ** feature.  */
#if !OS_VXWORKS
  struct stat sStat;                   /* Results of stat() call */

  /* A stat() call may fail for various reasons. If this happens, it is
  ** almost certain that an open() call on the same path will also fail.
  ** For this reason, if an error occurs in the stat() call here, it is
  ** ignored and -1 is returned. The caller will try to open a new file
  ** descriptor on the same path, fail, and return an error to SQLite.
  **
  ** Even if a subsequent open() call does succeed, the consequences of
  ** not searching for a reusable file descriptor are not dire.  */
  if( 0==osStat(zPath, &sStat) ){
    unixInodeInfo *pInode;

    unixEnterMutex();
    pInode = inodeList;
    while( pInode && (pInode->fileId.dev!=sStat.st_dev
                     || pInode->fileId.ino!=sStat.st_ino) ){
       pInode = pInode->pNext;
    }
    if( pInode ){
      UnixUnusedFd **pp;
      for(pp=&pInode->pUnused; *pp && (*pp)->flags!=flags; pp=&((*pp)->pNext));
      pUnused = *pp;
      if( pUnused ){
        *pp = pUnused->pNext;
      }
    }
    unixLeaveMutex();
  }
#endif    /* if !OS_VXWORKS */
  return pUnused;
}

/*
** This function is called by unixOpen() to determine the unix permissions
** to create new files with. If no error occurs, then SQLITE_OK is returned
** and a value suitable for passing as the third argument to open(2) is
** written to *pMode. If an IO error occurs, an SQLite error code is 
** returned and the value of *pMode is not modified.
**
** In most cases, this routine sets *pMode to 0, which will become
** an indication to robust_open() to create the file using
** SQLITE_DEFAULT_FILE_PERMISSIONS adjusted by the umask.
** But if the file being opened is a WAL or regular journal file, then 
** this function queries the file-system for the permissions on the 
** corresponding database file and sets *pMode to this value. Whenever 
** possible, WAL and journal files are created using the same permissions 
** as the associated database file.
*/
static int findCreateFileMode(
  const char *zPath,              /* Path of file (possibly) being created */
  int flags,                      /* Flags passed as 4th argument to xOpen() */
  mode_t *pMode,                  /* OUT: Permissions to open file with */
  uid_t *pUid,                    /* OUT: uid to set on the file */
  gid_t *pGid                     /* OUT: gid to set on the file */
){
  int rc = SQLITE_OK;             /* Return Code */
  *pMode = 0;
  *pUid = 0;
  *pGid = 0;
  if( flags & (SQLITE_OPEN_WAL|SQLITE_OPEN_MAIN_JOURNAL) ){
    char zDb[MAX_PATHNAME+1];     /* Database file path */
    int nDb;                      /* Number of valid bytes in zDb */
    struct stat sStat;            /* Output of stat() on database file */

    /* zPath is a path to a WAL or journal file. The following block derives
    ** the path to the associated database file from zPath. This block handles
    ** the following naming conventions:
    **
    **   "<path to db>-journal"
    **   "<path to db>-wal"
    **   "<path to db>-journalNN"
    **   "<path to db>-walNN"
    **
    ** where NN is a decimal number. The NN naming schemes are 
    ** used by the test_multiplex.c module.
    */
    nDb = sqlite3Strlen30(zPath) - 1; 
    while( zPath[nDb]!='-' ){
      assert( nDb>0 );
      assert( zPath[nDb]!='\n' );
      nDb--;
    }
    memcpy(zDb, zPath, nDb);
    zDb[nDb] = '\0';

    if( 0==osStat(zDb, &sStat) ){
      *pMode = sStat.st_mode & 0777;
      *pUid = sStat.st_uid;
      *pGid = sStat.st_gid;
    }else{
      rc = SQLITE_IOERR_FSTAT;
    }
  }else if( flags & SQLITE_OPEN_DELETEONCLOSE ){
    *pMode = 0600;
  }
  return rc;
}

/*
** Open the file zPath.
** 
** Previously, the SQLite OS layer used three functions in place of this
** one:
**
**     sqlite3OsOpenReadWrite();
**     sqlite3OsOpenReadOnly();
**     sqlite3OsOpenExclusive();
**
** These calls correspond to the following combinations of flags:
**
**     ReadWrite() ->     (READWRITE | CREATE)
**     ReadOnly()  ->     (READONLY) 
**     OpenExclusive() -> (READWRITE | CREATE | EXCLUSIVE)
**
** The old OpenExclusive() accepted a boolean argument - "delFlag". If
** true, the file was configured to be automatically deleted when the
** file handle closed. To achieve the same effect using this new 
** interface, add the DELETEONCLOSE flag to those specified above for 
** OpenExclusive().
*/
static int unixOpen(
  sqlite3_vfs *pVfs,           /* The VFS for which this is the xOpen method */
  const char *zPath,           /* Pathname of file to be opened */
  sqlite3_file *pFile,         /* The file descriptor to be filled in */
  int flags,                   /* Input flags to control the opening */
  int *pOutFlags               /* Output flags returned to SQLite core */
){
  unixFile *p = (unixFile *)pFile;
  int fd = -1;                   /* File descriptor returned by open() */
  int openFlags = 0;             /* Flags to pass to open() */
  int eType = flags&0xFFFFFF00;  /* Type of file to open */
  int noLock;                    /* True to omit locking primitives */
  int rc = SQLITE_OK;            /* Function Return Code */
  int ctrlFlags = 0;             /* UNIXFILE_* flags */

  int isExclusive  = (flags & SQLITE_OPEN_EXCLUSIVE);
  int isDelete     = (flags & SQLITE_OPEN_DELETEONCLOSE);
  int isCreate     = (flags & SQLITE_OPEN_CREATE);
  int isReadonly   = (flags & SQLITE_OPEN_READONLY);
  int isReadWrite  = (flags & SQLITE_OPEN_READWRITE);
#if SQLITE_ENABLE_LOCKING_STYLE
  int isAutoProxy  = (flags & SQLITE_OPEN_AUTOPROXY);
#endif
#if defined(__APPLE__) || SQLITE_ENABLE_LOCKING_STYLE
  struct statfs fsInfo;
#endif

  /* If creating a master or main-file journal, this function will open
  ** a file-descriptor on the directory too. The first time unixSync()
  ** is called the directory file descriptor will be fsync()ed and close()d.
  */
  int syncDir = (isCreate && (
        eType==SQLITE_OPEN_MASTER_JOURNAL 
     || eType==SQLITE_OPEN_MAIN_JOURNAL 
     || eType==SQLITE_OPEN_WAL
  ));

  /* If argument zPath is a NULL pointer, this function is required to open
  ** a temporary file. Use this buffer to store the file name in.
  */
  char zTmpname[MAX_PATHNAME+2];
  const char *zName = zPath;

  /* Check the following statements are true: 
  **
  **   (a) Exactly one of the READWRITE and READONLY flags must be set, and 
  **   (b) if CREATE is set, then READWRITE must also be set, and
  **   (c) if EXCLUSIVE is set, then CREATE must also be set.
  **   (d) if DELETEONCLOSE is set, then CREATE must also be set.
  */
  assert((isReadonly==0 || isReadWrite==0) && (isReadWrite || isReadonly));
  assert(isCreate==0 || isReadWrite);
  assert(isExclusive==0 || isCreate);
  assert(isDelete==0 || isCreate);

  /* The main DB, main journal, WAL file and master journal are never 
  ** automatically deleted. Nor are they ever temporary files.  */
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_DB );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_JOURNAL );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MASTER_JOURNAL );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_WAL );

  /* Assert that the upper layer has set one of the "file-type" flags. */
  assert( eType==SQLITE_OPEN_MAIN_DB      || eType==SQLITE_OPEN_TEMP_DB 
       || eType==SQLITE_OPEN_MAIN_JOURNAL || eType==SQLITE_OPEN_TEMP_JOURNAL 
       || eType==SQLITE_OPEN_SUBJOURNAL   || eType==SQLITE_OPEN_MASTER_JOURNAL 
       || eType==SQLITE_OPEN_TRANSIENT_DB || eType==SQLITE_OPEN_WAL
  );

  /* Detect a pid change and reset the PRNG.  There is a race condition
  ** here such that two or more threads all trying to open databases at
  ** the same instant might all reset the PRNG.  But multiple resets
  ** are harmless.
  */
  if( randomnessPid!=osGetpid(0) ){
    randomnessPid = osGetpid(0);
    sqlite3_randomness(0,0);
  }

  memset(p, 0, sizeof(unixFile));

  if( eType==SQLITE_OPEN_MAIN_DB ){
    UnixUnusedFd *pUnused;
    pUnused = findReusableFd(zName, flags);
    if( pUnused ){
      fd = pUnused->fd;
    }else{
      pUnused = sqlite3_malloc64(sizeof(*pUnused));
      if( !pUnused ){
        return SQLITE_NOMEM;
      }
    }
    p->pUnused = pUnused;

    /* Database filenames are double-zero terminated if they are not
    ** URIs with parameters.  Hence, they can always be passed into
    ** sqlite3_uri_parameter(). */
    assert( (flags & SQLITE_OPEN_URI) || zName[strlen(zName)+1]==0 );

  }else if( !zName ){
    /* If zName is NULL, the upper layer is requesting a temp file. */
    assert(isDelete && !syncDir);
    rc = unixGetTempname(MAX_PATHNAME+2, zTmpname);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    zName = zTmpname;

    /* Generated temporary filenames are always double-zero terminated
    ** for use by sqlite3_uri_parameter(). */
    assert( zName[strlen(zName)+1]==0 );
  }

  /* Determine the value of the flags parameter passed to POSIX function
  ** open(). These must be calculated even if open() is not called, as
  ** they may be stored as part of the file handle and used by the 
  ** 'conch file' locking functions later on.  */
  if( isReadonly )  openFlags |= O_RDONLY;
  if( isReadWrite ) openFlags |= O_RDWR;
  if( isCreate )    openFlags |= O_CREAT;
  if( isExclusive ) openFlags |= (O_EXCL|O_NOFOLLOW);
  openFlags |= (O_LARGEFILE|O_BINARY);

  if( fd<0 ){
    mode_t openMode;              /* Permissions to create file with */
    uid_t uid;                    /* Userid for the file */
    gid_t gid;                    /* Groupid for the file */
    rc = findCreateFileMode(zName, flags, &openMode, &uid, &gid);
    if( rc!=SQLITE_OK ){
      assert( !p->pUnused );
      assert( eType==SQLITE_OPEN_WAL || eType==SQLITE_OPEN_MAIN_JOURNAL );
      return rc;
    }
    fd = robust_open(zName, openFlags, openMode);
    OSTRACE(("OPENX   %-3d %s 0%o\n", fd, zName, openFlags));
    if( fd<0 && errno!=EISDIR && isReadWrite && !isExclusive ){
      /* Failed to open the file for read/write access. Try read-only. */
      flags &= ~(SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE);
      openFlags &= ~(O_RDWR|O_CREAT);
      flags |= SQLITE_OPEN_READONLY;
      openFlags |= O_RDONLY;
      isReadonly = 1;
      fd = robust_open(zName, openFlags, openMode);
    }
    if( fd<0 ){
      rc = unixLogError(SQLITE_CANTOPEN_BKPT, "open", zName);
      goto open_finished;
    }

    /* If this process is running as root and if creating a new rollback
    ** journal or WAL file, set the ownership of the journal or WAL to be
    ** the same as the original database.
    */
    if( flags & (SQLITE_OPEN_WAL|SQLITE_OPEN_MAIN_JOURNAL) ){
      osFchown(fd, uid, gid);
    }
  }
  assert( fd>=0 );
  if( pOutFlags ){
    *pOutFlags = flags;
  }

  if( p->pUnused ){
    p->pUnused->fd = fd;
    p->pUnused->flags = flags;
  }

  if( isDelete ){
#if OS_VXWORKS
    zPath = zName;
#elif defined(SQLITE_UNLINK_AFTER_CLOSE)
    zPath = sqlite3_mprintf("%s", zName);
    if( zPath==0 ){
      robust_close(p, fd, __LINE__);
      return SQLITE_NOMEM;
    }
#else
    osUnlink(zName);
#endif
  }
#if SQLITE_ENABLE_LOCKING_STYLE
  else{
    p->openFlags = openFlags;
  }
#endif

  noLock = eType!=SQLITE_OPEN_MAIN_DB;

  
#if defined(__APPLE__) || SQLITE_ENABLE_LOCKING_STYLE
  if( fstatfs(fd, &fsInfo) == -1 ){
    storeLastErrno(p, errno);
    robust_close(p, fd, __LINE__);
    return SQLITE_IOERR_ACCESS;
  }
  if (0 == strncmp("msdos", fsInfo.f_fstypename, 5)) {
    ((unixFile*)pFile)->fsFlags |= SQLITE_FSFLAGS_IS_MSDOS;
  }
  if (0 == strncmp("exfat", fsInfo.f_fstypename, 5)) {
    ((unixFile*)pFile)->fsFlags |= SQLITE_FSFLAGS_IS_MSDOS;
  }
#endif

  /* Set up appropriate ctrlFlags */
  if( isDelete )                ctrlFlags |= UNIXFILE_DELETE;
  if( isReadonly )              ctrlFlags |= UNIXFILE_RDONLY;
  if( noLock )                  ctrlFlags |= UNIXFILE_NOLOCK;
  if( syncDir )                 ctrlFlags |= UNIXFILE_DIRSYNC;
  if( flags & SQLITE_OPEN_URI ) ctrlFlags |= UNIXFILE_URI;

#if SQLITE_ENABLE_LOCKING_STYLE
#if SQLITE_PREFER_PROXY_LOCKING
  isAutoProxy = 1;
#endif
  if( isAutoProxy && (zPath!=NULL) && (!noLock) && pVfs->xOpen ){
    char *envforce = getenv("SQLITE_FORCE_PROXY_LOCKING");
    int useProxy = 0;

    /* SQLITE_FORCE_PROXY_LOCKING==1 means force always use proxy, 0 means 
    ** never use proxy, NULL means use proxy for non-local files only.  */
    if( envforce!=NULL ){
      useProxy = atoi(envforce)>0;
    }else{
      useProxy = !(fsInfo.f_flags&MNT_LOCAL);
    }
    if( useProxy ){
      rc = fillInUnixFile(pVfs, fd, pFile, zPath, ctrlFlags);
      if( rc==SQLITE_OK ){
        rc = proxyTransformUnixFile((unixFile*)pFile, ":auto:");
        if( rc!=SQLITE_OK ){
          /* Use unixClose to clean up the resources added in fillInUnixFile 
          ** and clear all the structure's references.  Specifically, 
          ** pFile->pMethods will be NULL so sqlite3OsClose will be a no-op 
          */
          unixClose(pFile);
          return rc;
        }
      }
      goto open_finished;
    }
  }
#endif
  
  rc = fillInUnixFile(pVfs, fd, pFile, zPath, ctrlFlags);

open_finished:
  if( rc!=SQLITE_OK ){
    sqlite3_free(p->pUnused);
  }
  return rc;
}


/*
** Delete the file at zPath. If the dirSync argument is true, fsync()
** the directory after deleting the file.
*/
static int unixDelete(
  sqlite3_vfs *NotUsed,     /* VFS containing this as the xDelete method */
  const char *zPath,        /* Name of file to be deleted */
  int dirSync               /* If true, fsync() directory after deleting file */
){
  int rc = SQLITE_OK;
  UNUSED_PARAMETER(NotUsed);
  SimulateIOError(return SQLITE_IOERR_DELETE);
  if( osUnlink(zPath)==(-1) ){
    if( errno==ENOENT
#if OS_VXWORKS
        || osAccess(zPath,0)!=0
#endif
    ){
      rc = SQLITE_IOERR_DELETE_NOENT;
    }else{
      rc = unixLogError(SQLITE_IOERR_DELETE, "unlink", zPath);
    }
    return rc;
  }
#ifndef SQLITE_DISABLE_DIRSYNC
  if( (dirSync & 1)!=0 ){
    int fd;
    rc = osOpenDirectory(zPath, &fd);
    if( rc==SQLITE_OK ){
#if OS_VXWORKS
      if( fsync(fd)==-1 )
#else
      if( fsync(fd) )
#endif
      {
        rc = unixLogError(SQLITE_IOERR_DIR_FSYNC, "fsync", zPath);
      }
      robust_close(0, fd, __LINE__);
    }else if( rc==SQLITE_CANTOPEN ){
      rc = SQLITE_OK;
    }
  }
#endif
  return rc;
}

/*
** Test the existence of or access permissions of file zPath. The
** test performed depends on the value of flags:
**
**     SQLITE_ACCESS_EXISTS: Return 1 if the file exists
**     SQLITE_ACCESS_READWRITE: Return 1 if the file is read and writable.
**     SQLITE_ACCESS_READONLY: Return 1 if the file is readable.
**
** Otherwise return 0.
*/
static int unixAccess(
  sqlite3_vfs *NotUsed,   /* The VFS containing this xAccess method */
  const char *zPath,      /* Path of the file to examine */
  int flags,              /* What do we want to learn about the zPath file? */
  int *pResOut            /* Write result boolean here */
){
  int amode = 0;
  UNUSED_PARAMETER(NotUsed);
  SimulateIOError( return SQLITE_IOERR_ACCESS; );
  switch( flags ){
    case SQLITE_ACCESS_EXISTS:
      amode = F_OK;
      break;
    case SQLITE_ACCESS_READWRITE:
      amode = W_OK|R_OK;
      break;
    case SQLITE_ACCESS_READ:
      amode = R_OK;
      break;

    default:
      assert(!"Invalid flags argument");
  }
  *pResOut = (osAccess(zPath, amode)==0);
  if( flags==SQLITE_ACCESS_EXISTS && *pResOut ){
    struct stat buf;
    if( 0==osStat(zPath, &buf) && buf.st_size==0 ){
      *pResOut = 0;
    }
  }
  return SQLITE_OK;
}


/*
** Turn a relative pathname into a full pathname. The relative path
** is stored as a nul-terminated string in the buffer pointed to by
** zPath. 
**
** zOut points to a buffer of at least sqlite3_vfs.mxPathname bytes 
** (in this case, MAX_PATHNAME bytes). The full-path is written to
** this buffer before returning.
*/
static int unixFullPathname(
  sqlite3_vfs *pVfs,            /* Pointer to vfs object */
  const char *zPath,            /* Possibly relative input path */
  int nOut,                     /* Size of output buffer in bytes */
  char *zOut                    /* Output buffer */
){

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing. This function could fail if, for example, the
  ** current working directory has been unlinked.
  */
  SimulateIOError( return SQLITE_ERROR );

  assert( pVfs->mxPathname==MAX_PATHNAME );
  UNUSED_PARAMETER(pVfs);

  zOut[nOut-1] = '\0';
  if( zPath[0]=='/' ){
    sqlite3_snprintf(nOut, zOut, "%s", zPath);
  }else{
    int nCwd;
    if( osGetcwd(zOut, nOut-1)==0 ){
      return unixLogError(SQLITE_CANTOPEN_BKPT, "getcwd", zPath);
    }
    nCwd = (int)strlen(zOut);
    sqlite3_snprintf(nOut-nCwd, &zOut[nCwd], "/%s", zPath);
  }
  return SQLITE_OK;
}

  #define unixDlOpen  0
  #define unixDlError 0
  #define unixDlSym   0
  #define unixDlClose 0

/*
** Write nBuf bytes of random data to the supplied buffer zBuf.
*/
static int unixRandomness(sqlite3_vfs *NotUsed, int nBuf, char *zBuf){
  UNUSED_PARAMETER(NotUsed);
  assert((size_t)nBuf>=(sizeof(time_t)+sizeof(int)));

  /* We have to initialize zBuf to prevent valgrind from reporting
  ** errors.  The reports issued by valgrind are incorrect - we would
  ** prefer that the randomness be increased by making use of the
  ** uninitialized space in zBuf - but valgrind errors tend to worry
  ** some users.  Rather than argue, it seems easier just to initialize
  ** the whole array and silence valgrind, even if that means less randomness
  ** in the random seed.
  **
  ** When testing, initializing zBuf[] to zero is all we do.  That means
  ** that we always use the same random number sequence.  This makes the
  ** tests repeatable.
  */
  memset(zBuf, 0, nBuf);
  randomnessPid = osGetpid(0);  
#if !defined(SQLITE_TEST) && !defined(SQLITE_OMIT_RANDOMNESS)
  {
    int fd, got;
    fd = robust_open("/dev/urandom", O_RDONLY, 0);
    if( fd<0 ){
      time_t t;
      time(&t);
      memcpy(zBuf, &t, sizeof(t));
      memcpy(&zBuf[sizeof(t)], &randomnessPid, sizeof(randomnessPid));
      assert( sizeof(t)+sizeof(randomnessPid)<=(size_t)nBuf );
      nBuf = sizeof(t) + sizeof(randomnessPid);
    }else{
      do{ got = osRead(fd, zBuf, nBuf); }while( got<0 && errno==EINTR );
      robust_close(0, fd, __LINE__);
    }
  }
#endif
  return nBuf;
}


/*
** Sleep for a little while.  Return the amount of time slept.
** The argument is the number of microseconds we want to sleep.
** The return value is the number of microseconds of sleep actually
** requested from the underlying operating system, a number which
** might be greater than or equal to the argument, but not less
** than the argument.
*/
static int unixSleep(sqlite3_vfs *NotUsed, int microseconds){
#if OS_VXWORKS
  struct timespec sp;

  sp.tv_sec = microseconds / 1000000;
  sp.tv_nsec = (microseconds % 1000000) * 1000;
  nanosleep(&sp, NULL);
  UNUSED_PARAMETER(NotUsed);
  return microseconds;
#elif defined(HAVE_USLEEP) && HAVE_USLEEP
  usleep(microseconds);
  UNUSED_PARAMETER(NotUsed);
  return microseconds;
#else
  int seconds = (microseconds+999999)/1000000;
  sleep(seconds);
  UNUSED_PARAMETER(NotUsed);
  return seconds*1000000;
#endif
}

/*
** The following variable, if set to a non-zero value, is interpreted as
** the number of seconds since 1970 and is used to set the result of
** sqlite3OsCurrentTime() during testing.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_current_time = 0;  /* Fake system time in seconds since 1970. */
#endif

/*
** Find the current time (in Universal Coordinated Time).  Write into *piNow
** the current time and date as a Julian Day number times 86_400_000.  In
** other words, write into *piNow the number of milliseconds since the Julian
** epoch of noon in Greenwich on November 24, 4714 B.C according to the
** proleptic Gregorian calendar.
**
** On success, return SQLITE_OK.  Return SQLITE_ERROR if the time and date 
** cannot be found.
*/
static int unixCurrentTimeInt64(sqlite3_vfs *NotUsed, sqlite3_int64 *piNow){
  static const sqlite3_int64 unixEpoch = 24405875*(sqlite3_int64)8640000;
  int rc = SQLITE_OK;
#if defined(NO_GETTOD)
  time_t t;
  time(&t);
  *piNow = ((sqlite3_int64)t)*1000 + unixEpoch;
#elif OS_VXWORKS
  struct timespec sNow;
  clock_gettime(CLOCK_REALTIME, &sNow);
  *piNow = unixEpoch + 1000*(sqlite3_int64)sNow.tv_sec + sNow.tv_nsec/1000000;
#else
  struct timeval sNow;
  if( gettimeofday(&sNow, 0)==0 ){
    *piNow = unixEpoch + 1000*(sqlite3_int64)sNow.tv_sec + sNow.tv_usec/1000;
  }else{
    rc = SQLITE_ERROR;
  }
#endif

#ifdef SQLITE_TEST
  if( sqlite3_current_time ){
    *piNow = 1000*(sqlite3_int64)sqlite3_current_time + unixEpoch;
  }
#endif
  UNUSED_PARAMETER(NotUsed);
  return rc;
}

/*
** Find the current time (in Universal Coordinated Time).  Write the
** current time and date as a Julian Day number into *prNow and
** return 0.  Return 1 if the time and date cannot be found.
*/
static int unixCurrentTime(sqlite3_vfs *NotUsed, double *prNow){
  sqlite3_int64 i = 0;
  int rc;
  UNUSED_PARAMETER(NotUsed);
  rc = unixCurrentTimeInt64(0, &i);
  *prNow = i/86400000.0;
  return rc;
}

/*
** We added the xGetLastError() method with the intention of providing
** better low-level error messages when operating-system problems come up
** during SQLite operation.  But so far, none of that has been implemented
** in the core.  So this routine is never called.  For now, it is merely
** a place-holder.
*/
static int unixGetLastError(sqlite3_vfs *NotUsed, int NotUsed2, char *NotUsed3){
  UNUSED_PARAMETER(NotUsed);
  UNUSED_PARAMETER(NotUsed2);
  UNUSED_PARAMETER(NotUsed3);
  return 0;
}


/*
************************ End of sqlite3_vfs methods ***************************
******************************************************************************/

/******************************************************************************
************************** Begin Proxy Locking ********************************
**
** Proxy locking is a "uber-locking-method" in this sense:  It uses the
** other locking methods on secondary lock files.  Proxy locking is a
** meta-layer over top of the primitive locking implemented above.  For
** this reason, the division that implements of proxy locking is deferred
** until late in the file (here) after all of the other I/O methods have
** been defined - so that the primitive locking methods are available
** as services to help with the implementation of proxy locking.
**
****
**
** The default locking schemes in SQLite use byte-range locks on the
** database file to coordinate safe, concurrent access by multiple readers
** and writers [http://sqlite.org/lockingv3.html].  The five file locking
** states (UNLOCKED, PENDING, SHARED, RESERVED, EXCLUSIVE) are implemented
** as POSIX read & write locks over fixed set of locations (via fsctl),
** on AFP and SMB only exclusive byte-range locks are available via fsctl
** with _IOWR('z', 23, struct ByteRangeLockPB2) to track the same 5 states.
** To simulate a F_RDLCK on the shared range, on AFP a randomly selected
** address in the shared range is taken for a SHARED lock, the entire
** shared range is taken for an EXCLUSIVE lock):
**
**      PENDING_BYTE        0x40000000
**      RESERVED_BYTE       0x40000001
**      SHARED_RANGE        0x40000002 -> 0x40000200
**
** This works well on the local file system, but shows a nearly 100x
** slowdown in read performance on AFP because the AFP client disables
** the read cache when byte-range locks are present.  Enabling the read
** cache exposes a cache coherency problem that is present on all OS X
** supported network file systems.  NFS and AFP both observe the
** close-to-open semantics for ensuring cache coherency
** [http://nfs.sourceforge.net/#faq_a8], which does not effectively
** address the requirements for concurrent database access by multiple
** readers and writers
** [http://www.nabble.com/SQLite-on-NFS-cache-coherency-td15655701.html].
**
** To address the performance and cache coherency issues, proxy file locking
** changes the way database access is controlled by limiting access to a
** single host at a time and moving file locks off of the database file
** and onto a proxy file on the local file system.  
**
**
** Using proxy locks
** -----------------
**
** C APIs
**
**  sqlite3_file_control(db, dbname, SQLITE_FCNTL_SET_LOCKPROXYFILE,
**                       <proxy_path> | ":auto:");
**  sqlite3_file_control(db, dbname, SQLITE_FCNTL_GET_LOCKPROXYFILE,
**                       &<proxy_path>);
**
**
** SQL pragmas
**
**  PRAGMA [database.]lock_proxy_file=<proxy_path> | :auto:
**  PRAGMA [database.]lock_proxy_file
**
** Specifying ":auto:" means that if there is a conch file with a matching
** host ID in it, the proxy path in the conch file will be used, otherwise
** a proxy path based on the user's temp dir
** (via confstr(_CS_DARWIN_USER_TEMP_DIR,...)) will be used and the
** actual proxy file name is generated from the name and path of the
** database file.  For example:
**
**       For database path "/Users/me/foo.db" 
**       The lock path will be "<tmpdir>/sqliteplocks/_Users_me_foo.db:auto:")
**
** Once a lock proxy is configured for a database connection, it can not
** be removed, however it may be switched to a different proxy path via
** the above APIs (assuming the conch file is not being held by another
** connection or process). 
**
**
** How proxy locking works
** -----------------------
**
** Proxy file locking relies primarily on two new supporting files: 
**
**   *  conch file to limit access to the database file to a single host
**      at a time
**
**   *  proxy file to act as a proxy for the advisory locks normally
**      taken on the database
**
** The conch file - to use a proxy file, sqlite must first "hold the conch"
** by taking an sqlite-style shared lock on the conch file, reading the
** contents and comparing the host's unique host ID (see below) and lock
** proxy path against the values stored in the conch.  The conch file is
** stored in the same directory as the database file and the file name
** is patterned after the database file name as ".<databasename>-conch".
** If the conch file does not exist, or its contents do not match the
** host ID and/or proxy path, then the lock is escalated to an exclusive
** lock and the conch file contents is updated with the host ID and proxy
** path and the lock is downgraded to a shared lock again.  If the conch
** is held by another process (with a shared lock), the exclusive lock
** will fail and SQLITE_BUSY is returned.
**
** The proxy file - a single-byte file used for all advisory file locks
** normally taken on the database file.   This allows for safe sharing
** of the database file for multiple readers and writers on the same
** host (the conch ensures that they all use the same local lock file).
**
** Requesting the lock proxy does not immediately take the conch, it is
** only taken when the first request to lock database file is made.  
** This matches the semantics of the traditional locking behavior, where
** opening a connection to a database file does not take a lock on it.
** The shared lock and an open file descriptor are maintained until 
** the connection to the database is closed. 
**
** The proxy file and the lock file are never deleted so they only need
** to be created the first time they are used.
**
** Configuration options
** ---------------------
**
**  SQLITE_PREFER_PROXY_LOCKING
**
**       Database files accessed on non-local file systems are
**       automatically configured for proxy locking, lock files are
**       named automatically using the same logic as
**       PRAGMA lock_proxy_file=":auto:"
**    
**  SQLITE_PROXY_DEBUG
**
**       Enables the logging of error messages during host id file
**       retrieval and creation
**
**  LOCKPROXYDIR
**
**       Overrides the default directory used for lock proxy files that
**       are named automatically via the ":auto:" setting
**
**  SQLITE_DEFAULT_PROXYDIR_PERMISSIONS
**
**       Permissions to use when creating a directory for storing the
**       lock proxy files, only used when LOCKPROXYDIR is not set.
**    
**    
** As mentioned above, when compiled with SQLITE_PREFER_PROXY_LOCKING,
** setting the environment variable SQLITE_FORCE_PROXY_LOCKING to 1 will
** force proxy locking to be used for every database file opened, and 0
** will force automatic proxy locking to be disabled for all database
** files (explicitly calling the SQLITE_FCNTL_SET_LOCKPROXYFILE pragma or
** sqlite_file_control API is not affected by SQLITE_FORCE_PROXY_LOCKING).
*/

/*
** Proxy locking is only available on MacOSX 
*/
#if defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE

/*
** The proxyLockingContext has the path and file structures for the remote 
** and local proxy files in it
*/
typedef struct proxyLockingContext proxyLockingContext;
struct proxyLockingContext {
  unixFile *conchFile;         /* Open conch file */
  char *conchFilePath;         /* Name of the conch file */
  unixFile *lockProxy;         /* Open proxy lock file */
  char *lockProxyPath;         /* Name of the proxy lock file */
  char *dbPath;                /* Name of the open file */
  int conchHeld;               /* 1 if the conch is held, -1 if lockless */
  int nFails;                  /* Number of conch taking failures */
  void *oldLockingContext;     /* Original lockingcontext to restore on close */
  sqlite3_io_methods const *pOldMethod;     /* Original I/O methods for close */
};

/* 
** The proxy lock file path for the database at dbPath is written into lPath, 
** which must point to valid, writable memory large enough for a maxLen length
** file path. 
*/
static int proxyGetLockPath(const char *dbPath, char *lPath, size_t maxLen){
  int len;
  int dbLen;
  int i;

#ifdef LOCKPROXYDIR
  len = strlcpy(lPath, LOCKPROXYDIR, maxLen);
#else
# ifdef _CS_DARWIN_USER_TEMP_DIR
  {
    if( !confstr(_CS_DARWIN_USER_TEMP_DIR, lPath, maxLen) ){
      OSTRACE(("GETLOCKPATH  failed %s errno=%d pid=%d\n",
               lPath, errno, osGetpid(0)));
      return SQLITE_IOERR_LOCK;
    }
    len = strlcat(lPath, "sqliteplocks", maxLen);    
  }
# else
  len = strlcpy(lPath, "/tmp/", maxLen);
# endif
#endif

  if( lPath[len-1]!='/' ){
    len = strlcat(lPath, "/", maxLen);
  }
  
  /* transform the db path to a unique cache name */
  dbLen = (int)strlen(dbPath);
  for( i=0; i<dbLen && (i+len+7)<(int)maxLen; i++){
    char c = dbPath[i];
    lPath[i+len] = (c=='/')?'_':c;
  }
  lPath[i+len]='\0';
  strlcat(lPath, ":auto:", maxLen);
  OSTRACE(("GETLOCKPATH  proxy lock path=%s pid=%d\n", lPath, osGetpid(0)));
  return SQLITE_OK;
}

/* 
 ** Creates the lock file and any missing directories in lockPath
 */
static int proxyCreateLockPath(const char *lockPath){
  int i, len;
  char buf[MAXPATHLEN];
  int start = 0;
  
  assert(lockPath!=NULL);
  /* try to create all the intermediate directories */
  len = (int)strlen(lockPath);
  buf[0] = lockPath[0];
  for( i=1; i<len; i++ ){
    if( lockPath[i] == '/' && (i - start > 0) ){
      /* only mkdir if leaf dir != "." or "/" or ".." */
      if( i-start>2 || (i-start==1 && buf[start] != '.' && buf[start] != '/') 
         || (i-start==2 && buf[start] != '.' && buf[start+1] != '.') ){
        buf[i]='\0';
        if( osMkdir(buf, SQLITE_DEFAULT_PROXYDIR_PERMISSIONS) ){
          int err=errno;
          if( err!=EEXIST ) {
            OSTRACE(("CREATELOCKPATH  FAILED creating %s, "
                     "'%s' proxy lock path=%s pid=%d\n",
                     buf, strerror(err), lockPath, osGetpid(0)));
            return err;
          }
        }
      }
      start=i+1;
    }
    buf[i] = lockPath[i];
  }
  OSTRACE(("CREATELOCKPATH  proxy lock path=%s pid=%d\n", lockPath, osGetpid(0)));
  return 0;
}

/*
** Create a new VFS file descriptor (stored in memory obtained from
** sqlite3_malloc) and open the file named "path" in the file descriptor.
**
** The caller is responsible not only for closing the file descriptor
** but also for freeing the memory associated with the file descriptor.
*/
static int proxyCreateUnixFile(
    const char *path,        /* path for the new unixFile */
    unixFile **ppFile,       /* unixFile created and returned by ref */
    int islockfile           /* if non zero missing dirs will be created */
) {
  int fd = -1;
  unixFile *pNew;
  int rc = SQLITE_OK;
  int openFlags = O_RDWR | O_CREAT;
  sqlite3_vfs dummyVfs;
  int terrno = 0;
  UnixUnusedFd *pUnused = NULL;

  /* 1. first try to open/create the file
  ** 2. if that fails, and this is a lock file (not-conch), try creating
  ** the parent directories and then try again.
  ** 3. if that fails, try to open the file read-only
  ** otherwise return BUSY (if lock file) or CANTOPEN for the conch file
  */
  pUnused = findReusableFd(path, openFlags);
  if( pUnused ){
    fd = pUnused->fd;
  }else{
    pUnused = sqlite3_malloc64(sizeof(*pUnused));
    if( !pUnused ){
      return SQLITE_NOMEM;
    }
  }
  if( fd<0 ){
    fd = robust_open(path, openFlags, 0);
    terrno = errno;
    if( fd<0 && errno==ENOENT && islockfile ){
      if( proxyCreateLockPath(path) == SQLITE_OK ){
        fd = robust_open(path, openFlags, 0);
      }
    }
  }
  if( fd<0 ){
    openFlags = O_RDONLY;
    fd = robust_open(path, openFlags, 0);
    terrno = errno;
  }
  if( fd<0 ){
    if( islockfile ){
      return SQLITE_BUSY;
    }
    switch (terrno) {
      case EACCES:
        return SQLITE_PERM;
      case EIO: 
        return SQLITE_IOERR_LOCK; /* even though it is the conch */
      default:
        return SQLITE_CANTOPEN_BKPT;
    }
  }
  
  pNew = (unixFile *)sqlite3_malloc64(sizeof(*pNew));
  if( pNew==NULL ){
    rc = SQLITE_NOMEM;
    goto end_create_proxy;
  }
  memset(pNew, 0, sizeof(unixFile));
  pNew->openFlags = openFlags;
  memset(&dummyVfs, 0, sizeof(dummyVfs));
  dummyVfs.pAppData = (void*)&autolockIoFinder;
  dummyVfs.zName = "dummy";
  pUnused->fd = fd;
  pUnused->flags = openFlags;
  pNew->pUnused = pUnused;
  
  rc = fillInUnixFile(&dummyVfs, fd, (sqlite3_file*)pNew, path, 0);
  if( rc==SQLITE_OK ){
    *ppFile = pNew;
    return SQLITE_OK;
  }
end_create_proxy:    
  robust_close(pNew, fd, __LINE__);
  sqlite3_free(pNew);
  sqlite3_free(pUnused);
  return rc;
}

#ifdef SQLITE_TEST
/* simulate multiple hosts by creating unique hostid file paths */
SQLITE_PRIVATE int sqlite3_hostid_num = 0;
#endif

#define PROXY_HOSTIDLEN    16  /* conch file host id length */

#ifdef HAVE_GETHOSTUUID
/* Not always defined in the headers as it ought to be */
extern int gethostuuid(uuid_t id, const struct timespec *wait);
#endif

/* get the host ID via gethostuuid(), pHostID must point to PROXY_HOSTIDLEN 
** bytes of writable memory.
*/
static int proxyGetHostID(unsigned char *pHostID, int *pError){
  assert(PROXY_HOSTIDLEN == sizeof(uuid_t));
  memset(pHostID, 0, PROXY_HOSTIDLEN);
#ifdef HAVE_GETHOSTUUID
  {
    struct timespec timeout = {1, 0}; /* 1 sec timeout */
    if( gethostuuid(pHostID, &timeout) ){
      int err = errno;
      if( pError ){
        *pError = err;
      }
      return SQLITE_IOERR;
    }
  }
#else
  UNUSED_PARAMETER(pError);
#endif
#ifdef SQLITE_TEST
  /* simulate multiple hosts by creating unique hostid file paths */
  if( sqlite3_hostid_num != 0){
    pHostID[0] = (char)(pHostID[0] + (char)(sqlite3_hostid_num & 0xFF));
  }
#endif
  
  return SQLITE_OK;
}

/* The conch file contains the header, host id and lock file path
 */
#define PROXY_CONCHVERSION 2   /* 1-byte header, 16-byte host id, path */
#define PROXY_HEADERLEN    1   /* conch file header length */
#define PROXY_PATHINDEX    (PROXY_HEADERLEN+PROXY_HOSTIDLEN)
#define PROXY_MAXCONCHLEN  (PROXY_HEADERLEN+PROXY_HOSTIDLEN+MAXPATHLEN)

/* 
** Takes an open conch file, copies the contents to a new path and then moves 
** it back.  The newly created file's file descriptor is assigned to the
** conch file structure and finally the original conch file descriptor is 
** closed.  Returns zero if successful.
*/
static int proxyBreakConchLock(unixFile *pFile, uuid_t myHostID){
  proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext; 
  unixFile *conchFile = pCtx->conchFile;
  char tPath[MAXPATHLEN];
  char buf[PROXY_MAXCONCHLEN];
  char *cPath = pCtx->conchFilePath;
  size_t readLen = 0;
  size_t pathLen = 0;
  char errmsg[64] = "";
  int fd = -1;
  int rc = -1;
  UNUSED_PARAMETER(myHostID);

  /* create a new path by replace the trailing '-conch' with '-break' */
  pathLen = strlcpy(tPath, cPath, MAXPATHLEN);
  if( pathLen>MAXPATHLEN || pathLen<6 || 
     (strlcpy(&tPath[pathLen-5], "break", 6) != 5) ){
    sqlite3_snprintf(sizeof(errmsg),errmsg,"path error (len %d)",(int)pathLen);
    goto end_breaklock;
  }
  /* read the conch content */
  readLen = osPread(conchFile->h, buf, PROXY_MAXCONCHLEN, 0);
  if( readLen<PROXY_PATHINDEX ){
    sqlite3_snprintf(sizeof(errmsg),errmsg,"read error (len %d)",(int)readLen);
    goto end_breaklock;
  }
  /* write it out to the temporary break file */
  fd = robust_open(tPath, (O_RDWR|O_CREAT|O_EXCL), 0);
  if( fd<0 ){
    sqlite3_snprintf(sizeof(errmsg), errmsg, "create failed (%d)", errno);
    goto end_breaklock;
  }
  if( osPwrite(fd, buf, readLen, 0) != (ssize_t)readLen ){
    sqlite3_snprintf(sizeof(errmsg), errmsg, "write failed (%d)", errno);
    goto end_breaklock;
  }
  if( rename(tPath, cPath) ){
    sqlite3_snprintf(sizeof(errmsg), errmsg, "rename failed (%d)", errno);
    goto end_breaklock;
  }
  rc = 0;
  fprintf(stderr, "broke stale lock on %s\n", cPath);
  robust_close(pFile, conchFile->h, __LINE__);
  conchFile->h = fd;
  conchFile->openFlags = O_RDWR | O_CREAT;

end_breaklock:
  if( rc ){
    if( fd>=0 ){
      osUnlink(tPath);
      robust_close(pFile, fd, __LINE__);
    }
    fprintf(stderr, "failed to break stale lock on %s, %s\n", cPath, errmsg);
  }
  return rc;
}

/* Take the requested lock on the conch file and break a stale lock if the 
** host id matches.
*/
static int proxyConchLock(unixFile *pFile, uuid_t myHostID, int lockType){
  proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext; 
  unixFile *conchFile = pCtx->conchFile;
  int rc = SQLITE_OK;
  int nTries = 0;
  struct timespec conchModTime;
  
  memset(&conchModTime, 0, sizeof(conchModTime));
  do {
    rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, lockType);
    nTries ++;
    if( rc==SQLITE_BUSY ){
      /* If the lock failed (busy):
       * 1st try: get the mod time of the conch, wait 0.5s and try again. 
       * 2nd try: fail if the mod time changed or host id is different, wait 
       *           10 sec and try again
       * 3rd try: break the lock unless the mod time has changed.
       */
      struct stat buf;
      if( osFstat(conchFile->h, &buf) ){
        storeLastErrno(pFile, errno);
        return SQLITE_IOERR_LOCK;
      }
      
      if( nTries==1 ){
        conchModTime = buf.st_mtimespec;
        usleep(500000); /* wait 0.5 sec and try the lock again*/
        continue;  
      }

      assert( nTries>1 );
      if( conchModTime.tv_sec != buf.st_mtimespec.tv_sec || 
         conchModTime.tv_nsec != buf.st_mtimespec.tv_nsec ){
        return SQLITE_BUSY;
      }
      
      if( nTries==2 ){  
        char tBuf[PROXY_MAXCONCHLEN];
        int len = osPread(conchFile->h, tBuf, PROXY_MAXCONCHLEN, 0);
        if( len<0 ){
          storeLastErrno(pFile, errno);
          return SQLITE_IOERR_LOCK;
        }
        if( len>PROXY_PATHINDEX && tBuf[0]==(char)PROXY_CONCHVERSION){
          /* don't break the lock if the host id doesn't match */
          if( 0!=memcmp(&tBuf[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN) ){
            return SQLITE_BUSY;
          }
        }else{
          /* don't break the lock on short read or a version mismatch */
          return SQLITE_BUSY;
        }
        usleep(10000000); /* wait 10 sec and try the lock again */
        continue; 
      }
      
      assert( nTries==3 );
      if( 0==proxyBreakConchLock(pFile, myHostID) ){
        rc = SQLITE_OK;
        if( lockType==EXCLUSIVE_LOCK ){
          rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, SHARED_LOCK);
        }
        if( !rc ){
          rc = conchFile->pMethod->xLock((sqlite3_file*)conchFile, lockType);
        }
      }
    }
  } while( rc==SQLITE_BUSY && nTries<3 );
  
  return rc;
}

/* Takes the conch by taking a shared lock and read the contents conch, if 
** lockPath is non-NULL, the host ID and lock file path must match.  A NULL 
** lockPath means that the lockPath in the conch file will be used if the 
** host IDs match, or a new lock path will be generated automatically 
** and written to the conch file.
*/
static int proxyTakeConch(unixFile *pFile){
  proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext; 
  
  if( pCtx->conchHeld!=0 ){
    return SQLITE_OK;
  }else{
    unixFile *conchFile = pCtx->conchFile;
    uuid_t myHostID;
    int pError = 0;
    char readBuf[PROXY_MAXCONCHLEN];
    char lockPath[MAXPATHLEN];
    char *tempLockPath = NULL;
    int rc = SQLITE_OK;
    int createConch = 0;
    int hostIdMatch = 0;
    int readLen = 0;
    int tryOldLockPath = 0;
    int forceNewLockPath = 0;
    
    OSTRACE(("TAKECONCH  %d for %s pid=%d\n", conchFile->h,
             (pCtx->lockProxyPath ? pCtx->lockProxyPath : ":auto:"),
             osGetpid(0)));

    rc = proxyGetHostID(myHostID, &pError);
    if( (rc&0xff)==SQLITE_IOERR ){
      storeLastErrno(pFile, pError);
      goto end_takeconch;
    }
    rc = proxyConchLock(pFile, myHostID, SHARED_LOCK);
    if( rc!=SQLITE_OK ){
      goto end_takeconch;
    }
    /* read the existing conch file */
    readLen = seekAndRead((unixFile*)conchFile, 0, readBuf, PROXY_MAXCONCHLEN);
    if( readLen<0 ){
      /* I/O error: lastErrno set by seekAndRead */
      storeLastErrno(pFile, conchFile->lastErrno);
      rc = SQLITE_IOERR_READ;
      goto end_takeconch;
    }else if( readLen<=(PROXY_HEADERLEN+PROXY_HOSTIDLEN) || 
             readBuf[0]!=(char)PROXY_CONCHVERSION ){
      /* a short read or version format mismatch means we need to create a new 
      ** conch file. 
      */
      createConch = 1;
    }
    /* if the host id matches and the lock path already exists in the conch
    ** we'll try to use the path there, if we can't open that path, we'll 
    ** retry with a new auto-generated path 
    */
    do { /* in case we need to try again for an :auto: named lock file */

      if( !createConch && !forceNewLockPath ){
        hostIdMatch = !memcmp(&readBuf[PROXY_HEADERLEN], myHostID, 
                                  PROXY_HOSTIDLEN);
        /* if the conch has data compare the contents */
        if( !pCtx->lockProxyPath ){
          /* for auto-named local lock file, just check the host ID and we'll
           ** use the local lock file path that's already in there
           */
          if( hostIdMatch ){
            size_t pathLen = (readLen - PROXY_PATHINDEX);
            
            if( pathLen>=MAXPATHLEN ){
              pathLen=MAXPATHLEN-1;
            }
            memcpy(lockPath, &readBuf[PROXY_PATHINDEX], pathLen);
            lockPath[pathLen] = 0;
            tempLockPath = lockPath;
            tryOldLockPath = 1;
            /* create a copy of the lock path if the conch is taken */
            goto end_takeconch;
          }
        }else if( hostIdMatch
               && !strncmp(pCtx->lockProxyPath, &readBuf[PROXY_PATHINDEX],
                           readLen-PROXY_PATHINDEX)
        ){
          /* conch host and lock path match */
          goto end_takeconch; 
        }
      }
      
      /* if the conch isn't writable and doesn't match, we can't take it */
      if( (conchFile->openFlags&O_RDWR) == 0 ){
        rc = SQLITE_BUSY;
        goto end_takeconch;
      }
      
      /* either the conch didn't match or we need to create a new one */
      if( !pCtx->lockProxyPath ){
        proxyGetLockPath(pCtx->dbPath, lockPath, MAXPATHLEN);
        tempLockPath = lockPath;
        /* create a copy of the lock path _only_ if the conch is taken */
      }
      
      /* update conch with host and path (this will fail if other process
      ** has a shared lock already), if the host id matches, use the big
      ** stick.
      */
      futimes(conchFile->h, NULL);
      if( hostIdMatch && !createConch ){
        if( conchFile->pInode && conchFile->pInode->nShared>1 ){
          /* We are trying for an exclusive lock but another thread in this
           ** same process is still holding a shared lock. */
          rc = SQLITE_BUSY;
        } else {          
          rc = proxyConchLock(pFile, myHostID, EXCLUSIVE_LOCK);
        }
      }else{
        rc = proxyConchLock(pFile, myHostID, EXCLUSIVE_LOCK);
      }
      if( rc==SQLITE_OK ){
        char writeBuffer[PROXY_MAXCONCHLEN];
        int writeSize = 0;
        
        writeBuffer[0] = (char)PROXY_CONCHVERSION;
        memcpy(&writeBuffer[PROXY_HEADERLEN], myHostID, PROXY_HOSTIDLEN);
        if( pCtx->lockProxyPath!=NULL ){
          strlcpy(&writeBuffer[PROXY_PATHINDEX], pCtx->lockProxyPath,
                  MAXPATHLEN);
        }else{
          strlcpy(&writeBuffer[PROXY_PATHINDEX], tempLockPath, MAXPATHLEN);
        }
        writeSize = PROXY_PATHINDEX + strlen(&writeBuffer[PROXY_PATHINDEX]);
        robust_ftruncate(conchFile->h, writeSize);
        rc = unixWrite((sqlite3_file *)conchFile, writeBuffer, writeSize, 0);
        fsync(conchFile->h);
        /* If we created a new conch file (not just updated the contents of a 
         ** valid conch file), try to match the permissions of the database 
         */
        if( rc==SQLITE_OK && createConch ){
          struct stat buf;
          int err = osFstat(pFile->h, &buf);
          if( err==0 ){
            mode_t cmode = buf.st_mode&(S_IRUSR|S_IWUSR | S_IRGRP|S_IWGRP |
                                        S_IROTH|S_IWOTH);
            /* try to match the database file R/W permissions, ignore failure */
#ifndef SQLITE_PROXY_DEBUG
            osFchmod(conchFile->h, cmode);
#else
            do{
              rc = osFchmod(conchFile->h, cmode);
            }while( rc==(-1) && errno==EINTR );
            if( rc!=0 ){
              int code = errno;
              fprintf(stderr, "fchmod %o FAILED with %d %s\n",
                      cmode, code, strerror(code));
            } else {
              fprintf(stderr, "fchmod %o SUCCEDED\n",cmode);
            }
          }else{
            int code = errno;
            fprintf(stderr, "STAT FAILED[%d] with %d %s\n", 
                    err, code, strerror(code));
#endif
          }
        }
      }
      conchFile->pMethod->xUnlock((sqlite3_file*)conchFile, SHARED_LOCK);
      
    end_takeconch:
      OSTRACE(("TRANSPROXY: CLOSE  %d\n", pFile->h));
      if( rc==SQLITE_OK && pFile->openFlags ){
        int fd;
        if( pFile->h>=0 ){
          robust_close(pFile, pFile->h, __LINE__);
        }
        pFile->h = -1;
        fd = robust_open(pCtx->dbPath, pFile->openFlags, 0);
        OSTRACE(("TRANSPROXY: OPEN  %d\n", fd));
        if( fd>=0 ){
          pFile->h = fd;
        }else{
          rc=SQLITE_CANTOPEN_BKPT; /* SQLITE_BUSY? proxyTakeConch called
           during locking */
        }
      }
      if( rc==SQLITE_OK && !pCtx->lockProxy ){
        char *path = tempLockPath ? tempLockPath : pCtx->lockProxyPath;
        rc = proxyCreateUnixFile(path, &pCtx->lockProxy, 1);
        if( rc!=SQLITE_OK && rc!=SQLITE_NOMEM && tryOldLockPath ){
          /* we couldn't create the proxy lock file with the old lock file path
           ** so try again via auto-naming 
           */
          forceNewLockPath = 1;
          tryOldLockPath = 0;
          continue; /* go back to the do {} while start point, try again */
        }
      }
      if( rc==SQLITE_OK ){
        /* Need to make a copy of path if we extracted the value
         ** from the conch file or the path was allocated on the stack
         */
        if( tempLockPath ){
          pCtx->lockProxyPath = sqlite3DbStrDup(0, tempLockPath);
          if( !pCtx->lockProxyPath ){
            rc = SQLITE_NOMEM;
          }
        }
      }
      if( rc==SQLITE_OK ){
        pCtx->conchHeld = 1;
        
        if( pCtx->lockProxy->pMethod == &afpIoMethods ){
          afpLockingContext *afpCtx;
          afpCtx = (afpLockingContext *)pCtx->lockProxy->lockingContext;
          afpCtx->dbPath = pCtx->lockProxyPath;
        }
      } else {
        conchFile->pMethod->xUnlock((sqlite3_file*)conchFile, NO_LOCK);
      }
      OSTRACE(("TAKECONCH  %d %s\n", conchFile->h,
               rc==SQLITE_OK?"ok":"failed"));
      return rc;
    } while (1); /* in case we need to retry the :auto: lock file - 
                 ** we should never get here except via the 'continue' call. */
  }
}

/*
** If pFile holds a lock on a conch file, then release that lock.
*/
static int proxyReleaseConch(unixFile *pFile){
  int rc = SQLITE_OK;         /* Subroutine return code */
  proxyLockingContext *pCtx;  /* The locking context for the proxy lock */
  unixFile *conchFile;        /* Name of the conch file */

  pCtx = (proxyLockingContext *)pFile->lockingContext;
  conchFile = pCtx->conchFile;
  OSTRACE(("RELEASECONCH  %d for %s pid=%d\n", conchFile->h,
           (pCtx->lockProxyPath ? pCtx->lockProxyPath : ":auto:"), 
           osGetpid(0)));
  if( pCtx->conchHeld>0 ){
    rc = conchFile->pMethod->xUnlock((sqlite3_file*)conchFile, NO_LOCK);
  }
  pCtx->conchHeld = 0;
  OSTRACE(("RELEASECONCH  %d %s\n", conchFile->h,
           (rc==SQLITE_OK ? "ok" : "failed")));
  return rc;
}

/*
** Given the name of a database file, compute the name of its conch file.
** Store the conch filename in memory obtained from sqlite3_malloc64().
** Make *pConchPath point to the new name.  Return SQLITE_OK on success
** or SQLITE_NOMEM if unable to obtain memory.
**
** The caller is responsible for ensuring that the allocated memory
** space is eventually freed.
**
** *pConchPath is set to NULL if a memory allocation error occurs.
*/
static int proxyCreateConchPathname(char *dbPath, char **pConchPath){
  int i;                        /* Loop counter */
  int len = (int)strlen(dbPath); /* Length of database filename - dbPath */
  char *conchPath;              /* buffer in which to construct conch name */

  /* Allocate space for the conch filename and initialize the name to
  ** the name of the original database file. */  
  *pConchPath = conchPath = (char *)sqlite3_malloc64(len + 8);
  if( conchPath==0 ){
    return SQLITE_NOMEM;
  }
  memcpy(conchPath, dbPath, len+1);
  
  /* now insert a "." before the last / character */
  for( i=(len-1); i>=0; i-- ){
    if( conchPath[i]=='/' ){
      i++;
      break;
    }
  }
  conchPath[i]='.';
  while ( i<len ){
    conchPath[i+1]=dbPath[i];
    i++;
  }

  /* append the "-conch" suffix to the file */
  memcpy(&conchPath[i+1], "-conch", 7);
  assert( (int)strlen(conchPath) == len+7 );

  return SQLITE_OK;
}


/* Takes a fully configured proxy locking-style unix file and switches
** the local lock file path 
*/
static int switchLockProxyPath(unixFile *pFile, const char *path) {
  proxyLockingContext *pCtx = (proxyLockingContext*)pFile->lockingContext;
  char *oldPath = pCtx->lockProxyPath;
  int rc = SQLITE_OK;

  if( pFile->eFileLock!=NO_LOCK ){
    return SQLITE_BUSY;
  }  

  /* nothing to do if the path is NULL, :auto: or matches the existing path */
  if( !path || path[0]=='\0' || !strcmp(path, ":auto:") ||
    (oldPath && !strncmp(oldPath, path, MAXPATHLEN)) ){
    return SQLITE_OK;
  }else{
    unixFile *lockProxy = pCtx->lockProxy;
    pCtx->lockProxy=NULL;
    pCtx->conchHeld = 0;
    if( lockProxy!=NULL ){
      rc=lockProxy->pMethod->xClose((sqlite3_file *)lockProxy);
      if( rc ) return rc;
      sqlite3_free(lockProxy);
    }
    sqlite3_free(oldPath);
    pCtx->lockProxyPath = sqlite3DbStrDup(0, path);
  }
  
  return rc;
}

/*
** pFile is a file that has been opened by a prior xOpen call.  dbPath
** is a string buffer at least MAXPATHLEN+1 characters in size.
**
** This routine find the filename associated with pFile and writes it
** int dbPath.
*/
static int proxyGetDbPathForUnixFile(unixFile *pFile, char *dbPath){
#if defined(__APPLE__)
  if( pFile->pMethod == &afpIoMethods ){
    /* afp style keeps a reference to the db path in the filePath field 
    ** of the struct */
    assert( (int)strlen((char*)pFile->lockingContext)<=MAXPATHLEN );
    strlcpy(dbPath, ((afpLockingContext *)pFile->lockingContext)->dbPath,
            MAXPATHLEN);
  } else
#endif
  if( pFile->pMethod == &dotlockIoMethods ){
    /* dot lock style uses the locking context to store the dot lock
    ** file path */
    int len = strlen((char *)pFile->lockingContext) - strlen(DOTLOCK_SUFFIX);
    memcpy(dbPath, (char *)pFile->lockingContext, len + 1);
  }else{
    /* all other styles use the locking context to store the db file path */
    assert( strlen((char*)pFile->lockingContext)<=MAXPATHLEN );
    strlcpy(dbPath, (char *)pFile->lockingContext, MAXPATHLEN);
  }
  return SQLITE_OK;
}

/*
** Takes an already filled in unix file and alters it so all file locking 
** will be performed on the local proxy lock file.  The following fields
** are preserved in the locking context so that they can be restored and 
** the unix structure properly cleaned up at close time:
**  ->lockingContext
**  ->pMethod
*/
static int proxyTransformUnixFile(unixFile *pFile, const char *path) {
  proxyLockingContext *pCtx;
  char dbPath[MAXPATHLEN+1];       /* Name of the database file */
  char *lockPath=NULL;
  int rc = SQLITE_OK;
  
  if( pFile->eFileLock!=NO_LOCK ){
    return SQLITE_BUSY;
  }
  proxyGetDbPathForUnixFile(pFile, dbPath);
  if( !path || path[0]=='\0' || !strcmp(path, ":auto:") ){
    lockPath=NULL;
  }else{
    lockPath=(char *)path;
  }
  
  OSTRACE(("TRANSPROXY  %d for %s pid=%d\n", pFile->h,
           (lockPath ? lockPath : ":auto:"), osGetpid(0)));

  pCtx = sqlite3_malloc64( sizeof(*pCtx) );
  if( pCtx==0 ){
    return SQLITE_NOMEM;
  }
  memset(pCtx, 0, sizeof(*pCtx));

  rc = proxyCreateConchPathname(dbPath, &pCtx->conchFilePath);
  if( rc==SQLITE_OK ){
    rc = proxyCreateUnixFile(pCtx->conchFilePath, &pCtx->conchFile, 0);
    if( rc==SQLITE_CANTOPEN && ((pFile->openFlags&O_RDWR) == 0) ){
      /* if (a) the open flags are not O_RDWR, (b) the conch isn't there, and
      ** (c) the file system is read-only, then enable no-locking access.
      ** Ugh, since O_RDONLY==0x0000 we test for !O_RDWR since unixOpen asserts
      ** that openFlags will have only one of O_RDONLY or O_RDWR.
      */
      struct statfs fsInfo;
      struct stat conchInfo;
      int goLockless = 0;

      if( osStat(pCtx->conchFilePath, &conchInfo) == -1 ) {
        int err = errno;
        if( (err==ENOENT) && (statfs(dbPath, &fsInfo) != -1) ){
          goLockless = (fsInfo.f_flags&MNT_RDONLY) == MNT_RDONLY;
        }
      }
      if( goLockless ){
        pCtx->conchHeld = -1; /* read only FS/ lockless */
        rc = SQLITE_OK;
      }
    }
  }  
  if( rc==SQLITE_OK && lockPath ){
    pCtx->lockProxyPath = sqlite3DbStrDup(0, lockPath);
  }

  if( rc==SQLITE_OK ){
    pCtx->dbPath = sqlite3DbStrDup(0, dbPath);
    if( pCtx->dbPath==NULL ){
      rc = SQLITE_NOMEM;
    }
  }
  if( rc==SQLITE_OK ){
    /* all memory is allocated, proxys are created and assigned, 
    ** switch the locking context and pMethod then return.
    */
    pCtx->oldLockingContext = pFile->lockingContext;
    pFile->lockingContext = pCtx;
    pCtx->pOldMethod = pFile->pMethod;
    pFile->pMethod = &proxyIoMethods;
  }else{
    if( pCtx->conchFile ){ 
      pCtx->conchFile->pMethod->xClose((sqlite3_file *)pCtx->conchFile);
      sqlite3_free(pCtx->conchFile);
    }
    sqlite3DbFree(0, pCtx->lockProxyPath);
    sqlite3_free(pCtx->conchFilePath); 
    sqlite3_free(pCtx);
  }
  OSTRACE(("TRANSPROXY  %d %s\n", pFile->h,
           (rc==SQLITE_OK ? "ok" : "failed")));
  return rc;
}


/*
** This routine handles sqlite3_file_control() calls that are specific
** to proxy locking.
*/
static int proxyFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_GET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      if( pFile->pMethod == &proxyIoMethods ){
        proxyLockingContext *pCtx = (proxyLockingContext*)pFile->lockingContext;
        proxyTakeConch(pFile);
        if( pCtx->lockProxyPath ){
          *(const char **)pArg = pCtx->lockProxyPath;
        }else{
          *(const char **)pArg = ":auto: (not held)";
        }
      } else {
        *(const char **)pArg = NULL;
      }
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SET_LOCKPROXYFILE: {
      unixFile *pFile = (unixFile*)id;
      int rc = SQLITE_OK;
      int isProxyStyle = (pFile->pMethod == &proxyIoMethods);
      if( pArg==NULL || (const char *)pArg==0 ){
        if( isProxyStyle ){
          /* turn off proxy locking - not supported.  If support is added for
          ** switching proxy locking mode off then it will need to fail if
          ** the journal mode is WAL mode. 
          */
          rc = SQLITE_ERROR /*SQLITE_PROTOCOL? SQLITE_MISUSE?*/;
        }else{
          /* turn off proxy locking - already off - NOOP */
          rc = SQLITE_OK;
        }
      }else{
        const char *proxyPath = (const char *)pArg;
        if( isProxyStyle ){
          proxyLockingContext *pCtx = 
            (proxyLockingContext*)pFile->lockingContext;
          if( !strcmp(pArg, ":auto:") 
           || (pCtx->lockProxyPath &&
               !strncmp(pCtx->lockProxyPath, proxyPath, MAXPATHLEN))
          ){
            rc = SQLITE_OK;
          }else{
            rc = switchLockProxyPath(pFile, proxyPath);
          }
        }else{
          /* turn on proxy file locking */
          rc = proxyTransformUnixFile(pFile, proxyPath);
        }
      }
      return rc;
    }
    default: {
      assert( 0 );  /* The call assures that only valid opcodes are sent */
    }
  }
  /*NOTREACHED*/
  return SQLITE_ERROR;
}

/*
** Within this division (the proxying locking implementation) the procedures
** above this point are all utilities.  The lock-related methods of the
** proxy-locking sqlite3_io_method object follow.
*/


/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, set *pResOut
** to a non-zero value otherwise *pResOut is set to zero.  The return value
** is set to SQLITE_OK unless an I/O error occurs during lock checking.
*/
static int proxyCheckReservedLock(sqlite3_file *id, int *pResOut) {
  unixFile *pFile = (unixFile*)id;
  int rc = proxyTakeConch(pFile);
  if( rc==SQLITE_OK ){
    proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext;
    if( pCtx->conchHeld>0 ){
      unixFile *proxy = pCtx->lockProxy;
      return proxy->pMethod->xCheckReservedLock((sqlite3_file*)proxy, pResOut);
    }else{ /* conchHeld < 0 is lockless */
      pResOut=0;
    }
  }
  return rc;
}

/*
** Lock the file with the lock specified by parameter eFileLock - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** This routine will only increase a lock.  Use the sqlite3OsUnlock()
** routine to lower a locking level.
*/
static int proxyLock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  int rc = proxyTakeConch(pFile);
  if( rc==SQLITE_OK ){
    proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext;
    if( pCtx->conchHeld>0 ){
      unixFile *proxy = pCtx->lockProxy;
      rc = proxy->pMethod->xLock((sqlite3_file*)proxy, eFileLock);
      pFile->eFileLock = proxy->eFileLock;
    }else{
      /* conchHeld < 0 is lockless */
    }
  }
  return rc;
}


/*
** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
*/
static int proxyUnlock(sqlite3_file *id, int eFileLock) {
  unixFile *pFile = (unixFile*)id;
  int rc = proxyTakeConch(pFile);
  if( rc==SQLITE_OK ){
    proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext;
    if( pCtx->conchHeld>0 ){
      unixFile *proxy = pCtx->lockProxy;
      rc = proxy->pMethod->xUnlock((sqlite3_file*)proxy, eFileLock);
      pFile->eFileLock = proxy->eFileLock;
    }else{
      /* conchHeld < 0 is lockless */
    }
  }
  return rc;
}

/*
** Close a file that uses proxy locks.
*/
static int proxyClose(sqlite3_file *id) {
  if( id ){
    unixFile *pFile = (unixFile*)id;
    proxyLockingContext *pCtx = (proxyLockingContext *)pFile->lockingContext;
    unixFile *lockProxy = pCtx->lockProxy;
    unixFile *conchFile = pCtx->conchFile;
    int rc = SQLITE_OK;
    
    if( lockProxy ){
      rc = lockProxy->pMethod->xUnlock((sqlite3_file*)lockProxy, NO_LOCK);
      if( rc ) return rc;
      rc = lockProxy->pMethod->xClose((sqlite3_file*)lockProxy);
      if( rc ) return rc;
      sqlite3_free(lockProxy);
      pCtx->lockProxy = 0;
    }
    if( conchFile ){
      if( pCtx->conchHeld ){
        rc = proxyReleaseConch(pFile);
        if( rc ) return rc;
      }
      rc = conchFile->pMethod->xClose((sqlite3_file*)conchFile);
      if( rc ) return rc;
      sqlite3_free(conchFile);
    }
    sqlite3DbFree(0, pCtx->lockProxyPath);
    sqlite3_free(pCtx->conchFilePath);
    sqlite3DbFree(0, pCtx->dbPath);
    /* restore the original locking context and pMethod then close it */
    pFile->lockingContext = pCtx->oldLockingContext;
    pFile->pMethod = pCtx->pOldMethod;
    sqlite3_free(pCtx);
    return pFile->pMethod->xClose(id);
  }
  return SQLITE_OK;
}



#endif /* defined(__APPLE__) && SQLITE_ENABLE_LOCKING_STYLE */
/*
** The proxy locking style is intended for use with AFP filesystems.
** And since AFP is only supported on MacOSX, the proxy locking is also
** restricted to MacOSX.
** 
**
******************* End of the proxy lock implementation **********************
******************************************************************************/

/*
** Initialize the operating system interface.
**
** This routine registers all VFS implementations for unix-like operating
** systems.  This routine, and the sqlite3_os_end() routine that follows,
** should be the only routines in this file that are visible from other
** files.
**
** This routine is called once during SQLite initialization and by a
** single thread.  The memory allocation and mutex subsystems have not
** necessarily been initialized when this routine is called, and so they
** should not be used.
*/
SQLITE_PRIVATE int sqlite3_os_init(void){ 
  /* 
  ** The following macro defines an initializer for an sqlite3_vfs object.
  ** The name of the VFS is NAME.  The pAppData is a pointer to a pointer
  ** to the "finder" function.  (pAppData is a pointer to a pointer because
  ** silly C90 rules prohibit a void* from being cast to a function pointer
  ** and so we have to go through the intermediate pointer to avoid problems
  ** when compiling with -pedantic-errors on GCC.)
  **
  ** The FINDER parameter to this macro is the name of the pointer to the
  ** finder-function.  The finder-function returns a pointer to the
  ** sqlite_io_methods object that implements the desired locking
  ** behaviors.  See the division above that contains the IOMETHODS
  ** macro for addition information on finder-functions.
  **
  ** Most finders simply return a pointer to a fixed sqlite3_io_methods
  ** object.  But the "autolockIoFinder" available on MacOSX does a little
  ** more than that; it looks at the filesystem type that hosts the 
  ** database file and tries to choose an locking method appropriate for
  ** that filesystem time.
  */
  #define UNIXVFS(VFSNAME, FINDER) {                        \
    3,                    /* iVersion */                    \
    sizeof(unixFile),     /* szOsFile */                    \
    MAX_PATHNAME,         /* mxPathname */                  \
    0,                    /* pNext */                       \
    VFSNAME,              /* zName */                       \
    (void*)&FINDER,       /* pAppData */                    \
    unixOpen,             /* xOpen */                       \
    unixDelete,           /* xDelete */                     \
    unixAccess,           /* xAccess */                     \
    unixFullPathname,     /* xFullPathname */               \
    unixDlOpen,           /* xDlOpen */                     \
    unixDlError,          /* xDlError */                    \
    unixDlSym,            /* xDlSym */                      \
    unixDlClose,          /* xDlClose */                    \
    unixRandomness,       /* xRandomness */                 \
    unixSleep,            /* xSleep */                      \
    unixCurrentTime,      /* xCurrentTime */                \
    unixGetLastError,     /* xGetLastError */               \
    unixCurrentTimeInt64, /* xCurrentTimeInt64 */           \
    unixSetSystemCall,    /* xSetSystemCall */              \
    unixGetSystemCall,    /* xGetSystemCall */              \
    unixNextSystemCall,   /* xNextSystemCall */             \
  }

  /*
  ** All default VFSes for unix are contained in the following array.
  **
  ** Note that the sqlite3_vfs.pNext field of the VFS object is modified
  ** by the SQLite core when the VFS is registered.  So the following
  ** array cannot be const.
  */
  static sqlite3_vfs aVfs[] = {
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    UNIXVFS("unix",          autolockIoFinder ),
#elif OS_VXWORKS
    UNIXVFS("unix",          vxworksIoFinder ),
#else
    UNIXVFS("unix",          posixIoFinder ),
#endif
    UNIXVFS("unix-none",     nolockIoFinder ),
    UNIXVFS("unix-dotfile",  dotlockIoFinder ),
    UNIXVFS("unix-excl",     posixIoFinder ),
#if OS_VXWORKS
    UNIXVFS("unix-namedsem", semIoFinder ),
#endif
#if SQLITE_ENABLE_LOCKING_STYLE || OS_VXWORKS
    UNIXVFS("unix-posix",    posixIoFinder ),
#endif
#if SQLITE_ENABLE_LOCKING_STYLE
    UNIXVFS("unix-flock",    flockIoFinder ),
#endif
#if SQLITE_ENABLE_LOCKING_STYLE && defined(__APPLE__)
    UNIXVFS("unix-afp",      afpIoFinder ),
    UNIXVFS("unix-nfs",      nfsIoFinder ),
    UNIXVFS("unix-proxy",    proxyIoFinder ),
#endif
  };
  unsigned int i;          /* Loop counter */

  /* Double-check that the aSyscall[] array has been constructed
  ** correctly.  See ticket [bb3a86e890c8e96ab] */
  assert( ArraySize(aSyscall)==25 );

  /* Register all VFSes defined in the aVfs[] array */
  for(i=0; i<(sizeof(aVfs)/sizeof(sqlite3_vfs)); i++){
    sqlite3_vfs_register(&aVfs[i], i==0);
  }
  return SQLITE_OK; 
}

/*
** Shutdown the operating system interface.
**
** Some operating systems might need to do some cleanup in this routine,
** to release dynamically allocated objects.  But not on unix.
** This routine is a no-op for unix.
*/
SQLITE_PRIVATE int sqlite3_os_end(void){ 
  return SQLITE_OK; 
}
 
#endif /* SQLITE_OS_UNIX */

/************** End of os_unix.c *********************************************/
/************** Begin file os_win.c ******************************************/
/*
** 2004 May 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains code that is specific to Windows.
*/
/* #include "sqliteInt.h" */
#if SQLITE_OS_WIN               /* This file is used for Windows only */

/*
** Include code that is common to all os_*.c files
*/
/************** Include os_common.h in the middle of os_win.c ****************/
/************** Begin file os_common.h ***************************************/
/*
** 2004 May 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
******************************************************************************
**
** This file contains macros and a little bit of code that is common to
** all of the platform-specific files (os_*.c) and is #included into those
** files.
**
** This file should be #included by the os_*.c files only.  It is not a
** general purpose header file.
*/
#ifndef _OS_COMMON_H_
#define _OS_COMMON_H_

/*
** At least two bugs have slipped in because we changed the MEMORY_DEBUG
** macro to SQLITE_DEBUG and some older makefiles have not yet made the
** switch.  The following code should catch this problem at compile-time.
*/
#ifdef MEMORY_DEBUG
# error "The MEMORY_DEBUG macro is obsolete.  Use SQLITE_DEBUG instead."
#endif

/*
** Macros for performance tracing.  Normally turned off.  Only works
** on i486 hardware.
*/
#ifdef SQLITE_PERFORMANCE_TRACE

/* 
** hwtime.h contains inline assembler code for implementing 
** high-performance timing routines.
*/
/* #include "hwtime.h" */

static sqlite_uint64 g_start;
static sqlite_uint64 g_elapsed;
#define TIMER_START       g_start=sqlite3Hwtime()
#define TIMER_END         g_elapsed=sqlite3Hwtime()-g_start
#define TIMER_ELAPSED     g_elapsed
#else
#define TIMER_START
#define TIMER_END
#define TIMER_ELAPSED     ((sqlite_uint64)0)
#endif

/*
** If we compile with the SQLITE_TEST macro set, then the following block
** of code will give us the ability to simulate a disk I/O error.  This
** is used for testing the I/O recovery logic.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_io_error_hit = 0;            /* Total number of I/O Errors */
SQLITE_PRIVATE int sqlite3_io_error_hardhit = 0;        /* Number of non-benign errors */
SQLITE_PRIVATE int sqlite3_io_error_pending = 0;        /* Count down to first I/O error */
SQLITE_PRIVATE int sqlite3_io_error_persist = 0;        /* True if I/O errors persist */
SQLITE_PRIVATE int sqlite3_io_error_benign = 0;         /* True if errors are benign */
SQLITE_PRIVATE int sqlite3_diskfull_pending = 0;
SQLITE_PRIVATE int sqlite3_diskfull = 0;
#define SimulateIOErrorBenign(X) sqlite3_io_error_benign=(X)
#define SimulateIOError(CODE)  \
  if( (sqlite3_io_error_persist && sqlite3_io_error_hit) \
       || sqlite3_io_error_pending-- == 1 )  \
              { local_ioerr(); CODE; }
static void local_ioerr(){
  IOTRACE(("IOERR\n"));
  sqlite3_io_error_hit++;
  if( !sqlite3_io_error_benign ) sqlite3_io_error_hardhit++;
}
#define SimulateDiskfullError(CODE) \
   if( sqlite3_diskfull_pending ){ \
     if( sqlite3_diskfull_pending == 1 ){ \
       local_ioerr(); \
       sqlite3_diskfull = 1; \
       sqlite3_io_error_hit = 1; \
       CODE; \
     }else{ \
       sqlite3_diskfull_pending--; \
     } \
   }
#else
#define SimulateIOErrorBenign(X)
#define SimulateIOError(A)
#define SimulateDiskfullError(A)
#endif

/*
** When testing, keep a count of the number of open files.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_open_file_count = 0;
#define OpenCounter(X)  sqlite3_open_file_count+=(X)
#else
#define OpenCounter(X)
#endif

#endif /* !defined(_OS_COMMON_H_) */

/************** End of os_common.h *******************************************/
/************** Continuing where we left off in os_win.c *********************/

/*
** Include the header file for the Windows VFS.
*/
/* #include "os_win.h" */

/*
** Compiling and using WAL mode requires several APIs that are only
** available in Windows platforms based on the NT kernel.
*/
#if !SQLITE_OS_WINNT && !defined(SQLITE_OMIT_WAL)
#  error "WAL mode requires support from the Windows NT kernel, compile\
 with SQLITE_OMIT_WAL."
#endif

#if !SQLITE_OS_WINNT && SQLITE_MAX_MMAP_SIZE>0
#  error "Memory mapped files require support from the Windows NT kernel,\
 compile with SQLITE_MAX_MMAP_SIZE=0."
#endif

/*
** Are most of the Win32 ANSI APIs available (i.e. with certain exceptions
** based on the sub-platform)?
*/
#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && !defined(SQLITE_WIN32_NO_ANSI)
#  define SQLITE_WIN32_HAS_ANSI
#endif

/*
** Are most of the Win32 Unicode APIs available (i.e. with certain exceptions
** based on the sub-platform)?
*/
#if (SQLITE_OS_WINCE || SQLITE_OS_WINNT || SQLITE_OS_WINRT) && \
    !defined(SQLITE_WIN32_NO_WIDE)
#  define SQLITE_WIN32_HAS_WIDE
#endif

/*
** Make sure at least one set of Win32 APIs is available.
*/
#if !defined(SQLITE_WIN32_HAS_ANSI) && !defined(SQLITE_WIN32_HAS_WIDE)
#  error "At least one of SQLITE_WIN32_HAS_ANSI and SQLITE_WIN32_HAS_WIDE\
 must be defined."
#endif

/*
** Define the required Windows SDK version constants if they are not
** already available.
*/
#ifndef NTDDI_WIN8
#  define NTDDI_WIN8                        0x06020000
#endif

#ifndef NTDDI_WINBLUE
#  define NTDDI_WINBLUE                     0x06030000
#endif

/*
** Check to see if the GetVersionEx[AW] functions are deprecated on the
** target system.  GetVersionEx was first deprecated in Win8.1.
*/
#ifndef SQLITE_WIN32_GETVERSIONEX
#  if defined(NTDDI_VERSION) && NTDDI_VERSION >= NTDDI_WINBLUE
#    define SQLITE_WIN32_GETVERSIONEX   0   /* GetVersionEx() is deprecated */
#  else
#    define SQLITE_WIN32_GETVERSIONEX   1   /* GetVersionEx() is current */
#  endif
#endif

/*
** This constant should already be defined (in the "WinDef.h" SDK file).
*/
#ifndef MAX_PATH
#  define MAX_PATH                      (260)
#endif

/*
** Maximum pathname length (in chars) for Win32.  This should normally be
** MAX_PATH.
*/
#ifndef SQLITE_WIN32_MAX_PATH_CHARS
#  define SQLITE_WIN32_MAX_PATH_CHARS   (MAX_PATH)
#endif

/*
** This constant should already be defined (in the "WinNT.h" SDK file).
*/
#ifndef UNICODE_STRING_MAX_CHARS
#  define UNICODE_STRING_MAX_CHARS      (32767)
#endif

/*
** Maximum pathname length (in chars) for WinNT.  This should normally be
** UNICODE_STRING_MAX_CHARS.
*/
#ifndef SQLITE_WINNT_MAX_PATH_CHARS
#  define SQLITE_WINNT_MAX_PATH_CHARS   (UNICODE_STRING_MAX_CHARS)
#endif

/*
** Maximum pathname length (in bytes) for Win32.  The MAX_PATH macro is in
** characters, so we allocate 4 bytes per character assuming worst-case of
** 4-bytes-per-character for UTF8.
*/
#ifndef SQLITE_WIN32_MAX_PATH_BYTES
#  define SQLITE_WIN32_MAX_PATH_BYTES   (SQLITE_WIN32_MAX_PATH_CHARS*4)
#endif

/*
** Maximum pathname length (in bytes) for WinNT.  This should normally be
** UNICODE_STRING_MAX_CHARS * sizeof(WCHAR).
*/
#ifndef SQLITE_WINNT_MAX_PATH_BYTES
#  define SQLITE_WINNT_MAX_PATH_BYTES   \
                            (sizeof(WCHAR) * SQLITE_WINNT_MAX_PATH_CHARS)
#endif

/*
** Maximum error message length (in chars) for WinRT.
*/
#ifndef SQLITE_WIN32_MAX_ERRMSG_CHARS
#  define SQLITE_WIN32_MAX_ERRMSG_CHARS (1024)
#endif

/*
** Returns non-zero if the character should be treated as a directory
** separator.
*/
#ifndef winIsDirSep
#  define winIsDirSep(a)                (((a) == '/') || ((a) == '\\'))
#endif

/*
** This macro is used when a local variable is set to a value that is
** [sometimes] not used by the code (e.g. via conditional compilation).
*/
#ifndef UNUSED_VARIABLE_VALUE
#  define UNUSED_VARIABLE_VALUE(x)      (void)(x)
#endif

/*
** Returns the character that should be used as the directory separator.
*/
#ifndef winGetDirSep
#  define winGetDirSep()                '\\'
#endif

/*
** Do we need to manually define the Win32 file mapping APIs for use with WAL
** mode or memory mapped files (e.g. these APIs are available in the Windows
** CE SDK; however, they are not present in the header file)?
*/
#if SQLITE_WIN32_FILEMAPPING_API && \
        (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0)
/*
** Two of the file mapping APIs are different under WinRT.  Figure out which
** set we need.
*/
#if SQLITE_OS_WINRT
WINBASEAPI HANDLE WINAPI CreateFileMappingFromApp(HANDLE, \
        LPSECURITY_ATTRIBUTES, ULONG, ULONG64, LPCWSTR);

WINBASEAPI LPVOID WINAPI MapViewOfFileFromApp(HANDLE, ULONG, ULONG64, SIZE_T);
#else
#if defined(SQLITE_WIN32_HAS_ANSI)
WINBASEAPI HANDLE WINAPI CreateFileMappingA(HANDLE, LPSECURITY_ATTRIBUTES, \
        DWORD, DWORD, DWORD, LPCSTR);
#endif /* defined(SQLITE_WIN32_HAS_ANSI) */

#if defined(SQLITE_WIN32_HAS_WIDE)
WINBASEAPI HANDLE WINAPI CreateFileMappingW(HANDLE, LPSECURITY_ATTRIBUTES, \
        DWORD, DWORD, DWORD, LPCWSTR);
#endif /* defined(SQLITE_WIN32_HAS_WIDE) */

WINBASEAPI LPVOID WINAPI MapViewOfFile(HANDLE, DWORD, DWORD, DWORD, SIZE_T);
#endif /* SQLITE_OS_WINRT */

/*
** These file mapping APIs are common to both Win32 and WinRT.
*/

WINBASEAPI BOOL WINAPI FlushViewOfFile(LPCVOID, SIZE_T);
WINBASEAPI BOOL WINAPI UnmapViewOfFile(LPCVOID);
#endif /* SQLITE_WIN32_FILEMAPPING_API */

/*
** Some Microsoft compilers lack this definition.
*/
#ifndef INVALID_FILE_ATTRIBUTES
# define INVALID_FILE_ATTRIBUTES ((DWORD)-1)
#endif

#ifndef FILE_FLAG_MASK
# define FILE_FLAG_MASK          (0xFF3C0000)
#endif

#ifndef FILE_ATTRIBUTE_MASK
# define FILE_ATTRIBUTE_MASK     (0x0003FFF7)
#endif

#ifndef SQLITE_OMIT_WAL
/* Forward references to structures used for WAL */
typedef struct winShm winShm;           /* A connection to shared-memory */
typedef struct winShmNode winShmNode;   /* A region of shared-memory */
#endif

/*
** WinCE lacks native support for file locking so we have to fake it
** with some code of our own.
*/
#if SQLITE_OS_WINCE
typedef struct winceLock {
  int nReaders;       /* Number of reader locks obtained */
  BOOL bPending;      /* Indicates a pending lock has been obtained */
  BOOL bReserved;     /* Indicates a reserved lock has been obtained */
  BOOL bExclusive;    /* Indicates an exclusive lock has been obtained */
} winceLock;
#endif

/*
** The winFile structure is a subclass of sqlite3_file* specific to the win32
** portability layer.
*/
typedef struct winFile winFile;
struct winFile {
  const sqlite3_io_methods *pMethod; /*** Must be first ***/
  sqlite3_vfs *pVfs;      /* The VFS used to open this file */
  HANDLE h;               /* Handle for accessing the file */
  u8 locktype;            /* Type of lock currently held on this file */
  short sharedLockByte;   /* Randomly chosen byte used as a shared lock */
  u8 ctrlFlags;           /* Flags.  See WINFILE_* below */
  DWORD lastErrno;        /* The Windows errno from the last I/O error */
#ifndef SQLITE_OMIT_WAL
  winShm *pShm;           /* Instance of shared memory on this file */
#endif
  const char *zPath;      /* Full pathname of this file */
  int szChunk;            /* Chunk size configured by FCNTL_CHUNK_SIZE */
#if SQLITE_OS_WINCE
  LPWSTR zDeleteOnClose;  /* Name of file to delete when closing */
  HANDLE hMutex;          /* Mutex used to control access to shared lock */
  HANDLE hShared;         /* Shared memory segment used for locking */
  winceLock local;        /* Locks obtained by this instance of winFile */
  winceLock *shared;      /* Global shared lock memory for the file  */
#endif
#if SQLITE_MAX_MMAP_SIZE>0
  int nFetchOut;                /* Number of outstanding xFetch references */
  HANDLE hMap;                  /* Handle for accessing memory mapping */
  void *pMapRegion;             /* Area memory mapped */
  sqlite3_int64 mmapSize;       /* Usable size of mapped region */
  sqlite3_int64 mmapSizeActual; /* Actual size of mapped region */
  sqlite3_int64 mmapSizeMax;    /* Configured FCNTL_MMAP_SIZE value */
#endif
};

/*
** Allowed values for winFile.ctrlFlags
*/
#define WINFILE_RDONLY          0x02   /* Connection is read only */
#define WINFILE_PERSIST_WAL     0x04   /* Persistent WAL mode */
#define WINFILE_PSOW            0x10   /* SQLITE_IOCAP_POWERSAFE_OVERWRITE */

/*
 * The size of the buffer used by sqlite3_win32_write_debug().
 */
#ifndef SQLITE_WIN32_DBG_BUF_SIZE
#  define SQLITE_WIN32_DBG_BUF_SIZE   ((int)(4096-sizeof(DWORD)))
#endif

/*
 * The value used with sqlite3_win32_set_directory() to specify that
 * the temporary directory should be changed.
 */
#ifndef SQLITE_WIN32_TEMP_DIRECTORY_TYPE
#  define SQLITE_WIN32_TEMP_DIRECTORY_TYPE (2)
#endif

/*
 * If compiled with SQLITE_WIN32_MALLOC on Windows, we will use the
 * various Win32 API heap functions instead of our own.
 */
#ifdef SQLITE_WIN32_MALLOC

/*
 * If this is non-zero, an isolated heap will be created by the native Win32
 * allocator subsystem; otherwise, the default process heap will be used.  This
 * setting has no effect when compiling for WinRT.  By default, this is enabled
 * and an isolated heap will be created to store all allocated data.
 *
 ******************************************************************************
 * WARNING: It is important to note that when this setting is non-zero and the
 *          winMemShutdown function is called (e.g. by the sqlite3BtreeShutdown
 *          function), all data that was allocated using the isolated heap will
 *          be freed immediately and any attempt to access any of that freed
 *          data will almost certainly result in an immediate access violation.
 ******************************************************************************
 */
#ifndef SQLITE_WIN32_HEAP_CREATE
#  define SQLITE_WIN32_HEAP_CREATE    (TRUE)
#endif

/*
 * The initial size of the Win32-specific heap.  This value may be zero.
 */
#ifndef SQLITE_WIN32_HEAP_INIT_SIZE
#  define SQLITE_WIN32_HEAP_INIT_SIZE ((SQLITE_DEFAULT_CACHE_SIZE) * \
                                       (SQLITE_DEFAULT_PAGE_SIZE) + 4194304)
#endif

/*
 * The maximum size of the Win32-specific heap.  This value may be zero.
 */
#ifndef SQLITE_WIN32_HEAP_MAX_SIZE
#  define SQLITE_WIN32_HEAP_MAX_SIZE  (0)
#endif

/*
 * The extra flags to use in calls to the Win32 heap APIs.  This value may be
 * zero for the default behavior.
 */
#ifndef SQLITE_WIN32_HEAP_FLAGS
#  define SQLITE_WIN32_HEAP_FLAGS     (0)
#endif


/*
** The winMemData structure stores information required by the Win32-specific
** sqlite3_mem_methods implementation.
*/
typedef struct winMemData winMemData;
struct winMemData {
#ifndef NDEBUG
  u32 magic1;   /* Magic number to detect structure corruption. */
#endif
  HANDLE hHeap; /* The handle to our heap. */
  BOOL bOwned;  /* Do we own the heap (i.e. destroy it on shutdown)? */
#ifndef NDEBUG
  u32 magic2;   /* Magic number to detect structure corruption. */
#endif
};

#ifndef NDEBUG
#define WINMEM_MAGIC1     0x42b2830b
#define WINMEM_MAGIC2     0xbd4d7cf4
#endif

static struct winMemData win_mem_data = {
#ifndef NDEBUG
  WINMEM_MAGIC1,
#endif
  NULL, FALSE
#ifndef NDEBUG
  ,WINMEM_MAGIC2
#endif
};

#ifndef NDEBUG
#define winMemAssertMagic1() assert( win_mem_data.magic1==WINMEM_MAGIC1 )
#define winMemAssertMagic2() assert( win_mem_data.magic2==WINMEM_MAGIC2 )
#define winMemAssertMagic()  winMemAssertMagic1(); winMemAssertMagic2();
#else
#define winMemAssertMagic()
#endif

#define winMemGetDataPtr()  &win_mem_data
#define winMemGetHeap()     win_mem_data.hHeap
#define winMemGetOwned()    win_mem_data.bOwned

static void *winMemMalloc(int nBytes);
static void winMemFree(void *pPrior);
static void *winMemRealloc(void *pPrior, int nBytes);
static int winMemSize(void *p);
static int winMemRoundup(int n);
static int winMemInit(void *pAppData);
static void winMemShutdown(void *pAppData);

SQLITE_PRIVATE const sqlite3_mem_methods *sqlite3MemGetWin32(void);
#endif /* SQLITE_WIN32_MALLOC */

/*
** The following variable is (normally) set once and never changes
** thereafter.  It records whether the operating system is Win9x
** or WinNT.
**
** 0:   Operating system unknown.
** 1:   Operating system is Win9x.
** 2:   Operating system is WinNT.
**
** In order to facilitate testing on a WinNT system, the test fixture
** can manually set this value to 1 to emulate Win98 behavior.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE LONG SQLITE_WIN32_VOLATILE sqlite3_os_type = 0;
#else
static LONG SQLITE_WIN32_VOLATILE sqlite3_os_type = 0;
#endif

#ifndef SYSCALL
#  define SYSCALL sqlite3_syscall_ptr
#endif

/*
** This function is not available on Windows CE or WinRT.
 */

#if SQLITE_OS_WINCE || SQLITE_OS_WINRT
#  define osAreFileApisANSI()       1
#endif

/*
** Many system calls are accessed through pointer-to-functions so that
** they may be overridden at runtime to facilitate fault injection during
** testing and sandboxing.  The following array holds the names and pointers
** to all overrideable system calls.
*/
static struct win_syscall {
  const char *zName;            /* Name of the system call */
  sqlite3_syscall_ptr pCurrent; /* Current value of the system call */
  sqlite3_syscall_ptr pDefault; /* Default value */
} aSyscall[] = {
#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT
  { "AreFileApisANSI",         (SYSCALL)AreFileApisANSI,         0 },
#else
  { "AreFileApisANSI",         (SYSCALL)0,                       0 },
#endif

#ifndef osAreFileApisANSI
#define osAreFileApisANSI ((BOOL(WINAPI*)(VOID))aSyscall[0].pCurrent)
#endif

#if SQLITE_OS_WINCE && defined(SQLITE_WIN32_HAS_WIDE)
  { "CharLowerW",              (SYSCALL)CharLowerW,              0 },
#else
  { "CharLowerW",              (SYSCALL)0,                       0 },
#endif

#define osCharLowerW ((LPWSTR(WINAPI*)(LPWSTR))aSyscall[1].pCurrent)

#if SQLITE_OS_WINCE && defined(SQLITE_WIN32_HAS_WIDE)
  { "CharUpperW",              (SYSCALL)CharUpperW,              0 },
#else
  { "CharUpperW",              (SYSCALL)0,                       0 },
#endif

#define osCharUpperW ((LPWSTR(WINAPI*)(LPWSTR))aSyscall[2].pCurrent)

  { "CloseHandle",             (SYSCALL)CloseHandle,             0 },

#define osCloseHandle ((BOOL(WINAPI*)(HANDLE))aSyscall[3].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "CreateFileA",             (SYSCALL)CreateFileA,             0 },
#else
  { "CreateFileA",             (SYSCALL)0,                       0 },
#endif

#define osCreateFileA ((HANDLE(WINAPI*)(LPCSTR,DWORD,DWORD, \
        LPSECURITY_ATTRIBUTES,DWORD,DWORD,HANDLE))aSyscall[4].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "CreateFileW",             (SYSCALL)CreateFileW,             0 },
#else
  { "CreateFileW",             (SYSCALL)0,                       0 },
#endif

#define osCreateFileW ((HANDLE(WINAPI*)(LPCWSTR,DWORD,DWORD, \
        LPSECURITY_ATTRIBUTES,DWORD,DWORD,HANDLE))aSyscall[5].pCurrent)

#if (!SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_ANSI) && \
        (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0))
  { "CreateFileMappingA",      (SYSCALL)CreateFileMappingA,      0 },
#else
  { "CreateFileMappingA",      (SYSCALL)0,                       0 },
#endif

#define osCreateFileMappingA ((HANDLE(WINAPI*)(HANDLE,LPSECURITY_ATTRIBUTES, \
        DWORD,DWORD,DWORD,LPCSTR))aSyscall[6].pCurrent)

#if SQLITE_OS_WINCE || (!SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE) && \
        (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0))
  { "CreateFileMappingW",      (SYSCALL)CreateFileMappingW,      0 },
#else
  { "CreateFileMappingW",      (SYSCALL)0,                       0 },
#endif

#define osCreateFileMappingW ((HANDLE(WINAPI*)(HANDLE,LPSECURITY_ATTRIBUTES, \
        DWORD,DWORD,DWORD,LPCWSTR))aSyscall[7].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "CreateMutexW",            (SYSCALL)CreateMutexW,            0 },
#else
  { "CreateMutexW",            (SYSCALL)0,                       0 },
#endif

#define osCreateMutexW ((HANDLE(WINAPI*)(LPSECURITY_ATTRIBUTES,BOOL, \
        LPCWSTR))aSyscall[8].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "DeleteFileA",             (SYSCALL)DeleteFileA,             0 },
#else
  { "DeleteFileA",             (SYSCALL)0,                       0 },
#endif

#define osDeleteFileA ((BOOL(WINAPI*)(LPCSTR))aSyscall[9].pCurrent)

#if defined(SQLITE_WIN32_HAS_WIDE)
  { "DeleteFileW",             (SYSCALL)DeleteFileW,             0 },
#else
  { "DeleteFileW",             (SYSCALL)0,                       0 },
#endif

#define osDeleteFileW ((BOOL(WINAPI*)(LPCWSTR))aSyscall[10].pCurrent)

#if SQLITE_OS_WINCE
  { "FileTimeToLocalFileTime", (SYSCALL)FileTimeToLocalFileTime, 0 },
#else
  { "FileTimeToLocalFileTime", (SYSCALL)0,                       0 },
#endif

#define osFileTimeToLocalFileTime ((BOOL(WINAPI*)(CONST FILETIME*, \
        LPFILETIME))aSyscall[11].pCurrent)

#if SQLITE_OS_WINCE
  { "FileTimeToSystemTime",    (SYSCALL)FileTimeToSystemTime,    0 },
#else
  { "FileTimeToSystemTime",    (SYSCALL)0,                       0 },
#endif

#define osFileTimeToSystemTime ((BOOL(WINAPI*)(CONST FILETIME*, \
        LPSYSTEMTIME))aSyscall[12].pCurrent)

  { "FlushFileBuffers",        (SYSCALL)FlushFileBuffers,        0 },

#define osFlushFileBuffers ((BOOL(WINAPI*)(HANDLE))aSyscall[13].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "FormatMessageA",          (SYSCALL)FormatMessageA,          0 },
#else
  { "FormatMessageA",          (SYSCALL)0,                       0 },
#endif

#define osFormatMessageA ((DWORD(WINAPI*)(DWORD,LPCVOID,DWORD,DWORD,LPSTR, \
        DWORD,va_list*))aSyscall[14].pCurrent)

#if defined(SQLITE_WIN32_HAS_WIDE)
  { "FormatMessageW",          (SYSCALL)FormatMessageW,          0 },
#else
  { "FormatMessageW",          (SYSCALL)0,                       0 },
#endif

#define osFormatMessageW ((DWORD(WINAPI*)(DWORD,LPCVOID,DWORD,DWORD,LPWSTR, \
        DWORD,va_list*))aSyscall[15].pCurrent)

  { "FreeLibrary",             (SYSCALL)0,                       0 },

#define osFreeLibrary ((BOOL(WINAPI*)(HMODULE))aSyscall[16].pCurrent)

  { "GetCurrentProcessId",     (SYSCALL)GetCurrentProcessId,     0 },

#define osGetCurrentProcessId ((DWORD(WINAPI*)(VOID))aSyscall[17].pCurrent)

#if !SQLITE_OS_WINCE && defined(SQLITE_WIN32_HAS_ANSI)
  { "GetDiskFreeSpaceA",       (SYSCALL)GetDiskFreeSpaceA,       0 },
#else
  { "GetDiskFreeSpaceA",       (SYSCALL)0,                       0 },
#endif

#define osGetDiskFreeSpaceA ((BOOL(WINAPI*)(LPCSTR,LPDWORD,LPDWORD,LPDWORD, \
        LPDWORD))aSyscall[18].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "GetDiskFreeSpaceW",       (SYSCALL)GetDiskFreeSpaceW,       0 },
#else
  { "GetDiskFreeSpaceW",       (SYSCALL)0,                       0 },
#endif

#define osGetDiskFreeSpaceW ((BOOL(WINAPI*)(LPCWSTR,LPDWORD,LPDWORD,LPDWORD, \
        LPDWORD))aSyscall[19].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "GetFileAttributesA",      (SYSCALL)GetFileAttributesA,      0 },
#else
  { "GetFileAttributesA",      (SYSCALL)0,                       0 },
#endif

#define osGetFileAttributesA ((DWORD(WINAPI*)(LPCSTR))aSyscall[20].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "GetFileAttributesW",      (SYSCALL)GetFileAttributesW,      0 },
#else
  { "GetFileAttributesW",      (SYSCALL)0,                       0 },
#endif

#define osGetFileAttributesW ((DWORD(WINAPI*)(LPCWSTR))aSyscall[21].pCurrent)

#if defined(SQLITE_WIN32_HAS_WIDE)
  { "GetFileAttributesExW",    (SYSCALL)GetFileAttributesExW,    0 },
#else
  { "GetFileAttributesExW",    (SYSCALL)0,                       0 },
#endif

#define osGetFileAttributesExW ((BOOL(WINAPI*)(LPCWSTR,GET_FILEEX_INFO_LEVELS, \
        LPVOID))aSyscall[22].pCurrent)

#if !SQLITE_OS_WINRT
  { "GetFileSize",             (SYSCALL)GetFileSize,             0 },
#else
  { "GetFileSize",             (SYSCALL)0,                       0 },
#endif

#define osGetFileSize ((DWORD(WINAPI*)(HANDLE,LPDWORD))aSyscall[23].pCurrent)

#if !SQLITE_OS_WINCE && defined(SQLITE_WIN32_HAS_ANSI)
  { "GetFullPathNameA",        (SYSCALL)GetFullPathNameA,        0 },
#else
  { "GetFullPathNameA",        (SYSCALL)0,                       0 },
#endif

#define osGetFullPathNameA ((DWORD(WINAPI*)(LPCSTR,DWORD,LPSTR, \
        LPSTR*))aSyscall[24].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "GetFullPathNameW",        (SYSCALL)GetFullPathNameW,        0 },
#else
  { "GetFullPathNameW",        (SYSCALL)0,                       0 },
#endif

#define osGetFullPathNameW ((DWORD(WINAPI*)(LPCWSTR,DWORD,LPWSTR, \
        LPWSTR*))aSyscall[25].pCurrent)

  { "GetLastError",            (SYSCALL)GetLastError,            0 },

#define osGetLastError ((DWORD(WINAPI*)(VOID))aSyscall[26].pCurrent)

  { "GetProcAddressA",         (SYSCALL)0,                       0 },

#define osGetProcAddressA ((FARPROC(WINAPI*)(HMODULE, \
        LPCSTR))aSyscall[27].pCurrent)

#if !SQLITE_OS_WINRT
  { "GetSystemInfo",           (SYSCALL)GetSystemInfo,           0 },
#else
  { "GetSystemInfo",           (SYSCALL)0,                       0 },
#endif

#define osGetSystemInfo ((VOID(WINAPI*)(LPSYSTEM_INFO))aSyscall[28].pCurrent)

  { "GetSystemTime",           (SYSCALL)GetSystemTime,           0 },

#define osGetSystemTime ((VOID(WINAPI*)(LPSYSTEMTIME))aSyscall[29].pCurrent)

#if !SQLITE_OS_WINCE
  { "GetSystemTimeAsFileTime", (SYSCALL)GetSystemTimeAsFileTime, 0 },
#else
  { "GetSystemTimeAsFileTime", (SYSCALL)0,                       0 },
#endif

#define osGetSystemTimeAsFileTime ((VOID(WINAPI*)( \
        LPFILETIME))aSyscall[30].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "GetTempPathA",            (SYSCALL)GetTempPathA,            0 },
#else
  { "GetTempPathA",            (SYSCALL)0,                       0 },
#endif

#define osGetTempPathA ((DWORD(WINAPI*)(DWORD,LPSTR))aSyscall[31].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "GetTempPathW",            (SYSCALL)GetTempPathW,            0 },
#else
  { "GetTempPathW",            (SYSCALL)0,                       0 },
#endif

#define osGetTempPathW ((DWORD(WINAPI*)(DWORD,LPWSTR))aSyscall[32].pCurrent)

#if !SQLITE_OS_WINRT
  { "GetTickCount",            (SYSCALL)GetTickCount,            0 },
#else
  { "GetTickCount",            (SYSCALL)0,                       0 },
#endif

#define osGetTickCount ((DWORD(WINAPI*)(VOID))aSyscall[33].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI) && defined(SQLITE_WIN32_GETVERSIONEX) && \
        SQLITE_WIN32_GETVERSIONEX
  { "GetVersionExA",           (SYSCALL)GetVersionExA,           0 },
#else
  { "GetVersionExA",           (SYSCALL)0,                       0 },
#endif

#define osGetVersionExA ((BOOL(WINAPI*)( \
        LPOSVERSIONINFOA))aSyscall[34].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE) && \
        defined(SQLITE_WIN32_GETVERSIONEX) && SQLITE_WIN32_GETVERSIONEX
  { "GetVersionExW",           (SYSCALL)GetVersionExW,           0 },
#else
  { "GetVersionExW",           (SYSCALL)0,                       0 },
#endif

#define osGetVersionExW ((BOOL(WINAPI*)( \
        LPOSVERSIONINFOW))aSyscall[35].pCurrent)

  { "HeapAlloc",               (SYSCALL)HeapAlloc,               0 },

#define osHeapAlloc ((LPVOID(WINAPI*)(HANDLE,DWORD, \
        SIZE_T))aSyscall[36].pCurrent)

#if !SQLITE_OS_WINRT
  { "HeapCreate",              (SYSCALL)HeapCreate,              0 },
#else
  { "HeapCreate",              (SYSCALL)0,                       0 },
#endif

#define osHeapCreate ((HANDLE(WINAPI*)(DWORD,SIZE_T, \
        SIZE_T))aSyscall[37].pCurrent)

#if !SQLITE_OS_WINRT
  { "HeapDestroy",             (SYSCALL)HeapDestroy,             0 },
#else
  { "HeapDestroy",             (SYSCALL)0,                       0 },
#endif

#define osHeapDestroy ((BOOL(WINAPI*)(HANDLE))aSyscall[38].pCurrent)

  { "HeapFree",                (SYSCALL)HeapFree,                0 },

#define osHeapFree ((BOOL(WINAPI*)(HANDLE,DWORD,LPVOID))aSyscall[39].pCurrent)

  { "HeapReAlloc",             (SYSCALL)HeapReAlloc,             0 },

#define osHeapReAlloc ((LPVOID(WINAPI*)(HANDLE,DWORD,LPVOID, \
        SIZE_T))aSyscall[40].pCurrent)

  { "HeapSize",                (SYSCALL)HeapSize,                0 },

#define osHeapSize ((SIZE_T(WINAPI*)(HANDLE,DWORD, \
        LPCVOID))aSyscall[41].pCurrent)

#if !SQLITE_OS_WINRT
  { "HeapValidate",            (SYSCALL)HeapValidate,            0 },
#else
  { "HeapValidate",            (SYSCALL)0,                       0 },
#endif

#define osHeapValidate ((BOOL(WINAPI*)(HANDLE,DWORD, \
        LPCVOID))aSyscall[42].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT
  { "HeapCompact",             (SYSCALL)HeapCompact,             0 },
#else
  { "HeapCompact",             (SYSCALL)0,                       0 },
#endif

#define osHeapCompact ((UINT(WINAPI*)(HANDLE,DWORD))aSyscall[43].pCurrent)

  { "LoadLibraryA",            (SYSCALL)0,                       0 },

#define osLoadLibraryA ((HMODULE(WINAPI*)(LPCSTR))aSyscall[44].pCurrent)

#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_HAS_WIDE)
  { "LoadLibraryW",            (SYSCALL)LoadLibraryW,            0 },
#else
  { "LoadLibraryW",            (SYSCALL)0,                       0 },
#endif

#define osLoadLibraryW ((HMODULE(WINAPI*)(LPCWSTR))aSyscall[45].pCurrent)

#if !SQLITE_OS_WINRT
  { "LocalFree",               (SYSCALL)LocalFree,               0 },
#else
  { "LocalFree",               (SYSCALL)0,                       0 },
#endif

#define osLocalFree ((HLOCAL(WINAPI*)(HLOCAL))aSyscall[46].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT
  { "LockFile",                (SYSCALL)LockFile,                0 },
#else
  { "LockFile",                (SYSCALL)0,                       0 },
#endif

#ifndef osLockFile
#define osLockFile ((BOOL(WINAPI*)(HANDLE,DWORD,DWORD,DWORD, \
        DWORD))aSyscall[47].pCurrent)
#endif

#if !SQLITE_OS_WINCE
  { "LockFileEx",              (SYSCALL)LockFileEx,              0 },
#else
  { "LockFileEx",              (SYSCALL)0,                       0 },
#endif

#ifndef osLockFileEx
#define osLockFileEx ((BOOL(WINAPI*)(HANDLE,DWORD,DWORD,DWORD,DWORD, \
        LPOVERLAPPED))aSyscall[48].pCurrent)
#endif

#if SQLITE_OS_WINCE || (!SQLITE_OS_WINRT && \
        (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0))
  { "MapViewOfFile",           (SYSCALL)MapViewOfFile,           0 },
#else
  { "MapViewOfFile",           (SYSCALL)0,                       0 },
#endif

#define osMapViewOfFile ((LPVOID(WINAPI*)(HANDLE,DWORD,DWORD,DWORD, \
        SIZE_T))aSyscall[49].pCurrent)

  { "MultiByteToWideChar",     (SYSCALL)MultiByteToWideChar,     0 },

#define osMultiByteToWideChar ((int(WINAPI*)(UINT,DWORD,LPCSTR,int,LPWSTR, \
        int))aSyscall[50].pCurrent)

  { "QueryPerformanceCounter", (SYSCALL)QueryPerformanceCounter, 0 },

#define osQueryPerformanceCounter ((BOOL(WINAPI*)( \
        LARGE_INTEGER*))aSyscall[51].pCurrent)

  { "ReadFile",                (SYSCALL)ReadFile,                0 },

#define osReadFile ((BOOL(WINAPI*)(HANDLE,LPVOID,DWORD,LPDWORD, \
        LPOVERLAPPED))aSyscall[52].pCurrent)

  { "SetEndOfFile",            (SYSCALL)SetEndOfFile,            0 },

#define osSetEndOfFile ((BOOL(WINAPI*)(HANDLE))aSyscall[53].pCurrent)

#if !SQLITE_OS_WINRT
  { "SetFilePointer",          (SYSCALL)SetFilePointer,          0 },
#else
  { "SetFilePointer",          (SYSCALL)0,                       0 },
#endif

#define osSetFilePointer ((DWORD(WINAPI*)(HANDLE,LONG,PLONG, \
        DWORD))aSyscall[54].pCurrent)

#if !SQLITE_OS_WINRT
  { "Sleep",                   (SYSCALL)Sleep,                   0 },
#else
  { "Sleep",                   (SYSCALL)0,                       0 },
#endif

#define osSleep ((VOID(WINAPI*)(DWORD))aSyscall[55].pCurrent)

  { "SystemTimeToFileTime",    (SYSCALL)SystemTimeToFileTime,    0 },

#define osSystemTimeToFileTime ((BOOL(WINAPI*)(CONST SYSTEMTIME*, \
        LPFILETIME))aSyscall[56].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT
  { "UnlockFile",              (SYSCALL)UnlockFile,              0 },
#else
  { "UnlockFile",              (SYSCALL)0,                       0 },
#endif

#ifndef osUnlockFile
#define osUnlockFile ((BOOL(WINAPI*)(HANDLE,DWORD,DWORD,DWORD, \
        DWORD))aSyscall[57].pCurrent)
#endif

#if !SQLITE_OS_WINCE
  { "UnlockFileEx",            (SYSCALL)UnlockFileEx,            0 },
#else
  { "UnlockFileEx",            (SYSCALL)0,                       0 },
#endif

#define osUnlockFileEx ((BOOL(WINAPI*)(HANDLE,DWORD,DWORD,DWORD, \
        LPOVERLAPPED))aSyscall[58].pCurrent)

#if SQLITE_OS_WINCE || !defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0
  { "UnmapViewOfFile",         (SYSCALL)UnmapViewOfFile,         0 },
#else
  { "UnmapViewOfFile",         (SYSCALL)0,                       0 },
#endif

#define osUnmapViewOfFile ((BOOL(WINAPI*)(LPCVOID))aSyscall[59].pCurrent)

  { "WideCharToMultiByte",     (SYSCALL)WideCharToMultiByte,     0 },

#define osWideCharToMultiByte ((int(WINAPI*)(UINT,DWORD,LPCWSTR,int,LPSTR,int, \
        LPCSTR,LPBOOL))aSyscall[60].pCurrent)

  { "WriteFile",               (SYSCALL)WriteFile,               0 },

#define osWriteFile ((BOOL(WINAPI*)(HANDLE,LPCVOID,DWORD,LPDWORD, \
        LPOVERLAPPED))aSyscall[61].pCurrent)

#if SQLITE_OS_WINRT
  { "CreateEventExW",          (SYSCALL)CreateEventExW,          0 },
#else
  { "CreateEventExW",          (SYSCALL)0,                       0 },
#endif

#define osCreateEventExW ((HANDLE(WINAPI*)(LPSECURITY_ATTRIBUTES,LPCWSTR, \
        DWORD,DWORD))aSyscall[62].pCurrent)

#if !SQLITE_OS_WINRT
  { "WaitForSingleObject",     (SYSCALL)WaitForSingleObject,     0 },
#else
  { "WaitForSingleObject",     (SYSCALL)0,                       0 },
#endif

#define osWaitForSingleObject ((DWORD(WINAPI*)(HANDLE, \
        DWORD))aSyscall[63].pCurrent)

#if !SQLITE_OS_WINCE
  { "WaitForSingleObjectEx",   (SYSCALL)WaitForSingleObjectEx,   0 },
#else
  { "WaitForSingleObjectEx",   (SYSCALL)0,                       0 },
#endif

#define osWaitForSingleObjectEx ((DWORD(WINAPI*)(HANDLE,DWORD, \
        BOOL))aSyscall[64].pCurrent)

#if SQLITE_OS_WINRT
  { "SetFilePointerEx",        (SYSCALL)SetFilePointerEx,        0 },
#else
  { "SetFilePointerEx",        (SYSCALL)0,                       0 },
#endif

#define osSetFilePointerEx ((BOOL(WINAPI*)(HANDLE,LARGE_INTEGER, \
        PLARGE_INTEGER,DWORD))aSyscall[65].pCurrent)

#if SQLITE_OS_WINRT
  { "GetFileInformationByHandleEx", (SYSCALL)GetFileInformationByHandleEx, 0 },
#else
  { "GetFileInformationByHandleEx", (SYSCALL)0,                  0 },
#endif

#define osGetFileInformationByHandleEx ((BOOL(WINAPI*)(HANDLE, \
        FILE_INFO_BY_HANDLE_CLASS,LPVOID,DWORD))aSyscall[66].pCurrent)

#if SQLITE_OS_WINRT && (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0)
  { "MapViewOfFileFromApp",    (SYSCALL)MapViewOfFileFromApp,    0 },
#else
  { "MapViewOfFileFromApp",    (SYSCALL)0,                       0 },
#endif

#define osMapViewOfFileFromApp ((LPVOID(WINAPI*)(HANDLE,ULONG,ULONG64, \
        SIZE_T))aSyscall[67].pCurrent)

#if SQLITE_OS_WINRT
  { "CreateFile2",             (SYSCALL)CreateFile2,             0 },
#else
  { "CreateFile2",             (SYSCALL)0,                       0 },
#endif

#define osCreateFile2 ((HANDLE(WINAPI*)(LPCWSTR,DWORD,DWORD,DWORD, \
        LPCREATEFILE2_EXTENDED_PARAMETERS))aSyscall[68].pCurrent)

  { "LoadPackagedLibrary",     (SYSCALL)0,                       0 },

#define osLoadPackagedLibrary ((HMODULE(WINAPI*)(LPCWSTR, \
        DWORD))aSyscall[69].pCurrent)

#if SQLITE_OS_WINRT
  { "GetTickCount64",          (SYSCALL)GetTickCount64,          0 },
#else
  { "GetTickCount64",          (SYSCALL)0,                       0 },
#endif

#define osGetTickCount64 ((ULONGLONG(WINAPI*)(VOID))aSyscall[70].pCurrent)

#if SQLITE_OS_WINRT
  { "GetNativeSystemInfo",     (SYSCALL)GetNativeSystemInfo,     0 },
#else
  { "GetNativeSystemInfo",     (SYSCALL)0,                       0 },
#endif

#define osGetNativeSystemInfo ((VOID(WINAPI*)( \
        LPSYSTEM_INFO))aSyscall[71].pCurrent)

#if defined(SQLITE_WIN32_HAS_ANSI)
  { "OutputDebugStringA",      (SYSCALL)OutputDebugStringA,      0 },
#else
  { "OutputDebugStringA",      (SYSCALL)0,                       0 },
#endif

#define osOutputDebugStringA ((VOID(WINAPI*)(LPCSTR))aSyscall[72].pCurrent)

#if defined(SQLITE_WIN32_HAS_WIDE)
  { "OutputDebugStringW",      (SYSCALL)OutputDebugStringW,      0 },
#else
  { "OutputDebugStringW",      (SYSCALL)0,                       0 },
#endif

#define osOutputDebugStringW ((VOID(WINAPI*)(LPCWSTR))aSyscall[73].pCurrent)

  { "GetProcessHeap",          (SYSCALL)GetProcessHeap,          0 },

#define osGetProcessHeap ((HANDLE(WINAPI*)(VOID))aSyscall[74].pCurrent)

#if SQLITE_OS_WINRT && (!defined(SQLITE_OMIT_WAL) || SQLITE_MAX_MMAP_SIZE>0)
  { "CreateFileMappingFromApp", (SYSCALL)CreateFileMappingFromApp, 0 },
#else
  { "CreateFileMappingFromApp", (SYSCALL)0,                      0 },
#endif

#define osCreateFileMappingFromApp ((HANDLE(WINAPI*)(HANDLE, \
        LPSECURITY_ATTRIBUTES,ULONG,ULONG64,LPCWSTR))aSyscall[75].pCurrent)

/*
** NOTE: On some sub-platforms, the InterlockedCompareExchange "function"
**       is really just a macro that uses a compiler intrinsic (e.g. x64).
**       So do not try to make this is into a redefinable interface.
*/
#if defined(InterlockedCompareExchange)
  { "InterlockedCompareExchange", (SYSCALL)0,                    0 },

#define osInterlockedCompareExchange InterlockedCompareExchange
#else
  { "InterlockedCompareExchange", (SYSCALL)InterlockedCompareExchange, 0 },

#define osInterlockedCompareExchange ((LONG(WINAPI*)(LONG \
        SQLITE_WIN32_VOLATILE*, LONG,LONG))aSyscall[76].pCurrent)
#endif /* defined(InterlockedCompareExchange) */

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && SQLITE_WIN32_USE_UUID
  { "UuidCreate",               (SYSCALL)UuidCreate,             0 },
#else
  { "UuidCreate",               (SYSCALL)0,                      0 },
#endif

#define osUuidCreate ((RPC_STATUS(RPC_ENTRY*)(UUID*))aSyscall[77].pCurrent)

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && SQLITE_WIN32_USE_UUID
  { "UuidCreateSequential",     (SYSCALL)UuidCreateSequential,   0 },
#else
  { "UuidCreateSequential",     (SYSCALL)0,                      0 },
#endif

#define osUuidCreateSequential \
        ((RPC_STATUS(RPC_ENTRY*)(UUID*))aSyscall[78].pCurrent)

#if !defined(SQLITE_NO_SYNC) && SQLITE_MAX_MMAP_SIZE>0
  { "FlushViewOfFile",          (SYSCALL)FlushViewOfFile,        0 },
#else
  { "FlushViewOfFile",          (SYSCALL)0,                      0 },
#endif

#define osFlushViewOfFile \
        ((BOOL(WINAPI*)(LPCVOID,SIZE_T))aSyscall[79].pCurrent)

}; /* End of the overrideable system calls */

/*
** This is the xSetSystemCall() method of sqlite3_vfs for all of the
** "win32" VFSes.  Return SQLITE_OK opon successfully updating the
** system call pointer, or SQLITE_NOTFOUND if there is no configurable
** system call named zName.
*/
static int winSetSystemCall(
  sqlite3_vfs *pNotUsed,        /* The VFS pointer.  Not used */
  const char *zName,            /* Name of system call to override */
  sqlite3_syscall_ptr pNewFunc  /* Pointer to new system call value */
){
  unsigned int i;
  int rc = SQLITE_NOTFOUND;

  UNUSED_PARAMETER(pNotUsed);
  if( zName==0 ){
    /* If no zName is given, restore all system calls to their default
    ** settings and return NULL
    */
    rc = SQLITE_OK;
    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
      if( aSyscall[i].pDefault ){
        aSyscall[i].pCurrent = aSyscall[i].pDefault;
      }
    }
  }else{
    /* If zName is specified, operate on only the one system call
    ** specified.
    */
    for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
      if( strcmp(zName, aSyscall[i].zName)==0 ){
        if( aSyscall[i].pDefault==0 ){
          aSyscall[i].pDefault = aSyscall[i].pCurrent;
        }
        rc = SQLITE_OK;
        if( pNewFunc==0 ) pNewFunc = aSyscall[i].pDefault;
        aSyscall[i].pCurrent = pNewFunc;
        break;
      }
    }
  }
  return rc;
}

/*
** Return the value of a system call.  Return NULL if zName is not a
** recognized system call name.  NULL is also returned if the system call
** is currently undefined.
*/
static sqlite3_syscall_ptr winGetSystemCall(
  sqlite3_vfs *pNotUsed,
  const char *zName
){
  unsigned int i;

  UNUSED_PARAMETER(pNotUsed);
  for(i=0; i<sizeof(aSyscall)/sizeof(aSyscall[0]); i++){
    if( strcmp(zName, aSyscall[i].zName)==0 ) return aSyscall[i].pCurrent;
  }
  return 0;
}

/*
** Return the name of the first system call after zName.  If zName==NULL
** then return the name of the first system call.  Return NULL if zName
** is the last system call or if zName is not the name of a valid
** system call.
*/
static const char *winNextSystemCall(sqlite3_vfs *p, const char *zName){
  int i = -1;

  UNUSED_PARAMETER(p);
  if( zName ){
    for(i=0; i<ArraySize(aSyscall)-1; i++){
      if( strcmp(zName, aSyscall[i].zName)==0 ) break;
    }
  }
  for(i++; i<ArraySize(aSyscall); i++){
    if( aSyscall[i].pCurrent!=0 ) return aSyscall[i].zName;
  }
  return 0;
}

#ifdef SQLITE_WIN32_MALLOC
/*
** If a Win32 native heap has been configured, this function will attempt to
** compact it.  Upon success, SQLITE_OK will be returned.  Upon failure, one
** of SQLITE_NOMEM, SQLITE_ERROR, or SQLITE_NOTFOUND will be returned.  The
** "pnLargest" argument, if non-zero, will be used to return the size of the
** largest committed free block in the heap, in bytes.
*/
SQLITE_PRIVATE int sqlite3_win32_compact_heap(LPUINT pnLargest){
  int rc = SQLITE_OK;
  UINT nLargest = 0;
  HANDLE hHeap;

  winMemAssertMagic();
  hHeap = winMemGetHeap();
  assert( hHeap!=0 );
  assert( hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(hHeap, SQLITE_WIN32_HEAP_FLAGS, NULL) );
#endif
#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT
  if( (nLargest=osHeapCompact(hHeap, SQLITE_WIN32_HEAP_FLAGS))==0 ){
    DWORD lastErrno = osGetLastError();
    if( lastErrno==NO_ERROR ){
      sqlite3_log(SQLITE_NOMEM, "failed to HeapCompact (no space), heap=%p",
                  (void*)hHeap);
      rc = SQLITE_NOMEM;
    }else{
      sqlite3_log(SQLITE_ERROR, "failed to HeapCompact (%lu), heap=%p",
                  osGetLastError(), (void*)hHeap);
      rc = SQLITE_ERROR;
    }
  }
#else
  sqlite3_log(SQLITE_NOTFOUND, "failed to HeapCompact, heap=%p",
              (void*)hHeap);
  rc = SQLITE_NOTFOUND;
#endif
  if( pnLargest ) *pnLargest = nLargest;
  return rc;
}

/*
** If a Win32 native heap has been configured, this function will attempt to
** destroy and recreate it.  If the Win32 native heap is not isolated and/or
** the sqlite3_memory_used() function does not return zero, SQLITE_BUSY will
** be returned and no changes will be made to the Win32 native heap.
*/
SQLITE_PRIVATE int sqlite3_win32_reset_heap(){
  int rc;
  MUTEX_LOGIC( sqlite3_mutex *pMaster; ) /* The main static mutex */
  MUTEX_LOGIC( sqlite3_mutex *pMem; )    /* The memsys static mutex */
  MUTEX_LOGIC( pMaster = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MASTER); )
  MUTEX_LOGIC( pMem = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_MEM); )
  sqlite3_mutex_enter(pMaster);
  sqlite3_mutex_enter(pMem);
  winMemAssertMagic();
  if( winMemGetHeap()!=NULL && winMemGetOwned() && sqlite3_memory_used()==0 ){
    /*
    ** At this point, there should be no outstanding memory allocations on
    ** the heap.  Also, since both the master and memsys locks are currently
    ** being held by us, no other function (i.e. from another thread) should
    ** be able to even access the heap.  Attempt to destroy and recreate our
    ** isolated Win32 native heap now.
    */
    assert( winMemGetHeap()!=NULL );
    assert( winMemGetOwned() );
    assert( sqlite3_memory_used()==0 );
    winMemShutdown(winMemGetDataPtr());
    assert( winMemGetHeap()==NULL );
    assert( !winMemGetOwned() );
    assert( sqlite3_memory_used()==0 );
    rc = winMemInit(winMemGetDataPtr());
    assert( rc!=SQLITE_OK || winMemGetHeap()!=NULL );
    assert( rc!=SQLITE_OK || winMemGetOwned() );
    assert( rc!=SQLITE_OK || sqlite3_memory_used()==0 );
  }else{
    /*
    ** The Win32 native heap cannot be modified because it may be in use.
    */
    rc = SQLITE_BUSY;
  }
  sqlite3_mutex_leave(pMem);
  sqlite3_mutex_leave(pMaster);
  return rc;
}
#endif /* SQLITE_WIN32_MALLOC */

/*
** This function outputs the specified (ANSI) string to the Win32 debugger
** (if available).
*/

SQLITE_PRIVATE void sqlite3_win32_write_debug(const char *zBuf, int nBuf){
  char zDbgBuf[SQLITE_WIN32_DBG_BUF_SIZE];
  int nMin = MIN(nBuf, (SQLITE_WIN32_DBG_BUF_SIZE - 1)); /* may be negative. */
  if( nMin<-1 ) nMin = -1; /* all negative values become -1. */
  assert( nMin==-1 || nMin==0 || nMin<SQLITE_WIN32_DBG_BUF_SIZE );
#if defined(SQLITE_WIN32_HAS_ANSI)
  if( nMin>0 ){
    memset(zDbgBuf, 0, SQLITE_WIN32_DBG_BUF_SIZE);
    memcpy(zDbgBuf, zBuf, nMin);
    osOutputDebugStringA(zDbgBuf);
  }else{
    osOutputDebugStringA(zBuf);
  }
#elif defined(SQLITE_WIN32_HAS_WIDE)
  memset(zDbgBuf, 0, SQLITE_WIN32_DBG_BUF_SIZE);
  if ( osMultiByteToWideChar(
          osAreFileApisANSI() ? CP_ACP : CP_OEMCP, 0, zBuf,
          nMin, (LPWSTR)zDbgBuf, SQLITE_WIN32_DBG_BUF_SIZE/sizeof(WCHAR))<=0 ){
    return;
  }
  osOutputDebugStringW((LPCWSTR)zDbgBuf);
#else
  if( nMin>0 ){
    memset(zDbgBuf, 0, SQLITE_WIN32_DBG_BUF_SIZE);
    memcpy(zDbgBuf, zBuf, nMin);
    fprintf(stderr, "%s", zDbgBuf);
  }else{
    fprintf(stderr, "%s", zBuf);
  }
#endif
}

/*
** The following routine suspends the current thread for at least ms
** milliseconds.  This is equivalent to the Win32 Sleep() interface.
*/
#if SQLITE_OS_WINRT
static HANDLE sleepObj = NULL;
#endif

SQLITE_PRIVATE void sqlite3_win32_sleep(DWORD milliseconds){
#if SQLITE_OS_WINRT
  if ( sleepObj==NULL ){
    sleepObj = osCreateEventExW(NULL, NULL, CREATE_EVENT_MANUAL_RESET,
                                SYNCHRONIZE);
  }
  assert( sleepObj!=NULL );
  osWaitForSingleObjectEx(sleepObj, milliseconds, FALSE);
#else
  osSleep(milliseconds);
#endif
}

#if SQLITE_MAX_WORKER_THREADS>0 && !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && \
        SQLITE_THREADSAFE>0
SQLITE_PRIVATE DWORD sqlite3Win32Wait(HANDLE hObject){
  DWORD rc;
  while( (rc = osWaitForSingleObjectEx(hObject, INFINITE,
                                       TRUE))==WAIT_IO_COMPLETION ){}
  return rc;
}
#endif

/*
** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
** or WinCE.  Return false (zero) for Win95, Win98, or WinME.
**
** Here is an interesting observation:  Win95, Win98, and WinME lack
** the LockFileEx() API.  But we can still statically link against that
** API as long as we don't call it when running Win95/98/ME.  A call to
** this routine is used to determine if the host is Win95/98/ME or
** WinNT/2K/XP so that we will know whether or not we can safely call
** the LockFileEx() API.
*/

#if !defined(SQLITE_WIN32_GETVERSIONEX) || !SQLITE_WIN32_GETVERSIONEX
# define osIsNT()  (1)
#elif SQLITE_OS_WINCE || SQLITE_OS_WINRT || !defined(SQLITE_WIN32_HAS_ANSI)
# define osIsNT()  (1)
#elif !defined(SQLITE_WIN32_HAS_WIDE)
# define osIsNT()  (0)
#else
# define osIsNT()  ((sqlite3_os_type==2) || sqlite3_win32_is_nt())
#endif

/*
** This function determines if the machine is running a version of Windows
** based on the NT kernel.
*/
SQLITE_PRIVATE int sqlite3_win32_is_nt(void){
#if SQLITE_OS_WINRT
  /*
  ** NOTE: The WinRT sub-platform is always assumed to be based on the NT
  **       kernel.
  */
  return 1;
#elif defined(SQLITE_WIN32_GETVERSIONEX) && SQLITE_WIN32_GETVERSIONEX
  if( osInterlockedCompareExchange(&sqlite3_os_type, 0, 0)==0 ){
#if defined(SQLITE_WIN32_HAS_ANSI)
    OSVERSIONINFOA sInfo;
    sInfo.dwOSVersionInfoSize = sizeof(sInfo);
    osGetVersionExA(&sInfo);
    osInterlockedCompareExchange(&sqlite3_os_type,
        (sInfo.dwPlatformId == VER_PLATFORM_WIN32_NT) ? 2 : 1, 0);
#elif defined(SQLITE_WIN32_HAS_WIDE)
    OSVERSIONINFOW sInfo;
    sInfo.dwOSVersionInfoSize = sizeof(sInfo);
    osGetVersionExW(&sInfo);
    osInterlockedCompareExchange(&sqlite3_os_type,
        (sInfo.dwPlatformId == VER_PLATFORM_WIN32_NT) ? 2 : 1, 0);
#endif
  }
  return osInterlockedCompareExchange(&sqlite3_os_type, 2, 2)==2;
#elif SQLITE_TEST
  return osInterlockedCompareExchange(&sqlite3_os_type, 2, 2)==2;
#else
  /*
  ** NOTE: All sub-platforms where the GetVersionEx[AW] functions are
  **       deprecated are always assumed to be based on the NT kernel.
  */
  return 1;
#endif
}

#ifdef SQLITE_WIN32_MALLOC
/*
** Allocate nBytes of memory.
*/
static void *winMemMalloc(int nBytes){
  HANDLE hHeap;
  void *p;

  winMemAssertMagic();
  hHeap = winMemGetHeap();
  assert( hHeap!=0 );
  assert( hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(hHeap, SQLITE_WIN32_HEAP_FLAGS, NULL) );
#endif
  assert( nBytes>=0 );
  p = osHeapAlloc(hHeap, SQLITE_WIN32_HEAP_FLAGS, (SIZE_T)nBytes);
  if( !p ){
    sqlite3_log(SQLITE_NOMEM, "failed to HeapAlloc %u bytes (%lu), heap=%p",
                nBytes, osGetLastError(), (void*)hHeap);
  }
  return p;
}

/*
** Free memory.
*/
static void winMemFree(void *pPrior){
  HANDLE hHeap;

  winMemAssertMagic();
  hHeap = winMemGetHeap();
  assert( hHeap!=0 );
  assert( hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(hHeap, SQLITE_WIN32_HEAP_FLAGS, pPrior) );
#endif
  if( !pPrior ) return; /* Passing NULL to HeapFree is undefined. */
  if( !osHeapFree(hHeap, SQLITE_WIN32_HEAP_FLAGS, pPrior) ){
    sqlite3_log(SQLITE_NOMEM, "failed to HeapFree block %p (%lu), heap=%p",
                pPrior, osGetLastError(), (void*)hHeap);
  }
}

/*
** Change the size of an existing memory allocation
*/
static void *winMemRealloc(void *pPrior, int nBytes){
  HANDLE hHeap;
  void *p;

  winMemAssertMagic();
  hHeap = winMemGetHeap();
  assert( hHeap!=0 );
  assert( hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(hHeap, SQLITE_WIN32_HEAP_FLAGS, pPrior) );
#endif
  assert( nBytes>=0 );
  if( !pPrior ){
    p = osHeapAlloc(hHeap, SQLITE_WIN32_HEAP_FLAGS, (SIZE_T)nBytes);
  }else{
    p = osHeapReAlloc(hHeap, SQLITE_WIN32_HEAP_FLAGS, pPrior, (SIZE_T)nBytes);
  }
  if( !p ){
    sqlite3_log(SQLITE_NOMEM, "failed to %s %u bytes (%lu), heap=%p",
                pPrior ? "HeapReAlloc" : "HeapAlloc", nBytes, osGetLastError(),
                (void*)hHeap);
  }
  return p;
}

/*
** Return the size of an outstanding allocation, in bytes.
*/
static int winMemSize(void *p){
  HANDLE hHeap;
  SIZE_T n;

  winMemAssertMagic();
  hHeap = winMemGetHeap();
  assert( hHeap!=0 );
  assert( hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(hHeap, SQLITE_WIN32_HEAP_FLAGS, p) );
#endif
  if( !p ) return 0;
  n = osHeapSize(hHeap, SQLITE_WIN32_HEAP_FLAGS, p);
  if( n==(SIZE_T)-1 ){
    sqlite3_log(SQLITE_NOMEM, "failed to HeapSize block %p (%lu), heap=%p",
                p, osGetLastError(), (void*)hHeap);
    return 0;
  }
  return (int)n;
}

/*
** Round up a request size to the next valid allocation size.
*/
static int winMemRoundup(int n){
  return n;
}

/*
** Initialize this module.
*/
static int winMemInit(void *pAppData){
  winMemData *pWinMemData = (winMemData *)pAppData;

  if( !pWinMemData ) return SQLITE_ERROR;
  assert( pWinMemData->magic1==WINMEM_MAGIC1 );
  assert( pWinMemData->magic2==WINMEM_MAGIC2 );

#if !SQLITE_OS_WINRT && SQLITE_WIN32_HEAP_CREATE
  if( !pWinMemData->hHeap ){
    DWORD dwInitialSize = SQLITE_WIN32_HEAP_INIT_SIZE;
    DWORD dwMaximumSize = (DWORD)sqlite3GlobalConfig.nHeap;
    if( dwMaximumSize==0 ){
      dwMaximumSize = SQLITE_WIN32_HEAP_MAX_SIZE;
    }else if( dwInitialSize>dwMaximumSize ){
      dwInitialSize = dwMaximumSize;
    }
    pWinMemData->hHeap = osHeapCreate(SQLITE_WIN32_HEAP_FLAGS,
                                      dwInitialSize, dwMaximumSize);
    if( !pWinMemData->hHeap ){
      sqlite3_log(SQLITE_NOMEM,
          "failed to HeapCreate (%lu), flags=%u, initSize=%lu, maxSize=%lu",
          osGetLastError(), SQLITE_WIN32_HEAP_FLAGS, dwInitialSize,
          dwMaximumSize);
      return SQLITE_NOMEM;
    }
    pWinMemData->bOwned = TRUE;
    assert( pWinMemData->bOwned );
  }
#else
  pWinMemData->hHeap = osGetProcessHeap();
  if( !pWinMemData->hHeap ){
    sqlite3_log(SQLITE_NOMEM,
        "failed to GetProcessHeap (%lu)", osGetLastError());
    return SQLITE_NOMEM;
  }
  pWinMemData->bOwned = FALSE;
  assert( !pWinMemData->bOwned );
#endif
  assert( pWinMemData->hHeap!=0 );
  assert( pWinMemData->hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
  assert( osHeapValidate(pWinMemData->hHeap, SQLITE_WIN32_HEAP_FLAGS, NULL) );
#endif
  return SQLITE_OK;
}

/*
** Deinitialize this module.
*/
static void winMemShutdown(void *pAppData){
  winMemData *pWinMemData = (winMemData *)pAppData;

  if( !pWinMemData ) return;
  assert( pWinMemData->magic1==WINMEM_MAGIC1 );
  assert( pWinMemData->magic2==WINMEM_MAGIC2 );

  if( pWinMemData->hHeap ){
    assert( pWinMemData->hHeap!=INVALID_HANDLE_VALUE );
#if !SQLITE_OS_WINRT && defined(SQLITE_WIN32_MALLOC_VALIDATE)
    assert( osHeapValidate(pWinMemData->hHeap, SQLITE_WIN32_HEAP_FLAGS, NULL) );
#endif
    if( pWinMemData->bOwned ){
      if( !osHeapDestroy(pWinMemData->hHeap) ){
        sqlite3_log(SQLITE_NOMEM, "failed to HeapDestroy (%lu), heap=%p",
                    osGetLastError(), (void*)pWinMemData->hHeap);
      }
      pWinMemData->bOwned = FALSE;
    }
    pWinMemData->hHeap = NULL;
  }
}

/*
** Populate the low-level memory allocation function pointers in
** sqlite3GlobalConfig.m with pointers to the routines in this file. The
** arguments specify the block of memory to manage.
**
** This routine is only called by sqlite3_config(), and therefore
** is not required to be threadsafe (it is not).
*/
SQLITE_PRIVATE const sqlite3_mem_methods *sqlite3MemGetWin32(void){
  static const sqlite3_mem_methods winMemMethods = {
    winMemMalloc,
    winMemFree,
    winMemRealloc,
    winMemSize,
    winMemRoundup,
    winMemInit,
    winMemShutdown,
    &win_mem_data
  };
  return &winMemMethods;
}

SQLITE_PRIVATE void sqlite3MemSetDefault(void){
  sqlite3_config(SQLITE_CONFIG_MALLOC, sqlite3MemGetWin32());
}
#endif /* SQLITE_WIN32_MALLOC */

/*
** Convert a UTF-8 string to Microsoft Unicode (UTF-16?).
**
** Space to hold the returned string is obtained from malloc.
*/
static LPWSTR winUtf8ToUnicode(const char *zFilename){
  int nChar;
  LPWSTR zWideFilename;

  nChar = osMultiByteToWideChar(CP_UTF8, 0, zFilename, -1, NULL, 0);
  if( nChar==0 ){
    return 0;
  }
  zWideFilename = sqlite3MallocZero( nChar*sizeof(zWideFilename[0]) );
  if( zWideFilename==0 ){
    return 0;
  }
  nChar = osMultiByteToWideChar(CP_UTF8, 0, zFilename, -1, zWideFilename,
                                nChar);
  if( nChar==0 ){
    sqlite3_free(zWideFilename);
    zWideFilename = 0;
  }
  return zWideFilename;
}

/*
** Convert Microsoft Unicode to UTF-8.  Space to hold the returned string is
** obtained from sqlite3_malloc().
*/
static char *winUnicodeToUtf8(LPCWSTR zWideFilename){
  int nByte;
  char *zFilename;

  nByte = osWideCharToMultiByte(CP_UTF8, 0, zWideFilename, -1, 0, 0, 0, 0);
  if( nByte == 0 ){
    return 0;
  }
  zFilename = sqlite3MallocZero( nByte );
  if( zFilename==0 ){
    return 0;
  }
  nByte = osWideCharToMultiByte(CP_UTF8, 0, zWideFilename, -1, zFilename, nByte,
                                0, 0);
  if( nByte == 0 ){
    sqlite3_free(zFilename);
    zFilename = 0;
  }
  return zFilename;
}

/*
** Convert an ANSI string to Microsoft Unicode, based on the
** current codepage settings for file apis.
**
** Space to hold the returned string is obtained
** from sqlite3_malloc.
*/
static LPWSTR winMbcsToUnicode(const char *zFilename){
  int nByte;
  LPWSTR zMbcsFilename;
  int codepage = osAreFileApisANSI() ? CP_ACP : CP_OEMCP;

  nByte = osMultiByteToWideChar(codepage, 0, zFilename, -1, NULL,
                                0)*sizeof(WCHAR);
  if( nByte==0 ){
    return 0;
  }
  zMbcsFilename = sqlite3MallocZero( nByte*sizeof(zMbcsFilename[0]) );
  if( zMbcsFilename==0 ){
    return 0;
  }
  nByte = osMultiByteToWideChar(codepage, 0, zFilename, -1, zMbcsFilename,
                                nByte);
  if( nByte==0 ){
    sqlite3_free(zMbcsFilename);
    zMbcsFilename = 0;
  }
  return zMbcsFilename;
}

/*
** Convert Microsoft Unicode to multi-byte character string, based on the
** user's ANSI codepage.
**
** Space to hold the returned string is obtained from
** sqlite3_malloc().
*/
static char *winUnicodeToMbcs(LPCWSTR zWideFilename){
  int nByte;
  char *zFilename;
  int codepage = osAreFileApisANSI() ? CP_ACP : CP_OEMCP;

  nByte = osWideCharToMultiByte(codepage, 0, zWideFilename, -1, 0, 0, 0, 0);
  if( nByte == 0 ){
    return 0;
  }
  zFilename = sqlite3MallocZero( nByte );
  if( zFilename==0 ){
    return 0;
  }
  nByte = osWideCharToMultiByte(codepage, 0, zWideFilename, -1, zFilename,
                                nByte, 0, 0);
  if( nByte == 0 ){
    sqlite3_free(zFilename);
    zFilename = 0;
  }
  return zFilename;
}

/*
** Convert multibyte character string to UTF-8.  Space to hold the
** returned string is obtained from sqlite3_malloc().
*/
SQLITE_PRIVATE char *sqlite3_win32_mbcs_to_utf8(const char *zFilename){
  char *zFilenameUtf8;
  LPWSTR zTmpWide;

  zTmpWide = winMbcsToUnicode(zFilename);
  if( zTmpWide==0 ){
    return 0;
  }
  zFilenameUtf8 = winUnicodeToUtf8(zTmpWide);
  sqlite3_free(zTmpWide);
  return zFilenameUtf8;
}

/*
** Convert UTF-8 to multibyte character string.  Space to hold the
** returned string is obtained from sqlite3_malloc().
*/
SQLITE_PRIVATE char *sqlite3_win32_utf8_to_mbcs(const char *zFilename){
  char *zFilenameMbcs;
  LPWSTR zTmpWide;

  zTmpWide = winUtf8ToUnicode(zFilename);
  if( zTmpWide==0 ){
    return 0;
  }
  zFilenameMbcs = winUnicodeToMbcs(zTmpWide);
  sqlite3_free(zTmpWide);
  return zFilenameMbcs;
}

/*
** This function sets the data directory or the temporary directory based on
** the provided arguments.  The type argument must be 1 in order to set the
** data directory or 2 in order to set the temporary directory.  The zValue
** argument is the name of the directory to use.  The return value will be
** SQLITE_OK if successful.
*/
SQLITE_PRIVATE int sqlite3_win32_set_directory(DWORD type, LPCWSTR zValue){
  char **ppDirectory = 0;
#ifndef SQLITE_OMIT_AUTOINIT
  int rc = sqlite3BtreeInitialize();
  if( rc ) return rc;
#endif
  if( type==SQLITE_WIN32_TEMP_DIRECTORY_TYPE ){
    ppDirectory = &sqlite3_temp_directory;
  }
  assert( !ppDirectory || type==SQLITE_WIN32_TEMP_DIRECTORY_TYPE
  );
  assert( !ppDirectory || sqlite3MemdebugHasType(*ppDirectory, MEMTYPE_HEAP) );
  if( ppDirectory ){
    char *zValueUtf8 = 0;
    if( zValue && zValue[0] ){
      zValueUtf8 = winUnicodeToUtf8(zValue);
      if ( zValueUtf8==0 ){
        return SQLITE_NOMEM;
      }
    }
    sqlite3_free(*ppDirectory);
    *ppDirectory = zValueUtf8;
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

/*
** The return value of winGetLastErrorMsg
** is zero if the error message fits in the buffer, or non-zero
** otherwise (if the message was truncated).
*/
static int winGetLastErrorMsg(DWORD lastErrno, int nBuf, char *zBuf){
  /* FormatMessage returns 0 on failure.  Otherwise it
  ** returns the number of TCHARs written to the output
  ** buffer, excluding the terminating null char.
  */
  DWORD dwLen = 0;
  char *zOut = 0;

  if( osIsNT() ){
#if SQLITE_OS_WINRT
    WCHAR zTempWide[SQLITE_WIN32_MAX_ERRMSG_CHARS+1];
    dwLen = osFormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM |
                             FORMAT_MESSAGE_IGNORE_INSERTS,
                             NULL,
                             lastErrno,
                             0,
                             zTempWide,
                             SQLITE_WIN32_MAX_ERRMSG_CHARS,
                             0);
#else
    LPWSTR zTempWide = NULL;
    dwLen = osFormatMessageW(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                             FORMAT_MESSAGE_FROM_SYSTEM |
                             FORMAT_MESSAGE_IGNORE_INSERTS,
                             NULL,
                             lastErrno,
                             0,
                             (LPWSTR) &zTempWide,
                             0,
                             0);
#endif
    if( dwLen > 0 ){
      /* allocate a buffer and convert to UTF8 */
      zOut = winUnicodeToUtf8(zTempWide);
#if !SQLITE_OS_WINRT
      /* free the system buffer allocated by FormatMessage */
      osLocalFree(zTempWide);
#endif
    }
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    char *zTemp = NULL;
    dwLen = osFormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                             FORMAT_MESSAGE_FROM_SYSTEM |
                             FORMAT_MESSAGE_IGNORE_INSERTS,
                             NULL,
                             lastErrno,
                             0,
                             (LPSTR) &zTemp,
                             0,
                             0);
    if( dwLen > 0 ){
      /* allocate a buffer and convert to UTF8 */
      zOut = sqlite3_win32_mbcs_to_utf8(zTemp);
      /* free the system buffer allocated by FormatMessage */
      osLocalFree(zTemp);
    }
  }
#endif
  if( 0 == dwLen ){
    sqlite3_snprintf(nBuf, zBuf, "OsError 0x%lx (%lu)", lastErrno, lastErrno);
  }else{
    /* copy a maximum of nBuf chars to output buffer */
    sqlite3_snprintf(nBuf, zBuf, "%s", zOut);
    /* free the UTF8 buffer */
    sqlite3_free(zOut);
  }
  return 0;
}

/*
**
** This function - winLogErrorAtLine() - is only ever called via the macro
** winLogError().
**
** This routine is invoked after an error occurs in an OS function.
** It logs a message using sqlite3_log() containing the current value of
** error code and, if possible, the human-readable equivalent from
** FormatMessage.
**
** The first argument passed to the macro should be the error code that
** will be returned to SQLite (e.g. SQLITE_IOERR_DELETE, SQLITE_CANTOPEN).
** The two subsequent arguments should be the name of the OS function that
** failed and the associated file-system path, if any.
*/
#define winLogError(a,b,c,d)   winLogErrorAtLine(a,b,c,d,__LINE__)
static int winLogErrorAtLine(
  int errcode,                    /* SQLite error code */
  DWORD lastErrno,                /* Win32 last error */
  const char *zFunc,              /* Name of OS function that failed */
  const char *zPath,              /* File path associated with error */
  int iLine                       /* Source line number where error occurred */
){
  char zMsg[500];                 /* Human readable error text */
  int i;                          /* Loop counter */

  zMsg[0] = 0;
  winGetLastErrorMsg(lastErrno, sizeof(zMsg), zMsg);
  assert( errcode!=SQLITE_OK );
  if( zPath==0 ) zPath = "";
  for(i=0; zMsg[i] && zMsg[i]!='\r' && zMsg[i]!='\n'; i++){}
  zMsg[i] = 0;
  sqlite3_log(errcode,
      "os_win.c:%d: (%lu) %s(%s) - %s",
      iLine, lastErrno, zFunc, zPath, zMsg
  );

  return errcode;
}

/*
** The number of times that a ReadFile(), WriteFile(), and DeleteFile()
** will be retried following a locking error - probably caused by
** antivirus software.  Also the initial delay before the first retry.
** The delay increases linearly with each retry.
*/
#ifndef SQLITE_WIN32_IOERR_RETRY
# define SQLITE_WIN32_IOERR_RETRY 10
#endif
#ifndef SQLITE_WIN32_IOERR_RETRY_DELAY
# define SQLITE_WIN32_IOERR_RETRY_DELAY 25
#endif
static int winIoerrRetry = SQLITE_WIN32_IOERR_RETRY;
static int winIoerrRetryDelay = SQLITE_WIN32_IOERR_RETRY_DELAY;

/*
** The "winIoerrCanRetry1" macro is used to determine if a particular I/O
** error code obtained via GetLastError() is eligible to be retried.  It
** must accept the error code DWORD as its only argument and should return
** non-zero if the error code is transient in nature and the operation
** responsible for generating the original error might succeed upon being
** retried.  The argument to this macro should be a variable.
**
** Additionally, a macro named "winIoerrCanRetry2" may be defined.  If it
** is defined, it will be consulted only when the macro "winIoerrCanRetry1"
** returns zero.  The "winIoerrCanRetry2" macro is completely optional and
** may be used to include additional error codes in the set that should
** result in the failing I/O operation being retried by the caller.  If
** defined, the "winIoerrCanRetry2" macro must exhibit external semantics
** identical to those of the "winIoerrCanRetry1" macro.
*/
#if !defined(winIoerrCanRetry1)
#define winIoerrCanRetry1(a) (((a)==ERROR_ACCESS_DENIED)        || \
                              ((a)==ERROR_SHARING_VIOLATION)    || \
                              ((a)==ERROR_LOCK_VIOLATION)       || \
                              ((a)==ERROR_DEV_NOT_EXIST)        || \
                              ((a)==ERROR_NETNAME_DELETED)      || \
                              ((a)==ERROR_SEM_TIMEOUT)          || \
                              ((a)==ERROR_NETWORK_UNREACHABLE))
#endif

/*
** If a ReadFile() or WriteFile() error occurs, invoke this routine
** to see if it should be retried.  Return TRUE to retry.  Return FALSE
** to give up with an error.
*/
static int winRetryIoerr(int *pnRetry, DWORD *pError){
  DWORD e = osGetLastError();
  if( *pnRetry>=winIoerrRetry ){
    if( pError ){
      *pError = e;
    }
    return 0;
  }
  if( winIoerrCanRetry1(e) ){
    sqlite3_win32_sleep(winIoerrRetryDelay*(1+*pnRetry));
    ++*pnRetry;
    return 1;
  }
#if defined(winIoerrCanRetry2)
  else if( winIoerrCanRetry2(e) ){
    sqlite3_win32_sleep(winIoerrRetryDelay*(1+*pnRetry));
    ++*pnRetry;
    return 1;
  }
#endif
  if( pError ){
    *pError = e;
  }
  return 0;
}

/*
** Log a I/O error retry episode.
*/
static void winLogIoerr(int nRetry, int lineno){
  if( nRetry ){
    sqlite3_log(SQLITE_NOTICE,
      "delayed %dms for lock/sharing conflict at line %d",
      winIoerrRetryDelay*nRetry*(nRetry+1)/2, lineno
    );
  }
}

#if SQLITE_OS_WINCE
/*************************************************************************
** This section contains code for WinCE only.
*/
#if !defined(SQLITE_MSVC_LOCALTIME_API) || !SQLITE_MSVC_LOCALTIME_API
/*
** The MSVC CRT on Windows CE may not have a localtime() function.  So
** create a substitute.
*/
/* #include <time.h> */
struct tm *__cdecl localtime(const time_t *t)
{
  static struct tm y;
  FILETIME uTm, lTm;
  SYSTEMTIME pTm;
  sqlite3_int64 t64;
  t64 = *t;
  t64 = (t64 + 11644473600)*10000000;
  uTm.dwLowDateTime = (DWORD)(t64 & 0xFFFFFFFF);
  uTm.dwHighDateTime= (DWORD)(t64 >> 32);
  osFileTimeToLocalFileTime(&uTm,&lTm);
  osFileTimeToSystemTime(&lTm,&pTm);
  y.tm_year = pTm.wYear - 1900;
  y.tm_mon = pTm.wMonth - 1;
  y.tm_wday = pTm.wDayOfWeek;
  y.tm_mday = pTm.wDay;
  y.tm_hour = pTm.wHour;
  y.tm_min = pTm.wMinute;
  y.tm_sec = pTm.wSecond;
  return &y;
}
#endif

#define HANDLE_TO_WINFILE(a) (winFile*)&((char*)a)[-(int)offsetof(winFile,h)]

/*
** Acquire a lock on the handle h
*/
static void winceMutexAcquire(HANDLE h){
   DWORD dwErr;
   do {
     dwErr = osWaitForSingleObject(h, INFINITE);
   } while (dwErr != WAIT_OBJECT_0 && dwErr != WAIT_ABANDONED);
}
/*
** Release a lock acquired by winceMutexAcquire()
*/
#define winceMutexRelease(h) ReleaseMutex(h)

/*
** Create the mutex and shared memory used for locking in the file
** descriptor pFile
*/
static int winceCreateLock(const char *zFilename, winFile *pFile){
  LPWSTR zTok;
  LPWSTR zName;
  DWORD lastErrno;
  BOOL bLogged = FALSE;
  BOOL bInit = TRUE;

  zName = winUtf8ToUnicode(zFilename);
  if( zName==0 ){
    /* out of memory */
    return SQLITE_IOERR_NOMEM;
  }

  /* Initialize the local lockdata */
  memset(&pFile->local, 0, sizeof(pFile->local));

  /* Replace the backslashes from the filename and lowercase it
  ** to derive a mutex name. */
  zTok = osCharLowerW(zName);
  for (;*zTok;zTok++){
    if (*zTok == '\\') *zTok = '_';
  }

  /* Create/open the named mutex */
  pFile->hMutex = osCreateMutexW(NULL, FALSE, zName);
  if (!pFile->hMutex){
    pFile->lastErrno = osGetLastError();
    sqlite3_free(zName);
    return winLogError(SQLITE_IOERR, pFile->lastErrno,
                       "winceCreateLock1", zFilename);
  }

  /* Acquire the mutex before continuing */
  winceMutexAcquire(pFile->hMutex);

  /* Since the names of named mutexes, semaphores, file mappings etc are
  ** case-sensitive, take advantage of that by uppercasing the mutex name
  ** and using that as the shared filemapping name.
  */
  osCharUpperW(zName);
  pFile->hShared = osCreateFileMappingW(INVALID_HANDLE_VALUE, NULL,
                                        PAGE_READWRITE, 0, sizeof(winceLock),
                                        zName);

  /* Set a flag that indicates we're the first to create the memory so it
  ** must be zero-initialized */
  lastErrno = osGetLastError();
  if (lastErrno == ERROR_ALREADY_EXISTS){
    bInit = FALSE;
  }

  sqlite3_free(zName);

  /* If we succeeded in making the shared memory handle, map it. */
  if( pFile->hShared ){
    pFile->shared = (winceLock*)osMapViewOfFile(pFile->hShared,
             FILE_MAP_READ|FILE_MAP_WRITE, 0, 0, sizeof(winceLock));
    /* If mapping failed, close the shared memory handle and erase it */
    if( !pFile->shared ){
      pFile->lastErrno = osGetLastError();
      winLogError(SQLITE_IOERR, pFile->lastErrno,
                  "winceCreateLock2", zFilename);
      bLogged = TRUE;
      osCloseHandle(pFile->hShared);
      pFile->hShared = NULL;
    }
  }

  /* If shared memory could not be created, then close the mutex and fail */
  if( pFile->hShared==NULL ){
    if( !bLogged ){
      pFile->lastErrno = lastErrno;
      winLogError(SQLITE_IOERR, pFile->lastErrno,
                  "winceCreateLock3", zFilename);
      bLogged = TRUE;
    }
    winceMutexRelease(pFile->hMutex);
    osCloseHandle(pFile->hMutex);
    pFile->hMutex = NULL;
    return SQLITE_IOERR;
  }

  /* Initialize the shared memory if we're supposed to */
  if( bInit ){
    memset(pFile->shared, 0, sizeof(winceLock));
  }

  winceMutexRelease(pFile->hMutex);
  return SQLITE_OK;
}

/*
** Destroy the part of winFile that deals with wince locks
*/
static void winceDestroyLock(winFile *pFile){
  if (pFile->hMutex){
    /* Acquire the mutex */
    winceMutexAcquire(pFile->hMutex);

    /* The following blocks should probably assert in debug mode, but they
       are to cleanup in case any locks remained open */
    if (pFile->local.nReaders){
      pFile->shared->nReaders --;
    }
    if (pFile->local.bReserved){
      pFile->shared->bReserved = FALSE;
    }
    if (pFile->local.bPending){
      pFile->shared->bPending = FALSE;
    }
    if (pFile->local.bExclusive){
      pFile->shared->bExclusive = FALSE;
    }

    /* De-reference and close our copy of the shared memory handle */
    osUnmapViewOfFile(pFile->shared);
    osCloseHandle(pFile->hShared);

    /* Done with the mutex */
    winceMutexRelease(pFile->hMutex);
    osCloseHandle(pFile->hMutex);
    pFile->hMutex = NULL;
  }
}

/*
** An implementation of the LockFile() API of Windows for CE
*/
static BOOL winceLockFile(
  LPHANDLE phFile,
  DWORD dwFileOffsetLow,
  DWORD dwFileOffsetHigh,
  DWORD nNumberOfBytesToLockLow,
  DWORD nNumberOfBytesToLockHigh
){
  winFile *pFile = HANDLE_TO_WINFILE(phFile);
  BOOL bReturn = FALSE;

  UNUSED_PARAMETER(dwFileOffsetHigh);
  UNUSED_PARAMETER(nNumberOfBytesToLockHigh);

  if (!pFile->hMutex) return TRUE;
  winceMutexAcquire(pFile->hMutex);

  /* Wanting an exclusive lock? */
  if (dwFileOffsetLow == (DWORD)SHARED_FIRST
       && nNumberOfBytesToLockLow == (DWORD)SHARED_SIZE){
    if (pFile->shared->nReaders == 0 && pFile->shared->bExclusive == 0){
       pFile->shared->bExclusive = TRUE;
       pFile->local.bExclusive = TRUE;
       bReturn = TRUE;
    }
  }

  /* Want a read-only lock? */
  else if (dwFileOffsetLow == (DWORD)SHARED_FIRST &&
           nNumberOfBytesToLockLow == 1){
    if (pFile->shared->bExclusive == 0){
      pFile->local.nReaders ++;
      if (pFile->local.nReaders == 1){
        pFile->shared->nReaders ++;
      }
      bReturn = TRUE;
    }
  }

  /* Want a pending lock? */
  else if (dwFileOffsetLow == (DWORD)PENDING_BYTE
           && nNumberOfBytesToLockLow == 1){
    /* If no pending lock has been acquired, then acquire it */
    if (pFile->shared->bPending == 0) {
      pFile->shared->bPending = TRUE;
      pFile->local.bPending = TRUE;
      bReturn = TRUE;
    }
  }

  /* Want a reserved lock? */
  else if (dwFileOffsetLow == (DWORD)RESERVED_BYTE
           && nNumberOfBytesToLockLow == 1){
    if (pFile->shared->bReserved == 0) {
      pFile->shared->bReserved = TRUE;
      pFile->local.bReserved = TRUE;
      bReturn = TRUE;
    }
  }

  winceMutexRelease(pFile->hMutex);
  return bReturn;
}

/*
** An implementation of the UnlockFile API of Windows for CE
*/
static BOOL winceUnlockFile(
  LPHANDLE phFile,
  DWORD dwFileOffsetLow,
  DWORD dwFileOffsetHigh,
  DWORD nNumberOfBytesToUnlockLow,
  DWORD nNumberOfBytesToUnlockHigh
){
  winFile *pFile = HANDLE_TO_WINFILE(phFile);
  BOOL bReturn = FALSE;

  UNUSED_PARAMETER(dwFileOffsetHigh);
  UNUSED_PARAMETER(nNumberOfBytesToUnlockHigh);

  if (!pFile->hMutex) return TRUE;
  winceMutexAcquire(pFile->hMutex);

  /* Releasing a reader lock or an exclusive lock */
  if (dwFileOffsetLow == (DWORD)SHARED_FIRST){
    /* Did we have an exclusive lock? */
    if (pFile->local.bExclusive){
      assert(nNumberOfBytesToUnlockLow == (DWORD)SHARED_SIZE);
      pFile->local.bExclusive = FALSE;
      pFile->shared->bExclusive = FALSE;
      bReturn = TRUE;
    }

    /* Did we just have a reader lock? */
    else if (pFile->local.nReaders){
      assert(nNumberOfBytesToUnlockLow == (DWORD)SHARED_SIZE
             || nNumberOfBytesToUnlockLow == 1);
      pFile->local.nReaders --;
      if (pFile->local.nReaders == 0)
      {
        pFile->shared->nReaders --;
      }
      bReturn = TRUE;
    }
  }

  /* Releasing a pending lock */
  else if (dwFileOffsetLow == (DWORD)PENDING_BYTE
           && nNumberOfBytesToUnlockLow == 1){
    if (pFile->local.bPending){
      pFile->local.bPending = FALSE;
      pFile->shared->bPending = FALSE;
      bReturn = TRUE;
    }
  }
  /* Releasing a reserved lock */
  else if (dwFileOffsetLow == (DWORD)RESERVED_BYTE
           && nNumberOfBytesToUnlockLow == 1){
    if (pFile->local.bReserved) {
      pFile->local.bReserved = FALSE;
      pFile->shared->bReserved = FALSE;
      bReturn = TRUE;
    }
  }

  winceMutexRelease(pFile->hMutex);
  return bReturn;
}
/*
** End of the special code for wince
*****************************************************************************/
#endif /* SQLITE_OS_WINCE */

/*
** Lock a file region.
*/
static BOOL winLockFile(
  LPHANDLE phFile,
  DWORD flags,
  DWORD offsetLow,
  DWORD offsetHigh,
  DWORD numBytesLow,
  DWORD numBytesHigh
){
#if SQLITE_OS_WINCE
  /*
  ** NOTE: Windows CE is handled differently here due its lack of the Win32
  **       API LockFile.
  */
  return winceLockFile(phFile, offsetLow, offsetHigh,
                       numBytesLow, numBytesHigh);
#else
  if( osIsNT() ){
    OVERLAPPED ovlp;
    memset(&ovlp, 0, sizeof(OVERLAPPED));
    ovlp.Offset = offsetLow;
    ovlp.OffsetHigh = offsetHigh;
    return osLockFileEx(*phFile, flags, 0, numBytesLow, numBytesHigh, &ovlp);
  }else{
    return osLockFile(*phFile, offsetLow, offsetHigh, numBytesLow,
                      numBytesHigh);
  }
#endif
}

/*
** Unlock a file region.
 */
static BOOL winUnlockFile(
  LPHANDLE phFile,
  DWORD offsetLow,
  DWORD offsetHigh,
  DWORD numBytesLow,
  DWORD numBytesHigh
){
#if SQLITE_OS_WINCE
  /*
  ** NOTE: Windows CE is handled differently here due its lack of the Win32
  **       API UnlockFile.
  */
  return winceUnlockFile(phFile, offsetLow, offsetHigh,
                         numBytesLow, numBytesHigh);
#else
  if( osIsNT() ){
    OVERLAPPED ovlp;
    memset(&ovlp, 0, sizeof(OVERLAPPED));
    ovlp.Offset = offsetLow;
    ovlp.OffsetHigh = offsetHigh;
    return osUnlockFileEx(*phFile, 0, numBytesLow, numBytesHigh, &ovlp);
  }else{
    return osUnlockFile(*phFile, offsetLow, offsetHigh, numBytesLow,
                        numBytesHigh);
  }
#endif
}

/*****************************************************************************
** The next group of routines implement the I/O methods specified
** by the sqlite3_io_methods object.
******************************************************************************/

/*
** Some Microsoft compilers lack this definition.
*/
#ifndef INVALID_SET_FILE_POINTER
# define INVALID_SET_FILE_POINTER ((DWORD)-1)
#endif

/*
** Move the current position of the file handle passed as the first
** argument to offset iOffset within the file. If successful, return 0.
** Otherwise, set pFile->lastErrno and return non-zero.
*/
static int winSeekFile(winFile *pFile, sqlite3_int64 iOffset){
#if !SQLITE_OS_WINRT
  LONG upperBits;                 /* Most sig. 32 bits of new offset */
  LONG lowerBits;                 /* Least sig. 32 bits of new offset */
  DWORD dwRet;                    /* Value returned by SetFilePointer() */
  DWORD lastErrno;                /* Value returned by GetLastError() */

  OSTRACE(("SEEK file=%p, offset=%lld\n", pFile->h, iOffset));

  upperBits = (LONG)((iOffset>>32) & 0x7fffffff);
  lowerBits = (LONG)(iOffset & 0xffffffff);

  /* API oddity: If successful, SetFilePointer() returns a dword
  ** containing the lower 32-bits of the new file-offset. Or, if it fails,
  ** it returns INVALID_SET_FILE_POINTER. However according to MSDN,
  ** INVALID_SET_FILE_POINTER may also be a valid new offset. So to determine
  ** whether an error has actually occurred, it is also necessary to call
  ** GetLastError().
  */
  dwRet = osSetFilePointer(pFile->h, lowerBits, &upperBits, FILE_BEGIN);

  if( (dwRet==INVALID_SET_FILE_POINTER
      && ((lastErrno = osGetLastError())!=NO_ERROR)) ){
    pFile->lastErrno = lastErrno;
    winLogError(SQLITE_IOERR_SEEK, pFile->lastErrno,
                "winSeekFile", pFile->zPath);
    OSTRACE(("SEEK file=%p, rc=SQLITE_IOERR_SEEK\n", pFile->h));
    return 1;
  }

  OSTRACE(("SEEK file=%p, rc=SQLITE_OK\n", pFile->h));
  return 0;
#else
  /*
  ** Same as above, except that this implementation works for WinRT.
  */

  LARGE_INTEGER x;                /* The new offset */
  BOOL bRet;                      /* Value returned by SetFilePointerEx() */

  x.QuadPart = iOffset;
  bRet = osSetFilePointerEx(pFile->h, x, 0, FILE_BEGIN);

  if(!bRet){
    pFile->lastErrno = osGetLastError();
    winLogError(SQLITE_IOERR_SEEK, pFile->lastErrno,
                "winSeekFile", pFile->zPath);
    OSTRACE(("SEEK file=%p, rc=SQLITE_IOERR_SEEK\n", pFile->h));
    return 1;
  }

  OSTRACE(("SEEK file=%p, rc=SQLITE_OK\n", pFile->h));
  return 0;
#endif
}

#if SQLITE_MAX_MMAP_SIZE>0
/* Forward references to VFS helper methods used for memory mapped files */
static int winMapfile(winFile*, sqlite3_int64);
static int winUnmapfile(winFile*);
#endif

/*
** Close a file.
**
** It is reported that an attempt to close a handle might sometimes
** fail.  This is a very unreasonable result, but Windows is notorious
** for being unreasonable so I do not doubt that it might happen.  If
** the close fails, we pause for 100 milliseconds and try again.  As
** many as MX_CLOSE_ATTEMPT attempts to close the handle are made before
** giving up and returning an error.
*/
#define MX_CLOSE_ATTEMPT 3
static int winClose(sqlite3_file *id){
  int rc, cnt = 0;
  winFile *pFile = (winFile*)id;

  assert( id!=0 );
#ifndef SQLITE_OMIT_WAL
  assert( pFile->pShm==0 );
#endif
  assert( pFile->h!=NULL && pFile->h!=INVALID_HANDLE_VALUE );
  OSTRACE(("CLOSE pid=%lu, pFile=%p, file=%p\n",
           osGetCurrentProcessId(), pFile, pFile->h));

#if SQLITE_MAX_MMAP_SIZE>0
  winUnmapfile(pFile);
#endif

  do{
    rc = osCloseHandle(pFile->h);
    /* SimulateIOError( rc=0; cnt=MX_CLOSE_ATTEMPT; ); */
  }while( rc==0 && ++cnt < MX_CLOSE_ATTEMPT && (sqlite3_win32_sleep(100), 1) );
#if SQLITE_OS_WINCE
#define WINCE_DELETION_ATTEMPTS 3
  winceDestroyLock(pFile);
  if( pFile->zDeleteOnClose ){
    int cnt = 0;
    while(
           osDeleteFileW(pFile->zDeleteOnClose)==0
        && osGetFileAttributesW(pFile->zDeleteOnClose)!=0xffffffff
        && cnt++ < WINCE_DELETION_ATTEMPTS
    ){
       sqlite3_win32_sleep(100);  /* Wait a little before trying again */
    }
    sqlite3_free(pFile->zDeleteOnClose);
  }
#endif
  if( rc ){
    pFile->h = NULL;
  }
  OpenCounter(-1);
  OSTRACE(("CLOSE pid=%lu, pFile=%p, file=%p, rc=%s\n",
           osGetCurrentProcessId(), pFile, pFile->h, rc ? "ok" : "failed"));
  return rc ? SQLITE_OK
            : winLogError(SQLITE_IOERR_CLOSE, osGetLastError(),
                          "winClose", pFile->zPath);
}

/*
** Read data from a file into a buffer.  Return SQLITE_OK if all
** bytes were read successfully and SQLITE_IOERR if anything goes
** wrong.
*/
static int winRead(
  sqlite3_file *id,          /* File to read from */
  void *pBuf,                /* Write content into this buffer */
  int amt,                   /* Number of bytes to read */
  sqlite3_int64 offset       /* Begin reading at this offset */
){
#if !SQLITE_OS_WINCE && !defined(SQLITE_WIN32_NO_OVERLAPPED)
  OVERLAPPED overlapped;          /* The offset for ReadFile. */
#endif
  winFile *pFile = (winFile*)id;  /* file handle */
  DWORD nRead;                    /* Number of bytes actually read from file */
  int nRetry = 0;                 /* Number of retrys */

  assert( id!=0 );
  assert( amt>0 );
  assert( offset>=0 );
  SimulateIOError(return SQLITE_IOERR_READ);
  OSTRACE(("READ pid=%lu, pFile=%p, file=%p, buffer=%p, amount=%d, "
           "offset=%lld, lock=%d\n", osGetCurrentProcessId(), pFile,
           pFile->h, pBuf, amt, offset, pFile->locktype));

#if SQLITE_MAX_MMAP_SIZE>0
  /* Deal with as much of this read request as possible by transfering
  ** data from the memory mapping using memcpy().  */
  if( offset<pFile->mmapSize ){
    if( offset+amt <= pFile->mmapSize ){
      memcpy(pBuf, &((u8 *)(pFile->pMapRegion))[offset], amt);
      OSTRACE(("READ-MMAP pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
               osGetCurrentProcessId(), pFile, pFile->h));
      return SQLITE_OK;
    }else{
      int nCopy = (int)(pFile->mmapSize - offset);
      memcpy(pBuf, &((u8 *)(pFile->pMapRegion))[offset], nCopy);
      pBuf = &((u8 *)pBuf)[nCopy];
      amt -= nCopy;
      offset += nCopy;
    }
  }
#endif

#if SQLITE_OS_WINCE || defined(SQLITE_WIN32_NO_OVERLAPPED)
  if( winSeekFile(pFile, offset) ){
    OSTRACE(("READ pid=%lu, pFile=%p, file=%p, rc=SQLITE_FULL\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return SQLITE_FULL;
  }
  while( !osReadFile(pFile->h, pBuf, amt, &nRead, 0) ){
#else
  memset(&overlapped, 0, sizeof(OVERLAPPED));
  overlapped.Offset = (LONG)(offset & 0xffffffff);
  overlapped.OffsetHigh = (LONG)((offset>>32) & 0x7fffffff);
  while( !osReadFile(pFile->h, pBuf, amt, &nRead, &overlapped) &&
         osGetLastError()!=ERROR_HANDLE_EOF ){
#endif
    DWORD lastErrno;
    if( winRetryIoerr(&nRetry, &lastErrno) ) continue;
    pFile->lastErrno = lastErrno;
    OSTRACE(("READ pid=%lu, pFile=%p, file=%p, rc=SQLITE_IOERR_READ\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return winLogError(SQLITE_IOERR_READ, pFile->lastErrno,
                       "winRead", pFile->zPath);
  }
  winLogIoerr(nRetry, __LINE__);
  if( nRead<(DWORD)amt ){
    /* Unread parts of the buffer must be zero-filled */
    memset(&((char*)pBuf)[nRead], 0, amt-nRead);
    OSTRACE(("READ pid=%lu, pFile=%p, file=%p, rc=SQLITE_IOERR_SHORT_READ\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return SQLITE_IOERR_SHORT_READ;
  }

  OSTRACE(("READ pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), pFile, pFile->h));
  return SQLITE_OK;
}

/*
** Write data from a buffer into a file.  Return SQLITE_OK on success
** or some other error code on failure.
*/
static int winWrite(
  sqlite3_file *id,               /* File to write into */
  const void *pBuf,               /* The bytes to be written */
  int amt,                        /* Number of bytes to write */
  sqlite3_int64 offset            /* Offset into the file to begin writing at */
){
  int rc = 0;                     /* True if error has occurred, else false */
  winFile *pFile = (winFile*)id;  /* File handle */
  int nRetry = 0;                 /* Number of retries */

  assert( amt>0 );
  assert( pFile );
  SimulateIOError(return SQLITE_IOERR_WRITE);
  SimulateDiskfullError(return SQLITE_FULL);

  OSTRACE(("WRITE pid=%lu, pFile=%p, file=%p, buffer=%p, amount=%d, "
           "offset=%lld, lock=%d\n", osGetCurrentProcessId(), pFile,
           pFile->h, pBuf, amt, offset, pFile->locktype));

#if SQLITE_MAX_MMAP_SIZE>0
  /* Deal with as much of this write request as possible by transfering
  ** data from the memory mapping using memcpy().  */
  if( offset<pFile->mmapSize ){
    if( offset+amt <= pFile->mmapSize ){
      memcpy(&((u8 *)(pFile->pMapRegion))[offset], pBuf, amt);
      OSTRACE(("WRITE-MMAP pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
               osGetCurrentProcessId(), pFile, pFile->h));
      return SQLITE_OK;
    }else{
      int nCopy = (int)(pFile->mmapSize - offset);
      memcpy(&((u8 *)(pFile->pMapRegion))[offset], pBuf, nCopy);
      pBuf = &((u8 *)pBuf)[nCopy];
      amt -= nCopy;
      offset += nCopy;
    }
  }
#endif

#if SQLITE_OS_WINCE || defined(SQLITE_WIN32_NO_OVERLAPPED)
  rc = winSeekFile(pFile, offset);
  if( rc==0 ){
#else
  {
#endif
#if !SQLITE_OS_WINCE && !defined(SQLITE_WIN32_NO_OVERLAPPED)
    OVERLAPPED overlapped;        /* The offset for WriteFile. */
#endif
    u8 *aRem = (u8 *)pBuf;        /* Data yet to be written */
    int nRem = amt;               /* Number of bytes yet to be written */
    DWORD nWrite;                 /* Bytes written by each WriteFile() call */
    DWORD lastErrno = NO_ERROR;   /* Value returned by GetLastError() */

#if !SQLITE_OS_WINCE && !defined(SQLITE_WIN32_NO_OVERLAPPED)
    memset(&overlapped, 0, sizeof(OVERLAPPED));
    overlapped.Offset = (LONG)(offset & 0xffffffff);
    overlapped.OffsetHigh = (LONG)((offset>>32) & 0x7fffffff);
#endif

    while( nRem>0 ){
#if SQLITE_OS_WINCE || defined(SQLITE_WIN32_NO_OVERLAPPED)
      if( !osWriteFile(pFile->h, aRem, nRem, &nWrite, 0) ){
#else
      if( !osWriteFile(pFile->h, aRem, nRem, &nWrite, &overlapped) ){
#endif
        if( winRetryIoerr(&nRetry, &lastErrno) ) continue;
        break;
      }
      assert( nWrite==0 || nWrite<=(DWORD)nRem );
      if( nWrite==0 || nWrite>(DWORD)nRem ){
        lastErrno = osGetLastError();
        break;
      }
#if !SQLITE_OS_WINCE && !defined(SQLITE_WIN32_NO_OVERLAPPED)
      offset += nWrite;
      overlapped.Offset = (LONG)(offset & 0xffffffff);
      overlapped.OffsetHigh = (LONG)((offset>>32) & 0x7fffffff);
#endif
      aRem += nWrite;
      nRem -= nWrite;
    }
    if( nRem>0 ){
      pFile->lastErrno = lastErrno;
      rc = 1;
    }
  }

  if( rc ){
    if(   ( pFile->lastErrno==ERROR_HANDLE_DISK_FULL )
       || ( pFile->lastErrno==ERROR_DISK_FULL )){
      OSTRACE(("WRITE pid=%lu, pFile=%p, file=%p, rc=SQLITE_FULL\n",
               osGetCurrentProcessId(), pFile, pFile->h));
      return winLogError(SQLITE_FULL, pFile->lastErrno,
                         "winWrite1", pFile->zPath);
    }
    OSTRACE(("WRITE pid=%lu, pFile=%p, file=%p, rc=SQLITE_IOERR_WRITE\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return winLogError(SQLITE_IOERR_WRITE, pFile->lastErrno,
                       "winWrite2", pFile->zPath);
  }else{
    winLogIoerr(nRetry, __LINE__);
  }
  OSTRACE(("WRITE pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), pFile, pFile->h));
  return SQLITE_OK;
}

/*
** Truncate an open file to a specified size
*/
static int winTruncate(sqlite3_file *id, sqlite3_int64 nByte){
  winFile *pFile = (winFile*)id;  /* File handle object */
  int rc = SQLITE_OK;             /* Return code for this function */
  DWORD lastErrno;

  assert( pFile );
  SimulateIOError(return SQLITE_IOERR_TRUNCATE);
  OSTRACE(("TRUNCATE pid=%lu, pFile=%p, file=%p, size=%lld, lock=%d\n",
           osGetCurrentProcessId(), pFile, pFile->h, nByte, pFile->locktype));

  /* If the user has configured a chunk-size for this file, truncate the
  ** file so that it consists of an integer number of chunks (i.e. the
  ** actual file size after the operation may be larger than the requested
  ** size).
  */
  if( pFile->szChunk>0 ){
    nByte = ((nByte + pFile->szChunk - 1)/pFile->szChunk) * pFile->szChunk;
  }

  /* SetEndOfFile() returns non-zero when successful, or zero when it fails. */
  if( winSeekFile(pFile, nByte) ){
    rc = winLogError(SQLITE_IOERR_TRUNCATE, pFile->lastErrno,
                     "winTruncate1", pFile->zPath);
  }else if( 0==osSetEndOfFile(pFile->h) &&
            ((lastErrno = osGetLastError())!=ERROR_USER_MAPPED_FILE) ){
    pFile->lastErrno = lastErrno;
    rc = winLogError(SQLITE_IOERR_TRUNCATE, pFile->lastErrno,
                     "winTruncate2", pFile->zPath);
  }

#if SQLITE_MAX_MMAP_SIZE>0
  /* If the file was truncated to a size smaller than the currently
  ** mapped region, reduce the effective mapping size as well. SQLite will
  ** use read() and write() to access data beyond this point from now on.
  */
  if( pFile->pMapRegion && nByte<pFile->mmapSize ){
    pFile->mmapSize = nByte;
  }
#endif

  OSTRACE(("TRUNCATE pid=%lu, pFile=%p, file=%p, rc=%s\n",
           osGetCurrentProcessId(), pFile, pFile->h, sqlite3ErrName(rc)));
  return rc;
}

#ifdef SQLITE_TEST
/*
** Count the number of fullsyncs and normal syncs.  This is used to test
** that syncs and fullsyncs are occuring at the right times.
*/
SQLITE_PRIVATE int sqlite3_sync_count = 0;
SQLITE_PRIVATE int sqlite3_fullsync_count = 0;
#endif

/*
** Make sure all writes to a particular file are committed to disk.
*/
static int winSync(sqlite3_file *id, int flags){
#ifndef SQLITE_NO_SYNC
  /*
  ** Used only when SQLITE_NO_SYNC is not defined.
   */
  BOOL rc;
#endif
#if !defined(NDEBUG) || !defined(SQLITE_NO_SYNC) || \
    defined(SQLITE_HAVE_OS_TRACE)
  /*
  ** Used when SQLITE_NO_SYNC is not defined and by the assert() and/or
  ** OSTRACE() macros.
   */
  winFile *pFile = (winFile*)id;
#else
  UNUSED_PARAMETER(id);
#endif

  assert( pFile );
  /* Check that one of SQLITE_SYNC_NORMAL or FULL was passed */
  assert((flags&0x0F)==SQLITE_SYNC_NORMAL
      || (flags&0x0F)==SQLITE_SYNC_FULL
  );

  /* Unix cannot, but some systems may return SQLITE_FULL from here. This
  ** line is to test that doing so does not cause any problems.
  */
  SimulateDiskfullError( return SQLITE_FULL );

  OSTRACE(("SYNC pid=%lu, pFile=%p, file=%p, flags=%x, lock=%d\n",
           osGetCurrentProcessId(), pFile, pFile->h, flags,
           pFile->locktype));

#ifndef SQLITE_TEST
  UNUSED_PARAMETER(flags);
#else
  if( (flags&0x0F)==SQLITE_SYNC_FULL ){
    sqlite3_fullsync_count++;
  }
  sqlite3_sync_count++;
#endif

  /* If we compiled with the SQLITE_NO_SYNC flag, then syncing is a
  ** no-op
  */
#ifdef SQLITE_NO_SYNC
  OSTRACE(("SYNC-NOP pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), pFile, pFile->h));
  return SQLITE_OK;
#else
#if SQLITE_MAX_MMAP_SIZE>0
  if( pFile->pMapRegion ){
    if( osFlushViewOfFile(pFile->pMapRegion, 0) ){
      OSTRACE(("SYNC-MMAP pid=%lu, pFile=%p, pMapRegion=%p, "
               "rc=SQLITE_OK\n", osGetCurrentProcessId(),
               pFile, pFile->pMapRegion));
    }else{
      pFile->lastErrno = osGetLastError();
      OSTRACE(("SYNC-MMAP pid=%lu, pFile=%p, pMapRegion=%p, "
               "rc=SQLITE_IOERR_MMAP\n", osGetCurrentProcessId(),
               pFile, pFile->pMapRegion));
      return winLogError(SQLITE_IOERR_MMAP, pFile->lastErrno,
                         "winSync1", pFile->zPath);
    }
  }
#endif
  rc = osFlushFileBuffers(pFile->h);
  SimulateIOError( rc=FALSE );
  if( rc ){
    OSTRACE(("SYNC pid=%lu, pFile=%p, file=%p, rc=SQLITE_OK\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return SQLITE_OK;
  }else{
    pFile->lastErrno = osGetLastError();
    OSTRACE(("SYNC pid=%lu, pFile=%p, file=%p, rc=SQLITE_IOERR_FSYNC\n",
             osGetCurrentProcessId(), pFile, pFile->h));
    return winLogError(SQLITE_IOERR_FSYNC, pFile->lastErrno,
                       "winSync2", pFile->zPath);
  }
#endif
}

/*
** Determine the current size of a file in bytes
*/
static int winFileSize(sqlite3_file *id, sqlite3_int64 *pSize){
  winFile *pFile = (winFile*)id;
  int rc = SQLITE_OK;

  assert( id!=0 );
  assert( pSize!=0 );
  SimulateIOError(return SQLITE_IOERR_FSTAT);
  OSTRACE(("SIZE file=%p, pSize=%p\n", pFile->h, pSize));

#if SQLITE_OS_WINRT
  {
    FILE_STANDARD_INFO info;
    if( osGetFileInformationByHandleEx(pFile->h, FileStandardInfo,
                                     &info, sizeof(info)) ){
      *pSize = info.EndOfFile.QuadPart;
    }else{
      pFile->lastErrno = osGetLastError();
      rc = winLogError(SQLITE_IOERR_FSTAT, pFile->lastErrno,
                       "winFileSize", pFile->zPath);
    }
  }
#else
  {
    DWORD upperBits;
    DWORD lowerBits;
    DWORD lastErrno;

    lowerBits = osGetFileSize(pFile->h, &upperBits);
    *pSize = (((sqlite3_int64)upperBits)<<32) + lowerBits;
    if(   (lowerBits == INVALID_FILE_SIZE)
       && ((lastErrno = osGetLastError())!=NO_ERROR) ){
      pFile->lastErrno = lastErrno;
      rc = winLogError(SQLITE_IOERR_FSTAT, pFile->lastErrno,
                       "winFileSize", pFile->zPath);
    }
  }
#endif
  OSTRACE(("SIZE file=%p, pSize=%p, *pSize=%lld, rc=%s\n",
           pFile->h, pSize, *pSize, sqlite3ErrName(rc)));
  return rc;
}

/*
** LOCKFILE_FAIL_IMMEDIATELY is undefined on some Windows systems.
*/
#ifndef LOCKFILE_FAIL_IMMEDIATELY
# define LOCKFILE_FAIL_IMMEDIATELY 1
#endif

#ifndef LOCKFILE_EXCLUSIVE_LOCK
# define LOCKFILE_EXCLUSIVE_LOCK 2
#endif

/*
** Historically, SQLite has used both the LockFile and LockFileEx functions.
** When the LockFile function was used, it was always expected to fail
** immediately if the lock could not be obtained.  Also, it always expected to
** obtain an exclusive lock.  These flags are used with the LockFileEx function
** and reflect those expectations; therefore, they should not be changed.
*/
#ifndef SQLITE_LOCKFILE_FLAGS
# define SQLITE_LOCKFILE_FLAGS   (LOCKFILE_FAIL_IMMEDIATELY | \
                                  LOCKFILE_EXCLUSIVE_LOCK)
#endif

/*
** Currently, SQLite never calls the LockFileEx function without wanting the
** call to fail immediately if the lock cannot be obtained.
*/
#ifndef SQLITE_LOCKFILEEX_FLAGS
# define SQLITE_LOCKFILEEX_FLAGS (LOCKFILE_FAIL_IMMEDIATELY)
#endif

/*
** Acquire a reader lock.
** Different API routines are called depending on whether or not this
** is Win9x or WinNT.
*/
static int winGetReadLock(winFile *pFile){
  int res;
  OSTRACE(("READ-LOCK file=%p, lock=%d\n", pFile->h, pFile->locktype));
  if( osIsNT() ){
#if SQLITE_OS_WINCE
    /*
    ** NOTE: Windows CE is handled differently here due its lack of the Win32
    **       API LockFileEx.
    */
    res = winceLockFile(&pFile->h, SHARED_FIRST, 0, 1, 0);
#else
    res = winLockFile(&pFile->h, SQLITE_LOCKFILEEX_FLAGS, SHARED_FIRST, 0,
                      SHARED_SIZE, 0);
#endif
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    int lk;
    sqlite3_randomness(sizeof(lk), &lk);
    pFile->sharedLockByte = (short)((lk & 0x7fffffff)%(SHARED_SIZE - 1));
    res = winLockFile(&pFile->h, SQLITE_LOCKFILE_FLAGS,
                      SHARED_FIRST+pFile->sharedLockByte, 0, 1, 0);
  }
#endif
  if( res == 0 ){
    pFile->lastErrno = osGetLastError();
    /* No need to log a failure to lock */
  }
  OSTRACE(("READ-LOCK file=%p, result=%d\n", pFile->h, res));
  return res;
}

/*
** Undo a readlock
*/
static int winUnlockReadLock(winFile *pFile){
  int res;
  DWORD lastErrno;
  OSTRACE(("READ-UNLOCK file=%p, lock=%d\n", pFile->h, pFile->locktype));
  if( osIsNT() ){
    res = winUnlockFile(&pFile->h, SHARED_FIRST, 0, SHARED_SIZE, 0);
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    res = winUnlockFile(&pFile->h, SHARED_FIRST+pFile->sharedLockByte, 0, 1, 0);
  }
#endif
  if( res==0 && ((lastErrno = osGetLastError())!=ERROR_NOT_LOCKED) ){
    pFile->lastErrno = lastErrno;
    winLogError(SQLITE_IOERR_UNLOCK, pFile->lastErrno,
                "winUnlockReadLock", pFile->zPath);
  }
  OSTRACE(("READ-UNLOCK file=%p, result=%d\n", pFile->h, res));
  return res;
}

/*
** Lock the file with the lock specified by parameter locktype - one
** of the following:
**
**     (1) SHARED_LOCK
**     (2) RESERVED_LOCK
**     (3) PENDING_LOCK
**     (4) EXCLUSIVE_LOCK
**
** Sometimes when requesting one lock state, additional lock states
** are inserted in between.  The locking might fail on one of the later
** transitions leaving the lock state different from what it started but
** still short of its goal.  The following chart shows the allowed
** transitions and the inserted intermediate states:
**
**    UNLOCKED -> SHARED
**    SHARED -> RESERVED
**    SHARED -> (PENDING) -> EXCLUSIVE
**    RESERVED -> (PENDING) -> EXCLUSIVE
**    PENDING -> EXCLUSIVE
**
** This routine will only increase a lock.  The winUnlock() routine
** erases all locks at once and returns us immediately to locking level 0.
** It is not possible to lower the locking level one step at a time.  You
** must go straight to locking level 0.
*/
static int winLock(sqlite3_file *id, int locktype){
  int rc = SQLITE_OK;    /* Return code from subroutines */
  int res = 1;           /* Result of a Windows lock call */
  int newLocktype;       /* Set pFile->locktype to this value before exiting */
  int gotPendingLock = 0;/* True if we acquired a PENDING lock this time */
  winFile *pFile = (winFile*)id;
  DWORD lastErrno = NO_ERROR;

  assert( id!=0 );
  OSTRACE(("LOCK file=%p, oldLock=%d(%d), newLock=%d\n",
           pFile->h, pFile->locktype, pFile->sharedLockByte, locktype));

  /* If there is already a lock of this type or more restrictive on the
  ** OsFile, do nothing. Don't use the end_lock: exit path, as
  ** sqlite3OsEnterMutex() hasn't been called yet.
  */
  if( pFile->locktype>=locktype ){
    OSTRACE(("LOCK-HELD file=%p, rc=SQLITE_OK\n", pFile->h));
    return SQLITE_OK;
  }

  /* Do not allow any kind of write-lock on a read-only database
  */
  if( (pFile->ctrlFlags & WINFILE_RDONLY)!=0 && locktype>=RESERVED_LOCK ){
    return SQLITE_IOERR_LOCK;
  }

  /* Make sure the locking sequence is correct
  */
  assert( pFile->locktype!=NO_LOCK || locktype==SHARED_LOCK );
  assert( locktype!=PENDING_LOCK );
  assert( locktype!=RESERVED_LOCK || pFile->locktype==SHARED_LOCK );

  /* Lock the PENDING_LOCK byte if we need to acquire a PENDING lock or
  ** a SHARED lock.  If we are acquiring a SHARED lock, the acquisition of
  ** the PENDING_LOCK byte is temporary.
  */
  newLocktype = pFile->locktype;
  if(   (pFile->locktype==NO_LOCK)
     || (   (locktype==EXCLUSIVE_LOCK)
         && (pFile->locktype==RESERVED_LOCK))
  ){
    int cnt = 3;
    while( cnt-->0 && (res = winLockFile(&pFile->h, SQLITE_LOCKFILE_FLAGS,
                                         PENDING_BYTE, 0, 1, 0))==0 ){
      /* Try 3 times to get the pending lock.  This is needed to work
      ** around problems caused by indexing and/or anti-virus software on
      ** Windows systems.
      ** If you are using this code as a model for alternative VFSes, do not
      ** copy this retry logic.  It is a hack intended for Windows only.
      */
      lastErrno = osGetLastError();
      OSTRACE(("LOCK-PENDING-FAIL file=%p, count=%d, result=%d\n",
               pFile->h, cnt, res));
      if( lastErrno==ERROR_INVALID_HANDLE ){
        pFile->lastErrno = lastErrno;
        rc = SQLITE_IOERR_LOCK;
        OSTRACE(("LOCK-FAIL file=%p, count=%d, rc=%s\n",
                 pFile->h, cnt, sqlite3ErrName(rc)));
        return rc;
      }
      if( cnt ) sqlite3_win32_sleep(1);
    }
    gotPendingLock = res;
    if( !res ){
      lastErrno = osGetLastError();
    }
  }

  /* Acquire a shared lock
  */
  if( locktype==SHARED_LOCK && res ){
    assert( pFile->locktype==NO_LOCK );
    res = winGetReadLock(pFile);
    if( res ){
      newLocktype = SHARED_LOCK;
    }else{
      lastErrno = osGetLastError();
    }
  }

  /* Acquire a RESERVED lock
  */
  if( locktype==RESERVED_LOCK && res ){
    assert( pFile->locktype==SHARED_LOCK );
    res = winLockFile(&pFile->h, SQLITE_LOCKFILE_FLAGS, RESERVED_BYTE, 0, 1, 0);
    if( res ){
      newLocktype = RESERVED_LOCK;
    }else{
      lastErrno = osGetLastError();
    }
  }

  /* Acquire a PENDING lock
  */
  if( locktype==EXCLUSIVE_LOCK && res ){
    newLocktype = PENDING_LOCK;
    gotPendingLock = 0;
  }

  /* Acquire an EXCLUSIVE lock
  */
  if( locktype==EXCLUSIVE_LOCK && res ){
    assert( pFile->locktype>=SHARED_LOCK );
    res = winUnlockReadLock(pFile);
    res = winLockFile(&pFile->h, SQLITE_LOCKFILE_FLAGS, SHARED_FIRST, 0,
                      SHARED_SIZE, 0);
    if( res ){
      newLocktype = EXCLUSIVE_LOCK;
    }else{
      lastErrno = osGetLastError();
      winGetReadLock(pFile);
    }
  }

  /* If we are holding a PENDING lock that ought to be released, then
  ** release it now.
  */
  if( gotPendingLock && locktype==SHARED_LOCK ){
    winUnlockFile(&pFile->h, PENDING_BYTE, 0, 1, 0);
  }

  /* Update the state of the lock has held in the file descriptor then
  ** return the appropriate result code.
  */
  if( res ){
    rc = SQLITE_OK;
  }else{
    pFile->lastErrno = lastErrno;
    rc = SQLITE_BUSY;
    OSTRACE(("LOCK-FAIL file=%p, wanted=%d, got=%d\n",
             pFile->h, locktype, newLocktype));
  }
  pFile->locktype = (u8)newLocktype;
  OSTRACE(("LOCK file=%p, lock=%d, rc=%s\n",
           pFile->h, pFile->locktype, sqlite3ErrName(rc)));
  return rc;
}

/*
** This routine checks if there is a RESERVED lock held on the specified
** file by this or any other process. If such a lock is held, return
** non-zero, otherwise zero.
*/
static int winCheckReservedLock(sqlite3_file *id, int *pResOut){
  int res;
  winFile *pFile = (winFile*)id;

  SimulateIOError( return SQLITE_IOERR_CHECKRESERVEDLOCK; );
  OSTRACE(("TEST-WR-LOCK file=%p, pResOut=%p\n", pFile->h, pResOut));

  assert( id!=0 );
  if( pFile->locktype>=RESERVED_LOCK ){
    res = 1;
    OSTRACE(("TEST-WR-LOCK file=%p, result=%d (local)\n", pFile->h, res));
  }else{
    res = winLockFile(&pFile->h, SQLITE_LOCKFILEEX_FLAGS,RESERVED_BYTE, 0, 1, 0);
    if( res ){
      winUnlockFile(&pFile->h, RESERVED_BYTE, 0, 1, 0);
    }
    res = !res;
    OSTRACE(("TEST-WR-LOCK file=%p, result=%d (remote)\n", pFile->h, res));
  }
  *pResOut = res;
  OSTRACE(("TEST-WR-LOCK file=%p, pResOut=%p, *pResOut=%d, rc=SQLITE_OK\n",
           pFile->h, pResOut, *pResOut));
  return SQLITE_OK;
}

/*
** Lower the locking level on file descriptor id to locktype.  locktype
** must be either NO_LOCK or SHARED_LOCK.
**
** If the locking level of the file descriptor is already at or below
** the requested locking level, this routine is a no-op.
**
** It is not possible for this routine to fail if the second argument
** is NO_LOCK.  If the second argument is SHARED_LOCK then this routine
** might return SQLITE_IOERR;
*/
static int winUnlock(sqlite3_file *id, int locktype){
  int type;
  winFile *pFile = (winFile*)id;
  int rc = SQLITE_OK;
  assert( pFile!=0 );
  assert( locktype<=SHARED_LOCK );
  OSTRACE(("UNLOCK file=%p, oldLock=%d(%d), newLock=%d\n",
           pFile->h, pFile->locktype, pFile->sharedLockByte, locktype));
  type = pFile->locktype;
  if( type>=EXCLUSIVE_LOCK ){
    winUnlockFile(&pFile->h, SHARED_FIRST, 0, SHARED_SIZE, 0);
    if( locktype==SHARED_LOCK && !winGetReadLock(pFile) ){
      /* This should never happen.  We should always be able to
      ** reacquire the read lock */
      rc = winLogError(SQLITE_IOERR_UNLOCK, osGetLastError(),
                       "winUnlock", pFile->zPath);
    }
  }
  if( type>=RESERVED_LOCK ){
    winUnlockFile(&pFile->h, RESERVED_BYTE, 0, 1, 0);
  }
  if( locktype==NO_LOCK && type>=SHARED_LOCK ){
    winUnlockReadLock(pFile);
  }
  if( type>=PENDING_LOCK ){
    winUnlockFile(&pFile->h, PENDING_BYTE, 0, 1, 0);
  }
  pFile->locktype = (u8)locktype;
  OSTRACE(("UNLOCK file=%p, lock=%d, rc=%s\n",
           pFile->h, pFile->locktype, sqlite3ErrName(rc)));
  return rc;
}

/*
** If *pArg is initially negative then this is a query.  Set *pArg to
** 1 or 0 depending on whether or not bit mask of pFile->ctrlFlags is set.
**
** If *pArg is 0 or 1, then clear or set the mask bit of pFile->ctrlFlags.
*/
static void winModeBit(winFile *pFile, unsigned char mask, int *pArg){
  if( *pArg<0 ){
    *pArg = (pFile->ctrlFlags & mask)!=0;
  }else if( (*pArg)==0 ){
    pFile->ctrlFlags &= ~mask;
  }else{
    pFile->ctrlFlags |= mask;
  }
}

/* Forward references to VFS helper methods used for temporary files */
static int winGetTempname(sqlite3_vfs *, char **);
static int winIsDir(const void *);
static BOOL winIsDriveLetterAndColon(const char *);

/*
** Control and query of the open file handle.
*/
static int winFileControl(sqlite3_file *id, int op, void *pArg){
  winFile *pFile = (winFile*)id;
  OSTRACE(("FCNTL file=%p, op=%d, pArg=%p\n", pFile->h, op, pArg));
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = pFile->locktype;
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_LAST_ERRNO: {
      *(int*)pArg = (int)pFile->lastErrno;
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_CHUNK_SIZE: {
      pFile->szChunk = *(int *)pArg;
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_SIZE_HINT: {
      if( pFile->szChunk>0 ){
        sqlite3_int64 oldSz;
        int rc = winFileSize(id, &oldSz);
        if( rc==SQLITE_OK ){
          sqlite3_int64 newSz = *(sqlite3_int64*)pArg;
          if( newSz>oldSz ){
            SimulateIOErrorBenign(1);
            rc = winTruncate(id, newSz);
            SimulateIOErrorBenign(0);
          }
        }
        OSTRACE(("FCNTL file=%p, rc=%s\n", pFile->h, sqlite3ErrName(rc)));
        return rc;
      }
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_PERSIST_WAL: {
      winModeBit(pFile, WINFILE_PERSIST_WAL, (int*)pArg);
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_POWERSAFE_OVERWRITE: {
      winModeBit(pFile, WINFILE_PSOW, (int*)pArg);
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_VFSNAME: {
      *(char**)pArg = sqlite3_mprintf("%s", pFile->pVfs->zName);
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
    case SQLITE_FCNTL_WIN32_AV_RETRY: {
      int *a = (int*)pArg;
      if( a[0]>0 ){
        winIoerrRetry = a[0];
      }else{
        a[0] = winIoerrRetry;
      }
      if( a[1]>0 ){
        winIoerrRetryDelay = a[1];
      }else{
        a[1] = winIoerrRetryDelay;
      }
      OSTRACE(("FCNTL file=%p, rc=SQLITE_OK\n", pFile->h));
      return SQLITE_OK;
    }
#ifdef SQLITE_TEST
    case SQLITE_FCNTL_WIN32_SET_HANDLE: {
      LPHANDLE phFile = (LPHANDLE)pArg;
      HANDLE hOldFile = pFile->h;
      pFile->h = *phFile;
      *phFile = hOldFile;
      OSTRACE(("FCNTL oldFile=%p, newFile=%p, rc=SQLITE_OK\n",
               hOldFile, pFile->h));
      return SQLITE_OK;
    }
#endif
    case SQLITE_FCNTL_TEMPFILENAME: {
      char *zTFile = 0;
      int rc = winGetTempname(pFile->pVfs, &zTFile);
      if( rc==SQLITE_OK ){
        *(char**)pArg = zTFile;
      }
      OSTRACE(("FCNTL file=%p, rc=%s\n", pFile->h, sqlite3ErrName(rc)));
      return rc;
    }
#if SQLITE_MAX_MMAP_SIZE>0
    case SQLITE_FCNTL_MMAP_SIZE: {
      i64 newLimit = *(i64*)pArg;
      int rc = SQLITE_OK;
      if( newLimit>sqlite3GlobalConfig.mxMmap ){
        newLimit = sqlite3GlobalConfig.mxMmap;
      }
      *(i64*)pArg = pFile->mmapSizeMax;
      if( newLimit>=0 && newLimit!=pFile->mmapSizeMax && pFile->nFetchOut==0 ){
        pFile->mmapSizeMax = newLimit;
        if( pFile->mmapSize>0 ){
          winUnmapfile(pFile);
          rc = winMapfile(pFile, -1);
        }
      }
      OSTRACE(("FCNTL file=%p, rc=%s\n", pFile->h, sqlite3ErrName(rc)));
      return rc;
    }
#endif
  }
  OSTRACE(("FCNTL file=%p, rc=SQLITE_NOTFOUND\n", pFile->h));
  return SQLITE_NOTFOUND;
}

/*
** Return the sector size in bytes of the underlying block device for
** the specified file. This is almost always 512 bytes, but may be
** larger for some devices.
**
** SQLite code assumes this function cannot fail. It also assumes that
** if two files are created in the same file-system directory (i.e.
** a database and its journal file) that the sector size will be the
** same for both.
*/
static int winSectorSize(sqlite3_file *id){
  (void)id;
  return SQLITE_DEFAULT_SECTOR_SIZE;
}

/*
** Return a vector of device characteristics.
*/
static int winDeviceCharacteristics(sqlite3_file *id){
  winFile *p = (winFile*)id;
  return SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN |
         ((p->ctrlFlags & WINFILE_PSOW)?SQLITE_IOCAP_POWERSAFE_OVERWRITE:0);
}

/*
** Windows will only let you create file view mappings
** on allocation size granularity boundaries.
** During sqlite3_os_init() we do a GetSystemInfo()
** to get the granularity size.
*/
static SYSTEM_INFO winSysInfo;

#ifndef SQLITE_OMIT_WAL

/*
** Helper functions to obtain and relinquish the global mutex. The
** global mutex is used to protect the winLockInfo objects used by
** this file, all of which may be shared by multiple threads.
**
** Function winShmMutexHeld() is used to assert() that the global mutex
** is held when required. This function is only used as part of assert()
** statements. e.g.
**
**   winShmEnterMutex()
**     assert( winShmMutexHeld() );
**   winShmLeaveMutex()
*/
static void winShmEnterMutex(void){
  sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}
static void winShmLeaveMutex(void){
  sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}
#ifndef NDEBUG
static int winShmMutexHeld(void) {
  return sqlite3_mutex_held(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1));
}
#endif

/*
** Object used to represent a single file opened and mmapped to provide
** shared memory.  When multiple threads all reference the same
** log-summary, each thread has its own winFile object, but they all
** point to a single instance of this object.  In other words, each
** log-summary is opened only once per process.
**
** winShmMutexHeld() must be true when creating or destroying
** this object or while reading or writing the following fields:
**
**      nRef
**      pNext
**
** The following fields are read-only after the object is created:
**
**      fid
**      zFilename
**
** Either winShmNode.mutex must be held or winShmNode.nRef==0 and
** winShmMutexHeld() is true when reading or writing any other field
** in this structure.
**
*/
struct winShmNode {
  sqlite3_mutex *mutex;      /* Mutex to access this object */
  char *zFilename;           /* Name of the file */
  winFile hFile;             /* File handle from winOpen */

  int szRegion;              /* Size of shared-memory regions */
  int nRegion;               /* Size of array apRegion */
  struct ShmRegion {
    HANDLE hMap;             /* File handle from CreateFileMapping */
    void *pMap;
  } *aRegion;
  DWORD lastErrno;           /* The Windows errno from the last I/O error */

  int nRef;                  /* Number of winShm objects pointing to this */
  winShm *pFirst;            /* All winShm objects pointing to this */
  winShmNode *pNext;         /* Next in list of all winShmNode objects */
#if defined(SQLITE_DEBUG) || defined(SQLITE_HAVE_OS_TRACE)
  u8 nextShmId;              /* Next available winShm.id value */
#endif
};

/*
** A global array of all winShmNode objects.
**
** The winShmMutexHeld() must be true while reading or writing this list.
*/
static winShmNode *winShmNodeList = 0;

/*
** Structure used internally by this VFS to record the state of an
** open shared memory connection.
**
** The following fields are initialized when this object is created and
** are read-only thereafter:
**
**    winShm.pShmNode
**    winShm.id
**
** All other fields are read/write.  The winShm.pShmNode->mutex must be held
** while accessing any read/write fields.
*/
struct winShm {
  winShmNode *pShmNode;      /* The underlying winShmNode object */
  winShm *pNext;             /* Next winShm with the same winShmNode */
  u8 hasMutex;               /* True if holding the winShmNode mutex */
  u16 sharedMask;            /* Mask of shared locks held */
  u16 exclMask;              /* Mask of exclusive locks held */
#if defined(SQLITE_DEBUG) || defined(SQLITE_HAVE_OS_TRACE)
  u8 id;                     /* Id of this connection with its winShmNode */
#endif
};

/*
** Constants used for locking
*/
#define WIN_SHM_BASE   ((22+SQLITE_SHM_NLOCK)*4)        /* first lock byte */
#define WIN_SHM_DMS    (WIN_SHM_BASE+SQLITE_SHM_NLOCK)  /* deadman switch */

/*
** Apply advisory locks for all n bytes beginning at ofst.
*/
#define _SHM_UNLCK  1
#define _SHM_RDLCK  2
#define _SHM_WRLCK  3
static int winShmSystemLock(
  winShmNode *pFile,    /* Apply locks to this open shared-memory segment */
  int lockType,         /* _SHM_UNLCK, _SHM_RDLCK, or _SHM_WRLCK */
  int ofst,             /* Offset to first byte to be locked/unlocked */
  int nByte             /* Number of bytes to lock or unlock */
){
  int rc = 0;           /* Result code form Lock/UnlockFileEx() */

  /* Access to the winShmNode object is serialized by the caller */
  assert( sqlite3_mutex_held(pFile->mutex) || pFile->nRef==0 );

  OSTRACE(("SHM-LOCK file=%p, lock=%d, offset=%d, size=%d\n",
           pFile->hFile.h, lockType, ofst, nByte));

  /* Release/Acquire the system-level lock */
  if( lockType==_SHM_UNLCK ){
    rc = winUnlockFile(&pFile->hFile.h, ofst, 0, nByte, 0);
  }else{
    /* Initialize the locking parameters */
    DWORD dwFlags = LOCKFILE_FAIL_IMMEDIATELY;
    if( lockType == _SHM_WRLCK ) dwFlags |= LOCKFILE_EXCLUSIVE_LOCK;
    rc = winLockFile(&pFile->hFile.h, dwFlags, ofst, 0, nByte, 0);
  }

  if( rc!= 0 ){
    rc = SQLITE_OK;
  }else{
    pFile->lastErrno =  osGetLastError();
    rc = SQLITE_BUSY;
  }

  OSTRACE(("SHM-LOCK file=%p, func=%s, errno=%lu, rc=%s\n",
           pFile->hFile.h, (lockType == _SHM_UNLCK) ? "winUnlockFile" :
           "winLockFile", pFile->lastErrno, sqlite3ErrName(rc)));

  return rc;
}

/* Forward references to VFS methods */
static int winOpen(sqlite3_vfs*,const char*,sqlite3_file*,int,int*);
static int winDelete(sqlite3_vfs *,const char*,int);

/*
** Purge the winShmNodeList list of all entries with winShmNode.nRef==0.
**
** This is not a VFS shared-memory method; it is a utility function called
** by VFS shared-memory methods.
*/
static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
  winShmNode **pp;
  winShmNode *p;
  assert( winShmMutexHeld() );
  OSTRACE(("SHM-PURGE pid=%lu, deleteFlag=%d\n",
           osGetCurrentProcessId(), deleteFlag));
  pp = &winShmNodeList;
  while( (p = *pp)!=0 ){
    if( p->nRef==0 ){
      int i;
      if( p->mutex ){ sqlite3_mutex_free(p->mutex); }
      for(i=0; i<p->nRegion; i++){
        BOOL bRc = osUnmapViewOfFile(p->aRegion[i].pMap);
        OSTRACE(("SHM-PURGE-UNMAP pid=%lu, region=%d, rc=%s\n",
                 osGetCurrentProcessId(), i, bRc ? "ok" : "failed"));
        UNUSED_VARIABLE_VALUE(bRc);
        bRc = osCloseHandle(p->aRegion[i].hMap);
        OSTRACE(("SHM-PURGE-CLOSE pid=%lu, region=%d, rc=%s\n",
                 osGetCurrentProcessId(), i, bRc ? "ok" : "failed"));
        UNUSED_VARIABLE_VALUE(bRc);
      }
      if( p->hFile.h!=NULL && p->hFile.h!=INVALID_HANDLE_VALUE ){
        SimulateIOErrorBenign(1);
        winClose((sqlite3_file *)&p->hFile);
        SimulateIOErrorBenign(0);
      }
      if( deleteFlag ){
        SimulateIOErrorBenign(1);
        winDelete(pVfs, p->zFilename, 0);
        SimulateIOErrorBenign(0);
      }
      *pp = p->pNext;
      sqlite3_free(p->aRegion);
      sqlite3_free(p);
    }else{
      pp = &p->pNext;
    }
  }
}

/*
** Open the shared-memory area associated with database file pDbFd.
**
** When opening a new shared-memory file, if no other instances of that
** file are currently open, in this process or in other processes, then
** the file must be truncated to zero length or have its header cleared.
*/
static int winOpenSharedMemory(winFile *pDbFd){
  struct winShm *p;                  /* The connection to be opened */
  struct winShmNode *pShmNode = 0;   /* The underlying mmapped file */
  int rc;                            /* Result code */
  struct winShmNode *pNew;           /* Newly allocated winShmNode */
  int nName;                         /* Size of zName in bytes */

  assert( pDbFd->pShm==0 );    /* Not previously opened */

  /* Allocate space for the new sqlite3_shm object.  Also speculatively
  ** allocate space for a new winShmNode and filename.
  */
  p = sqlite3MallocZero( sizeof(*p) );
  if( p==0 ) return SQLITE_IOERR_NOMEM;
  nName = sqlite3Strlen30(pDbFd->zPath);
  pNew = sqlite3MallocZero( sizeof(*pShmNode) + nName + 17 );
  if( pNew==0 ){
    sqlite3_free(p);
    return SQLITE_IOERR_NOMEM;
  }
  pNew->zFilename = (char*)&pNew[1];
  sqlite3_snprintf(nName+15, pNew->zFilename, "%s-shm", pDbFd->zPath);

  /* Look to see if there is an existing winShmNode that can be used.
  ** If no matching winShmNode currently exists, create a new one.
  */
  winShmEnterMutex();
  for(pShmNode = winShmNodeList; pShmNode; pShmNode=pShmNode->pNext){
    /* TBD need to come up with better match here.  Perhaps
    ** use FILE_ID_BOTH_DIR_INFO Structure.
    */
    if( sqlite3StrICmp(pShmNode->zFilename, pNew->zFilename)==0 ) break;
  }
  if( pShmNode ){
    sqlite3_free(pNew);
  }else{
    pShmNode = pNew;
    pNew = 0;
    ((winFile*)(&pShmNode->hFile))->h = INVALID_HANDLE_VALUE;
    pShmNode->pNext = winShmNodeList;
    winShmNodeList = pShmNode;

    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_IOERR_NOMEM;
      goto shm_open_err;
    }

    rc = winOpen(pDbFd->pVfs,
                 pShmNode->zFilename,             /* Name of the file (UTF-8) */
                 (sqlite3_file*)&pShmNode->hFile,  /* File handle here */
                 SQLITE_OPEN_WAL | SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE,
                 0);
    if( SQLITE_OK!=rc ){
      goto shm_open_err;
    }

    /* Check to see if another process is holding the dead-man switch.
    ** If not, truncate the file to zero length.
    */
    if( winShmSystemLock(pShmNode, _SHM_WRLCK, WIN_SHM_DMS, 1)==SQLITE_OK ){
      rc = winTruncate((sqlite3_file *)&pShmNode->hFile, 0);
      if( rc!=SQLITE_OK ){
        rc = winLogError(SQLITE_IOERR_SHMOPEN, osGetLastError(),
                         "winOpenShm", pDbFd->zPath);
      }
    }
    if( rc==SQLITE_OK ){
      winShmSystemLock(pShmNode, _SHM_UNLCK, WIN_SHM_DMS, 1);
      rc = winShmSystemLock(pShmNode, _SHM_RDLCK, WIN_SHM_DMS, 1);
    }
    if( rc ) goto shm_open_err;
  }

  /* Make the new connection a child of the winShmNode */
  p->pShmNode = pShmNode;
#if defined(SQLITE_DEBUG) || defined(SQLITE_HAVE_OS_TRACE)
  p->id = pShmNode->nextShmId++;
#endif
  pShmNode->nRef++;
  pDbFd->pShm = p;
  winShmLeaveMutex();

  /* The reference count on pShmNode has already been incremented under
  ** the cover of the winShmEnterMutex() mutex and the pointer from the
  ** new (struct winShm) object to the pShmNode has been set. All that is
  ** left to do is to link the new object into the linked list starting
  ** at pShmNode->pFirst. This must be done while holding the pShmNode->mutex
  ** mutex.
  */
  sqlite3_mutex_enter(pShmNode->mutex);
  p->pNext = pShmNode->pFirst;
  pShmNode->pFirst = p;
  sqlite3_mutex_leave(pShmNode->mutex);
  return SQLITE_OK;

  /* Jump here on any error */
shm_open_err:
  winShmSystemLock(pShmNode, _SHM_UNLCK, WIN_SHM_DMS, 1);
  winShmPurge(pDbFd->pVfs, 0);      /* This call frees pShmNode if required */
  sqlite3_free(p);
  sqlite3_free(pNew);
  winShmLeaveMutex();
  return rc;
}

/*
** Close a connection to shared-memory.  Delete the underlying
** storage if deleteFlag is true.
*/
static int winShmUnmap(
  sqlite3_file *fd,          /* Database holding shared memory */
  int deleteFlag             /* Delete after closing if true */
){
  winFile *pDbFd;       /* Database holding shared-memory */
  winShm *p;            /* The connection to be closed */
  winShmNode *pShmNode; /* The underlying shared-memory file */
  winShm **pp;          /* For looping over sibling connections */

  pDbFd = (winFile*)fd;
  p = pDbFd->pShm;
  if( p==0 ) return SQLITE_OK;
  pShmNode = p->pShmNode;

  /* Remove connection p from the set of connections associated
  ** with pShmNode */
  sqlite3_mutex_enter(pShmNode->mutex);
  for(pp=&pShmNode->pFirst; (*pp)!=p; pp = &(*pp)->pNext){}
  *pp = p->pNext;

  /* Free the connection p */
  sqlite3_free(p);
  pDbFd->pShm = 0;
  sqlite3_mutex_leave(pShmNode->mutex);

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  winShmEnterMutex();
  assert( pShmNode->nRef>0 );
  pShmNode->nRef--;
  if( pShmNode->nRef==0 ){
    winShmPurge(pDbFd->pVfs, deleteFlag);
  }
  winShmLeaveMutex();

  return SQLITE_OK;
}

/*
** Change the lock state for a shared-memory segment.
*/
static int winShmLock(
  sqlite3_file *fd,          /* Database file holding the shared memory */
  int ofst,                  /* First lock to acquire or release */
  int n,                     /* Number of locks to acquire or release */
  int flags                  /* What to do with the lock */
){
  winFile *pDbFd = (winFile*)fd;        /* Connection holding shared memory */
  winShm *p = pDbFd->pShm;              /* The shared memory being locked */
  winShm *pX;                           /* For looping over all siblings */
  winShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;                   /* Result code */
  u16 mask;                             /* Mask of locks to take or release */

  assert( ofst>=0 && ofst+n<=SQLITE_SHM_NLOCK );
  assert( n>=1 );
  assert( flags==(SQLITE_SHM_LOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED)
       || flags==(SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE) );
  assert( n==1 || (flags & SQLITE_SHM_EXCLUSIVE)!=0 );

  mask = (u16)((1U<<(ofst+n)) - (1U<<ofst));
  assert( n>1 || mask==(1<<ofst) );
  sqlite3_mutex_enter(pShmNode->mutex);
  if( flags & SQLITE_SHM_UNLOCK ){
    u16 allMask = 0; /* Mask of locks held by siblings */

    /* See if any siblings hold this same lock */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( pX==p ) continue;
      assert( (pX->exclMask & (p->exclMask|p->sharedMask))==0 );
      allMask |= pX->sharedMask;
    }

    /* Unlock the system-level locks */
    if( (mask & allMask)==0 ){
      rc = winShmSystemLock(pShmNode, _SHM_UNLCK, ofst+WIN_SHM_BASE, n);
    }else{
      rc = SQLITE_OK;
    }

    /* Undo the local locks */
    if( rc==SQLITE_OK ){
      p->exclMask &= ~mask;
      p->sharedMask &= ~mask;
    }
  }else if( flags & SQLITE_SHM_SHARED ){
    u16 allShared = 0;  /* Union of locks held by connections other than "p" */

    /* Find out which shared locks are already held by sibling connections.
    ** If any sibling already holds an exclusive lock, go ahead and return
    ** SQLITE_BUSY.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
      allShared |= pX->sharedMask;
    }

    /* Get shared locks at the system level, if necessary */
    if( rc==SQLITE_OK ){
      if( (allShared & mask)==0 ){
        rc = winShmSystemLock(pShmNode, _SHM_RDLCK, ofst+WIN_SHM_BASE, n);
      }else{
        rc = SQLITE_OK;
      }
    }

    /* Get the local shared locks */
    if( rc==SQLITE_OK ){
      p->sharedMask |= mask;
    }
  }else{
    /* Make sure no sibling connections hold locks that will block this
    ** lock.  If any do, return SQLITE_BUSY right away.
    */
    for(pX=pShmNode->pFirst; pX; pX=pX->pNext){
      if( (pX->exclMask & mask)!=0 || (pX->sharedMask & mask)!=0 ){
        rc = SQLITE_BUSY;
        break;
      }
    }

    /* Get the exclusive locks at the system level.  Then if successful
    ** also mark the local connection as being locked.
    */
    if( rc==SQLITE_OK ){
      rc = winShmSystemLock(pShmNode, _SHM_WRLCK, ofst+WIN_SHM_BASE, n);
      if( rc==SQLITE_OK ){
        assert( (p->sharedMask & mask)==0 );
        p->exclMask |= mask;
      }
    }
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  OSTRACE(("SHM-LOCK pid=%lu, id=%d, sharedMask=%03x, exclMask=%03x, rc=%s\n",
           osGetCurrentProcessId(), p->id, p->sharedMask, p->exclMask,
           sqlite3ErrName(rc)));
  return rc;
}

/*
** Implement a memory barrier or memory fence on shared memory.
**
** All loads and stores begun before the barrier must complete before
** any load or store begun after the barrier.
*/
static void winShmBarrier(
  sqlite3_file *fd          /* Database holding the shared memory */
){
  UNUSED_PARAMETER(fd);
  sqlite3MemoryBarrier();   /* compiler-defined memory barrier */
  winShmEnterMutex();       /* Also mutex, for redundancy */
  winShmLeaveMutex();
}

/*
** This function is called to obtain a pointer to region iRegion of the
** shared-memory associated with the database file fd. Shared-memory regions
** are numbered starting from zero. Each shared-memory region is szRegion
** bytes in size.
**
** If an error occurs, an error code is returned and *pp is set to NULL.
**
** Otherwise, if the isWrite parameter is 0 and the requested shared-memory
** region has not been allocated (by any client, including one running in a
** separate process), then *pp is set to NULL and SQLITE_OK returned. If
** isWrite is non-zero and the requested shared-memory region has not yet
** been allocated, it is allocated by this function.
**
** If the shared-memory region has already been allocated or is allocated by
** this call as described above, then it is mapped into this processes
** address space (if it is not already), *pp is set to point to the mapped
** memory and SQLITE_OK returned.
*/
static int winShmMap(
  sqlite3_file *fd,               /* Handle open on database file */
  int iRegion,                    /* Region to retrieve */
  int szRegion,                   /* Size of regions */
  int isWrite,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  winFile *pDbFd = (winFile*)fd;
  winShm *pShm = pDbFd->pShm;
  winShmNode *pShmNode;
  int rc = SQLITE_OK;

  if( !pShm ){
    rc = winOpenSharedMemory(pDbFd);
    if( rc!=SQLITE_OK ) return rc;
    pShm = pDbFd->pShm;
  }
  pShmNode = pShm->pShmNode;

  sqlite3_mutex_enter(pShmNode->mutex);
  assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );

  if( pShmNode->nRegion<=iRegion ){
    struct ShmRegion *apNew;           /* New aRegion[] array */
    int nByte = (iRegion+1)*szRegion;  /* Minimum required file size */
    sqlite3_int64 sz;                  /* Current size of wal-index file */

    pShmNode->szRegion = szRegion;

    /* The requested region is not mapped into this processes address space.
    ** Check to see if it has been allocated (i.e. if the wal-index file is
    ** large enough to contain the requested region).
    */
    rc = winFileSize((sqlite3_file *)&pShmNode->hFile, &sz);
    if( rc!=SQLITE_OK ){
      rc = winLogError(SQLITE_IOERR_SHMSIZE, osGetLastError(),
                       "winShmMap1", pDbFd->zPath);
      goto shmpage_out;
    }

    if( sz<nByte ){
      /* The requested memory region does not exist. If isWrite is set to
      ** zero, exit early. *pp will be set to NULL and SQLITE_OK returned.
      **
      ** Alternatively, if isWrite is non-zero, use ftruncate() to allocate
      ** the requested memory region.
      */
      if( !isWrite ) goto shmpage_out;
      rc = winTruncate((sqlite3_file *)&pShmNode->hFile, nByte);
      if( rc!=SQLITE_OK ){
        rc = winLogError(SQLITE_IOERR_SHMSIZE, osGetLastError(),
                         "winShmMap2", pDbFd->zPath);
        goto shmpage_out;
      }
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (struct ShmRegion *)sqlite3_realloc64(
        pShmNode->aRegion, (iRegion+1)*sizeof(apNew[0])
    );
    if( !apNew ){
      rc = SQLITE_IOERR_NOMEM;
      goto shmpage_out;
    }
    pShmNode->aRegion = apNew;

    while( pShmNode->nRegion<=iRegion ){
      HANDLE hMap = NULL;         /* file-mapping handle */
      void *pMap = 0;             /* Mapped memory region */

#if SQLITE_OS_WINRT
      hMap = osCreateFileMappingFromApp(pShmNode->hFile.h,
          NULL, PAGE_READWRITE, nByte, NULL
      );
#elif defined(SQLITE_WIN32_HAS_WIDE)
      hMap = osCreateFileMappingW(pShmNode->hFile.h,
          NULL, PAGE_READWRITE, 0, nByte, NULL
      );
#elif defined(SQLITE_WIN32_HAS_ANSI)
      hMap = osCreateFileMappingA(pShmNode->hFile.h,
          NULL, PAGE_READWRITE, 0, nByte, NULL
      );
#endif
      OSTRACE(("SHM-MAP-CREATE pid=%lu, region=%d, size=%d, rc=%s\n",
               osGetCurrentProcessId(), pShmNode->nRegion, nByte,
               hMap ? "ok" : "failed"));
      if( hMap ){
        int iOffset = pShmNode->nRegion*szRegion;
        int iOffsetShift = iOffset % winSysInfo.dwAllocationGranularity;
#if SQLITE_OS_WINRT
        pMap = osMapViewOfFileFromApp(hMap, FILE_MAP_WRITE | FILE_MAP_READ,
            iOffset - iOffsetShift, szRegion + iOffsetShift
        );
#else
        pMap = osMapViewOfFile(hMap, FILE_MAP_WRITE | FILE_MAP_READ,
            0, iOffset - iOffsetShift, szRegion + iOffsetShift
        );
#endif
        OSTRACE(("SHM-MAP-MAP pid=%lu, region=%d, offset=%d, size=%d, rc=%s\n",
                 osGetCurrentProcessId(), pShmNode->nRegion, iOffset,
                 szRegion, pMap ? "ok" : "failed"));
      }
      if( !pMap ){
        pShmNode->lastErrno = osGetLastError();
        rc = winLogError(SQLITE_IOERR_SHMMAP, pShmNode->lastErrno,
                         "winShmMap3", pDbFd->zPath);
        if( hMap ) osCloseHandle(hMap);
        goto shmpage_out;
      }

      pShmNode->aRegion[pShmNode->nRegion].pMap = pMap;
      pShmNode->aRegion[pShmNode->nRegion].hMap = hMap;
      pShmNode->nRegion++;
    }
  }

shmpage_out:
  if( pShmNode->nRegion>iRegion ){
    int iOffset = iRegion*szRegion;
    int iOffsetShift = iOffset % winSysInfo.dwAllocationGranularity;
    char *p = (char *)pShmNode->aRegion[iRegion].pMap;
    *pp = (void *)&p[iOffsetShift];
  }else{
    *pp = 0;
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  return rc;
}

#else
# define winShmMap     0
# define winShmLock    0
# define winShmBarrier 0
# define winShmUnmap   0
#endif /* #ifndef SQLITE_OMIT_WAL */

/*
** Cleans up the mapped region of the specified file, if any.
*/
#if SQLITE_MAX_MMAP_SIZE>0
static int winUnmapfile(winFile *pFile){
  assert( pFile!=0 );
  OSTRACE(("UNMAP-FILE pid=%lu, pFile=%p, hMap=%p, pMapRegion=%p, "
           "mmapSize=%lld, mmapSizeActual=%lld, mmapSizeMax=%lld\n",
           osGetCurrentProcessId(), pFile, pFile->hMap, pFile->pMapRegion,
           pFile->mmapSize, pFile->mmapSizeActual, pFile->mmapSizeMax));
  if( pFile->pMapRegion ){
    if( !osUnmapViewOfFile(pFile->pMapRegion) ){
      pFile->lastErrno = osGetLastError();
      OSTRACE(("UNMAP-FILE pid=%lu, pFile=%p, pMapRegion=%p, "
               "rc=SQLITE_IOERR_MMAP\n", osGetCurrentProcessId(), pFile,
               pFile->pMapRegion));
      return winLogError(SQLITE_IOERR_MMAP, pFile->lastErrno,
                         "winUnmapfile1", pFile->zPath);
    }
    pFile->pMapRegion = 0;
    pFile->mmapSize = 0;
    pFile->mmapSizeActual = 0;
  }
  if( pFile->hMap!=NULL ){
    if( !osCloseHandle(pFile->hMap) ){
      pFile->lastErrno = osGetLastError();
      OSTRACE(("UNMAP-FILE pid=%lu, pFile=%p, hMap=%p, rc=SQLITE_IOERR_MMAP\n",
               osGetCurrentProcessId(), pFile, pFile->hMap));
      return winLogError(SQLITE_IOERR_MMAP, pFile->lastErrno,
                         "winUnmapfile2", pFile->zPath);
    }
    pFile->hMap = NULL;
  }
  OSTRACE(("UNMAP-FILE pid=%lu, pFile=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), pFile));
  return SQLITE_OK;
}

/*
** Memory map or remap the file opened by file-descriptor pFd (if the file
** is already mapped, the existing mapping is replaced by the new). Or, if
** there already exists a mapping for this file, and there are still
** outstanding xFetch() references to it, this function is a no-op.
**
** If parameter nByte is non-negative, then it is the requested size of
** the mapping to create. Otherwise, if nByte is less than zero, then the
** requested size is the size of the file on disk. The actual size of the
** created mapping is either the requested size or the value configured
** using SQLITE_FCNTL_MMAP_SIZE, whichever is smaller.
**
** SQLITE_OK is returned if no error occurs (even if the mapping is not
** recreated as a result of outstanding references) or an SQLite error
** code otherwise.
*/
static int winMapfile(winFile *pFd, sqlite3_int64 nByte){
  sqlite3_int64 nMap = nByte;
  int rc;

  assert( nMap>=0 || pFd->nFetchOut==0 );
  OSTRACE(("MAP-FILE pid=%lu, pFile=%p, size=%lld\n",
           osGetCurrentProcessId(), pFd, nByte));

  if( pFd->nFetchOut>0 ) return SQLITE_OK;

  if( nMap<0 ){
    rc = winFileSize((sqlite3_file*)pFd, &nMap);
    if( rc ){
      OSTRACE(("MAP-FILE pid=%lu, pFile=%p, rc=SQLITE_IOERR_FSTAT\n",
               osGetCurrentProcessId(), pFd));
      return SQLITE_IOERR_FSTAT;
    }
  }
  if( nMap>pFd->mmapSizeMax ){
    nMap = pFd->mmapSizeMax;
  }
  nMap &= ~(sqlite3_int64)(winSysInfo.dwPageSize - 1);

  if( nMap==0 && pFd->mmapSize>0 ){
    winUnmapfile(pFd);
  }
  if( nMap!=pFd->mmapSize ){
    void *pNew = 0;
    DWORD protect = PAGE_READONLY;
    DWORD flags = FILE_MAP_READ;

    winUnmapfile(pFd);
    if( (pFd->ctrlFlags & WINFILE_RDONLY)==0 ){
      protect = PAGE_READWRITE;
      flags |= FILE_MAP_WRITE;
    }
#if SQLITE_OS_WINRT
    pFd->hMap = osCreateFileMappingFromApp(pFd->h, NULL, protect, nMap, NULL);
#elif defined(SQLITE_WIN32_HAS_WIDE)
    pFd->hMap = osCreateFileMappingW(pFd->h, NULL, protect,
                                (DWORD)((nMap>>32) & 0xffffffff),
                                (DWORD)(nMap & 0xffffffff), NULL);
#elif defined(SQLITE_WIN32_HAS_ANSI)
    pFd->hMap = osCreateFileMappingA(pFd->h, NULL, protect,
                                (DWORD)((nMap>>32) & 0xffffffff),
                                (DWORD)(nMap & 0xffffffff), NULL);
#endif
    if( pFd->hMap==NULL ){
      pFd->lastErrno = osGetLastError();
      rc = winLogError(SQLITE_IOERR_MMAP, pFd->lastErrno,
                       "winMapfile1", pFd->zPath);
      /* Log the error, but continue normal operation using xRead/xWrite */
      OSTRACE(("MAP-FILE-CREATE pid=%lu, pFile=%p, rc=%s\n",
               osGetCurrentProcessId(), pFd, sqlite3ErrName(rc)));
      return SQLITE_OK;
    }
    assert( (nMap % winSysInfo.dwPageSize)==0 );
    assert( sizeof(SIZE_T)==sizeof(sqlite3_int64) || nMap<=0xffffffff );
#if SQLITE_OS_WINRT
    pNew = osMapViewOfFileFromApp(pFd->hMap, flags, 0, (SIZE_T)nMap);
#else
    pNew = osMapViewOfFile(pFd->hMap, flags, 0, 0, (SIZE_T)nMap);
#endif
    if( pNew==NULL ){
      osCloseHandle(pFd->hMap);
      pFd->hMap = NULL;
      pFd->lastErrno = osGetLastError();
      rc = winLogError(SQLITE_IOERR_MMAP, pFd->lastErrno,
                       "winMapfile2", pFd->zPath);
      /* Log the error, but continue normal operation using xRead/xWrite */
      OSTRACE(("MAP-FILE-MAP pid=%lu, pFile=%p, rc=%s\n",
               osGetCurrentProcessId(), pFd, sqlite3ErrName(rc)));
      return SQLITE_OK;
    }
    pFd->pMapRegion = pNew;
    pFd->mmapSize = nMap;
    pFd->mmapSizeActual = nMap;
  }

  OSTRACE(("MAP-FILE pid=%lu, pFile=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), pFd));
  return SQLITE_OK;
}
#endif /* SQLITE_MAX_MMAP_SIZE>0 */

/*
** If possible, return a pointer to a mapping of file fd starting at offset
** iOff. The mapping must be valid for at least nAmt bytes.
**
** If such a pointer can be obtained, store it in *pp and return SQLITE_OK.
** Or, if one cannot but no error occurs, set *pp to 0 and return SQLITE_OK.
** Finally, if an error does occur, return an SQLite error code. The final
** value of *pp is undefined in this case.
**
** If this function does return a pointer, the caller must eventually
** release the reference by calling winUnfetch().
*/
static int winFetch(sqlite3_file *fd, i64 iOff, int nAmt, void **pp){
#if SQLITE_MAX_MMAP_SIZE>0
  winFile *pFd = (winFile*)fd;   /* The underlying database file */
#endif
  *pp = 0;

  OSTRACE(("FETCH pid=%lu, pFile=%p, offset=%lld, amount=%d, pp=%p\n",
           osGetCurrentProcessId(), fd, iOff, nAmt, pp));

#if SQLITE_MAX_MMAP_SIZE>0
  if( pFd->mmapSizeMax>0 ){
    if( pFd->pMapRegion==0 ){
      int rc = winMapfile(pFd, -1);
      if( rc!=SQLITE_OK ){
        OSTRACE(("FETCH pid=%lu, pFile=%p, rc=%s\n",
                 osGetCurrentProcessId(), pFd, sqlite3ErrName(rc)));
        return rc;
      }
    }
    if( pFd->mmapSize >= iOff+nAmt ){
      *pp = &((u8 *)pFd->pMapRegion)[iOff];
      pFd->nFetchOut++;
    }
  }
#endif

  OSTRACE(("FETCH pid=%lu, pFile=%p, pp=%p, *pp=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), fd, pp, *pp));
  return SQLITE_OK;
}

/*
** If the third argument is non-NULL, then this function releases a
** reference obtained by an earlier call to winFetch(). The second
** argument passed to this function must be the same as the corresponding
** argument that was passed to the winFetch() invocation.
**
** Or, if the third argument is NULL, then this function is being called
** to inform the VFS layer that, according to POSIX, any existing mapping
** may now be invalid and should be unmapped.
*/
static int winUnfetch(sqlite3_file *fd, i64 iOff, void *p){
#if SQLITE_MAX_MMAP_SIZE>0
  winFile *pFd = (winFile*)fd;   /* The underlying database file */

  /* If p==0 (unmap the entire file) then there must be no outstanding
  ** xFetch references. Or, if p!=0 (meaning it is an xFetch reference),
  ** then there must be at least one outstanding.  */
  assert( (p==0)==(pFd->nFetchOut==0) );

  /* If p!=0, it must match the iOff value. */
  assert( p==0 || p==&((u8 *)pFd->pMapRegion)[iOff] );

  OSTRACE(("UNFETCH pid=%lu, pFile=%p, offset=%lld, p=%p\n",
           osGetCurrentProcessId(), pFd, iOff, p));

  if( p ){
    pFd->nFetchOut--;
  }else{
    /* FIXME:  If Windows truly always prevents truncating or deleting a
    ** file while a mapping is held, then the following winUnmapfile() call
    ** is unnecessary can be omitted - potentially improving
    ** performance.  */
    winUnmapfile(pFd);
  }

  assert( pFd->nFetchOut>=0 );
#endif

  OSTRACE(("UNFETCH pid=%lu, pFile=%p, rc=SQLITE_OK\n",
           osGetCurrentProcessId(), fd));
  return SQLITE_OK;
}

/*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/

/*
** This vector defines all the methods that can operate on an
** sqlite3_file for win32.
*/
static const sqlite3_io_methods winIoMethod = {
  3,                              /* iVersion */
  winClose,                       /* xClose */
  winRead,                        /* xRead */
  winWrite,                       /* xWrite */
  winTruncate,                    /* xTruncate */
  winSync,                        /* xSync */
  winFileSize,                    /* xFileSize */
  winLock,                        /* xLock */
  winUnlock,                      /* xUnlock */
  winCheckReservedLock,           /* xCheckReservedLock */
  winFileControl,                 /* xFileControl */
  winSectorSize,                  /* xSectorSize */
  winDeviceCharacteristics,       /* xDeviceCharacteristics */
  winShmMap,                      /* xShmMap */
  winShmLock,                     /* xShmLock */
  winShmBarrier,                  /* xShmBarrier */
  winShmUnmap,                    /* xShmUnmap */
  winFetch,                       /* xFetch */
  winUnfetch                      /* xUnfetch */
};

/****************************************************************************
**************************** sqlite3_vfs methods ****************************
**
** This division contains the implementation of methods on the
** sqlite3_vfs object.
*/

#if defined(__CYGWIN__)
/*
** Convert a filename from whatever the underlying operating system
** supports for filenames into UTF-8.  Space to hold the result is
** obtained from malloc and must be freed by the calling function.
*/
static char *winConvertToUtf8Filename(const void *zFilename){
  char *zConverted = 0;
  if( osIsNT() ){
    zConverted = winUnicodeToUtf8(zFilename);
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    zConverted = sqlite3_win32_mbcs_to_utf8(zFilename);
  }
#endif
  /* caller will handle out of memory */
  return zConverted;
}
#endif

/*
** Convert a UTF-8 filename into whatever form the underlying
** operating system wants filenames in.  Space to hold the result
** is obtained from malloc and must be freed by the calling
** function.
*/
static void *winConvertFromUtf8Filename(const char *zFilename){
  void *zConverted = 0;
  if( osIsNT() ){
    zConverted = winUtf8ToUnicode(zFilename);
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    zConverted = sqlite3_win32_utf8_to_mbcs(zFilename);
  }
#endif
  /* caller will handle out of memory */
  return zConverted;
}

/*
** This function returns non-zero if the specified UTF-8 string buffer
** ends with a directory separator character or one was successfully
** added to it.
*/
static int winMakeEndInDirSep(int nBuf, char *zBuf){
  if( zBuf ){
    int nLen = sqlite3Strlen30(zBuf);
    if( nLen>0 ){
      if( winIsDirSep(zBuf[nLen-1]) ){
        return 1;
      }else if( nLen+1<nBuf ){
        zBuf[nLen] = winGetDirSep();
        zBuf[nLen+1] = '\0';
        return 1;
      }
    }
  }
  return 0;
}

/*
** Create a temporary file name and store the resulting pointer into pzBuf.
** The pointer returned in pzBuf must be freed via sqlite3_free().
*/
static int winGetTempname(sqlite3_vfs *pVfs, char **pzBuf){
  static char zChars[] =
    "abcdefghijklmnopqrstuvwxyz"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "0123456789";
  size_t i, j;
  int nPre = sqlite3Strlen30(SQLITE_TEMP_FILE_PREFIX);
  int nMax, nBuf, nDir, nLen;
  char *zBuf;

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing.
  */
  SimulateIOError( return SQLITE_IOERR );

  /* Allocate a temporary buffer to store the fully qualified file
  ** name for the temporary file.  If this fails, we cannot continue.
  */
  nMax = pVfs->mxPathname; nBuf = nMax + 2;
  zBuf = sqlite3MallocZero( nBuf );
  if( !zBuf ){
    OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
    return SQLITE_IOERR_NOMEM;
  }

  /* Figure out the effective temporary directory.  First, check if one
  ** has been explicitly set by the application; otherwise, use the one
  ** configured by the operating system.
  */
  nDir = nMax - (nPre + 15);
  assert( nDir>0 );
  if( sqlite3_temp_directory ){
    int nDirLen = sqlite3Strlen30(sqlite3_temp_directory);
    if( nDirLen>0 ){
      if( !winIsDirSep(sqlite3_temp_directory[nDirLen-1]) ){
        nDirLen++;
      }
      if( nDirLen>nDir ){
        sqlite3_free(zBuf);
        OSTRACE(("TEMP-FILENAME rc=SQLITE_ERROR\n"));
        return winLogError(SQLITE_ERROR, 0, "winGetTempname1", 0);
      }
      sqlite3_snprintf(nMax, zBuf, "%s", sqlite3_temp_directory);
    }
  }
#if defined(__CYGWIN__)
  else{
    static const char *azDirs[] = {
       0, /* getenv("SQLITE_TMPDIR") */
       0, /* getenv("TMPDIR") */
       0, /* getenv("TMP") */
       0, /* getenv("TEMP") */
       0, /* getenv("USERPROFILE") */
       "/var/tmp",
       "/usr/tmp",
       "/tmp",
       ".",
       0        /* List terminator */
    };
    unsigned int i;
    const char *zDir = 0;

    if( !azDirs[0] ) azDirs[0] = getenv("SQLITE_TMPDIR");
    if( !azDirs[1] ) azDirs[1] = getenv("TMPDIR");
    if( !azDirs[2] ) azDirs[2] = getenv("TMP");
    if( !azDirs[3] ) azDirs[3] = getenv("TEMP");
    if( !azDirs[4] ) azDirs[4] = getenv("USERPROFILE");
    for(i=0; i<sizeof(azDirs)/sizeof(azDirs[0]); zDir=azDirs[i++]){
      void *zConverted;
      if( zDir==0 ) continue;
      /* If the path starts with a drive letter followed by the colon
      ** character, assume it is already a native Win32 path; otherwise,
      ** it must be converted to a native Win32 path via the Cygwin API
      ** prior to using it.
      */
      if( winIsDriveLetterAndColon(zDir) ){
        zConverted = winConvertFromUtf8Filename(zDir);
        if( !zConverted ){
          sqlite3_free(zBuf);
          OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
          return SQLITE_IOERR_NOMEM;
        }
        if( winIsDir(zConverted) ){
          sqlite3_snprintf(nMax, zBuf, "%s", zDir);
          sqlite3_free(zConverted);
          break;
        }
        sqlite3_free(zConverted);
      }else{
        zConverted = sqlite3MallocZero( nMax+1 );
        if( !zConverted ){
          sqlite3_free(zBuf);
          OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
          return SQLITE_IOERR_NOMEM;
        }
        if( cygwin_conv_path(
                osIsNT() ? CCP_POSIX_TO_WIN_W : CCP_POSIX_TO_WIN_A, zDir,
                zConverted, nMax+1)<0 ){
          sqlite3_free(zConverted);
          sqlite3_free(zBuf);
          OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_CONVPATH\n"));
          return winLogError(SQLITE_IOERR_CONVPATH, (DWORD)errno,
                             "winGetTempname2", zDir);
        }
        if( winIsDir(zConverted) ){
          /* At this point, we know the candidate directory exists and should
          ** be used.  However, we may need to convert the string containing
          ** its name into UTF-8 (i.e. if it is UTF-16 right now).
          */
          char *zUtf8 = winConvertToUtf8Filename(zConverted);
          if( !zUtf8 ){
            sqlite3_free(zConverted);
            sqlite3_free(zBuf);
            OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
            return SQLITE_IOERR_NOMEM;
          }
          sqlite3_snprintf(nMax, zBuf, "%s", zUtf8);
          sqlite3_free(zUtf8);
          sqlite3_free(zConverted);
          break;
        }
        sqlite3_free(zConverted);
      }
    }
  }
#elif !SQLITE_OS_WINRT && !defined(__CYGWIN__)
  else if( osIsNT() ){
    char *zMulti;
    LPWSTR zWidePath = sqlite3MallocZero( nMax*sizeof(WCHAR) );
    if( !zWidePath ){
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
      return SQLITE_IOERR_NOMEM;
    }
    if( osGetTempPathW(nMax, zWidePath)==0 ){
      sqlite3_free(zWidePath);
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_GETTEMPPATH\n"));
      return winLogError(SQLITE_IOERR_GETTEMPPATH, osGetLastError(),
                         "winGetTempname2", 0);
    }
    zMulti = winUnicodeToUtf8(zWidePath);
    if( zMulti ){
      sqlite3_snprintf(nMax, zBuf, "%s", zMulti);
      sqlite3_free(zMulti);
      sqlite3_free(zWidePath);
    }else{
      sqlite3_free(zWidePath);
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
      return SQLITE_IOERR_NOMEM;
    }
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    char *zUtf8;
    char *zMbcsPath = sqlite3MallocZero( nMax );
    if( !zMbcsPath ){
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
      return SQLITE_IOERR_NOMEM;
    }
    if( osGetTempPathA(nMax, zMbcsPath)==0 ){
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_GETTEMPPATH\n"));
      return winLogError(SQLITE_IOERR_GETTEMPPATH, osGetLastError(),
                         "winGetTempname3", 0);
    }
    zUtf8 = sqlite3_win32_mbcs_to_utf8(zMbcsPath);
    if( zUtf8 ){
      sqlite3_snprintf(nMax, zBuf, "%s", zUtf8);
      sqlite3_free(zUtf8);
    }else{
      sqlite3_free(zBuf);
      OSTRACE(("TEMP-FILENAME rc=SQLITE_IOERR_NOMEM\n"));
      return SQLITE_IOERR_NOMEM;
    }
  }
#endif /* SQLITE_WIN32_HAS_ANSI */
#endif /* !SQLITE_OS_WINRT */

  /*
  ** Check to make sure the temporary directory ends with an appropriate
  ** separator.  If it does not and there is not enough space left to add
  ** one, fail.
  */
  if( !winMakeEndInDirSep(nDir+1, zBuf) ){
    sqlite3_free(zBuf);
    OSTRACE(("TEMP-FILENAME rc=SQLITE_ERROR\n"));
    return winLogError(SQLITE_ERROR, 0, "winGetTempname4", 0);
  }

  /*
  ** Check that the output buffer is large enough for the temporary file
  ** name in the following format:
  **
  **   "<temporary_directory>/etilqs_XXXXXXXXXXXXXXX\0\0"
  **
  ** If not, return SQLITE_ERROR.  The number 17 is used here in order to
  ** account for the space used by the 15 character random suffix and the
  ** two trailing NUL characters.  The final directory separator character
  ** has already added if it was not already present.
  */
  nLen = sqlite3Strlen30(zBuf);
  if( (nLen + nPre + 17) > nBuf ){
    sqlite3_free(zBuf);
    OSTRACE(("TEMP-FILENAME rc=SQLITE_ERROR\n"));
    return winLogError(SQLITE_ERROR, 0, "winGetTempname5", 0);
  }

  sqlite3_snprintf(nBuf-16-nLen, zBuf+nLen, SQLITE_TEMP_FILE_PREFIX);

  j = sqlite3Strlen30(zBuf);
  sqlite3_randomness(15, &zBuf[j]);
  for(i=0; i<15; i++, j++){
    zBuf[j] = (char)zChars[ ((unsigned char)zBuf[j])%(sizeof(zChars)-1) ];
  }
  zBuf[j] = 0;
  zBuf[j+1] = 0;
  *pzBuf = zBuf;

  OSTRACE(("TEMP-FILENAME name=%s, rc=SQLITE_OK\n", zBuf));
  return SQLITE_OK;
}

/*
** Return TRUE if the named file is really a directory.  Return false if
** it is something other than a directory, or if there is any kind of memory
** allocation failure.
*/
static int winIsDir(const void *zConverted){
  DWORD attr;
  int rc = 0;
  DWORD lastErrno;

  if( osIsNT() ){
    int cnt = 0;
    WIN32_FILE_ATTRIBUTE_DATA sAttrData;
    memset(&sAttrData, 0, sizeof(sAttrData));
    while( !(rc = osGetFileAttributesExW((LPCWSTR)zConverted,
                             GetFileExInfoStandard,
                             &sAttrData)) && winRetryIoerr(&cnt, &lastErrno) ){}
    if( !rc ){
      return 0; /* Invalid name? */
    }
    attr = sAttrData.dwFileAttributes;
#if SQLITE_OS_WINCE==0
  }else{
    attr = osGetFileAttributesA((char*)zConverted);
#endif
  }
  return (attr!=INVALID_FILE_ATTRIBUTES) && (attr&FILE_ATTRIBUTE_DIRECTORY);
}

/*
** Open a file.
*/
static int winOpen(
  sqlite3_vfs *pVfs,        /* Used to get maximum path name length */
  const char *zName,        /* Name of the file (UTF-8) */
  sqlite3_file *id,         /* Write the SQLite file handle here */
  int flags,                /* Open mode flags */
  int *pOutFlags            /* Status return flags */
){
  HANDLE h;
  DWORD lastErrno = 0;
  DWORD dwDesiredAccess;
  DWORD dwShareMode;
  DWORD dwCreationDisposition;
  DWORD dwFlagsAndAttributes = 0;
#if SQLITE_OS_WINCE
  int isTemp = 0;
#endif
  winFile *pFile = (winFile*)id;
  void *zConverted;              /* Filename in OS encoding */
  const char *zUtf8Name = zName; /* Filename in UTF-8 encoding */
  int cnt = 0;

  /* If argument zPath is a NULL pointer, this function is required to open
  ** a temporary file. Use this buffer to store the file name in.
  */
  char *zTmpname = 0; /* For temporary filename, if necessary. */

  int rc = SQLITE_OK;            /* Function Return Code */
#if !defined(NDEBUG) || SQLITE_OS_WINCE
  int eType = flags&0xFFFFFF00;  /* Type of file to open */
#endif

  int isExclusive  = (flags & SQLITE_OPEN_EXCLUSIVE);
  int isDelete     = (flags & SQLITE_OPEN_DELETEONCLOSE);
  int isCreate     = (flags & SQLITE_OPEN_CREATE);
  int isReadonly   = (flags & SQLITE_OPEN_READONLY);
  int isReadWrite  = (flags & SQLITE_OPEN_READWRITE);

#ifndef NDEBUG
  int isOpenJournal = (isCreate && (
        eType==SQLITE_OPEN_MASTER_JOURNAL
     || eType==SQLITE_OPEN_MAIN_JOURNAL
     || eType==SQLITE_OPEN_WAL
  ));
#endif

  OSTRACE(("OPEN name=%s, pFile=%p, flags=%x, pOutFlags=%p\n",
           zUtf8Name, id, flags, pOutFlags));

  /* Check the following statements are true:
  **
  **   (a) Exactly one of the READWRITE and READONLY flags must be set, and
  **   (b) if CREATE is set, then READWRITE must also be set, and
  **   (c) if EXCLUSIVE is set, then CREATE must also be set.
  **   (d) if DELETEONCLOSE is set, then CREATE must also be set.
  */
  assert((isReadonly==0 || isReadWrite==0) && (isReadWrite || isReadonly));
  assert(isCreate==0 || isReadWrite);
  assert(isExclusive==0 || isCreate);
  assert(isDelete==0 || isCreate);

  /* The main DB, main journal, WAL file and master journal are never
  ** automatically deleted. Nor are they ever temporary files.  */
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_DB );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MAIN_JOURNAL );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_MASTER_JOURNAL );
  assert( (!isDelete && zName) || eType!=SQLITE_OPEN_WAL );

  /* Assert that the upper layer has set one of the "file-type" flags. */
  assert( eType==SQLITE_OPEN_MAIN_DB      || eType==SQLITE_OPEN_TEMP_DB
       || eType==SQLITE_OPEN_MAIN_JOURNAL || eType==SQLITE_OPEN_TEMP_JOURNAL
       || eType==SQLITE_OPEN_SUBJOURNAL   || eType==SQLITE_OPEN_MASTER_JOURNAL
       || eType==SQLITE_OPEN_TRANSIENT_DB || eType==SQLITE_OPEN_WAL
  );

  assert( pFile!=0 );
  memset(pFile, 0, sizeof(winFile));
  pFile->h = INVALID_HANDLE_VALUE;

#if SQLITE_OS_WINRT
  if( !zUtf8Name && !sqlite3_temp_directory ){
    sqlite3_log(SQLITE_ERROR,
        "sqlite3_temp_directory variable should be set for WinRT");
  }
#endif

  /* If the second argument to this function is NULL, generate a
  ** temporary file name to use
  */
  if( !zUtf8Name ){
    assert( isDelete && !isOpenJournal );
    rc = winGetTempname(pVfs, &zTmpname);
    if( rc!=SQLITE_OK ){
      OSTRACE(("OPEN name=%s, rc=%s", zUtf8Name, sqlite3ErrName(rc)));
      return rc;
    }
    zUtf8Name = zTmpname;
  }

  /* Database filenames are double-zero terminated if they are not
  ** URIs with parameters.  Hence, they can always be passed into
  ** sqlite3_uri_parameter().
  */
  assert( (eType!=SQLITE_OPEN_MAIN_DB) || (flags & SQLITE_OPEN_URI) ||
       zUtf8Name[sqlite3Strlen30(zUtf8Name)+1]==0 );

  /* Convert the filename to the system encoding. */
  zConverted = winConvertFromUtf8Filename(zUtf8Name);
  if( zConverted==0 ){
    sqlite3_free(zTmpname);
    OSTRACE(("OPEN name=%s, rc=SQLITE_IOERR_NOMEM", zUtf8Name));
    return SQLITE_IOERR_NOMEM;
  }

  if( winIsDir(zConverted) ){
    sqlite3_free(zConverted);
    sqlite3_free(zTmpname);
    OSTRACE(("OPEN name=%s, rc=SQLITE_CANTOPEN_ISDIR", zUtf8Name));
    return SQLITE_CANTOPEN_ISDIR;
  }

  if( isReadWrite ){
    dwDesiredAccess = GENERIC_READ | GENERIC_WRITE;
  }else{
    dwDesiredAccess = GENERIC_READ;
  }

  /* SQLITE_OPEN_EXCLUSIVE is used to make sure that a new file is
  ** created. SQLite doesn't use it to indicate "exclusive access"
  ** as it is usually understood.
  */
  if( isExclusive ){
    /* Creates a new file, only if it does not already exist. */
    /* If the file exists, it fails. */
    dwCreationDisposition = CREATE_NEW;
  }else if( isCreate ){
    /* Open existing file, or create if it doesn't exist */
    dwCreationDisposition = OPEN_ALWAYS;
  }else{
    /* Opens a file, only if it exists. */
    dwCreationDisposition = OPEN_EXISTING;
  }

  dwShareMode = FILE_SHARE_READ | FILE_SHARE_WRITE;

  if( isDelete ){
#if SQLITE_OS_WINCE
    dwFlagsAndAttributes = FILE_ATTRIBUTE_HIDDEN;
    isTemp = 1;
#else
    dwFlagsAndAttributes = FILE_ATTRIBUTE_TEMPORARY
                               | FILE_ATTRIBUTE_HIDDEN
                               | FILE_FLAG_DELETE_ON_CLOSE;
#endif
  }else{
    dwFlagsAndAttributes = FILE_ATTRIBUTE_NORMAL;
  }
  /* Reports from the internet are that performance is always
  ** better if FILE_FLAG_RANDOM_ACCESS is used.  Ticket #2699. */
#if SQLITE_OS_WINCE
  dwFlagsAndAttributes |= FILE_FLAG_RANDOM_ACCESS;
#endif

  if( osIsNT() ){
#if SQLITE_OS_WINRT
    CREATEFILE2_EXTENDED_PARAMETERS extendedParameters;
    extendedParameters.dwSize = sizeof(CREATEFILE2_EXTENDED_PARAMETERS);
    extendedParameters.dwFileAttributes =
            dwFlagsAndAttributes & FILE_ATTRIBUTE_MASK;
    extendedParameters.dwFileFlags = dwFlagsAndAttributes & FILE_FLAG_MASK;
    extendedParameters.dwSecurityQosFlags = SECURITY_ANONYMOUS;
    extendedParameters.lpSecurityAttributes = NULL;
    extendedParameters.hTemplateFile = NULL;
    while( (h = osCreateFile2((LPCWSTR)zConverted,
                              dwDesiredAccess,
                              dwShareMode,
                              dwCreationDisposition,
                              &extendedParameters))==INVALID_HANDLE_VALUE &&
                              winRetryIoerr(&cnt, &lastErrno) ){
               /* Noop */
    }
#else
    while( (h = osCreateFileW((LPCWSTR)zConverted,
                              dwDesiredAccess,
                              dwShareMode, NULL,
                              dwCreationDisposition,
                              dwFlagsAndAttributes,
                              NULL))==INVALID_HANDLE_VALUE &&
                              winRetryIoerr(&cnt, &lastErrno) ){
               /* Noop */
    }
#endif
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    while( (h = osCreateFileA((LPCSTR)zConverted,
                              dwDesiredAccess,
                              dwShareMode, NULL,
                              dwCreationDisposition,
                              dwFlagsAndAttributes,
                              NULL))==INVALID_HANDLE_VALUE &&
                              winRetryIoerr(&cnt, &lastErrno) ){
               /* Noop */
    }
  }
#endif
  winLogIoerr(cnt, __LINE__);

  OSTRACE(("OPEN file=%p, name=%s, access=%lx, rc=%s\n", h, zUtf8Name,
           dwDesiredAccess, (h==INVALID_HANDLE_VALUE) ? "failed" : "ok"));

  if( h==INVALID_HANDLE_VALUE ){
    pFile->lastErrno = lastErrno;
    winLogError(SQLITE_CANTOPEN, pFile->lastErrno, "winOpen", zUtf8Name);
    sqlite3_free(zConverted);
    sqlite3_free(zTmpname);
    if( isReadWrite && !isExclusive ){
      return winOpen(pVfs, zName, id,
         ((flags|SQLITE_OPEN_READONLY) &
                     ~(SQLITE_OPEN_CREATE|SQLITE_OPEN_READWRITE)),
         pOutFlags);
    }else{
      return SQLITE_CANTOPEN_BKPT;
    }
  }

  if( pOutFlags ){
    if( isReadWrite ){
      *pOutFlags = SQLITE_OPEN_READWRITE;
    }else{
      *pOutFlags = SQLITE_OPEN_READONLY;
    }
  }

  OSTRACE(("OPEN file=%p, name=%s, access=%lx, pOutFlags=%p, *pOutFlags=%d, "
           "rc=%s\n", h, zUtf8Name, dwDesiredAccess, pOutFlags, pOutFlags ?
           *pOutFlags : 0, (h==INVALID_HANDLE_VALUE) ? "failed" : "ok"));

#if SQLITE_OS_WINCE
  if( isReadWrite && eType==SQLITE_OPEN_MAIN_DB
       && (rc = winceCreateLock(zName, pFile))!=SQLITE_OK
  ){
    osCloseHandle(h);
    sqlite3_free(zConverted);
    sqlite3_free(zTmpname);
    OSTRACE(("OPEN-CE-LOCK name=%s, rc=%s\n", zName, sqlite3ErrName(rc)));
    return rc;
  }
  if( isTemp ){
    pFile->zDeleteOnClose = zConverted;
  }else
#endif
  {
    sqlite3_free(zConverted);
  }

  sqlite3_free(zTmpname);
  pFile->pMethod = &winIoMethod;
  pFile->pVfs = pVfs;
  pFile->h = h;
  if( isReadonly ){
    pFile->ctrlFlags |= WINFILE_RDONLY;
  }
  if( sqlite3_uri_boolean(zName, "psow", SQLITE_POWERSAFE_OVERWRITE) ){
    pFile->ctrlFlags |= WINFILE_PSOW;
  }
  pFile->lastErrno = NO_ERROR;
  pFile->zPath = zName;
#if SQLITE_MAX_MMAP_SIZE>0
  pFile->hMap = NULL;
  pFile->pMapRegion = 0;
  pFile->mmapSize = 0;
  pFile->mmapSizeActual = 0;
  pFile->mmapSizeMax = sqlite3GlobalConfig.szMmap;
#endif

  OpenCounter(+1);
  return rc;
}

/*
** Delete the named file.
**
** Note that Windows does not allow a file to be deleted if some other
** process has it open.  Sometimes a virus scanner or indexing program
** will open a journal file shortly after it is created in order to do
** whatever it does.  While this other process is holding the
** file open, we will be unable to delete it.  To work around this
** problem, we delay 100 milliseconds and try to delete again.  Up
** to MX_DELETION_ATTEMPTs deletion attempts are run before giving
** up and returning an error.
*/
static int winDelete(
  sqlite3_vfs *pVfs,          /* Not used on win32 */
  const char *zFilename,      /* Name of file to delete */
  int syncDir                 /* Not used on win32 */
){
  int cnt = 0;
  int rc;
  DWORD attr;
  DWORD lastErrno = 0;
  void *zConverted;
  UNUSED_PARAMETER(pVfs);
  UNUSED_PARAMETER(syncDir);

  SimulateIOError(return SQLITE_IOERR_DELETE);
  OSTRACE(("DELETE name=%s, syncDir=%d\n", zFilename, syncDir));

  zConverted = winConvertFromUtf8Filename(zFilename);
  if( zConverted==0 ){
    OSTRACE(("DELETE name=%s, rc=SQLITE_IOERR_NOMEM\n", zFilename));
    return SQLITE_IOERR_NOMEM;
  }
  if( osIsNT() ){
    do {
#if SQLITE_OS_WINRT
      WIN32_FILE_ATTRIBUTE_DATA sAttrData;
      memset(&sAttrData, 0, sizeof(sAttrData));
      if ( osGetFileAttributesExW(zConverted, GetFileExInfoStandard,
                                  &sAttrData) ){
        attr = sAttrData.dwFileAttributes;
      }else{
        lastErrno = osGetLastError();
        if( lastErrno==ERROR_FILE_NOT_FOUND
         || lastErrno==ERROR_PATH_NOT_FOUND ){
          rc = SQLITE_IOERR_DELETE_NOENT; /* Already gone? */
        }else{
          rc = SQLITE_ERROR;
        }
        break;
      }
#else
      attr = osGetFileAttributesW(zConverted);
#endif
      if ( attr==INVALID_FILE_ATTRIBUTES ){
        lastErrno = osGetLastError();
        if( lastErrno==ERROR_FILE_NOT_FOUND
         || lastErrno==ERROR_PATH_NOT_FOUND ){
          rc = SQLITE_IOERR_DELETE_NOENT; /* Already gone? */
        }else{
          rc = SQLITE_ERROR;
        }
        break;
      }
      if ( attr&FILE_ATTRIBUTE_DIRECTORY ){
        rc = SQLITE_ERROR; /* Files only. */
        break;
      }
      if ( osDeleteFileW(zConverted) ){
        rc = SQLITE_OK; /* Deleted OK. */
        break;
      }
      if ( !winRetryIoerr(&cnt, &lastErrno) ){
        rc = SQLITE_ERROR; /* No more retries. */
        break;
      }
    } while(1);
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    do {
      attr = osGetFileAttributesA(zConverted);
      if ( attr==INVALID_FILE_ATTRIBUTES ){
        lastErrno = osGetLastError();
        if( lastErrno==ERROR_FILE_NOT_FOUND
         || lastErrno==ERROR_PATH_NOT_FOUND ){
          rc = SQLITE_IOERR_DELETE_NOENT; /* Already gone? */
        }else{
          rc = SQLITE_ERROR;
        }
        break;
      }
      if ( attr&FILE_ATTRIBUTE_DIRECTORY ){
        rc = SQLITE_ERROR; /* Files only. */
        break;
      }
      if ( osDeleteFileA(zConverted) ){
        rc = SQLITE_OK; /* Deleted OK. */
        break;
      }
      if ( !winRetryIoerr(&cnt, &lastErrno) ){
        rc = SQLITE_ERROR; /* No more retries. */
        break;
      }
    } while(1);
  }
#endif
  if( rc && rc!=SQLITE_IOERR_DELETE_NOENT ){
    rc = winLogError(SQLITE_IOERR_DELETE, lastErrno, "winDelete", zFilename);
  }else{
    winLogIoerr(cnt, __LINE__);
  }
  sqlite3_free(zConverted);
  OSTRACE(("DELETE name=%s, rc=%s\n", zFilename, sqlite3ErrName(rc)));
  return rc;
}

/*
** Check the existence and status of a file.
*/
static int winAccess(
  sqlite3_vfs *pVfs,         /* Not used on win32 */
  const char *zFilename,     /* Name of file to check */
  int flags,                 /* Type of test to make on this file */
  int *pResOut               /* OUT: Result */
){
  DWORD attr;
  int rc = 0;
  DWORD lastErrno = 0;
  void *zConverted;
  UNUSED_PARAMETER(pVfs);

  SimulateIOError( return SQLITE_IOERR_ACCESS; );
  OSTRACE(("ACCESS name=%s, flags=%x, pResOut=%p\n",
           zFilename, flags, pResOut));

  zConverted = winConvertFromUtf8Filename(zFilename);
  if( zConverted==0 ){
    OSTRACE(("ACCESS name=%s, rc=SQLITE_IOERR_NOMEM\n", zFilename));
    return SQLITE_IOERR_NOMEM;
  }
  if( osIsNT() ){
    int cnt = 0;
    WIN32_FILE_ATTRIBUTE_DATA sAttrData;
    memset(&sAttrData, 0, sizeof(sAttrData));
    while( !(rc = osGetFileAttributesExW((LPCWSTR)zConverted,
                             GetFileExInfoStandard,
                             &sAttrData)) && winRetryIoerr(&cnt, &lastErrno) ){}
    if( rc ){
      /* For an SQLITE_ACCESS_EXISTS query, treat a zero-length file
      ** as if it does not exist.
      */
      if(    flags==SQLITE_ACCESS_EXISTS
          && sAttrData.nFileSizeHigh==0
          && sAttrData.nFileSizeLow==0 ){
        attr = INVALID_FILE_ATTRIBUTES;
      }else{
        attr = sAttrData.dwFileAttributes;
      }
    }else{
      winLogIoerr(cnt, __LINE__);
      if( lastErrno!=ERROR_FILE_NOT_FOUND && lastErrno!=ERROR_PATH_NOT_FOUND ){
        sqlite3_free(zConverted);
        return winLogError(SQLITE_IOERR_ACCESS, lastErrno, "winAccess",
                           zFilename);
      }else{
        attr = INVALID_FILE_ATTRIBUTES;
      }
    }
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    attr = osGetFileAttributesA((char*)zConverted);
  }
#endif
  sqlite3_free(zConverted);
  switch( flags ){
    case SQLITE_ACCESS_READ:
    case SQLITE_ACCESS_EXISTS:
      rc = attr!=INVALID_FILE_ATTRIBUTES;
      break;
    case SQLITE_ACCESS_READWRITE:
      rc = attr!=INVALID_FILE_ATTRIBUTES &&
             (attr & FILE_ATTRIBUTE_READONLY)==0;
      break;
    default:
      assert(!"Invalid flags argument");
  }
  *pResOut = rc;
  OSTRACE(("ACCESS name=%s, pResOut=%p, *pResOut=%d, rc=SQLITE_OK\n",
           zFilename, pResOut, *pResOut));
  return SQLITE_OK;
}

/*
** Returns non-zero if the specified path name starts with a drive letter
** followed by a colon character.
*/
static BOOL winIsDriveLetterAndColon(
  const char *zPathname
){
  return ( sqlite3Isalpha(zPathname[0]) && zPathname[1]==':' );
}

/*
** Returns non-zero if the specified path name should be used verbatim.  If
** non-zero is returned from this function, the calling function must simply
** use the provided path name verbatim -OR- resolve it into a full path name
** using the GetFullPathName Win32 API function (if available).
*/
static BOOL winIsVerbatimPathname(
  const char *zPathname
){
  /*
  ** If the path name starts with a forward slash or a backslash, it is either
  ** a legal UNC name, a volume relative path, or an absolute path name in the
  ** "Unix" format on Windows.  There is no easy way to differentiate between
  ** the final two cases; therefore, we return the safer return value of TRUE
  ** so that callers of this function will simply use it verbatim.
  */
  if ( winIsDirSep(zPathname[0]) ){
    return TRUE;
  }

  /*
  ** If the path name starts with a letter and a colon it is either a volume
  ** relative path or an absolute path.  Callers of this function must not
  ** attempt to treat it as a relative path name (i.e. they should simply use
  ** it verbatim).
  */
  if ( winIsDriveLetterAndColon(zPathname) ){
    return TRUE;
  }

  /*
  ** If we get to this point, the path name should almost certainly be a purely
  ** relative one (i.e. not a UNC name, not absolute, and not volume relative).
  */
  return FALSE;
}

/*
** Turn a relative pathname into a full pathname.  Write the full
** pathname into zOut[].  zOut[] will be at least pVfs->mxPathname
** bytes in size.
*/
static int winFullPathname(
  sqlite3_vfs *pVfs,            /* Pointer to vfs object */
  const char *zRelative,        /* Possibly relative input path */
  int nFull,                    /* Size of output buffer in bytes */
  char *zFull                   /* Output buffer */
){

#if defined(__CYGWIN__)
  SimulateIOError( return SQLITE_ERROR );
  UNUSED_PARAMETER(nFull);
  assert( nFull>=pVfs->mxPathname );
  char *zOut = sqlite3MallocZero( pVfs->mxPathname+1 );
  if( !zOut ){
    return SQLITE_IOERR_NOMEM;
  }
  if( cygwin_conv_path(
          (osIsNT() ? CCP_POSIX_TO_WIN_W : CCP_POSIX_TO_WIN_A),
          zRelative, zOut, pVfs->mxPathname+1)<0 ){
    sqlite3_free(zOut);
    return winLogError(SQLITE_CANTOPEN_CONVPATH, (DWORD)errno,
                       "winFullPathname2", zRelative);
  }else{
    char *zUtf8 = winConvertToUtf8Filename(zOut);
    if( !zUtf8 ){
      sqlite3_free(zOut);
      return SQLITE_IOERR_NOMEM;
    }
    sqlite3_snprintf(MIN(nFull, pVfs->mxPathname), zFull, "%s", zUtf8);
    sqlite3_free(zUtf8);
    sqlite3_free(zOut);
  }
  return SQLITE_OK;
#endif

#if (SQLITE_OS_WINCE || SQLITE_OS_WINRT) && !defined(__CYGWIN__)
  SimulateIOError( return SQLITE_ERROR );
  /* WinCE has no concept of a relative pathname, or so I am told. */
  /* WinRT has no way to convert a relative path to an absolute one. */
  sqlite3_snprintf(MIN(nFull, pVfs->mxPathname), zFull, "%s", zRelative);
  return SQLITE_OK;
#endif

#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && !defined(__CYGWIN__)
  DWORD nByte;
  void *zConverted;
  char *zOut;

  /* If this path name begins with "/X:", where "X" is any alphabetic
  ** character, discard the initial "/" from the pathname.
  */
  if( zRelative[0]=='/' && winIsDriveLetterAndColon(zRelative+1) ){
    zRelative++;
  }

  /* It's odd to simulate an io-error here, but really this is just
  ** using the io-error infrastructure to test that SQLite handles this
  ** function failing. This function could fail if, for example, the
  ** current working directory has been unlinked.
  */
  SimulateIOError( return SQLITE_ERROR );
  zConverted = winConvertFromUtf8Filename(zRelative);
  if( zConverted==0 ){
    return SQLITE_IOERR_NOMEM;
  }
  if( osIsNT() ){
    LPWSTR zTemp;
    nByte = osGetFullPathNameW((LPCWSTR)zConverted, 0, 0, 0);
    if( nByte==0 ){
      sqlite3_free(zConverted);
      return winLogError(SQLITE_CANTOPEN_FULLPATH, osGetLastError(),
                         "winFullPathname1", zRelative);
    }
    nByte += 3;
    zTemp = sqlite3MallocZero( nByte*sizeof(zTemp[0]) );
    if( zTemp==0 ){
      sqlite3_free(zConverted);
      return SQLITE_IOERR_NOMEM;
    }
    nByte = osGetFullPathNameW((LPCWSTR)zConverted, nByte, zTemp, 0);
    if( nByte==0 ){
      sqlite3_free(zConverted);
      sqlite3_free(zTemp);
      return winLogError(SQLITE_CANTOPEN_FULLPATH, osGetLastError(),
                         "winFullPathname2", zRelative);
    }
    sqlite3_free(zConverted);
    zOut = winUnicodeToUtf8(zTemp);
    sqlite3_free(zTemp);
  }
#ifdef SQLITE_WIN32_HAS_ANSI
  else{
    char *zTemp;
    nByte = osGetFullPathNameA((char*)zConverted, 0, 0, 0);
    if( nByte==0 ){
      sqlite3_free(zConverted);
      return winLogError(SQLITE_CANTOPEN_FULLPATH, osGetLastError(),
                         "winFullPathname3", zRelative);
    }
    nByte += 3;
    zTemp = sqlite3MallocZero( nByte*sizeof(zTemp[0]) );
    if( zTemp==0 ){
      sqlite3_free(zConverted);
      return SQLITE_IOERR_NOMEM;
    }
    nByte = osGetFullPathNameA((char*)zConverted, nByte, zTemp, 0);
    if( nByte==0 ){
      sqlite3_free(zConverted);
      sqlite3_free(zTemp);
      return winLogError(SQLITE_CANTOPEN_FULLPATH, osGetLastError(),
                         "winFullPathname4", zRelative);
    }
    sqlite3_free(zConverted);
    zOut = sqlite3_win32_mbcs_to_utf8(zTemp);
    sqlite3_free(zTemp);
  }
#endif
  if( zOut ){
    sqlite3_snprintf(MIN(nFull, pVfs->mxPathname), zFull, "%s", zOut);
    sqlite3_free(zOut);
    return SQLITE_OK;
  }else{
    return SQLITE_IOERR_NOMEM;
  }
#endif
}

  #define winDlOpen  0
  #define winDlError 0
  #define winDlSym   0
  #define winDlClose 0


/*
** Write up to nBuf bytes of randomness into zBuf.
*/
static int winRandomness(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
  int n = 0;
  UNUSED_PARAMETER(pVfs);
#if defined(SQLITE_TEST) || defined(SQLITE_OMIT_RANDOMNESS)
  n = nBuf;
  memset(zBuf, 0, nBuf);
#else
  if( sizeof(SYSTEMTIME)<=nBuf-n ){
    SYSTEMTIME x;
    osGetSystemTime(&x);
    memcpy(&zBuf[n], &x, sizeof(x));
    n += sizeof(x);
  }
  if( sizeof(DWORD)<=nBuf-n ){
    DWORD pid = osGetCurrentProcessId();
    memcpy(&zBuf[n], &pid, sizeof(pid));
    n += sizeof(pid);
  }
#if SQLITE_OS_WINRT
  if( sizeof(ULONGLONG)<=nBuf-n ){
    ULONGLONG cnt = osGetTickCount64();
    memcpy(&zBuf[n], &cnt, sizeof(cnt));
    n += sizeof(cnt);
  }
#else
  if( sizeof(DWORD)<=nBuf-n ){
    DWORD cnt = osGetTickCount();
    memcpy(&zBuf[n], &cnt, sizeof(cnt));
    n += sizeof(cnt);
  }
#endif
  if( sizeof(LARGE_INTEGER)<=nBuf-n ){
    LARGE_INTEGER i;
    osQueryPerformanceCounter(&i);
    memcpy(&zBuf[n], &i, sizeof(i));
    n += sizeof(i);
  }
#if !SQLITE_OS_WINCE && !SQLITE_OS_WINRT && SQLITE_WIN32_USE_UUID
  if( sizeof(UUID)<=nBuf-n ){
    UUID id;
    memset(&id, 0, sizeof(UUID));
    osUuidCreate(&id);
    memcpy(&zBuf[n], &id, sizeof(UUID));
    n += sizeof(UUID);
  }
  if( sizeof(UUID)<=nBuf-n ){
    UUID id;
    memset(&id, 0, sizeof(UUID));
    osUuidCreateSequential(&id);
    memcpy(&zBuf[n], &id, sizeof(UUID));
    n += sizeof(UUID);
  }
#endif
#endif /* defined(SQLITE_TEST) || defined(SQLITE_ZERO_PRNG_SEED) */
  return n;
}


/*
** Sleep for a little while.  Return the amount of time slept.
*/
static int winSleep(sqlite3_vfs *pVfs, int microsec){
  sqlite3_win32_sleep((microsec+999)/1000);
  UNUSED_PARAMETER(pVfs);
  return ((microsec+999)/1000)*1000;
}

/*
** The following variable, if set to a non-zero value, is interpreted as
** the number of seconds since 1970 and is used to set the result of
** sqlite3OsCurrentTime() during testing.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_current_time = 0;  /* Fake system time in seconds since 1970. */
#endif

/*
** Find the current time (in Universal Coordinated Time).  Write into *piNow
** the current time and date as a Julian Day number times 86_400_000.  In
** other words, write into *piNow the number of milliseconds since the Julian
** epoch of noon in Greenwich on November 24, 4714 B.C according to the
** proleptic Gregorian calendar.
**
** On success, return SQLITE_OK.  Return SQLITE_ERROR if the time and date
** cannot be found.
*/
static int winCurrentTimeInt64(sqlite3_vfs *pVfs, sqlite3_int64 *piNow){
  /* FILETIME structure is a 64-bit value representing the number of
     100-nanosecond intervals since January 1, 1601 (= JD 2305813.5).
  */
  FILETIME ft;
  static const sqlite3_int64 winFiletimeEpoch = 23058135*(sqlite3_int64)8640000;
#ifdef SQLITE_TEST
  static const sqlite3_int64 unixEpoch = 24405875*(sqlite3_int64)8640000;
#endif
  /* 2^32 - to avoid use of LL and warnings in gcc */
  static const sqlite3_int64 max32BitValue =
      (sqlite3_int64)2000000000 + (sqlite3_int64)2000000000 +
      (sqlite3_int64)294967296;

#if SQLITE_OS_WINCE
  SYSTEMTIME time;
  osGetSystemTime(&time);
  /* if SystemTimeToFileTime() fails, it returns zero. */
  if (!osSystemTimeToFileTime(&time,&ft)){
    return SQLITE_ERROR;
  }
#else
  osGetSystemTimeAsFileTime( &ft );
#endif

  *piNow = winFiletimeEpoch +
            ((((sqlite3_int64)ft.dwHighDateTime)*max32BitValue) +
               (sqlite3_int64)ft.dwLowDateTime)/(sqlite3_int64)10000;

#ifdef SQLITE_TEST
  if( sqlite3_current_time ){
    *piNow = 1000*(sqlite3_int64)sqlite3_current_time + unixEpoch;
  }
#endif
  UNUSED_PARAMETER(pVfs);
  return SQLITE_OK;
}

/*
** Find the current time (in Universal Coordinated Time).  Write the
** current time and date as a Julian Day number into *prNow and
** return 0.  Return 1 if the time and date cannot be found.
*/
static int winCurrentTime(sqlite3_vfs *pVfs, double *prNow){
  int rc;
  sqlite3_int64 i;
  rc = winCurrentTimeInt64(pVfs, &i);
  if( !rc ){
    *prNow = i/86400000.0;
  }
  return rc;
}

/*
** The idea is that this function works like a combination of
** GetLastError() and FormatMessage() on Windows (or errno and
** strerror_r() on Unix). After an error is returned by an OS
** function, SQLite calls this function with zBuf pointing to
** a buffer of nBuf bytes. The OS layer should populate the
** buffer with a nul-terminated UTF-8 encoded error message
** describing the last IO error to have occurred within the calling
** thread.
**
** If the error message is too large for the supplied buffer,
** it should be truncated. The return value of xGetLastError
** is zero if the error message fits in the buffer, or non-zero
** otherwise (if the message was truncated). If non-zero is returned,
** then it is not necessary to include the nul-terminator character
** in the output buffer.
**
** Not supplying an error message will have no adverse effect
** on SQLite. It is fine to have an implementation that never
** returns an error message:
**
**   int xGetLastError(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
**     assert(zBuf[0]=='\0');
**     return 0;
**   }
**
** However if an error message is supplied, it will be incorporated
** by sqlite into the error message available to the user using
** sqlite3_errmsg(), possibly making IO errors easier to debug.
*/
static int winGetLastError(sqlite3_vfs *pVfs, int nBuf, char *zBuf){
  UNUSED_PARAMETER(pVfs);
  return winGetLastErrorMsg(osGetLastError(), nBuf, zBuf);
}

/*
** Initialize and deinitialize the operating system interface.
*/
SQLITE_PRIVATE int sqlite3_os_init(void){
  static sqlite3_vfs winVfs = {
    3,                   /* iVersion */
    sizeof(winFile),     /* szOsFile */
    SQLITE_WIN32_MAX_PATH_BYTES, /* mxPathname */
    0,                   /* pNext */
    "win32",             /* zName */
    0,                   /* pAppData */
    winOpen,             /* xOpen */
    winDelete,           /* xDelete */
    winAccess,           /* xAccess */
    winFullPathname,     /* xFullPathname */
    winDlOpen,           /* xDlOpen */
    winDlError,          /* xDlError */
    winDlSym,            /* xDlSym */
    winDlClose,          /* xDlClose */
    winRandomness,       /* xRandomness */
    winSleep,            /* xSleep */
    winCurrentTime,      /* xCurrentTime */
    winGetLastError,     /* xGetLastError */
    winCurrentTimeInt64, /* xCurrentTimeInt64 */
    winSetSystemCall,    /* xSetSystemCall */
    winGetSystemCall,    /* xGetSystemCall */
    winNextSystemCall,   /* xNextSystemCall */
  };
#if defined(SQLITE_WIN32_HAS_WIDE)
  static sqlite3_vfs winLongPathVfs = {
    3,                   /* iVersion */
    sizeof(winFile),     /* szOsFile */
    SQLITE_WINNT_MAX_PATH_BYTES, /* mxPathname */
    0,                   /* pNext */
    "win32-longpath",    /* zName */
    0,                   /* pAppData */
    winOpen,             /* xOpen */
    winDelete,           /* xDelete */
    winAccess,           /* xAccess */
    winFullPathname,     /* xFullPathname */
    winDlOpen,           /* xDlOpen */
    winDlError,          /* xDlError */
    winDlSym,            /* xDlSym */
    winDlClose,          /* xDlClose */
    winRandomness,       /* xRandomness */
    winSleep,            /* xSleep */
    winCurrentTime,      /* xCurrentTime */
    winGetLastError,     /* xGetLastError */
    winCurrentTimeInt64, /* xCurrentTimeInt64 */
    winSetSystemCall,    /* xSetSystemCall */
    winGetSystemCall,    /* xGetSystemCall */
    winNextSystemCall,   /* xNextSystemCall */
  };
#endif

  /* Double-check that the aSyscall[] array has been constructed
  ** correctly.  See ticket [bb3a86e890c8e96ab] */
  assert( ArraySize(aSyscall)==80 );

  /* get memory map allocation granularity */
  memset(&winSysInfo, 0, sizeof(SYSTEM_INFO));
#if SQLITE_OS_WINRT
  osGetNativeSystemInfo(&winSysInfo);
#else
  osGetSystemInfo(&winSysInfo);
#endif
  assert( winSysInfo.dwAllocationGranularity>0 );
  assert( winSysInfo.dwPageSize>0 );

  sqlite3_vfs_register(&winVfs, 1);

#if defined(SQLITE_WIN32_HAS_WIDE)
  sqlite3_vfs_register(&winLongPathVfs, 0);
#endif

  return SQLITE_OK;
}

SQLITE_PRIVATE int sqlite3_os_end(void){
#if SQLITE_OS_WINRT
  if( sleepObj!=NULL ){
    osCloseHandle(sleepObj);
    sleepObj = NULL;
  }
#endif
  return SQLITE_OK;
}

#endif /* SQLITE_OS_WIN */

/************** End of os_win.c **********************************************/
/************** Begin file bitvec.c ******************************************/
/*
** 2008 February 16
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements an object that represents a fixed-length
** bitmap.  Bits are numbered starting with 1.
**
** A bitmap is used to record which pages of a database file have been
** journalled during a transaction, or which pages have the "dont-write"
** property.  Usually only a few pages are meet either condition.
** So the bitmap is usually sparse and has low cardinality.
** But sometimes (for example when during a DROP of a large table) most
** or all of the pages in a database can get journalled.  In those cases, 
** the bitmap becomes dense with high cardinality.  The algorithm needs 
** to handle both cases well.
**
** The size of the bitmap is fixed when the object is created.
**
** All bits are clear when the bitmap is created.  Individual bits
** may be set or cleared one at a time.
**
** Test operations are about 100 times more common that set operations.
** Clear operations are exceedingly rare.  There are usually between
** 5 and 500 set operations per Bitvec object, though the number of sets can
** sometimes grow into tens of thousands or larger.  The size of the
** Bitvec object is the number of pages in the database file at the
** start of a transaction, and is thus usually less than a few thousand,
** but can be as large as 2 billion for a really big database.
*/
/* #include "sqliteInt.h" */

/* Size of the Bitvec structure in bytes. */
#define BITVEC_SZ        512

/* Round the union size down to the nearest pointer boundary, since that's how 
** it will be aligned within the Bitvec struct. */
#define BITVEC_USIZE     (((BITVEC_SZ-(3*sizeof(u32)))/sizeof(Bitvec*))*sizeof(Bitvec*))

/* Type of the array "element" for the bitmap representation. 
** Should be a power of 2, and ideally, evenly divide into BITVEC_USIZE. 
** Setting this to the "natural word" size of your CPU may improve
** performance. */
#define BITVEC_TELEM     u8
/* Size, in bits, of the bitmap element. */
#define BITVEC_SZELEM    8
/* Number of elements in a bitmap array. */
#define BITVEC_NELEM     (BITVEC_USIZE/sizeof(BITVEC_TELEM))
/* Number of bits in the bitmap array. */
#define BITVEC_NBIT      (BITVEC_NELEM*BITVEC_SZELEM)

/* Number of u32 values in hash table. */
#define BITVEC_NINT      (BITVEC_USIZE/sizeof(u32))
/* Maximum number of entries in hash table before 
** sub-dividing and re-hashing. */
#define BITVEC_MXHASH    (BITVEC_NINT/2)
/* Hashing function for the aHash representation.
** Empirical testing showed that the *37 multiplier 
** (an arbitrary prime)in the hash function provided 
** no fewer collisions than the no-op *1. */
#define BITVEC_HASH(X)   (((X)*1)%BITVEC_NINT)

#define BITVEC_NPTR      (BITVEC_USIZE/sizeof(Bitvec *))


/*
** A bitmap is an instance of the following structure.
**
** This bitmap records the existence of zero or more bits
** with values between 1 and iSize, inclusive.
**
** There are three possible representations of the bitmap.
** If iSize<=BITVEC_NBIT, then Bitvec.u.aBitmap[] is a straight
** bitmap.  The least significant bit is bit 1.
**
** If iSize>BITVEC_NBIT and iDivisor==0 then Bitvec.u.aHash[] is
** a hash table that will hold up to BITVEC_MXHASH distinct values.
**
** Otherwise, the value i is redirected into one of BITVEC_NPTR
** sub-bitmaps pointed to by Bitvec.u.apSub[].  Each subbitmap
** handles up to iDivisor separate values of i.  apSub[0] holds
** values between 1 and iDivisor.  apSub[1] holds values between
** iDivisor+1 and 2*iDivisor.  apSub[N] holds values between
** N*iDivisor+1 and (N+1)*iDivisor.  Each subbitmap is normalized
** to hold deal with values between 1 and iDivisor.
*/
struct Bitvec {
  u32 iSize;      /* Maximum bit index.  Max iSize is 4,294,967,296. */
  u32 nSet;       /* Number of bits that are set - only valid for aHash
                  ** element.  Max is BITVEC_NINT.  For BITVEC_SZ of 512,
                  ** this would be 125. */
  u32 iDivisor;   /* Number of bits handled by each apSub[] entry. */
                  /* Should >=0 for apSub element. */
                  /* Max iDivisor is max(u32) / BITVEC_NPTR + 1.  */
                  /* For a BITVEC_SZ of 512, this would be 34,359,739. */
  union {
    BITVEC_TELEM aBitmap[BITVEC_NELEM];    /* Bitmap representation */
    u32 aHash[BITVEC_NINT];      /* Hash table representation */
    Bitvec *apSub[BITVEC_NPTR];  /* Recursive representation */
  } u;
};

/*
** Create a new bitmap object able to handle bits between 0 and iSize,
** inclusive.  Return a pointer to the new object.  Return NULL if 
** malloc fails.
*/
SQLITE_PRIVATE Bitvec *sqlite3BitvecCreate(u32 iSize){
  Bitvec *p;
  assert( sizeof(*p)==BITVEC_SZ );
  p = sqlite3MallocZero( sizeof(*p) );
  if( p ){
    p->iSize = iSize;
  }
  return p;
}

/*
** Check to see if the i-th bit is set.  Return true or false.
** If p is NULL (if the bitmap has not been created) or if
** i is out of range, then return false.
*/
SQLITE_PRIVATE int sqlite3BitvecTestNotNull(Bitvec *p, u32 i){
  assert( p!=0 );
  i--;
  if( i>=p->iSize ) return 0;
  while( p->iDivisor ){
    u32 bin = i/p->iDivisor;
    i = i%p->iDivisor;
    p = p->u.apSub[bin];
    if (!p) {
      return 0;
    }
  }
  if( p->iSize<=BITVEC_NBIT ){
    return (p->u.aBitmap[i/BITVEC_SZELEM] & (1<<(i&(BITVEC_SZELEM-1))))!=0;
  } else{
    u32 h = BITVEC_HASH(i++);
    while( p->u.aHash[h] ){
      if( p->u.aHash[h]==i ) return 1;
      h = (h+1) % BITVEC_NINT;
    }
    return 0;
  }
}
SQLITE_PRIVATE int sqlite3BitvecTest(Bitvec *p, u32 i){
  return p!=0 && sqlite3BitvecTestNotNull(p,i);
}

/*
** Set the i-th bit.  Return 0 on success and an error code if
** anything goes wrong.
**
** This routine might cause sub-bitmaps to be allocated.  Failing
** to get the memory needed to hold the sub-bitmap is the only
** that can go wrong with an insert, assuming p and i are valid.
**
** The calling function must ensure that p is a valid Bitvec object
** and that the value for "i" is within range of the Bitvec object.
** Otherwise the behavior is undefined.
*/
SQLITE_PRIVATE int sqlite3BitvecSet(Bitvec *p, u32 i){
  u32 h;
  if( p==0 ) return SQLITE_OK;
  assert( i>0 );
  assert( i<=p->iSize );
  i--;
  while((p->iSize > BITVEC_NBIT) && p->iDivisor) {
    u32 bin = i/p->iDivisor;
    i = i%p->iDivisor;
    if( p->u.apSub[bin]==0 ){
      p->u.apSub[bin] = sqlite3BitvecCreate( p->iDivisor );
      if( p->u.apSub[bin]==0 ) return SQLITE_NOMEM;
    }
    p = p->u.apSub[bin];
  }
  if( p->iSize<=BITVEC_NBIT ){
    p->u.aBitmap[i/BITVEC_SZELEM] |= 1 << (i&(BITVEC_SZELEM-1));
    return SQLITE_OK;
  }
  h = BITVEC_HASH(i++);
  /* if there wasn't a hash collision, and this doesn't */
  /* completely fill the hash, then just add it without */
  /* worring about sub-dividing and re-hashing. */
  if( !p->u.aHash[h] ){
    if (p->nSet<(BITVEC_NINT-1)) {
      goto bitvec_set_end;
    } else {
      goto bitvec_set_rehash;
    }
  }
  /* there was a collision, check to see if it's already */
  /* in hash, if not, try to find a spot for it */
  do {
    if( p->u.aHash[h]==i ) return SQLITE_OK;
    h++;
    if( h>=BITVEC_NINT ) h = 0;
  } while( p->u.aHash[h] );
  /* we didn't find it in the hash.  h points to the first */
  /* available free spot. check to see if this is going to */
  /* make our hash too "full".  */
bitvec_set_rehash:
  if( p->nSet>=BITVEC_MXHASH ){
    unsigned int j;
    int rc;
    u32 *aiValues = sqlite3StackAllocRaw(0, sizeof(p->u.aHash));
    if( aiValues==0 ){
      return SQLITE_NOMEM;
    }else{
      memcpy(aiValues, p->u.aHash, sizeof(p->u.aHash));
      memset(p->u.apSub, 0, sizeof(p->u.apSub));
      p->iDivisor = (p->iSize + BITVEC_NPTR - 1)/BITVEC_NPTR;
      rc = sqlite3BitvecSet(p, i);
      for(j=0; j<BITVEC_NINT; j++){
        if( aiValues[j] ) rc |= sqlite3BitvecSet(p, aiValues[j]);
      }
      sqlite3StackFree(0, aiValues);
      return rc;
    }
  }
bitvec_set_end:
  p->nSet++;
  p->u.aHash[h] = i;
  return SQLITE_OK;
}

/*
** Clear the i-th bit.
**
** pBuf must be a pointer to at least BITVEC_SZ bytes of temporary storage
** that BitvecClear can use to rebuilt its hash table.
*/
SQLITE_PRIVATE void sqlite3BitvecClear(Bitvec *p, u32 i, void *pBuf){
  if( p==0 ) return;
  assert( i>0 );
  i--;
  while( p->iDivisor ){
    u32 bin = i/p->iDivisor;
    i = i%p->iDivisor;
    p = p->u.apSub[bin];
    if (!p) {
      return;
    }
  }
  if( p->iSize<=BITVEC_NBIT ){
    p->u.aBitmap[i/BITVEC_SZELEM] &= ~(1 << (i&(BITVEC_SZELEM-1)));
  }else{
    unsigned int j;
    u32 *aiValues = pBuf;
    memcpy(aiValues, p->u.aHash, sizeof(p->u.aHash));
    memset(p->u.aHash, 0, sizeof(p->u.aHash));
    p->nSet = 0;
    for(j=0; j<BITVEC_NINT; j++){
      if( aiValues[j] && aiValues[j]!=(i+1) ){
        u32 h = BITVEC_HASH(aiValues[j]-1);
        p->nSet++;
        while( p->u.aHash[h] ){
          h++;
          if( h>=BITVEC_NINT ) h = 0;
        }
        p->u.aHash[h] = aiValues[j];
      }
    }
  }
}

/*
** Destroy a bitmap object.  Reclaim all memory used.
*/
SQLITE_PRIVATE void sqlite3BitvecDestroy(Bitvec *p){
  if( p==0 ) return;
  if( p->iDivisor ){
    unsigned int i;
    for(i=0; i<BITVEC_NPTR; i++){
      sqlite3BitvecDestroy(p->u.apSub[i]);
    }
  }
  sqlite3_free(p);
}

/*
** Return the value of the iSize parameter specified when Bitvec *p
** was created.
*/
SQLITE_PRIVATE u32 sqlite3BitvecSize(Bitvec *p){
  return p->iSize;
}

/************** End of bitvec.c **********************************************/
/************** Begin file pcache.c ******************************************/
/*
** 2008 August 05
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements that page cache.
*/
/* #include "sqliteInt.h" */

/*
** A complete page cache is an instance of this structure.
*/
struct PCache {
  PgHdr *pDirty, *pDirtyTail;         /* List of dirty pages in LRU order */
  PgHdr *pSynced;                     /* Last synced page in dirty page list */
  int nRefSum;                        /* Sum of ref counts over all pages */
  int szCache;                        /* Configured cache size */
  int szPage;                         /* Size of every page in this cache */
  int szExtra;                        /* Size of extra space for each page */
  u8 bPurgeable;                      /* True if pages are on backing store */
  u8 eCreate;                         /* eCreate value for for xFetch() */
  int (*xStress)(void*,PgHdr*);       /* Call to try make a page clean */
  void *pStress;                      /* Argument to xStress */
  sqlite3_pcache *pCache;             /* Pluggable cache module */
};

/********************************** Linked List Management ********************/

/* Allowed values for second argument to pcacheManageDirtyList() */
#define PCACHE_DIRTYLIST_REMOVE   1    /* Remove pPage from dirty list */
#define PCACHE_DIRTYLIST_ADD      2    /* Add pPage to the dirty list */
#define PCACHE_DIRTYLIST_FRONT    3    /* Move pPage to the front of the list */

/*
** Manage pPage's participation on the dirty list.  Bits of the addRemove
** argument determines what operation to do.  The 0x01 bit means first
** remove pPage from the dirty list.  The 0x02 means add pPage back to
** the dirty list.  Doing both moves pPage to the front of the dirty list.
*/
static void pcacheManageDirtyList(PgHdr *pPage, u8 addRemove){
  PCache *p = pPage->pCache;

  if( addRemove & PCACHE_DIRTYLIST_REMOVE ){
    assert( pPage->pDirtyNext || pPage==p->pDirtyTail );
    assert( pPage->pDirtyPrev || pPage==p->pDirty );
  
    /* Update the PCache1.pSynced variable if necessary. */
    if( p->pSynced==pPage ){
      PgHdr *pSynced = pPage->pDirtyPrev;
      while( pSynced && (pSynced->flags&PGHDR_NEED_SYNC) ){
        pSynced = pSynced->pDirtyPrev;
      }
      p->pSynced = pSynced;
    }
  
    if( pPage->pDirtyNext ){
      pPage->pDirtyNext->pDirtyPrev = pPage->pDirtyPrev;
    }else{
      assert( pPage==p->pDirtyTail );
      p->pDirtyTail = pPage->pDirtyPrev;
    }
    if( pPage->pDirtyPrev ){
      pPage->pDirtyPrev->pDirtyNext = pPage->pDirtyNext;
    }else{
      assert( pPage==p->pDirty );
      p->pDirty = pPage->pDirtyNext;
      if( p->pDirty==0 && p->bPurgeable ){
        assert( p->eCreate==1 );
        p->eCreate = 2;
      }
    }
    pPage->pDirtyNext = 0;
    pPage->pDirtyPrev = 0;
  }
  if( addRemove & PCACHE_DIRTYLIST_ADD ){
    assert( pPage->pDirtyNext==0 && pPage->pDirtyPrev==0 && p->pDirty!=pPage );
  
    pPage->pDirtyNext = p->pDirty;
    if( pPage->pDirtyNext ){
      assert( pPage->pDirtyNext->pDirtyPrev==0 );
      pPage->pDirtyNext->pDirtyPrev = pPage;
    }else{
      p->pDirtyTail = pPage;
      if( p->bPurgeable ){
        assert( p->eCreate==2 );
        p->eCreate = 1;
      }
    }
    p->pDirty = pPage;
    if( !p->pSynced && 0==(pPage->flags&PGHDR_NEED_SYNC) ){
      p->pSynced = pPage;
    }
  }
}

/*
** Wrapper around the pluggable caches xUnpin method. If the cache is
** being used for an in-memory database, this function is a no-op.
*/
static void pcacheUnpin(PgHdr *p){
  if( p->pCache->bPurgeable ){
    sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 0);
  }
}

/*
** Compute the number of pages of cache requested.  p->szCache is the
** cache size requested by the "PRAGMA cache_size" statement.
**
**
*/
static int numberOfCachePages(PCache *p){
  if( p->szCache>=0 ){
    /* IMPLEMENTATION-OF: R-42059-47211 If the argument N is positive then the
    ** suggested cache size is set to N. */
    return p->szCache;
  }else{
    /* IMPLEMENTATION-OF: R-61436-13639 If the argument N is negative, then
    ** the number of cache pages is adjusted to use approximately abs(N*1024)
    ** bytes of memory. */
    return (int)((-1024*(i64)p->szCache)/(p->szPage+p->szExtra));
  }
}

/*************************************************** General Interfaces ******
**
** Initialize and shutdown the page cache subsystem. Neither of these 
** functions are threadsafe.
*/
SQLITE_PRIVATE int sqlite3PcacheInitialize(void){
  if( sqlite3GlobalConfig.pcache2.xInit==0 ){
    /* IMPLEMENTATION-OF: R-26801-64137 If the xInit() method is NULL, then the
    ** built-in default page cache is used instead of the application defined
    ** page cache. */
    sqlite3PCacheSetDefault();
  }
  return sqlite3GlobalConfig.pcache2.xInit(sqlite3GlobalConfig.pcache2.pArg);
}
SQLITE_PRIVATE void sqlite3PcacheShutdown(void){
  if( sqlite3GlobalConfig.pcache2.xShutdown ){
    /* IMPLEMENTATION-OF: R-26000-56589 The xShutdown() method may be NULL. */
    sqlite3GlobalConfig.pcache2.xShutdown(sqlite3GlobalConfig.pcache2.pArg);
  }
}

/*
** Return the size in bytes of a PCache object.
*/
SQLITE_PRIVATE int sqlite3PcacheSize(void){ return sizeof(PCache); }

/*
** Create a new PCache object. Storage space to hold the object
** has already been allocated and is passed in as the p pointer. 
** The caller discovers how much space needs to be allocated by 
** calling sqlite3PcacheSize().
*/
SQLITE_PRIVATE int sqlite3PcacheOpen(
  int szPage,                  /* Size of every page */
  int szExtra,                 /* Extra space associated with each page */
  int bPurgeable,              /* True if pages are on backing store */
  int (*xStress)(void*,PgHdr*),/* Call to try to make pages clean */
  void *pStress,               /* Argument to xStress */
  PCache *p                    /* Preallocated space for the PCache */
){
  memset(p, 0, sizeof(PCache));
  p->szPage = 1;
  p->szExtra = szExtra;
  p->bPurgeable = bPurgeable;
  p->eCreate = 2;
  p->xStress = xStress;
  p->pStress = pStress;
  p->szCache = 100;
  return sqlite3PcacheSetPageSize(p, szPage);
}

/*
** Change the page size for PCache object. The caller must ensure that there
** are no outstanding page references when this function is called.
*/
SQLITE_PRIVATE int sqlite3PcacheSetPageSize(PCache *pCache, int szPage){
  assert( pCache->nRefSum==0 && pCache->pDirty==0 );
  if( pCache->szPage ){
    sqlite3_pcache *pNew;
    pNew = sqlite3GlobalConfig.pcache2.xCreate(
                szPage, pCache->szExtra + ROUND8(sizeof(PgHdr)),
                pCache->bPurgeable
    );
    if( pNew==0 ) return SQLITE_NOMEM;
    sqlite3GlobalConfig.pcache2.xCachesize(pNew, numberOfCachePages(pCache));
    if( pCache->pCache ){
      sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
    }
    pCache->pCache = pNew;
    pCache->szPage = szPage;
  }
  return SQLITE_OK;
}

/*
** Try to obtain a page from the cache.
**
** This routine returns a pointer to an sqlite3_pcache_page object if
** such an object is already in cache, or if a new one is created.
** This routine returns a NULL pointer if the object was not in cache
** and could not be created.
**
** The createFlags should be 0 to check for existing pages and should
** be 3 (not 1, but 3) to try to create a new page.
**
** If the createFlag is 0, then NULL is always returned if the page
** is not already in the cache.  If createFlag is 1, then a new page
** is created only if that can be done without spilling dirty pages
** and without exceeding the cache size limit.
**
** The caller needs to invoke sqlite3PcacheFetchFinish() to properly
** initialize the sqlite3_pcache_page object and convert it into a
** PgHdr object.  The sqlite3PcacheFetch() and sqlite3PcacheFetchFinish()
** routines are split this way for performance reasons. When separated
** they can both (usually) operate without having to push values to
** the stack on entry and pop them back off on exit, which saves a
** lot of pushing and popping.
*/
SQLITE_PRIVATE sqlite3_pcache_page *sqlite3PcacheFetch(
  PCache *pCache,       /* Obtain the page from this cache */
  Pgno pgno,            /* Page number to obtain */
  int createFlag        /* If true, create page if it does not exist already */
){
  int eCreate;

  assert( pCache!=0 );
  assert( pCache->pCache!=0 );
  assert( createFlag==3 || createFlag==0 );
  assert( pgno>0 );

  /* eCreate defines what to do if the page does not exist.
  **    0     Do not allocate a new page.  (createFlag==0)
  **    1     Allocate a new page if doing so is inexpensive.
  **          (createFlag==1 AND bPurgeable AND pDirty)
  **    2     Allocate a new page even it doing so is difficult.
  **          (createFlag==1 AND !(bPurgeable AND pDirty)
  */
  eCreate = createFlag & pCache->eCreate;
  assert( eCreate==0 || eCreate==1 || eCreate==2 );
  assert( createFlag==0 || pCache->eCreate==eCreate );
  assert( createFlag==0 || eCreate==1+(!pCache->bPurgeable||!pCache->pDirty) );
  return sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, eCreate);
}

/*
** If the sqlite3PcacheFetch() routine is unable to allocate a new
** page because new clean pages are available for reuse and the cache
** size limit has been reached, then this routine can be invoked to 
** try harder to allocate a page.  This routine might invoke the stress
** callback to spill dirty pages to the journal.  It will then try to
** allocate the new page and will only fail to allocate a new page on
** an OOM error.
**
** This routine should be invoked only after sqlite3PcacheFetch() fails.
*/
SQLITE_PRIVATE int sqlite3PcacheFetchStress(
  PCache *pCache,                 /* Obtain the page from this cache */
  Pgno pgno,                      /* Page number to obtain */
  sqlite3_pcache_page **ppPage    /* Write result here */
){
  PgHdr *pPg;
  if( pCache->eCreate==2 ) return 0;


  /* Find a dirty page to write-out and recycle. First try to find a 
  ** page that does not require a journal-sync (one with PGHDR_NEED_SYNC
  ** cleared), but if that is not possible settle for any other 
  ** unreferenced dirty page.
  */
  for(pPg=pCache->pSynced; 
      pPg && (pPg->nRef || (pPg->flags&PGHDR_NEED_SYNC)); 
      pPg=pPg->pDirtyPrev
  );
  pCache->pSynced = pPg;
  if( !pPg ){
    for(pPg=pCache->pDirtyTail; pPg && pPg->nRef; pPg=pPg->pDirtyPrev);
  }
  if( pPg ){
    int rc;
#ifdef SQLITE_LOG_CACHE_SPILL
    sqlite3_log(SQLITE_FULL, 
                "spill page %d making room for %d - cache used: %d/%d",
                pPg->pgno, pgno,
                sqlite3GlobalConfig.pcache.xPagecount(pCache->pCache),
                numberOfCachePages(pCache));
#endif
    rc = pCache->xStress(pCache->pStress, pPg);
    if( rc!=SQLITE_OK && rc!=SQLITE_BUSY ){
      return rc;
    }
  }
  *ppPage = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, pgno, 2);
  return *ppPage==0 ? SQLITE_NOMEM : SQLITE_OK;
}

/*
** This is a helper routine for sqlite3PcacheFetchFinish()
**
** In the uncommon case where the page being fetched has not been
** initialized, this routine is invoked to do the initialization.
** This routine is broken out into a separate function since it
** requires extra stack manipulation that can be avoided in the common
** case.
*/
static SQLITE_NOINLINE PgHdr *pcacheFetchFinishWithInit(
  PCache *pCache,             /* Obtain the page from this cache */
  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;
  assert( pPage!=0 );
  pPgHdr = (PgHdr*)pPage->pExtra;
  assert( pPgHdr->pPage==0 );
  memset(pPgHdr, 0, sizeof(PgHdr));
  pPgHdr->pPage = pPage;
  pPgHdr->pData = pPage->pBuf;
  pPgHdr->pExtra = (void *)&pPgHdr[1];
  memset(pPgHdr->pExtra, 0, pCache->szExtra);
  pPgHdr->pCache = pCache;
  pPgHdr->pgno = pgno;
  pPgHdr->flags = PGHDR_CLEAN;
  return sqlite3PcacheFetchFinish(pCache,pgno,pPage);
}

/*
** This routine converts the sqlite3_pcache_page object returned by
** sqlite3PcacheFetch() into an initialized PgHdr object.  This routine
** must be called after sqlite3PcacheFetch() in order to get a usable
** result.
*/
SQLITE_PRIVATE PgHdr *sqlite3PcacheFetchFinish(
  PCache *pCache,             /* Obtain the page from this cache */
  Pgno pgno,                  /* Page number obtained */
  sqlite3_pcache_page *pPage  /* Page obtained by prior PcacheFetch() call */
){
  PgHdr *pPgHdr;

  assert( pPage!=0 );
  pPgHdr = (PgHdr *)pPage->pExtra;

  if( !pPgHdr->pPage ){
    return pcacheFetchFinishWithInit(pCache, pgno, pPage);
  }
  pCache->nRefSum++;
  pPgHdr->nRef++;
  return pPgHdr;
}

/*
** Decrement the reference count on a page. If the page is clean and the
** reference count drops to 0, then it is made eligible for recycling.
*/
SQLITE_PRIVATE void SQLITE_NOINLINE sqlite3PcacheRelease(PgHdr *p){
  assert( p->nRef>0 );
  p->pCache->nRefSum--;
  if( (--p->nRef)==0 ){
    if( p->flags&PGHDR_CLEAN ){
      pcacheUnpin(p);
    }else if( p->pDirtyPrev!=0 ){
      /* Move the page to the head of the dirty list. */
      pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
    }
  }
}

/*
** Increase the reference count of a supplied page by 1.
*/
SQLITE_PRIVATE void sqlite3PcacheRef(PgHdr *p){
  assert(p->nRef>0);
  p->nRef++;
  p->pCache->nRefSum++;
}

/*
** Drop a page from the cache. There must be exactly one reference to the
** page. This function deletes that reference, so after it returns the
** page pointed to by p is invalid.
*/
SQLITE_PRIVATE void sqlite3PcacheDrop(PgHdr *p){
  assert( p->nRef==1 );
  if( p->flags&PGHDR_DIRTY ){
    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
  }
  p->pCache->nRefSum--;
  sqlite3GlobalConfig.pcache2.xUnpin(p->pCache->pCache, p->pPage, 1);
}

/*
** Make sure the page is marked as dirty. If it isn't dirty already,
** make it so.
*/
SQLITE_PRIVATE void sqlite3PcacheMakeDirty(PgHdr *p){
  assert( p->nRef>0 );
  if( p->flags & (PGHDR_CLEAN|PGHDR_DONT_WRITE) ){
    p->flags &= ~PGHDR_DONT_WRITE;
    if( p->flags & PGHDR_CLEAN ){
      p->flags ^= (PGHDR_DIRTY|PGHDR_CLEAN);
      assert( (p->flags & (PGHDR_DIRTY|PGHDR_CLEAN))==PGHDR_DIRTY );
      pcacheManageDirtyList(p, PCACHE_DIRTYLIST_ADD);
    }
  }
}

/*
** Make sure the page is marked as clean. If it isn't clean already,
** make it so.
*/
SQLITE_PRIVATE void sqlite3PcacheMakeClean(PgHdr *p){
  if( (p->flags & PGHDR_DIRTY) ){
    assert( (p->flags & PGHDR_CLEAN)==0 );
    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_REMOVE);
    p->flags &= ~(PGHDR_DIRTY|PGHDR_NEED_SYNC|PGHDR_WRITEABLE);
    p->flags |= PGHDR_CLEAN;
    if( p->nRef==0 ){
      pcacheUnpin(p);
    }
  }
}

/*
** Make every page in the cache clean.
*/
SQLITE_PRIVATE void sqlite3PcacheCleanAll(PCache *pCache){
  PgHdr *p;
  while( (p = pCache->pDirty)!=0 ){
    sqlite3PcacheMakeClean(p);
  }
}

/*
** Clear the PGHDR_NEED_SYNC flag from all dirty pages.
*/
SQLITE_PRIVATE void sqlite3PcacheClearSyncFlags(PCache *pCache){
  PgHdr *p;
  for(p=pCache->pDirty; p; p=p->pDirtyNext){
    p->flags &= ~PGHDR_NEED_SYNC;
  }
  pCache->pSynced = pCache->pDirtyTail;
}

/*
** Change the page number of page p to newPgno. 
*/
SQLITE_PRIVATE void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
  PCache *pCache = p->pCache;
  assert( p->nRef>0 );
  assert( newPgno>0 );
  sqlite3GlobalConfig.pcache2.xRekey(pCache->pCache, p->pPage, p->pgno,newPgno);
  p->pgno = newPgno;
  if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
    pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
  }
}

/*
** Drop every cache entry whose page number is greater than "pgno". The
** caller must ensure that there are no outstanding references to any pages
** other than page 1 with a page number greater than pgno.
**
** If there is a reference to page 1 and the pgno parameter passed to this
** function is 0, then the data area associated with page 1 is zeroed, but
** the page object is not dropped.
*/
SQLITE_PRIVATE void sqlite3PcacheTruncate(PCache *pCache, Pgno pgno){
  if( pCache->pCache ){
    PgHdr *p;
    PgHdr *pNext;
    for(p=pCache->pDirty; p; p=pNext){
      pNext = p->pDirtyNext;
      /* This routine never gets call with a positive pgno except right
      ** after sqlite3PcacheCleanAll().  So if there are dirty pages,
      ** it must be that pgno==0.
      */
      assert( p->pgno>0 );
      if( ALWAYS(p->pgno>pgno) ){
        assert( p->flags&PGHDR_DIRTY );
        sqlite3PcacheMakeClean(p);
      }
    }
    if( pgno==0 && pCache->nRefSum ){
      sqlite3_pcache_page *pPage1;
      pPage1 = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache,1,0);
      if( ALWAYS(pPage1) ){  /* Page 1 is always available in cache, because
                             ** pCache->nRefSum>0 */
        memset(pPage1->pBuf, 0, pCache->szPage);
        pgno = 1;
      }
    }
    sqlite3GlobalConfig.pcache2.xTruncate(pCache->pCache, pgno+1);
  }
}

/*
** Close a cache.
*/
SQLITE_PRIVATE void sqlite3PcacheClose(PCache *pCache){
  assert( pCache->pCache!=0 );
  sqlite3GlobalConfig.pcache2.xDestroy(pCache->pCache);
}

/* 
** Discard the contents of the cache.
*/
SQLITE_PRIVATE void sqlite3PcacheClear(PCache *pCache){
  sqlite3PcacheTruncate(pCache, 0);
}

/*
** Merge two lists of pages connected by pDirty and in pgno order.
** Do not both fixing the pDirtyPrev pointers.
*/
static PgHdr *pcacheMergeDirtyList(PgHdr *pA, PgHdr *pB){
  PgHdr result, *pTail;
  pTail = &result;
  while( pA && pB ){
    if( pA->pgno<pB->pgno ){
      pTail->pDirty = pA;
      pTail = pA;
      pA = pA->pDirty;
    }else{
      pTail->pDirty = pB;
      pTail = pB;
      pB = pB->pDirty;
    }
  }
  if( pA ){
    pTail->pDirty = pA;
  }else if( pB ){
    pTail->pDirty = pB;
  }else{
    pTail->pDirty = 0;
  }
  return result.pDirty;
}

/*
** Sort the list of pages in accending order by pgno.  Pages are
** connected by pDirty pointers.  The pDirtyPrev pointers are
** corrupted by this sort.
**
** Since there cannot be more than 2^31 distinct pages in a database,
** there cannot be more than 31 buckets required by the merge sorter.
** One extra bucket is added to catch overflow in case something
** ever changes to make the previous sentence incorrect.
*/
#define N_SORT_BUCKET  32
static PgHdr *pcacheSortDirtyList(PgHdr *pIn){
  PgHdr *a[N_SORT_BUCKET], *p;
  int i;
  memset(a, 0, sizeof(a));
  while( pIn ){
    p = pIn;
    pIn = p->pDirty;
    p->pDirty = 0;
    for(i=0; ALWAYS(i<N_SORT_BUCKET-1); i++){
      if( a[i]==0 ){
        a[i] = p;
        break;
      }else{
        p = pcacheMergeDirtyList(a[i], p);
        a[i] = 0;
      }
    }
    if( NEVER(i==N_SORT_BUCKET-1) ){
      /* To get here, there need to be 2^(N_SORT_BUCKET) elements in
      ** the input list.  But that is impossible.
      */
      a[i] = pcacheMergeDirtyList(a[i], p);
    }
  }
  p = a[0];
  for(i=1; i<N_SORT_BUCKET; i++){
    p = pcacheMergeDirtyList(p, a[i]);
  }
  return p;
}

/*
** Return a list of all dirty pages in the cache, sorted by page number.
*/
SQLITE_PRIVATE PgHdr *sqlite3PcacheDirtyList(PCache *pCache){
  PgHdr *p;
  for(p=pCache->pDirty; p; p=p->pDirtyNext){
    p->pDirty = p->pDirtyNext;
  }
  return pcacheSortDirtyList(pCache->pDirty);
}

/* 
** Return the total number of references to all pages held by the cache.
**
** This is not the total number of pages referenced, but the sum of the
** reference count for all pages.
*/
SQLITE_PRIVATE int sqlite3PcacheRefCount(PCache *pCache){
  return pCache->nRefSum;
}

/*
** Return the number of references to the page supplied as an argument.
*/
SQLITE_PRIVATE int sqlite3PcachePageRefcount(PgHdr *p){
  return p->nRef;
}

#ifdef SQLITE_TEST
/* 
** Return the total number of pages in the cache.
*/
SQLITE_PRIVATE int sqlite3PcachePagecount(PCache *pCache){
  assert( pCache->pCache!=0 );
  return sqlite3GlobalConfig.pcache2.xPagecount(pCache->pCache);
}

/*
** Get the suggested cache-size value.
*/
SQLITE_PRIVATE int sqlite3PcacheGetCachesize(PCache *pCache){
  return numberOfCachePages(pCache);
}
#endif

/*
** Set the suggested cache-size value.
*/
SQLITE_PRIVATE void sqlite3PcacheSetCachesize(PCache *pCache, int mxPage){
  assert( pCache->pCache!=0 );
  pCache->szCache = mxPage;
  sqlite3GlobalConfig.pcache2.xCachesize(pCache->pCache,
                                         numberOfCachePages(pCache));
}

#if 0
/*
** Free up as much memory as possible from the page cache.
*/
SQLITE_PRIVATE void sqlite3PcacheShrink(PCache *pCache){
  assert( pCache->pCache!=0 );
  sqlite3GlobalConfig.pcache2.xShrink(pCache->pCache);
}
#endif

/*
** Return the size of the header added by this middleware layer
** in the page-cache hierarchy.
*/
SQLITE_PRIVATE int sqlite3HeaderSizePcache(void){ return ROUND8(sizeof(PgHdr)); }


#if defined(SQLITE_CHECK_PAGES) || defined(SQLITE_DEBUG)
/*
** For all dirty pages currently in the cache, invoke the specified
** callback. This is only used if the SQLITE_CHECK_PAGES macro is
** defined.
*/
SQLITE_PRIVATE void sqlite3PcacheIterateDirty(PCache *pCache, void (*xIter)(PgHdr *)){
  PgHdr *pDirty;
  for(pDirty=pCache->pDirty; pDirty; pDirty=pDirty->pDirtyNext){
    xIter(pDirty);
  }
}
#endif

/************** End of pcache.c **********************************************/
/************** Begin file pcache1.c *****************************************/
/*
** 2008 November 05
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file implements the default page cache implementation (the
** sqlite3_pcache interface). It also contains part of the implementation
** of the SQLITE_CONFIG_PAGECACHE and sqlite3_release_memory() features.
** If the default page cache implementation is overridden, then neither of
** these two features are available.
**
** A Page cache line looks like this:
**
**  -------------------------------------------------------------
**  |  database page content   |  PgHdr1  |  MemPage  |  PgHdr  |
**  -------------------------------------------------------------
**
** The database page content is up front (so that buffer overreads tend to
** flow harmlessly into the PgHdr1, MemPage, and PgHdr extensions).   MemPage
** is the extension added by the btree.c module containing information such
** as the database page number and how that database page is used.  PgHdr
** is added by the pcache.c layer and contains information used to keep track
** of which pages are "dirty".  PgHdr1 is an extension added by this
** module (pcache1.c).  The PgHdr1 header is a subclass of sqlite3_pcache_page.
** PgHdr1 contains information needed to look up a page by its page number.
** The superclass sqlite3_pcache_page.pBuf points to the start of the
** database page content and sqlite3_pcache_page.pExtra points to PgHdr.
**
** The size of the extension (MemPage+PgHdr+PgHdr1) can be determined at
** runtime using sqlite3_config(SQLITE_CONFIG_PCACHE_HDRSZ, &size).  The
** sizes of the extensions sum to 272 bytes on x64 for 3.8.10, but this
** size can vary according to architecture, compile-time options, and
** SQLite library version number.
**
** If SQLITE_PCACHE_SEPARATE_HEADER is defined, then the extension is obtained
** using a separate memory allocation from the database page content.  This
** seeks to overcome the "clownshoe" problem (also called "internal
** fragmentation" in academic literature) of allocating a few bytes more
** than a power of two with the memory allocator rounding up to the next
** power of two, and leaving the rounded-up space unused.
**
** This module tracks pointers to PgHdr1 objects.  Only pcache.c communicates
** with this module.  Information is passed back and forth as PgHdr1 pointers.
**
** The pcache.c and pager.c modules deal pointers to PgHdr objects.
** The btree.c module deals with pointers to MemPage objects.
**
** SOURCE OF PAGE CACHE MEMORY:
**
** Memory for a page might come from any of three sources:
**
**    (1)  The general-purpose memory allocator - sqlite3Malloc()
**    (2)  Global page-cache memory provided using sqlite3_config() with
**         SQLITE_CONFIG_PAGECACHE.
**    (3)  PCache-local bulk allocation.
**
** The third case is a chunk of heap memory (defaulting to 100 pages worth)
** that is allocated when the page cache is created.  The size of the local
** bulk allocation can be adjusted using 
**
**     sqlite3_config(SQLITE_CONFIG_PAGECACHE, 0, 0, N).
**
** If N is positive, then N pages worth of memory are allocated using a single
** sqlite3Malloc() call and that memory is used for the first N pages allocated.
** Or if N is negative, then -1024*N bytes of memory are allocated and used
** for as many pages as can be accomodated.
**
** Only one of (2) or (3) can be used.  Once the memory available to (2) or
** (3) is exhausted, subsequent allocations fail over to the general-purpose
** memory allocator (1).
**
** Earlier versions of SQLite used only methods (1) and (2).  But experiments
** show that method (3) with N==100 provides about a 5% performance boost for
** common workloads.
*/
/* #include "sqliteInt.h" */

typedef struct PCache1 PCache1;
typedef struct PgHdr1 PgHdr1;
typedef struct PgFreeslot PgFreeslot;
typedef struct PGroup PGroup;

/*
** Each cache entry is represented by an instance of the following 
** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of
** PgHdr1.pCache->szPage bytes is allocated directly before this structure 
** in memory.
*/
struct PgHdr1 {
  sqlite3_pcache_page page;      /* Base class. Must be first. pBuf & pExtra */
  unsigned int iKey;             /* Key value (page number) */
  u8 isPinned;                   /* Page in use, not on the LRU list */
  u8 isBulkLocal;                /* This page from bulk local storage */
  u8 isAnchor;                   /* This is the PGroup.lru element */
  PgHdr1 *pNext;                 /* Next in hash table chain */
  PCache1 *pCache;               /* Cache that currently owns this page */
  PgHdr1 *pLruNext;              /* Next in LRU list of unpinned pages */
  PgHdr1 *pLruPrev;              /* Previous in LRU list of unpinned pages */
};

/* Each page cache (or PCache) belongs to a PGroup.  A PGroup is a set 
** of one or more PCaches that are able to recycle each other's unpinned
** pages when they are under memory pressure.  A PGroup is an instance of
** the following object.
**
** This page cache implementation works in one of two modes:
**
**   (1)  Every PCache is the sole member of its own PGroup.  There is
**        one PGroup per PCache.
**
**   (2)  There is a single global PGroup that all PCaches are a member
**        of.
**
** Mode 1 uses more memory (since PCache instances are not able to rob
** unused pages from other PCaches) but it also operates without a mutex,
** and is therefore often faster.  Mode 2 requires a mutex in order to be
** threadsafe, but recycles pages more efficiently.
**
** For mode (1), PGroup.mutex is NULL.  For mode (2) there is only a single
** PGroup which is the pcache1.grp global variable and its mutex is
** SQLITE_MUTEX_STATIC_LRU.
*/
struct PGroup {
  sqlite3_mutex *mutex;          /* MUTEX_STATIC_LRU or NULL */
  unsigned int nMaxPage;         /* Sum of nMax for purgeable caches */
  unsigned int nMinPage;         /* Sum of nMin for purgeable caches */
  unsigned int mxPinned;         /* nMaxpage + 10 - nMinPage */
  unsigned int nCurrentPage;     /* Number of purgeable pages allocated */
  PgHdr1 lru;                    /* The beginning and end of the LRU list */
};

/* Each page cache is an instance of the following object.  Every
** open database file (including each in-memory database and each
** temporary or transient database) has a single page cache which
** is an instance of this object.
**
** Pointers to structures of this type are cast and returned as 
** opaque sqlite3_pcache* handles.
*/
struct PCache1 {
  /* Cache configuration parameters. Page size (szPage) and the purgeable
  ** flag (bPurgeable) are set when the cache is created. nMax may be 
  ** modified at any time by a call to the pcache1Cachesize() method.
  ** The PGroup mutex must be held when accessing nMax.
  */
  PGroup *pGroup;                     /* PGroup this cache belongs to */
  int szPage;                         /* Size of database content section */
  int szExtra;                        /* sizeof(MemPage)+sizeof(PgHdr) */
  int szAlloc;                        /* Total size of one pcache line */
  int bPurgeable;                     /* True if cache is purgeable */
  unsigned int nMin;                  /* Minimum number of pages reserved */
  unsigned int nMax;                  /* Configured "cache_size" value */
  unsigned int n90pct;                /* nMax*9/10 */
  unsigned int iMaxKey;               /* Largest key seen since xTruncate() */

  /* Hash table of all pages. The following variables may only be accessed
  ** when the accessor is holding the PGroup mutex.
  */
  unsigned int nRecyclable;           /* Number of pages in the LRU list */
  unsigned int nPage;                 /* Total number of pages in apHash */
  unsigned int nHash;                 /* Number of slots in apHash[] */
  PgHdr1 **apHash;                    /* Hash table for fast lookup by key */
  PgHdr1 *pFree;                      /* List of unused pcache-local pages */
  void *pBulk;                        /* Bulk memory used by pcache-local */
};

/*
** Free slots in the allocator used to divide up the global page cache
** buffer provided using the SQLITE_CONFIG_PAGECACHE mechanism.
*/
struct PgFreeslot {
  PgFreeslot *pNext;  /* Next free slot */
};

/*
** Global data used by this cache.
*/
static SQLITE_WSD struct PCacheGlobal {
  PGroup grp;                    /* The global PGroup for mode (2) */

  /* Variables related to SQLITE_CONFIG_PAGECACHE settings.  The
  ** szSlot, nSlot, pStart, pEnd, nReserve, and isInit values are all
  ** fixed at sqlite3BtreeInitialize() time and do not require mutex protection.
  ** The nFreeSlot and pFree values do require mutex protection.
  */
  int isInit;                    /* True if initialized */
  int separateCache;             /* Use a new PGroup for each PCache */
  int nInitPage;                 /* Initial bulk allocation size */   
  int szSlot;                    /* Size of each free slot */
  int nSlot;                     /* The number of pcache slots */
  int nReserve;                  /* Try to keep nFreeSlot above this */
  void *pStart, *pEnd;           /* Bounds of global page cache memory */
  /* Above requires no mutex.  Use mutex below for variable that follow. */
  sqlite3_mutex *mutex;          /* Mutex for accessing the following: */
  PgFreeslot *pFree;             /* Free page blocks */
  int nFreeSlot;                 /* Number of unused pcache slots */
  /* The following value requires a mutex to change.  We skip the mutex on
  ** reading because (1) most platforms read a 32-bit integer atomically and
  ** (2) even if an incorrect value is read, no great harm is done since this
  ** is really just an optimization. */
  int bUnderPressure;            /* True if low on PAGECACHE memory */
} pcache1_g;

/*
** All code in this file should access the global structure above via the
** alias "pcache1". This ensures that the WSD emulation is used when
** compiling for systems that do not support real WSD.
*/
#define pcache1 (GLOBAL(struct PCacheGlobal, pcache1_g))

/*
** Macros to enter and leave the PCache LRU mutex.
*/
#if !defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) || SQLITE_THREADSAFE==0
# define pcache1EnterMutex(X)  assert((X)->mutex==0)
# define pcache1LeaveMutex(X)  assert((X)->mutex==0)
# define PCACHE1_MIGHT_USE_GROUP_MUTEX 0
#else
# define pcache1EnterMutex(X) sqlite3_mutex_enter((X)->mutex)
# define pcache1LeaveMutex(X) sqlite3_mutex_leave((X)->mutex)
# define PCACHE1_MIGHT_USE_GROUP_MUTEX 1
#endif

/******************************************************************************/
/******** Page Allocation/SQLITE_CONFIG_PCACHE Related Functions **************/


/*
** This function is called during initialization if a static buffer is 
** supplied to use for the page-cache by passing the SQLITE_CONFIG_PAGECACHE
** verb to sqlite3_config(). Parameter pBuf points to an allocation large
** enough to contain 'n' buffers of 'sz' bytes each.
**
** This routine is called from sqlite3_initialize() and so it is guaranteed
** to be serialized already.  There is no need for further mutexing.
*/
SQLITE_PRIVATE void sqlite3PCacheBufferSetup(void *pBuf, int sz, int n){
  if( pcache1.isInit ){
    PgFreeslot *p;
    if( pBuf==0 ) sz = n = 0;
    sz = ROUNDDOWN8(sz);
    pcache1.szSlot = sz;
    pcache1.nSlot = pcache1.nFreeSlot = n;
    pcache1.nReserve = n>90 ? 10 : (n/10 + 1);
    pcache1.pStart = pBuf;
    pcache1.pFree = 0;
    pcache1.bUnderPressure = 0;
    while( n-- ){
      p = (PgFreeslot*)pBuf;
      p->pNext = pcache1.pFree;
      pcache1.pFree = p;
      pBuf = (void*)&((char*)pBuf)[sz];
    }
    pcache1.pEnd = pBuf;
  }
}

/*
** Try to initialize the pCache->pFree and pCache->pBulk fields.  Return
** true if pCache->pFree ends up containing one or more free pages.
*/
static int pcache1InitBulk(PCache1 *pCache){
  i64 szBulk;
  char *zBulk;
  if( pcache1.nInitPage==0 ) return 0;
  /* Do not bother with a bulk allocation if the cache size very small */
  if( pCache->nMax<3 ) return 0;
  if( pcache1.nInitPage>0 ){
    szBulk = pCache->szAlloc * (i64)pcache1.nInitPage;
  }else{
    szBulk = -1024 * (i64)pcache1.nInitPage;
  }
  if( szBulk > pCache->szAlloc*(i64)pCache->nMax ){
    szBulk = pCache->szAlloc*pCache->nMax;
  }
  zBulk = pCache->pBulk = sqlite3Malloc( szBulk );
  if( zBulk ){
    int nBulk = sqlite3MallocSize(zBulk)/pCache->szAlloc;
    int i;
    for(i=0; i<nBulk; i++){
      PgHdr1 *pX = (PgHdr1*)&zBulk[pCache->szPage];
      pX->page.pBuf = zBulk;
      pX->page.pExtra = &pX[1];
      pX->isBulkLocal = 1;
      pX->isAnchor = 0;
      pX->pNext = pCache->pFree;
      pCache->pFree = pX;
      zBulk += pCache->szAlloc;
    }
  }
  return pCache->pFree!=0;
}

/*
** Malloc function used within this file to allocate space from the buffer
** configured using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no 
** such buffer exists or there is no space left in it, this function falls 
** back to sqlite3Malloc().
**
** Multiple threads can run this routine at the same time.  Global variables
** in pcache1 need to be protected via mutex.
*/
static void *pcache1Alloc(int nByte){
  void *p = 0;
  assert( sqlite3_mutex_notheld(pcache1.grp.mutex) );
  if( nByte<=pcache1.szSlot ){
    sqlite3_mutex_enter(pcache1.mutex);
    p = (PgHdr1 *)pcache1.pFree;
    if( p ){
      pcache1.pFree = pcache1.pFree->pNext;
      pcache1.nFreeSlot--;
      pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve;
      assert( pcache1.nFreeSlot>=0 );
      sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, nByte);
      sqlite3StatusUp(SQLITE_STATUS_PAGECACHE_USED, 1);
    }
    sqlite3_mutex_leave(pcache1.mutex);
  }
  if( p==0 ){
    /* Memory is not available in the SQLITE_CONFIG_PAGECACHE pool.  Get
    ** it from sqlite3Malloc instead.
    */
    p = sqlite3Malloc(nByte);
#ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS
    if( p ){
      int sz = sqlite3MallocSize(p);
      sqlite3_mutex_enter(pcache1.mutex);
      sqlite3StatusSet(SQLITE_STATUS_PAGECACHE_SIZE, nByte);
      sqlite3StatusUp(SQLITE_STATUS_PAGECACHE_OVERFLOW, sz);
      sqlite3_mutex_leave(pcache1.mutex);
    }
#endif
    sqlite3MemdebugSetType(p, MEMTYPE_PCACHE);
  }
  return p;
}

/*
** Free an allocated buffer obtained from pcache1Alloc().
*/
static void pcache1Free(void *p){
  int nFreed = 0;
  if( p==0 ) return;
  if( p>=pcache1.pStart && p<pcache1.pEnd ){
    PgFreeslot *pSlot;
    sqlite3_mutex_enter(pcache1.mutex);
    sqlite3StatusDown(SQLITE_STATUS_PAGECACHE_USED, 1);
    pSlot = (PgFreeslot*)p;
    pSlot->pNext = pcache1.pFree;
    pcache1.pFree = pSlot;
    pcache1.nFreeSlot++;
    pcache1.bUnderPressure = pcache1.nFreeSlot<pcache1.nReserve;
    assert( pcache1.nFreeSlot<=pcache1.nSlot );
    sqlite3_mutex_leave(pcache1.mutex);
  }else{
    assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) );
    sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
#ifndef SQLITE_DISABLE_PAGECACHE_OVERFLOW_STATS
    nFreed = sqlite3MallocSize(p);
    sqlite3_mutex_enter(pcache1.mutex);
    sqlite3StatusDown(SQLITE_STATUS_PAGECACHE_OVERFLOW, nFreed);
    sqlite3_mutex_leave(pcache1.mutex);
#endif
    sqlite3_free(p);
  }
}

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** Return the size of a pcache allocation
*/
static int pcache1MemSize(void *p){
  if( p>=pcache1.pStart && p<pcache1.pEnd ){
    return pcache1.szSlot;
  }else{
    int iSize;
    assert( sqlite3MemdebugHasType(p, MEMTYPE_PCACHE) );
    sqlite3MemdebugSetType(p, MEMTYPE_HEAP);
    iSize = sqlite3MallocSize(p);
    sqlite3MemdebugSetType(p, MEMTYPE_PCACHE);
    return iSize;
  }
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

/*
** Allocate a new page object initially associated with cache pCache.
*/
static PgHdr1 *pcache1AllocPage(PCache1 *pCache, int benignMalloc){
  PgHdr1 *p = 0;
  void *pPg;

  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  if( pCache->pFree || (pCache->nPage==0 && pcache1InitBulk(pCache)) ){
    p = pCache->pFree;
    pCache->pFree = p->pNext;
    p->pNext = 0;
  }else{
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
    /* The group mutex must be released before pcache1Alloc() is called. This
    ** is because it might call sqlite3_release_memory(), which assumes that 
    ** this mutex is not held. */
    assert( pcache1.separateCache==0 );
    assert( pCache->pGroup==&pcache1.grp );
    pcache1LeaveMutex(pCache->pGroup);
#endif
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
    pPg = pcache1Alloc(pCache->szPage);
    p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra);
    if( !pPg || !p ){
      pcache1Free(pPg);
      sqlite3_free(p);
      pPg = 0;
    }
#else
    pPg = pcache1Alloc(pCache->szAlloc);
    p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
#endif
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
    pcache1EnterMutex(pCache->pGroup);
#endif
    if( pPg==0 ) return 0;
    p->page.pBuf = pPg;
    p->page.pExtra = &p[1];
    p->isBulkLocal = 0;
    p->isAnchor = 0;
  }
  if( pCache->bPurgeable ){
    pCache->pGroup->nCurrentPage++;
  }
  return p;
}

/*
** Free a page object allocated by pcache1AllocPage().
*/
static void pcache1FreePage(PgHdr1 *p){
  PCache1 *pCache;
  assert( p!=0 );
  pCache = p->pCache;
  assert( sqlite3_mutex_held(p->pCache->pGroup->mutex) );
  if( p->isBulkLocal ){
    p->pNext = pCache->pFree;
    pCache->pFree = p;
  }else{
    pcache1Free(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
    sqlite3_free(p);
#endif
  }
  if( pCache->bPurgeable ){
    pCache->pGroup->nCurrentPage--;
  }
}

/*
** Malloc function used by SQLite to obtain space from the buffer configured
** using sqlite3_config(SQLITE_CONFIG_PAGECACHE) option. If no such buffer
** exists, this function falls back to sqlite3Malloc().
*/
SQLITE_PRIVATE void *sqlite3PageMalloc(int sz){
  return pcache1Alloc(sz);
}

/*
** Free an allocated buffer obtained from sqlite3PageMalloc().
*/
SQLITE_PRIVATE void sqlite3PageFree(void *p){
  pcache1Free(p);
}


/*
** Return true if it desirable to avoid allocating a new page cache
** entry.
**
** If memory was allocated specifically to the page cache using
** SQLITE_CONFIG_PAGECACHE but that memory has all been used, then
** it is desirable to avoid allocating a new page cache entry because
** presumably SQLITE_CONFIG_PAGECACHE was suppose to be sufficient
** for all page cache needs and we should not need to spill the
** allocation onto the heap.
**
** Or, the heap is used for all page cache memory but the heap is
** under memory pressure, then again it is desirable to avoid
** allocating a new page cache entry in order to avoid stressing
** the heap even further.
*/
static int pcache1UnderMemoryPressure(PCache1 *pCache){
  if( pcache1.nSlot && (pCache->szPage+pCache->szExtra)<=pcache1.szSlot ){
    return pcache1.bUnderPressure;
  }else{
    return sqlite3HeapNearlyFull();
  }
}

/******************************************************************************/
/******** General Implementation Functions ************************************/

/*
** This function is used to resize the hash table used by the cache passed
** as the first argument.
**
** The PCache mutex must be held when this function is called.
*/
static void pcache1ResizeHash(PCache1 *p){
  PgHdr1 **apNew;
  unsigned int nNew;
  unsigned int i;

  assert( sqlite3_mutex_held(p->pGroup->mutex) );

  nNew = p->nHash*2;
  if( nNew<256 ){
    nNew = 256;
  }

  pcache1LeaveMutex(p->pGroup);
  apNew = (PgHdr1 **)sqlite3MallocZero(sizeof(PgHdr1 *)*nNew);
  pcache1EnterMutex(p->pGroup);
  if( apNew ){
    for(i=0; i<p->nHash; i++){
      PgHdr1 *pPage;
      PgHdr1 *pNext = p->apHash[i];
      while( (pPage = pNext)!=0 ){
        unsigned int h = pPage->iKey % nNew;
        pNext = pPage->pNext;
        pPage->pNext = apNew[h];
        apNew[h] = pPage;
      }
    }
    sqlite3_free(p->apHash);
    p->apHash = apNew;
    p->nHash = nNew;
  }
}

/*
** This function is used internally to remove the page pPage from the 
** PGroup LRU list, if is part of it. If pPage is not part of the PGroup
** LRU list, then this function is a no-op.
**
** The PGroup mutex must be held when this function is called.
*/
static PgHdr1 *pcache1PinPage(PgHdr1 *pPage){
  PCache1 *pCache;

  assert( pPage!=0 );
  assert( pPage->isPinned==0 );
  pCache = pPage->pCache;
  assert( pPage->pLruNext );
  assert( pPage->pLruPrev );
  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  pPage->pLruPrev->pLruNext = pPage->pLruNext;
  pPage->pLruNext->pLruPrev = pPage->pLruPrev;
  pPage->pLruNext = 0;
  pPage->pLruPrev = 0;
  pPage->isPinned = 1;
  assert( pPage->isAnchor==0 );
  assert( pCache->pGroup->lru.isAnchor==1 );
  pCache->nRecyclable--;
  return pPage;
}


/*
** Remove the page supplied as an argument from the hash table 
** (PCache1.apHash structure) that it is currently stored in.
** Also free the page if freePage is true.
**
** The PGroup mutex must be held when this function is called.
*/
static void pcache1RemoveFromHash(PgHdr1 *pPage, int freeFlag){
  unsigned int h;
  PCache1 *pCache = pPage->pCache;
  PgHdr1 **pp;

  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  h = pPage->iKey % pCache->nHash;
  for(pp=&pCache->apHash[h]; (*pp)!=pPage; pp=&(*pp)->pNext);
  *pp = (*pp)->pNext;

  pCache->nPage--;
  if( freeFlag ) pcache1FreePage(pPage);
}

/*
** If there are currently more than nMaxPage pages allocated, try
** to recycle pages to reduce the number allocated to nMaxPage.
*/
static void pcache1EnforceMaxPage(PCache1 *pCache){
  PGroup *pGroup = pCache->pGroup;
  PgHdr1 *p;
  assert( sqlite3_mutex_held(pGroup->mutex) );
  while( pGroup->nCurrentPage>pGroup->nMaxPage
      && (p=pGroup->lru.pLruPrev)->isAnchor==0
  ){
    assert( p->pCache->pGroup==pGroup );
    assert( p->isPinned==0 );
    pcache1PinPage(p);
    pcache1RemoveFromHash(p, 1);
  }
  if( pCache->nPage==0 && pCache->pBulk ){
    sqlite3_free(pCache->pBulk);
    pCache->pBulk = pCache->pFree = 0;
  }
}

/*
** Discard all pages from cache pCache with a page number (key value) 
** greater than or equal to iLimit. Any pinned pages that meet this 
** criteria are unpinned before they are discarded.
**
** The PCache mutex must be held when this function is called.
*/
static void pcache1TruncateUnsafe(
  PCache1 *pCache,             /* The cache to truncate */
  unsigned int iLimit          /* Drop pages with this pgno or larger */
){
  TESTONLY( unsigned int nPage = 0; )  /* To assert pCache->nPage is correct */
  unsigned int h;
  assert( sqlite3_mutex_held(pCache->pGroup->mutex) );
  for(h=0; h<pCache->nHash; h++){
    PgHdr1 **pp = &pCache->apHash[h]; 
    PgHdr1 *pPage;
    while( (pPage = *pp)!=0 ){
      if( pPage->iKey>=iLimit ){
        pCache->nPage--;
        *pp = pPage->pNext;
        if( !pPage->isPinned ) pcache1PinPage(pPage);
        pcache1FreePage(pPage);
      }else{
        pp = &pPage->pNext;
        TESTONLY( nPage++; )
      }
    }
  }
  assert( pCache->nPage==nPage );
}

/******************************************************************************/
/******** sqlite3_pcache Methods **********************************************/

/*
** Implementation of the sqlite3_pcache.xInit method.
*/
static int pcache1Init(void *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  assert( pcache1.isInit==0 );
  memset(&pcache1, 0, sizeof(pcache1));


  /*
  ** The pcache1.separateCache variable is true if each PCache has its own
  ** private PGroup (mode-1).  pcache1.separateCache is false if the single
  ** PGroup in pcache1.grp is used for all page caches (mode-2).
  **
  **   *  Always use a unified cache (mode-2) if ENABLE_MEMORY_MANAGEMENT
  **
  **   *  Use a unified cache in single-threaded applications that have
  **      configured a start-time buffer for use as page-cache memory using
  **      sqlite3_config(SQLITE_CONFIG_PAGECACHE, pBuf, sz, N) with non-NULL 
  **      pBuf argument.
  **
  **   *  Otherwise use separate caches (mode-1)
  */
#if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT)
  pcache1.separateCache = 0;
#elif SQLITE_THREADSAFE
  pcache1.separateCache = sqlite3GlobalConfig.pPage==0
                          || sqlite3GlobalConfig.bCoreMutex>0;
#else
  pcache1.separateCache = sqlite3GlobalConfig.pPage==0;
#endif

#if SQLITE_THREADSAFE
  if( sqlite3GlobalConfig.bCoreMutex ){
    pcache1.grp.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_LRU);
    pcache1.mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PMEM);
  }
#endif
  if( pcache1.separateCache
   && sqlite3GlobalConfig.nPage!=0
   && sqlite3GlobalConfig.pPage==0
  ){
    pcache1.nInitPage = sqlite3GlobalConfig.nPage;
  }else{
    pcache1.nInitPage = 0;
  }
  pcache1.grp.mxPinned = 10;
  pcache1.isInit = 1;
  return SQLITE_OK;
}

/*
** Implementation of the sqlite3_pcache.xShutdown method.
** Note that the static mutex allocated in xInit does 
** not need to be freed.
*/
static void pcache1Shutdown(void *NotUsed){
  UNUSED_PARAMETER(NotUsed);
  assert( pcache1.isInit!=0 );
  memset(&pcache1, 0, sizeof(pcache1));
}

/* forward declaration */
static void pcache1Destroy(sqlite3_pcache *p);

/*
** Implementation of the sqlite3_pcache.xCreate method.
**
** Allocate a new cache.
*/
static sqlite3_pcache *pcache1Create(int szPage, int szExtra, int bPurgeable){
  PCache1 *pCache;      /* The newly created page cache */
  PGroup *pGroup;       /* The group the new page cache will belong to */
  int sz;               /* Bytes of memory required to allocate the new cache */

  assert( (szPage & (szPage-1))==0 && szPage>=512 && szPage<=65536 );
  assert( szExtra < 300 );

  sz = sizeof(PCache1) + sizeof(PGroup)*pcache1.separateCache;
  pCache = (PCache1 *)sqlite3MallocZero(sz);
  if( pCache ){
    if( pcache1.separateCache ){
      pGroup = (PGroup*)&pCache[1];
      pGroup->mxPinned = 10;
    }else{
      pGroup = &pcache1.grp;
    }
    if( pGroup->lru.isAnchor==0 ){
      pGroup->lru.isAnchor = 1;
      pGroup->lru.pLruPrev = pGroup->lru.pLruNext = &pGroup->lru;
    }
    pCache->pGroup = pGroup;
    pCache->szPage = szPage;
    pCache->szExtra = szExtra;
    pCache->szAlloc = szPage + szExtra + ROUND8(sizeof(PgHdr1));
    pCache->bPurgeable = (bPurgeable ? 1 : 0);
    pcache1EnterMutex(pGroup);
    pcache1ResizeHash(pCache);
    if( bPurgeable ){
      pCache->nMin = 10;
      pGroup->nMinPage += pCache->nMin;
      pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
    }
    pcache1LeaveMutex(pGroup);
    if( pCache->nHash==0 ){
      pcache1Destroy((sqlite3_pcache*)pCache);
      pCache = 0;
    }
  }
  return (sqlite3_pcache *)pCache;
}

/*
** Implementation of the sqlite3_pcache.xCachesize method. 
**
** Configure the cache_size limit for a cache.
*/
static void pcache1Cachesize(sqlite3_pcache *p, int nMax){
  PCache1 *pCache = (PCache1 *)p;
  if( pCache->bPurgeable ){
    PGroup *pGroup = pCache->pGroup;
    pcache1EnterMutex(pGroup);
    pGroup->nMaxPage += (nMax - pCache->nMax);
    pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
    pCache->nMax = nMax;
    pCache->n90pct = pCache->nMax*9/10;
    pcache1EnforceMaxPage(pCache);
    pcache1LeaveMutex(pGroup);
  }
}

/*
** Implementation of the sqlite3_pcache.xShrink method. 
**
** Free up as much memory as possible.
*/
static void pcache1Shrink(sqlite3_pcache *p){
  PCache1 *pCache = (PCache1*)p;
  if( pCache->bPurgeable ){
    PGroup *pGroup = pCache->pGroup;
    int savedMaxPage;
    pcache1EnterMutex(pGroup);
    savedMaxPage = pGroup->nMaxPage;
    pGroup->nMaxPage = 0;
    pcache1EnforceMaxPage(pCache);
    pGroup->nMaxPage = savedMaxPage;
    pcache1LeaveMutex(pGroup);
  }
}

/*
** Implementation of the sqlite3_pcache.xPagecount method. 
*/
static int pcache1Pagecount(sqlite3_pcache *p){
  int n;
  PCache1 *pCache = (PCache1*)p;
  pcache1EnterMutex(pCache->pGroup);
  n = pCache->nPage;
  pcache1LeaveMutex(pCache->pGroup);
  return n;
}


/*
** Implement steps 3, 4, and 5 of the pcache1Fetch() algorithm described
** in the header of the pcache1Fetch() procedure.
**
** This steps are broken out into a separate procedure because they are
** usually not needed, and by avoiding the stack initialization required
** for these steps, the main pcache1Fetch() procedure can run faster.
*/
static SQLITE_NOINLINE PgHdr1 *pcache1FetchStage2(
  PCache1 *pCache, 
  unsigned int iKey, 
  int createFlag
){
  unsigned int nPinned;
  PGroup *pGroup = pCache->pGroup;
  PgHdr1 *pPage = 0;

  /* Step 3: Abort if createFlag is 1 but the cache is nearly full */
  assert( pCache->nPage >= pCache->nRecyclable );
  nPinned = pCache->nPage - pCache->nRecyclable;
  assert( pGroup->mxPinned == pGroup->nMaxPage + 10 - pGroup->nMinPage );
  assert( pCache->n90pct == pCache->nMax*9/10 );
  if( createFlag==1 && (
        nPinned>=pGroup->mxPinned
     || nPinned>=pCache->n90pct
     || (pcache1UnderMemoryPressure(pCache) && pCache->nRecyclable<nPinned)
  )){
    return 0;
  }

  if( pCache->nPage>=pCache->nHash ) pcache1ResizeHash(pCache);
  assert( pCache->nHash>0 && pCache->apHash );

  /* Step 4. Try to recycle a page. */
  if( pCache->bPurgeable
   && !pGroup->lru.pLruPrev->isAnchor
   && ((pCache->nPage+1>=pCache->nMax) || pcache1UnderMemoryPressure(pCache))
  ){
    PCache1 *pOther;
    pPage = pGroup->lru.pLruPrev;
    assert( pPage->isPinned==0 );
    pcache1RemoveFromHash(pPage, 0);
    pcache1PinPage(pPage);
    pOther = pPage->pCache;
    if( pOther->szAlloc != pCache->szAlloc ){
      pcache1FreePage(pPage);
      pPage = 0;
    }else{
      pGroup->nCurrentPage -= (pOther->bPurgeable - pCache->bPurgeable);
    }
  }

  /* Step 5. If a usable page buffer has still not been found, 
  ** attempt to allocate a new one. 
  */
  if( !pPage ){
    pPage = pcache1AllocPage(pCache, createFlag==1);
  }

  if( pPage ){
    unsigned int h = iKey % pCache->nHash;
    pCache->nPage++;
    pPage->iKey = iKey;
    pPage->pNext = pCache->apHash[h];
    pPage->pCache = pCache;
    pPage->pLruPrev = 0;
    pPage->pLruNext = 0;
    pPage->isPinned = 1;
    *(void **)pPage->page.pExtra = 0;
    pCache->apHash[h] = pPage;
    if( iKey>pCache->iMaxKey ){
      pCache->iMaxKey = iKey;
    }
  }
  return pPage;
}

/*
** Implementation of the sqlite3_pcache.xFetch method. 
**
** Fetch a page by key value.
**
** Whether or not a new page may be allocated by this function depends on
** the value of the createFlag argument.  0 means do not allocate a new
** page.  1 means allocate a new page if space is easily available.  2 
** means to try really hard to allocate a new page.
**
** For a non-purgeable cache (a cache used as the storage for an in-memory
** database) there is really no difference between createFlag 1 and 2.  So
** the calling function (pcache.c) will never have a createFlag of 1 on
** a non-purgeable cache.
**
** There are three different approaches to obtaining space for a page,
** depending on the value of parameter createFlag (which may be 0, 1 or 2).
**
**   1. Regardless of the value of createFlag, the cache is searched for a 
**      copy of the requested page. If one is found, it is returned.
**
**   2. If createFlag==0 and the page is not already in the cache, NULL is
**      returned.
**
**   3. If createFlag is 1, and the page is not already in the cache, then
**      return NULL (do not allocate a new page) if any of the following
**      conditions are true:
**
**       (a) the number of pages pinned by the cache is greater than
**           PCache1.nMax, or
**
**       (b) the number of pages pinned by the cache is greater than
**           the sum of nMax for all purgeable caches, less the sum of 
**           nMin for all other purgeable caches, or
**
**   4. If none of the first three conditions apply and the cache is marked
**      as purgeable, and if one of the following is true:
**
**       (a) The number of pages allocated for the cache is already 
**           PCache1.nMax, or
**
**       (b) The number of pages allocated for all purgeable caches is
**           already equal to or greater than the sum of nMax for all
**           purgeable caches,
**
**       (c) The system is under memory pressure and wants to avoid
**           unnecessary pages cache entry allocations
**
**      then attempt to recycle a page from the LRU list. If it is the right
**      size, return the recycled buffer. Otherwise, free the buffer and
**      proceed to step 5. 
**
**   5. Otherwise, allocate and return a new page buffer.
**
** There are two versions of this routine.  pcache1FetchWithMutex() is
** the general case.  pcache1FetchNoMutex() is a faster implementation for
** the common case where pGroup->mutex is NULL.  The pcache1Fetch() wrapper
** invokes the appropriate routine.
*/
static PgHdr1 *pcache1FetchNoMutex(
  sqlite3_pcache *p, 
  unsigned int iKey, 
  int createFlag
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = 0;

  /* Step 1: Search the hash table for an existing entry. */
  pPage = pCache->apHash[iKey % pCache->nHash];
  while( pPage && pPage->iKey!=iKey ){ pPage = pPage->pNext; }

  /* Step 2: If the page was found in the hash table, then return it.
  ** If the page was not in the hash table and createFlag is 0, abort.
  ** Otherwise (page not in hash and createFlag!=0) continue with
  ** subsequent steps to try to create the page. */
  if( pPage ){
    if( !pPage->isPinned ){
      return pcache1PinPage(pPage);
    }else{
      return pPage;
    }
  }else if( createFlag ){
    /* Steps 3, 4, and 5 implemented by this subroutine */
    return pcache1FetchStage2(pCache, iKey, createFlag);
  }else{
    return 0;
  }
}
#if PCACHE1_MIGHT_USE_GROUP_MUTEX
static PgHdr1 *pcache1FetchWithMutex(
  sqlite3_pcache *p, 
  unsigned int iKey, 
  int createFlag
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage;

  pcache1EnterMutex(pCache->pGroup);
  pPage = pcache1FetchNoMutex(p, iKey, createFlag);
  assert( pPage==0 || pCache->iMaxKey>=iKey );
  pcache1LeaveMutex(pCache->pGroup);
  return pPage;
}
#endif
static sqlite3_pcache_page *pcache1Fetch(
  sqlite3_pcache *p, 
  unsigned int iKey, 
  int createFlag
){
#if PCACHE1_MIGHT_USE_GROUP_MUTEX || defined(SQLITE_DEBUG)
  PCache1 *pCache = (PCache1 *)p;
#endif

  assert( offsetof(PgHdr1,page)==0 );
  assert( pCache->bPurgeable || createFlag!=1 );
  assert( pCache->bPurgeable || pCache->nMin==0 );
  assert( pCache->bPurgeable==0 || pCache->nMin==10 );
  assert( pCache->nMin==0 || pCache->bPurgeable );
  assert( pCache->nHash>0 );
#if PCACHE1_MIGHT_USE_GROUP_MUTEX
  if( pCache->pGroup->mutex ){
    return (sqlite3_pcache_page*)pcache1FetchWithMutex(p, iKey, createFlag);
  }else
#endif
  {
    return (sqlite3_pcache_page*)pcache1FetchNoMutex(p, iKey, createFlag);
  }
}


/*
** Implementation of the sqlite3_pcache.xUnpin method.
**
** Mark a page as unpinned (eligible for asynchronous recycling).
*/
static void pcache1Unpin(
  sqlite3_pcache *p, 
  sqlite3_pcache_page *pPg, 
  int reuseUnlikely
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = (PgHdr1 *)pPg;
  PGroup *pGroup = pCache->pGroup;
 
  assert( pPage->pCache==pCache );
  pcache1EnterMutex(pGroup);

  /* It is an error to call this function if the page is already 
  ** part of the PGroup LRU list.
  */
  assert( pPage->pLruPrev==0 && pPage->pLruNext==0 );
  assert( pPage->isPinned==1 );

  if( reuseUnlikely || pGroup->nCurrentPage>pGroup->nMaxPage ){
    pcache1RemoveFromHash(pPage, 1);
  }else{
    /* Add the page to the PGroup LRU list. */
    PgHdr1 **ppFirst = &pGroup->lru.pLruNext;
    pPage->pLruPrev = &pGroup->lru;
    (pPage->pLruNext = *ppFirst)->pLruPrev = pPage;
    *ppFirst = pPage;
    pCache->nRecyclable++;
    pPage->isPinned = 0;
  }

  pcache1LeaveMutex(pCache->pGroup);
}

/*
** Implementation of the sqlite3_pcache.xRekey method. 
*/
static void pcache1Rekey(
  sqlite3_pcache *p,
  sqlite3_pcache_page *pPg,
  unsigned int iOld,
  unsigned int iNew
){
  PCache1 *pCache = (PCache1 *)p;
  PgHdr1 *pPage = (PgHdr1 *)pPg;
  PgHdr1 **pp;
  unsigned int h; 
  assert( pPage->iKey==iOld );
  assert( pPage->pCache==pCache );

  pcache1EnterMutex(pCache->pGroup);

  h = iOld%pCache->nHash;
  pp = &pCache->apHash[h];
  while( (*pp)!=pPage ){
    pp = &(*pp)->pNext;
  }
  *pp = pPage->pNext;

  h = iNew%pCache->nHash;
  pPage->iKey = iNew;
  pPage->pNext = pCache->apHash[h];
  pCache->apHash[h] = pPage;
  if( iNew>pCache->iMaxKey ){
    pCache->iMaxKey = iNew;
  }

  pcache1LeaveMutex(pCache->pGroup);
}

/*
** Implementation of the sqlite3_pcache.xTruncate method. 
**
** Discard all unpinned pages in the cache with a page number equal to
** or greater than parameter iLimit. Any pinned pages with a page number
** equal to or greater than iLimit are implicitly unpinned.
*/
static void pcache1Truncate(sqlite3_pcache *p, unsigned int iLimit){
  PCache1 *pCache = (PCache1 *)p;
  pcache1EnterMutex(pCache->pGroup);
  if( iLimit<=pCache->iMaxKey ){
    pcache1TruncateUnsafe(pCache, iLimit);
    pCache->iMaxKey = iLimit-1;
  }
  pcache1LeaveMutex(pCache->pGroup);
}

/*
** Implementation of the sqlite3_pcache.xDestroy method. 
**
** Destroy a cache allocated using pcache1Create().
*/
static void pcache1Destroy(sqlite3_pcache *p){
  PCache1 *pCache = (PCache1 *)p;
  PGroup *pGroup = pCache->pGroup;
  assert( pCache->bPurgeable || (pCache->nMax==0 && pCache->nMin==0) );
  pcache1EnterMutex(pGroup);
  pcache1TruncateUnsafe(pCache, 0);
  assert( pGroup->nMaxPage >= pCache->nMax );
  pGroup->nMaxPage -= pCache->nMax;
  assert( pGroup->nMinPage >= pCache->nMin );
  pGroup->nMinPage -= pCache->nMin;
  pGroup->mxPinned = pGroup->nMaxPage + 10 - pGroup->nMinPage;
  pcache1EnforceMaxPage(pCache);
  pcache1LeaveMutex(pGroup);
  sqlite3_free(pCache->pBulk);
  sqlite3_free(pCache->apHash);
  sqlite3_free(pCache);
}

/*
** This function is called during initialization (sqlite3BtreeInitialize()) to
** install the default pluggable cache module, assuming the user has not
** already provided an alternative.
*/
SQLITE_PRIVATE void sqlite3PCacheSetDefault(void){
  static const sqlite3_pcache_methods2 defaultMethods = {
    1,                       /* iVersion */
    0,                       /* pArg */
    pcache1Init,             /* xInit */
    pcache1Shutdown,         /* xShutdown */
    pcache1Create,           /* xCreate */
    pcache1Cachesize,        /* xCachesize */
    pcache1Pagecount,        /* xPagecount */
    pcache1Fetch,            /* xFetch */
    pcache1Unpin,            /* xUnpin */
    pcache1Rekey,            /* xRekey */
    pcache1Truncate,         /* xTruncate */
    pcache1Destroy,          /* xDestroy */
    pcache1Shrink            /* xShrink */
  };
  sqlite3_config(SQLITE_CONFIG_PCACHE2, &defaultMethods);
}

/*
** Return the size of the header on each page of this PCACHE implementation.
*/
SQLITE_PRIVATE int sqlite3HeaderSizePcache1(void){ return ROUND8(sizeof(PgHdr1)); }

/*
** Return the global mutex used by this PCACHE implementation.  The
** sqlite3_status() routine needs access to this mutex.
*/
#ifndef NDEBUG
SQLITE_PRIVATE sqlite3_mutex *sqlite3Pcache1Mutex(void){
  return pcache1.mutex;
}
#endif

#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
/*
** This function is called to free superfluous dynamically allocated memory
** held by the pager system. Memory in use by any SQLite pager allocated
** by the current thread may be sqlite3_free()ed.
**
** nReq is the number of bytes of memory required. Once this much has
** been released, the function returns. The return value is the total number 
** of bytes of memory released.
*/
SQLITE_PRIVATE int sqlite3PcacheReleaseMemory(int nReq){
  int nFree = 0;
  assert( sqlite3_mutex_notheld(pcache1.grp.mutex) );
  assert( sqlite3_mutex_notheld(pcache1.mutex) );
  if( sqlite3GlobalConfig.nPage==0 ){
    PgHdr1 *p;
    pcache1EnterMutex(&pcache1.grp);
    while( (nReq<0 || nFree<nReq)
       &&  (p=pcache1.grp.lru.pLruPrev)!=0
       &&  p->isAnchor==0
    ){
      nFree += pcache1MemSize(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
      nFree += sqlite3MemSize(p);
#endif
      assert( p->isPinned==0 );
      pcache1PinPage(p);
      pcache1RemoveFromHash(p, 1);
    }
    pcache1LeaveMutex(&pcache1.grp);
  }
  return nFree;
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

#ifdef SQLITE_TEST
/*
** This function is used by test procedures to inspect the internal state
** of the global cache.
*/
SQLITE_PRIVATE void sqlite3PcacheStats(
  int *pnCurrent,      /* OUT: Total number of pages cached */
  int *pnMax,          /* OUT: Global maximum cache size */
  int *pnMin,          /* OUT: Sum of PCache1.nMin for purgeable caches */
  int *pnRecyclable    /* OUT: Total number of pages available for recycling */
){
  PgHdr1 *p;
  int nRecyclable = 0;
  for(p=pcache1.grp.lru.pLruNext; p && !p->isAnchor; p=p->pLruNext){
    assert( p->isPinned==0 );
    nRecyclable++;
  }
  *pnCurrent = pcache1.grp.nCurrentPage;
  *pnMax = (int)pcache1.grp.nMaxPage;
  *pnMin = (int)pcache1.grp.nMinPage;
  *pnRecyclable = nRecyclable;
}
#endif

/************** End of pcache1.c *********************************************/
/************** Begin file pager.c *******************************************/
/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This is the implementation of the page cache subsystem or "pager".
** 
** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
*/
#ifndef SQLITE_OMIT_DISKIO
/* #include "sqliteInt.h" */
/************** Include wal.h in the middle of pager.c ***********************/
/************** Begin file wal.h *********************************************/
/*
** 2010 February 1
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface to the write-ahead logging 
** system. Refer to the comments below and the header comment attached to 
** the implementation of each function in log.c for further details.
*/

#ifndef _WAL_H_
#define _WAL_H_

/* #include "sqliteInt.h" */

/* Additional values that can be added to the sync_flags argument of
** sqlite3WalFrames():
*/
#define WAL_SYNC_TRANSACTIONS  0x20   /* Sync at the end of each transaction */
#define SQLITE_SYNC_MASK       0x13   /* Mask off the SQLITE_SYNC_* values */

#ifdef SQLITE_OMIT_WAL
# define sqlite3WalOpen(x,y,z)                   0
#if 0
# define sqlite3WalLimit(x,y)
#endif
# define sqlite3WalClose(w,x,y,z)                0
# define sqlite3WalBeginReadTransaction(y,z)     0
# define sqlite3WalEndReadTransaction(z)
# define sqlite3WalDbsize(y)                     0
# define sqlite3WalBeginWriteTransaction(y)      0
# define sqlite3WalEndWriteTransaction(x)        0
# define sqlite3WalUndo(x,y,z)                   0
# define sqlite3WalSavepoint(y,z)
# define sqlite3WalSavepointUndo(y,z)            0
# define sqlite3WalFrames(u,v,w,x,y,z)           0
# define sqlite3WalCheckpoint(r,s,t,u,v,w,x,y,z) 0
#if 0
# define sqlite3WalCallback(z)                   0
#endif
# define sqlite3WalExclusiveMode(y,z)            0
#if 0
# define sqlite3WalHeapMemory(z)                 0
#endif
# define sqlite3WalFramesize(z)                  0
# define sqlite3WalFindFrame(x,y,z)              0
#else

#define WAL_SAVEPOINT_NDATA 4

/* Connection to a write-ahead log (WAL) file. 
** There is one object of this type for each pager. 
*/
typedef struct Wal Wal;

/* Open and close a connection to a write-ahead log. */
SQLITE_PRIVATE int sqlite3WalOpen(sqlite3_vfs*, sqlite3_file*, const char *, int, i64, Wal**);
SQLITE_PRIVATE int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);

#if 0
/* Set the limiting size of a WAL file. */
SQLITE_PRIVATE void sqlite3WalLimit(Wal*, i64);
#endif

/* Used by readers to open (lock) and close (unlock) a snapshot.  A 
** snapshot is like a read-transaction.  It is the state of the database
** at an instant in time.  sqlite3WalOpenSnapshot gets a read lock and
** preserves the current state even if the other threads or processes
** write to or checkpoint the WAL.  sqlite3WalCloseSnapshot() closes the
** transaction and releases the lock.
*/
SQLITE_PRIVATE int sqlite3WalBeginReadTransaction(Wal *pWal, int *);
SQLITE_PRIVATE void sqlite3WalEndReadTransaction(Wal *pWal);

/* Read a page from the write-ahead log, if it is present. */
SQLITE_PRIVATE int sqlite3WalFindFrame(Wal *, Pgno, u32 *);
SQLITE_PRIVATE int sqlite3WalReadFrame(Wal *, u32, int, u8 *);

/* If the WAL is not empty, return the size of the database. */
SQLITE_PRIVATE Pgno sqlite3WalDbsize(Wal *pWal);

/* Obtain or release the WRITER lock. */
SQLITE_PRIVATE int sqlite3WalBeginWriteTransaction(Wal *pWal);
SQLITE_PRIVATE int sqlite3WalEndWriteTransaction(Wal *pWal);

/* Undo any frames written (but not committed) to the log */
SQLITE_PRIVATE int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx);

/* Return an integer that records the current (uncommitted) write
** position in the WAL */
SQLITE_PRIVATE void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData);

/* Move the write position of the WAL back to iFrame.  Called in
** response to a ROLLBACK TO command. */
SQLITE_PRIVATE int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData);

/* Write a frame or frames to the log. */
SQLITE_PRIVATE int sqlite3WalFrames(Wal *pWal, int, PgHdr *, Pgno, int, int);

/* Copy pages from the log to the database file */ 
SQLITE_PRIVATE int sqlite3WalCheckpoint(
  Wal *pWal,                      /* Write-ahead log connection */
  int eMode,                      /* One of PASSIVE, FULL and RESTART */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  int nBuf,                       /* Size of buffer nBuf */
  u8 *zBuf,                       /* Temporary buffer to use */
  int *pnLog,                     /* OUT: Number of frames in WAL */
  int *pnCkpt                     /* OUT: Number of backfilled frames in WAL */
);

#if 0
/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called.  If no commits have occurred since
** the last call, then return 0.
*/
SQLITE_PRIVATE int sqlite3WalCallback(Wal *pWal);
#endif

/* Tell the wal layer that an EXCLUSIVE lock has been obtained (or released)
** by the pager layer on the database file.
*/
SQLITE_PRIVATE int sqlite3WalExclusiveMode(Wal *pWal, int op);

#if 0
/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
SQLITE_PRIVATE int sqlite3WalHeapMemory(Wal *pWal);
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
/* If the WAL file is not empty, return the number of bytes of content
** stored in each frame (i.e. the db page-size when the WAL was created).
*/
SQLITE_PRIVATE int sqlite3WalFramesize(Wal *pWal);
#endif

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */

/************** End of wal.h *************************************************/
/************** Continuing where we left off in pager.c **********************/


/******************* NOTES ON THE DESIGN OF THE PAGER ************************
**
** This comment block describes invariants that hold when using a rollback
** journal.  These invariants do not apply for journal_mode=WAL,
** journal_mode=MEMORY, or journal_mode=OFF.
**
** Within this comment block, a page is deemed to have been synced
** automatically as soon as it is written when PRAGMA synchronous=OFF.
** Otherwise, the page is not synced until the xSync method of the VFS
** is called successfully on the file containing the page.
**
** Definition:  A page of the database file is said to be "overwriteable" if
** one or more of the following are true about the page:
** 
**     (a)  The original content of the page as it was at the beginning of
**          the transaction has been written into the rollback journal and
**          synced.
** 
**     (b)  The page was a freelist leaf page at the start of the transaction.
** 
**     (c)  The page number is greater than the largest page that existed in
**          the database file at the start of the transaction.
** 
** (1) A page of the database file is never overwritten unless one of the
**     following are true:
** 
**     (a) The page and all other pages on the same sector are overwriteable.
** 
**     (b) The atomic page write optimization is enabled, and the entire
**         transaction other than the update of the transaction sequence
**         number consists of a single page change.
** 
** (2) The content of a page written into the rollback journal exactly matches
**     both the content in the database when the rollback journal was written
**     and the content in the database at the beginning of the current
**     transaction.
** 
** (3) Writes to the database file are an integer multiple of the page size
**     in length and are aligned on a page boundary.
** 
** (4) Reads from the database file are either aligned on a page boundary and
**     an integer multiple of the page size in length or are taken from the
**     first 100 bytes of the database file.
** 
** (5) All writes to the database file are synced prior to the rollback journal
**     being deleted, truncated, or zeroed.
** 
** (6) If a master journal file is used, then all writes to the database file
**     are synced prior to the master journal being deleted.
** 
** Definition: Two databases (or the same database at two points it time)
** are said to be "logically equivalent" if they give the same answer to
** all queries.  Note in particular the content of freelist leaf
** pages can be changed arbitrarily without affecting the logical equivalence
** of the database.
** 
** (7) At any time, if any subset, including the empty set and the total set,
**     of the unsynced changes to a rollback journal are removed and the 
**     journal is rolled back, the resulting database file will be logically
**     equivalent to the database file at the beginning of the transaction.
** 
** (8) When a transaction is rolled back, the xTruncate method of the VFS
**     is called to restore the database file to the same size it was at
**     the beginning of the transaction.  (In some VFSes, the xTruncate
**     method is a no-op, but that does not change the fact the SQLite will
**     invoke it.)
** 
** (9) Whenever the database file is modified, at least one bit in the range
**     of bytes from 24 through 39 inclusive will be changed prior to releasing
**     the EXCLUSIVE lock, thus signaling other connections on the same
**     database to flush their caches.
**
** (10) The pattern of bits in bytes 24 through 39 shall not repeat in less
**      than one billion transactions.
**
** (11) A database file is well-formed at the beginning and at the conclusion
**      of every transaction.
**
** (12) An EXCLUSIVE lock is held on the database file when writing to
**      the database file.
**
** (13) A SHARED lock is held on the database file while reading any
**      content out of the database file.
**
******************************************************************************/

/*
** Macros for troubleshooting.  Normally turned off
*/
#if 0
int sqlite3PagerTrace=1;  /* True to enable tracing */
#define sqlite3DebugPrintf printf
#define PAGERTRACE(X)     if( sqlite3PagerTrace ){ sqlite3DebugPrintf X; }
#else
#define PAGERTRACE(X)
#endif

/*
** The following two macros are used within the PAGERTRACE() macros above
** to print out file-descriptors. 
**
** PAGERID() takes a pointer to a Pager struct as its argument. The
** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
** struct as its argument.
*/
#define PAGERID(p) ((int)(p->fd))
#define FILEHANDLEID(fd) ((int)fd)

/*
** The Pager.eState variable stores the current 'state' of a pager. A
** pager may be in any one of the seven states shown in the following
** state diagram.
**
**                            OPEN <------+------+
**                              |         |      |
**                              V         |      |
**               +---------> READER-------+      |
**               |              |                |
**               |              V                |
**               |<-------WRITER_LOCKED------> ERROR
**               |              |                ^  
**               |              V                |
**               |<------WRITER_CACHEMOD-------->|
**               |              |                |
**               |              V                |
**               |<-------WRITER_DBMOD---------->|
**               |              |                |
**               |              V                |
**               +<------WRITER_FINISHED-------->+
**
**
** List of state transitions and the C [function] that performs each:
** 
**   OPEN              -> READER              [sqlite3PagerSharedLock]
**   READER            -> OPEN                [pager_unlock]
**
**   READER            -> WRITER_LOCKED       [sqlite3PagerBegin]
**   WRITER_LOCKED     -> WRITER_CACHEMOD     [pager_open_journal]
**   WRITER_CACHEMOD   -> WRITER_DBMOD        [syncJournal]
**   WRITER_DBMOD      -> WRITER_FINISHED     [sqlite3PagerCommitPhaseOne]
**   WRITER_***        -> READER              [pager_end_transaction]
**
**   WRITER_***        -> ERROR               [pager_error]
**   ERROR             -> OPEN                [pager_unlock]
** 
**
**  OPEN:
**
**    The pager starts up in this state. Nothing is guaranteed in this
**    state - the file may or may not be locked and the database size is
**    unknown. The database may not be read or written.
**
**    * No read or write transaction is active.
**    * Any lock, or no lock at all, may be held on the database file.
**    * The dbSize, dbOrigSize and dbFileSize variables may not be trusted.
**
**  READER:
**
**    In this state all the requirements for reading the database in 
**    rollback (non-WAL) mode are met. Unless the pager is (or recently
**    was) in exclusive-locking mode, a user-level read transaction is 
**    open. The database size is known in this state.
**
**    A connection running with locking_mode=normal enters this state when
**    it opens a read-transaction on the database and returns to state
**    OPEN after the read-transaction is completed. However a connection
**    running in locking_mode=exclusive (including temp databases) remains in
**    this state even after the read-transaction is closed. The only way
**    a locking_mode=exclusive connection can transition from READER to OPEN
**    is via the ERROR state (see below).
** 
**    * A read transaction may be active (but a write-transaction cannot).
**    * A SHARED or greater lock is held on the database file.
**    * The dbSize variable may be trusted (even if a user-level read 
**      transaction is not active). The dbOrigSize and dbFileSize variables
**      may not be trusted at this point.
**    * If the database is a WAL database, then the WAL connection is open.
**    * Even if a read-transaction is not open, it is guaranteed that 
**      there is no hot-journal in the file-system.
**
**  WRITER_LOCKED:
**
**    The pager moves to this state from READER when a write-transaction
**    is first opened on the database. In WRITER_LOCKED state, all locks 
**    required to start a write-transaction are held, but no actual 
**    modifications to the cache or database have taken place.
**
**    In rollback mode, a RESERVED or (if the transaction was opened with 
**    BEGIN EXCLUSIVE) EXCLUSIVE lock is obtained on the database file when
**    moving to this state, but the journal file is not written to or opened 
**    to in this state. If the transaction is committed or rolled back while 
**    in WRITER_LOCKED state, all that is required is to unlock the database 
**    file.
**
**    IN WAL mode, WalBeginWriteTransaction() is called to lock the log file.
**    If the connection is running with locking_mode=exclusive, an attempt
**    is made to obtain an EXCLUSIVE lock on the database file.
**
**    * A write transaction is active.
**    * If the connection is open in rollback-mode, a RESERVED or greater 
**      lock is held on the database file.
**    * If the connection is open in WAL-mode, a WAL write transaction
**      is open (i.e. sqlite3WalBeginWriteTransaction() has been successfully
**      called).
**    * The dbSize, dbOrigSize and dbFileSize variables are all valid.
**    * The contents of the pager cache have not been modified.
**    * The journal file may or may not be open.
**    * Nothing (not even the first header) has been written to the journal.
**
**  WRITER_CACHEMOD:
**
**    A pager moves from WRITER_LOCKED state to this state when a page is
**    first modified by the upper layer. In rollback mode the journal file
**    is opened (if it is not already open) and a header written to the
**    start of it. The database file on disk has not been modified.
**
**    * A write transaction is active.
**    * A RESERVED or greater lock is held on the database file.
**    * The journal file is open and the first header has been written 
**      to it, but the header has not been synced to disk.
**    * The contents of the page cache have been modified.
**
**  WRITER_DBMOD:
**
**    The pager transitions from WRITER_CACHEMOD into WRITER_DBMOD state
**    when it modifies the contents of the database file. WAL connections
**    never enter this state (since they do not modify the database file,
**    just the log file).
**
**    * A write transaction is active.
**    * An EXCLUSIVE or greater lock is held on the database file.
**    * The journal file is open and the first header has been written 
**      and synced to disk.
**    * The contents of the page cache have been modified (and possibly
**      written to disk).
**
**  WRITER_FINISHED:
**
**    It is not possible for a WAL connection to enter this state.
**
**    A rollback-mode pager changes to WRITER_FINISHED state from WRITER_DBMOD
**    state after the entire transaction has been successfully written into the
**    database file. In this state the transaction may be committed simply
**    by finalizing the journal file. Once in WRITER_FINISHED state, it is 
**    not possible to modify the database further. At this point, the upper 
**    layer must either commit or rollback the transaction.
**
**    * A write transaction is active.
**    * An EXCLUSIVE or greater lock is held on the database file.
**    * All writing and syncing of journal and database data has finished.
**      If no error occurred, all that remains is to finalize the journal to
**      commit the transaction. If an error did occur, the caller will need
**      to rollback the transaction. 
**
**  ERROR:
**
**    The ERROR state is entered when an IO or disk-full error (including
**    SQLITE_IOERR_NOMEM) occurs at a point in the code that makes it 
**    difficult to be sure that the in-memory pager state (cache contents, 
**    db size etc.) are consistent with the contents of the file-system.
**
**    Temporary pager files may enter the ERROR state, but in-memory pagers
**    cannot.
**
**    For example, if an IO error occurs while performing a rollback, 
**    the contents of the page-cache may be left in an inconsistent state.
**    At this point it would be dangerous to change back to READER state
**    (as usually happens after a rollback). Any subsequent readers might
**    report database corruption (due to the inconsistent cache), and if
**    they upgrade to writers, they may inadvertently corrupt the database
**    file. To avoid this hazard, the pager switches into the ERROR state
**    instead of READER following such an error.
**
**    Once it has entered the ERROR state, any attempt to use the pager
**    to read or write data returns an error. Eventually, once all 
**    outstanding transactions have been abandoned, the pager is able to
**    transition back to OPEN state, discarding the contents of the 
**    page-cache and any other in-memory state at the same time. Everything
**    is reloaded from disk (and, if necessary, hot-journal rollback peformed)
**    when a read-transaction is next opened on the pager (transitioning
**    the pager into READER state). At that point the system has recovered 
**    from the error.
**
**    Specifically, the pager jumps into the ERROR state if:
**
**      1. An error occurs while attempting a rollback. This happens in
**         function sqlite3PagerRollback().
**
**      2. An error occurs while attempting to finalize a journal file
**         following a commit in function sqlite3PagerCommitPhaseTwo().
**
**      3. An error occurs while attempting to write to the journal or
**         database file in function pagerStress() in order to free up
**         memory.
**
**    In other cases, the error is returned to the b-tree layer. The b-tree
**    layer then attempts a rollback operation. If the error condition 
**    persists, the pager enters the ERROR state via condition (1) above.
**
**    Condition (3) is necessary because it can be triggered by a read-only
**    statement executed within a transaction. In this case, if the error
**    code were simply returned to the user, the b-tree layer would not
**    automatically attempt a rollback, as it assumes that an error in a
**    read-only statement cannot leave the pager in an internally inconsistent 
**    state.
**
**    * The Pager.errCode variable is set to something other than SQLITE_OK.
**    * There are one or more outstanding references to pages (after the
**      last reference is dropped the pager should move back to OPEN state).
**    * The pager is not an in-memory pager.
**    
**
** Notes:
**
**   * A pager is never in WRITER_DBMOD or WRITER_FINISHED state if the
**     connection is open in WAL mode. A WAL connection is always in one
**     of the first four states.
**
**   * Normally, a connection open in exclusive mode is never in PAGER_OPEN
**     state. There are two exceptions: immediately after exclusive-mode has
**     been turned on (and before any read or write transactions are 
**     executed), and when the pager is leaving the "error state".
**
**   * See also: assert_pager_state().
*/
#define PAGER_OPEN                  0
#define PAGER_READER                1
#define PAGER_WRITER_LOCKED         2
#define PAGER_WRITER_CACHEMOD       3
#define PAGER_WRITER_DBMOD          4
#define PAGER_WRITER_FINISHED       5
#define PAGER_ERROR                 6

/*
** The Pager.eLock variable is almost always set to one of the 
** following locking-states, according to the lock currently held on
** the database file: NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
** This variable is kept up to date as locks are taken and released by
** the pagerLockDb() and pagerUnlockDb() wrappers.
**
** If the VFS xLock() or xUnlock() returns an error other than SQLITE_BUSY
** (i.e. one of the SQLITE_IOERR subtypes), it is not clear whether or not
** the operation was successful. In these circumstances pagerLockDb() and
** pagerUnlockDb() take a conservative approach - eLock is always updated
** when unlocking the file, and only updated when locking the file if the
** VFS call is successful. This way, the Pager.eLock variable may be set
** to a less exclusive (lower) value than the lock that is actually held
** at the system level, but it is never set to a more exclusive value.
**
** This is usually safe. If an xUnlock fails or appears to fail, there may 
** be a few redundant xLock() calls or a lock may be held for longer than
** required, but nothing really goes wrong.
**
** The exception is when the database file is unlocked as the pager moves
** from ERROR to OPEN state. At this point there may be a hot-journal file 
** in the file-system that needs to be rolled back (as part of an OPEN->SHARED
** transition, by the same pager or any other). If the call to xUnlock()
** fails at this point and the pager is left holding an EXCLUSIVE lock, this
** can confuse the call to xCheckReservedLock() call made later as part
** of hot-journal detection.
**
** xCheckReservedLock() is defined as returning true "if there is a RESERVED 
** lock held by this process or any others". So xCheckReservedLock may 
** return true because the caller itself is holding an EXCLUSIVE lock (but
** doesn't know it because of a previous error in xUnlock). If this happens
** a hot-journal may be mistaken for a journal being created by an active
** transaction in another process, causing SQLite to read from the database
** without rolling it back.
**
** To work around this, if a call to xUnlock() fails when unlocking the
** database in the ERROR state, Pager.eLock is set to UNKNOWN_LOCK. It
** is only changed back to a real locking state after a successful call
** to xLock(EXCLUSIVE). Also, the code to do the OPEN->SHARED state transition
** omits the check for a hot-journal if Pager.eLock is set to UNKNOWN_LOCK 
** lock. Instead, it assumes a hot-journal exists and obtains an EXCLUSIVE
** lock on the database file before attempting to roll it back. See function
** PagerSharedLock() for more detail.
**
** Pager.eLock may only be set to UNKNOWN_LOCK when the pager is in 
** PAGER_OPEN state.
*/
#define UNKNOWN_LOCK                (EXCLUSIVE_LOCK+1)

/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
# define CODEC2(P,D,N,X,E,O) \
    if( P->xCodec==0 ){ O=(char*)D; }else \
    if( (O=(char*)(P->xCodec(P->pCodec,D,N,X)))==0 ){ E; }
#else
# define CODEC1(P,D,N,X,E)   /* NO-OP */
# define CODEC2(P,D,N,X,E,O) O=(char*)D
#endif

/*
** The maximum allowed sector size. 64KiB. If the xSectorsize() method 
** returns a value larger than this, then MAX_SECTOR_SIZE is used instead.
** This could conceivably cause corruption following a power failure on
** such a system. This is currently an undocumented limit.
*/
#define MAX_SECTOR_SIZE 0x10000

/*
** An instance of the following structure is allocated for each active
** savepoint and statement transaction in the system. All such structures
** are stored in the Pager.aSavepoint[] array, which is allocated and
** resized using sqlite3Realloc().
**
** When a savepoint is created, the PagerSavepoint.iHdrOffset field is
** set to 0. If a journal-header is written into the main journal while
** the savepoint is active, then iHdrOffset is set to the byte offset 
** immediately following the last journal record written into the main
** journal before the journal-header. This is required during savepoint
** rollback (see pagerPlaybackSavepoint()).
*/
typedef struct PagerSavepoint PagerSavepoint;
struct PagerSavepoint {
  i64 iOffset;                 /* Starting offset in main journal */
  i64 iHdrOffset;              /* See above */
  Bitvec *pInSavepoint;        /* Set of pages in this savepoint */
  Pgno nOrig;                  /* Original number of pages in file */
  Pgno iSubRec;                /* Index of first record in sub-journal */
#ifndef SQLITE_OMIT_WAL
  u32 aWalData[WAL_SAVEPOINT_NDATA];        /* WAL savepoint context */
#endif
};

/*
** Bits of the Pager.doNotSpill flag.  See further description below.
*/
#define SPILLFLAG_OFF         0x01 /* Never spill cache.  Set via pragma */
#define SPILLFLAG_ROLLBACK    0x02 /* Current rolling back, so do not spill */
#define SPILLFLAG_NOSYNC      0x04 /* Spill is ok, but do not sync */

/*
** An open page cache is an instance of struct Pager. A description of
** some of the more important member variables follows:
**
** eState
**
**   The current 'state' of the pager object. See the comment and state
**   diagram above for a description of the pager state.
**
** eLock
**
**   For a real on-disk database, the current lock held on the database file -
**   NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
**
**   For a temporary or in-memory database (neither of which require any
**   locks), this variable is always set to EXCLUSIVE_LOCK. Since such
**   databases always have Pager.exclusiveMode==1, this tricks the pager
**   logic into thinking that it already has all the locks it will ever
**   need (and no reason to release them).
**
**   In some (obscure) circumstances, this variable may also be set to
**   UNKNOWN_LOCK. See the comment above the #define of UNKNOWN_LOCK for
**   details.
**
** changeCountDone
**
**   This boolean variable is used to make sure that the change-counter 
**   (the 4-byte header field at byte offset 24 of the database file) is 
**   not updated more often than necessary. 
**
**   It is set to true when the change-counter field is updated, which 
**   can only happen if an exclusive lock is held on the database file.
**   It is cleared (set to false) whenever an exclusive lock is 
**   relinquished on the database file. Each time a transaction is committed,
**   The changeCountDone flag is inspected. If it is true, the work of
**   updating the change-counter is omitted for the current transaction.
**
**   This mechanism means that when running in exclusive mode, a connection 
**   need only update the change-counter once, for the first transaction
**   committed.
**
** setMaster
**
**   When PagerCommitPhaseOne() is called to commit a transaction, it may
**   (or may not) specify a master-journal name to be written into the 
**   journal file before it is synced to disk.
**
**   Whether or not a journal file contains a master-journal pointer affects 
**   the way in which the journal file is finalized after the transaction is 
**   committed or rolled back when running in "journal_mode=PERSIST" mode.
**   If a journal file does not contain a master-journal pointer, it is
**   finalized by overwriting the first journal header with zeroes. If
**   it does contain a master-journal pointer the journal file is finalized 
**   by truncating it to zero bytes, just as if the connection were 
**   running in "journal_mode=truncate" mode.
**
**   Journal files that contain master journal pointers cannot be finalized
**   simply by overwriting the first journal-header with zeroes, as the
**   master journal pointer could interfere with hot-journal rollback of any
**   subsequently interrupted transaction that reuses the journal file.
**
**   The flag is cleared as soon as the journal file is finalized (either
**   by PagerCommitPhaseTwo or PagerRollback). If an IO error prevents the
**   journal file from being successfully finalized, the setMaster flag
**   is cleared anyway (and the pager will move to ERROR state).
**
** doNotSpill
**
**   This variables control the behavior of cache-spills  (calls made by
**   the pcache module to the pagerStress() routine to write cached data
**   to the file-system in order to free up memory).
**
**   When bits SPILLFLAG_OFF or SPILLFLAG_ROLLBACK of doNotSpill are set,
**   writing to the database from pagerStress() is disabled altogether.
**   The SPILLFLAG_ROLLBACK case is done in a very obscure case that
**   comes up during savepoint rollback that requires the pcache module
**   to allocate a new page to prevent the journal file from being written
**   while it is being traversed by code in pager_playback().  The SPILLFLAG_OFF
**   case is a user preference.
** 
**   If the SPILLFLAG_NOSYNC bit is set, writing to the database from
**   pagerStress() is permitted, but syncing the journal file is not.
**   This flag is set by sqlite3PagerWrite() when the file-system sector-size
**   is larger than the database page-size in order to prevent a journal sync
**   from happening in between the journalling of two pages on the same sector. 
**
** subjInMemory
**
**   This is a boolean variable. If true, then any required sub-journal
**   is opened as an in-memory journal file. If false, then in-memory
**   sub-journals are only used for in-memory pager files.
**
**   This variable is updated by the upper layer each time a new 
**   write-transaction is opened.
**
** dbSize, dbOrigSize, dbFileSize
**
**   Variable dbSize is set to the number of pages in the database file.
**   It is valid in PAGER_READER and higher states (all states except for
**   OPEN and ERROR). 
**
**   dbSize is set based on the size of the database file, which may be 
**   larger than the size of the database (the value stored at offset
**   28 of the database header by the btree). If the size of the file
**   is not an integer multiple of the page-size, the value stored in
**   dbSize is rounded down (i.e. a 5KB file with 2K page-size has dbSize==2).
**   Except, any file that is greater than 0 bytes in size is considered
**   to have at least one page. (i.e. a 1KB file with 2K page-size leads
**   to dbSize==1).
**
**   During a write-transaction, if pages with page-numbers greater than
**   dbSize are modified in the cache, dbSize is updated accordingly.
**   Similarly, if the database is truncated using PagerTruncateImage(), 
**   dbSize is updated.
**
**   Variables dbOrigSize and dbFileSize are valid in states 
**   PAGER_WRITER_LOCKED and higher. dbOrigSize is a copy of the dbSize
**   variable at the start of the transaction. It is used during rollback,
**   and to determine whether or not pages need to be journalled before
**   being modified.
**
**   Throughout a write-transaction, dbFileSize contains the size of
**   the file on disk in pages. It is set to a copy of dbSize when the
**   write-transaction is first opened, and updated when VFS calls are made
**   to write or truncate the database file on disk. 
**
**   The only reason the dbFileSize variable is required is to suppress 
**   unnecessary calls to xTruncate() after committing a transaction. If, 
**   when a transaction is committed, the dbFileSize variable indicates 
**   that the database file is larger than the database image (Pager.dbSize), 
**   pager_truncate() is called. The pager_truncate() call uses xFilesize()
**   to measure the database file on disk, and then truncates it if required.
**   dbFileSize is not used when rolling back a transaction. In this case
**   pager_truncate() is called unconditionally (which means there may be
**   a call to xFilesize() that is not strictly required). In either case,
**   pager_truncate() may cause the file to become smaller or larger.
**
** dbHintSize
**
**   The dbHintSize variable is used to limit the number of calls made to
**   the VFS xFileControl(FCNTL_SIZE_HINT) method. 
**
**   dbHintSize is set to a copy of the dbSize variable when a
**   write-transaction is opened (at the same time as dbFileSize and
**   dbOrigSize). If the xFileControl(FCNTL_SIZE_HINT) method is called,
**   dbHintSize is increased to the number of pages that correspond to the
**   size-hint passed to the method call. See pager_write_pagelist() for 
**   details.
**
** errCode
**
**   The Pager.errCode variable is only ever used in PAGER_ERROR state. It
**   is set to zero in all other states. In PAGER_ERROR state, Pager.errCode 
**   is always set to SQLITE_FULL, SQLITE_IOERR or one of the SQLITE_IOERR_XXX 
**   sub-codes.
*/
struct Pager {
  sqlite3_vfs *pVfs;          /* OS functions to use for IO */
  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
  u8 journalMode;             /* One of the PAGER_JOURNALMODE_* values */
  u8 useJournal;              /* Use a rollback journal on this file */
  u8 noSync;                  /* Do not sync the journal if true */
  u8 fullSync;                /* Do extra syncs of the journal for robustness */
  u8 ckptSyncFlags;           /* SYNC_NORMAL or SYNC_FULL for checkpoint */
  u8 walSyncFlags;            /* SYNC_NORMAL or SYNC_FULL for wal writes */
  u8 syncFlags;               /* SYNC_NORMAL or SYNC_FULL otherwise */
  u8 tempFile;                /* zFilename is a temporary or immutable file */
  u8 noLock;                  /* Do not lock (except in WAL mode) */
  u8 readOnly;                /* True for a read-only database */
  u8 memDb;                   /* True to inhibit all file I/O */

  /**************************************************************************
  ** The following block contains those class members that change during
  ** routine operation.  Class members not in this block are either fixed
  ** when the pager is first created or else only change when there is a
  ** significant mode change (such as changing the page_size, locking_mode,
  ** or the journal_mode).  From another view, these class members describe
  ** the "state" of the pager, while other class members describe the
  ** "configuration" of the pager.
  */
  u8 eState;                  /* Pager state (OPEN, READER, WRITER_LOCKED..) */
  u8 eLock;                   /* Current lock held on database file */
  u8 changeCountDone;         /* Set after incrementing the change-counter */
  u8 setMaster;               /* True if a m-j name has been written to jrnl */
  u8 doNotSpill;              /* Do not spill the cache when non-zero */
  u8 subjInMemory;            /* True to use in-memory sub-journals */
  u8 bUseFetch;               /* True to use xFetch() */
  u8 hasHeldSharedLock;       /* True if a shared lock has ever been held */
  Pgno dbSize;                /* Number of pages in the database */
  Pgno dbOrigSize;            /* dbSize before the current transaction */
  Pgno dbFileSize;            /* Number of pages in the database file */
  Pgno dbHintSize;            /* Value passed to FCNTL_SIZE_HINT call */
  int errCode;                /* One of several kinds of errors */
  int nRec;                   /* Pages journalled since last j-header written */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  u32 nSubRec;                /* Number of records written to sub-journal */
  Bitvec *pInJournal;         /* One bit for each page in the database file */
  sqlite3_file *fd;           /* File descriptor for database */
  sqlite3_file *jfd;          /* File descriptor for main journal */
  sqlite3_file *sjfd;         /* File descriptor for sub-journal */
  i64 journalOff;             /* Current write offset in the journal file */
  i64 journalHdr;             /* Byte offset to previous journal header */
  sqlite3_backup *pBackup;    /* Pointer to list of ongoing backup processes */
  PagerSavepoint *aSavepoint; /* Array of active savepoints */
  int nSavepoint;             /* Number of elements in aSavepoint[] */
  u32 iDataVersion;           /* Changes whenever database content changes */
  char dbFileVers[16];        /* Changes whenever database file changes */

  int nMmapOut;               /* Number of mmap pages currently outstanding */
  sqlite3_int64 szMmap;       /* Desired maximum mmap size */
  PgHdr *pMmapFreelist;       /* List of free mmap page headers (pDirty) */
  /*
  ** End of the routinely-changing class members
  ***************************************************************************/

  u16 nExtra;                 /* Add this many bytes to each in-memory page */
  i16 nReserve;               /* Number of unused bytes at end of each page */
  u32 vfsFlags;               /* Flags for sqlite3_vfs.xOpen() */
  u32 sectorSize;             /* Assumed sector size during rollback */
  int pageSize;               /* Number of bytes in a page */
  Pgno mxPgno;                /* Maximum allowed size of the database */
  i64 journalSizeLimit;       /* Size limit for persistent journal files */
  char *zFilename;            /* Name of the database file */
  char *zJournal;             /* Name of the journal file */
  int (*xBusyHandler)(void*); /* Function to call when busy */
  void *pBusyHandlerArg;      /* Context argument for xBusyHandler */
  int aStat[3];               /* Total cache hits, misses and writes */
#ifdef SQLITE_TEST
  int nRead;                  /* Database pages read */
#endif
  void (*xReiniter)(DbPage*); /* Call this routine when reloading pages */
#ifdef SQLITE_HAS_CODEC
  void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
  void (*xCodecSizeChng)(void*,int,int); /* Notify of page size changes */
  void (*xCodecFree)(void*);             /* Destructor for the codec */
  void *pCodec;               /* First argument to xCodec... methods */
#endif
  char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
  PCache *pPCache;            /* Pointer to page cache object */
#ifndef SQLITE_OMIT_WAL
  Wal *pWal;                  /* Write-ahead log used by "journal_mode=wal" */
  char *zWal;                 /* File name for write-ahead log */
#endif
};

/*
** Indexes for use with Pager.aStat[]. The Pager.aStat[] array contains
** the values accessed by passing SQLITE_DBSTATUS_CACHE_HIT, CACHE_MISS 
** or CACHE_WRITE to sqlite3_db_status().
*/
#define PAGER_STAT_HIT   0
#define PAGER_STAT_MISS  1
#define PAGER_STAT_WRITE 2

/*
** The following global variables hold counters used for
** testing purposes only.  These variables do not exist in
** a non-testing build.  These variables are not thread-safe.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_pager_readdb_count = 0;    /* Number of full pages read from DB */
SQLITE_PRIVATE int sqlite3_pager_writedb_count = 0;   /* Number of full pages written to DB */
SQLITE_PRIVATE int sqlite3_pager_writej_count = 0;    /* Number of pages written to journal */
# define PAGER_INCR(v)  v++
#else
# define PAGER_INCR(v)
#endif



/*
** Journal files begin with the following magic string.  The data
** was obtained from /dev/random.  It is used only as a sanity check.
**
** Since version 2.8.0, the journal format contains additional sanity
** checking information.  If the power fails while the journal is being
** written, semi-random garbage data might appear in the journal
** file after power is restored.  If an attempt is then made
** to roll the journal back, the database could be corrupted.  The additional
** sanity checking data is an attempt to discover the garbage in the
** journal and ignore it.
**
** The sanity checking information for the new journal format consists
** of a 32-bit checksum on each page of data.  The checksum covers both
** the page number and the pPager->pageSize bytes of data for the page.
** This cksum is initialized to a 32-bit random value that appears in the
** journal file right after the header.  The random initializer is important,
** because garbage data that appears at the end of a journal is likely
** data that was once in other files that have now been deleted.  If the
** garbage data came from an obsolete journal file, the checksums might
** be correct.  But by initializing the checksum to random value which
** is different for every journal, we minimize that risk.
*/
static const unsigned char aJournalMagic[] = {
  0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
};

/*
** The size of the of each page record in the journal is given by
** the following macro.
*/
#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)

/*
** The journal header size for this pager. This is usually the same 
** size as a single disk sector. See also setSectorSize().
*/
#define JOURNAL_HDR_SZ(pPager) (pPager->sectorSize)

/*
** The macro USEFETCH is true if we are allowed to use the xFetch and xUnfetch
** interfaces to access the database using memory-mapped I/O.
*/
#if SQLITE_MAX_MMAP_SIZE>0
# define USEFETCH(x) ((x)->bUseFetch)
#else
# define USEFETCH(x) 0
#endif

/*
** The maximum legal page number is (2^31 - 1).
*/
#define PAGER_MAX_PGNO 2147483647

/*
** The argument to this macro is a file descriptor (type sqlite3_file*).
** Return 0 if it is not open, or non-zero (but not 1) if it is.
**
** This is so that expressions can be written as:
**
**   if( isOpen(pPager->jfd) ){ ...
**
** instead of
**
**   if( pPager->jfd->pMethods ){ ...
*/
#define isOpen(pFd) ((pFd)->pMethods!=0)

/*
** Return true if this pager uses a write-ahead log instead of the usual
** rollback journal. Otherwise false.
*/
#ifndef SQLITE_OMIT_WAL
static int pagerUseWal(Pager *pPager){
  return (pPager->pWal!=0);
}
#else
# define pagerUseWal(x) 0
# define pagerRollbackWal(x) 0
# define pagerWalFrames(v,w,x,y) 0
# define pagerOpenWalIfPresent(z) SQLITE_OK
# define pagerBeginReadTransaction(z) SQLITE_OK
#endif

#ifndef NDEBUG 
/*
** Usage:
**
**   assert( assert_pager_state(pPager) );
**
** This function runs many asserts to try to find inconsistencies in
** the internal state of the Pager object.
*/
static int assert_pager_state(Pager *p){
  Pager *pPager = p;

  /* State must be valid. */
  assert( p->eState==PAGER_OPEN
       || p->eState==PAGER_READER
       || p->eState==PAGER_WRITER_LOCKED
       || p->eState==PAGER_WRITER_CACHEMOD
       || p->eState==PAGER_WRITER_DBMOD
       || p->eState==PAGER_WRITER_FINISHED
       || p->eState==PAGER_ERROR
  );

  /* Regardless of the current state, a temp-file connection always behaves
  ** as if it has an exclusive lock on the database file. It never updates
  ** the change-counter field, so the changeCountDone flag is always set.
  */
  assert( p->tempFile==0 || p->eLock==EXCLUSIVE_LOCK );
  assert( p->tempFile==0 || pPager->changeCountDone );

  /* If the useJournal flag is clear, the journal-mode must be "OFF". 
  ** And if the journal-mode is "OFF", the journal file must not be open.
  */
  assert( p->journalMode==PAGER_JOURNALMODE_OFF || p->useJournal );
  assert( p->journalMode!=PAGER_JOURNALMODE_OFF || !isOpen(p->jfd) );

  /* If changeCountDone is set, a RESERVED lock or greater must be held
  ** on the file.
  */
  assert( pPager->changeCountDone==0 || pPager->eLock>=RESERVED_LOCK );
  assert( p->eLock!=PENDING_LOCK );

  switch( p->eState ){
    case PAGER_OPEN:
      assert( pPager->errCode==SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)==0 || pPager->tempFile );
      break;

    case PAGER_READER:
      assert( pPager->errCode==SQLITE_OK );
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( p->eLock>=SHARED_LOCK );
      break;

    case PAGER_WRITER_LOCKED:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
      assert( pPager->dbSize==pPager->dbOrigSize );
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      assert( pPager->setMaster==0 );
      break;

    case PAGER_WRITER_CACHEMOD:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        /* It is possible that if journal_mode=wal here that neither the
        ** journal file nor the WAL file are open. This happens during
        ** a rollback transaction that switches from journal_mode=off
        ** to journal_mode=wal.
        */
        assert( p->eLock>=RESERVED_LOCK );
        assert( isOpen(p->jfd) 
             || p->journalMode==PAGER_JOURNALMODE_OFF 
             || p->journalMode==PAGER_JOURNALMODE_WAL 
        );
      }
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->dbOrigSize==pPager->dbHintSize );
      break;

    case PAGER_WRITER_DBMOD:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( p->eLock>=EXCLUSIVE_LOCK );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      assert( pPager->dbOrigSize<=pPager->dbHintSize );
      break;

    case PAGER_WRITER_FINISHED:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_ERROR:
      /* There must be at least one outstanding reference to the pager if
      ** in ERROR state. Otherwise the pager should have already dropped
      ** back to OPEN state.
      */
      assert( pPager->errCode!=SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)>0 );
      break;
  }

  return 1;
}
#endif /* ifndef NDEBUG */

#ifdef SQLITE_DEBUG 
/*
** Return a pointer to a human readable string in a static buffer
** containing the state of the Pager object passed as an argument. This
** is intended to be used within debuggers. For example, as an alternative
** to "print *pPager" in gdb:
**
** (gdb) printf "%s", print_pager_state(pPager)
*/
static char *print_pager_state(Pager *p){
  static char zRet[1024];

  sqlite3_snprintf(1024, zRet,
      "Filename:      %s\n"
      "State:         %s errCode=%d\n"
      "Lock:          %s\n"
      "Locking mode:  locking_mode=%s\n"
      "Journal mode:  journal_mode=%s\n"
      "Backing store: tempFile=%d memDb=%d useJournal=%d\n"
      "Journal:       journalOff=%lld journalHdr=%lld\n"
      "Size:          dbsize=%d dbOrigSize=%d dbFileSize=%d\n"
      , p->zFilename
      , p->eState==PAGER_OPEN            ? "OPEN" :
        p->eState==PAGER_READER          ? "READER" :
        p->eState==PAGER_WRITER_LOCKED   ? "WRITER_LOCKED" :
        p->eState==PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
        p->eState==PAGER_WRITER_DBMOD    ? "WRITER_DBMOD" :
        p->eState==PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
        p->eState==PAGER_ERROR           ? "ERROR" : "?error?"
      , (int)p->errCode
      , p->eLock==NO_LOCK         ? "NO_LOCK" :
        p->eLock==RESERVED_LOCK   ? "RESERVED" :
        p->eLock==EXCLUSIVE_LOCK  ? "EXCLUSIVE" :
        p->eLock==SHARED_LOCK     ? "SHARED" :
        p->eLock==UNKNOWN_LOCK    ? "UNKNOWN" : "?error?"
      , p->exclusiveMode ? "exclusive" : "normal"
      , p->journalMode==PAGER_JOURNALMODE_MEMORY   ? "memory" :
        p->journalMode==PAGER_JOURNALMODE_OFF      ? "off" :
        p->journalMode==PAGER_JOURNALMODE_DELETE   ? "delete" :
        p->journalMode==PAGER_JOURNALMODE_PERSIST  ? "persist" :
        p->journalMode==PAGER_JOURNALMODE_TRUNCATE ? "truncate" :
        p->journalMode==PAGER_JOURNALMODE_WAL      ? "wal" : "?error?"
      , (int)p->tempFile, (int)p->memDb, (int)p->useJournal
      , p->journalOff, p->journalHdr
      , (int)p->dbSize, (int)p->dbOrigSize, (int)p->dbFileSize
  );

  return zRet;
}
#endif

/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
**   * The page-number is less than or equal to PagerSavepoint.nOrig, and
**   * The bit corresponding to the page-number is not set in
**     PagerSavepoint.pInSavepoint.
*/
static int subjRequiresPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  PagerSavepoint *p;
  Pgno pgno = pPg->pgno;
  int i;
  for(i=0; i<pPager->nSavepoint; i++){
    p = &pPager->aSavepoint[i];
    if( p->nOrig>=pgno && 0==sqlite3BitvecTestNotNull(p->pInSavepoint, pgno) ){
      return 1;
    }
  }
  return 0;
}

#ifdef SQLITE_DEBUG
/*
** Return true if the page is already in the journal file.
*/
static int pageInJournal(Pager *pPager, PgHdr *pPg){
  return sqlite3BitvecTest(pPager->pInJournal, pPg->pgno);
}
#endif

/*
** Read a 32-bit integer from the given file descriptor.  Store the integer
** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
** error code is something goes wrong.
**
** All values are stored on disk as big-endian.
*/
static int read32bits(sqlite3_file *fd, i64 offset, u32 *pRes){
  unsigned char ac[4];
  int rc = sqlite3OsRead(fd, ac, sizeof(ac), offset);
  if( rc==SQLITE_OK ){
    *pRes = sqlite3Get4byte(ac);
  }
  return rc;
}

/*
** Write a 32-bit integer into a string buffer in big-endian byte order.
*/
#define put32bits(A,B)  sqlite3Put4byte((u8*)A,B)


/*
** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
** on success or an error code is something goes wrong.
*/
static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
  char ac[4];
  put32bits(ac, val);
  return sqlite3OsWrite(fd, ac, 4, offset);
}

/*
** Unlock the database file to level eLock, which must be either NO_LOCK
** or SHARED_LOCK. Regardless of whether or not the call to xUnlock()
** succeeds, set the Pager.eLock variable to match the (attempted) new lock.
**
** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
** called, do not modify it. See the comment above the #define of 
** UNKNOWN_LOCK for an explanation of this.
*/
static int pagerUnlockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  assert( !pPager->exclusiveMode || pPager->eLock==eLock );
  assert( eLock==NO_LOCK || eLock==SHARED_LOCK );
  assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    rc = pPager->noLock ? SQLITE_OK : sqlite3OsUnlock(pPager->fd, eLock);
    if( pPager->eLock!=UNKNOWN_LOCK ){
      pPager->eLock = (u8)eLock;
    }
    IOTRACE(("UNLOCK %p %d\n", pPager, eLock))
  }
  return rc;
}

/*
** Lock the database file to level eLock, which must be either SHARED_LOCK,
** RESERVED_LOCK or EXCLUSIVE_LOCK. If the caller is successful, set the
** Pager.eLock variable to the new locking state. 
**
** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is 
** called, do not modify it unless the new locking state is EXCLUSIVE_LOCK. 
** See the comment above the #define of UNKNOWN_LOCK for an explanation 
** of this.
*/
static int pagerLockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  assert( eLock==SHARED_LOCK || eLock==RESERVED_LOCK || eLock==EXCLUSIVE_LOCK );
  if( pPager->eLock<eLock || pPager->eLock==UNKNOWN_LOCK ){
    rc = pPager->noLock ? SQLITE_OK : sqlite3OsLock(pPager->fd, eLock);
    if( rc==SQLITE_OK && (pPager->eLock!=UNKNOWN_LOCK||eLock==EXCLUSIVE_LOCK) ){
      pPager->eLock = (u8)eLock;
      IOTRACE(("LOCK %p %d\n", pPager, eLock))
    }
  }
  return rc;
}

/*
** This function determines whether or not the atomic-write optimization
** can be used with this pager. The optimization can be used if:
**
**  (a) the value returned by OsDeviceCharacteristics() indicates that
**      a database page may be written atomically, and
**  (b) the value returned by OsSectorSize() is less than or equal
**      to the page size.
**
** The optimization is also always enabled for temporary files. It is
** an error to call this function if pPager is opened on an in-memory
** database.
**
** If the optimization cannot be used, 0 is returned. If it can be used,
** then the value returned is the size of the journal file when it
** contains rollback data for exactly one page.
*/
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
static int jrnlBufferSize(Pager *pPager){
  if( !pPager->tempFile ){
    int dc;                           /* Device characteristics */
    int nSector;                      /* Sector size */
    int szPage;                       /* Page size */

    assert( isOpen(pPager->fd) );
    dc = sqlite3OsDeviceCharacteristics(pPager->fd);
    nSector = pPager->sectorSize;
    szPage = pPager->pageSize;

    assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
    assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
    if( 0==(dc&(SQLITE_IOCAP_ATOMIC|(szPage>>8)) || nSector>szPage) ){
      return 0;
    }
  }

  return JOURNAL_HDR_SZ(pPager) + JOURNAL_PG_SZ(pPager);
}
#endif

/*
** If SQLITE_CHECK_PAGES is defined then we do some sanity checking
** on the cache using a hash function.  This is used for testing
** and debugging only.
*/
#ifdef SQLITE_CHECK_PAGES
/*
** Return a 32-bit hash of the page data for pPage.
*/
static u32 pager_datahash(int nByte, unsigned char *pData){
  u32 hash = 0;
  int i;
  for(i=0; i<nByte; i++){
    hash = (hash*1039) + pData[i];
  }
  return hash;
}
static u32 pager_pagehash(PgHdr *pPage){
  return pager_datahash(pPage->pPager->pageSize, (unsigned char *)pPage->pData);
}
static void pager_set_pagehash(PgHdr *pPage){
  pPage->pageHash = pager_pagehash(pPage);
}

/*
** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
** is defined, and NDEBUG is not defined, an assert() statement checks
** that the page is either dirty or still matches the calculated page-hash.
*/
#define CHECK_PAGE(x) checkPage(x)
static void checkPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  assert( pPager->eState!=PAGER_ERROR );
  assert( (pPg->flags&PGHDR_DIRTY) || pPg->pageHash==pager_pagehash(pPg) );
}

#else
#define pager_datahash(X,Y)  0
#define pager_pagehash(X)  0
#define pager_set_pagehash(X)
#define CHECK_PAGE(x)
#endif  /* SQLITE_CHECK_PAGES */

/*
** When this is called the journal file for pager pPager must be open.
** This function attempts to read a master journal file name from the 
** end of the file and, if successful, copies it into memory supplied 
** by the caller. See comments above writeMasterJournal() for the format
** used to store a master journal file name at the end of a journal file.
**
** zMaster must point to a buffer of at least nMaster bytes allocated by
** the caller. This should be sqlite3_vfs.mxPathname+1 (to ensure there is
** enough space to write the master journal name). If the master journal
** name in the journal is longer than nMaster bytes (including a
** nul-terminator), then this is handled as if no master journal name
** were present in the journal.
**
** If a master journal file name is present at the end of the journal
** file, then it is copied into the buffer pointed to by zMaster. A
** nul-terminator byte is appended to the buffer following the master
** journal file name.
**
** If it is determined that no master journal file name is present 
** zMaster[0] is set to 0 and SQLITE_OK returned.
**
** If an error occurs while reading from the journal file, an SQLite
** error code is returned.
*/
static int readMasterJournal(sqlite3_file *pJrnl, char *zMaster, u32 nMaster){
  int rc;                    /* Return code */
  u32 len;                   /* Length in bytes of master journal name */
  i64 szJ;                   /* Total size in bytes of journal file pJrnl */
  u32 cksum;                 /* MJ checksum value read from journal */
  u32 u;                     /* Unsigned loop counter */
  unsigned char aMagic[8];   /* A buffer to hold the magic header */
  zMaster[0] = '\0';

  if( SQLITE_OK!=(rc = sqlite3OsFileSize(pJrnl, &szJ))
   || szJ<16
   || SQLITE_OK!=(rc = read32bits(pJrnl, szJ-16, &len))
   || len>=nMaster 
   || len==0 
   || SQLITE_OK!=(rc = read32bits(pJrnl, szJ-12, &cksum))
   || SQLITE_OK!=(rc = sqlite3OsRead(pJrnl, aMagic, 8, szJ-8))
   || memcmp(aMagic, aJournalMagic, 8)
   || SQLITE_OK!=(rc = sqlite3OsRead(pJrnl, zMaster, len, szJ-16-len))
  ){
    return rc;
  }

  /* See if the checksum matches the master journal name */
  for(u=0; u<len; u++){
    cksum -= zMaster[u];
  }
  if( cksum ){
    /* If the checksum doesn't add up, then one or more of the disk sectors
    ** containing the master journal filename is corrupted. This means
    ** definitely roll back, so just return SQLITE_OK and report a (nul)
    ** master-journal filename.
    */
    len = 0;
  }
  zMaster[len] = '\0';
   
  return SQLITE_OK;
}

/*
** Return the offset of the sector boundary at or immediately 
** following the value in pPager->journalOff, assuming a sector 
** size of pPager->sectorSize bytes.
**
** i.e for a sector size of 512:
**
**   Pager.journalOff          Return value
**   ---------------------------------------
**   0                         0
**   512                       512
**   100                       512
**   2000                      2048
** 
*/
static i64 journalHdrOffset(Pager *pPager){
  i64 offset = 0;
  i64 c = pPager->journalOff;
  if( c ){
    offset = ((c-1)/JOURNAL_HDR_SZ(pPager) + 1) * JOURNAL_HDR_SZ(pPager);
  }
  assert( offset%JOURNAL_HDR_SZ(pPager)==0 );
  assert( offset>=c );
  assert( (offset-c)<JOURNAL_HDR_SZ(pPager) );
  return offset;
}

/*
** The journal file must be open when this function is called.
**
** This function is a no-op if the journal file has not been written to
** within the current transaction (i.e. if Pager.journalOff==0).
**
** If doTruncate is non-zero or the Pager.journalSizeLimit variable is
** set to 0, then truncate the journal file to zero bytes in size. Otherwise,
** zero the 28-byte header at the start of the journal file. In either case, 
** if the pager is not in no-sync mode, sync the journal file immediately 
** after writing or truncating it.
**
** If Pager.journalSizeLimit is set to a positive, non-zero value, and
** following the truncation or zeroing described above the size of the 
** journal file in bytes is larger than this value, then truncate the
** journal file to Pager.journalSizeLimit bytes. The journal file does
** not need to be synced following this operation.
**
** If an IO error occurs, abandon processing and return the IO error code.
** Otherwise, return SQLITE_OK.
*/
static int zeroJournalHdr(Pager *pPager, int doTruncate){
  int rc = SQLITE_OK;                               /* Return code */
  assert( isOpen(pPager->jfd) );
  if( pPager->journalOff ){
    const i64 iLimit = pPager->journalSizeLimit;    /* Local cache of jsl */

    IOTRACE(("JZEROHDR %p\n", pPager))
    if( doTruncate || iLimit==0 ){
      rc = sqlite3OsTruncate(pPager->jfd, 0);
    }else{
      static const char zeroHdr[28] = {0};
      rc = sqlite3OsWrite(pPager->jfd, zeroHdr, sizeof(zeroHdr), 0);
    }
    if( rc==SQLITE_OK && !pPager->noSync ){
      rc = sqlite3OsSync(pPager->jfd, SQLITE_SYNC_DATAONLY|pPager->syncFlags);
    }

    /* At this point the transaction is committed but the write lock 
    ** is still held on the file. If there is a size limit configured for 
    ** the persistent journal and the journal file currently consumes more
    ** space than that limit allows for, truncate it now. There is no need
    ** to sync the file following this operation.
    */
    if( rc==SQLITE_OK && iLimit>0 ){
      i64 sz;
      rc = sqlite3OsFileSize(pPager->jfd, &sz);
      if( rc==SQLITE_OK && sz>iLimit ){
        rc = sqlite3OsTruncate(pPager->jfd, iLimit);
      }
    }
  }
  return rc;
}

/*
** The journal file must be open when this routine is called. A journal
** header (JOURNAL_HDR_SZ bytes) is written into the journal file at the
** current location.
**
** The format for the journal header is as follows:
** - 8 bytes: Magic identifying journal format.
** - 4 bytes: Number of records in journal, or -1 no-sync mode is on.
** - 4 bytes: Random number used for page hash.
** - 4 bytes: Initial database page count.
** - 4 bytes: Sector size used by the process that wrote this journal.
** - 4 bytes: Database page size.
** 
** Followed by (JOURNAL_HDR_SZ - 28) bytes of unused space.
*/
static int writeJournalHdr(Pager *pPager){
  int rc = SQLITE_OK;                 /* Return code */
  char *zHeader = pPager->pTmpSpace;  /* Temporary space used to build header */
  u32 nHeader = (u32)pPager->pageSize;/* Size of buffer pointed to by zHeader */
  u32 nWrite;                         /* Bytes of header sector written */
  int ii;                             /* Loop counter */

  assert( isOpen(pPager->jfd) );      /* Journal file must be open. */

  if( nHeader>JOURNAL_HDR_SZ(pPager) ){
    nHeader = JOURNAL_HDR_SZ(pPager);
  }

  /* If there are active savepoints and any of them were created 
  ** since the most recent journal header was written, update the 
  ** PagerSavepoint.iHdrOffset fields now.
  */
  for(ii=0; ii<pPager->nSavepoint; ii++){
    if( pPager->aSavepoint[ii].iHdrOffset==0 ){
      pPager->aSavepoint[ii].iHdrOffset = pPager->journalOff;
    }
  }

  pPager->journalHdr = pPager->journalOff = journalHdrOffset(pPager);

  /* 
  ** Write the nRec Field - the number of page records that follow this
  ** journal header. Normally, zero is written to this value at this time.
  ** After the records are added to the journal (and the journal synced, 
  ** if in full-sync mode), the zero is overwritten with the true number
  ** of records (see syncJournal()).
  **
  ** A faster alternative is to write 0xFFFFFFFF to the nRec field. When
  ** reading the journal this value tells SQLite to assume that the
  ** rest of the journal file contains valid page records. This assumption
  ** is dangerous, as if a failure occurred whilst writing to the journal
  ** file it may contain some garbage data. There are two scenarios
  ** where this risk can be ignored:
  **
  **   * When the pager is in no-sync mode. Corruption can follow a
  **     power failure in this case anyway.
  **
  **   * When the SQLITE_IOCAP_SAFE_APPEND flag is set. This guarantees
  **     that garbage data is never appended to the journal file.
  */
  assert( isOpen(pPager->fd) || pPager->noSync );
  if( pPager->noSync || (pPager->journalMode==PAGER_JOURNALMODE_MEMORY)
   || (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND) 
  ){
    memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
    put32bits(&zHeader[sizeof(aJournalMagic)], 0xffffffff);
  }else{
    memset(zHeader, 0, sizeof(aJournalMagic)+4);
  }

  /* The random check-hash initializer */ 
  sqlite3_randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
  put32bits(&zHeader[sizeof(aJournalMagic)+4], pPager->cksumInit);
  /* The initial database size */
  put32bits(&zHeader[sizeof(aJournalMagic)+8], pPager->dbOrigSize);
  /* The assumed sector size for this process */
  put32bits(&zHeader[sizeof(aJournalMagic)+12], pPager->sectorSize);

  /* The page size */
  put32bits(&zHeader[sizeof(aJournalMagic)+16], pPager->pageSize);

  /* Initializing the tail of the buffer is not necessary.  Everything
  ** works find if the following memset() is omitted.  But initializing
  ** the memory prevents valgrind from complaining, so we are willing to
  ** take the performance hit.
  */
  memset(&zHeader[sizeof(aJournalMagic)+20], 0,
         nHeader-(sizeof(aJournalMagic)+20));

  /* In theory, it is only necessary to write the 28 bytes that the 
  ** journal header consumes to the journal file here. Then increment the 
  ** Pager.journalOff variable by JOURNAL_HDR_SZ so that the next 
  ** record is written to the following sector (leaving a gap in the file
  ** that will be implicitly filled in by the OS).
  **
  ** However it has been discovered that on some systems this pattern can 
  ** be significantly slower than contiguously writing data to the file,
  ** even if that means explicitly writing data to the block of 
  ** (JOURNAL_HDR_SZ - 28) bytes that will not be used. So that is what
  ** is done. 
  **
  ** The loop is required here in case the sector-size is larger than the 
  ** database page size. Since the zHeader buffer is only Pager.pageSize
  ** bytes in size, more than one call to sqlite3OsWrite() may be required
  ** to populate the entire journal header sector.
  */ 
  for(nWrite=0; rc==SQLITE_OK&&nWrite<JOURNAL_HDR_SZ(pPager); nWrite+=nHeader){
    IOTRACE(("JHDR %p %lld %d\n", pPager, pPager->journalHdr, nHeader))
    rc = sqlite3OsWrite(pPager->jfd, zHeader, nHeader, pPager->journalOff);
    assert( pPager->journalHdr <= pPager->journalOff );
    pPager->journalOff += nHeader;
  }

  return rc;
}

/*
** The journal file must be open when this is called. A journal header file
** (JOURNAL_HDR_SZ bytes) is read from the current location in the journal
** file. The current location in the journal file is given by
** pPager->journalOff. See comments above function writeJournalHdr() for
** a description of the journal header format.
**
** If the header is read successfully, *pNRec is set to the number of
** page records following this header and *pDbSize is set to the size of the
** database before the transaction began, in pages. Also, pPager->cksumInit
** is set to the value read from the journal header. SQLITE_OK is returned
** in this case.
**
** If the journal header file appears to be corrupted, SQLITE_DONE is
** returned and *pNRec and *PDbSize are undefined.  If JOURNAL_HDR_SZ bytes
** cannot be read from the journal file an error code is returned.
*/
static int readJournalHdr(
  Pager *pPager,               /* Pager object */
  int isHot,
  i64 journalSize,             /* Size of the open journal file in bytes */
  u32 *pNRec,                  /* OUT: Value read from the nRec field */
  u32 *pDbSize                 /* OUT: Value of original database size field */
){
  int rc;                      /* Return code */
  unsigned char aMagic[8];     /* A buffer to hold the magic header */
  i64 iHdrOff;                 /* Offset of journal header being read */

  assert( isOpen(pPager->jfd) );      /* Journal file must be open. */

  /* Advance Pager.journalOff to the start of the next sector. If the
  ** journal file is too small for there to be a header stored at this
  ** point, return SQLITE_DONE.
  */
  pPager->journalOff = journalHdrOffset(pPager);
  if( pPager->journalOff+JOURNAL_HDR_SZ(pPager) > journalSize ){
    return SQLITE_DONE;
  }
  iHdrOff = pPager->journalOff;

  /* Read in the first 8 bytes of the journal header. If they do not match
  ** the  magic string found at the start of each journal header, return
  ** SQLITE_DONE. If an IO error occurs, return an error code. Otherwise,
  ** proceed.
  */
  if( isHot || iHdrOff!=pPager->journalHdr ){
    rc = sqlite3OsRead(pPager->jfd, aMagic, sizeof(aMagic), iHdrOff);
    if( rc ){
      return rc;
    }
    if( memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
      return SQLITE_DONE;
    }
  }

  /* Read the first three 32-bit fields of the journal header: The nRec
  ** field, the checksum-initializer and the database size at the start
  ** of the transaction. Return an error code if anything goes wrong.
  */
  if( SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+8, pNRec))
   || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+12, &pPager->cksumInit))
   || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+16, pDbSize))
  ){
    return rc;
  }

  if( pPager->journalOff==0 ){
    u32 iPageSize;               /* Page-size field of journal header */
    u32 iSectorSize;             /* Sector-size field of journal header */

    /* Read the page-size and sector-size journal header fields. */
    if( SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+20, &iSectorSize))
     || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+24, &iPageSize))
    ){
      return rc;
    }

    /* Versions of SQLite prior to 3.5.8 set the page-size field of the
    ** journal header to zero. In this case, assume that the Pager.pageSize
    ** variable is already set to the correct page size.
    */
    if( iPageSize==0 ){
      iPageSize = pPager->pageSize;
    }

    /* Check that the values read from the page-size and sector-size fields
    ** are within range. To be 'in range', both values need to be a power
    ** of two greater than or equal to 512 or 32, and not greater than their 
    ** respective compile time maximum limits.
    */
    if( iPageSize<512                  || iSectorSize<32
     || iPageSize>SQLITE_MAX_PAGE_SIZE || iSectorSize>MAX_SECTOR_SIZE
     || ((iPageSize-1)&iPageSize)!=0   || ((iSectorSize-1)&iSectorSize)!=0 
    ){
      /* If the either the page-size or sector-size in the journal-header is 
      ** invalid, then the process that wrote the journal-header must have 
      ** crashed before the header was synced. In this case stop reading 
      ** the journal file here.
      */
      return SQLITE_DONE;
    }

    /* Update the page-size to match the value read from the journal. 
    ** Use a testcase() macro to make sure that malloc failure within 
    ** PagerSetPagesize() is tested.
    */
    rc = sqlite3PagerSetPagesize(pPager, &iPageSize, -1);
    testcase( rc!=SQLITE_OK );

    /* Update the assumed sector-size to match the value used by 
    ** the process that created this journal. If this journal was
    ** created by a process other than this one, then this routine
    ** is being called from within pager_playback(). The local value
    ** of Pager.sectorSize is restored at the end of that routine.
    */
    pPager->sectorSize = iSectorSize;
  }

  pPager->journalOff += JOURNAL_HDR_SZ(pPager);
  return rc;
}


/*
** Write the supplied master journal name into the journal file for pager
** pPager at the current location. The master journal name must be the last
** thing written to a journal file. If the pager is in full-sync mode, the
** journal file descriptor is advanced to the next sector boundary before
** anything is written. The format is:
**
**   + 4 bytes: PAGER_MJ_PGNO.
**   + N bytes: Master journal filename in utf-8.
**   + 4 bytes: N (length of master journal name in bytes, no nul-terminator).
**   + 4 bytes: Master journal name checksum.
**   + 8 bytes: aJournalMagic[].
**
** The master journal page checksum is the sum of the bytes in the master
** journal name, where each byte is interpreted as a signed 8-bit integer.
**
** If zMaster is a NULL pointer (occurs for a single database transaction), 
** this call is a no-op.
*/
static int writeMasterJournal(Pager *pPager, const char *zMaster){
  int rc;                          /* Return code */
  int nMaster;                     /* Length of string zMaster */
  i64 iHdrOff;                     /* Offset of header in journal file */
  i64 jrnlSize;                    /* Size of journal file on disk */
  u32 cksum = 0;                   /* Checksum of string zMaster */

  assert( pPager->setMaster==0 );
  assert( !pagerUseWal(pPager) );

  if( !zMaster 
   || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
   || !isOpen(pPager->jfd)
  ){
    return SQLITE_OK;
  }
  pPager->setMaster = 1;
  assert( pPager->journalHdr <= pPager->journalOff );

  /* Calculate the length in bytes and the checksum of zMaster */
  for(nMaster=0; zMaster[nMaster]; nMaster++){
    cksum += zMaster[nMaster];
  }

  /* If in full-sync mode, advance to the next disk sector before writing
  ** the master journal name. This is in case the previous page written to
  ** the journal has already been synced.
  */
  if( pPager->fullSync ){
    pPager->journalOff = journalHdrOffset(pPager);
  }
  iHdrOff = pPager->journalOff;

  /* Write the master journal data to the end of the journal file. If
  ** an error occurs, return the error code to the caller.
  */
  if( (0 != (rc = write32bits(pPager->jfd, iHdrOff, PAGER_MJ_PGNO(pPager))))
   || (0 != (rc = sqlite3OsWrite(pPager->jfd, zMaster, nMaster, iHdrOff+4)))
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster, nMaster)))
   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster+4, cksum)))
   || (0 != (rc = sqlite3OsWrite(pPager->jfd, aJournalMagic, 8,
                                 iHdrOff+4+nMaster+8)))
  ){
    return rc;
  }
  pPager->journalOff += (nMaster+20);

  /* If the pager is in peristent-journal mode, then the physical 
  ** journal-file may extend past the end of the master-journal name
  ** and 8 bytes of magic data just written to the file. This is 
  ** dangerous because the code to rollback a hot-journal file
  ** will not be able to find the master-journal name to determine 
  ** whether or not the journal is hot. 
  **
  ** Easiest thing to do in this scenario is to truncate the journal 
  ** file to the required size.
  */ 
  if( SQLITE_OK==(rc = sqlite3OsFileSize(pPager->jfd, &jrnlSize))
   && jrnlSize>pPager->journalOff
  ){
    rc = sqlite3OsTruncate(pPager->jfd, pPager->journalOff);
  }
  return rc;
}

/*
** Discard the entire contents of the in-memory page-cache.
*/
static void pager_reset(Pager *pPager){
  pPager->iDataVersion++;
  sqlite3BackupRestart(pPager->pBackup);
  sqlite3PcacheClear(pPager->pPCache);
}

/*
** Return the pPager->iDataVersion value
*/
SQLITE_PRIVATE u32 sqlite3PagerDataVersion(Pager *pPager){
  assert( pPager->eState>PAGER_OPEN );
  return pPager->iDataVersion;
}

/*
** Free all structures in the Pager.aSavepoint[] array and set both
** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal
** if it is open and the pager is not in exclusive mode.
*/
static void releaseAllSavepoints(Pager *pPager){
  int ii;               /* Iterator for looping through Pager.aSavepoint */
  for(ii=0; ii<pPager->nSavepoint; ii++){
    sqlite3BitvecDestroy(pPager->aSavepoint[ii].pInSavepoint);
  }
  if( !pPager->exclusiveMode || sqlite3IsMemJournal(pPager->sjfd) ){
    sqlite3OsClose(pPager->sjfd);
  }
  sqlite3_free(pPager->aSavepoint);
  pPager->aSavepoint = 0;
  pPager->nSavepoint = 0;
  pPager->nSubRec = 0;
}

/*
** Set the bit number pgno in the PagerSavepoint.pInSavepoint 
** bitvecs of all open savepoints. Return SQLITE_OK if successful
** or SQLITE_NOMEM if a malloc failure occurs.
*/
static int addToSavepointBitvecs(Pager *pPager, Pgno pgno){
  int ii;                   /* Loop counter */
  int rc = SQLITE_OK;       /* Result code */

  for(ii=0; ii<pPager->nSavepoint; ii++){
    PagerSavepoint *p = &pPager->aSavepoint[ii];
    if( pgno<=p->nOrig ){
      rc |= sqlite3BitvecSet(p->pInSavepoint, pgno);
      testcase( rc==SQLITE_NOMEM );
      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
    }
  }
  return rc;
}

/*
** This function is a no-op if the pager is in exclusive mode and not
** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
** state.
**
** If the pager is not in exclusive-access mode, the database file is
** completely unlocked. If the file is unlocked and the file-system does
** not exhibit the UNDELETABLE_WHEN_OPEN property, the journal file is
** closed (if it is open).
**
** If the pager is in ERROR state when this function is called, the 
** contents of the pager cache are discarded before switching back to 
** the OPEN state. Regardless of whether the pager is in exclusive-mode
** or not, any journal file left in the file-system will be treated
** as a hot-journal and rolled back the next time a read-transaction
** is opened (by this or by any other connection).
*/
static void pager_unlock(Pager *pPager){

  assert( pPager->eState==PAGER_READER 
       || pPager->eState==PAGER_OPEN 
       || pPager->eState==PAGER_ERROR 
  );

  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  releaseAllSavepoints(pPager);

  if( pagerUseWal(pPager) ){
    assert( !isOpen(pPager->jfd) );
    sqlite3WalEndReadTransaction(pPager->pWal);
    pPager->eState = PAGER_OPEN;
  }else if( !pPager->exclusiveMode ){
    int rc;                       /* Error code returned by pagerUnlockDb() */
    int iDc = isOpen(pPager->fd)?sqlite3OsDeviceCharacteristics(pPager->fd):0;

    /* If the operating system support deletion of open files, then
    ** close the journal file when dropping the database lock.  Otherwise
    ** another connection with journal_mode=delete might delete the file
    ** out from under us.
    */
    assert( (PAGER_JOURNALMODE_MEMORY   & 5)!=1 );
    assert( (PAGER_JOURNALMODE_OFF      & 5)!=1 );
    assert( (PAGER_JOURNALMODE_WAL      & 5)!=1 );
    assert( (PAGER_JOURNALMODE_DELETE   & 5)!=1 );
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST  & 5)==1 );
    if( 0==(iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
     || 1!=(pPager->journalMode & 5)
    ){
      sqlite3OsClose(pPager->jfd);
    }

    /* If the pager is in the ERROR state and the call to unlock the database
    ** file fails, set the current lock to UNKNOWN_LOCK. See the comment
    ** above the #define for UNKNOWN_LOCK for an explanation of why this
    ** is necessary.
    */
    rc = pagerUnlockDb(pPager, NO_LOCK);
    if( rc!=SQLITE_OK && pPager->eState==PAGER_ERROR ){
      pPager->eLock = UNKNOWN_LOCK;
    }

    /* The pager state may be changed from PAGER_ERROR to PAGER_OPEN here
    ** without clearing the error code. This is intentional - the error
    ** code is cleared and the cache reset in the block below.
    */
    assert( pPager->errCode || pPager->eState!=PAGER_ERROR );
    pPager->changeCountDone = 0;
    pPager->eState = PAGER_OPEN;
  }

  /* If Pager.errCode is set, the contents of the pager cache cannot be
  ** trusted. Now that there are no outstanding references to the pager,
  ** it can safely move back to PAGER_OPEN state. This happens in both
  ** normal and exclusive-locking mode.
  */
  if( pPager->errCode ){
    pager_reset(pPager);
    pPager->changeCountDone = pPager->tempFile;
    pPager->eState = PAGER_OPEN;
    pPager->errCode = SQLITE_OK;
    if( USEFETCH(pPager) ) sqlite3OsUnfetch(pPager->fd, 0, 0);
  }

  pPager->journalOff = 0;
  pPager->journalHdr = 0;
  pPager->setMaster = 0;
}

/*
** This function is called whenever an IOERR or FULL error that requires
** the pager to transition into the ERROR state may ahve occurred.
** The first argument is a pointer to the pager structure, the second 
** the error-code about to be returned by a pager API function. The 
** value returned is a copy of the second argument to this function. 
**
** If the second argument is SQLITE_FULL, SQLITE_IOERR or one of the
** IOERR sub-codes, the pager enters the ERROR state and the error code
** is stored in Pager.errCode. While the pager remains in the ERROR state,
** all major API calls on the Pager will immediately return Pager.errCode.
**
** The ERROR state indicates that the contents of the pager-cache 
** cannot be trusted. This state can be cleared by completely discarding 
** the contents of the pager-cache. If a transaction was active when
** the persistent error occurred, then the rollback journal may need
** to be replayed to restore the contents of the database file (as if
** it were a hot-journal).
*/
static int pager_error(Pager *pPager, int rc){
  int rc2 = rc & 0xff;
  assert( rc==SQLITE_OK );
  assert(
       pPager->errCode==SQLITE_FULL ||
       pPager->errCode==SQLITE_OK ||
       (pPager->errCode & 0xff)==SQLITE_IOERR
  );
  if( rc2==SQLITE_FULL || rc2==SQLITE_IOERR ){
    pPager->errCode = rc;
    pPager->eState = PAGER_ERROR;
  }
  return rc;
}

static int pager_truncate(Pager *pPager, Pgno nPage);

/*
** This routine ends a transaction. A transaction is usually ended by 
** either a COMMIT or a ROLLBACK operation. This routine may be called 
** after rollback of a hot-journal, or if an error occurs while opening
** the journal file or writing the very first journal-header of a
** database transaction.
** 
** This routine is never called in PAGER_ERROR state. If it is called
** in PAGER_NONE or PAGER_SHARED state and the lock held is less
** exclusive than a RESERVED lock, it is a no-op.
**
** Otherwise, any active savepoints are released.
**
** If the journal file is open, then it is "finalized". Once a journal 
** file has been finalized it is not possible to use it to roll back a 
** transaction. Nor will it be considered to be a hot-journal by this
** or any other database connection. Exactly how a journal is finalized
** depends on whether or not the pager is running in exclusive mode and
** the current journal-mode (Pager.journalMode value), as follows:
**
**   journalMode==MEMORY
**     Journal file descriptor is simply closed. This destroys an 
**     in-memory journal.
**
**   journalMode==TRUNCATE
**     Journal file is truncated to zero bytes in size.
**
**   journalMode==PERSIST
**     The first 28 bytes of the journal file are zeroed. This invalidates
**     the first journal header in the file, and hence the entire journal
**     file. An invalid journal file cannot be rolled back.
**
**   journalMode==DELETE
**     The journal file is closed and deleted using sqlite3OsDelete().
**
**     If the pager is running in exclusive mode, this method of finalizing
**     the journal file is never used. Instead, if the journalMode is
**     DELETE and the pager is in exclusive mode, the method described under
**     journalMode==PERSIST is used instead.
**
** After the journal is finalized, the pager moves to PAGER_READER state.
** If running in non-exclusive rollback mode, the lock on the file is 
** downgraded to a SHARED_LOCK.
**
** SQLITE_OK is returned if no error occurs. If an error occurs during
** any of the IO operations to finalize the journal file or unlock the
** database then the IO error code is returned to the user. If the 
** operation to finalize the journal file fails, then the code still
** tries to unlock the database file if not in exclusive mode. If the
** unlock operation fails as well, then the first error code related
** to the first error encountered (the journal finalization one) is
** returned.
*/
static int pager_end_transaction(Pager *pPager, int hasMaster, int bCommit){
  int rc = SQLITE_OK;      /* Error code from journal finalization operation */
  int rc2 = SQLITE_OK;     /* Error code from db file unlock operation */

  /* Do nothing if the pager does not have an open write transaction
  ** or at least a RESERVED lock. This function may be called when there
  ** is no write-transaction active but a RESERVED or greater lock is
  ** held under two circumstances:
  **
  **   1. After a successful hot-journal rollback, it is called with
  **      eState==PAGER_NONE and eLock==EXCLUSIVE_LOCK.
  **
  **   2. If a connection with locking_mode=exclusive holding an EXCLUSIVE 
  **      lock switches back to locking_mode=normal and then executes a
  **      read-transaction, this function is called with eState==PAGER_READER 
  **      and eLock==EXCLUSIVE_LOCK when the read-transaction is closed.
  */
  assert( assert_pager_state(pPager) );
  assert( pPager->eState!=PAGER_ERROR );
  if( pPager->eState<PAGER_WRITER_LOCKED && pPager->eLock<RESERVED_LOCK ){
    return SQLITE_OK;
  }

  releaseAllSavepoints(pPager);
  assert( isOpen(pPager->jfd) || pPager->pInJournal==0 );
  if( isOpen(pPager->jfd) ){
    assert( !pagerUseWal(pPager) );

    /* Finalize the journal file. */
    if( sqlite3IsMemJournal(pPager->jfd) ){
      assert( pPager->journalMode==PAGER_JOURNALMODE_MEMORY );
      sqlite3OsClose(pPager->jfd);
    }else if( pPager->journalMode==PAGER_JOURNALMODE_TRUNCATE ){
      if( pPager->journalOff==0 ){
        rc = SQLITE_OK;
      }else{
        rc = sqlite3OsTruncate(pPager->jfd, 0);
        if( rc==SQLITE_OK && pPager->fullSync ){
          /* Make sure the new file size is written into the inode right away.
          ** Otherwise the journal might resurrect following a power loss and
          ** cause the last transaction to roll back.  See
          ** https://bugzilla.mozilla.org/show_bug.cgi?id=1072773
          */
          rc = sqlite3OsSync(pPager->jfd, pPager->syncFlags);
        }
      }
      pPager->journalOff = 0;
    }else if( pPager->journalMode==PAGER_JOURNALMODE_PERSIST
      || (pPager->exclusiveMode && pPager->journalMode!=PAGER_JOURNALMODE_WAL)
    ){
      rc = zeroJournalHdr(pPager, hasMaster);
      pPager->journalOff = 0;
    }else{
      /* This branch may be executed with Pager.journalMode==MEMORY if
      ** a hot-journal was just rolled back. In this case the journal
      ** file should be closed and deleted. If this connection writes to
      ** the database file, it will do so using an in-memory journal. 
      */
      int bDelete = (!pPager->tempFile && sqlite3JournalExists(pPager->jfd));
      assert( pPager->journalMode==PAGER_JOURNALMODE_DELETE 
           || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
           || pPager->journalMode==PAGER_JOURNALMODE_WAL 
      );
      sqlite3OsClose(pPager->jfd);
      if( bDelete ){
        rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
    }
  }

#ifdef SQLITE_CHECK_PAGES
  sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
  if( pPager->dbSize==0 && sqlite3PcacheRefCount(pPager->pPCache)>0 ){
    PgHdr *p = sqlite3PagerLookup(pPager, 1);
    if( p ){
      p->pageHash = 0;
      sqlite3PagerUnrefNotNull(p);
    }
  }
#endif

  sqlite3BitvecDestroy(pPager->pInJournal);
  pPager->pInJournal = 0;
  pPager->nRec = 0;
  sqlite3PcacheCleanAll(pPager->pPCache);
  sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);

  if( pagerUseWal(pPager) ){
    /* Drop the WAL write-lock, if any. Also, if the connection was in 
    ** locking_mode=exclusive mode but is no longer, drop the EXCLUSIVE 
    ** lock held on the database file.
    */
    rc2 = sqlite3WalEndWriteTransaction(pPager->pWal);
    assert( rc2==SQLITE_OK );
  }else if( rc==SQLITE_OK && bCommit && pPager->dbFileSize>pPager->dbSize ){
    /* This branch is taken when committing a transaction in rollback-journal
    ** mode if the database file on disk is larger than the database image.
    ** At this point the journal has been finalized and the transaction 
    ** successfully committed, but the EXCLUSIVE lock is still held on the
    ** file. So it is safe to truncate the database file to its minimum
    ** required size.  */
    assert( pPager->eLock==EXCLUSIVE_LOCK );
    rc = pager_truncate(pPager, pPager->dbSize);
  }

  if( rc==SQLITE_OK && bCommit && isOpen(pPager->fd) ){
    rc = sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_COMMIT_PHASETWO, 0);
    if( rc==SQLITE_NOTFOUND ) rc = SQLITE_OK;
  }

  if( !pPager->exclusiveMode 
   && (!pagerUseWal(pPager) || sqlite3WalExclusiveMode(pPager->pWal, 0))
  ){
    rc2 = pagerUnlockDb(pPager, SHARED_LOCK);
    pPager->changeCountDone = 0;
  }
  pPager->eState = PAGER_READER;
  pPager->setMaster = 0;

  return (rc==SQLITE_OK?rc2:rc);
}

/*
** Execute a rollback if a transaction is active and unlock the 
** database file. 
**
** If the pager has already entered the ERROR state, do not attempt 
** the rollback at this time. Instead, pager_unlock() is called. The
** call to pager_unlock() will discard all in-memory pages, unlock
** the database file and move the pager back to OPEN state. If this 
** means that there is a hot-journal left in the file-system, the next 
** connection to obtain a shared lock on the pager (which may be this one) 
** will roll it back.
**
** If the pager has not already entered the ERROR state, but an IO or
** malloc error occurs during a rollback, then this will itself cause 
** the pager to enter the ERROR state. Which will be cleared by the
** call to pager_unlock(), as described above.
*/
static void pagerUnlockAndRollback(Pager *pPager){
  if( pPager->eState!=PAGER_ERROR && pPager->eState!=PAGER_OPEN ){
    assert( assert_pager_state(pPager) );
    if( pPager->eState>=PAGER_WRITER_LOCKED ){
      sqlite3PagerRollback(pPager);
    }else if( !pPager->exclusiveMode ){
      assert( pPager->eState==PAGER_READER );
      pager_end_transaction(pPager, 0, 0);
    }
  }
  pager_unlock(pPager);
}

/*
** Parameter aData must point to a buffer of pPager->pageSize bytes
** of data. Compute and return a checksum based ont the contents of the 
** page of data and the current value of pPager->cksumInit.
**
** This is not a real checksum. It is really just the sum of the 
** random initial value (pPager->cksumInit) and every 200th byte
** of the page data, starting with byte offset (pPager->pageSize%200).
** Each byte is interpreted as an 8-bit unsigned integer.
**
** Changing the formula used to compute this checksum results in an
** incompatible journal file format.
**
** If journal corruption occurs due to a power failure, the most likely 
** scenario is that one end or the other of the record will be changed. 
** It is much less likely that the two ends of the journal record will be
** correct and the middle be corrupt.  Thus, this "checksum" scheme,
** though fast and simple, catches the mostly likely kind of corruption.
*/
static u32 pager_cksum(Pager *pPager, const u8 *aData){
  u32 cksum = pPager->cksumInit;         /* Checksum value to return */
  int i = pPager->pageSize-200;          /* Loop counter */
  while( i>0 ){
    cksum += aData[i];
    i -= 200;
  }
  return cksum;
}

/*
** Report the current page size and number of reserved bytes back
** to the codec.
*/
#ifdef SQLITE_HAS_CODEC
static void pagerReportSize(Pager *pPager){
  if( pPager->xCodecSizeChng ){
    pPager->xCodecSizeChng(pPager->pCodec, pPager->pageSize,
                           (int)pPager->nReserve);
  }
}
#else
# define pagerReportSize(X)     /* No-op if we do not support a codec */
#endif

#ifdef SQLITE_HAS_CODEC
/*
** Make sure the number of reserved bits is the same in the destination
** pager as it is in the source.  This comes up when a VACUUM changes the
** number of reserved bits to the "optimal" amount.
*/
SQLITE_PRIVATE void sqlite3PagerAlignReserve(Pager *pDest, Pager *pSrc){
  if( pDest->nReserve!=pSrc->nReserve ){
    pDest->nReserve = pSrc->nReserve;
    pagerReportSize(pDest);
  }
}
#endif

/*
** Read a single page from either the journal file (if isMainJrnl==1) or
** from the sub-journal (if isMainJrnl==0) and playback that page.
** The page begins at offset *pOffset into the file. The *pOffset
** value is increased to the start of the next page in the journal.
**
** The main rollback journal uses checksums - the statement journal does 
** not.
**
** If the page number of the page record read from the (sub-)journal file
** is greater than the current value of Pager.dbSize, then playback is
** skipped and SQLITE_OK is returned.
**
** If pDone is not NULL, then it is a record of pages that have already
** been played back.  If the page at *pOffset has already been played back
** (if the corresponding pDone bit is set) then skip the playback.
** Make sure the pDone bit corresponding to the *pOffset page is set
** prior to returning.
**
** If the page record is successfully read from the (sub-)journal file
** and played back, then SQLITE_OK is returned. If an IO error occurs
** while reading the record from the (sub-)journal file or while writing
** to the database file, then the IO error code is returned. If data
** is successfully read from the (sub-)journal file but appears to be
** corrupted, SQLITE_DONE is returned. Data is considered corrupted in
** two circumstances:
** 
**   * If the record page-number is illegal (0 or PAGER_MJ_PGNO), or
**   * If the record is being rolled back from the main journal file
**     and the checksum field does not match the record content.
**
** Neither of these two scenarios are possible during a savepoint rollback.
**
** If this is a savepoint rollback, then memory may have to be dynamically
** allocated by this function. If this is the case and an allocation fails,
** SQLITE_NOMEM is returned.
*/
static int pager_playback_one_page(
  Pager *pPager,                /* The pager being played back */
  i64 *pOffset,                 /* Offset of record to playback */
  Bitvec *pDone,                /* Bitvec of pages already played back */
  int isMainJrnl,               /* 1 -> main journal. 0 -> sub-journal. */
  int isSavepnt                 /* True for a savepoint rollback */
){
  int rc;
  PgHdr *pPg;                   /* An existing page in the cache */
  Pgno pgno;                    /* The page number of a page in journal */
  u32 cksum;                    /* Checksum used for sanity checking */
  char *aData;                  /* Temporary storage for the page */
  sqlite3_file *jfd;            /* The file descriptor for the journal file */
  int isSynced;                 /* True if journal page is synced */

  assert( (isMainJrnl&~1)==0 );      /* isMainJrnl is 0 or 1 */
  assert( (isSavepnt&~1)==0 );       /* isSavepnt is 0 or 1 */
  assert( isMainJrnl || pDone );     /* pDone always used on sub-journals */
  assert( isSavepnt || pDone==0 );   /* pDone never used on non-savepoint */

  aData = pPager->pTmpSpace;
  assert( aData );         /* Temp storage must have already been allocated */
  assert( pagerUseWal(pPager)==0 || (!isMainJrnl && isSavepnt) );

  /* Either the state is greater than PAGER_WRITER_CACHEMOD (a transaction 
  ** or savepoint rollback done at the request of the caller) or this is
  ** a hot-journal rollback. If it is a hot-journal rollback, the pager
  ** is in state OPEN and holds an EXCLUSIVE lock. Hot-journal rollback
  ** only reads from the main journal, not the sub-journal.
  */
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD
       || (pPager->eState==PAGER_OPEN && pPager->eLock==EXCLUSIVE_LOCK)
  );
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD || isMainJrnl );

  /* Read the page number and page data from the journal or sub-journal
  ** file. Return an error code to the caller if an IO error occurs.
  */
  jfd = isMainJrnl ? pPager->jfd : pPager->sjfd;
  rc = read32bits(jfd, *pOffset, &pgno);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlite3OsRead(jfd, (u8*)aData, pPager->pageSize, (*pOffset)+4);
  if( rc!=SQLITE_OK ) return rc;
  *pOffset += pPager->pageSize + 4 + isMainJrnl*4;

  /* Sanity checking on the page.  This is more important that I originally
  ** thought.  If a power failure occurs while the journal is being written,
  ** it could cause invalid data to be written into the journal.  We need to
  ** detect this invalid data (with high probability) and ignore it.
  */
  if( pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
    assert( !isSavepnt );
    return SQLITE_DONE;
  }
  if( pgno>(Pgno)pPager->dbSize || sqlite3BitvecTest(pDone, pgno) ){
    return SQLITE_OK;
  }
  if( isMainJrnl ){
    rc = read32bits(jfd, (*pOffset)-4, &cksum);
    if( rc ) return rc;
    if( !isSavepnt && pager_cksum(pPager, (u8*)aData)!=cksum ){
      return SQLITE_DONE;
    }
  }

  /* If this page has already been played back before during the current
  ** rollback, then don't bother to play it back again.
  */
  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
    return rc;
  }

  /* When playing back page 1, restore the nReserve setting
  */
  if( pgno==1 && pPager->nReserve!=((u8*)aData)[20] ){
    pPager->nReserve = ((u8*)aData)[20];
    pagerReportSize(pPager);
  }

  /* If the pager is in CACHEMOD state, then there must be a copy of this
  ** page in the pager cache. In this case just update the pager cache,
  ** not the database file. The page is left marked dirty in this case.
  **
  ** An exception to the above rule: If the database is in no-sync mode
  ** and a page is moved during an incremental vacuum then the page may
  ** not be in the pager cache. Later: if a malloc() or IO error occurs
  ** during a Movepage() call, then the page may not be in the cache
  ** either. So the condition described in the above paragraph is not
  ** assert()able.
  **
  ** If in WRITER_DBMOD, WRITER_FINISHED or OPEN state, then we update the
  ** pager cache if it exists and the main file. The page is then marked 
  ** not dirty. Since this code is only executed in PAGER_OPEN state for
  ** a hot-journal rollback, it is guaranteed that the page-cache is empty
  ** if the pager is in OPEN state.
  **
  ** Ticket #1171:  The statement journal might contain page content that is
  ** different from the page content at the start of the transaction.
  ** This occurs when a page is changed prior to the start of a statement
  ** then changed again within the statement.  When rolling back such a
  ** statement we must not write to the original database unless we know
  ** for certain that original page contents are synced into the main rollback
  ** journal.  Otherwise, a power loss might leave modified data in the
  ** database file without an entry in the rollback journal that can
  ** restore the database to its original form.  Two conditions must be
  ** met before writing to the database files. (1) the database must be
  ** locked.  (2) we know that the original page content is fully synced
  ** in the main journal either because the page is not in cache or else
  ** the page is marked as needSync==0.
  **
  ** 2008-04-14:  When attempting to vacuum a corrupt database file, it
  ** is possible to fail a statement on a database that does not yet exist.
  ** Do not attempt to write if database file has never been opened.
  */
  if( pagerUseWal(pPager) ){
    pPg = 0;
  }else{
    pPg = sqlite3PagerLookup(pPager, pgno);
  }
  assert( pPg );
  assert( pPager->eState!=PAGER_OPEN || pPg==0 );
  PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
           PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, (u8*)aData),
           (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( isMainJrnl ){
    isSynced = pPager->noSync || (*pOffset <= pPager->journalHdr);
  }else{
    isSynced = (pPg==0 || 0==(pPg->flags & PGHDR_NEED_SYNC));
  }
  if( isOpen(pPager->fd)
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );
    rc = sqlite3OsWrite(pPager->fd, (u8 *)aData, pPager->pageSize, ofst);
    if( pgno>pPager->dbFileSize ){
      pPager->dbFileSize = pgno;
    }
    if( pPager->pBackup ){
      CODEC1(pPager, aData, pgno, 3, rc=SQLITE_NOMEM);
      sqlite3BackupUpdate(pPager->pBackup, pgno, (u8*)aData);
      CODEC2(pPager, aData, pgno, 7, rc=SQLITE_NOMEM, aData);
    }
  }else if( !isMainJrnl && pPg==0 ){
    /* If this is a rollback of a savepoint and data was not written to
    ** the database and the page is not in-memory, there is a potential
    ** problem. When the page is next fetched by the b-tree layer, it 
    ** will be read from the database file, which may or may not be 
    ** current. 
    **
    ** There are a couple of different ways this can happen. All are quite
    ** obscure. When running in synchronous mode, this can only happen 
    ** if the page is on the free-list at the start of the transaction, then
    ** populated, then moved using sqlite3PagerMovepage().
    **
    ** The solution is to add an in-memory page to the cache containing
    ** the data just read from the sub-journal. Mark the page as dirty 
    ** and if the pager requires a journal-sync, then mark the page as 
    ** requiring a journal-sync before it is written.
    */
    assert( isSavepnt );
    assert( (pPager->doNotSpill & SPILLFLAG_ROLLBACK)==0 );
    pPager->doNotSpill |= SPILLFLAG_ROLLBACK;
    rc = sqlite3PagerAcquire(pPager, pgno, &pPg, 1);
    assert( (pPager->doNotSpill & SPILLFLAG_ROLLBACK)!=0 );
    pPager->doNotSpill &= ~SPILLFLAG_ROLLBACK;
    if( rc!=SQLITE_OK ) return rc;
    pPg->flags &= ~PGHDR_NEED_READ;
    sqlite3PcacheMakeDirty(pPg);
  }
  if( pPg ){
    /* No page should ever be explicitly rolled back that is in use, except
    ** for page 1 which is held in use in order to keep the lock on the
    ** database active. However such a page may be rolled back as a result
    ** of an internal error resulting in an automatic call to
    ** sqlite3PagerRollback().
    */
    void *pData;
    pData = pPg->pData;
    memcpy(pData, (u8*)aData, pPager->pageSize);
    pPager->xReiniter(pPg);
    if( isMainJrnl && (!isSavepnt || *pOffset<=pPager->journalHdr) ){
      /* If the contents of this page were just restored from the main 
      ** journal file, then its content must be as they were when the 
      ** transaction was first opened. In this case we can mark the page
      ** as clean, since there will be no need to write it out to the
      ** database.
      **
      ** There is one exception to this rule. If the page is being rolled
      ** back as part of a savepoint (or statement) rollback from an 
      ** unsynced portion of the main journal file, then it is not safe
      ** to mark the page as clean. This is because marking the page as
      ** clean will clear the PGHDR_NEED_SYNC flag. Since the page is
      ** already in the journal file (recorded in Pager.pInJournal) and
      ** the PGHDR_NEED_SYNC flag is cleared, if the page is written to
      ** again within this transaction, it will be marked as dirty but
      ** the PGHDR_NEED_SYNC flag will not be set. It could then potentially
      ** be written out into the database file before its journal file
      ** segment is synced. If a crash occurs during or following this,
      ** database corruption may ensue.
      */
      assert( !pagerUseWal(pPager) );
      sqlite3PcacheMakeClean(pPg);
    }
    pager_set_pagehash(pPg);

    /* If this was page 1, then restore the value of Pager.dbFileVers.
    ** Do this before any decoding. */
    if( pgno==1 ){
      memcpy(&pPager->dbFileVers, &((u8*)pData)[24],sizeof(pPager->dbFileVers));
    }

    /* Decode the page just read from disk */
    CODEC1(pPager, pData, pPg->pgno, 3, rc=SQLITE_NOMEM);
    sqlite3PcacheRelease(pPg);
  }
  return rc;
}

/*
** Parameter zMaster is the name of a master journal file. A single journal
** file that referred to the master journal file has just been rolled back.
** This routine checks if it is possible to delete the master journal file,
** and does so if it is.
**
** Argument zMaster may point to Pager.pTmpSpace. So that buffer is not 
** available for use within this function.
**
** When a master journal file is created, it is populated with the names 
** of all of its child journals, one after another, formatted as utf-8 
** encoded text. The end of each child journal file is marked with a 
** nul-terminator byte (0x00). i.e. the entire contents of a master journal
** file for a transaction involving two databases might be:
**
**   "/home/bill/a.db-journal\x00/home/bill/b.db-journal\x00"
**
** A master journal file may only be deleted once all of its child 
** journals have been rolled back.
**
** This function reads the contents of the master-journal file into 
** memory and loops through each of the child journal names. For
** each child journal, it checks if:
**
**   * if the child journal exists, and if so
**   * if the child journal contains a reference to master journal 
**     file zMaster
**
** If a child journal can be found that matches both of the criteria
** above, this function returns without doing anything. Otherwise, if
** no such child journal can be found, file zMaster is deleted from
** the file-system using sqlite3OsDelete().
**
** If an IO error within this function, an error code is returned. This
** function allocates memory by calling sqlite3Malloc(). If an allocation
** fails, SQLITE_NOMEM is returned. Otherwise, if no IO or malloc errors 
** occur, SQLITE_OK is returned.
**
** TODO: This function allocates a single block of memory to load
** the entire contents of the master journal file. This could be
** a couple of kilobytes or so - potentially larger than the page 
** size.
*/
static int pager_delmaster(Pager *pPager, const char *zMaster){
  sqlite3_vfs *pVfs = pPager->pVfs;
  int rc;                   /* Return code */
  sqlite3_file *pMaster;    /* Malloc'd master-journal file descriptor */
  sqlite3_file *pJournal;   /* Malloc'd child-journal file descriptor */
  char *zMasterJournal = 0; /* Contents of master journal file */
  i64 nMasterJournal;       /* Size of master journal file */
  char *zJournal;           /* Pointer to one journal within MJ file */
  char *zMasterPtr;         /* Space to hold MJ filename from a journal file */
  int nMasterPtr;           /* Amount of space allocated to zMasterPtr[] */

  /* Allocate space for both the pJournal and pMaster file descriptors.
  ** If successful, open the master journal file for reading.
  */
  pMaster = (sqlite3_file *)sqlite3MallocZero(pVfs->szOsFile * 2);
  pJournal = (sqlite3_file *)(((u8 *)pMaster) + pVfs->szOsFile);
  if( !pMaster ){
    rc = SQLITE_NOMEM;
  }else{
    const int flags = (SQLITE_OPEN_READONLY|SQLITE_OPEN_MASTER_JOURNAL);
    rc = sqlite3OsOpen(pVfs, zMaster, pMaster, flags, 0);
  }
  if( rc!=SQLITE_OK ) goto delmaster_out;

  /* Load the entire master journal file into space obtained from
  ** sqlite3_malloc() and pointed to by zMasterJournal.   Also obtain
  ** sufficient space (in zMasterPtr) to hold the names of master
  ** journal files extracted from regular rollback-journals.
  */
  rc = sqlite3OsFileSize(pMaster, &nMasterJournal);
  if( rc!=SQLITE_OK ) goto delmaster_out;
  nMasterPtr = pVfs->mxPathname+1;
  zMasterJournal = sqlite3Malloc(nMasterJournal + nMasterPtr + 1);
  if( !zMasterJournal ){
    rc = SQLITE_NOMEM;
    goto delmaster_out;
  }
  zMasterPtr = &zMasterJournal[nMasterJournal+1];
  rc = sqlite3OsRead(pMaster, zMasterJournal, (int)nMasterJournal, 0);
  if( rc!=SQLITE_OK ) goto delmaster_out;
  zMasterJournal[nMasterJournal] = 0;

  zJournal = zMasterJournal;
  while( (zJournal-zMasterJournal)<nMasterJournal ){
    int exists;
    rc = sqlite3OsAccess(pVfs, zJournal, SQLITE_ACCESS_EXISTS, &exists);
    if( rc!=SQLITE_OK ){
      goto delmaster_out;
    }
    if( exists ){
      /* One of the journals pointed to by the master journal exists.
      ** Open it and check if it points at the master journal. If
      ** so, return without deleting the master journal file.
      */
      int c;
      int flags = (SQLITE_OPEN_READONLY|SQLITE_OPEN_MAIN_JOURNAL);
      rc = sqlite3OsOpen(pVfs, zJournal, pJournal, flags, 0);
      if( rc!=SQLITE_OK ){
        goto delmaster_out;
      }

      rc = readMasterJournal(pJournal, zMasterPtr, nMasterPtr);
      sqlite3OsClose(pJournal);
      if( rc!=SQLITE_OK ){
        goto delmaster_out;
      }

      c = zMasterPtr[0]!=0 && strcmp(zMasterPtr, zMaster)==0;
      if( c ){
        /* We have a match. Do not delete the master journal file. */
        goto delmaster_out;
      }
    }
    zJournal += (sqlite3Strlen30(zJournal)+1);
  }
 
  sqlite3OsClose(pMaster);
  rc = sqlite3OsDelete(pVfs, zMaster, 0);

delmaster_out:
  sqlite3_free(zMasterJournal);
  if( pMaster ){
    sqlite3OsClose(pMaster);
    assert( !isOpen(pJournal) );
    sqlite3_free(pMaster);
  }
  return rc;
}


/*
** This function is used to change the actual size of the database 
** file in the file-system. This only happens when committing a transaction,
** or rolling back a transaction (including rolling back a hot-journal).
**
** If the main database file is not open, or the pager is not in either
** DBMOD or OPEN state, this function is a no-op. Otherwise, the size 
** of the file is changed to nPage pages (nPage*pPager->pageSize bytes). 
** If the file on disk is currently larger than nPage pages, then use the VFS
** xTruncate() method to truncate it.
**
** Or, it might be the case that the file on disk is smaller than 
** nPage pages. Some operating system implementations can get confused if 
** you try to truncate a file to some size that is larger than it 
** currently is, so detect this case and write a single zero byte to 
** the end of the new file instead.
**
** If successful, return SQLITE_OK. If an IO error occurs while modifying
** the database file, return the error code to the caller.
*/
static int pager_truncate(Pager *pPager, Pgno nPage){
  int rc = SQLITE_OK;
  assert( pPager->eState!=PAGER_ERROR );
  assert( pPager->eState!=PAGER_READER );
  
  if( isOpen(pPager->fd) 
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN) 
  ){
    i64 currentSize, newSize;
    int szPage = pPager->pageSize;
    assert( pPager->eLock==EXCLUSIVE_LOCK );
    /* TODO: Is it safe to use Pager.dbFileSize here? */
    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
    newSize = szPage*(i64)nPage;
    if( rc==SQLITE_OK && currentSize!=newSize ){
      if( currentSize>newSize ){
        rc = sqlite3OsTruncate(pPager->fd, newSize);
      }else if( (currentSize+szPage)<=newSize ){
        char *pTmp = pPager->pTmpSpace;
        memset(pTmp, 0, szPage);
        testcase( (newSize-szPage) == currentSize );
        testcase( (newSize-szPage) >  currentSize );
        rc = sqlite3OsWrite(pPager->fd, pTmp, szPage, newSize-szPage);
      }
      if( rc==SQLITE_OK ){
        pPager->dbFileSize = nPage;
      }
    }
  }
  return rc;
}

/*
** Return a sanitized version of the sector-size of OS file pFile. The
** return value is guaranteed to lie between 32 and MAX_SECTOR_SIZE.
*/
SQLITE_PRIVATE int sqlite3SectorSize(sqlite3_file *pFile){
  int iRet = sqlite3OsSectorSize(pFile);
  if( iRet<32 ){
    iRet = 512;
  }else if( iRet>MAX_SECTOR_SIZE ){
    assert( MAX_SECTOR_SIZE>=512 );
    iRet = MAX_SECTOR_SIZE;
  }
  return iRet;
}

/*
** Set the value of the Pager.sectorSize variable for the given
** pager based on the value returned by the xSectorSize method
** of the open database file. The sector size will be used 
** to determine the size and alignment of journal header and 
** master journal pointers within created journal files.
**
** For temporary files the effective sector size is always 512 bytes.
**
** Otherwise, for non-temporary files, the effective sector size is
** the value returned by the xSectorSize() method rounded up to 32 if
** it is less than 32, or rounded down to MAX_SECTOR_SIZE if it
** is greater than MAX_SECTOR_SIZE.
**
** If the file has the SQLITE_IOCAP_POWERSAFE_OVERWRITE property, then set
** the effective sector size to its minimum value (512).  The purpose of
** pPager->sectorSize is to define the "blast radius" of bytes that
** might change if a crash occurs while writing to a single byte in
** that range.  But with POWERSAFE_OVERWRITE, the blast radius is zero
** (that is what POWERSAFE_OVERWRITE means), so we minimize the sector
** size.  For backwards compatibility of the rollback journal file format,
** we cannot reduce the effective sector size below 512.
*/
static void setSectorSize(Pager *pPager){
  assert( isOpen(pPager->fd) || pPager->tempFile );

  if( pPager->tempFile
   || (sqlite3OsDeviceCharacteristics(pPager->fd) & 
              SQLITE_IOCAP_POWERSAFE_OVERWRITE)!=0
  ){
    /* Sector size doesn't matter for temporary files. Also, the file
    ** may not have been opened yet, in which case the OsSectorSize()
    ** call will segfault. */
    pPager->sectorSize = 512;
  }else{
    pPager->sectorSize = sqlite3SectorSize(pPager->fd);
  }
}

/*
** Playback the journal and thus restore the database file to
** the state it was in before we started making changes.  
**
** The journal file format is as follows: 
**
**  (1)  8 byte prefix.  A copy of aJournalMagic[].
**  (2)  4 byte big-endian integer which is the number of valid page records
**       in the journal.  If this value is 0xffffffff, then compute the
**       number of page records from the journal size.
**  (3)  4 byte big-endian integer which is the initial value for the 
**       sanity checksum.
**  (4)  4 byte integer which is the number of pages to truncate the
**       database to during a rollback.
**  (5)  4 byte big-endian integer which is the sector size.  The header
**       is this many bytes in size.
**  (6)  4 byte big-endian integer which is the page size.
**  (7)  zero padding out to the next sector size.
**  (8)  Zero or more pages instances, each as follows:
**        +  4 byte page number.
**        +  pPager->pageSize bytes of data.
**        +  4 byte checksum
**
** When we speak of the journal header, we mean the first 7 items above.
** Each entry in the journal is an instance of the 8th item.
**
** Call the value from the second bullet "nRec".  nRec is the number of
** valid page entries in the journal.  In most cases, you can compute the
** value of nRec from the size of the journal file.  But if a power
** failure occurred while the journal was being written, it could be the
** case that the size of the journal file had already been increased but
** the extra entries had not yet made it safely to disk.  In such a case,
** the value of nRec computed from the file size would be too large.  For
** that reason, we always use the nRec value in the header.
**
** If the nRec value is 0xffffffff it means that nRec should be computed
** from the file size.  This value is used when the user selects the
** no-sync option for the journal.  A power failure could lead to corruption
** in this case.  But for things like temporary table (which will be
** deleted when the power is restored) we don't care.  
**
** If the file opened as the journal file is not a well-formed
** journal file then all pages up to the first corrupted page are rolled
** back (or no pages if the journal header is corrupted). The journal file
** is then deleted and SQLITE_OK returned, just as if no corruption had
** been encountered.
**
** If an I/O or malloc() error occurs, the journal-file is not deleted
** and an error code is returned.
**
** The isHot parameter indicates that we are trying to rollback a journal
** that might be a hot journal.  Or, it could be that the journal is 
** preserved because of JOURNALMODE_PERSIST or JOURNALMODE_TRUNCATE.
** If the journal really is hot, reset the pager cache prior rolling
** back any content.  If the journal is merely persistent, no reset is
** needed.
*/
static int pager_playback(Pager *pPager, int isHot){
  sqlite3_vfs *pVfs = pPager->pVfs;
  i64 szJ;                 /* Size of the journal file in bytes */
  u32 nRec;                /* Number of Records in the journal */
  u32 u;                   /* Unsigned loop counter */
  Pgno mxPg = 0;           /* Size of the original file in pages */
  int rc;                  /* Result code of a subroutine */
  int res = 1;             /* Value returned by sqlite3OsAccess() */
  char *zMaster = 0;       /* Name of master journal file if any */
  int needPagerReset;      /* True to reset page prior to first page rollback */
  int nPlayback = 0;       /* Total number of pages restored from journal */

  /* Figure out how many records are in the journal.  Abort early if
  ** the journal is empty.
  */
  assert( isOpen(pPager->jfd) );
  rc = sqlite3OsFileSize(pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_playback;
  }

  /* Read the master journal name from the journal, if it is present.
  ** If a master journal file name is specified, but the file is not
  ** present on disk, then the journal is not hot and does not need to be
  ** played back.
  **
  ** TODO: Technically the following is an error because it assumes that
  ** buffer Pager.pTmpSpace is (mxPathname+1) bytes or larger. i.e. that
  ** (pPager->pageSize >= pPager->pVfs->mxPathname+1). Using os_unix.c,
  **  mxPathname is 512, which is the same as the minimum allowable value
  ** for pageSize.
  */
  zMaster = pPager->pTmpSpace;
  rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
  if( rc==SQLITE_OK && zMaster[0] ){
    rc = sqlite3OsAccess(pVfs, zMaster, SQLITE_ACCESS_EXISTS, &res);
  }
  zMaster = 0;
  if( rc!=SQLITE_OK || !res ){
    goto end_playback;
  }
  pPager->journalOff = 0;
  needPagerReset = isHot;

  /* This loop terminates either when a readJournalHdr() or 
  ** pager_playback_one_page() call returns SQLITE_DONE or an IO error 
  ** occurs. 
  */
  while( 1 ){
    /* Read the next journal header from the journal file.  If there are
    ** not enough bytes left in the journal file for a complete header, or
    ** it is corrupted, then a process must have failed while writing it.
    ** This indicates nothing more needs to be rolled back.
    */
    rc = readJournalHdr(pPager, isHot, szJ, &nRec, &mxPg);
    if( rc!=SQLITE_OK ){ 
      if( rc==SQLITE_DONE ){
        rc = SQLITE_OK;
      }
      goto end_playback;
    }

    /* If nRec is 0xffffffff, then this journal was created by a process
    ** working in no-sync mode. This means that the rest of the journal
    ** file consists of pages, there are no more journal headers. Compute
    ** the value of nRec based on this assumption.
    */
    if( nRec==0xffffffff ){
      assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) );
      nRec = (int)((szJ - JOURNAL_HDR_SZ(pPager))/JOURNAL_PG_SZ(pPager));
    }

    /* If nRec is 0 and this rollback is of a transaction created by this
    ** process and if this is the final header in the journal, then it means
    ** that this part of the journal was being filled but has not yet been
    ** synced to disk.  Compute the number of pages based on the remaining
    ** size of the file.
    **
    ** The third term of the test was added to fix ticket #2565.
    ** When rolling back a hot journal, nRec==0 always means that the next
    ** chunk of the journal contains zero pages to be rolled back.  But
    ** when doing a ROLLBACK and the nRec==0 chunk is the last chunk in
    ** the journal, it means that the journal might contain additional
    ** pages that need to be rolled back and that the number of pages 
    ** should be computed based on the journal file size.
    */
    if( nRec==0 && !isHot &&
        pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff ){
      nRec = (int)((szJ - pPager->journalOff) / JOURNAL_PG_SZ(pPager));
    }

    /* If this is the first header read from the journal, truncate the
    ** database file back to its original size.
    */
    if( pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){
      rc = pager_truncate(pPager, mxPg);
      if( rc!=SQLITE_OK ){
        goto end_playback;
      }
      pPager->dbSize = mxPg;
    }

    /* Copy original pages out of the journal and back into the 
    ** database file and/or page cache.
    */
    for(u=0; u<nRec; u++){
      if( needPagerReset ){
        pager_reset(pPager);
        needPagerReset = 0;
      }
      rc = pager_playback_one_page(pPager,&pPager->journalOff,0,1,0);
      if( rc==SQLITE_OK ){
        nPlayback++;
      }else{
        if( rc==SQLITE_DONE ){
          pPager->journalOff = szJ;
          break;
        }else if( rc==SQLITE_IOERR_SHORT_READ ){
          /* If the journal has been truncated, simply stop reading and
          ** processing the journal. This might happen if the journal was
          ** not completely written and synced prior to a crash.  In that
          ** case, the database should have never been written in the
          ** first place so it is OK to simply abandon the rollback. */
          rc = SQLITE_OK;
          goto end_playback;
        }else{
          /* If we are unable to rollback, quit and return the error
          ** code.  This will cause the pager to enter the error state
          ** so that no further harm will be done.  Perhaps the next
          ** process to come along will be able to rollback the database.
          */
          goto end_playback;
        }
      }
    }
  }
  /*NOTREACHED*/
  assert( 0 );

end_playback:
  /* Following a rollback, the database file should be back in its original
  ** state prior to the start of the transaction, so invoke the
  ** SQLITE_FCNTL_DB_UNCHANGED file-control method to disable the
  ** assertion that the transaction counter was modified.
  */
#ifdef SQLITE_DEBUG
  if( pPager->fd->pMethods ){
    sqlite3OsFileControlHint(pPager->fd,SQLITE_FCNTL_DB_UNCHANGED,0);
  }
#endif

  /* If this playback is happening automatically as a result of an IO or 
  ** malloc error that occurred after the change-counter was updated but 
  ** before the transaction was committed, then the change-counter 
  ** modification may just have been reverted. If this happens in exclusive 
  ** mode, then subsequent transactions performed by the connection will not
  ** update the change-counter at all. This may lead to cache inconsistency
  ** problems for other processes at some point in the future. So, just
  ** in case this has happened, clear the changeCountDone flag now.
  */
  pPager->changeCountDone = pPager->tempFile;

  if( rc==SQLITE_OK ){
    zMaster = pPager->pTmpSpace;
    rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)
  ){
    rc = sqlite3PagerSync(pPager, 0);
  }
  if( rc==SQLITE_OK ){
    rc = pager_end_transaction(pPager, zMaster[0]!='\0', 0);
    testcase( rc!=SQLITE_OK );
  }
  if( rc==SQLITE_OK && zMaster[0] && res ){
    /* If there was a master journal and this routine will return success,
    ** see if it is possible to delete the master journal.
    */
    rc = pager_delmaster(pPager, zMaster);
    testcase( rc!=SQLITE_OK );
  }
  if( isHot && nPlayback ){
    sqlite3_log(SQLITE_NOTICE_RECOVER_ROLLBACK, "recovered %d pages from %s",
                nPlayback, pPager->zJournal);
  }

  /* The Pager.sectorSize variable may have been updated while rolling
  ** back a journal created by a process with a different sector size
  ** value. Reset it to the correct value for this process.
  */
  setSectorSize(pPager);
  return rc;
}


/*
** Read the content for page pPg out of the database file and into 
** pPg->pData. A shared lock or greater must be held on the database
** file before this function is called.
**
** If page 1 is read, then the value of Pager.dbFileVers[] is set to
** the value read from the database file.
**
** If an IO error occurs, then the IO error is returned to the caller.
** Otherwise, SQLITE_OK is returned.
*/
static int readDbPage(PgHdr *pPg, u32 iFrame){
  Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
  Pgno pgno = pPg->pgno;       /* Page number to read */
  int rc = SQLITE_OK;          /* Return code */
  int pgsz = pPager->pageSize; /* Number of bytes to read */

  assert( pPager->eState>=PAGER_READER );
  assert( isOpen(pPager->fd) );

#ifndef SQLITE_OMIT_WAL
  if( iFrame ){
    /* Try to pull the page from the write-ahead log. */
    rc = sqlite3WalReadFrame(pPager->pWal, iFrame, pgsz, pPg->pData);
  }else
#endif
  {
    i64 iOffset = (pgno-1)*(i64)pPager->pageSize;
    rc = sqlite3OsRead(pPager->fd, pPg->pData, pgsz, iOffset);
    if( rc==SQLITE_IOERR_SHORT_READ ){
      rc = SQLITE_OK;
    }
  }

  if( pgno==1 ){
    if( rc ){
      /* If the read is unsuccessful, set the dbFileVers[] to something
      ** that will never be a valid file version.  dbFileVers[] is a copy
      ** of bytes 24..39 of the database.  Bytes 28..31 should always be
      ** zero or the size of the database in page. Bytes 32..35 and 35..39
      ** should be page numbers which are never 0xffffffff.  So filling
      ** pPager->dbFileVers[] with all 0xff bytes should suffice.
      **
      ** For an encrypted database, the situation is more complex:  bytes
      ** 24..39 of the database are white noise.  But the probability of
      ** white noise equaling 16 bytes of 0xff is vanishingly small so
      ** we should still be ok.
      */
      memset(pPager->dbFileVers, 0xff, sizeof(pPager->dbFileVers));
    }else{
      u8 *dbFileVers = &((u8*)pPg->pData)[24];
      memcpy(&pPager->dbFileVers, dbFileVers, sizeof(pPager->dbFileVers));
    }
  }
  CODEC1(pPager, pPg->pData, pgno, 3, rc = SQLITE_NOMEM);

  PAGER_INCR(sqlite3_pager_readdb_count);
  PAGER_INCR(pPager->nRead);
  IOTRACE(("PGIN %p %d\n", pPager, pgno));
  PAGERTRACE(("FETCH %d page %d hash(%08x)\n",
               PAGERID(pPager), pgno, pager_pagehash(pPg)));

  return rc;
}

/*
** Update the value of the change-counter at offsets 24 and 92 in
** the header and the sqlite version number at offset 96.
**
** This is an unconditional update.  See also the pager_incr_changecounter()
** routine which only updates the change-counter if the update is actually
** needed, as determined by the pPager->changeCountDone state variable.
*/
static void pager_write_changecounter(PgHdr *pPg){
  u32 change_counter;

  /* Increment the value just read and write it back to byte 24. */
  change_counter = sqlite3Get4byte((u8*)pPg->pPager->dbFileVers)+1;
  put32bits(((char*)pPg->pData)+24, change_counter);

  /* Also store the SQLite version number in bytes 96..99 and in
  ** bytes 92..95 store the change counter for which the version number
  ** is valid. */
  put32bits(((char*)pPg->pData)+92, change_counter);
  put32bits(((char*)pPg->pData)+96, SQLITE_VERSION_NUMBER);
}

#ifndef SQLITE_OMIT_WAL
/*
** This function is invoked once for each page that has already been 
** written into the log file when a WAL transaction is rolled back.
** Parameter iPg is the page number of said page. The pCtx argument 
** is actually a pointer to the Pager structure.
**
** If page iPg is present in the cache, and has no outstanding references,
** it is discarded. Otherwise, if there are one or more outstanding
** references, the page content is reloaded from the database. If the
** attempt to reload content from the database is required and fails, 
** return an SQLite error code. Otherwise, SQLITE_OK.
*/
static int pagerUndoCallback(void *pCtx, Pgno iPg){
  int rc = SQLITE_OK;
  Pager *pPager = (Pager *)pCtx;
  PgHdr *pPg;

  assert( pagerUseWal(pPager) );
  pPg = sqlite3PagerLookup(pPager, iPg);
  if( pPg ){
    if( sqlite3PcachePageRefcount(pPg)==1 ){
      sqlite3PcacheDrop(pPg);
    }else{
      u32 iFrame = 0;
      rc = sqlite3WalFindFrame(pPager->pWal, pPg->pgno, &iFrame);
      if( rc==SQLITE_OK ){
        rc = readDbPage(pPg, iFrame);
      }
      if( rc==SQLITE_OK ){
        pPager->xReiniter(pPg);
      }
      sqlite3PagerUnrefNotNull(pPg);
    }
  }

  /* Normally, if a transaction is rolled back, any backup processes are
  ** updated as data is copied out of the rollback journal and into the
  ** database. This is not generally possible with a WAL database, as
  ** rollback involves simply truncating the log file. Therefore, if one
  ** or more frames have already been written to the log (and therefore 
  ** also copied into the backup databases) as part of this transaction,
  ** the backups must be restarted.
  */
  sqlite3BackupRestart(pPager->pBackup);

  return rc;
}

/*
** This function is called to rollback a transaction on a WAL database.
*/
static int pagerRollbackWal(Pager *pPager){
  int rc;                         /* Return Code */
  PgHdr *pList;                   /* List of dirty pages to revert */

  /* For all pages in the cache that are currently dirty or have already
  ** been written (but not committed) to the log file, do one of the 
  ** following:
  **
  **   + Discard the cached page (if refcount==0), or
  **   + Reload page content from the database (if refcount>0).
  */
  pPager->dbSize = pPager->dbOrigSize;
  rc = sqlite3WalUndo(pPager->pWal, pagerUndoCallback, (void *)pPager);
  pList = sqlite3PcacheDirtyList(pPager->pPCache);
  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;
    rc = pagerUndoCallback((void *)pPager, pList->pgno);
    pList = pNext;
  }

  return rc;
}

/*
** This function is a wrapper around sqlite3WalFrames(). As well as logging
** the contents of the list of pages headed by pList (connected by pDirty),
** this function notifies any active backup processes that the pages have
** changed. 
**
** The list of pages passed into this routine is always sorted by page number.
** Hence, if page 1 appears anywhere on the list, it will be the first page.
*/ 
static int pagerWalFrames(
  Pager *pPager,                  /* Pager object */
  PgHdr *pList,                   /* List of frames to log */
  Pgno nTruncate,                 /* Database size after this commit */
  int isCommit                    /* True if this is a commit */
){
  int rc;                         /* Return code */
  int nList;                      /* Number of pages in pList */
  PgHdr *p;                       /* For looping over pages */

  assert( pPager->pWal );
  assert( pList );
#ifdef SQLITE_DEBUG
  /* Verify that the page list is in accending order */
  for(p=pList; p && p->pDirty; p=p->pDirty){
    assert( p->pgno < p->pDirty->pgno );
  }
#endif

  assert( pList->pDirty==0 || isCommit );
  if( isCommit ){
    /* If a WAL transaction is being committed, there is no point in writing
    ** any pages with page numbers greater than nTruncate into the WAL file.
    ** They will never be read by any client. So remove them from the pDirty
    ** list here. */
    PgHdr **ppNext = &pList;
    nList = 0;
    for(p=pList; (*ppNext = p)!=0; p=p->pDirty){
      if( p->pgno<=nTruncate ){
        ppNext = &p->pDirty;
        nList++;
      }
    }
    assert( pList );
  }else{
    nList = 1;
  }
  pPager->aStat[PAGER_STAT_WRITE] += nList;

  if( pList->pgno==1 ) pager_write_changecounter(pList);
  rc = sqlite3WalFrames(pPager->pWal, 
      pPager->pageSize, pList, nTruncate, isCommit, pPager->walSyncFlags
  );
  if( rc==SQLITE_OK && pPager->pBackup ){
    for(p=pList; p; p=p->pDirty){
      sqlite3BackupUpdate(pPager->pBackup, p->pgno, (u8 *)p->pData);
    }
  }

#ifdef SQLITE_CHECK_PAGES
  pList = sqlite3PcacheDirtyList(pPager->pPCache);
  for(p=pList; p; p=p->pDirty){
    pager_set_pagehash(p);
  }
#endif

  return rc;
}

/*
** Begin a read transaction on the WAL.
**
** This routine used to be called "pagerOpenSnapshot()" because it essentially
** makes a snapshot of the database at the current point in time and preserves
** that snapshot for use by the reader in spite of concurrently changes by
** other writers or checkpointers.
*/
static int pagerBeginReadTransaction(Pager *pPager){
  int rc;                         /* Return code */
  int changed = 0;                /* True if cache must be reset */

  assert( pagerUseWal(pPager) );
  assert( pPager->eState==PAGER_OPEN || pPager->eState==PAGER_READER );

  /* sqlite3WalEndReadTransaction() was not called for the previous
  ** transaction in locking_mode=EXCLUSIVE.  So call it now.  If we
  ** are in locking_mode=NORMAL and EndRead() was previously called,
  ** the duplicate call is harmless.
  */
  sqlite3WalEndReadTransaction(pPager->pWal);

  rc = sqlite3WalBeginReadTransaction(pPager->pWal, &changed);
  if( rc!=SQLITE_OK || changed ){
    pager_reset(pPager);
    if( USEFETCH(pPager) ) sqlite3OsUnfetch(pPager->fd, 0, 0);
  }

  return rc;
}
#endif

/*
** This function is called as part of the transition from PAGER_OPEN
** to PAGER_READER state to determine the size of the database file
** in pages (assuming the page size currently stored in Pager.pageSize).
**
** If no error occurs, SQLITE_OK is returned and the size of the database
** in pages is stored in *pnPage. Otherwise, an error code (perhaps
** SQLITE_IOERR_FSTAT) is returned and *pnPage is left unmodified.
*/
static int pagerPagecount(Pager *pPager, Pgno *pnPage){
  Pgno nPage;                     /* Value to return via *pnPage */

  /* Query the WAL sub-system for the database size. The WalDbsize()
  ** function returns zero if the WAL is not open (i.e. Pager.pWal==0), or
  ** if the database size is not available. The database size is not
  ** available from the WAL sub-system if the log file is empty or
  ** contains no valid committed transactions.
  */
  assert( pPager->eState==PAGER_OPEN );
  assert( pPager->eLock>=SHARED_LOCK );
  nPage = sqlite3WalDbsize(pPager->pWal);

  /* If the number of pages in the database is not available from the
  ** WAL sub-system, determine the page counte based on the size of
  ** the database file.  If the size of the database file is not an
  ** integer multiple of the page-size, round up the result.
  */
  if( nPage==0 ){
    i64 n = 0;                    /* Size of db file in bytes */
    assert( isOpen(pPager->fd) || pPager->tempFile );
    if( isOpen(pPager->fd) ){
      int rc = sqlite3OsFileSize(pPager->fd, &n);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
    nPage = (Pgno)((n+pPager->pageSize-1) / pPager->pageSize);
  }

  /* If the current number of pages in the file is greater than the
  ** configured maximum pager number, increase the allowed limit so
  ** that the file can be read.
  */
  if( nPage>pPager->mxPgno ){
    pPager->mxPgno = (Pgno)nPage;
  }

  *pnPage = nPage;
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_WAL
/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
** if no error occurs, make sure Pager.journalMode is not set to
** PAGER_JOURNALMODE_WAL.
**
** Return SQLITE_OK or an error code.
**
** The caller must hold a SHARED lock on the database file to call this
** function. Because an EXCLUSIVE lock on the db file is required to delete 
** a WAL on a none-empty database, this ensures there is no race condition 
** between the xAccess() below and an xDelete() being executed by some 
** other connection.
*/
static int pagerOpenWalIfPresent(Pager *pPager){
  int rc = SQLITE_OK;
  assert( pPager->eState==PAGER_OPEN );
  assert( pPager->eLock>=SHARED_LOCK );

  if( !pPager->tempFile ){
    int isWal;                    /* True if WAL file exists */
    Pgno nPage;                   /* Size of the database file */

    rc = pagerPagecount(pPager, &nPage);
    if( rc ) return rc;
    if( nPage==0 ){
      rc = sqlite3OsDelete(pPager->pVfs, pPager->zWal, 0);
      if( rc==SQLITE_IOERR_DELETE_NOENT ) rc = SQLITE_OK;
      isWal = 0;
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        testcase( sqlite3PcachePagecount(pPager->pPCache)==0 );
        rc = sqlite3PagerOpenWal(pPager, 0);
      }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
        pPager->journalMode = PAGER_JOURNALMODE_DELETE;
      }
    }
  }
  return rc;
}
#endif

/*
** Playback savepoint pSavepoint. Or, if pSavepoint==NULL, then playback
** the entire master journal file. The case pSavepoint==NULL occurs when 
** a ROLLBACK TO command is invoked on a SAVEPOINT that is a transaction 
** savepoint.
**
** When pSavepoint is not NULL (meaning a non-transaction savepoint is 
** being rolled back), then the rollback consists of up to three stages,
** performed in the order specified:
**
**   * Pages are played back from the main journal starting at byte
**     offset PagerSavepoint.iOffset and continuing to 
**     PagerSavepoint.iHdrOffset, or to the end of the main journal
**     file if PagerSavepoint.iHdrOffset is zero.
**
**   * If PagerSavepoint.iHdrOffset is not zero, then pages are played
**     back starting from the journal header immediately following 
**     PagerSavepoint.iHdrOffset to the end of the main journal file.
**
**   * Pages are then played back from the sub-journal file, starting
**     with the PagerSavepoint.iSubRec and continuing to the end of
**     the journal file.
**
** Throughout the rollback process, each time a page is rolled back, the
** corresponding bit is set in a bitvec structure (variable pDone in the
** implementation below). This is used to ensure that a page is only
** rolled back the first time it is encountered in either journal.
**
** If pSavepoint is NULL, then pages are only played back from the main
** journal file. There is no need for a bitvec in this case.
**
** In either case, before playback commences the Pager.dbSize variable
** is reset to the value that it held at the start of the savepoint 
** (or transaction). No page with a page-number greater than this value
** is played back. If one is encountered it is simply skipped.
*/
static int pagerPlaybackSavepoint(Pager *pPager, PagerSavepoint *pSavepoint){
  i64 szJ;                 /* Effective size of the main journal */
  i64 iHdrOff;             /* End of first segment of main-journal records */
  int rc = SQLITE_OK;      /* Return code */
  Bitvec *pDone = 0;       /* Bitvec to ensure pages played back only once */

  assert( pPager->eState!=PAGER_ERROR );
  assert( pPager->eState>=PAGER_WRITER_LOCKED );

  /* Allocate a bitvec to use to store the set of pages rolled back */
  if( pSavepoint ){
    pDone = sqlite3BitvecCreate(pSavepoint->nOrig);
    if( !pDone ){
      return SQLITE_NOMEM;
    }
  }

  /* Set the database size back to the value it was before the savepoint 
  ** being reverted was opened.
  */
  pPager->dbSize = pSavepoint ? pSavepoint->nOrig : pPager->dbOrigSize;
  pPager->changeCountDone = pPager->tempFile;

  if( !pSavepoint && pagerUseWal(pPager) ){
    return pagerRollbackWal(pPager);
  }

  /* Use pPager->journalOff as the effective size of the main rollback
  ** journal.  The actual file might be larger than this in
  ** PAGER_JOURNALMODE_TRUNCATE or PAGER_JOURNALMODE_PERSIST.  But anything
  ** past pPager->journalOff is off-limits to us.
  */
  szJ = pPager->journalOff;
  assert( pagerUseWal(pPager)==0 || szJ==0 );

  /* Begin by rolling back records from the main journal starting at
  ** PagerSavepoint.iOffset and continuing to the next journal header.
  ** There might be records in the main journal that have a page number
  ** greater than the current database size (pPager->dbSize) but those
  ** will be skipped automatically.  Pages are added to pDone as they
  ** are played back.
  */
  if( pSavepoint && !pagerUseWal(pPager) ){
    iHdrOff = pSavepoint->iHdrOffset ? pSavepoint->iHdrOffset : szJ;
    pPager->journalOff = pSavepoint->iOffset;
    while( rc==SQLITE_OK && pPager->journalOff<iHdrOff ){
      rc = pager_playback_one_page(pPager, &pPager->journalOff, pDone, 1, 1);
    }
    assert( rc!=SQLITE_DONE );
  }else{
    pPager->journalOff = 0;
  }

  /* Continue rolling back records out of the main journal starting at
  ** the first journal header seen and continuing until the effective end
  ** of the main journal file.  Continue to skip out-of-range pages and
  ** continue adding pages rolled back to pDone.
  */
  while( rc==SQLITE_OK && pPager->journalOff<szJ ){
    u32 ii;            /* Loop counter */
    u32 nJRec = 0;     /* Number of Journal Records */
    u32 dummy;
    rc = readJournalHdr(pPager, 0, szJ, &nJRec, &dummy);
    assert( rc!=SQLITE_DONE );

    /*
    ** The "pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff"
    ** test is related to ticket #2565.  See the discussion in the
    ** pager_playback() function for additional information.
    */
    if( nJRec==0 
     && pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff
    ){
      nJRec = (u32)((szJ - pPager->journalOff)/JOURNAL_PG_SZ(pPager));
    }
    for(ii=0; rc==SQLITE_OK && ii<nJRec && pPager->journalOff<szJ; ii++){
      rc = pager_playback_one_page(pPager, &pPager->journalOff, pDone, 1, 1);
    }
    assert( rc!=SQLITE_DONE );
  }
  assert( rc!=SQLITE_OK || pPager->journalOff>=szJ );

  /* Finally,  rollback pages from the sub-journal.  Page that were
  ** previously rolled back out of the main journal (and are hence in pDone)
  ** will be skipped.  Out-of-range pages are also skipped.
  */
  if( pSavepoint ){
    u32 ii;            /* Loop counter */
    i64 offset = (i64)pSavepoint->iSubRec*(4+pPager->pageSize);

    if( pagerUseWal(pPager) ){
      rc = sqlite3WalSavepointUndo(pPager->pWal, pSavepoint->aWalData);
    }
    for(ii=pSavepoint->iSubRec; rc==SQLITE_OK && ii<pPager->nSubRec; ii++){
      assert( offset==(i64)ii*(4+pPager->pageSize) );
      rc = pager_playback_one_page(pPager, &offset, pDone, 0, 1);
    }
    assert( rc!=SQLITE_DONE );
  }

  sqlite3BitvecDestroy(pDone);
  if( rc==SQLITE_OK ){
    pPager->journalOff = szJ;
  }

  return rc;
}

/*
** Change the maximum number of in-memory pages that are allowed.
*/
SQLITE_PRIVATE void sqlite3PagerSetCachesize(Pager *pPager, int mxPage){
  sqlite3PcacheSetCachesize(pPager->pPCache, mxPage);
}

/*
** Invoke SQLITE_FCNTL_MMAP_SIZE based on the current value of szMmap.
*/
static void pagerFixMaplimit(Pager *pPager){
#if SQLITE_MAX_MMAP_SIZE>0
  sqlite3_file *fd = pPager->fd;
  if( isOpen(fd) && fd->pMethods->iVersion>=3 ){
    sqlite3_int64 sz;
    sz = pPager->szMmap;
    pPager->bUseFetch = (sz>0);
    sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_MMAP_SIZE, &sz);
  }
#endif
}

/*
** Change the maximum size of any memory mapping made of the database file.
*/
SQLITE_PRIVATE void sqlite3PagerSetMmapLimit(Pager *pPager, sqlite3_int64 szMmap){
  pPager->szMmap = szMmap;
  pagerFixMaplimit(pPager);
}

/*
** Adjust settings of the pager to those specified in the pgFlags parameter.
**
** The "level" in pgFlags & PAGER_SYNCHRONOUS_MASK sets the robustness
** of the database to damage due to OS crashes or power failures by
** changing the number of syncs()s when writing the journals.
** There are three levels:
**
**    OFF       sqlite3OsSync() is never called.  This is the default
**              for temporary and transient files.
**
**    NORMAL    The journal is synced once before writes begin on the
**              database.  This is normally adequate protection, but
**              it is theoretically possible, though very unlikely,
**              that an inopertune power failure could leave the journal
**              in a state which would cause damage to the database
**              when it is rolled back.
**
**    FULL      The journal is synced twice before writes begin on the
**              database (with some additional information - the nRec field
**              of the journal header - being written in between the two
**              syncs).  If we assume that writing a
**              single disk sector is atomic, then this mode provides
**              assurance that the journal will not be corrupted to the
**              point of causing damage to the database during rollback.
**
** The above is for a rollback-journal mode.  For WAL mode, OFF continues
** to mean that no syncs ever occur.  NORMAL means that the WAL is synced
** prior to the start of checkpoint and that the database file is synced
** at the conclusion of the checkpoint if the entire content of the WAL
** was written back into the database.  But no sync operations occur for
** an ordinary commit in NORMAL mode with WAL.  FULL means that the WAL
** file is synced following each commit operation, in addition to the
** syncs associated with NORMAL.
**
** Do not confuse synchronous=FULL with SQLITE_SYNC_FULL.  The
** SQLITE_SYNC_FULL macro means to use the MacOSX-style full-fsync
** using fcntl(F_FULLFSYNC).  SQLITE_SYNC_NORMAL means to do an
** ordinary fsync() call.  There is no difference between SQLITE_SYNC_FULL
** and SQLITE_SYNC_NORMAL on platforms other than MacOSX.  But the
** synchronous=FULL versus synchronous=NORMAL setting determines when
** the xSync primitive is called and is relevant to all platforms.
**
** Numeric values associated with these states are OFF==1, NORMAL=2,
** and FULL=3.
*/
#ifndef SQLITE_OMIT_PAGER_PRAGMAS
SQLITE_PRIVATE void sqlite3PagerSetFlags(
  Pager *pPager,        /* The pager to set safety level for */
  unsigned pgFlags      /* Various flags */
){
  unsigned level = pgFlags & PAGER_SYNCHRONOUS_MASK;
  assert( level>=1 && level<=3 );
  pPager->noSync =  (level==1 || pPager->tempFile) ?1:0;
  pPager->fullSync = (level==3 && !pPager->tempFile) ?1:0;
  if( pPager->noSync ){
    pPager->syncFlags = 0;
    pPager->ckptSyncFlags = 0;
  }else if( pgFlags & PAGER_FULLFSYNC ){
    pPager->syncFlags = SQLITE_SYNC_FULL;
    pPager->ckptSyncFlags = SQLITE_SYNC_FULL;
  }else if( pgFlags & PAGER_CKPT_FULLFSYNC ){
    pPager->syncFlags = SQLITE_SYNC_NORMAL;
    pPager->ckptSyncFlags = SQLITE_SYNC_FULL;
  }else{
    pPager->syncFlags = SQLITE_SYNC_NORMAL;
    pPager->ckptSyncFlags = SQLITE_SYNC_NORMAL;
  }
  pPager->walSyncFlags = pPager->syncFlags;
  if( pPager->fullSync ){
    pPager->walSyncFlags |= WAL_SYNC_TRANSACTIONS;
  }
  if( pgFlags & PAGER_CACHESPILL ){
    pPager->doNotSpill &= ~SPILLFLAG_OFF;
  }else{
    pPager->doNotSpill |= SPILLFLAG_OFF;
  }
}
#endif

/*
** The following global variable is incremented whenever the library
** attempts to open a temporary file.  This information is used for
** testing and analysis only.  
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_opentemp_count = 0;
#endif

/*
** Open a temporary file.
**
** Write the file descriptor into *pFile. Return SQLITE_OK on success 
** or some other error code if we fail. The OS will automatically 
** delete the temporary file when it is closed.
**
** The flags passed to the VFS layer xOpen() call are those specified
** by parameter vfsFlags ORed with the following:
**
**     SQLITE_OPEN_READWRITE
**     SQLITE_OPEN_CREATE
**     SQLITE_OPEN_EXCLUSIVE
**     SQLITE_OPEN_DELETEONCLOSE
*/
static int pagerOpentemp(
  Pager *pPager,        /* The pager object */
  sqlite3_file *pFile,  /* Write the file descriptor here */
  int vfsFlags          /* Flags passed through to the VFS */
){
  int rc;               /* Return code */

#ifdef SQLITE_TEST
  sqlite3_opentemp_count++;  /* Used for testing and analysis only */
#endif

  vfsFlags |=  SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
            SQLITE_OPEN_EXCLUSIVE | SQLITE_OPEN_DELETEONCLOSE;
  rc = sqlite3OsOpen(pPager->pVfs, 0, pFile, vfsFlags, 0);
  assert( rc!=SQLITE_OK || isOpen(pFile) );
  return rc;
}

/*
** Set the busy handler function.
**
** The pager invokes the busy-handler if sqlite3OsLock() returns 
** SQLITE_BUSY when trying to upgrade from no-lock to a SHARED lock,
** or when trying to upgrade from a RESERVED lock to an EXCLUSIVE 
** lock. It does *not* invoke the busy handler when upgrading from
** SHARED to RESERVED, or when upgrading from SHARED to EXCLUSIVE
** (which occurs during hot-journal rollback). Summary:
**
**   Transition                        | Invokes xBusyHandler
**   --------------------------------------------------------
**   NO_LOCK       -> SHARED_LOCK      | Yes
**   SHARED_LOCK   -> RESERVED_LOCK    | No
**   SHARED_LOCK   -> EXCLUSIVE_LOCK   | No
**   RESERVED_LOCK -> EXCLUSIVE_LOCK   | Yes
**
** If the busy-handler callback returns non-zero, the lock is 
** retried. If it returns zero, then the SQLITE_BUSY error is
** returned to the caller of the pager API function.
*/
SQLITE_PRIVATE void sqlite3PagerSetBusyhandler(
  Pager *pPager,                       /* Pager object */
  int (*xBusyHandler)(void *),         /* Pointer to busy-handler function */
  void *pBusyHandlerArg                /* Argument to pass to xBusyHandler */
){
  pPager->xBusyHandler = xBusyHandler;
  pPager->pBusyHandlerArg = pBusyHandlerArg;

  if( isOpen(pPager->fd) ){
    void **ap = (void **)&pPager->xBusyHandler;
    assert( ((int(*)(void *))(ap[0]))==xBusyHandler );
    assert( ap[1]==pBusyHandlerArg );
    sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_BUSYHANDLER, (void *)ap);
  }
}

/*
** Change the page size used by the Pager object. The new page size 
** is passed in *pPageSize.
**
** If the pager is in the error state when this function is called, it
** is a no-op. The value returned is the error state error code (i.e. 
** one of SQLITE_IOERR, an SQLITE_IOERR_xxx sub-code or SQLITE_FULL).
**
** Otherwise, if all of the following are true:
**
**   * the new page size (value of *pPageSize) is valid (a power 
**     of two between 512 and SQLITE_MAX_PAGE_SIZE, inclusive), and
**
**   * there are no outstanding page references, and
**
**   * the database is either not an in-memory database or it is
**     an in-memory database that currently consists of zero pages.
**
** then the pager object page size is set to *pPageSize.
**
** If the page size is changed, then this function uses sqlite3PagerMalloc() 
** to obtain a new Pager.pTmpSpace buffer. If this allocation attempt 
** fails, SQLITE_NOMEM is returned and the page size remains unchanged. 
** In all other cases, SQLITE_OK is returned.
**
** If the page size is not changed, either because one of the enumerated
** conditions above is not true, the pager was in error state when this
** function was called, or because the memory allocation attempt failed, 
** then *pPageSize is set to the old, retained page size before returning.
*/
SQLITE_PRIVATE int sqlite3PagerSetPagesize(Pager *pPager, u32 *pPageSize, int nReserve){
  int rc = SQLITE_OK;

  /* It is not possible to do a full assert_pager_state() here, as this
  ** function may be called from within PagerOpen(), before the state
  ** of the Pager object is internally consistent.
  **
  ** At one point this function returned an error if the pager was in 
  ** PAGER_ERROR state. But since PAGER_ERROR state guarantees that
  ** there is at least one outstanding page reference, this function
  ** is a no-op for that case anyhow.
  */

  u32 pageSize = *pPageSize;
  assert( pageSize==0 || (pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE) );
  if( (pPager->memDb==0 || pPager->dbSize==0)
   && sqlite3PcacheRefCount(pPager->pPCache)==0 
   && pageSize && pageSize!=(u32)pPager->pageSize 
  ){
    char *pNew = NULL;             /* New temp space */
    i64 nByte = 0;

    if( pPager->eState>PAGER_OPEN && isOpen(pPager->fd) ){
      rc = sqlite3OsFileSize(pPager->fd, &nByte);
    }
    if( rc==SQLITE_OK ){
      pNew = (char *)sqlite3PageMalloc(pageSize);
      if( !pNew ) rc = SQLITE_NOMEM;
    }

    if( rc==SQLITE_OK ){
      pager_reset(pPager);
      rc = sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
    }
    if( rc==SQLITE_OK ){
      sqlite3PageFree(pPager->pTmpSpace);
      pPager->pTmpSpace = pNew;
      pPager->dbSize = (Pgno)((nByte+pageSize-1)/pageSize);
      pPager->pageSize = pageSize;
    }else{
      sqlite3PageFree(pNew);
    }
  }

  *pPageSize = pPager->pageSize;
  if( rc==SQLITE_OK ){
    if( nReserve<0 ) nReserve = pPager->nReserve;
    assert( nReserve>=0 && nReserve<1000 );
    pPager->nReserve = (i16)nReserve;
    pagerReportSize(pPager);
    pagerFixMaplimit(pPager);
  }
  return rc;
}

/*
** Return a pointer to the "temporary page" buffer held internally
** by the pager.  This is a buffer that is big enough to hold the
** entire content of a database page.  This buffer is used internally
** during rollback and will be overwritten whenever a rollback
** occurs.  But other modules are free to use it too, as long as
** no rollbacks are happening.
*/
SQLITE_PRIVATE void *sqlite3PagerTempSpace(Pager *pPager){
  return pPager->pTmpSpace;
}

/*
** Attempt to set the maximum database page count if mxPage is positive. 
** Make no changes if mxPage is zero or negative.  And never reduce the
** maximum page count below the current size of the database.
**
** Regardless of mxPage, return the current maximum page count.
*/
SQLITE_PRIVATE int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
  if( mxPage>0 ){
    pPager->mxPgno = mxPage;
  }
  assert( pPager->eState!=PAGER_OPEN );      /* Called only by OP_MaxPgcnt */
  assert( pPager->mxPgno>=pPager->dbSize );  /* OP_MaxPgcnt enforces this */
  return pPager->mxPgno;
}

/*
** The following set of routines are used to disable the simulated
** I/O error mechanism.  These routines are used to avoid simulated
** errors in places where we do not care about errors.
**
** Unless -DSQLITE_TEST=1 is used, these routines are all no-ops
** and generate no code.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE int sqlite3_io_error_pending;
SQLITE_PRIVATE int sqlite3_io_error_hit;
static int saved_cnt;
void disable_simulated_io_errors(void){
  saved_cnt = sqlite3_io_error_pending;
  sqlite3_io_error_pending = -1;
}
void enable_simulated_io_errors(void){
  sqlite3_io_error_pending = saved_cnt;
}
#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

/*
** Read the first N bytes from the beginning of the file into memory
** that pDest points to. 
**
** If the pager was opened on a transient file (zFilename==""), or
** opened on a file less than N bytes in size, the output buffer is
** zeroed and SQLITE_OK returned. The rationale for this is that this 
** function is used to read database headers, and a new transient or
** zero sized database has a header than consists entirely of zeroes.
**
** If any IO error apart from SQLITE_IOERR_SHORT_READ is encountered,
** the error code is returned to the caller and the contents of the
** output buffer undefined.
*/
SQLITE_PRIVATE int sqlite3PagerReadFileheader(Pager *pPager, int N, unsigned char *pDest){
  int rc = SQLITE_OK;
  memset(pDest, 0, N);
  assert( isOpen(pPager->fd) || pPager->tempFile );

  /* This routine is only called by btree immediately after creating
  ** the Pager object.  There has not been an opportunity to transition
  ** to WAL mode yet.
  */
  assert( !pagerUseWal(pPager) );

  if( isOpen(pPager->fd) ){
    IOTRACE(("DBHDR %p 0 %d\n", pPager, N))
    rc = sqlite3OsRead(pPager->fd, pDest, N, 0);
    if( rc==SQLITE_IOERR_SHORT_READ ){
      rc = SQLITE_OK;
    }
  }
  return rc;
}

/*
** This function may only be called when a read-transaction is open on
** the pager. It returns the total number of pages in the database.
**
** However, if the file is between 1 and <page-size> bytes in size, then 
** this is considered a 1 page file.
*/
SQLITE_PRIVATE void sqlite3PagerPagecount(Pager *pPager, int *pnPage){
  assert( pPager->eState>=PAGER_READER );
  assert( pPager->eState!=PAGER_WRITER_FINISHED );
  *pnPage = (int)pPager->dbSize;
}


/*
** Try to obtain a lock of type locktype on the database file. If
** a similar or greater lock is already held, this function is a no-op
** (returning SQLITE_OK immediately).
**
** Otherwise, attempt to obtain the lock using sqlite3OsLock(). Invoke 
** the busy callback if the lock is currently not available. Repeat 
** until the busy callback returns false or until the attempt to 
** obtain the lock succeeds.
**
** Return SQLITE_OK on success and an error code if we cannot obtain
** the lock. If the lock is obtained successfully, set the Pager.state 
** variable to locktype before returning.
*/
static int pager_wait_on_lock(Pager *pPager, int locktype){
  int rc;                              /* Return code */

  /* Check that this is either a no-op (because the requested lock is 
  ** already held), or one of the transitions that the busy-handler
  ** may be invoked during, according to the comment above
  ** sqlite3PagerSetBusyhandler().
  */
  assert( (pPager->eLock>=locktype)
       || (pPager->eLock==NO_LOCK && locktype==SHARED_LOCK)
       || (pPager->eLock==RESERVED_LOCK && locktype==EXCLUSIVE_LOCK)
  );

  do {
    rc = pagerLockDb(pPager, locktype);
  }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );
  return rc;
}

/*
** Function assertTruncateConstraint(pPager) checks that one of the 
** following is true for all dirty pages currently in the page-cache:
**
**   a) The page number is less than or equal to the size of the 
**      current database image, in pages, OR
**
**   b) if the page content were written at this time, it would not
**      be necessary to write the current content out to the sub-journal
**      (as determined by function subjRequiresPage()).
**
** If the condition asserted by this function were not true, and the
** dirty page were to be discarded from the cache via the pagerStress()
** routine, pagerStress() would not write the current page content to
** the database file. If a savepoint transaction were rolled back after
** this happened, the correct behavior would be to restore the current
** content of the page. However, since this content is not present in either
** the database file or the portion of the rollback journal and 
** sub-journal rolled back the content could not be restored and the
** database image would become corrupt. It is therefore fortunate that 
** this circumstance cannot arise.
*/
#if defined(SQLITE_DEBUG)
static void assertTruncateConstraintCb(PgHdr *pPg){
  assert( pPg->flags&PGHDR_DIRTY );
  assert( !subjRequiresPage(pPg) || pPg->pgno<=pPg->pPager->dbSize );
}
static void assertTruncateConstraint(Pager *pPager){
  sqlite3PcacheIterateDirty(pPager->pPCache, assertTruncateConstraintCb);
}
#else
# define assertTruncateConstraint(pPager)
#endif

/*
** Truncate the in-memory database file image to nPage pages. This 
** function does not actually modify the database file on disk. It 
** just sets the internal state of the pager object so that the 
** truncation will be done when the current transaction is committed.
**
** This function is only called right before committing a transaction.
** Once this function has been called, the transaction must either be
** rolled back or committed. It is not safe to call this function and
** then continue writing to the database.
*/
SQLITE_PRIVATE void sqlite3PagerTruncateImage(Pager *pPager, Pgno nPage){
  assert( pPager->dbSize>=nPage );
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  pPager->dbSize = nPage;

  /* At one point the code here called assertTruncateConstraint() to
  ** ensure that all pages being truncated away by this operation are,
  ** if one or more savepoints are open, present in the savepoint 
  ** journal so that they can be restored if the savepoint is rolled
  ** back. This is no longer necessary as this function is now only
  ** called right before committing a transaction. So although the 
  ** Pager object may still have open savepoints (Pager.nSavepoint!=0), 
  ** they cannot be rolled back. So the assertTruncateConstraint() call
  ** is no longer correct. */
}


/*
** This function is called before attempting a hot-journal rollback. It
** syncs the journal file to disk, then sets pPager->journalHdr to the
** size of the journal file so that the pager_playback() routine knows
** that the entire journal file has been synced.
**
** Syncing a hot-journal to disk before attempting to roll it back ensures 
** that if a power-failure occurs during the rollback, the process that
** attempts rollback following system recovery sees the same journal
** content as this process.
**
** If everything goes as planned, SQLITE_OK is returned. Otherwise, 
** an SQLite error code.
*/
static int pagerSyncHotJournal(Pager *pPager){
  int rc = SQLITE_OK;
  if( !pPager->noSync ){
    rc = sqlite3OsSync(pPager->jfd, SQLITE_SYNC_NORMAL);
  }
  if( rc==SQLITE_OK ){
    rc = sqlite3OsFileSize(pPager->jfd, &pPager->journalHdr);
  }
  return rc;
}

/*
** Obtain a reference to a memory mapped page object for page number pgno. 
** The new object will use the pointer pData, obtained from xFetch().
** If successful, set *ppPage to point to the new page reference
** and return SQLITE_OK. Otherwise, return an SQLite error code and set
** *ppPage to zero.
**
** Page references obtained by calling this function should be released
** by calling pagerReleaseMapPage().
*/
static int pagerAcquireMapPage(
  Pager *pPager,                  /* Pager object */
  Pgno pgno,                      /* Page number */
  void *pData,                    /* xFetch()'d data for this page */
  PgHdr **ppPage                  /* OUT: Acquired page object */
){
  PgHdr *p;                       /* Memory mapped page to return */
  
  if( pPager->pMmapFreelist ){
    *ppPage = p = pPager->pMmapFreelist;
    pPager->pMmapFreelist = p->pDirty;
    p->pDirty = 0;
    memset(p->pExtra, 0, pPager->nExtra);
  }else{
    *ppPage = p = (PgHdr *)sqlite3MallocZero(sizeof(PgHdr) + pPager->nExtra);
    if( p==0 ){
      sqlite3OsUnfetch(pPager->fd, (i64)(pgno-1) * pPager->pageSize, pData);
      return SQLITE_NOMEM;
    }
    p->pExtra = (void *)&p[1];
    p->flags = PGHDR_MMAP;
    p->nRef = 1;
    p->pPager = pPager;
  }

  assert( p->pExtra==(void *)&p[1] );
  assert( p->pPage==0 );
  assert( p->flags==PGHDR_MMAP );
  assert( p->pPager==pPager );
  assert( p->nRef==1 );

  p->pgno = pgno;
  p->pData = pData;
  pPager->nMmapOut++;

  return SQLITE_OK;
}

/*
** Release a reference to page pPg. pPg must have been returned by an 
** earlier call to pagerAcquireMapPage().
*/
static void pagerReleaseMapPage(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  pPager->nMmapOut--;
  pPg->pDirty = pPager->pMmapFreelist;
  pPager->pMmapFreelist = pPg;

  assert( pPager->fd->pMethods->iVersion>=3 );
  sqlite3OsUnfetch(pPager->fd, (i64)(pPg->pgno-1)*pPager->pageSize, pPg->pData);
}

/*
** Free all PgHdr objects stored in the Pager.pMmapFreelist list.
*/
static void pagerFreeMapHdrs(Pager *pPager){
  PgHdr *p;
  PgHdr *pNext;
  for(p=pPager->pMmapFreelist; p; p=pNext){
    pNext = p->pDirty;
    sqlite3_free(p);
  }
}


/*
** Shutdown the page cache.  Free all memory and close all files.
**
** If a transaction was in progress when this routine is called, that
** transaction is rolled back.  All outstanding pages are invalidated
** and their memory is freed.  Any attempt to use a page associated
** with this page cache after this function returns will likely
** result in a coredump.
**
** This function always succeeds. If a transaction is active an attempt
** is made to roll it back. If an error occurs during the rollback 
** a hot journal may be left in the filesystem but no error is returned
** to the caller.
*/
SQLITE_PRIVATE int sqlite3PagerClose(Pager *pPager){
  u8 *pTmp = (u8 *)pPager->pTmpSpace;

  assert( assert_pager_state(pPager) );
  disable_simulated_io_errors();
  pagerFreeMapHdrs(pPager);
  /* pPager->errCode = 0; */
  pPager->exclusiveMode = 0;
#ifndef SQLITE_OMIT_WAL
  sqlite3WalClose(pPager->pWal, pPager->ckptSyncFlags, pPager->pageSize, pTmp);
  pPager->pWal = 0;
#endif
  pager_reset(pPager);

  /* If it is open, sync the journal file before calling UnlockAndRollback.
   ** If this is not done, then an unsynced portion of the open journal 
   ** file may be played back into the database. If a power failure occurs 
   ** while this is happening, the database could become corrupt.
   **
   ** If an error occurs while trying to sync the journal, shift the pager
   ** into the ERROR state. This causes UnlockAndRollback to unlock the
   ** database and close the journal file without attempting to roll it
   ** back or finalize it. The next database user will have to do hot-journal
   ** rollback before accessing the database file.
   */
  if( isOpen(pPager->jfd) ){
    pager_error(pPager, pagerSyncHotJournal(pPager));
  }
  pagerUnlockAndRollback(pPager);

  enable_simulated_io_errors();
  PAGERTRACE(("CLOSE %d\n", PAGERID(pPager)));
  IOTRACE(("CLOSE %p\n", pPager))
  sqlite3OsClose(pPager->jfd);
  sqlite3OsClose(pPager->fd);
  sqlite3PageFree(pTmp);
  sqlite3PcacheClose(pPager->pPCache);

#ifdef SQLITE_HAS_CODEC
  if( pPager->xCodecFree ) pPager->xCodecFree(pPager->pCodec);
#endif

  assert( !pPager->aSavepoint && !pPager->pInJournal );
  assert( !isOpen(pPager->jfd) && !isOpen(pPager->sjfd) );

  sqlite3_free(pPager);
  return SQLITE_OK;
}

#if !defined(NDEBUG) || defined(SQLITE_TEST)
/*
** Return the page number for page pPg.
*/
SQLITE_PRIVATE Pgno sqlite3PagerPagenumber(DbPage *pPg){
  return pPg->pgno;
}
#endif

/*
** Increment the reference count for page pPg.
*/
SQLITE_PRIVATE void sqlite3PagerRef(DbPage *pPg){
  sqlite3PcacheRef(pPg);
}

/*
** Sync the journal. In other words, make sure all the pages that have
** been written to the journal have actually reached the surface of the
** disk and can be restored in the event of a hot-journal rollback.
**
** If the Pager.noSync flag is set, then this function is a no-op.
** Otherwise, the actions required depend on the journal-mode and the 
** device characteristics of the file-system, as follows:
**
**   * If the journal file is an in-memory journal file, no action need
**     be taken.
**
**   * Otherwise, if the device does not support the SAFE_APPEND property,
**     then the nRec field of the most recently written journal header
**     is updated to contain the number of journal records that have
**     been written following it. If the pager is operating in full-sync
**     mode, then the journal file is synced before this field is updated.
**
**   * If the device does not support the SEQUENTIAL property, then 
**     journal file is synced.
**
** Or, in pseudo-code:
**
**   if( NOT <in-memory journal> ){
**     if( NOT SAFE_APPEND ){
**       if( <full-sync mode> ) xSync(<journal file>);
**       <update nRec field>
**     } 
**     if( NOT SEQUENTIAL ) xSync(<journal file>);
**   }
**
** If successful, this routine clears the PGHDR_NEED_SYNC flag of every 
** page currently held in memory before returning SQLITE_OK. If an IO
** error is encountered, then the IO error code is returned to the caller.
*/
static int syncJournal(Pager *pPager, int newHdr){
  int rc;                         /* Return code */

  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );
  assert( !pagerUseWal(pPager) );

  rc = sqlite3PagerExclusiveLock(pPager);
  if( rc!=SQLITE_OK ) return rc;

  if( !pPager->noSync ){
    assert( !pPager->tempFile );
    if( isOpen(pPager->jfd) && pPager->journalMode!=PAGER_JOURNALMODE_MEMORY ){
      const int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
      assert( isOpen(pPager->jfd) );

      if( 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
        /* This block deals with an obscure problem. If the last connection
        ** that wrote to this database was operating in persistent-journal
        ** mode, then the journal file may at this point actually be larger
        ** than Pager.journalOff bytes. If the next thing in the journal
        ** file happens to be a journal-header (written as part of the
        ** previous connection's transaction), and a crash or power-failure 
        ** occurs after nRec is updated but before this connection writes 
        ** anything else to the journal file (or commits/rolls back its 
        ** transaction), then SQLite may become confused when doing the 
        ** hot-journal rollback following recovery. It may roll back all
        ** of this connections data, then proceed to rolling back the old,
        ** out-of-date data that follows it. Database corruption.
        **
        ** To work around this, if the journal file does appear to contain
        ** a valid header following Pager.journalOff, then write a 0x00
        ** byte to the start of it to prevent it from being recognized.
        **
        ** Variable iNextHdrOffset is set to the offset at which this
        ** problematic header will occur, if it exists. aMagic is used 
        ** as a temporary buffer to inspect the first couple of bytes of
        ** the potential journal header.
        */
        i64 iNextHdrOffset;
        u8 aMagic[8];
        u8 zHeader[sizeof(aJournalMagic)+4];

        memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
        put32bits(&zHeader[sizeof(aJournalMagic)], pPager->nRec);

        iNextHdrOffset = journalHdrOffset(pPager);
        rc = sqlite3OsRead(pPager->jfd, aMagic, 8, iNextHdrOffset);
        if( rc==SQLITE_OK && 0==memcmp(aMagic, aJournalMagic, 8) ){
          static const u8 zerobyte = 0;
          rc = sqlite3OsWrite(pPager->jfd, &zerobyte, 1, iNextHdrOffset);
        }
        if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
          return rc;
        }

        /* Write the nRec value into the journal file header. If in
        ** full-synchronous mode, sync the journal first. This ensures that
        ** all data has really hit the disk before nRec is updated to mark
        ** it as a candidate for rollback.
        **
        ** This is not required if the persistent media supports the
        ** SAFE_APPEND property. Because in this case it is not possible 
        ** for garbage data to be appended to the file, the nRec field
        ** is populated with 0xFFFFFFFF when the journal header is written
        ** and never needs to be updated.
        */
        if( pPager->fullSync && 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
          PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
          IOTRACE(("JSYNC %p\n", pPager))
          rc = sqlite3OsSync(pPager->jfd, pPager->syncFlags);
          if( rc!=SQLITE_OK ) return rc;
        }
        IOTRACE(("JHDR %p %lld\n", pPager, pPager->journalHdr));
        rc = sqlite3OsWrite(
            pPager->jfd, zHeader, sizeof(zHeader), pPager->journalHdr
        );
        if( rc!=SQLITE_OK ) return rc;
      }
      if( 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
        PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
        IOTRACE(("JSYNC %p\n", pPager))
        rc = sqlite3OsSync(pPager->jfd, pPager->syncFlags| 
          (pPager->syncFlags==SQLITE_SYNC_FULL?SQLITE_SYNC_DATAONLY:0)
        );
        if( rc!=SQLITE_OK ) return rc;
      }

      pPager->journalHdr = pPager->journalOff;
      if( newHdr && 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
        pPager->nRec = 0;
        rc = writeJournalHdr(pPager);
        if( rc!=SQLITE_OK ) return rc;
      }
    }else{
      pPager->journalHdr = pPager->journalOff;
    }
  }

  /* Unless the pager is in noSync mode, the journal file was just 
  ** successfully synced. Either way, clear the PGHDR_NEED_SYNC flag on 
  ** all pages.
  */
  sqlite3PcacheClearSyncFlags(pPager->pPCache);
  pPager->eState = PAGER_WRITER_DBMOD;
  assert( assert_pager_state(pPager) );
  return SQLITE_OK;
}

/*
** The argument is the first in a linked list of dirty pages connected
** by the PgHdr.pDirty pointer. This function writes each one of the
** in-memory pages in the list to the database file. The argument may
** be NULL, representing an empty list. In this case this function is
** a no-op.
**
** The pager must hold at least a RESERVED lock when this function
** is called. Before writing anything to the database file, this lock
** is upgraded to an EXCLUSIVE lock. If the lock cannot be obtained,
** SQLITE_BUSY is returned and no data is written to the database file.
** 
** If the pager is a temp-file pager and the actual file-system file
** is not yet open, it is created and opened before any data is 
** written out.
**
** Once the lock has been upgraded and, if necessary, the file opened,
** the pages are written out to the database file in list order. Writing
** a page is skipped if it meets either of the following criteria:
**
**   * The page number is greater than Pager.dbSize, or
**   * The PGHDR_DONT_WRITE flag is set on the page.
**
** If writing out a page causes the database file to grow, Pager.dbFileSize
** is updated accordingly. If page 1 is written out, then the value cached
** in Pager.dbFileVers[] is updated to match the new value stored in
** the database file.
**
** If everything is successful, SQLITE_OK is returned. If an IO error 
** occurs, an IO error code is returned. Or, if the EXCLUSIVE lock cannot
** be obtained, SQLITE_BUSY is returned.
*/
static int pager_write_pagelist(Pager *pPager, PgHdr *pList){
  int rc = SQLITE_OK;                  /* Return code */

  /* This function is only called for rollback pagers in WRITER_DBMOD state. */
  assert( !pagerUseWal(pPager) );
  assert( pPager->eState==PAGER_WRITER_DBMOD );
  assert( pPager->eLock==EXCLUSIVE_LOCK );

  /* If the file is a temp-file has not yet been opened, open it now. It
  ** is not possible for rc to be other than SQLITE_OK if this branch
  ** is taken, as pager_wait_on_lock() is a no-op for temp-files.
  */
  if( !isOpen(pPager->fd) ){
    assert( pPager->tempFile && rc==SQLITE_OK );
    rc = pagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
  }

  /* Before the first write, give the VFS a hint of what the final
  ** file size will be.
  */
  assert( rc!=SQLITE_OK || isOpen(pPager->fd) );
  if( rc==SQLITE_OK 
   && pPager->dbHintSize<pPager->dbSize
   && (pList->pDirty || pList->pgno>pPager->dbHintSize)
  ){
    sqlite3_int64 szFile = pPager->pageSize * (sqlite3_int64)pPager->dbSize;
    sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_SIZE_HINT, &szFile);
    pPager->dbHintSize = pPager->dbSize;
  }

  while( rc==SQLITE_OK && pList ){
    Pgno pgno = pList->pgno;

    /* If there are dirty pages in the page cache with page numbers greater
    ** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to
    ** make the file smaller (presumably by auto-vacuum code). Do not write
    ** any such pages to the file.
    **
    ** Also, do not write out any page that has the PGHDR_DONT_WRITE flag
    ** set (set by sqlite3PagerDontWrite()).
    */
    if( pgno<=pPager->dbSize && 0==(pList->flags&PGHDR_DONT_WRITE) ){
      i64 offset = (pgno-1)*(i64)pPager->pageSize;   /* Offset to write */
      char *pData;                                   /* Data to write */    

      assert( (pList->flags&PGHDR_NEED_SYNC)==0 );
      if( pList->pgno==1 ) pager_write_changecounter(pList);

      /* Encode the database */
      CODEC2(pPager, pList->pData, pgno, 6, return SQLITE_NOMEM, pData);

      /* Write out the page data. */
      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize, offset);

      /* If page 1 was just written, update Pager.dbFileVers to match
      ** the value now stored in the database file. If writing this 
      ** page caused the database file to grow, update dbFileSize. 
      */
      if( pgno==1 ){
        memcpy(&pPager->dbFileVers, &pData[24], sizeof(pPager->dbFileVers));
      }
      if( pgno>pPager->dbFileSize ){
        pPager->dbFileSize = pgno;
      }
      pPager->aStat[PAGER_STAT_WRITE]++;

      /* Update any backup objects copying the contents of this pager. */
      sqlite3BackupUpdate(pPager->pBackup, pgno, (u8*)pList->pData);

      PAGERTRACE(("STORE %d page %d hash(%08x)\n",
                   PAGERID(pPager), pgno, pager_pagehash(pList)));
      IOTRACE(("PGOUT %p %d\n", pPager, pgno));
      PAGER_INCR(sqlite3_pager_writedb_count);
    }else{
      PAGERTRACE(("NOSTORE %d page %d\n", PAGERID(pPager), pgno));
    }
    pager_set_pagehash(pList);
    pList = pList->pDirty;
  }

  return rc;
}

/*
** Ensure that the sub-journal file is open. If it is already open, this 
** function is a no-op.
**
** SQLITE_OK is returned if everything goes according to plan. An 
** SQLITE_IOERR_XXX error code is returned if a call to sqlite3OsOpen() 
** fails.
*/
static int openSubJournal(Pager *pPager){
  int rc = SQLITE_OK;
  if( !isOpen(pPager->sjfd) ){
    if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY || pPager->subjInMemory ){
      sqlite3MemJournalOpen(pPager->sjfd);
    }else{
      rc = pagerOpentemp(pPager, pPager->sjfd, SQLITE_OPEN_SUBJOURNAL);
    }
  }
  return rc;
}

/*
** Append a record of the current state of page pPg to the sub-journal. 
**
** If successful, set the bit corresponding to pPg->pgno in the bitvecs
** for all open savepoints before returning.
**
** This function returns SQLITE_OK if everything is successful, an IO
** error code if the attempt to write to the sub-journal fails, or 
** SQLITE_NOMEM if a malloc fails while setting a bit in a savepoint
** bitvec.
*/
static int subjournalPage(PgHdr *pPg){
  int rc = SQLITE_OK;
  Pager *pPager = pPg->pPager;
  if( pPager->journalMode!=PAGER_JOURNALMODE_OFF ){

    /* Open the sub-journal, if it has not already been opened */
    assert( pPager->useJournal );
    assert( isOpen(pPager->jfd) || pagerUseWal(pPager) );
    assert( isOpen(pPager->sjfd) || pPager->nSubRec==0 );
    assert( pagerUseWal(pPager) 
         || pageInJournal(pPager, pPg) 
         || pPg->pgno>pPager->dbOrigSize 
    );
    rc = openSubJournal(pPager);

    /* If the sub-journal was opened successfully (or was already open),
    ** write the journal record into the file.  */
    if( rc==SQLITE_OK ){
      void *pData = pPg->pData;
      i64 offset = (i64)pPager->nSubRec*(4+pPager->pageSize);
      char *pData2;
  
      CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
      PAGERTRACE(("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno));
      rc = write32bits(pPager->sjfd, offset, pPg->pgno);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsWrite(pPager->sjfd, pData2, pPager->pageSize, offset+4);
      }
    }
  }
  if( rc==SQLITE_OK ){
    pPager->nSubRec++;
    assert( pPager->nSavepoint>0 );
    rc = addToSavepointBitvecs(pPager, pPg->pgno);
  }
  return rc;
}
static int subjournalPageIfRequired(PgHdr *pPg){
  if( subjRequiresPage(pPg) ){
    return subjournalPage(pPg);
  }else{
    return SQLITE_OK;
  }
}

/*
** This function is called by the pcache layer when it has reached some
** soft memory limit. The first argument is a pointer to a Pager object
** (cast as a void*). The pager is always 'purgeable' (not an in-memory
** database). The second argument is a reference to a page that is 
** currently dirty but has no outstanding references. The page
** is always associated with the Pager object passed as the first 
** argument.
**
** The job of this function is to make pPg clean by writing its contents
** out to the database file, if possible. This may involve syncing the
** journal file. 
**
** If successful, sqlite3PcacheMakeClean() is called on the page and
** SQLITE_OK returned. If an IO error occurs while trying to make the
** page clean, the IO error code is returned. If the page cannot be
** made clean for some other reason, but no error occurs, then SQLITE_OK
** is returned by sqlite3PcacheMakeClean() is not called.
*/
static int pagerStress(void *p, PgHdr *pPg){
  Pager *pPager = (Pager *)p;
  int rc = SQLITE_OK;

  assert( pPg->pPager==pPager );
  assert( pPg->flags&PGHDR_DIRTY );

  /* The doNotSpill NOSYNC bit is set during times when doing a sync of
  ** journal (and adding a new header) is not allowed.  This occurs
  ** during calls to sqlite3PagerWrite() while trying to journal multiple
  ** pages belonging to the same sector.
  **
  ** The doNotSpill ROLLBACK and OFF bits inhibits all cache spilling
  ** regardless of whether or not a sync is required.  This is set during
  ** a rollback or by user request, respectively.
  **
  ** Spilling is also prohibited when in an error state since that could
  ** lead to database corruption.   In the current implementation it 
  ** is impossible for sqlite3PcacheFetch() to be called with createFlag==3
  ** while in the error state, hence it is impossible for this routine to
  ** be called in the error state.  Nevertheless, we include a NEVER()
  ** test for the error state as a safeguard against future changes.
  */
  if( NEVER(pPager->errCode) ) return SQLITE_OK;
  testcase( pPager->doNotSpill & SPILLFLAG_ROLLBACK );
  testcase( pPager->doNotSpill & SPILLFLAG_OFF );
  testcase( pPager->doNotSpill & SPILLFLAG_NOSYNC );
  if( pPager->doNotSpill
   && ((pPager->doNotSpill & (SPILLFLAG_ROLLBACK|SPILLFLAG_OFF))!=0
      || (pPg->flags & PGHDR_NEED_SYNC)!=0)
  ){
    return SQLITE_OK;
  }

  pPg->pDirty = 0;
  if( pagerUseWal(pPager) ){
    /* Write a single frame for this page to the log. */
    rc = subjournalPageIfRequired(pPg); 
    if( rc==SQLITE_OK ){
      rc = pagerWalFrames(pPager, pPg, 0, 0);
    }
  }else{
  
    /* Sync the journal file if required. */
    if( pPg->flags&PGHDR_NEED_SYNC 
     || pPager->eState==PAGER_WRITER_CACHEMOD
    ){
      rc = syncJournal(pPager, 1);
    }
  
    /* Write the contents of the page out to the database file. */
    if( rc==SQLITE_OK ){
      assert( (pPg->flags&PGHDR_NEED_SYNC)==0 );
      rc = pager_write_pagelist(pPager, pPg);
    }
  }

  /* Mark the page as clean. */
  if( rc==SQLITE_OK ){
    PAGERTRACE(("STRESS %d page %d\n", PAGERID(pPager), pPg->pgno));
    sqlite3PcacheMakeClean(pPg);
  }

  return pager_error(pPager, rc); 
}


/*
** Allocate and initialize a new Pager object and put a pointer to it
** in *ppPager. The pager should eventually be freed by passing it
** to sqlite3PagerClose().
**
** The zFilename argument is the path to the database file to open.
** If zFilename is NULL then a randomly-named temporary file is created
** and used as the file to be cached. Temporary files are be deleted
** automatically when they are closed. If zFilename is ":memory:" then 
** all information is held in cache. It is never written to disk. 
** This can be used to implement an in-memory database.
**
** The nExtra parameter specifies the number of bytes of space allocated
** along with each page reference. This space is available to the user
** via the sqlite3PagerGetExtra() API.
**
** The flags argument is used to specify properties that affect the
** operation of the pager. It should be passed some bitwise combination
** of the PAGER_* flags.
**
** The vfsFlags parameter is a bitmask to pass to the flags parameter
** of the xOpen() method of the supplied VFS when opening files. 
**
** If the pager object is allocated and the specified file opened 
** successfully, SQLITE_OK is returned and *ppPager set to point to
** the new pager object. If an error occurs, *ppPager is set to NULL
** and error code returned. This function may return SQLITE_NOMEM
** (sqlite3Malloc() is used to allocate memory), SQLITE_CANTOPEN or 
** various SQLITE_IO_XXX errors.
*/
SQLITE_PRIVATE int sqlite3PagerOpen(
  sqlite3_vfs *pVfs,       /* The virtual file system to use */
  Pager **ppPager,         /* OUT: Return the Pager structure here */
  const char *zFilename,   /* Name of the database file to open */
  int nExtra,              /* Extra bytes append to each in-memory page */
  int flags,               /* flags controlling this file */
  int vfsFlags,            /* flags passed through to sqlite3_vfs.xOpen() */
  void (*xReinit)(DbPage*) /* Function to reinitialize pages */
){
  u8 *pPtr;
  Pager *pPager = 0;       /* Pager object to allocate and return */
  int rc = SQLITE_OK;      /* Return code */
  int tempFile = 0;        /* True for temp files (incl. in-memory files) */
  int memDb = 0;           /* True if this is an in-memory file */
  int readOnly = 0;        /* True if this is a read-only file */
  int journalFileSize;     /* Bytes to allocate for each journal fd */
  char *zPathname = 0;     /* Full path to database file */
  int nPathname = 0;       /* Number of bytes in zPathname */
  int useJournal = (flags & PAGER_OMIT_JOURNAL)==0; /* False to omit journal */
  int pcacheSize = sqlite3PcacheSize();       /* Bytes to allocate for PCache */
  u32 szPageDflt = SQLITE_DEFAULT_PAGE_SIZE;  /* Default page size */
  const char *zUri = 0;    /* URI args to copy */
  int nUri = 0;            /* Number of bytes of URI args at *zUri */

  /* Figure out how much space is required for each journal file-handle
  ** (there are two of them, the main journal and the sub-journal). This
  ** is the maximum space required for an in-memory journal file handle 
  ** and a regular journal file-handle. Note that a "regular journal-handle"
  ** may be a wrapper capable of caching the first portion of the journal
  ** file in memory to implement the atomic-write optimization (see 
  ** source file journal.c).
  */
  if( sqlite3JournalSize(pVfs)>sqlite3MemJournalSize() ){
    journalFileSize = ROUND8(sqlite3JournalSize(pVfs));
  }else{
    journalFileSize = ROUND8(sqlite3MemJournalSize());
  }

  /* Set the output variable to NULL in case an error occurs. */
  *ppPager = 0;

  /* Compute and store the full pathname in an allocated buffer pointed
  ** to by zPathname, length nPathname. Or, if this is a temporary file,
  ** leave both nPathname and zPathname set to 0.
  */
  if( zFilename && zFilename[0] ){
    const char *z;
    nPathname = pVfs->mxPathname+1;
    zPathname = sqlite3DbMallocRaw(0, nPathname*2);
    if( zPathname==0 ){
      return SQLITE_NOMEM;
    }
    zPathname[0] = 0; /* Make sure initialized even if FullPathname() fails */
    rc = sqlite3OsFullPathname(pVfs, zFilename, nPathname, zPathname);
    nPathname = sqlite3Strlen30(zPathname);
    z = zUri = &zFilename[sqlite3Strlen30(zFilename)+1];
    while( *z ){
      z += sqlite3Strlen30(z)+1;
      z += sqlite3Strlen30(z)+1;
    }
    nUri = (int)(&z[1] - zUri);
    assert( nUri>=0 );
    if( rc==SQLITE_OK && nPathname+8>pVfs->mxPathname ){
      /* This branch is taken when the journal path required by
      ** the database being opened will be more than pVfs->mxPathname
      ** bytes in length. This means the database cannot be opened,
      ** as it will not be possible to open the journal file or even
      ** check for a hot-journal before reading.
      */
      rc = SQLITE_CANTOPEN_BKPT;
    }
    if( rc!=SQLITE_OK ){
      sqlite3DbFree(0, zPathname);
      return rc;
    }
  }

  /* Allocate memory for the Pager structure, PCache object, the
  ** three file descriptors, the database file name and the journal 
  ** file name. The layout in memory is as follows:
  **
  **     Pager object                    (sizeof(Pager) bytes)
  **     PCache object                   (sqlite3PcacheSize() bytes)
  **     Database file handle            (pVfs->szOsFile bytes)
  **     Sub-journal file handle         (journalFileSize bytes)
  **     Main journal file handle        (journalFileSize bytes)
  **     Database file name              (nPathname+1 bytes)
  **     Journal file name               (nPathname+8+1 bytes)
  */
  pPtr = (u8 *)sqlite3MallocZero(
    ROUND8(sizeof(*pPager)) +      /* Pager structure */
    ROUND8(pcacheSize) +           /* PCache object */
    ROUND8(pVfs->szOsFile) +       /* The main db file */
    journalFileSize * 2 +          /* The two journal files */ 
    nPathname + 1 + nUri +         /* zFilename */
    nPathname + 8 + 2              /* zJournal */
#ifndef SQLITE_OMIT_WAL
    + nPathname + 4 + 2            /* zWal */
#endif
  );
  assert( EIGHT_BYTE_ALIGNMENT(SQLITE_INT_TO_PTR(journalFileSize)) );
  if( !pPtr ){
    sqlite3DbFree(0, zPathname);
    return SQLITE_NOMEM;
  }
  pPager =              (Pager*)(pPtr);
  pPager->pPCache =    (PCache*)(pPtr += ROUND8(sizeof(*pPager)));
  pPager->fd =   (sqlite3_file*)(pPtr += ROUND8(pcacheSize));
  pPager->sjfd = (sqlite3_file*)(pPtr += ROUND8(pVfs->szOsFile));
  pPager->jfd =  (sqlite3_file*)(pPtr += journalFileSize);
  pPager->zFilename =    (char*)(pPtr += journalFileSize);
  assert( EIGHT_BYTE_ALIGNMENT(pPager->jfd) );

  /* Fill in the Pager.zFilename and Pager.zJournal buffers, if required. */
  if( zPathname ){
    assert( nPathname>0 );
    pPager->zJournal =   (char*)(pPtr += nPathname + 1 + nUri);
    memcpy(pPager->zFilename, zPathname, nPathname);
    if( nUri ) memcpy(&pPager->zFilename[nPathname+1], zUri, nUri);
    memcpy(pPager->zJournal, zPathname, nPathname);
    memcpy(&pPager->zJournal[nPathname], "-journal\000", 8+2);
#ifndef SQLITE_OMIT_WAL
    pPager->zWal = &pPager->zJournal[nPathname+8+1];
    memcpy(pPager->zWal, zPathname, nPathname);
    memcpy(&pPager->zWal[nPathname], "-wal\000", 4+1);
#endif
    sqlite3DbFree(0, zPathname);
  }
  pPager->pVfs = pVfs;
  pPager->vfsFlags = vfsFlags;

  /* Open the pager file.
  */
  if( zFilename && zFilename[0] ){
    int fout = 0;                    /* VFS flags returned by xOpen() */
    rc = sqlite3OsOpen(pVfs, pPager->zFilename, pPager->fd, vfsFlags, &fout);
    assert( !memDb );
    readOnly = (fout&SQLITE_OPEN_READONLY);

    /* If the file was successfully opened for read/write access,
    ** choose a default page size in case we have to create the
    ** database file. The default page size is the maximum of:
    **
    **    + SQLITE_DEFAULT_PAGE_SIZE,
    **    + The value returned by sqlite3OsSectorSize()
    **    + The largest page size that can be written atomically.
    */
    if( rc==SQLITE_OK ){
      int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
      if( !readOnly ){
        setSectorSize(pPager);
        assert(SQLITE_DEFAULT_PAGE_SIZE<=SQLITE_MAX_DEFAULT_PAGE_SIZE);
        if( szPageDflt<pPager->sectorSize ){
          if( pPager->sectorSize>SQLITE_MAX_DEFAULT_PAGE_SIZE ){
            szPageDflt = SQLITE_MAX_DEFAULT_PAGE_SIZE;
          }else{
            szPageDflt = (u32)pPager->sectorSize;
          }
        }
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
        {
          int ii;
          assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
          assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
          assert(SQLITE_MAX_DEFAULT_PAGE_SIZE<=65536);
          for(ii=szPageDflt; ii<=SQLITE_MAX_DEFAULT_PAGE_SIZE; ii=ii*2){
            if( iDc&(SQLITE_IOCAP_ATOMIC|(ii>>8)) ){
              szPageDflt = ii;
            }
          }
        }
#endif
      }
      pPager->noLock = 0;
      if( (iDc & SQLITE_IOCAP_IMMUTABLE)!=0 ){
          vfsFlags |= SQLITE_OPEN_READONLY;
          goto act_like_temp_file;
      }
    }
  }else{
    /* If a temporary file is requested, it is not opened immediately.
    ** In this case we accept the default page size and delay actually
    ** opening the file until the first call to OsWrite().
    **
    ** This branch is also run for an in-memory database. An in-memory
    ** database is the same as a temp-file that is never written out to
    ** disk and uses an in-memory rollback journal.
    **
    ** This branch also runs for files marked as immutable.
    */ 
act_like_temp_file:
    tempFile = 1;
    pPager->eState = PAGER_READER;     /* Pretend we already have a lock */
    pPager->eLock = EXCLUSIVE_LOCK;    /* Pretend we are in EXCLUSIVE mode */
    pPager->noLock = 1;                /* Do no locking */
    readOnly = (vfsFlags&SQLITE_OPEN_READONLY);
  }

  /* The following call to PagerSetPagesize() serves to set the value of 
  ** Pager.pageSize and to allocate the Pager.pTmpSpace buffer.
  */
  if( rc==SQLITE_OK ){
    assert( pPager->memDb==0 );
    rc = sqlite3PagerSetPagesize(pPager, &szPageDflt, -1);
    testcase( rc!=SQLITE_OK );
  }

  /* Initialize the PCache object. */
  if( rc==SQLITE_OK ){
    assert( nExtra<1000 );
    nExtra = ROUND8(nExtra);
    rc = sqlite3PcacheOpen(szPageDflt, nExtra, !memDb,
                       !memDb?pagerStress:0, (void *)pPager, pPager->pPCache);
  }

  /* If an error occurred above, free the  Pager structure and close the file.
  */
  if( rc!=SQLITE_OK ){
    sqlite3OsClose(pPager->fd);
    sqlite3PageFree(pPager->pTmpSpace);
    sqlite3_free(pPager);
    return rc;
  }

  PAGERTRACE(("OPEN %d %s\n", FILEHANDLEID(pPager->fd), pPager->zFilename));
  IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))

  pPager->useJournal = (u8)useJournal;
  /* pPager->stmtOpen = 0; */
  /* pPager->stmtInUse = 0; */
  /* pPager->nRef = 0; */
  /* pPager->stmtSize = 0; */
  /* pPager->stmtJSize = 0; */
  /* pPager->nPage = 0; */
  pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
  /* pPager->state = PAGER_UNLOCK; */
  /* pPager->errMask = 0; */
  pPager->tempFile = (u8)tempFile;
  assert( tempFile==PAGER_LOCKINGMODE_NORMAL 
          || tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
  pPager->exclusiveMode = (u8)tempFile; 
  pPager->changeCountDone = pPager->tempFile;
  pPager->memDb = (u8)memDb;
  pPager->readOnly = (u8)readOnly;
  assert( useJournal || pPager->tempFile );
  pPager->noSync = pPager->tempFile;
  if( pPager->noSync ){
    assert( pPager->fullSync==0 );
    assert( pPager->syncFlags==0 );
    assert( pPager->walSyncFlags==0 );
    assert( pPager->ckptSyncFlags==0 );
  }else{
    pPager->fullSync = 1;
    pPager->syncFlags = SQLITE_SYNC_NORMAL;
    pPager->walSyncFlags = SQLITE_SYNC_NORMAL | WAL_SYNC_TRANSACTIONS;
    pPager->ckptSyncFlags = SQLITE_SYNC_NORMAL;
  }
  /* pPager->pFirst = 0; */
  /* pPager->pFirstSynced = 0; */
  /* pPager->pLast = 0; */
  pPager->nExtra = (u16)nExtra;
  pPager->journalSizeLimit = SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT;
  assert( isOpen(pPager->fd) || tempFile );
  setSectorSize(pPager);
  if( !useJournal ){
    pPager->journalMode = PAGER_JOURNALMODE_OFF;
  }else if( memDb ){
    pPager->journalMode = PAGER_JOURNALMODE_MEMORY;
  }
  /* pPager->xBusyHandler = 0; */
  /* pPager->pBusyHandlerArg = 0; */
  pPager->xReiniter = xReinit;
  /* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
  /* pPager->szMmap = SQLITE_DEFAULT_MMAP_SIZE // will be set by btree.c */

  *ppPager = pPager;
  return SQLITE_OK;
}


/* Verify that the database file has not be deleted or renamed out from
** under the pager.  Return SQLITE_OK if the database is still were it ought
** to be on disk.  Return non-zero (SQLITE_READONLY_DBMOVED or some other error
** code from sqlite3OsAccess()) if the database has gone missing.
*/
static int databaseIsUnmoved(Pager *pPager){
  int bHasMoved = 0;
  int rc;

  if( pPager->tempFile ) return SQLITE_OK;
  if( pPager->dbSize==0 ) return SQLITE_OK;
  assert( pPager->zFilename && pPager->zFilename[0] );
  rc = sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_HAS_MOVED, &bHasMoved);
  if( rc==SQLITE_NOTFOUND ){
    /* If the HAS_MOVED file-control is unimplemented, assume that the file
    ** has not been moved.  That is the historical behavior of SQLite: prior to
    ** version 3.8.3, it never checked */
    rc = SQLITE_OK;
  }else if( rc==SQLITE_OK && bHasMoved ){
    rc = SQLITE_READONLY_DBMOVED;
  }
  return rc;
}


/*
** This function is called after transitioning from PAGER_UNLOCK to
** PAGER_SHARED state. It tests if there is a hot journal present in
** the file-system for the given pager. A hot journal is one that 
** needs to be played back. According to this function, a hot-journal
** file exists if the following criteria are met:
**
**   * The journal file exists in the file system, and
**   * No process holds a RESERVED or greater lock on the database file, and
**   * The database file itself is greater than 0 bytes in size, and
**   * The first byte of the journal file exists and is not 0x00.
**
** If the current size of the database file is 0 but a journal file
** exists, that is probably an old journal left over from a prior
** database with the same name. In this case the journal file is
** just deleted using OsDelete, *pExists is set to 0 and SQLITE_OK
** is returned.
**
** This routine does not check if there is a master journal filename
** at the end of the file. If there is, and that master journal file
** does not exist, then the journal file is not really hot. In this
** case this routine will return a false-positive. The pager_playback()
** routine will discover that the journal file is not really hot and 
** will not roll it back. 
**
** If a hot-journal file is found to exist, *pExists is set to 1 and 
** SQLITE_OK returned. If no hot-journal file is present, *pExists is
** set to 0 and SQLITE_OK returned. If an IO error occurs while trying
** to determine whether or not a hot-journal file exists, the IO error
** code is returned and the value of *pExists is undefined.
*/
static int hasHotJournal(Pager *pPager, int *pExists){
  sqlite3_vfs * const pVfs = pPager->pVfs;
  int rc = SQLITE_OK;           /* Return code */
  int exists = 1;               /* True if a journal file is present */
  int jrnlOpen = !!isOpen(pPager->jfd);

  assert( pPager->useJournal );
  assert( isOpen(pPager->fd) );
  assert( pPager->eState==PAGER_OPEN );

  assert( jrnlOpen==0 || ( sqlite3OsDeviceCharacteristics(pPager->jfd) &
    SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN
  ));

  *pExists = 0;
  if( !jrnlOpen ){
    rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
  }
  if( rc==SQLITE_OK && exists ){
    int locked = 0;             /* True if some process holds a RESERVED lock */

    /* Race condition here:  Another process might have been holding the
    ** the RESERVED lock and have a journal open at the sqlite3OsAccess() 
    ** call above, but then delete the journal and drop the lock before
    ** we get to the following sqlite3OsCheckReservedLock() call.  If that
    ** is the case, this routine might think there is a hot journal when
    ** in fact there is none.  This results in a false-positive which will
    ** be dealt with by the playback routine.  Ticket #3883.
    */
    rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    if( rc==SQLITE_OK && !locked ){
      Pgno nPage;                 /* Number of pages in database file */

      rc = pagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        /* If the database is zero pages in size, that means that either (1) the
        ** journal is a remnant from a prior database with the same name where
        ** the database file but not the journal was deleted, or (2) the initial
        ** transaction that populates a new database is being rolled back.
        ** In either case, the journal file can be deleted.  However, take care
        ** not to delete the journal file if it is already open due to
        ** journal_mode=PERSIST.
        */
        if( nPage==0 && !jrnlOpen ){
          if( pagerLockDb(pPager, RESERVED_LOCK)==SQLITE_OK ){
            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
            if( !pPager->exclusiveMode ) pagerUnlockDb(pPager, SHARED_LOCK);
          }
        }else{
          /* The journal file exists and no other connection has a reserved
          ** or greater lock on the database file. Now check that there is
          ** at least one non-zero bytes at the start of the journal file.
          ** If there is, then we consider this journal to be hot. If not, 
          ** it can be ignored.
          */
          if( !jrnlOpen ){
            int f = SQLITE_OPEN_READONLY|SQLITE_OPEN_MAIN_JOURNAL;
            rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &f);
          }
          if( rc==SQLITE_OK ){
            u8 first = 0;
            rc = sqlite3OsRead(pPager->jfd, (void *)&first, 1, 0);
            if( rc==SQLITE_IOERR_SHORT_READ ){
              rc = SQLITE_OK;
            }
            if( !jrnlOpen ){
              sqlite3OsClose(pPager->jfd);
            }
            *pExists = (first!=0);
          }else if( rc==SQLITE_CANTOPEN ){
            /* If we cannot open the rollback journal file in order to see if
            ** it has a zero header, that might be due to an I/O error, or
            ** it might be due to the race condition described above and in
            ** ticket #3883.  Either way, assume that the journal is hot.
            ** This might be a false positive.  But if it is, then the
            ** automatic journal playback and recovery mechanism will deal
            ** with it under an EXCLUSIVE lock where we do not need to
            ** worry so much with race conditions.
            */
            *pExists = 1;
            rc = SQLITE_OK;
          }
        }
      }
    }
  }

  return rc;
}

/*
** This function is called to obtain a shared lock on the database file.
** It is illegal to call sqlite3PagerAcquire() until after this function
** has been successfully called. If a shared-lock is already held when
** this function is called, it is a no-op.
**
** The following operations are also performed by this function.
**
**   1) If the pager is currently in PAGER_OPEN state (no lock held
**      on the database file), then an attempt is made to obtain a
**      SHARED lock on the database file. Immediately after obtaining
**      the SHARED lock, the file-system is checked for a hot-journal,
**      which is played back if present. Following any hot-journal 
**      rollback, the contents of the cache are validated by checking
**      the 'change-counter' field of the database file header and
**      discarded if they are found to be invalid.
**
**   2) If the pager is running in exclusive-mode, and there are currently
**      no outstanding references to any pages, and is in the error state,
**      then an attempt is made to clear the error state by discarding
**      the contents of the page cache and rolling back any open journal
**      file.
**
** If everything is successful, SQLITE_OK is returned. If an IO error 
** occurs while locking the database, checking for a hot-journal file or 
** rolling back a journal file, the IO error code is returned.
*/
SQLITE_PRIVATE int sqlite3PagerSharedLock(Pager *pPager){
  int rc = SQLITE_OK;                /* Return code */

  /* This routine is only called from b-tree and only when there are no
  ** outstanding pages. This implies that the pager state should either
  ** be OPEN or READER. READER is only possible if the pager is or was in 
  ** exclusive access mode.
  */
  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
  assert( assert_pager_state(pPager) );
  assert( pPager->eState==PAGER_OPEN || pPager->eState==PAGER_READER );

  if( !pagerUseWal(pPager) && pPager->eState==PAGER_OPEN ){
    int bHotJournal = 1;          /* True if there exists a hot journal-file */

    rc = pager_wait_on_lock(pPager, SHARED_LOCK);
    if( rc!=SQLITE_OK ){
      assert( pPager->eLock==NO_LOCK || pPager->eLock==UNKNOWN_LOCK );
      goto failed;
    }

    /* If a journal file exists, and there is no RESERVED lock on the
    ** database file, then it either needs to be played back or deleted.
    */
    if( pPager->eLock<=SHARED_LOCK ){
      rc = hasHotJournal(pPager, &bHotJournal);
    }
    if( rc!=SQLITE_OK ){
      goto failed;
    }
    if( bHotJournal ){
      if( pPager->readOnly ){
        rc = SQLITE_READONLY_ROLLBACK;
        goto failed;
      }

      /* Get an EXCLUSIVE lock on the database file. At this point it is
      ** important that a RESERVED lock is not obtained on the way to the
      ** EXCLUSIVE lock. If it were, another process might open the
      ** database file, detect the RESERVED lock, and conclude that the
      ** database is safe to read while this process is still rolling the 
      ** hot-journal back.
      ** 
      ** Because the intermediate RESERVED lock is not requested, any
      ** other process attempting to access the database file will get to 
      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
      ** on the database file.
      **
      ** Unless the pager is in locking_mode=exclusive mode, the lock is
      ** downgraded to SHARED_LOCK before this function returns.
      */
      rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
      if( rc!=SQLITE_OK ){
        goto failed;
      }
 
      /* If it is not already open and the file exists on disk, open the 
      ** journal for read/write access. Write access is required because 
      ** in exclusive-access mode the file descriptor will be kept open 
      ** and possibly used for a transaction later on. Also, write-access 
      ** is usually required to finalize the journal in journal_mode=persist 
      ** mode (and also for journal_mode=truncate on some systems).
      **
      ** If the journal does not exist, it usually means that some 
      ** other connection managed to get in and roll it back before 
      ** this connection obtained the exclusive lock above. Or, it 
      ** may mean that the pager was in the error-state when this
      ** function was called and the journal file does not exist.
      */
      if( !isOpen(pPager->jfd) ){
        sqlite3_vfs * const pVfs = pPager->pVfs;
        int bExists;              /* True if journal file exists */
        rc = sqlite3OsAccess(
            pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &bExists);
        if( rc==SQLITE_OK && bExists ){
          int fout = 0;
          int f = SQLITE_OPEN_READWRITE|SQLITE_OPEN_MAIN_JOURNAL;
          assert( !pPager->tempFile );
          rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &fout);
          assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
          if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
            rc = SQLITE_CANTOPEN_BKPT;
            sqlite3OsClose(pPager->jfd);
          }
        }
      }
 
      /* Playback and delete the journal.  Drop the database write
      ** lock and reacquire the read lock. Purge the cache before
      ** playing back the hot-journal so that we don't end up with
      ** an inconsistent cache.  Sync the hot journal before playing
      ** it back since the process that crashed and left the hot journal
      ** probably did not sync it and we are required to always sync
      ** the journal before playing it back.
      */
      if( isOpen(pPager->jfd) ){
        assert( rc==SQLITE_OK );
        rc = pagerSyncHotJournal(pPager);
        if( rc==SQLITE_OK ){
          rc = pager_playback(pPager, 1);
          pPager->eState = PAGER_OPEN;
        }
      }else if( !pPager->exclusiveMode ){
        pagerUnlockDb(pPager, SHARED_LOCK);
      }

      if( rc!=SQLITE_OK ){
        /* This branch is taken if an error occurs while trying to open
        ** or roll back a hot-journal while holding an EXCLUSIVE lock. The
        ** pager_unlock() routine will be called before returning to unlock
        ** the file. If the unlock attempt fails, then Pager.eLock must be
        ** set to UNKNOWN_LOCK (see the comment above the #define for 
        ** UNKNOWN_LOCK above for an explanation). 
        **
        ** In order to get pager_unlock() to do this, set Pager.eState to
        ** PAGER_ERROR now. This is not actually counted as a transition
        ** to ERROR state in the state diagram at the top of this file,
        ** since we know that the same call to pager_unlock() will very
        ** shortly transition the pager object to the OPEN state. Calling
        ** assert_pager_state() would fail now, as it should not be possible
        ** to be in ERROR state when there are zero outstanding page 
        ** references.
        */
        pager_error(pPager, rc);
        goto failed;
      }

      assert( pPager->eState==PAGER_OPEN );
      assert( (pPager->eLock==SHARED_LOCK)
           || (pPager->exclusiveMode && pPager->eLock>SHARED_LOCK)
      );
    }

    if( !pPager->tempFile && pPager->hasHeldSharedLock ){
      /* The shared-lock has just been acquired then check to
      ** see if the database has been modified.  If the database has changed,
      ** flush the cache.  The hasHeldSharedLock flag prevents this from
      ** occurring on the very first access to a file, in order to save a
      ** single unnecessary sqlite3OsRead() call at the start-up.
      **
      ** Database changes are detected by looking at 15 bytes beginning
      ** at offset 24 into the file.  The first 4 of these 16 bytes are
      ** a 32-bit counter that is incremented with each change.  The
      ** other bytes change randomly with each file change when
      ** a codec is in use.
      ** 
      ** There is a vanishingly small chance that a change will not be 
      ** detected.  The chance of an undetected change is so small that
      ** it can be neglected.
      */
      Pgno nPage = 0;
      char dbFileVers[sizeof(pPager->dbFileVers)];

      rc = pagerPagecount(pPager, &nPage);
      if( rc ) goto failed;

      if( nPage>0 ){
        IOTRACE(("CKVERS %p %d\n", pPager, sizeof(dbFileVers)));
        rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers), 24);
        if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
          goto failed;
        }
      }else{
        memset(dbFileVers, 0, sizeof(dbFileVers));
      }

      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
        pager_reset(pPager);

        /* Unmap the database file. It is possible that external processes
        ** may have truncated the database file and then extended it back
        ** to its original size while this process was not holding a lock.
        ** In this case there may exist a Pager.pMap mapping that appears
        ** to be the right size but is not actually valid. Avoid this
        ** possibility by unmapping the db here. */
        if( USEFETCH(pPager) ){
          sqlite3OsUnfetch(pPager->fd, 0, 0);
        }
      }
    }

    /* If there is a WAL file in the file-system, open this database in WAL
    ** mode. Otherwise, the following function call is a no-op.
    */
    rc = pagerOpenWalIfPresent(pPager);
#ifndef SQLITE_OMIT_WAL
    assert( pPager->pWal==0 || rc==SQLITE_OK );
#endif
  }

  if( pagerUseWal(pPager) ){
    assert( rc==SQLITE_OK );
    rc = pagerBeginReadTransaction(pPager);
  }

  if( pPager->eState==PAGER_OPEN && rc==SQLITE_OK ){
    rc = pagerPagecount(pPager, &pPager->dbSize);
  }

 failed:
  if( rc!=SQLITE_OK ){
    pager_unlock(pPager);
    assert( pPager->eState==PAGER_OPEN );
  }else{
    pPager->eState = PAGER_READER;
    pPager->hasHeldSharedLock = 1;
  }
  return rc;
}

/*
** If the reference count has reached zero, rollback any active
** transaction and unlock the pager.
**
** Except, in locking_mode=EXCLUSIVE when there is nothing to in
** the rollback journal, the unlock is not performed and there is
** nothing to rollback, so this routine is a no-op.
*/ 
static void pagerUnlockIfUnused(Pager *pPager){
  if( pPager->nMmapOut==0 && (sqlite3PcacheRefCount(pPager->pPCache)==0) ){
    pagerUnlockAndRollback(pPager);
  }
}

/*
** Acquire a reference to page number pgno in pager pPager (a page
** reference has type DbPage*). If the requested reference is 
** successfully obtained, it is copied to *ppPage and SQLITE_OK returned.
**
** If the requested page is already in the cache, it is returned. 
** Otherwise, a new page object is allocated and populated with data
** read from the database file. In some cases, the pcache module may
** choose not to allocate a new page object and may reuse an existing
** object with no outstanding references.
**
** The extra data appended to a page is always initialized to zeros the 
** first time a page is loaded into memory. If the page requested is 
** already in the cache when this function is called, then the extra
** data is left as it was when the page object was last used.
**
** If the database image is smaller than the requested page or if a 
** non-zero value is passed as the noContent parameter and the 
** requested page is not already stored in the cache, then no 
** actual disk read occurs. In this case the memory image of the 
** page is initialized to all zeros. 
**
** If noContent is true, it means that we do not care about the contents
** of the page. This occurs in two scenarios:
**
**   a) When reading a free-list leaf page from the database, and
**
**   b) When a savepoint is being rolled back and we need to load
**      a new page into the cache to be filled with the data read
**      from the savepoint journal.
**
** If noContent is true, then the data returned is zeroed instead of
** being read from the database. Additionally, the bits corresponding
** to pgno in Pager.pInJournal (bitvec of pages already written to the
** journal file) and the PagerSavepoint.pInSavepoint bitvecs of any open
** savepoints are set. This means if the page is made writable at any
** point in the future, using a call to sqlite3PagerWrite(), its contents
** will not be journaled. This saves IO.
**
** The acquisition might fail for several reasons.  In all cases,
** an appropriate error code is returned and *ppPage is set to NULL.
**
** See also sqlite3PagerLookup().  Both this routine and Lookup() attempt
** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas Lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since Lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
SQLITE_PRIVATE int sqlite3PagerAcquire(
  Pager *pPager,      /* The pager open on the database file */
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int flags           /* PAGER_GET_XXX flags */
){
  int rc = SQLITE_OK;
  PgHdr *pPg = 0;
  u32 iFrame = 0;                 /* Frame to read from WAL file */
  const int noContent = (flags & PAGER_GET_NOCONTENT);

  /* It is acceptable to use a read-only (mmap) page for any page except
  ** page 1 if there is no write-transaction open or the ACQUIRE_READONLY
  ** flag was specified by the caller. And so long as the db is not a 
  ** temporary or in-memory database.  */
  const int bMmapOk = (pgno>1 && USEFETCH(pPager)
   && (pPager->eState==PAGER_READER || (flags & PAGER_GET_READONLY))
#ifdef SQLITE_HAS_CODEC
   && pPager->xCodec==0
#endif
  );

  /* Optimization note:  Adding the "pgno<=1" term before "pgno==0" here
  ** allows the compiler optimizer to reuse the results of the "pgno>1"
  ** test in the previous statement, and avoid testing pgno==0 in the
  ** common case where pgno is large. */
  if( pgno<=1 && pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );
  assert( noContent==0 || bMmapOk==0 );

  assert( pPager->hasHeldSharedLock==1 );

  /* If the pager is in the error state, return an error immediately. 
  ** Otherwise, request the page from the PCache layer. */
  if( pPager->errCode!=SQLITE_OK ){
    rc = pPager->errCode;
  }else{
    if( bMmapOk && pagerUseWal(pPager) ){
      rc = sqlite3WalFindFrame(pPager->pWal, pgno, &iFrame);
      if( rc!=SQLITE_OK ) goto pager_acquire_err;
    }

    if( bMmapOk && iFrame==0 ){
      void *pData = 0;

      rc = sqlite3OsFetch(pPager->fd, 
          (i64)(pgno-1) * pPager->pageSize, pPager->pageSize, &pData
      );

      if( rc==SQLITE_OK && pData ){
        if( pPager->eState>PAGER_READER ){
          pPg = sqlite3PagerLookup(pPager, pgno);
        }
        if( pPg==0 ){
          rc = pagerAcquireMapPage(pPager, pgno, pData, &pPg);
        }else{
          sqlite3OsUnfetch(pPager->fd, (i64)(pgno-1)*pPager->pageSize, pData);
        }
        if( pPg ){
          assert( rc==SQLITE_OK );
          *ppPage = pPg;
          return SQLITE_OK;
        }
      }
      if( rc!=SQLITE_OK ){
        goto pager_acquire_err;
      }
    }

    {
      sqlite3_pcache_page *pBase;
      pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
      if( pBase==0 ){
        rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);
        if( rc!=SQLITE_OK ) goto pager_acquire_err;
        if( pBase==0 ){
          pPg = *ppPage = 0;
          rc = SQLITE_NOMEM;
          goto pager_acquire_err;
        }
      }
      pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);
      assert( pPg!=0 );
    }
  }

  if( rc!=SQLITE_OK ){
    /* Either the call to sqlite3PcacheFetch() returned an error or the
    ** pager was already in the error-state when this function was called.
    ** Set pPg to 0 and jump to the exception handler.  */
    pPg = 0;
    goto pager_acquire_err;
  }
  assert( pPg==(*ppPage) );
  assert( pPg->pgno==pgno );
  assert( pPg->pPager==pPager || pPg->pPager==0 );

  if( pPg->pPager && !noContent ){
    /* In this case the pcache already contains an initialized copy of
    ** the page. Return without further ado.  */
    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
    pPager->aStat[PAGER_STAT_HIT]++;
    return SQLITE_OK;

  }else{
    /* The pager cache has created a new page. Its content needs to 
    ** be initialized.  */

    pPg->pPager = pPager;

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }

    if( pPager->dbSize<pgno || noContent || !isOpen(pPager->fd) ){
      if( pgno>pPager->mxPgno ){
        rc = SQLITE_FULL;
        goto pager_acquire_err;
      }
      if( noContent ){
        /* Failure to set the bits in the InJournal bit-vectors is benign.
        ** It merely means that we might do some extra work to journal a 
        ** page that does not need to be journaled.  Nevertheless, be sure 
        ** to test the case where a malloc error occurs while trying to set 
        ** a bit in a bit vector.
        */
        if( pgno<=pPager->dbOrigSize ){
          TESTONLY( rc = ) sqlite3BitvecSet(pPager->pInJournal, pgno);
          testcase( rc==SQLITE_NOMEM );
        }
        TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno);
        testcase( rc==SQLITE_NOMEM );
      }
      memset(pPg->pData, 0, pPager->pageSize);
      IOTRACE(("ZERO %p %d\n", pPager, pgno));
    }else{
      if( pagerUseWal(pPager) && bMmapOk==0 ){
        rc = sqlite3WalFindFrame(pPager->pWal, pgno, &iFrame);
        if( rc!=SQLITE_OK ) goto pager_acquire_err;
      }
      assert( pPg->pPager==pPager );
      pPager->aStat[PAGER_STAT_MISS]++;
      rc = readDbPage(pPg, iFrame);
      if( rc!=SQLITE_OK ){
        goto pager_acquire_err;
      }
    }
    pager_set_pagehash(pPg);
  }

  return SQLITE_OK;

pager_acquire_err:
  assert( rc!=SQLITE_OK );
  if( pPg ){
    sqlite3PcacheDrop(pPg);
  }
  pagerUnlockIfUnused(pPager);

  *ppPage = 0;
  return rc;
}

/*
** Acquire a page if it is already in the in-memory cache.  Do
** not read the page from disk.  Return a pointer to the page,
** or 0 if the page is not in cache. 
**
** See also sqlite3PagerGet().  The difference between this routine
** and sqlite3PagerGet() is that _get() will go to the disk and read
** in the page if the page is not already in cache.  This routine
** returns NULL if the page is not in cache or if a disk I/O error 
** has ever happened.
*/
SQLITE_PRIVATE DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
  sqlite3_pcache_page *pPage;
  assert( pPager!=0 );
  assert( pgno!=0 );
  assert( pPager->pPCache!=0 );
  pPage = sqlite3PcacheFetch(pPager->pPCache, pgno, 0);
  assert( pPage==0 || pPager->hasHeldSharedLock );
  if( pPage==0 ) return 0;
  return sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pPage);
}

/*
** Release a page reference.
**
** If the number of references to the page drop to zero, then the
** page is added to the LRU list.  When all references to all pages
** are released, a rollback occurs and the lock on the database is
** removed.
*/
SQLITE_PRIVATE void sqlite3PagerUnrefNotNull(DbPage *pPg){
  Pager *pPager;
  assert( pPg!=0 );
  pPager = pPg->pPager;
  if( pPg->flags & PGHDR_MMAP ){
    pagerReleaseMapPage(pPg);
  }else{
    sqlite3PcacheRelease(pPg);
  }
  pagerUnlockIfUnused(pPager);
}
SQLITE_PRIVATE void sqlite3PagerUnref(DbPage *pPg){
  if( pPg ) sqlite3PagerUnrefNotNull(pPg);
}

/*
** This function is called at the start of every write transaction.
** There must already be a RESERVED or EXCLUSIVE lock on the database 
** file when this routine is called.
**
** Open the journal file for pager pPager and write a journal header
** to the start of it. If there are active savepoints, open the sub-journal
** as well. This function is only used when the journal file is being 
** opened to write a rollback log for a transaction. It is not used 
** when opening a hot journal file to roll it back.
**
** If the journal file is already open (as it may be in exclusive mode),
** then this function just writes a journal header to the start of the
** already open file. 
**
** Whether or not the journal file is opened by this function, the
** Pager.pInJournal bitvec structure is allocated.
**
** Return SQLITE_OK if everything is successful. Otherwise, return 
** SQLITE_NOMEM if the attempt to allocate Pager.pInJournal fails, or 
** an IO error code if opening or writing the journal file fails.
*/
static int pager_open_journal(Pager *pPager){
  int rc = SQLITE_OK;                        /* Return code */
  sqlite3_vfs * const pVfs = pPager->pVfs;   /* Local cache of vfs pointer */

  assert( pPager->eState==PAGER_WRITER_LOCKED );
  assert( assert_pager_state(pPager) );
  assert( pPager->pInJournal==0 );
  
  /* If already in the error state, this function is a no-op.  But on
  ** the other hand, this routine is never called if we are already in
  ** an error state. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  if( !pagerUseWal(pPager) && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
    pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
    if( pPager->pInJournal==0 ){
      return SQLITE_NOMEM;
    }
  
    /* Open the journal file if it is not already open. */
    if( !isOpen(pPager->jfd) ){
      if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY ){
        sqlite3MemJournalOpen(pPager->jfd);
      }else{
        const int flags =                   /* VFS flags to open journal file */
          SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|
          (pPager->tempFile ? 
            (SQLITE_OPEN_DELETEONCLOSE|SQLITE_OPEN_TEMP_JOURNAL):
            (SQLITE_OPEN_MAIN_JOURNAL)
          );

        /* Verify that the database still has the same name as it did when
        ** it was originally opened. */
        rc = databaseIsUnmoved(pPager);
        if( rc==SQLITE_OK ){
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
          rc = sqlite3JournalOpen(
              pVfs, pPager->zJournal, pPager->jfd, flags, jrnlBufferSize(pPager)
          );
#else
          rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, flags, 0);
#endif
        }
      }
      assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
    }
  
  
    /* Write the first journal header to the journal file and open 
    ** the sub-journal if necessary.
    */
    if( rc==SQLITE_OK ){
      /* TODO: Check if all of these are really required. */
      pPager->nRec = 0;
      pPager->journalOff = 0;
      pPager->setMaster = 0;
      pPager->journalHdr = 0;
      rc = writeJournalHdr(pPager);
    }
  }

  if( rc!=SQLITE_OK ){
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
  }else{
    assert( pPager->eState==PAGER_WRITER_LOCKED );
    pPager->eState = PAGER_WRITER_CACHEMOD;
  }

  return rc;
}

/*
** Begin a write-transaction on the specified pager object. If a 
** write-transaction has already been opened, this function is a no-op.
**
** If the exFlag argument is false, then acquire at least a RESERVED
** lock on the database file. If exFlag is true, then acquire at least
** an EXCLUSIVE lock. If such a lock is already held, no locking 
** functions need be called.
**
** If the subjInMemory argument is non-zero, then any sub-journal opened
** within this transaction will be opened as an in-memory file. This
** has no effect if the sub-journal is already opened (as it may be when
** running in exclusive mode) or if the transaction does not require a
** sub-journal. If the subjInMemory argument is zero, then any required
** sub-journal is implemented in-memory if pPager is an in-memory database, 
** or using a temporary file otherwise.
*/
SQLITE_PRIVATE int sqlite3PagerBegin(Pager *pPager, int exFlag, int subjInMemory){
  int rc = SQLITE_OK;

  if( pPager->errCode ) return pPager->errCode;
  assert( pPager->eState>=PAGER_READER && pPager->eState<PAGER_ERROR );
  pPager->subjInMemory = (u8)subjInMemory;

  if( ALWAYS(pPager->eState==PAGER_READER) ){
    assert( pPager->pInJournal==0 );

    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
      ** PAGER_RESERVED state. Otherwise, return an error code to the caller.
      ** The busy-handler is not invoked if another connection already
      ** holds the write-lock. If possible, the upper layer will call it.
      */
      rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
      */
      rc = pagerLockDb(pPager, RESERVED_LOCK);
      if( rc==SQLITE_OK && exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }

    if( rc==SQLITE_OK ){
      /* Change to WRITER_LOCKED state.
      **
      ** WAL mode sets Pager.eState to PAGER_WRITER_LOCKED or CACHEMOD
      ** when it has an open transaction, but never to DBMOD or FINISHED.
      ** This is because in those states the code to roll back savepoint 
      ** transactions may copy data from the sub-journal into the database 
      ** file as well as into the page cache. Which would be incorrect in 
      ** WAL mode.
      */
      pPager->eState = PAGER_WRITER_LOCKED;
      pPager->dbHintSize = pPager->dbSize;
      pPager->dbFileSize = pPager->dbSize;
      pPager->dbOrigSize = pPager->dbSize;
      pPager->journalOff = 0;
    }

    assert( rc==SQLITE_OK || pPager->eState==PAGER_READER );
    assert( rc!=SQLITE_OK || pPager->eState==PAGER_WRITER_LOCKED );
    assert( assert_pager_state(pPager) );
  }

  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));
  return rc;
}

/*
** Write page pPg onto the end of the rollback journal.
*/
static SQLITE_NOINLINE int pagerAddPageToRollbackJournal(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  int rc;
  u32 cksum;
  char *pData2;
  i64 iOff = pPager->journalOff;

  /* We should never write to the journal file the page that
  ** contains the database locks.  The following assert verifies
  ** that we do not. */
  assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );

  assert( pPager->journalHdr<=pPager->journalOff );
  CODEC2(pPager, pPg->pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
  cksum = pager_cksum(pPager, (u8*)pData2);

  /* Even if an IO or diskfull error occurs while journalling the
  ** page in the block above, set the need-sync flag for the page.
  ** Otherwise, when the transaction is rolled back, the logic in
  ** playback_one_page() will think that the page needs to be restored
  ** in the database file. And if an IO error occurs while doing so,
  ** then corruption may follow.
  */
  pPg->flags |= PGHDR_NEED_SYNC;

  rc = write32bits(pPager->jfd, iOff, pPg->pgno);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlite3OsWrite(pPager->jfd, pData2, pPager->pageSize, iOff+4);
  if( rc!=SQLITE_OK ) return rc;
  rc = write32bits(pPager->jfd, iOff+pPager->pageSize+4, cksum);
  if( rc!=SQLITE_OK ) return rc;

  IOTRACE(("JOUT %p %d %lld %d\n", pPager, pPg->pgno, 
           pPager->journalOff, pPager->pageSize));
  PAGER_INCR(sqlite3_pager_writej_count);
  PAGERTRACE(("JOURNAL %d page %d needSync=%d hash(%08x)\n",
       PAGERID(pPager), pPg->pgno, 
       ((pPg->flags&PGHDR_NEED_SYNC)?1:0), pager_pagehash(pPg)));

  pPager->journalOff += 8 + pPager->pageSize;
  pPager->nRec++;
  assert( pPager->pInJournal!=0 );
  rc = sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
  testcase( rc==SQLITE_NOMEM );
  assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
  rc |= addToSavepointBitvecs(pPager, pPg->pgno);
  assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
  return rc;
}

/*
** Mark a single data page as writeable. The page is written into the 
** main journal or sub-journal as required. If the page is written into
** one of the journals, the corresponding bit is set in the 
** Pager.pInJournal bitvec and the PagerSavepoint.pInSavepoint bitvecs
** of any open savepoints as appropriate.
*/
static int pager_write(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;

  /* This routine is not called unless a write-transaction has already 
  ** been started. The journal file may or may not be open at this point.
  ** It is never called in the ERROR state.
  */
  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );
  assert( pPager->errCode==0 );
  assert( pPager->readOnly==0 );
  CHECK_PAGE(pPg);

  /* The journal file needs to be opened. Higher level routines have already
  ** obtained the necessary locks to begin the write-transaction, but the
  ** rollback journal might not yet be open. Open it now if this is the case.
  **
  ** This is done before calling sqlite3PcacheMakeDirty() on the page. 
  ** Otherwise, if it were done after calling sqlite3PcacheMakeDirty(), then
  ** an error might occur and the pager would end up in WRITER_LOCKED state
  ** with pages marked as dirty in the cache.
  */
  if( pPager->eState==PAGER_WRITER_LOCKED ){
    rc = pager_open_journal(pPager);
    if( rc!=SQLITE_OK ) return rc;
  }
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );
  assert( assert_pager_state(pPager) );

  /* Mark the page that is about to be modified as dirty. */
  sqlite3PcacheMakeDirty(pPg);

  /* If a rollback journal is in use, them make sure the page that is about
  ** to change is in the rollback journal, or if the page is a new page off
  ** then end of the file, make sure it is marked as PGHDR_NEED_SYNC.
  */
  assert( (pPager->pInJournal!=0) == isOpen(pPager->jfd) );
  if( pPager->pInJournal!=0
   && sqlite3BitvecTestNotNull(pPager->pInJournal, pPg->pgno)==0
  ){
    assert( pagerUseWal(pPager)==0 );
    if( pPg->pgno<=pPager->dbOrigSize ){
      rc = pagerAddPageToRollbackJournal(pPg);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }else{
      if( pPager->eState!=PAGER_WRITER_DBMOD ){
        pPg->flags |= PGHDR_NEED_SYNC;
      }
      PAGERTRACE(("APPEND %d page %d needSync=%d\n",
              PAGERID(pPager), pPg->pgno,
             ((pPg->flags&PGHDR_NEED_SYNC)?1:0)));
    }
  }

  /* The PGHDR_DIRTY bit is set above when the page was added to the dirty-list
  ** and before writing the page into the rollback journal.  Wait until now,
  ** after the page has been successfully journalled, before setting the
  ** PGHDR_WRITEABLE bit that indicates that the page can be safely modified.
  */
  pPg->flags |= PGHDR_WRITEABLE;
  
  /* If the statement journal is open and the page is not in it,
  ** then write the page into the statement journal.
  */
  if( pPager->nSavepoint>0 ){
    rc = subjournalPageIfRequired(pPg);
  }

  /* Update the database size and return. */
  if( pPager->dbSize<pPg->pgno ){
    pPager->dbSize = pPg->pgno;
  }
  return rc;
}

/*
** This is a variant of sqlite3PagerWrite() that runs when the sector size
** is larger than the page size.  SQLite makes the (reasonable) assumption that
** all bytes of a sector are written together by hardware.  Hence, all bytes of
** a sector need to be journalled in case of a power loss in the middle of
** a write.
**
** Usually, the sector size is less than or equal to the page size, in which
** case pages can be individually written.  This routine only runs in the
** exceptional case where the page size is smaller than the sector size.
*/
static SQLITE_NOINLINE int pagerWriteLargeSector(PgHdr *pPg){
  int rc = SQLITE_OK;          /* Return code */
  Pgno nPageCount;             /* Total number of pages in database file */
  Pgno pg1;                    /* First page of the sector pPg is located on. */
  int nPage = 0;               /* Number of pages starting at pg1 to journal */
  int ii;                      /* Loop counter */
  int needSync = 0;            /* True if any page has PGHDR_NEED_SYNC */
  Pager *pPager = pPg->pPager; /* The pager that owns pPg */
  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);

  /* Set the doNotSpill NOSYNC bit to 1. This is because we cannot allow
  ** a journal header to be written between the pages journaled by
  ** this function.
  */
  assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)==0 );
  pPager->doNotSpill |= SPILLFLAG_NOSYNC;

  /* This trick assumes that both the page-size and sector-size are
  ** an integer power of 2. It sets variable pg1 to the identifier
  ** of the first page of the sector pPg is located on.
  */
  pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

  nPageCount = pPager->dbSize;
  if( pPg->pgno>nPageCount ){
    nPage = (pPg->pgno - pg1)+1;
  }else if( (pg1+nPagePerSector-1)>nPageCount ){
    nPage = nPageCount+1-pg1;
  }else{
    nPage = nPagePerSector;
  }
  assert(nPage>0);
  assert(pg1<=pPg->pgno);
  assert((pg1+nPage)>pPg->pgno);

  for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
    Pgno pg = pg1+ii;
    PgHdr *pPage;
    if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
      if( pg!=PAGER_MJ_PGNO(pPager) ){
        rc = sqlite3PagerGet(pPager, pg, &pPage);
        if( rc==SQLITE_OK ){
          rc = pager_write(pPage);
          if( pPage->flags&PGHDR_NEED_SYNC ){
            needSync = 1;
          }
          sqlite3PagerUnrefNotNull(pPage);
        }
      }
    }else if( (pPage = sqlite3PagerLookup(pPager, pg))!=0 ){
      if( pPage->flags&PGHDR_NEED_SYNC ){
        needSync = 1;
      }
      sqlite3PagerUnrefNotNull(pPage);
    }
  }

  /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
  ** starting at pg1, then it needs to be set for all of them. Because
  ** writing to any of these nPage pages may damage the others, the
  ** journal file must contain sync()ed copies of all of them
  ** before any of them can be written out to the database file.
  */
  if( rc==SQLITE_OK && needSync ){
    for(ii=0; ii<nPage; ii++){
      PgHdr *pPage = sqlite3PagerLookup(pPager, pg1+ii);
      if( pPage ){
        pPage->flags |= PGHDR_NEED_SYNC;
        sqlite3PagerUnrefNotNull(pPage);
      }
    }
  }

  assert( (pPager->doNotSpill & SPILLFLAG_NOSYNC)!=0 );
  pPager->doNotSpill &= ~SPILLFLAG_NOSYNC;
  return rc;
}

/*
** Mark a data page as writeable. This routine must be called before 
** making changes to a page. The caller must check the return value 
** of this function and be careful not to change any page data unless 
** this routine returns SQLITE_OK.
**
** The difference between this function and pager_write() is that this
** function also deals with the special case where 2 or more pages
** fit on a single disk sector. In this case all co-resident pages
** must have been written to the journal file before returning.
**
** If an error occurs, SQLITE_NOMEM or an IO error code is returned
** as appropriate. Otherwise, SQLITE_OK.
*/
SQLITE_PRIVATE int sqlite3PagerWrite(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  assert( (pPg->flags & PGHDR_MMAP)==0 );
  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( pPager->eState!=PAGER_ERROR );
  assert( assert_pager_state(pPager) );
  if( (pPg->flags & PGHDR_WRITEABLE)!=0 && pPager->dbSize>=pPg->pgno ){
    if( pPager->nSavepoint ) return subjournalPageIfRequired(pPg);
    return SQLITE_OK;
  }else if( pPager->sectorSize > (u32)pPager->pageSize ){
    return pagerWriteLargeSector(pPg);
  }else{
    return pager_write(pPg);
  }
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
#ifndef NDEBUG
SQLITE_PRIVATE int sqlite3PagerIswriteable(DbPage *pPg){
  return pPg->flags & PGHDR_WRITEABLE;
}
#endif

/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page pPg back to the disk, even though
** that page might be marked as dirty.  This happens, for example, when
** the page has been added as a leaf of the freelist and so its
** content no longer matters.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused. The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization can quadruple the speed of large 
** DELETE operations.
*/
SQLITE_PRIVATE void sqlite3PagerDontWrite(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  if( (pPg->flags&PGHDR_DIRTY) && pPager->nSavepoint==0 ){
    PAGERTRACE(("DONT_WRITE page %d of %d\n", pPg->pgno, PAGERID(pPager)));
    IOTRACE(("CLEAN %p %d\n", pPager, pPg->pgno))
    pPg->flags |= PGHDR_DONT_WRITE;
    pPg->flags &= ~PGHDR_WRITEABLE;
    pager_set_pagehash(pPg);
  }
}

/*
** This routine is called to increment the value of the database file 
** change-counter, stored as a 4-byte big-endian integer starting at 
** byte offset 24 of the pager file.  The secondary change counter at
** 92 is also updated, as is the SQLite version number at offset 96.
**
** But this only happens if the pPager->changeCountDone flag is false.
** To avoid excess churning of page 1, the update only happens once.
** See also the pager_write_changecounter() routine that does an 
** unconditional update of the change counters.
**
** If the isDirectMode flag is zero, then this is done by calling 
** sqlite3PagerWrite() on page 1, then modifying the contents of the
** page data. In this case the file will be updated when the current
** transaction is committed.
**
** The isDirectMode flag may only be non-zero if the library was compiled
** with the SQLITE_ENABLE_ATOMIC_WRITE macro defined. In this case,
** if isDirect is non-zero, then the database file is updated directly
** by writing an updated version of page 1 using a call to the 
** sqlite3OsWrite() function.
*/
static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
  int rc = SQLITE_OK;

  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );

  /* Declare and initialize constant integer 'isDirect'. If the
  ** atomic-write optimization is enabled in this build, then isDirect
  ** is initialized to the value passed as the isDirectMode parameter
  ** to this function. Otherwise, it is always set to zero.
  **
  ** The idea is that if the atomic-write optimization is not
  ** enabled at compile time, the compiler can omit the tests of
  ** 'isDirect' below, as well as the block enclosed in the
  ** "if( isDirect )" condition.
  */
#ifndef SQLITE_ENABLE_ATOMIC_WRITE
# define DIRECT_MODE 0
  assert( isDirectMode==0 );
  UNUSED_PARAMETER(isDirectMode);
#else
# define DIRECT_MODE isDirectMode
#endif

  if( !pPager->changeCountDone && ALWAYS(pPager->dbSize>0) ){
    PgHdr *pPgHdr;                /* Reference to page 1 */

    assert( !pPager->tempFile && isOpen(pPager->fd) );

    /* Open page 1 of the file for writing. */
    rc = sqlite3PagerGet(pPager, 1, &pPgHdr);
    assert( pPgHdr==0 || rc==SQLITE_OK );

    /* If page one was fetched successfully, and this function is not
    ** operating in direct-mode, make page 1 writable.  When not in 
    ** direct mode, page 1 is always held in cache and hence the PagerGet()
    ** above is always successful - hence the ALWAYS on rc==SQLITE_OK.
    */
    if( !DIRECT_MODE && ALWAYS(rc==SQLITE_OK) ){
      rc = sqlite3PagerWrite(pPgHdr);
    }

    if( rc==SQLITE_OK ){
      /* Actually do the update of the change counter */
      pager_write_changecounter(pPgHdr);

      /* If running in direct mode, write the contents of page 1 to the file. */
      if( DIRECT_MODE ){
        const void *zBuf;
        assert( pPager->dbFileSize>0 );
        CODEC2(pPager, pPgHdr->pData, 1, 6, rc=SQLITE_NOMEM, zBuf);
        if( rc==SQLITE_OK ){
          rc = sqlite3OsWrite(pPager->fd, zBuf, pPager->pageSize, 0);
          pPager->aStat[PAGER_STAT_WRITE]++;
        }
        if( rc==SQLITE_OK ){
          /* Update the pager's copy of the change-counter. Otherwise, the
          ** next time a read transaction is opened the cache will be
          ** flushed (as the change-counter values will not match).  */
          const void *pCopy = (const void *)&((const char *)zBuf)[24];
          memcpy(&pPager->dbFileVers, pCopy, sizeof(pPager->dbFileVers));
          pPager->changeCountDone = 1;
        }
      }else{
        pPager->changeCountDone = 1;
      }
    }

    /* Release the page reference. */
    sqlite3PagerUnref(pPgHdr);
  }
  return rc;
}

/*
** Sync the database file to disk. This is a no-op for in-memory databases
** or pages with the Pager.noSync flag set.
**
** If successful, or if called on a pager for which it is a no-op, this
** function returns SQLITE_OK. Otherwise, an IO error code is returned.
*/
SQLITE_PRIVATE int sqlite3PagerSync(Pager *pPager, const char *zMaster){
  int rc = SQLITE_OK;

  if( isOpen(pPager->fd) ){
    void *pArg = (void*)zMaster;
    rc = sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_SYNC, pArg);
    if( rc==SQLITE_NOTFOUND ) rc = SQLITE_OK;
  }
  if( rc==SQLITE_OK && !pPager->noSync ){
    rc = sqlite3OsSync(pPager->fd, pPager->syncFlags);
  }
  return rc;
}

/*
** This function may only be called while a write-transaction is active in
** rollback. If the connection is in WAL mode, this call is a no-op. 
** Otherwise, if the connection does not already have an EXCLUSIVE lock on 
** the database file, an attempt is made to obtain one.
**
** If the EXCLUSIVE lock is already held or the attempt to obtain it is
** successful, or the connection is in WAL mode, SQLITE_OK is returned.
** Otherwise, either SQLITE_BUSY or an SQLITE_IOERR_XXX error code is 
** returned.
*/
SQLITE_PRIVATE int sqlite3PagerExclusiveLock(Pager *pPager){
  int rc = SQLITE_OK;
  assert( pPager->eState==PAGER_WRITER_CACHEMOD 
       || pPager->eState==PAGER_WRITER_DBMOD 
       || pPager->eState==PAGER_WRITER_LOCKED 
  );
  assert( assert_pager_state(pPager) );
  if( 0==pagerUseWal(pPager) ){
    rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
  }
  return rc;
}

/*
** Sync the database file for the pager pPager. zMaster points to the name
** of a master journal file that should be written into the individual
** journal file. zMaster may be NULL, which is interpreted as no master
** journal (a single database transaction).
**
** This routine ensures that:
**
**   * The database file change-counter is updated,
**   * the journal is synced (unless the atomic-write optimization is used),
**   * all dirty pages are written to the database file, 
**   * the database file is truncated (if required), and
**   * the database file synced. 
**
** The only thing that remains to commit the transaction is to finalize 
** (delete, truncate or zero the first part of) the journal file (or 
** delete the master journal file if specified).
**
** Note that if zMaster==NULL, this does not overwrite a previous value
** passed to an sqlite3PagerCommitPhaseOne() call.
**
** If the final parameter - noSync - is true, then the database file itself
** is not synced. The caller must call sqlite3PagerSync() directly to
** sync the database file before calling CommitPhaseTwo() to delete the
** journal file in this case.
*/
SQLITE_PRIVATE int sqlite3PagerCommitPhaseOne(
  Pager *pPager,                  /* Pager object */
  const char *zMaster,            /* If not NULL, the master journal name */
  int noSync                      /* True to omit the xSync on the db file */
){
  int rc = SQLITE_OK;             /* Return code */

  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
       || pPager->eState==PAGER_ERROR
  );
  assert( assert_pager_state(pPager) );

  /* If a prior error occurred, report that error again. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  PAGERTRACE(("DATABASE SYNC: File=%s zMaster=%s nSize=%d\n", 
      pPager->zFilename, zMaster, pPager->dbSize));

  /* If no database changes have been made, return early. */
  if( pPager->eState<PAGER_WRITER_CACHEMOD ) return SQLITE_OK;

  {
    if( pagerUseWal(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      PgHdr *pPageOne = 0;
      if( pList==0 ){
        /* Must have at least one page for the WAL commit flag.
        ** Ticket [2d1a5c67dfc2363e44f29d9bbd57f] 2011-05-18 */
        rc = sqlite3PagerGet(pPager, 1, &pPageOne);
        pList = pPageOne;
        pList->pDirty = 0;
      }
      assert( rc==SQLITE_OK );
      if( ALWAYS(pList) ){
        rc = pagerWalFrames(pPager, pList, pPager->dbSize, 1);
      }
      sqlite3PagerUnref(pPageOne);
      if( rc==SQLITE_OK ){
        sqlite3PcacheCleanAll(pPager->pPCache);
      }
    }else{
      /* The following block updates the change-counter. Exactly how it
      ** does this depends on whether or not the atomic-update optimization
      ** was enabled at compile time, and if this transaction meets the 
      ** runtime criteria to use the operation: 
      **
      **    * The file-system supports the atomic-write property for
      **      blocks of size page-size, and 
      **    * This commit is not part of a multi-file transaction, and
      **    * Exactly one page has been modified and store in the journal file.
      **
      ** If the optimization was not enabled at compile time, then the
      ** pager_incr_changecounter() function is called to update the change
      ** counter in 'indirect-mode'. If the optimization is compiled in but
      ** is not applicable to this transaction, call sqlite3JournalCreate()
      ** to make sure the journal file has actually been created, then call
      ** pager_incr_changecounter() to update the change-counter in indirect
      ** mode. 
      **
      ** Otherwise, if the optimization is both enabled and applicable,
      ** then call pager_incr_changecounter() to update the change-counter
      ** in 'direct' mode. In this case the journal file will never be
      ** created for this transaction.
      */
  #ifdef SQLITE_ENABLE_ATOMIC_WRITE
      PgHdr *pPg;
      assert( isOpen(pPager->jfd) 
           || pPager->journalMode==PAGER_JOURNALMODE_OFF 
           || pPager->journalMode==PAGER_JOURNALMODE_WAL 
      );
      if( !zMaster && isOpen(pPager->jfd) 
       && pPager->journalOff==jrnlBufferSize(pPager) 
       && pPager->dbSize>=pPager->dbOrigSize
       && (0==(pPg = sqlite3PcacheDirtyList(pPager->pPCache)) || 0==pPg->pDirty)
      ){
        /* Update the db file change counter via the direct-write method. The 
        ** following call will modify the in-memory representation of page 1 
        ** to include the updated change counter and then write page 1 
        ** directly to the database file. Because of the atomic-write 
        ** property of the host file-system, this is safe.
        */
        rc = pager_incr_changecounter(pPager, 1);
      }else{
        rc = sqlite3JournalCreate(pPager->jfd);
        if( rc==SQLITE_OK ){
          rc = pager_incr_changecounter(pPager, 0);
        }
      }
  #else
      rc = pager_incr_changecounter(pPager, 0);
  #endif
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  
      /* Write the master journal name into the journal file. If a master 
      ** journal file name has already been written to the journal file, 
      ** or if zMaster is NULL (no master journal), then this call is a no-op.
      */
      rc = writeMasterJournal(pPager, zMaster);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  
      /* Sync the journal file and write all dirty pages to the database.
      ** If the atomic-update optimization is being used, this sync will not 
      ** create the journal file or perform any real IO.
      **
      ** Because the change-counter page was just modified, unless the
      ** atomic-update optimization is used it is almost certain that the
      ** journal requires a sync here. However, in locking_mode=exclusive
      ** on a system under memory pressure it is just possible that this is 
      ** not the case. In this case it is likely enough that the redundant
      ** xSync() call will be changed to a no-op by the OS anyhow. 
      */
      rc = syncJournal(pPager, 0);
      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
  
      rc = pager_write_pagelist(pPager,sqlite3PcacheDirtyList(pPager->pPCache));
      if( rc!=SQLITE_OK ){
        assert( rc!=SQLITE_IOERR_BLOCKED );
        goto commit_phase_one_exit;
      }
      sqlite3PcacheCleanAll(pPager->pPCache);

      /* If the file on disk is smaller than the database image, use 
      ** pager_truncate to grow the file here. This can happen if the database
      ** image was extended as part of the current transaction and then the
      ** last page in the db image moved to the free-list. In this case the
      ** last page is never written out to disk, leaving the database file
      ** undersized. Fix this now if it is the case.  */
      if( pPager->dbSize>pPager->dbFileSize ){
        Pgno nNew = pPager->dbSize - (pPager->dbSize==PAGER_MJ_PGNO(pPager));
        assert( pPager->eState==PAGER_WRITER_DBMOD );
        rc = pager_truncate(pPager, nNew);
        if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
      }
  
      /* Finally, sync the database file. */
      if( !noSync ){
        rc = sqlite3PagerSync(pPager, zMaster);
      }
      IOTRACE(("DBSYNC %p\n", pPager))
    }
  }

commit_phase_one_exit:
  if( rc==SQLITE_OK && !pagerUseWal(pPager) ){
    pPager->eState = PAGER_WRITER_FINISHED;
  }
  return rc;
}


/*
** When this function is called, the database file has been completely
** updated to reflect the changes made by the current transaction and
** synced to disk. The journal file still exists in the file-system 
** though, and if a failure occurs at this point it will eventually
** be used as a hot-journal and the current transaction rolled back.
**
** This function finalizes the journal file, either by deleting, 
** truncating or partially zeroing it, so that it cannot be used 
** for hot-journal rollback. Once this is done the transaction is
** irrevocably committed.
**
** If an error occurs, an IO error code is returned and the pager
** moves into the error state. Otherwise, SQLITE_OK is returned.
*/
SQLITE_PRIVATE int sqlite3PagerCommitPhaseTwo(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */

  /* This routine should not be called if a prior error has occurred.
  ** But if (due to a coding error elsewhere in the system) it does get
  ** called, just return the same error code without doing anything. */
  if( NEVER(pPager->errCode) ) return pPager->errCode;

  assert( pPager->eState==PAGER_WRITER_LOCKED
       || pPager->eState==PAGER_WRITER_FINISHED
       || (pagerUseWal(pPager) && pPager->eState==PAGER_WRITER_CACHEMOD)
  );
  assert( assert_pager_state(pPager) );

  /* An optimization. If the database was not actually modified during
  ** this transaction, the pager is running in exclusive-mode and is
  ** using persistent journals, then this function is a no-op.
  **
  ** The start of the journal file currently contains a single journal 
  ** header with the nRec field set to 0. If such a journal is used as
  ** a hot-journal during hot-journal rollback, 0 changes will be made
  ** to the database file. So there is no need to zero the journal 
  ** header. Since the pager is in exclusive mode, there is no need
  ** to drop any locks either.
  */
  if( pPager->eState==PAGER_WRITER_LOCKED 
   && pPager->exclusiveMode 
   && pPager->journalMode==PAGER_JOURNALMODE_PERSIST
  ){
    assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) || !pPager->journalOff );
    pPager->eState = PAGER_READER;
    return SQLITE_OK;
  }

  PAGERTRACE(("COMMIT %d\n", PAGERID(pPager)));
  pPager->iDataVersion++;
  rc = pager_end_transaction(pPager, pPager->setMaster, 1);
  return pager_error(pPager, rc);
}

/*
** If a write transaction is open, then all changes made within the 
** transaction are reverted and the current write-transaction is closed.
** The pager falls back to PAGER_READER state if successful, or PAGER_ERROR
** state if an error occurs.
**
** If the pager is already in PAGER_ERROR state when this function is called,
** it returns Pager.errCode immediately. No work is performed in this case.
**
** Otherwise, in rollback mode, this function performs two functions:
**
**   1) It rolls back the journal file, restoring all database file and 
**      in-memory cache pages to the state they were in when the transaction
**      was opened, and
**
**   2) It finalizes the journal file, so that it is not used for hot
**      rollback at any point in the future.
**
** Finalization of the journal file (task 2) is only performed if the 
** rollback is successful.
**
** In WAL mode, all cache-entries containing data modified within the
** current transaction are either expelled from the cache or reverted to
** their pre-transaction state by re-reading data from the database or
** WAL files. The WAL transaction is then closed.
*/
SQLITE_PRIVATE int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */
  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));

  /* PagerRollback() is a no-op if called in READER or OPEN state. If
  ** the pager is already in the ERROR state, the rollback is not 
  ** attempted here. Instead, the error code is returned to the caller.
  */
  assert( assert_pager_state(pPager) );
  if( pPager->eState==PAGER_ERROR ) return pPager->errCode;
  if( pPager->eState<=PAGER_READER ) return SQLITE_OK;

  if( pagerUseWal(pPager) ){
    int rc2;
    rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
    rc2 = pager_end_transaction(pPager, pPager->setMaster, 0);
    if( rc==SQLITE_OK ) rc = rc2;
  }else if( !isOpen(pPager->jfd) || pPager->eState==PAGER_WRITER_LOCKED ){
    int eState = pPager->eState;
    rc = pager_end_transaction(pPager, 0, 0);
    if( eState>PAGER_WRITER_LOCKED ){
      /* This can happen using journal_mode=off. Move the pager to the error 
      ** state to indicate that the contents of the cache may not be trusted.
      ** Any active readers will get SQLITE_ABORT.
      */
      pPager->errCode = SQLITE_ABORT;
      pPager->eState = PAGER_ERROR;
      return rc;
    }
  }else{
    rc = pager_playback(pPager, 0);
  }

  assert( pPager->eState==PAGER_READER || rc!=SQLITE_OK );
  assert( rc==SQLITE_OK || rc==SQLITE_FULL || rc==SQLITE_CORRUPT
          || rc==SQLITE_NOMEM || (rc&0xFF)==SQLITE_IOERR 
          || rc==SQLITE_CANTOPEN
  );

  /* If an error occurs during a ROLLBACK, we can no longer trust the pager
  ** cache. So call pager_error() on the way out to make any error persistent.
  */
  return pager_error(pPager, rc);
}

/*
** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
SQLITE_PRIVATE u8 sqlite3PagerIsreadonly(Pager *pPager){
  return pPager->readOnly;
}

#ifdef SQLITE_DEBUG
/*
** Return the sum of the reference counts for all pages held by pPager.
*/
SQLITE_PRIVATE int sqlite3PagerRefcount(Pager *pPager){
  return sqlite3PcacheRefCount(pPager->pPCache);
}
#endif

#if 0
/*
** Return the approximate number of bytes of memory currently
** used by the pager and its associated cache.
*/
SQLITE_PRIVATE int sqlite3PagerMemUsed(Pager *pPager){
  int perPageSize = pPager->pageSize + pPager->nExtra + sizeof(PgHdr)
                                     + 5*sizeof(void*);
  return perPageSize*sqlite3PcachePagecount(pPager->pPCache)
           + sqlite3MallocSize(pPager)
           + pPager->pageSize;
}
#endif

/*
** Return the number of references to the specified page.
*/
SQLITE_PRIVATE int sqlite3PagerPageRefcount(DbPage *pPage){
  return sqlite3PcachePageRefcount(pPage);
}

#ifdef SQLITE_TEST
/*
** This routine is used for testing and analysis only.
*/
SQLITE_PRIVATE int *sqlite3PagerStats(Pager *pPager){
  static int a[11];
  a[0] = sqlite3PcacheRefCount(pPager->pPCache);
  a[1] = sqlite3PcachePagecount(pPager->pPCache);
  a[2] = sqlite3PcacheGetCachesize(pPager->pPCache);
  a[3] = pPager->eState==PAGER_OPEN ? -1 : (int) pPager->dbSize;
  a[4] = pPager->eState;
  a[5] = pPager->errCode;
  a[6] = pPager->aStat[PAGER_STAT_HIT];
  a[7] = pPager->aStat[PAGER_STAT_MISS];
  a[8] = 0;  /* Used to be pPager->nOvfl */
  a[9] = pPager->nRead;
  a[10] = pPager->aStat[PAGER_STAT_WRITE];
  return a;
}
#endif

#if 0
/*
** Parameter eStat must be either SQLITE_DBSTATUS_CACHE_HIT or
** SQLITE_DBSTATUS_CACHE_MISS. Before returning, *pnVal is incremented by the
** current cache hit or miss count, according to the value of eStat. If the 
** reset parameter is non-zero, the cache hit or miss count is zeroed before 
** returning.
*/
SQLITE_PRIVATE void sqlite3PagerCacheStat(Pager *pPager, int eStat, int reset, int *pnVal){

  assert( eStat==SQLITE_DBSTATUS_CACHE_HIT
       || eStat==SQLITE_DBSTATUS_CACHE_MISS
       || eStat==SQLITE_DBSTATUS_CACHE_WRITE
  );

  assert( SQLITE_DBSTATUS_CACHE_HIT+1==SQLITE_DBSTATUS_CACHE_MISS );
  assert( SQLITE_DBSTATUS_CACHE_HIT+2==SQLITE_DBSTATUS_CACHE_WRITE );
  assert( PAGER_STAT_HIT==0 && PAGER_STAT_MISS==1 && PAGER_STAT_WRITE==2 );

  *pnVal += pPager->aStat[eStat - SQLITE_DBSTATUS_CACHE_HIT];
  if( reset ){
    pPager->aStat[eStat - SQLITE_DBSTATUS_CACHE_HIT] = 0;
  }
}
#endif

/*
** Check that there are at least nSavepoint savepoints open. If there are
** currently less than nSavepoints open, then open one or more savepoints
** to make up the difference. If the number of savepoints is already
** equal to nSavepoint, then this function is a no-op.
**
** If a memory allocation fails, SQLITE_NOMEM is returned. If an error 
** occurs while opening the sub-journal file, then an IO error code is
** returned. Otherwise, SQLITE_OK.
*/
static SQLITE_NOINLINE int pagerOpenSavepoint(Pager *pPager, int nSavepoint){
  int rc = SQLITE_OK;                       /* Return code */
  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */
  int ii;                                   /* Iterator variable */
  PagerSavepoint *aNew;                     /* New Pager.aSavepoint array */

  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( assert_pager_state(pPager) );
  assert( nSavepoint>nCurrent && pPager->useJournal );

  /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
  ** if the allocation fails. Otherwise, zero the new portion in case a 
  ** malloc failure occurs while populating it in the for(...) loop below.
  */
  aNew = (PagerSavepoint *)sqlite3Realloc(
      pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
  );
  if( !aNew ){
    return SQLITE_NOMEM;
  }
  memset(&aNew[nCurrent], 0, (nSavepoint-nCurrent) * sizeof(PagerSavepoint));
  pPager->aSavepoint = aNew;

  /* Populate the PagerSavepoint structures just allocated. */
  for(ii=nCurrent; ii<nSavepoint; ii++){
    aNew[ii].nOrig = pPager->dbSize;
    if( isOpen(pPager->jfd) && pPager->journalOff>0 ){
      aNew[ii].iOffset = pPager->journalOff;
    }else{
      aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
    }
    aNew[ii].iSubRec = pPager->nSubRec;
    aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
    if( !aNew[ii].pInSavepoint ){
      return SQLITE_NOMEM;
    }
    if( pagerUseWal(pPager) ){
      sqlite3WalSavepoint(pPager->pWal, aNew[ii].aWalData);
    }
    pPager->nSavepoint = ii+1;
  }
  assert( pPager->nSavepoint==nSavepoint );
  assertTruncateConstraint(pPager);
  return rc;
}
SQLITE_PRIVATE int sqlite3PagerOpenSavepoint(Pager *pPager, int nSavepoint){
  assert( pPager->eState>=PAGER_WRITER_LOCKED );
  assert( assert_pager_state(pPager) );

  if( nSavepoint>pPager->nSavepoint && pPager->useJournal ){
    return pagerOpenSavepoint(pPager, nSavepoint);
  }else{
    return SQLITE_OK;
  }
}


/*
** This function is called to rollback or release (commit) a savepoint.
** The savepoint to release or rollback need not be the most recently 
** created savepoint.
**
** Parameter op is always either SAVEPOINT_ROLLBACK or SAVEPOINT_RELEASE.
** If it is SAVEPOINT_RELEASE, then release and destroy the savepoint with
** index iSavepoint. If it is SAVEPOINT_ROLLBACK, then rollback all changes
** that have occurred since the specified savepoint was created.
**
** The savepoint to rollback or release is identified by parameter 
** iSavepoint. A value of 0 means to operate on the outermost savepoint
** (the first created). A value of (Pager.nSavepoint-1) means operate
** on the most recently created savepoint. If iSavepoint is greater than
** (Pager.nSavepoint-1), then this function is a no-op.
**
** If a negative value is passed to this function, then the current
** transaction is rolled back. This is different to calling 
** sqlite3PagerRollback() because this function does not terminate
** the transaction or unlock the database, it just restores the 
** contents of the database to its original state. 
**
** In any case, all savepoints with an index greater than iSavepoint 
** are destroyed. If this is a release operation (op==SAVEPOINT_RELEASE),
** then savepoint iSavepoint is also destroyed.
**
** This function may return SQLITE_NOMEM if a memory allocation fails,
** or an IO error code if an IO error occurs while rolling back a 
** savepoint. If no errors occur, SQLITE_OK is returned.
*/ 
SQLITE_PRIVATE int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
  int rc = pPager->errCode;       /* Return code */

  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );

  if( rc==SQLITE_OK && iSavepoint<pPager->nSavepoint ){
    int ii;            /* Iterator variable */
    int nNew;          /* Number of remaining savepoints after this op. */

    /* Figure out how many savepoints will still be active after this
    ** operation. Store this value in nNew. Then free resources associated 
    ** with any savepoints that are destroyed by this operation.
    */
    nNew = iSavepoint + (( op==SAVEPOINT_RELEASE ) ? 0 : 1);
    for(ii=nNew; ii<pPager->nSavepoint; ii++){
      sqlite3BitvecDestroy(pPager->aSavepoint[ii].pInSavepoint);
    }
    pPager->nSavepoint = nNew;

    /* If this is a release of the outermost savepoint, truncate 
    ** the sub-journal to zero bytes in size. */
    if( op==SAVEPOINT_RELEASE ){
      if( nNew==0 && isOpen(pPager->sjfd) ){
        /* Only truncate if it is an in-memory sub-journal. */
        if( sqlite3IsMemJournal(pPager->sjfd) ){
          rc = sqlite3OsTruncate(pPager->sjfd, 0);
          assert( rc==SQLITE_OK );
        }
        pPager->nSubRec = 0;
      }
    }
    /* Else this is a rollback operation, playback the specified savepoint.
    ** If this is a temp-file, it is possible that the journal file has
    ** not yet been opened. In this case there have been no changes to
    ** the database file, so the playback operation can be skipped.
    */
    else if( pagerUseWal(pPager) || isOpen(pPager->jfd) ){
      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
      assert(rc!=SQLITE_DONE);
    }
  }

  return rc;
}

/*
** Return the full pathname of the database file.
**
** Except, if the pager is in-memory only, then return an empty string if
** nullIfMemDb is true.  This routine is called with nullIfMemDb==1 when
** used to report the filename to the user, for compatibility with legacy
** behavior.  But when the Btree needs to know the filename for matching to
** shared cache, it uses nullIfMemDb==0 so that in-memory databases can
** participate in shared-cache.
*/
SQLITE_PRIVATE const char *sqlite3PagerFilename(Pager *pPager, int nullIfMemDb){
  return (nullIfMemDb && pPager->memDb) ? "" : pPager->zFilename;
}

/*
** Return the VFS structure for the pager.
*/
SQLITE_PRIVATE const sqlite3_vfs *sqlite3PagerVfs(Pager *pPager){
  return pPager->pVfs;
}

#ifdef SQLITE_DIRECT_OVERFLOW_READ
/*
** Return the file handle for the database file associated
** with the pager.  This might return NULL if the file has
** not yet been opened.
*/
SQLITE_PRIVATE sqlite3_file *sqlite3PagerFile(Pager *pPager){
  return pPager->fd;
}
#endif

/*
** Return the full pathname of the journal file.
*/
SQLITE_PRIVATE const char *sqlite3PagerJournalname(Pager *pPager){
  return pPager->zJournal;
}

/*
** Return true if fsync() calls are disabled for this pager.  Return FALSE
** if fsync()s are executed normally.
*/
SQLITE_PRIVATE int sqlite3PagerNosync(Pager *pPager){
  return pPager->noSync;
}

#ifdef SQLITE_HAS_CODEC
/*
** Set or retrieve the codec for this pager
*/
SQLITE_PRIVATE void sqlite3PagerSetCodec(
  Pager *pPager,
  void *(*xCodec)(void*,void*,Pgno,int),
  void (*xCodecSizeChng)(void*,int,int),
  void (*xCodecFree)(void*),
  void *pCodec
){
  if( pPager->xCodecFree ) pPager->xCodecFree(pPager->pCodec);
  pPager->xCodec = pPager->memDb ? 0 : xCodec;
  pPager->xCodecSizeChng = xCodecSizeChng;
  pPager->xCodecFree = xCodecFree;
  pPager->pCodec = pCodec;
  pagerReportSize(pPager);
}
SQLITE_PRIVATE void *sqlite3PagerGetCodec(Pager *pPager){
  return pPager->pCodec;
}

/*
** This function is called by the wal module when writing page content
** into the log file.
**
** This function returns a pointer to a buffer containing the encrypted
** page content. If a malloc fails, this function may return NULL.
*/
SQLITE_PRIVATE void *sqlite3PagerCodec(PgHdr *pPg){
  void *aData = 0;
  CODEC2(pPg->pPager, pPg->pData, pPg->pgno, 6, return 0, aData);
  return aData;
}

/*
** Return the current pager state
*/
SQLITE_PRIVATE int sqlite3PagerState(Pager *pPager){
  return pPager->eState;
}
#endif /* SQLITE_HAS_CODEC */

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Move the page pPg to location pgno in the file.
**
** There must be no references to the page previously located at
** pgno (which we call pPgOld) though that page is allowed to be
** in cache.  If the page previously located at pgno is not already
** in the rollback journal, it is not put there by by this routine.
**
** References to the page pPg remain valid. Updating any
** meta-data associated with pPg (i.e. data stored in the nExtra bytes
** allocated along with the page) is the responsibility of the caller.
**
** A transaction must be active when this routine is called. It used to be
** required that a statement transaction was not active, but this restriction
** has been removed (CREATE INDEX needs to move a page when a statement
** transaction is active).
**
** If the fourth argument, isCommit, is non-zero, then this page is being
** moved as part of a database reorganization just before the transaction 
** is being committed. In this case, it is guaranteed that the database page 
** pPg refers to will not be written to again within this transaction.
**
** This function may return SQLITE_NOMEM or an IO error code if an error
** occurs. Otherwise, it returns SQLITE_OK.
*/
SQLITE_PRIVATE int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
  PgHdr *pPgOld;               /* The page being overwritten. */
  Pgno needSyncPgno = 0;       /* Old value of pPg->pgno, if sync is required */
  int rc;                      /* Return code */

  assert( pPg->nRef>0 );
  assert( pPager->eState==PAGER_WRITER_CACHEMOD
       || pPager->eState==PAGER_WRITER_DBMOD
  );
  assert( assert_pager_state(pPager) );

  /* If the page being moved is dirty and has not been saved by the latest
  ** savepoint, then save the current contents of the page into the 
  ** sub-journal now. This is required to handle the following scenario:
  **
  **   BEGIN;
  **     <journal page X, then modify it in memory>
  **     SAVEPOINT one;
  **       <Move page X to location Y>
  **     ROLLBACK TO one;
  **
  ** If page X were not written to the sub-journal here, it would not
  ** be possible to restore its contents when the "ROLLBACK TO one"
  ** statement were is processed.
  **
  ** subjournalPage() may need to allocate space to store pPg->pgno into
  ** one or more savepoint bitvecs. This is the reason this function
  ** may return SQLITE_NOMEM.
  */
  if( (pPg->flags & PGHDR_DIRTY)!=0
   && SQLITE_OK!=(rc = subjournalPageIfRequired(pPg))
  ){
    return rc;
  }

  PAGERTRACE(("MOVE %d page %d (needSync=%d) moves to %d\n", 
      PAGERID(pPager), pPg->pgno, (pPg->flags&PGHDR_NEED_SYNC)?1:0, pgno));
  IOTRACE(("MOVE %p %d %d\n", pPager, pPg->pgno, pgno))

  /* If the journal needs to be sync()ed before page pPg->pgno can
  ** be written to, store pPg->pgno in local variable needSyncPgno.
  **
  ** If the isCommit flag is set, there is no need to remember that
  ** the journal needs to be sync()ed before database page pPg->pgno 
  ** can be written to. The caller has already promised not to write to it.
  */
  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
    needSyncPgno = pPg->pgno;
    assert( pPager->journalMode==PAGER_JOURNALMODE_OFF ||
            pageInJournal(pPager, pPg) || pPg->pgno>pPager->dbOrigSize );
    assert( pPg->flags&PGHDR_DIRTY );
  }

  /* If the cache contains a page with page-number pgno, remove it
  ** from its hash chain. Also, if the PGHDR_NEED_SYNC flag was set for 
  ** page pgno before the 'move' operation, it needs to be retained 
  ** for the page moved there.
  */
  pPg->flags &= ~PGHDR_NEED_SYNC;
  pPgOld = sqlite3PagerLookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
    sqlite3PcacheDrop(pPgOld);
  }

  sqlite3PcacheMove(pPg, pgno);
  sqlite3PcacheMakeDirty(pPg);

  if( needSyncPgno ){
    /* If needSyncPgno is non-zero, then the journal file needs to be 
    ** sync()ed before any data is written to database file page needSyncPgno.
    ** Currently, no such page exists in the page-cache and the 
    ** "is journaled" bitvec flag has been set. This needs to be remedied by
    ** loading the page into the pager-cache and setting the PGHDR_NEED_SYNC
    ** flag.
    **
    ** If the attempt to load the page into the page-cache fails, (due
    ** to a malloc() or IO failure), clear the bit in the pInJournal[]
    ** array. Otherwise, if the page is loaded and written again in
    ** this transaction, it may be written to the database file before
    ** it is synced into the journal file. This way, it may end up in
    ** the journal file twice, but that is not a problem.
    */
    PgHdr *pPgHdr;
    rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
    if( rc!=SQLITE_OK ){
      if( needSyncPgno<=pPager->dbOrigSize ){
        assert( pPager->pTmpSpace!=0 );
        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno, pPager->pTmpSpace);
      }
      return rc;
    }
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnrefNotNull(pPgHdr);
  }

  return SQLITE_OK;
}
#endif

/*
** The page handle passed as the first argument refers to a dirty page 
** with a page number other than iNew. This function changes the page's 
** page number to iNew and sets the value of the PgHdr.flags field to 
** the value passed as the third parameter.
*/
SQLITE_PRIVATE void sqlite3PagerRekey(DbPage *pPg, Pgno iNew, u16 flags){
  assert( pPg->pgno!=iNew );
  pPg->flags = flags;
  sqlite3PcacheMove(pPg, iNew);
}

/*
** Return a pointer to the data for the specified page.
*/
SQLITE_PRIVATE void *sqlite3PagerGetData(DbPage *pPg){
  assert( pPg->nRef>0 || pPg->pPager->memDb );
  return pPg->pData;
}

/*
** Return a pointer to the Pager.nExtra bytes of "extra" space 
** allocated along with the specified page.
*/
SQLITE_PRIVATE void *sqlite3PagerGetExtra(DbPage *pPg){
  return pPg->pExtra;
}

#if 0
/*
** Get/set the locking-mode for this pager. Parameter eMode must be one
** of PAGER_LOCKINGMODE_QUERY, PAGER_LOCKINGMODE_NORMAL or 
** PAGER_LOCKINGMODE_EXCLUSIVE. If the parameter is not _QUERY, then
** the locking-mode is set to the value specified.
**
** The returned value is either PAGER_LOCKINGMODE_NORMAL or
** PAGER_LOCKINGMODE_EXCLUSIVE, indicating the current (possibly updated)
** locking-mode.
*/
SQLITE_PRIVATE int sqlite3PagerLockingMode(Pager *pPager, int eMode){
  assert( eMode==PAGER_LOCKINGMODE_QUERY
            || eMode==PAGER_LOCKINGMODE_NORMAL
            || eMode==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_QUERY<0 );
  assert( PAGER_LOCKINGMODE_NORMAL>=0 && PAGER_LOCKINGMODE_EXCLUSIVE>=0 );
  assert( pPager->exclusiveMode || 0==sqlite3WalHeapMemory(pPager->pWal) );
  if( eMode>=0 && !pPager->tempFile && !sqlite3WalHeapMemory(pPager->pWal) ){
    pPager->exclusiveMode = (u8)eMode;
  }
  return (int)pPager->exclusiveMode;
}

/*
** Set the journal-mode for this pager. Parameter eMode must be one of:
**
**    PAGER_JOURNALMODE_DELETE
**    PAGER_JOURNALMODE_TRUNCATE
**    PAGER_JOURNALMODE_PERSIST
**    PAGER_JOURNALMODE_OFF
**    PAGER_JOURNALMODE_MEMORY
**    PAGER_JOURNALMODE_WAL
**
** The journalmode is set to the value specified if the change is allowed.
** The change may be disallowed for the following reasons:
**
**   *  An in-memory database can only have its journal_mode set to _OFF
**      or _MEMORY.
**
**   *  Temporary databases cannot have _WAL journalmode.
**
** The returned indicate the current (possibly updated) journal-mode.
*/
SQLITE_PRIVATE int sqlite3PagerSetJournalMode(Pager *pPager, int eMode){
  u8 eOld = pPager->journalMode;    /* Prior journalmode */

#ifdef SQLITE_DEBUG
  /* The print_pager_state() routine is intended to be used by the debugger
  ** only.  We invoke it once here to suppress a compiler warning. */
  print_pager_state(pPager);
#endif


  /* The eMode parameter is always valid */
  assert(      eMode==PAGER_JOURNALMODE_DELETE
            || eMode==PAGER_JOURNALMODE_TRUNCATE
            || eMode==PAGER_JOURNALMODE_PERSIST
            || eMode==PAGER_JOURNALMODE_OFF 
            || eMode==PAGER_JOURNALMODE_WAL 
            || eMode==PAGER_JOURNALMODE_MEMORY );

  /* This routine is only called from the OP_JournalMode opcode, and
  ** the logic there will never allow a temporary file to be changed
  ** to WAL mode.
  */
  assert( pPager->tempFile==0 || eMode!=PAGER_JOURNALMODE_WAL );

  if( eMode!=eOld ){

    /* Change the journal mode. */
    assert( pPager->eState!=PAGER_ERROR );
    pPager->journalMode = (u8)eMode;

    /* When transistioning from TRUNCATE or PERSIST to any other journal
    ** mode except WAL, unless the pager is in locking_mode=exclusive mode,
    ** delete the journal file.
    */
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST & 5)==1 );
    assert( (PAGER_JOURNALMODE_DELETE & 5)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 5)==4 );
    assert( (PAGER_JOURNALMODE_OFF & 5)==0 );
    assert( (PAGER_JOURNALMODE_WAL & 5)==5 );

    assert( isOpen(pPager->fd) || pPager->exclusiveMode );
    if( !pPager->exclusiveMode && (eOld & 5)==1 && (eMode & 1)==0 ){

      /* In this case we would like to delete the journal file. If it is
      ** not possible, then that is not a problem. Deleting the journal file
      ** here is an optimization only.
      **
      ** Before deleting the journal file, obtain a RESERVED lock on the
      ** database file. This ensures that the journal file is not deleted
      ** while it is in use by some other client.
      */
      sqlite3OsClose(pPager->jfd);
      if( pPager->eLock>=RESERVED_LOCK ){
        sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }else{
        int rc = SQLITE_OK;
        int state = pPager->eState;
        assert( state==PAGER_OPEN || state==PAGER_READER );
        if( state==PAGER_OPEN ){
          rc = sqlite3PagerSharedLock(pPager);
        }
        if( pPager->eState==PAGER_READER ){
          assert( rc==SQLITE_OK );
          rc = pagerLockDb(pPager, RESERVED_LOCK);
        }
        if( rc==SQLITE_OK ){
          sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
        }
        if( rc==SQLITE_OK && state==PAGER_READER ){
          pagerUnlockDb(pPager, SHARED_LOCK);
        }else if( state==PAGER_OPEN ){
          pager_unlock(pPager);
        }
        assert( state==pPager->eState );
      }
    }else if( eMode==PAGER_JOURNALMODE_OFF ){
      sqlite3OsClose(pPager->jfd);
    }
  }

  /* Return the new journal mode */
  return (int)pPager->journalMode;
}

/*
** Return the current journal mode.
*/
SQLITE_PRIVATE int sqlite3PagerGetJournalMode(Pager *pPager){
  return (int)pPager->journalMode;
}

/*
** Return TRUE if the pager is in a state where it is OK to change the
** journalmode.  Journalmode changes can only happen when the database
** is unmodified.
*/
SQLITE_PRIVATE int sqlite3PagerOkToChangeJournalMode(Pager *pPager){
  assert( assert_pager_state(pPager) );
  if( pPager->eState>=PAGER_WRITER_CACHEMOD ) return 0;
  if( NEVER(isOpen(pPager->jfd) && pPager->journalOff>0) ) return 0;
  return 1;
}

/*
** Get/set the size-limit used for persistent journal files.
**
** Setting the size limit to -1 means no limit is enforced.
** An attempt to set a limit smaller than -1 is a no-op.
*/
SQLITE_PRIVATE i64 sqlite3PagerJournalSizeLimit(Pager *pPager, i64 iLimit){
  if( iLimit>=-1 ){
    pPager->journalSizeLimit = iLimit;
    sqlite3WalLimit(pPager->pWal, iLimit);
  }
  return pPager->journalSizeLimit;
}
#endif

#ifndef SQLITE_OMIT_VACUUM
#if 0
/*
** Clear the pager cache.
*/
SQLITE_PRIVATE void sqlite3PagerClearCache(Pager *pPager){
  if( pPager->tempFile==0 ) pager_reset(pPager);
}
#endif
#endif

#ifndef SQLITE_OMIT_WAL
/*
** This function is called when the user invokes "PRAGMA wal_checkpoint",
** "PRAGMA wal_blocking_checkpoint" or calls the sqlite3_wal_checkpoint()
** or wal_blocking_checkpoint() API functions.
**
** Parameter eMode is one of SQLITE_CHECKPOINT_PASSIVE, FULL or RESTART.
*/
SQLITE_PRIVATE int sqlite3PagerCheckpoint(Pager *pPager, int eMode, int *pnLog, int *pnCkpt){
  int rc = SQLITE_OK;
  if( pPager->pWal ){
    rc = sqlite3WalCheckpoint(pPager->pWal, eMode,
        (eMode==SQLITE_CHECKPOINT_PASSIVE ? 0 : pPager->xBusyHandler),
        pPager->pBusyHandlerArg,
        pPager->ckptSyncFlags, pPager->pageSize, (u8 *)pPager->pTmpSpace,
        pnLog, pnCkpt
    );
  }
  return rc;
}

#if 0
SQLITE_PRIVATE int sqlite3PagerWalCallback(Pager *pPager){
  return sqlite3WalCallback(pPager->pWal);
}
#endif

/*
** Return true if the underlying VFS for the given pager supports the
** primitives necessary for write-ahead logging.
*/
SQLITE_PRIVATE int sqlite3PagerWalSupported(Pager *pPager){
  const sqlite3_io_methods *pMethods = pPager->fd->pMethods;
  return pPager->exclusiveMode || (pMethods->iVersion>=2 && pMethods->xShmMap);
}

/*
** Attempt to take an exclusive lock on the database file. If a PENDING lock
** is obtained instead, immediately release it.
*/
static int pagerExclusiveLock(Pager *pPager){
  int rc;                         /* Return code */

  assert( pPager->eLock==SHARED_LOCK || pPager->eLock==EXCLUSIVE_LOCK );
  rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
  if( rc!=SQLITE_OK ){
    /* If the attempt to grab the exclusive lock failed, release the 
    ** pending lock that may have been obtained instead.  */
    pagerUnlockDb(pPager, SHARED_LOCK);
  }

  return rc;
}

/*
** Call sqlite3WalOpen() to open the WAL handle. If the pager is in 
** exclusive-locking mode when this function is called, take an EXCLUSIVE
** lock on the database file and use heap-memory to store the wal-index
** in. Otherwise, use the normal shared-memory.
*/
static int pagerOpenWal(Pager *pPager){
  int rc = SQLITE_OK;

  assert( pPager->pWal==0 && pPager->tempFile==0 );
  assert( pPager->eLock==SHARED_LOCK || pPager->eLock==EXCLUSIVE_LOCK );

  /* If the pager is already in exclusive-mode, the WAL module will use 
  ** heap-memory for the wal-index instead of the VFS shared-memory 
  ** implementation. Take the exclusive lock now, before opening the WAL
  ** file, to make sure this is safe.
  */
  if( pPager->exclusiveMode ){
    rc = pagerExclusiveLock(pPager);
  }

  /* Open the connection to the log file. If this operation fails, 
  ** (e.g. due to malloc() failure), return an error code.
  */
  if( rc==SQLITE_OK ){
    rc = sqlite3WalOpen(pPager->pVfs,
        pPager->fd, pPager->zWal, pPager->exclusiveMode,
        pPager->journalSizeLimit, &pPager->pWal
    );
  }
  pagerFixMaplimit(pPager);

  return rc;
}


/*
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
** is not already open, make an attempt to open it now. If successful,
** return SQLITE_OK. If an error occurs or the VFS used by the pager does 
** not support the xShmXXX() methods, return an error code. *pbOpen is
** not modified in either case.
**
** If the pager is open on a temp-file (or in-memory database), or if
** the WAL file is already open, set *pbOpen to 1 and return SQLITE_OK
** without doing anything.
*/
SQLITE_PRIVATE int sqlite3PagerOpenWal(
  Pager *pPager,                  /* Pager object */
  int *pbOpen                     /* OUT: Set to true if call is a no-op */
){
  int rc = SQLITE_OK;             /* Return code */

  assert( assert_pager_state(pPager) );
  assert( pPager->eState==PAGER_OPEN   || pbOpen );
  assert( pPager->eState==PAGER_READER || !pbOpen );
  assert( pbOpen==0 || *pbOpen==0 );
  assert( pbOpen!=0 || (!pPager->tempFile && !pPager->pWal) );

  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

    /* Close any rollback journal previously open */
    sqlite3OsClose(pPager->jfd);

    rc = pagerOpenWal(pPager);
    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
      pPager->eState = PAGER_OPEN;
    }
  }else{
    *pbOpen = 1;
  }

  return rc;
}

/*
** This function is called to close the connection to the log file prior
** to switching from WAL to rollback mode.
**
** Before closing the log file, this function attempts to take an 
** EXCLUSIVE lock on the database file. If this cannot be obtained, an
** error (SQLITE_BUSY) is returned and the log connection is not closed.
** If successful, the EXCLUSIVE lock is not released before returning.
*/
#if 0
SQLITE_PRIVATE int sqlite3PagerCloseWal(Pager *pPager){
  int rc = SQLITE_OK;

  assert( pPager->journalMode==PAGER_JOURNALMODE_WAL );

  /* If the log file is not already open, but does exist in the file-system,
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pWal ){
    int logexists = 0;
    rc = pagerLockDb(pPager, SHARED_LOCK);
    if( rc==SQLITE_OK ){
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &logexists
      );
    }
    if( rc==SQLITE_OK && logexists ){
      rc = pagerOpenWal(pPager);
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pWal ){
    rc = pagerExclusiveLock(pPager);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal, pPager->ckptSyncFlags,
                           pPager->pageSize, (u8*)pPager->pTmpSpace);
      pPager->pWal = 0;
      pagerFixMaplimit(pPager);
    }
  }
  return rc;
}
#endif
#endif /* !SQLITE_OMIT_WAL */

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** A read-lock must be held on the pager when this function is called. If
** the pager is in WAL mode and the WAL file currently contains one or more
** frames, return the size in bytes of the page images stored within the
** WAL frames. Otherwise, if this is not a WAL database or the WAL file
** is empty, return 0.
*/
SQLITE_PRIVATE int sqlite3PagerWalFramesize(Pager *pPager){
  assert( pPager->eState>=PAGER_READER );
  return sqlite3WalFramesize(pPager->pWal);
}
#endif


#endif /* SQLITE_OMIT_DISKIO */

/************** End of pager.c ***********************************************/
/************** Begin file wal.c *********************************************/
/*
** 2010 February 1
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains the implementation of a write-ahead log (WAL) used in 
** "journal_mode=WAL" mode.
**
** WRITE-AHEAD LOG (WAL) FILE FORMAT
**
** A WAL file consists of a header followed by zero or more "frames".
** Each frame records the revised content of a single page from the
** database file.  All changes to the database are recorded by writing
** frames into the WAL.  Transactions commit when a frame is written that
** contains a commit marker.  A single WAL can and usually does record 
** multiple transactions.  Periodically, the content of the WAL is
** transferred back into the database file in an operation called a
** "checkpoint".
**
** A single WAL file can be used multiple times.  In other words, the
** WAL can fill up with frames and then be checkpointed and then new
** frames can overwrite the old ones.  A WAL always grows from beginning
** toward the end.  Checksums and counters attached to each frame are
** used to determine which frames within the WAL are valid and which
** are leftovers from prior checkpoints.
**
** The WAL header is 32 bytes in size and consists of the following eight
** big-endian 32-bit unsigned integer values:
**
**     0: Magic number.  0x377f0682 or 0x377f0683
**     4: File format version.  Currently 3007000
**     8: Database page size.  Example: 1024
**    12: Checkpoint sequence number
**    16: Salt-1, random integer incremented with each checkpoint
**    20: Salt-2, a different random integer changing with each ckpt
**    24: Checksum-1 (first part of checksum for first 24 bytes of header).
**    28: Checksum-2 (second part of checksum for first 24 bytes of header).
**
** Immediately following the wal-header are zero or more frames. Each
** frame consists of a 24-byte frame-header followed by a <page-size> bytes
** of page data. The frame-header is six big-endian 32-bit unsigned 
** integer values, as follows:
**
**     0: Page number.
**     4: For commit records, the size of the database image in pages 
**        after the commit. For all other records, zero.
**     8: Salt-1 (copied from the header)
**    12: Salt-2 (copied from the header)
**    16: Checksum-1.
**    20: Checksum-2.
**
** A frame is considered valid if and only if the following conditions are
** true:
**
**    (1) The salt-1 and salt-2 values in the frame-header match
**        salt values in the wal-header
**
**    (2) The checksum values in the final 8 bytes of the frame-header
**        exactly match the checksum computed consecutively on the
**        WAL header and the first 8 bytes and the content of all frames
**        up to and including the current frame.
**
** The checksum is computed using 32-bit big-endian integers if the
** magic number in the first 4 bytes of the WAL is 0x377f0683 and it
** is computed using little-endian if the magic number is 0x377f0682.
** The checksum values are always stored in the frame header in a
** big-endian format regardless of which byte order is used to compute
** the checksum.  The checksum is computed by interpreting the input as
** an even number of unsigned 32-bit integers: x[0] through x[N].  The
** algorithm used for the checksum is as follows:
** 
**   for i from 0 to n-1 step 2:
**     s0 += x[i] + s1;
**     s1 += x[i+1] + s0;
**   endfor
**
** Note that s0 and s1 are both weighted checksums using fibonacci weights
** in reverse order (the largest fibonacci weight occurs on the first element
** of the sequence being summed.)  The s1 value spans all 32-bit 
** terms of the sequence whereas s0 omits the final term.
**
** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the
** WAL is transferred into the database, then the database is VFS.xSync-ed.
** The VFS.xSync operations serve as write barriers - all writes launched
** before the xSync must complete before any write that launches after the
** xSync begins.
**
** After each checkpoint, the salt-1 value is incremented and the salt-2
** value is randomized.  This prevents old and new frames in the WAL from
** being considered valid at the same time and being checkpointing together
** following a crash.
**
** READER ALGORITHM
**
** To read a page from the database (call it page number P), a reader
** first checks the WAL to see if it contains page P.  If so, then the
** last valid instance of page P that is a followed by a commit frame
** or is a commit frame itself becomes the value read.  If the WAL
** contains no copies of page P that are valid and which are a commit
** frame or are followed by a commit frame, then page P is read from
** the database file.
**
** To start a read transaction, the reader records the index of the last
** valid frame in the WAL.  The reader uses this recorded "mxFrame" value
** for all subsequent read operations.  New transactions can be appended
** to the WAL, but as long as the reader uses its original mxFrame value
** and ignores the newly appended content, it will see a consistent snapshot
** of the database from a single point in time.  This technique allows
** multiple concurrent readers to view different versions of the database
** content simultaneously.
**
** The reader algorithm in the previous paragraphs works correctly, but 
** because frames for page P can appear anywhere within the WAL, the
** reader has to scan the entire WAL looking for page P frames.  If the
** WAL is large (multiple megabytes is typical) that scan can be slow,
** and read performance suffers.  To overcome this problem, a separate
** data structure called the wal-index is maintained to expedite the
** search for frames of a particular page.
** 
** WAL-INDEX FORMAT
**
** Conceptually, the wal-index is shared memory, though VFS implementations
** might choose to implement the wal-index using a mmapped file.  Because
** the wal-index is shared memory, SQLite does not support journal_mode=WAL 
** on a network filesystem.  All users of the database must be able to
** share memory.
**
** The wal-index is transient.  After a crash, the wal-index can (and should
** be) reconstructed from the original WAL file.  In fact, the VFS is required
** to either truncate or zero the header of the wal-index when the last
** connection to it closes.  Because the wal-index is transient, it can
** use an architecture-specific format; it does not have to be cross-platform.
** Hence, unlike the database and WAL file formats which store all values
** as big endian, the wal-index can store multi-byte values in the native
** byte order of the host computer.
**
** The purpose of the wal-index is to answer this question quickly:  Given
** a page number P and a maximum frame index M, return the index of the 
** last frame in the wal before frame M for page P in the WAL, or return
** NULL if there are no frames for page P in the WAL prior to M.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.  
**
** The wal-index header contains the total number of frames within the WAL
** in the mxFrame field.
**
** Each index block except for the first contains information on 
** HASHTABLE_NPAGE frames. The first index block contains information on
** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and 
** HASHTABLE_NPAGE are selected so that together the wal-index header and
** first index block are the same size as all other index blocks in the
** wal-index.
**
** Each index block contains two sections, a page-mapping that contains the
** database page number associated with each wal frame, and a hash-table 
** that allows readers to query an index block for a specific page number.
** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE
** for the first index block) 32-bit page numbers. The first entry in the 
** first index-block contains the database page number corresponding to the
** first frame in the WAL file. The first entry in the second index block
** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in
** the log, and so on.
**
** The last index block in a wal-index usually contains less than the full
** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers,
** depending on the contents of the WAL file. This does not change the
** allocated size of the page-mapping array - the page-mapping array merely
** contains unused entries.
**
** Even without using the hash table, the last frame for page P
** can be found by scanning the page-mapping sections of each index block
** starting with the last index block and moving toward the first, and
** within each index block, starting at the end and moving toward the
** beginning.  The first entry that equals P corresponds to the frame
** holding the content for that page.
**
** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers.
** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the
** hash table for each page number in the mapping section, so the hash 
** table is never more than half full.  The expected number of collisions 
** prior to finding a match is 1.  Each entry of the hash table is an
** 1-based index of an entry in the mapping section of the same
** index block.   Let K be the 1-based index of the largest entry in
** the mapping section.  (For index blocks other than the last, K will
** always be exactly HASHTABLE_NPAGE (4096) and for the last index block
** K will be (mxFrame%HASHTABLE_NPAGE).)  Unused slots of the hash table
** contain a value of 0.
**
** To look for page P in the hash table, first compute a hash iKey on
** P as follows:
**
**      iKey = (P * 383) % HASHTABLE_NSLOT
**
** Then start scanning entries of the hash table, starting with iKey
** (wrapping around to the beginning when the end of the hash table is
** reached) until an unused hash slot is found. Let the first unused slot
** be at index iUnused.  (iUnused might be less than iKey if there was
** wrap-around.) Because the hash table is never more than half full,
** the search is guaranteed to eventually hit an unused entry.  Let 
** iMax be the value between iKey and iUnused, closest to iUnused,
** where aHash[iMax]==P.  If there is no iMax entry (if there exists
** no hash slot such that aHash[i]==p) then page P is not in the
** current index block.  Otherwise the iMax-th mapping entry of the
** current index block corresponds to the last entry that references 
** page P.
**
** A hash search begins with the last index block and moves toward the
** first index block, looking for entries corresponding to page P.  On
** average, only two or three slots in each index block need to be
** examined in order to either find the last entry for page P, or to
** establish that no such entry exists in the block.  Each index block
** holds over 4000 entries.  So two or three index blocks are sufficient
** to cover a typical 10 megabyte WAL file, assuming 1K pages.  8 or 10
** comparisons (on average) suffice to either locate a frame in the
** WAL or to establish that the frame does not exist in the WAL.  This
** is much faster than scanning the entire 10MB WAL.
**
** Note that entries are added in order of increasing K.  Hence, one
** reader might be using some value K0 and a second reader that started
** at a later time (after additional transactions were added to the WAL
** and to the wal-index) might be using a different value K1, where K1>K0.
** Both readers can use the same hash table and mapping section to get
** the correct result.  There may be entries in the hash table with
** K>K0 but to the first reader, those entries will appear to be unused
** slots in the hash table and so the first reader will get an answer as
** if no values greater than K0 had ever been inserted into the hash table
** in the first place - which is what reader one wants.  Meanwhile, the
** second reader using K1 will see additional values that were inserted
** later, which is exactly what reader two wants.  
**
** When a rollback occurs, the value of K is decreased. Hash table entries
** that correspond to frames greater than the new K value are removed
** from the hash table at this point.
*/
#ifndef SQLITE_OMIT_WAL

/* #include "wal.h" */

/*
** Trace output macros
*/
#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
SQLITE_PRIVATE int sqlite3WalTrace = 0;
# define WALTRACE(X)  if(sqlite3WalTrace) sqlite3DebugPrintf X
#else
# define WALTRACE(X)
#endif

/*
** The maximum (and only) versions of the wal and wal-index formats
** that may be interpreted by this version of SQLite.
**
** If a client begins recovering a WAL file and finds that (a) the checksum
** values in the wal-header are correct and (b) the version field is not
** WAL_MAX_VERSION, recovery fails and SQLite returns SQLITE_CANTOPEN.
**
** Similarly, if a client successfully reads a wal-index header (i.e. the 
** checksum test is successful) and finds that the version field is not
** WALINDEX_MAX_VERSION, then no read-transaction is opened and SQLite
** returns SQLITE_CANTOPEN.
*/
#define WAL_MAX_VERSION      3007000
#define WALINDEX_MAX_VERSION 3007000

/*
** Indices of various locking bytes.   WAL_NREADER is the number
** of available reader locks and should be at least 3.
*/
#define WAL_WRITE_LOCK         0
#define WAL_ALL_BUT_WRITE      1
#define WAL_CKPT_LOCK          1
#define WAL_RECOVER_LOCK       2
#define WAL_READ_LOCK(I)       (3+(I))
#define WAL_NREADER            (SQLITE_SHM_NLOCK-3)


/* Object declarations */
typedef struct WalIndexHdr WalIndexHdr;
typedef struct WalIterator WalIterator;
typedef struct WalCkptInfo WalCkptInfo;


/*
** The following object holds a copy of the wal-index header content.
**
** The actual header in the wal-index consists of two copies of this
** object.
**
** The szPage value can be any power of 2 between 512 and 32768, inclusive.
** Or it can be 1 to represent a 65536-byte page.  The latter case was
** added in 3.7.1 when support for 64K pages was added.  
*/
struct WalIndexHdr {
  u32 iVersion;                   /* Wal-index version */
  u32 unused;                     /* Unused (padding) field */
  u32 iChange;                    /* Counter incremented each transaction */
  u8 isInit;                      /* 1 when initialized */
  u8 bigEndCksum;                 /* True if checksums in WAL are big-endian */
  u16 szPage;                     /* Database page size in bytes. 1==64K */
  u32 mxFrame;                    /* Index of last valid frame in the WAL */
  u32 nPage;                      /* Size of database in pages */
  u32 aFrameCksum[2];             /* Checksum of last frame in log */
  u32 aSalt[2];                   /* Two salt values copied from WAL header */
  u32 aCksum[2];                  /* Checksum over all prior fields */
};

/*
** A copy of the following object occurs in the wal-index immediately
** following the second copy of the WalIndexHdr.  This object stores
** information used by checkpoint.
**
** nBackfill is the number of frames in the WAL that have been written
** back into the database. (We call the act of moving content from WAL to
** database "backfilling".)  The nBackfill number is never greater than
** WalIndexHdr.mxFrame.  nBackfill can only be increased by threads
** holding the WAL_CKPT_LOCK lock (which includes a recovery thread).
** However, a WAL_WRITE_LOCK thread can move the value of nBackfill from
** mxFrame back to zero when the WAL is reset.
**
** There is one entry in aReadMark[] for each reader lock.  If a reader
** holds read-lock K, then the value in aReadMark[K] is no greater than
** the mxFrame for that reader.  The value READMARK_NOT_USED (0xffffffff)
** for any aReadMark[] means that entry is unused.  aReadMark[0] is 
** a special case; its value is never used and it exists as a place-holder
** to avoid having to offset aReadMark[] indexs by one.  Readers holding
** WAL_READ_LOCK(0) always ignore the entire WAL and read all content
** directly from the database.
**
** The value of aReadMark[K] may only be changed by a thread that
** is holding an exclusive lock on WAL_READ_LOCK(K).  Thus, the value of
** aReadMark[K] cannot changed while there is a reader is using that mark
** since the reader will be holding a shared lock on WAL_READ_LOCK(K).
**
** The checkpointer may only transfer frames from WAL to database where
** the frame numbers are less than or equal to every aReadMark[] that is
** in use (that is, every aReadMark[j] for which there is a corresponding
** WAL_READ_LOCK(j)).  New readers (usually) pick the aReadMark[] with the
** largest value and will increase an unused aReadMark[] to mxFrame if there
** is not already an aReadMark[] equal to mxFrame.  The exception to the
** previous sentence is when nBackfill equals mxFrame (meaning that everything
** in the WAL has been backfilled into the database) then new readers
** will choose aReadMark[0] which has value 0 and hence such reader will
** get all their all content directly from the database file and ignore 
** the WAL.
**
** Writers normally append new frames to the end of the WAL.  However,
** if nBackfill equals mxFrame (meaning that all WAL content has been
** written back into the database) and if no readers are using the WAL
** (in other words, if there are no WAL_READ_LOCK(i) where i>0) then
** the writer will first "reset" the WAL back to the beginning and start
** writing new content beginning at frame 1.
**
** We assume that 32-bit loads are atomic and so no locks are needed in
** order to read from any aReadMark[] entries.
*/
struct WalCkptInfo {
  u32 nBackfill;                  /* Number of WAL frames backfilled into DB */
  u32 aReadMark[WAL_NREADER];     /* Reader marks */
};
#define READMARK_NOT_USED  0xffffffff


/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
** WALINDEX_LOCK_OFFSET is reserved for locks. Since some systems
** only support mandatory file-locks, we do not read or write data
** from the region of the file on which locks are applied.
*/
#define WALINDEX_LOCK_OFFSET   (sizeof(WalIndexHdr)*2 + sizeof(WalCkptInfo))
#define WALINDEX_LOCK_RESERVED 16
#define WALINDEX_HDR_SIZE      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)

/* Size of header before each frame in wal */
#define WAL_FRAME_HDRSIZE 24

/* Size of write ahead log header, including checksum. */
/* #define WAL_HDRSIZE 24 */
#define WAL_HDRSIZE 32

/* WAL magic value. Either this value, or the same value with the least
** significant bit also set (WAL_MAGIC | 0x00000001) is stored in 32-bit
** big-endian format in the first 4 bytes of a WAL file.
**
** If the LSB is set, then the checksums for each frame within the WAL
** file are calculated by treating all data as an array of 32-bit 
** big-endian words. Otherwise, they are calculated by interpreting 
** all data as 32-bit little-endian words.
*/
#define WAL_MAGIC 0x377f0682

/*
** Return the offset of frame iFrame in the write-ahead log file, 
** assuming a database page size of szPage bytes. The offset returned
** is to the start of the write-ahead log frame-header.
*/
#define walFrameOffset(iFrame, szPage) (                               \
  WAL_HDRSIZE + ((iFrame)-1)*(i64)((szPage)+WAL_FRAME_HDRSIZE)         \
)

/*
** An open write-ahead log file is represented by an instance of the
** following object.
*/
struct Wal {
  sqlite3_vfs *pVfs;         /* The VFS used to create pDbFd */
  sqlite3_file *pDbFd;       /* File handle for the database file */
  sqlite3_file *pWalFd;      /* File handle for WAL file */
  u32 iCallback;             /* Value to pass to log callback (or 0) */
  i64 mxWalSize;             /* Truncate WAL to this size upon reset */
  int nWiData;               /* Size of array apWiData */
  int szFirstBlock;          /* Size of first block written to WAL file */
  volatile u32 **apWiData;   /* Pointer to wal-index content in memory */
  u32 szPage;                /* Database page size */
  i16 readLock;              /* Which read lock is being held.  -1 for none */
  u8 syncFlags;              /* Flags to use to sync header writes */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */
  u8 readOnly;               /* WAL_RDWR, WAL_RDONLY, or WAL_SHM_RDONLY */
  u8 truncateOnCommit;       /* True to truncate WAL file on commit */
  u8 syncHeader;             /* Fsync the WAL header if true */
  u8 padToSectorBoundary;    /* Pad transactions out to the next sector */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
  u32 minFrame;              /* Ignore wal frames before this one */
  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     
#define WAL_HEAPMEMORY_MODE 2

/*
** Possible values for WAL.readOnly
*/
#define WAL_RDWR        0    /* Normal read/write connection */
#define WAL_RDONLY      1    /* The WAL file is readonly */
#define WAL_SHM_RDONLY  2    /* The SHM file is readonly */

/*
** Each page of the wal-index mapping contains a hash-table made up of
** an array of HASHTABLE_NSLOT elements of the following type.
*/
typedef u16 ht_slot;

/*
** This structure is used to implement an iterator that loops through
** all frames in the WAL in database page order. Where two or more frames
** correspond to the same database page, the iterator visits only the 
** frame most recently written to the WAL (in other words, the frame with
** the largest index).
**
** The internals of this structure are only accessed by:
**
**   walIteratorInit() - Create a new iterator,
**   walIteratorNext() - Step an iterator,
**   walIteratorFree() - Free an iterator.
**
** This functionality is used by the checkpoint code (see walCheckpoint()).
*/
struct WalIterator {
  int iPrior;                     /* Last result returned from the iterator */
  int nSegment;                   /* Number of entries in aSegment[] */
  struct WalSegment {
    int iNext;                    /* Next slot in aIndex[] not yet returned */
    ht_slot *aIndex;              /* i0, i1, i2... such that aPgno[iN] ascend */
    u32 *aPgno;                   /* Array of page numbers. */
    int nEntry;                   /* Nr. of entries in aPgno[] and aIndex[] */
    int iZero;                    /* Frame number associated with aPgno[0] */
  } aSegment[1];                  /* One for every 32KB page in the wal-index */
};

/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
*/
#define HASHTABLE_NPAGE      4096                 /* Must be power of 2 */
#define HASHTABLE_HASH_1     383                  /* Should be prime */
#define HASHTABLE_NSLOT      (HASHTABLE_NPAGE*2)  /* Must be a power of 2 */

/* 
** The block of page numbers associated with the first hash-table in a
** wal-index is smaller than usual. This is so that there is a complete
** hash-table on each aligned 32KB page of the wal-index.
*/
#define HASHTABLE_NPAGE_ONE  (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32)))

/* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */
#define WALINDEX_PGSZ   (                                         \
    sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \
)

/*
** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
** numbered from zero.
**
** If this call is successful, *ppPage is set to point to the wal-index
** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs,
** then an SQLite error code is returned and *ppPage is set to 0.
*/
static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
  int rc = SQLITE_OK;

  /* Enlarge the pWal->apWiData[] array if required */
  if( pWal->nWiData<=iPage ){
    int nByte = sizeof(u32*)*(iPage+1);
    volatile u32 **apNew;
    apNew = (volatile u32 **)sqlite3_realloc64((void *)pWal->apWiData, nByte);
    if( !apNew ){
      *ppPage = 0;
      return SQLITE_NOMEM;
    }
    memset((void*)&apNew[pWal->nWiData], 0,
           sizeof(u32*)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){
    if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
      pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ);
      if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM;
    }else{
      rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 
          pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
      );
      if( rc==SQLITE_READONLY ){
        pWal->readOnly |= WAL_SHM_RDONLY;
        rc = SQLITE_OK;
      }
    }
  }

  *ppPage = pWal->apWiData[iPage];
  assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
  return rc;
}

/*
** Return a pointer to the WalCkptInfo structure in the wal-index.
*/
static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
  assert( pWal->nWiData>0 && pWal->apWiData[0] );
  return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]);
}

/*
** Return a pointer to the WalIndexHdr structure in the wal-index.
*/
static volatile WalIndexHdr *walIndexHdr(Wal *pWal){
  assert( pWal->nWiData>0 && pWal->apWiData[0] );
  return (volatile WalIndexHdr*)pWal->apWiData[0];
}

/*
** The argument to this macro must be of type u32. On a little-endian
** architecture, it returns the u32 value that results from interpreting
** the 4 bytes as a big-endian value. On a big-endian architecture, it
** returns the value that would be produced by interpreting the 4 bytes
** of the input value as a little-endian integer.
*/
#define BYTESWAP32(x) ( \
    (((x)&0x000000FF)<<24) + (((x)&0x0000FF00)<<8)  \
  + (((x)&0x00FF0000)>>8)  + (((x)&0xFF000000)>>24) \
)

/*
** Generate or extend an 8 byte checksum based on the data in 
** array aByte[] and the initial values of aIn[0] and aIn[1] (or
** initial values of 0 and 0 if aIn==NULL).
**
** The checksum is written back into aOut[] before returning.
**
** nByte must be a positive multiple of 8.
*/
static void walChecksumBytes(
  int nativeCksum, /* True for native byte-order, false for non-native */
  u8 *a,           /* Content to be checksummed */
  int nByte,       /* Bytes of content in a[].  Must be a multiple of 8. */
  const u32 *aIn,  /* Initial checksum value input */
  u32 *aOut        /* OUT: Final checksum value output */
){
  u32 s1, s2;
  u32 *aData = (u32 *)a;
  u32 *aEnd = (u32 *)&a[nByte];

  if( aIn ){
    s1 = aIn[0];
    s2 = aIn[1];
  }else{
    s1 = s2 = 0;
  }

  assert( nByte>=8 );
  assert( (nByte&0x00000007)==0 );

  if( nativeCksum ){
    do {
      s1 += *aData++ + s2;
      s2 += *aData++ + s1;
    }while( aData<aEnd );
  }else{
    do {
      s1 += BYTESWAP32(aData[0]) + s2;
      s2 += BYTESWAP32(aData[1]) + s1;
      aData += 2;
    }while( aData<aEnd );
  }

  aOut[0] = s1;
  aOut[1] = s2;
}

static void walShmBarrier(Wal *pWal){
  if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
    sqlite3OsShmBarrier(pWal->pDbFd);
  }
}

/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
  volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
  const int nCksum = offsetof(WalIndexHdr, aCksum);

  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
  walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
  memcpy((void*)&aHdr[1], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
  walShmBarrier(pWal);
  memcpy((void*)&aHdr[0], (const void*)&pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of 
** 4-byte big-endian integers, as follows:
**
**     0: Page number.
**     4: For commit records, the size of the database image in pages 
**        after the commit. For all other records, zero.
**     8: Salt-1 (copied from the wal-header)
**    12: Salt-2 (copied from the wal-header)
**    16: Checksum-1.
**    20: Checksum-2.
*/
static void walEncodeFrame(
  Wal *pWal,                      /* The write-ahead log */
  u32 iPage,                      /* Database page number for frame */
  u32 nTruncate,                  /* New db size (or 0 for non-commit frames) */
  u8 *aData,                      /* Pointer to page data */
  u8 *aFrame                      /* OUT: Write encoded frame here */
){
  int nativeCksum;                /* True for native byte-order checksums */
  u32 *aCksum = pWal->hdr.aFrameCksum;
  assert( WAL_FRAME_HDRSIZE==24 );
  sqlite3Put4byte(&aFrame[0], iPage);
  sqlite3Put4byte(&aFrame[4], nTruncate);
  memcpy(&aFrame[8], pWal->hdr.aSalt, 8);

  nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
  walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
  walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);

  sqlite3Put4byte(&aFrame[16], aCksum[0]);
  sqlite3Put4byte(&aFrame[20], aCksum[1]);
}

/*
** Check to see if the frame with header in aFrame[] and content
** in aData[] is valid.  If it is a valid frame, fill *piPage and
** *pnTruncate and return true.  Return if the frame is not valid.
*/
static int walDecodeFrame(
  Wal *pWal,                      /* The write-ahead log */
  u32 *piPage,                    /* OUT: Database page number for frame */
  u32 *pnTruncate,                /* OUT: New db size (or 0 if not commit) */
  u8 *aData,                      /* Pointer to page data (for checksum) */
  u8 *aFrame                      /* Frame data */
){
  int nativeCksum;                /* True for native byte-order checksums */
  u32 *aCksum = pWal->hdr.aFrameCksum;
  u32 pgno;                       /* Page number of the frame */
  assert( WAL_FRAME_HDRSIZE==24 );

  /* A frame is only valid if the salt values in the frame-header
  ** match the salt values in the wal-header. 
  */
  if( memcmp(&pWal->hdr.aSalt, &aFrame[8], 8)!=0 ){
    return 0;
  }

  /* A frame is only valid if the page number is creater than zero.
  */
  pgno = sqlite3Get4byte(&aFrame[0]);
  if( pgno==0 ){
    return 0;
  }

  /* A frame is only valid if a checksum of the WAL header,
  ** all prior frams, the first 16 bytes of this frame-header, 
  ** and the frame-data matches the checksum in the last 8 
  ** bytes of this frame-header.
  */
  nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
  walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
  walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
  if( aCksum[0]!=sqlite3Get4byte(&aFrame[16]) 
   || aCksum[1]!=sqlite3Get4byte(&aFrame[20]) 
  ){
    /* Checksum failed. */
    return 0;
  }

  /* If we reach this point, the frame is valid.  Return the page number
  ** and the new database size.
  */
  *piPage = pgno;
  *pnTruncate = sqlite3Get4byte(&aFrame[4]);
  return 1;
}


#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
/*
** Names of locks.  This routine is used to provide debugging output and is not
** a part of an ordinary build.
*/
static const char *walLockName(int lockIdx){
  if( lockIdx==WAL_WRITE_LOCK ){
    return "WRITE-LOCK";
  }else if( lockIdx==WAL_CKPT_LOCK ){
    return "CKPT-LOCK";
  }else if( lockIdx==WAL_RECOVER_LOCK ){
    return "RECOVER-LOCK";
  }else{
    static char zName[15];
    sqlite3_snprintf(sizeof(zName), zName, "READ-LOCK[%d]",
                     lockIdx-WAL_READ_LOCK(0));
    return zName;
  }
}
#endif /*defined(SQLITE_TEST) || defined(SQLITE_DEBUG) */
    

/*
** Set or release locks on the WAL.  Locks are either shared or exclusive.
** A lock cannot be moved directly between shared and exclusive - it must go
** through the unlocked state first.
**
** In locking_mode=EXCLUSIVE, all of these routines become no-ops.
*/
static int walLockShared(Wal *pWal, int lockIdx){
  int rc;
  if( pWal->exclusiveMode ) return SQLITE_OK;
  rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
                        SQLITE_SHM_LOCK | SQLITE_SHM_SHARED);
  WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal,
            walLockName(lockIdx), rc ? "failed" : "ok"));
  VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
  return rc;
}
static void walUnlockShared(Wal *pWal, int lockIdx){
  if( pWal->exclusiveMode ) return;
  (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, 1,
                         SQLITE_SHM_UNLOCK | SQLITE_SHM_SHARED);
  WALTRACE(("WAL%p: release SHARED-%s\n", pWal, walLockName(lockIdx)));
}
static int walLockExclusive(Wal *pWal, int lockIdx, int n, int fBlock){
  int rc;
  if( pWal->exclusiveMode ) return SQLITE_OK;
  if( fBlock ) sqlite3OsFileControl(pWal->pDbFd, SQLITE_FCNTL_WAL_BLOCK, 0);
  rc = sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
                        SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE);
  WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
            walLockName(lockIdx), n, rc ? "failed" : "ok"));
  VVA_ONLY( pWal->lockError = (u8)(rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
  return rc;
}
static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
  if( pWal->exclusiveMode ) return;
  (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
                         SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
  WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
             walLockName(lockIdx), n));
}

/*
** Compute a hash on a page number.  The resulting hash value must land
** between 0 and (HASHTABLE_NSLOT-1).  The walHashNext() function advances
** the hash to the next value in the event of a collision.
*/
static int walHash(u32 iPage){
  assert( iPage>0 );
  assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 );
  return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1);
}
static int walNextHash(int iPriorHash){
  return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
}

/* 
** Return pointers to the hash table and page number array stored on
** page iHash of the wal-index. The wal-index is broken into 32KB pages
** numbered starting from 0.
**
** Set output variable *paHash to point to the start of the hash table
** in the wal-index file. Set *piZero to one less than the frame 
** number of the first frame indexed by this hash table. If a
** slot in the hash table is set to N, it refers to frame number 
** (*piZero+N) in the log.
**
** Finally, set *paPgno so that *paPgno[1] is the page number of the
** first frame indexed by the hash table, frame (*piZero+1).
*/
static int walHashGet(
  Wal *pWal,                      /* WAL handle */
  int iHash,                      /* Find the iHash'th table */
  volatile ht_slot **paHash,      /* OUT: Pointer to hash index */
  volatile u32 **paPgno,          /* OUT: Pointer to page number array */
  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
){
  int rc;                         /* Return code */
  volatile u32 *aPgno;

  rc = walIndexPage(pWal, iHash, &aPgno);
  assert( rc==SQLITE_OK || iHash>0 );

  if( rc==SQLITE_OK ){
    u32 iZero;
    volatile ht_slot *aHash;

    aHash = (volatile ht_slot *)&aPgno[HASHTABLE_NPAGE];
    if( iHash==0 ){
      aPgno = &aPgno[WALINDEX_HDR_SIZE/sizeof(u32)];
      iZero = 0;
    }else{
      iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE;
    }
  
    *paPgno = &aPgno[-1];
    *paHash = aHash;
    *piZero = iZero;
  }
  return rc;
}

/*
** Return the number of the wal-index page that contains the hash-table
** and page-number array that contain entries corresponding to WAL frame
** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages 
** are numbered starting from 0.
*/
static int walFramePage(u32 iFrame){
  int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE;
  assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE)
       && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE)
       && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE))
       && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)
       && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE))
  );
  return iHash;
}

/*
** Return the page number associated with frame iFrame in this WAL.
*/
static u32 walFramePgno(Wal *pWal, u32 iFrame){
  int iHash = walFramePage(iFrame);
  if( iHash==0 ){
    return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
  }
  return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE];
}

/*
** Remove entries from the hash table that point to WAL slots greater
** than pWal->hdr.mxFrame.
**
** This function is called whenever pWal->hdr.mxFrame is decreased due
** to a rollback or savepoint.
**
** At most only the hash table containing pWal->hdr.mxFrame needs to be
** updated.  Any later hash tables will be automatically cleared when
** pWal->hdr.mxFrame advances to the point where those hash tables are
** actually needed.
*/
static void walCleanupHash(Wal *pWal){
  volatile ht_slot *aHash = 0;    /* Pointer to hash table to clear */
  volatile u32 *aPgno = 0;        /* Page number array for hash table */
  u32 iZero = 0;                  /* frame == (aHash[x]+iZero) */
  int iLimit = 0;                 /* Zero values greater than this */
  int nByte;                      /* Number of bytes to zero in aPgno[] */
  int i;                          /* Used to iterate through aHash[] */

  assert( pWal->writeLock );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE-1 );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE_ONE+1 );

  if( pWal->hdr.mxFrame==0 ) return;

  /* Obtain pointers to the hash-table and page-number array containing 
  ** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed
  ** that the page said hash-table and array reside on is already mapped.
  */
  assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) );
  assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] );
  walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &aHash, &aPgno, &iZero);

  /* Zero all hash-table entries that correspond to frame numbers greater
  ** than pWal->hdr.mxFrame.
  */
  iLimit = pWal->hdr.mxFrame - iZero;
  assert( iLimit>0 );
  for(i=0; i<HASHTABLE_NSLOT; i++){
    if( aHash[i]>iLimit ){
      aHash[i] = 0;
    }
  }
  
  /* Zero the entries in the aPgno array that correspond to frames with
  ** frame numbers greater than pWal->hdr.mxFrame. 
  */
  nByte = (int)((char *)aHash - (char *)&aPgno[iLimit+1]);
  memset((void *)&aPgno[iLimit+1], 0, nByte);

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* Verify that the every entry in the mapping region is still reachable
  ** via the hash table even after the cleanup.
  */
  if( iLimit ){
    int j;           /* Loop counter */
    int iKey;        /* Hash key */
    for(j=1; j<=iLimit; j++){
      for(iKey=walHash(aPgno[j]); aHash[iKey]; iKey=walNextHash(iKey)){
        if( aHash[iKey]==j ) break;
      }
      assert( aHash[iKey]==j );
    }
  }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
}


/*
** Set an entry in the wal-index that will map database page number
** pPage into WAL frame iFrame.
*/
static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
  int rc;                         /* Return code */
  u32 iZero = 0;                  /* One less than frame number of aPgno[1] */
  volatile u32 *aPgno = 0;        /* Page number array */
  volatile ht_slot *aHash = 0;    /* Hash table */

  rc = walHashGet(pWal, walFramePage(iFrame), &aHash, &aPgno, &iZero);

  /* Assuming the wal-index file was successfully mapped, populate the
  ** page number array and hash table entry.
  */
  if( rc==SQLITE_OK ){
    int iKey;                     /* Hash table key */
    int idx;                      /* Value to write to hash-table slot */
    int nCollide;                 /* Number of hash collisions */

    idx = iFrame - iZero;
    assert( idx <= HASHTABLE_NSLOT/2 + 1 );
    
    /* If this is the first entry to be added to this hash-table, zero the
    ** entire hash table and aPgno[] array before proceeding. 
    */
    if( idx==1 ){
      int nByte = (int)((u8 *)&aHash[HASHTABLE_NSLOT] - (u8 *)&aPgno[1]);
      memset((void*)&aPgno[1], 0, nByte);
    }

    /* If the entry in aPgno[] is already set, then the previous writer
    ** must have exited unexpectedly in the middle of a transaction (after
    ** writing one or more dirty pages to the WAL to free up memory). 
    ** Remove the remnants of that writers uncommitted transaction from 
    ** the hash-table before writing any new entries.
    */
    if( aPgno[idx] ){
      walCleanupHash(pWal);
      assert( !aPgno[idx] );
    }

    /* Write the aPgno[] array entry and the hash-table slot. */
    nCollide = idx;
    for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
      if( (nCollide--)==0 ) return SQLITE_CORRUPT_BKPT;
    }
    aPgno[idx] = iPage;
    aHash[iKey] = (ht_slot)idx;

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
    /* Verify that the number of entries in the hash table exactly equals
    ** the number of entries in the mapping region.
    */
    {
      int i;           /* Loop counter */
      int nEntry = 0;  /* Number of entries in the hash table */
      for(i=0; i<HASHTABLE_NSLOT; i++){ if( aHash[i] ) nEntry++; }
      assert( nEntry==idx );
    }

    /* Verify that the every entry in the mapping region is reachable
    ** via the hash table.  This turns out to be a really, really expensive
    ** thing to check, so only do this occasionally - not on every
    ** iteration.
    */
    if( (idx&0x3ff)==0 ){
      int i;           /* Loop counter */
      for(i=1; i<=idx; i++){
        for(iKey=walHash(aPgno[i]); aHash[iKey]; iKey=walNextHash(iKey)){
          if( aHash[iKey]==i ) break;
        }
        assert( aHash[iKey]==i );
      }
    }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
  }


  return rc;
}


/*
** Recover the wal-index by reading the write-ahead log file. 
**
** This routine first tries to establish an exclusive lock on the
** wal-index to prevent other threads/processes from doing anything
** with the WAL or wal-index while recovery is running.  The
** WAL_RECOVER_LOCK is also held so that other threads will know
** that this thread is running recovery.  If unable to establish
** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
  int rc;                         /* Return Code */
  i64 nSize;                      /* Size of log file */
  u32 aFrameCksum[2] = {0, 0};
  int iLock;                      /* Lock offset to lock for checkpoint */
  int nLock;                      /* Number of locks to hold */

  /* Obtain an exclusive lock on all byte in the locking range not already
  ** locked by the caller. The caller is guaranteed to have locked the
  ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
  ** If successful, the same bytes that are locked here are unlocked before
  ** this function returns.
  */
  assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
  assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
  assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
  assert( pWal->writeLock );
  iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
  nLock = SQLITE_SHM_NLOCK - iLock;
  rc = walLockExclusive(pWal, iLock, nLock, 0);
  if( rc ){
    return rc;
  }
  WALTRACE(("WAL%p: recovery begin...\n", pWal));

  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));

  rc = sqlite3OsFileSize(pWal->pWalFd, &nSize);
  if( rc!=SQLITE_OK ){
    goto recovery_error;
  }

  if( nSize>WAL_HDRSIZE ){
    u8 aBuf[WAL_HDRSIZE];         /* Buffer to load WAL header into */
    u8 *aFrame = 0;               /* Malloc'd buffer to load entire frame */
    int szFrame;                  /* Number of bytes in buffer aFrame[] */
    u8 *aData;                    /* Pointer to data part of aFrame buffer */
    int iFrame;                   /* Index of last frame read */
    i64 iOffset;                  /* Next offset to read from log file */
    int szPage;                   /* Page size according to the log */
    u32 magic;                    /* Magic value read from WAL header */
    u32 version;                  /* Magic value read from WAL header */
    int isValid;                  /* True if this frame is valid */

    /* Read in the WAL header. */
    rc = sqlite3OsRead(pWal->pWalFd, aBuf, WAL_HDRSIZE, 0);
    if( rc!=SQLITE_OK ){
      goto recovery_error;
    }

    /* If the database page size is not a power of two, or is greater than
    ** SQLITE_MAX_PAGE_SIZE, conclude that the WAL file contains no valid 
    ** data. Similarly, if the 'magic' value is invalid, ignore the whole
    ** WAL file.
    */
    magic = sqlite3Get4byte(&aBuf[0]);
    szPage = sqlite3Get4byte(&aBuf[8]);
    if( (magic&0xFFFFFFFE)!=WAL_MAGIC 
     || szPage&(szPage-1) 
     || szPage>SQLITE_MAX_PAGE_SIZE 
     || szPage<512 
    ){
      goto finished;
    }
    pWal->hdr.bigEndCksum = (u8)(magic&0x00000001);
    pWal->szPage = szPage;
    pWal->nCkpt = sqlite3Get4byte(&aBuf[12]);
    memcpy(&pWal->hdr.aSalt, &aBuf[16], 8);

    /* Verify that the WAL header checksum is correct */
    walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN, 
        aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum
    );
    if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24])
     || pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28])
    ){
      goto finished;
    }

    /* Verify that the version number on the WAL format is one that
    ** are able to understand */
    version = sqlite3Get4byte(&aBuf[4]);
    if( version!=WAL_MAX_VERSION ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto finished;
    }

    /* Malloc a buffer to read frames into. */
    szFrame = szPage + WAL_FRAME_HDRSIZE;
    aFrame = (u8 *)sqlite3_malloc64(szFrame);
    if( !aFrame ){
      rc = SQLITE_NOMEM;
      goto recovery_error;
    }
    aData = &aFrame[WAL_FRAME_HDRSIZE];

    /* Read all frames from the log file. */
    iFrame = 0;
    for(iOffset=WAL_HDRSIZE; (iOffset+szFrame)<=nSize; iOffset+=szFrame){
      u32 pgno;                   /* Database page number for frame */
      u32 nTruncate;              /* dbsize field from frame header */

      /* Read and decode the next log frame. */
      iFrame++;
      rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
      if( rc!=SQLITE_OK ) break;
      isValid = walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame);
      if( !isValid ) break;
      rc = walIndexAppend(pWal, iFrame, pgno);
      if( rc!=SQLITE_OK ) break;

      /* If nTruncate is non-zero, this is a commit record. */
      if( nTruncate ){
        pWal->hdr.mxFrame = iFrame;
        pWal->hdr.nPage = nTruncate;
        pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
        testcase( szPage<=32768 );
        testcase( szPage>=65536 );
        aFrameCksum[0] = pWal->hdr.aFrameCksum[0];
        aFrameCksum[1] = pWal->hdr.aFrameCksum[1];
      }
    }

    sqlite3_free(aFrame);
  }

finished:
  if( rc==SQLITE_OK ){
    volatile WalCkptInfo *pInfo;
    int i;
    pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
    pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
    walIndexWriteHdr(pWal);

    /* Reset the checkpoint-header. This is safe because this thread is 
    ** currently holding locks that exclude all other readers, writers and
    ** checkpointers.
    */
    pInfo = walCkptInfo(pWal);
    pInfo->nBackfill = 0;
    pInfo->aReadMark[0] = 0;
    for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
    if( pWal->hdr.mxFrame ) pInfo->aReadMark[1] = pWal->hdr.mxFrame;

    /* If more than one frame was recovered from the log file, report an
    ** event via sqlite3_log(). This is to help with identifying performance
    ** problems caused by applications routinely shutting down without
    ** checkpointing the log file.
    */
    if( pWal->hdr.nPage ){
      sqlite3_log(SQLITE_NOTICE_RECOVER_WAL,
          "recovered %d frames from WAL file %s",
          pWal->hdr.mxFrame, pWal->zWalName
      );
    }
  }

recovery_error:
  WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
  walUnlockExclusive(pWal, iLock, nLock);
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){
  if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
    int i;
    for(i=0; i<pWal->nWiData; i++){
      sqlite3_free((void *)pWal->apWiData[i]);
      pWal->apWiData[i] = 0;
    }
  }else{
    sqlite3OsShmUnmap(pWal->pDbFd, isDelete);
  }
}

/* 
** Open a connection to the WAL file zWalName. The database file must 
** already be opened on connection pDbFd. The buffer that zWalName points
** to must remain valid for the lifetime of the returned Wal* handle.
**
** A SHARED lock should be held on the database file when this function
** is called. The purpose of this SHARED lock is to prevent any other
** client from unlinking the WAL or wal-index file. If another process
** were to do this just after this client opened one of these files, the
** system would be badly broken.
**
** If the log file is successfully opened, SQLITE_OK is returned and 
** *ppWal is set to point to a new WAL handle. If an error occurs,
** an SQLite error code is returned and *ppWal is left unmodified.
*/
SQLITE_PRIVATE int sqlite3WalOpen(
  sqlite3_vfs *pVfs,              /* vfs module to open wal and wal-index */
  sqlite3_file *pDbFd,            /* The open database file */
  const char *zWalName,           /* Name of the WAL file */
  int bNoShm,                     /* True to run in heap-memory mode */
  i64 mxWalSize,                  /* Truncate WAL to this size on reset */
  Wal **ppWal                     /* OUT: Allocated Wal handle */
){
  int rc;                         /* Return Code */
  Wal *pRet;                      /* Object to allocate and return */
  int flags;                      /* Flags passed to OsOpen() */

  assert( zWalName && zWalName[0] );
  assert( pDbFd );

  /* In the amalgamation, the os_unix.c and os_win.c source files come before
  ** this source file.  Verify that the #defines of the locking byte offsets
  ** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.
  */
#ifdef WIN_SHM_BASE
  assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
#ifdef UNIX_SHM_BASE
  assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif


  /* Allocate an instance of struct Wal to return. */
  *ppWal = 0;
  pRet = (Wal*)sqlite3MallocZero(sizeof(Wal) + pVfs->szOsFile);
  if( !pRet ){
    return SQLITE_NOMEM;
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;
  pRet->readLock = -1;
  pRet->mxWalSize = mxWalSize;
  pRet->zWalName = zWalName;
  pRet->syncHeader = 1;
  pRet->padToSectorBoundary = 1;
  pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE);

  /* Open file handle on the write-ahead log file. */
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
  rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
  if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
    pRet->readOnly = WAL_RDONLY;
  }

  if( rc!=SQLITE_OK ){
    walIndexClose(pRet, 0);
    sqlite3OsClose(pRet->pWalFd);
    sqlite3_free(pRet);
  }else{
    int iDC = sqlite3OsDeviceCharacteristics(pDbFd);
    if( iDC & SQLITE_IOCAP_SEQUENTIAL ){ pRet->syncHeader = 0; }
    if( iDC & SQLITE_IOCAP_POWERSAFE_OVERWRITE ){
      pRet->padToSectorBoundary = 0;
    }
    *ppWal = pRet;
    WALTRACE(("WAL%d: opened\n", pRet));
  }
  return rc;
}

#if 0
/*
** Change the size to which the WAL file is trucated on each reset.
*/
SQLITE_PRIVATE void sqlite3WalLimit(Wal *pWal, i64 iLimit){
  if( pWal ) pWal->mxWalSize = iLimit;
}
#endif

/*
** Find the smallest page number out of all pages held in the WAL that
** has not been returned by any prior invocation of this method on the
** same WalIterator object.   Write into *piFrame the frame index where
** that page was last written into the WAL.  Write into *piPage the page
** number.
**
** Return 0 on success.  If there are no pages in the WAL with a page
** number larger than *piPage, then return 1.
*/
static int walIteratorNext(
  WalIterator *p,               /* Iterator */
  u32 *piPage,                  /* OUT: The page number of the next page */
  u32 *piFrame                  /* OUT: Wal frame index of next page */
){
  u32 iMin;                     /* Result pgno must be greater than iMin */
  u32 iRet = 0xFFFFFFFF;        /* 0xffffffff is never a valid page number */
  int i;                        /* For looping through segments */

  iMin = p->iPrior;
  assert( iMin<0xffffffff );
  for(i=p->nSegment-1; i>=0; i--){
    struct WalSegment *pSegment = &p->aSegment[i];
    while( pSegment->iNext<pSegment->nEntry ){
      u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
      if( iPg>iMin ){
        if( iPg<iRet ){
          iRet = iPg;
          *piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext];
        }
        break;
      }
      pSegment->iNext++;
    }
  }

  *piPage = p->iPrior = iRet;
  return (iRet==0xFFFFFFFF);
}

/*
** This function merges two sorted lists into a single sorted list.
**
** aLeft[] and aRight[] are arrays of indices.  The sort key is
** aContent[aLeft[]] and aContent[aRight[]].  Upon entry, the following
** is guaranteed for all J<K:
**
**        aContent[aLeft[J]] < aContent[aLeft[K]]
**        aContent[aRight[J]] < aContent[aRight[K]]
**
** This routine overwrites aRight[] with a new (probably longer) sequence
** of indices such that the aRight[] contains every index that appears in
** either aLeft[] or the old aRight[] and such that the second condition
** above is still met.
**
** The aContent[aLeft[X]] values will be unique for all X.  And the
** aContent[aRight[X]] values will be unique too.  But there might be
** one or more combinations of X and Y such that
**
**      aLeft[X]!=aRight[Y]  &&  aContent[aLeft[X]] == aContent[aRight[Y]]
**
** When that happens, omit the aLeft[X] and use the aRight[Y] index.
*/
static void walMerge(
  const u32 *aContent,            /* Pages in wal - keys for the sort */
  ht_slot *aLeft,                 /* IN: Left hand input list */
  int nLeft,                      /* IN: Elements in array *paLeft */
  ht_slot **paRight,              /* IN/OUT: Right hand input list */
  int *pnRight,                   /* IN/OUT: Elements in *paRight */
  ht_slot *aTmp                   /* Temporary buffer */
){
  int iLeft = 0;                  /* Current index in aLeft */
  int iRight = 0;                 /* Current index in aRight */
  int iOut = 0;                   /* Current index in output buffer */
  int nRight = *pnRight;
  ht_slot *aRight = *paRight;

  assert( nLeft>0 && nRight>0 );
  while( iRight<nRight || iLeft<nLeft ){
    ht_slot logpage;
    Pgno dbpage;

    if( (iLeft<nLeft) 
     && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
    ){
      logpage = aLeft[iLeft++];
    }else{
      logpage = aRight[iRight++];
    }
    dbpage = aContent[logpage];

    aTmp[iOut++] = logpage;
    if( iLeft<nLeft && aContent[aLeft[iLeft]]==dbpage ) iLeft++;

    assert( iLeft>=nLeft || aContent[aLeft[iLeft]]>dbpage );
    assert( iRight>=nRight || aContent[aRight[iRight]]>dbpage );
  }

  *paRight = aLeft;
  *pnRight = iOut;
  memcpy(aLeft, aTmp, sizeof(aTmp[0])*iOut);
}

/*
** Sort the elements in list aList using aContent[] as the sort key.
** Remove elements with duplicate keys, preferring to keep the
** larger aList[] values.
**
** The aList[] entries are indices into aContent[].  The values in
** aList[] are to be sorted so that for all J<K:
**
**      aContent[aList[J]] < aContent[aList[K]]
**
** For any X and Y such that
**
**      aContent[aList[X]] == aContent[aList[Y]]
**
** Keep the larger of the two values aList[X] and aList[Y] and discard
** the smaller.
*/
static void walMergesort(
  const u32 *aContent,            /* Pages in wal */
  ht_slot *aBuffer,               /* Buffer of at least *pnList items to use */
  ht_slot *aList,                 /* IN/OUT: List to sort */
  int *pnList                     /* IN/OUT: Number of elements in aList[] */
){
  struct Sublist {
    int nList;                    /* Number of elements in aList */
    ht_slot *aList;               /* Pointer to sub-list content */
  };

  const int nList = *pnList;      /* Size of input list */
  int nMerge = 0;                 /* Number of elements in list aMerge */
  ht_slot *aMerge = 0;            /* List to be merged */
  int iList;                      /* Index into input list */
  u32 iSub = 0;                   /* Index into aSub array */
  struct Sublist aSub[13];        /* Array of sub-lists */

  memset(aSub, 0, sizeof(aSub));
  assert( nList<=HASHTABLE_NPAGE && nList>0 );
  assert( HASHTABLE_NPAGE==(1<<(ArraySize(aSub)-1)) );

  for(iList=0; iList<nList; iList++){
    nMerge = 1;
    aMerge = &aList[iList];
    for(iSub=0; iList & (1<<iSub); iSub++){
      struct Sublist *p;
      assert( iSub<ArraySize(aSub) );
      p = &aSub[iSub];
      assert( p->aList && p->nList<=(1<<iSub) );
      assert( p->aList==&aList[iList&~((2<<iSub)-1)] );
      walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
    }
    aSub[iSub].aList = aMerge;
    aSub[iSub].nList = nMerge;
  }

  for(iSub++; iSub<ArraySize(aSub); iSub++){
    if( nList & (1<<iSub) ){
      struct Sublist *p;
      assert( iSub<ArraySize(aSub) );
      p = &aSub[iSub];
      assert( p->nList<=(1<<iSub) );
      assert( p->aList==&aList[nList&~((2<<iSub)-1)] );
      walMerge(aContent, p->aList, p->nList, &aMerge, &nMerge, aBuffer);
    }
  }
  assert( aMerge==aList );
  *pnList = nMerge;

#ifdef SQLITE_DEBUG
  {
    int i;
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }
  }
#endif
}

/* 
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);
}

/*
** Construct a WalInterator object that can be used to loop over all 
** pages in the WAL in ascending order. The caller must hold the checkpoint
** lock.
**
** On success, make *pp point to the newly allocated WalInterator object
** return SQLITE_OK. Otherwise, return an error code. If this routine
** returns an error, the value of *pp is undefined.
**
** The calling routine should invoke walIteratorFree() to destroy the
** WalIterator object when it has finished with it.
*/
static int walIteratorInit(Wal *pWal, WalIterator **pp){
  WalIterator *p;                 /* Return value */
  int nSegment;                   /* Number of segments to merge */
  u32 iLast;                      /* Last frame in log */
  int nByte;                      /* Number of bytes to allocate */
  int i;                          /* Iterator variable */
  ht_slot *aTmp;                  /* Temp space used by merge-sort */
  int rc = SQLITE_OK;             /* Return Code */

  /* This routine only runs while holding the checkpoint lock. And
  ** it only runs if there is actually content in the log (mxFrame>0).
  */
  assert( pWal->ckptLock && pWal->hdr.mxFrame>0 );
  iLast = pWal->hdr.mxFrame;

  /* Allocate space for the WalIterator object. */
  nSegment = walFramePage(iLast) + 1;
  nByte = sizeof(WalIterator) 
        + (nSegment-1)*sizeof(struct WalSegment)
        + iLast*sizeof(ht_slot);
  p = (WalIterator *)sqlite3_malloc64(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }
  memset(p, 0, nByte);
  p->nSegment = nSegment;

  /* Allocate temporary space used by the merge-sort routine. This block
  ** of memory will be freed before this function returns.
  */
  aTmp = (ht_slot *)sqlite3_malloc64(
      sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
  );
  if( !aTmp ){
    rc = SQLITE_NOMEM;
  }

  for(i=0; rc==SQLITE_OK && i<nSegment; i++){
    volatile ht_slot *aHash;
    u32 iZero;
    volatile u32 *aPgno;

    rc = walHashGet(pWal, i, &aHash, &aPgno, &iZero);
    if( rc==SQLITE_OK ){
      int j;                      /* Counter variable */
      int nEntry;                 /* Number of entries in this segment */
      ht_slot *aIndex;            /* Sorted index for this segment */

      aPgno++;
      if( (i+1)==nSegment ){
        nEntry = (int)(iLast - iZero);
      }else{
        nEntry = (int)((u32*)aHash - (u32*)aPgno);
      }
      aIndex = &((ht_slot *)&p->aSegment[p->nSegment])[iZero];
      iZero++;
  
      for(j=0; j<nEntry; j++){
        aIndex[j] = (ht_slot)j;
      }
      walMergesort((u32 *)aPgno, aTmp, aIndex, &nEntry);
      p->aSegment[i].iZero = iZero;
      p->aSegment[i].nEntry = nEntry;
      p->aSegment[i].aIndex = aIndex;
      p->aSegment[i].aPgno = (u32 *)aPgno;
    }
  }
  sqlite3_free(aTmp);

  if( rc!=SQLITE_OK ){
    walIteratorFree(p);
  }
  *pp = p;
  return rc;
}

/*
** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and
** n. If the attempt fails and parameter xBusy is not NULL, then it is a
** busy-handler function. Invoke it and retry the lock until either the
** lock is successfully obtained or the busy-handler returns 0.
*/
static int walBusyLock(
  Wal *pWal,                      /* WAL connection */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int lockIdx,                    /* Offset of first byte to lock */
  int n                           /* Number of bytes to lock */
){
  int rc;
  do {
    rc = walLockExclusive(pWal, lockIdx, n, 0);
  }while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) );
  return rc;
}

/*
** The cache of the wal-index header must be valid to call this function.
** Return the page-size in bytes used by the database.
*/
static int walPagesize(Wal *pWal){
  return (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
}

/*
** The following is guaranteed when this function is called:
**
**   a) the WRITER lock is held,
**   b) the entire log file has been checkpointed, and
**   c) any existing readers are reading exclusively from the database
**      file - there are no readers that may attempt to read a frame from
**      the log file.
**
** This function updates the shared-memory structures so that the next
** client to write to the database (which may be this one) does so by
** writing frames into the start of the log file.
**
** The value of parameter salt1 is used as the aSalt[1] value in the 
** new wal-index header. It should be passed a pseudo-random value (i.e. 
** one obtained from sqlite3_randomness()).
*/
static void walRestartHdr(Wal *pWal, u32 salt1){
  volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
  int i;                          /* Loop counter */
  u32 *aSalt = pWal->hdr.aSalt;   /* Big-endian salt values */
  pWal->nCkpt++;
  pWal->hdr.mxFrame = 0;
  sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
  memcpy(&pWal->hdr.aSalt[1], &salt1, 4);
  walIndexWriteHdr(pWal);
  pInfo->nBackfill = 0;
  pInfo->aReadMark[1] = 0;
  for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
  assert( pInfo->aReadMark[0]==0 );
}

/*
** Copy as much content as we can from the WAL back into the database file
** in response to an sqlite3_wal_checkpoint() request or the equivalent.
**
** The amount of information copies from WAL to database might be limited
** by active readers.  This routine will never overwrite a database page
** that a concurrent reader might be using.
**
** All I/O barrier operations (a.k.a fsyncs) occur in this routine when
** SQLite is in WAL-mode in synchronous=NORMAL.  That means that if 
** checkpoints are always run by a background thread or background 
** process, foreground threads will never block on a lengthy fsync call.
**
** Fsync is called on the WAL before writing content out of the WAL and
** into the database.  This ensures that if the new content is persistent
** in the WAL and can be recovered following a power-loss or hard reset.
**
** Fsync is also called on the database file if (and only if) the entire
** WAL content is copied into the database file.  This second fsync makes
** it safe to delete the WAL since the new content will persist in the
** database file.
**
** This routine uses and updates the nBackfill field of the wal-index header.
** This is the only routine that will increase the value of nBackfill.  
** (A WAL reset or recovery will revert nBackfill to zero, but not increase
** its value.)
**
** The caller must be holding sufficient locks to ensure that no other
** checkpoint is running (in any other thread or process) at the same
** time.
*/
static int walCheckpoint(
  Wal *pWal,                      /* Wal connection */
  int eMode,                      /* One of PASSIVE, FULL or RESTART */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags for OsSync() (or 0) */
  u8 *zBuf                        /* Temporary buffer to use */
){
  int rc = SQLITE_OK;             /* Return code */
  int szPage;                     /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  u32 mxPage;                     /* Max database page to write */
  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  szPage = walPagesize(pWal);
  testcase( szPage<=32768 );
  testcase( szPage>=65536 );
  pInfo = walCkptInfo(pWal);
  if( pInfo->nBackfill<pWal->hdr.mxFrame ){

    /* Allocate the iterator */
    rc = walIteratorInit(pWal, &pIter);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    assert( pIter );

    /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
    ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
    assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );

    /* Compute in mxSafeFrame the index of the last frame of the WAL that is
    ** safe to write into the database.  Frames beyond mxSafeFrame might
    ** overwrite database pages that are in use by active readers and thus
    ** cannot be backfilled from the WAL.
    */
    mxSafeFrame = pWal->hdr.mxFrame;
    mxPage = pWal->hdr.nPage;
    for(i=1; i<WAL_NREADER; i++){
      /* Thread-sanitizer reports that the following is an unsafe read,
      ** as some other thread may be in the process of updating the value
      ** of the aReadMark[] slot. The assumption here is that if that is
      ** happening, the other client may only be increasing the value,
      ** not decreasing it. So assuming either that either the "old" or
      ** "new" version of the value is read, and not some arbitrary value
      ** that would never be written by a real client, things are still 
      ** safe.  */
      u32 y = pInfo->aReadMark[i];
      if( mxSafeFrame>y ){
        assert( y<=pWal->hdr.mxFrame );
        rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(i), 1);
        if( rc==SQLITE_OK ){
          pInfo->aReadMark[i] = (i==1 ? mxSafeFrame : READMARK_NOT_USED);
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
        }else if( rc==SQLITE_BUSY ){
          mxSafeFrame = y;
          xBusy = 0;
        }else{
          goto walcheckpoint_out;
        }
      }
    }

    if( pInfo->nBackfill<mxSafeFrame
     && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0),1))==SQLITE_OK
    ){
      i64 nSize;                    /* Current size of database file */
      u32 nBackfill = pInfo->nBackfill;

      /* Sync the WAL to disk */
      if( sync_flags ){
        rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
      }

      /* If the database may grow as a result of this checkpoint, hint
      ** about the eventual size of the db file to the VFS layer.
      */
      if( rc==SQLITE_OK ){
        i64 nReq = ((i64)mxPage * szPage);
        rc = sqlite3OsFileSize(pWal->pDbFd, &nSize);
        if( rc==SQLITE_OK && nSize<nReq ){
          sqlite3OsFileControlHint(pWal->pDbFd, SQLITE_FCNTL_SIZE_HINT, &nReq);
        }
      }


      /* Iterate through the contents of the WAL, copying data to the db file */
      while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
        i64 iOffset;
        assert( walFramePgno(pWal, iFrame)==iDbpage );
        if( iFrame<=nBackfill || iFrame>mxSafeFrame || iDbpage>mxPage ){
          continue;
        }
        iOffset = walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE;
        /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL file */
        rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, iOffset);
        if( rc!=SQLITE_OK ) break;
        iOffset = (iDbpage-1)*(i64)szPage;
        testcase( IS_BIG_INT(iOffset) );
        rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, iOffset);
        if( rc!=SQLITE_OK ) break;
      }

      /* If work was actually accomplished... */
      if( rc==SQLITE_OK ){
        if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
          i64 szDb = pWal->hdr.nPage*(i64)szPage;
          testcase( IS_BIG_INT(szDb) );
          rc = sqlite3OsTruncate(pWal->pDbFd, szDb);
          if( rc==SQLITE_OK && sync_flags ){
            rc = sqlite3OsSync(pWal->pDbFd, sync_flags);
          }
        }
        if( rc==SQLITE_OK ){
          pInfo->nBackfill = mxSafeFrame;
        }
      }

      /* Release the reader lock held while backfilling */
      walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1);
    }

    if( rc==SQLITE_BUSY ){
      /* Reset the return code so as not to report a checkpoint failure
      ** just because there are active readers.  */
      rc = SQLITE_OK;
    }
  }

  /* If this is an SQLITE_CHECKPOINT_RESTART or TRUNCATE operation, and the
  ** entire wal file has been copied into the database file, then block 
  ** until all readers have finished using the wal file. This ensures that 
  ** the next process to write to the database restarts the wal file.
  */
  if( rc==SQLITE_OK && eMode!=SQLITE_CHECKPOINT_PASSIVE ){
    assert( pWal->writeLock );
    if( pInfo->nBackfill<pWal->hdr.mxFrame ){
      rc = SQLITE_BUSY;
    }else if( eMode>=SQLITE_CHECKPOINT_RESTART ){
      u32 salt1;
      sqlite3_randomness(4, &salt1);
      assert( pInfo->nBackfill==pWal->hdr.mxFrame );
      rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1);
      if( rc==SQLITE_OK ){
        if( eMode==SQLITE_CHECKPOINT_TRUNCATE ){
          /* IMPLEMENTATION-OF: R-44699-57140 This mode works the same way as
          ** SQLITE_CHECKPOINT_RESTART with the addition that it also
          ** truncates the log file to zero bytes just prior to a
          ** successful return.
          **
          ** In theory, it might be safe to do this without updating the
          ** wal-index header in shared memory, as all subsequent reader or
          ** writer clients should see that the entire log file has been
          ** checkpointed and behave accordingly. This seems unsafe though,
          ** as it would leave the system in a state where the contents of
          ** the wal-index header do not match the contents of the 
          ** file-system. To avoid this, update the wal-index header to
          ** indicate that the log file contains zero valid frames.  */
          walRestartHdr(pWal, salt1);
          rc = sqlite3OsTruncate(pWal->pWalFd, 0);
        }
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }
    }
  }

 walcheckpoint_out:
  walIteratorFree(pIter);
  return rc;
}

/*
** If the WAL file is currently larger than nMax bytes in size, truncate
** it to exactly nMax bytes. If an error occurs while doing so, ignore it.
*/
static void walLimitSize(Wal *pWal, i64 nMax){
  i64 sz;
  int rx;
  rx = sqlite3OsFileSize(pWal->pWalFd, &sz);
  if( rx==SQLITE_OK && (sz > nMax ) ){
    rx = sqlite3OsTruncate(pWal->pWalFd, nMax);
  }
  if( rx ){
    sqlite3_log(rx, "cannot limit WAL size: %s", pWal->zWalName);
  }
}

/*
** Close a connection to a log file.
*/
SQLITE_PRIVATE int sqlite3WalClose(
  Wal *pWal,                      /* Wal to close */
  int sync_flags,                 /* Flags to pass to OsSync() (or 0) */
  int nBuf,
  u8 *zBuf                        /* Buffer of at least nBuf bytes */
){
  int rc = SQLITE_OK;
  if( pWal ){
    int isDelete = 0;             /* True to unlink wal and wal-index files */

    /* If an EXCLUSIVE lock can be obtained on the database file (using the
    ** ordinary, rollback-mode locking methods, this guarantees that the
    ** connection associated with this log file is the only connection to
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
        pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
      }
      rc = sqlite3WalCheckpoint(
          pWal, SQLITE_CHECKPOINT_PASSIVE, 0, 0, sync_flags, nBuf, zBuf, 0, 0
      );
      if( rc==SQLITE_OK ){
        int bPersist = -1;
        sqlite3OsFileControlHint(
            pWal->pDbFd, SQLITE_FCNTL_PERSIST_WAL, &bPersist
        );
        if( bPersist!=1 ){
          /* Try to delete the WAL file if the checkpoint completed and
          ** fsyned (rc==SQLITE_OK) and if we are not in persistent-wal
          ** mode (!bPersist) */
          isDelete = 1;
        }else if( pWal->mxWalSize>=0 ){
          /* Try to truncate the WAL file to zero bytes if the checkpoint
          ** completed and fsynced (rc==SQLITE_OK) and we are in persistent
          ** WAL mode (bPersist) and if the PRAGMA journal_size_limit is a
          ** non-negative value (pWal->mxWalSize>=0).  Note that we truncate
          ** to zero bytes as truncating to the journal_size_limit might
          ** leave a corrupt WAL file on disk. */
          walLimitSize(pWal, 0);
        }
      }
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
      sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
    }
    WALTRACE(("WAL%p: closed\n", pWal));
    sqlite3_free((void *)pWal->apWiData);
    sqlite3_free(pWal);
  }
  return rc;
}

/*
** Try to read the wal-index header.  Return 0 on success and 1 if
** there is a problem.
**
** The wal-index is in shared memory.  Another thread or process might
** be writing the header at the same time this procedure is trying to
** read it, which might result in inconsistency.  A dirty read is detected
** by verifying that both copies of the header are the same and also by
** a checksum on the header.
**
** If and only if the read is consistent and the header is different from
** pWal->hdr, then pWal->hdr is updated to the content of the new header
** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
static int walIndexTryHdr(Wal *pWal, int *pChanged){
  u32 aCksum[2];                  /* Checksum on the header content */
  WalIndexHdr h1, h2;             /* Two copies of the header content */
  WalIndexHdr volatile *aHdr;     /* Header in shared memory */

  /* The first page of the wal-index must be mapped at this point. */
  assert( pWal->nWiData>0 && pWal->apWiData[0] );

  /* Read the header. This might happen concurrently with a write to the
  ** same area of shared memory on a different CPU in a SMP,
  ** meaning it is possible that an inconsistent snapshot is read
  ** from the file. If this happens, return non-zero.
  **
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.
  */
  aHdr = walIndexHdr(pWal);
  memcpy(&h1, (void *)&aHdr[0], sizeof(h1));
  walShmBarrier(pWal);
  memcpy(&h2, (void *)&aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){
    return 1;   /* Malformed header - probably all zeros */
  }
  walChecksumBytes(1, (u8*)&h1, sizeof(h1)-sizeof(h1.aCksum), 0, aCksum);
  if( aCksum[0]!=h1.aCksum[0] || aCksum[1]!=h1.aCksum[1] ){
    return 1;   /* Checksum does not match */
  }

  if( memcmp(&pWal->hdr, &h1, sizeof(WalIndexHdr)) ){
    *pChanged = 1;
    memcpy(&pWal->hdr, &h1, sizeof(WalIndexHdr));
    pWal->szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
    testcase( pWal->szPage<=32768 );
    testcase( pWal->szPage>=65536 );
  }

  /* The header was successfully read. Return zero. */
  return 0;
}

/*
** Read the wal-index header from the wal-index and into pWal->hdr.
** If the wal-header appears to be corrupt, try to reconstruct the
** wal-index from the WAL before returning.
**
** Set *pChanged to 1 if the wal-index header value in pWal->hdr is
** changed by this operation.  If pWal->hdr is unchanged, set *pChanged
** to 0.
**
** If the wal-index header is successfully read, return SQLITE_OK. 
** Otherwise an SQLite error code.
*/
static int walIndexReadHdr(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int badHdr;                     /* True if a header read failed */
  volatile u32 *page0;            /* Chunk of wal-index containing header */

  /* Ensure that page 0 of the wal-index (the page that contains the 
  ** wal-index header) is mapped. Return early if an error occurs here.
  */
  assert( pChanged );
  rc = walIndexPage(pWal, 0, &page0);
  if( rc!=SQLITE_OK ){
    return rc;
  };
  assert( page0 || pWal->writeLock==0 );

  /* If the first page of the wal-index has been mapped, try to read the
  ** wal-index header immediately, without holding any lock. This usually
  ** works, but may fail if the wal-index header is corrupt or currently 
  ** being modified by another thread or process.
  */
  badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1);

  /* If the first attempt failed, it might have been due to a race
  ** with a writer.  So get a WRITE lock and try again.
  */
  assert( badHdr==0 || pWal->writeLock==0 );
  if( badHdr ){
    if( pWal->readOnly & WAL_SHM_RDONLY ){
      if( SQLITE_OK==(rc = walLockShared(pWal, WAL_WRITE_LOCK)) ){
        walUnlockShared(pWal, WAL_WRITE_LOCK);
        rc = SQLITE_READONLY_RECOVERY;
      }
    }else if( SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1, 1)) ){
      pWal->writeLock = 1;
      if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
        badHdr = walIndexTryHdr(pWal, pChanged);
        if( badHdr ){
          /* If the wal-index header is still malformed even while holding
          ** a WRITE lock, it can only mean that the header is corrupted and
          ** needs to be reconstructed.  So run recovery to do exactly that.
          */
          rc = walIndexRecover(pWal);
          *pChanged = 1;
        }
      }
      pWal->writeLock = 0;
      walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    }
  }

  /* If the header is read successfully, check the version number to make
  ** sure the wal-index was not constructed with some future format that
  ** this version of SQLite cannot understand.
  */
  if( badHdr==0 && pWal->hdr.iVersion!=WALINDEX_MAX_VERSION ){
    rc = SQLITE_CANTOPEN_BKPT;
  }

  return rc;
}

/*
** This is the value that walTryBeginRead returns when it needs to
** be retried.
*/
#define WAL_RETRY  (-1)

/*
** Attempt to start a read transaction.  This might fail due to a race or
** other transient condition.  When that happens, it returns WAL_RETRY to
** indicate to the caller that it is safe to retry immediately.
**
** On success return SQLITE_OK.  On a permanent failure (such an
** I/O error or an SQLITE_BUSY because another process is running
** recovery) return a positive error code.
**
** The useWal parameter is true to force the use of the WAL and disable
** the case where the WAL is bypassed because it has been completely
** checkpointed.  If useWal==0 then this routine calls walIndexReadHdr() 
** to make a copy of the wal-index header into pWal->hdr.  If the 
** wal-index header has changed, *pChanged is set to 1 (as an indication 
** to the caller that the local paget cache is obsolete and needs to be 
** flushed.)  When useWal==1, the wal-index header is assumed to already
** be loaded and the pChanged parameter is unused.
**
** The caller must set the cnt parameter to the number of prior calls to
** this routine during the current read attempt that returned WAL_RETRY.
** This routine will start taking more aggressive measures to clear the
** race conditions after multiple WAL_RETRY returns, and after an excessive
** number of errors will ultimately return SQLITE_PROTOCOL.  The
** SQLITE_PROTOCOL return indicates that some other process has gone rogue
** and is not honoring the locking protocol.  There is a vanishingly small
** chance that SQLITE_PROTOCOL could be returned because of a run of really
** bad luck when there is lots of contention for the wal-index, but that
** possibility is so small that it can be safely neglected, we believe.
**
** On success, this routine obtains a read lock on 
** WAL_READ_LOCK(pWal->readLock).  The pWal->readLock integer is
** in the range 0 <= pWal->readLock < WAL_NREADER.  If pWal->readLock==(-1)
** that means the Wal does not hold any read lock.  The reader must not
** access any database page that is modified by a WAL frame up to and
** including frame number aReadMark[pWal->readLock].  The reader will
** use WAL frames up to and including pWal->hdr.mxFrame if pWal->readLock>0
** Or if pWal->readLock==0, then the reader will ignore the WAL
** completely and get all content directly from the database file.
** If the useWal parameter is 1 then the WAL will never be ignored and
** this routine will always set pWal->readLock>0 on success.
** When the read transaction is completed, the caller must release the
** lock on WAL_READ_LOCK(pWal->readLock) and set pWal->readLock to -1.
**
** This routine uses the nBackfill and aReadMark[] fields of the header
** to select a particular WAL_READ_LOCK() that strives to let the
** checkpoint process do as much work as possible.  This routine might
** update values of the aReadMark[] array in the header, but if it does
** so it takes care to hold an exclusive lock on the corresponding
** WAL_READ_LOCK() while changing values.
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
  volatile WalCkptInfo *pInfo;    /* Checkpoint information in wal-index */
  u32 mxReadMark;                 /* Largest aReadMark[] value */
  int mxI;                        /* Index of largest aReadMark[] value */
  int i;                          /* Loop counter */
  int rc = SQLITE_OK;             /* Return code  */

  assert( pWal->readLock<0 );     /* Not currently locked */

  /* Take steps to avoid spinning forever if there is a protocol error.
  **
  ** Circumstances that cause a RETRY should only last for the briefest
  ** instances of time.  No I/O or other system calls are done while the
  ** locks are held, so the locks should not be held for very long. But 
  ** if we are unlucky, another process that is holding a lock might get
  ** paged out or take a page-fault that is time-consuming to resolve, 
  ** during the few nanoseconds that it is holding the lock.  In that case,
  ** it might take longer than normal for the lock to free.
  **
  ** After 5 RETRYs, we begin calling sqlite3OsSleep().  The first few
  ** calls to sqlite3OsSleep() have a delay of 1 microsecond.  Really this
  ** is more of a scheduler yield than an actual delay.  But on the 10th
  ** an subsequent retries, the delays start becoming longer and longer, 
  ** so that on the 100th (and last) RETRY we delay for 323 milliseconds.
  ** The total delay time before giving up is less than 10 seconds.
  */
  if( cnt>5 ){
    int nDelay = 1;                      /* Pause time in microseconds */
    if( cnt>100 ){
      VVA_ONLY( pWal->lockError = 1; )
      return SQLITE_PROTOCOL;
    }
    if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39;
    sqlite3OsSleep(pWal->pVfs, nDelay);
  }

  if( !useWal ){
    rc = walIndexReadHdr(pWal, pChanged);
    if( rc==SQLITE_BUSY ){
      /* If there is not a recovery running in another thread or process
      ** then convert BUSY errors to WAL_RETRY.  If recovery is known to
      ** be running, convert BUSY to BUSY_RECOVERY.  There is a race here
      ** which might cause WAL_RETRY to be returned even if BUSY_RECOVERY
      ** would be technically correct.  But the race is benign since with
      ** WAL_RETRY this routine will be called again and will probably be
      ** right on the second iteration.
      */
      if( pWal->apWiData[0]==0 ){
        /* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
        ** We assume this is a transient condition, so return WAL_RETRY. The
        ** xShmMap() implementation used by the default unix and win32 VFS 
        ** modules may return SQLITE_BUSY due to a race condition in the 
        ** code that determines whether or not the shared-memory region 
        ** must be zeroed before the requested page is returned.
        */
        rc = WAL_RETRY;
      }else if( SQLITE_OK==(rc = walLockShared(pWal, WAL_RECOVER_LOCK)) ){
        walUnlockShared(pWal, WAL_RECOVER_LOCK);
        rc = WAL_RETRY;
      }else if( rc==SQLITE_BUSY ){
        rc = SQLITE_BUSY_RECOVERY;
      }
    }
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    walShmBarrier(pWal);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
        /* It is not safe to allow the reader to continue here if frames
        ** may have been appended to the log before READ_LOCK(0) was obtained.
        ** When holding READ_LOCK(0), the reader ignores the entire log file,
        ** which implies that the database file contains a trustworthy
        ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
        ** happening, this is usually correct.
        **
        ** However, if frames have been appended to the log (or if the log 
        ** is wrapped and written for that matter) before the READ_LOCK(0)
        ** is obtained, that is not necessarily true. A checkpointer may
        ** have started to backfill the appended frames but crashed before
        ** it finished. Leaving a corrupt image in the database file.
        */
        walUnlockShared(pWal, WAL_READ_LOCK(0));
        return WAL_RETRY;
      }
      pWal->readLock = 0;
      return SQLITE_OK;
    }else if( rc!=SQLITE_BUSY ){
      return rc;
    }
  }

  /* If we get this far, it means that the reader will want to use
  ** the WAL to get at content from recent commits.  The job now is
  ** to select one of the aReadMark[] entries that is closest to
  ** but not exceeding pWal->hdr.mxFrame and lock that entry.
  */
  mxReadMark = 0;
  mxI = 0;
  for(i=1; i<WAL_NREADER; i++){
    u32 thisMark = pInfo->aReadMark[i];
    if( mxReadMark<=thisMark && thisMark<=pWal->hdr.mxFrame ){
      assert( thisMark!=READMARK_NOT_USED );
      mxReadMark = thisMark;
      mxI = i;
    }
  }
  /* There was once an "if" here. The extra "{" is to preserve indentation. */
  {
    if( (pWal->readOnly & WAL_SHM_RDONLY)==0
     && (mxReadMark<pWal->hdr.mxFrame || mxI==0)
    ){
      for(i=1; i<WAL_NREADER; i++){
        rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1, 0);
        if( rc==SQLITE_OK ){
          mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame;
          mxI = i;
          walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
          break;
        }else if( rc!=SQLITE_BUSY ){
          return rc;
        }
      }
    }
    if( mxI==0 ){
      assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
      return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTLOCK;
    }

    rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
    if( rc ){
      return rc==SQLITE_BUSY ? WAL_RETRY : rc;
    }
    /* Now that the read-lock has been obtained, check that neither the
    ** value in the aReadMark[] array or the contents of the wal-index
    ** header have changed.
    **
    ** It is necessary to check that the wal-index header did not change
    ** between the time it was read and when the shared-lock was obtained
    ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
    ** that the log file may have been wrapped by a writer, or that frames
    ** that occur later in the log than pWal->hdr.mxFrame may have been
    ** copied into the database by a checkpointer. If either of these things
    ** happened, then reading the database with the current value of
    ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
    ** instead.
    **
    ** Before checking that the live wal-index header has not changed
    ** since it was read, set Wal.minFrame to the first frame in the wal
    ** file that has not yet been checkpointed. This client will not need
    ** to read any frames earlier than minFrame from the wal file - they
    ** can be safely read directly from the database file.
    **
    ** Because a ShmBarrier() call is made between taking the copy of 
    ** nBackfill and checking that the wal-header in shared-memory still
    ** matches the one cached in pWal->hdr, it is guaranteed that the 
    ** checkpointer that set nBackfill was not working with a wal-index
    ** header newer than that cached in pWal->hdr. If it were, that could
    ** cause a problem. The checkpointer could omit to checkpoint
    ** a version of page X that lies before pWal->minFrame (call that version
    ** A) on the basis that there is a newer version (version B) of the same
    ** page later in the wal file. But if version B happens to like past
    ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
    ** that it can read version A from the database file. However, since
    ** we can guarantee that the checkpointer that set nBackfill could not
    ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
    */
    pWal->minFrame = pInfo->nBackfill+1;
    walShmBarrier(pWal);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
      pWal->readLock = (i16)mxI;
    }
  }
  return rc;
}

/*
** Begin a read transaction on the database.
**
** This routine used to be called sqlite3OpenSnapshot() and with good reason:
** it takes a snapshot of the state of the WAL and wal-index for the current
** instant in time.  The current thread will continue to use this snapshot.
** Other threads might append new content to the WAL and wal-index but
** that extra content is ignored by the current thread.
**
** If the database contents have changes since the previous read
** transaction, then *pChanged is set to 1 before returning.  The
** Pager layer will use this to know that is cache is stale and
** needs to be flushed.
*/
SQLITE_PRIVATE int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int cnt = 0;                    /* Number of TryBeginRead attempts */

  do{
    rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
  }while( rc==WAL_RETRY );
  testcase( (rc&0xff)==SQLITE_BUSY );
  testcase( (rc&0xff)==SQLITE_IOERR );
  testcase( rc==SQLITE_PROTOCOL );
  testcase( rc==SQLITE_OK );
  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
SQLITE_PRIVATE void sqlite3WalEndReadTransaction(Wal *pWal){
  sqlite3WalEndWriteTransaction(pWal);
  if( pWal->readLock>=0 ){
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->readLock = -1;
  }
}

/*
** Search the wal file for page pgno. If found, set *piRead to the frame that
** contains the page. Otherwise, if pgno is not in the wal file, set *piRead
** to zero.
**
** Return SQLITE_OK if successful, or an error code if an error occurs. If an
** error does occur, the final value of *piRead is undefined.
*/
SQLITE_PRIVATE int sqlite3WalFindFrame(
  Wal *pWal,                      /* WAL handle */
  Pgno pgno,                      /* Database page number to read data for */
  u32 *piRead                     /* OUT: Frame number (or zero) */
){
  u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
  u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
  int iHash;                      /* Used to loop through N hash tables */
  int iMinHash;

  /* This routine is only be called from within a read transaction. */
  assert( pWal->readLock>=0 || pWal->lockError );

  /* If the "last page" field of the wal-index header snapshot is 0, then
  ** no data will be read from the wal under any circumstances. Return early
  ** in this case as an optimization.  Likewise, if pWal->readLock==0, 
  ** then the WAL is ignored by the reader so return early, as if the 
  ** WAL were empty.
  */
  if( iLast==0 || pWal->readLock==0 ){
    *piRead = 0;
    return SQLITE_OK;
  }

  /* Search the hash table or tables for an entry matching page number
  ** pgno. Each iteration of the following for() loop searches one
  ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
  **
  ** This code might run concurrently to the code in walIndexAppend()
  ** that adds entries to the wal-index (and possibly to this hash 
  ** table). This means the value just read from the hash 
  ** slot (aHash[iKey]) may have been added before or after the 
  ** current read transaction was opened. Values added after the
  ** read transaction was opened may have been written incorrectly -
  ** i.e. these slots may contain garbage data. However, we assume
  ** that any slots written before the current read transaction was
  ** opened remain unmodified.
  **
  ** For the reasons above, the if(...) condition featured in the inner
  ** loop of the following block is more stringent that would be required 
  ** if we had exclusive access to the hash-table:
  **
  **   (aPgno[iFrame]==pgno): 
  **     This condition filters out normal hash-table collisions.
  **
  **   (iFrame<=iLast): 
  **     This condition filters out entries that were added to the hash
  **     table after the current read-transaction had started.
  */
  iMinHash = walFramePage(pWal->minFrame);
  for(iHash=walFramePage(iLast); iHash>=iMinHash && iRead==0; iHash--){
    volatile ht_slot *aHash;      /* Pointer to hash table */
    volatile u32 *aPgno;          /* Pointer to array of page numbers */
    u32 iZero;                    /* Frame number corresponding to aPgno[0] */
    int iKey;                     /* Hash slot index */
    int nCollide;                 /* Number of hash collisions remaining */
    int rc;                       /* Error code */

    rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    nCollide = HASHTABLE_NSLOT;
    for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
      u32 iFrame = aHash[iKey] + iZero;
      if( iFrame<=iLast && iFrame>=pWal->minFrame && aPgno[aHash[iKey]]==pgno ){
        assert( iFrame>iRead || CORRUPT_DB );
        iRead = iFrame;
      }
      if( (nCollide--)==0 ){
        return SQLITE_CORRUPT_BKPT;
      }
    }
  }

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */
  {
    u32 iRead2 = 0;
    u32 iTest;
    assert( pWal->minFrame>0 );
    for(iTest=iLast; iTest>=pWal->minFrame; iTest--){
      if( walFramePgno(pWal, iTest)==pgno ){
        iRead2 = iTest;
        break;
      }
    }
    assert( iRead==iRead2 );
  }
#endif

  *piRead = iRead;
  return SQLITE_OK;
}

/*
** Read the contents of frame iRead from the wal file into buffer pOut
** (which is nOut bytes in size). Return SQLITE_OK if successful, or an
** error code otherwise.
*/
SQLITE_PRIVATE int sqlite3WalReadFrame(
  Wal *pWal,                      /* WAL handle */
  u32 iRead,                      /* Frame to read */
  int nOut,                       /* Size of buffer pOut in bytes */
  u8 *pOut                        /* Buffer to write page data to */
){
  int sz;
  i64 iOffset;
  sz = pWal->hdr.szPage;
  sz = (sz&0xfe00) + ((sz&0x0001)<<16);
  testcase( sz<=32768 );
  testcase( sz>=65536 );
  iOffset = walFrameOffset(iRead, sz) + WAL_FRAME_HDRSIZE;
  /* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */
  return sqlite3OsRead(pWal->pWalFd, pOut, (nOut>sz ? sz : nOut), iOffset);
}

/* 
** Return the size of the database in pages (or zero, if unknown).
*/
SQLITE_PRIVATE Pgno sqlite3WalDbsize(Wal *pWal){
  if( pWal && ALWAYS(pWal->readLock>=0) ){
    return pWal->hdr.nPage;
  }
  return 0;
}


/* 
** This function starts a write transaction on the WAL.
**
** A read transaction must have already been started by a prior call
** to sqlite3WalBeginReadTransaction().
**
** If another thread or process has written into the database since
** the read transaction was started, then it is not possible for this
** thread to write as doing so would cause a fork.  So this routine
** returns SQLITE_BUSY in that case and no write transaction is started.
**
** There can only be a single writer active at a time.
*/
SQLITE_PRIVATE int sqlite3WalBeginWriteTransaction(Wal *pWal){
  int rc;

  /* Cannot start a write transaction without first holding a read
  ** transaction. */
  assert( pWal->readLock>=0 );

  if( pWal->readOnly ){
    return SQLITE_READONLY;
  }

  /* Only one writer allowed at a time.  Get the write lock.  Return
  ** SQLITE_BUSY if unable.
  */
  rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1, 0);
  if( rc ){
    return rc;
  }
  pWal->writeLock = 1;

  /* If another connection has written to the database file since the
  ** time the read transaction on this connection was started, then
  ** the write is disallowed.
  */
  if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    pWal->writeLock = 0;
    rc = SQLITE_BUSY_SNAPSHOT;
  }

  return rc;
}

/*
** End a write transaction.  The commit has already been done.  This
** routine merely releases the lock.
*/
SQLITE_PRIVATE int sqlite3WalEndWriteTransaction(Wal *pWal){
  if( pWal->writeLock ){
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    pWal->writeLock = 0;
    pWal->truncateOnCommit = 0;
  }
  return SQLITE_OK;
}

/*
** If any data has been written (but not committed) to the log file, this
** function moves the write-pointer back to the start of the transaction.
**
** Additionally, the callback function is invoked for each frame written
** to the WAL since the start of the transaction. If the callback returns
** other than SQLITE_OK, it is not invoked again and the error code is
** returned to the caller.
**
** Otherwise, if the callback function does not return an error, this
** function returns SQLITE_OK.
*/
SQLITE_PRIVATE int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
  int rc = SQLITE_OK;
  if( ALWAYS(pWal->writeLock) ){
    Pgno iMax = pWal->hdr.mxFrame;
    Pgno iFrame;
  
    /* Restore the clients cache of the wal-index header to the state it
    ** was in before the client began writing to the database. 
    */
    memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));

    for(iFrame=pWal->hdr.mxFrame+1; 
        ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; 
        iFrame++
    ){
      /* This call cannot fail. Unless the page for which the page number
      ** is passed as the second argument is (a) in the cache and 
      ** (b) has an outstanding reference, then xUndo is either a no-op
      ** (if (a) is false) or simply expels the page from the cache (if (b)
      ** is false).
      **
      ** If the upper layer is doing a rollback, it is guaranteed that there
      ** are no outstanding references to any page other than page 1. And
      ** page 1 is never written to the log until the transaction is
      ** committed. As a result, the call to xUndo may not fail.
      */
      assert( walFramePgno(pWal, iFrame)!=1 );
      rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
    }
    if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
  }
  return rc;
}

/* 
** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32 
** values. This function populates the array with values required to 
** "rollback" the write position of the WAL handle back to the current 
** point in the event of a savepoint rollback (via WalSavepointUndo()).
*/
SQLITE_PRIVATE void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData){
  assert( pWal->writeLock );
  aWalData[0] = pWal->hdr.mxFrame;
  aWalData[1] = pWal->hdr.aFrameCksum[0];
  aWalData[2] = pWal->hdr.aFrameCksum[1];
  aWalData[3] = pWal->nCkpt;
}

/* 
** Move the write position of the WAL back to the point identified by
** the values in the aWalData[] array. aWalData must point to an array
** of WAL_SAVEPOINT_NDATA u32 values that has been previously populated
** by a call to WalSavepoint().
*/
SQLITE_PRIVATE int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
  int rc = SQLITE_OK;

  assert( pWal->writeLock );
  assert( aWalData[3]!=pWal->nCkpt || aWalData[0]<=pWal->hdr.mxFrame );

  if( aWalData[3]!=pWal->nCkpt ){
    /* This savepoint was opened immediately after the write-transaction
    ** was started. Right after that, the writer decided to wrap around
    ** to the start of the log. Update the savepoint values to match.
    */
    aWalData[0] = 0;
    aWalData[3] = pWal->nCkpt;
  }

  if( aWalData[0]<pWal->hdr.mxFrame ){
    pWal->hdr.mxFrame = aWalData[0];
    pWal->hdr.aFrameCksum[0] = aWalData[1];
    pWal->hdr.aFrameCksum[1] = aWalData[2];
    walCleanupHash(pWal);
  }

  return rc;
}

/*
** This function is called just before writing a set of frames to the log
** file (see sqlite3WalFrames()). It checks to see if, instead of appending
** to the current log file, it is possible to overwrite the start of the
** existing log file with the new frames (i.e. "reset" the log). If so,
** it sets pWal->hdr.mxFrame to 0. Otherwise, pWal->hdr.mxFrame is left
** unchanged.
**
** SQLITE_OK is returned if no error is encountered (regardless of whether
** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned
** if an error occurs.
*/
static int walRestartLog(Wal *pWal){
  int rc = SQLITE_OK;
  int cnt;

  if( pWal->readLock==0 ){
    volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
    assert( pInfo->nBackfill==pWal->hdr.mxFrame );
    if( pInfo->nBackfill>0 ){
      u32 salt1;
      sqlite3_randomness(4, &salt1);
      rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1, 0);
      if( rc==SQLITE_OK ){
        /* If all readers are using WAL_READ_LOCK(0) (in other words if no
        ** readers are currently using the WAL), then the transactions
        ** frames will overwrite the start of the existing log. Update the
        ** wal-index header to reflect this.
        **
        ** In theory it would be Ok to update the cache of the header only
        ** at this point. But updating the actual wal-index header is also
        ** safe and means there is no special case for sqlite3WalUndo()
        ** to handle if this transaction is rolled back.  */
        walRestartHdr(pWal, salt1);
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }else if( rc!=SQLITE_BUSY ){
        return rc;
      }
    }
    walUnlockShared(pWal, WAL_READ_LOCK(0));
    pWal->readLock = -1;
    cnt = 0;
    do{
      int notUsed;
      rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
    }while( rc==WAL_RETRY );
    assert( (rc&0xff)!=SQLITE_BUSY ); /* BUSY not possible when useWal==1 */
    testcase( (rc&0xff)==SQLITE_IOERR );
    testcase( rc==SQLITE_PROTOCOL );
    testcase( rc==SQLITE_OK );
  }
  return rc;
}

/*
** Information about the current state of the WAL file and where
** the next fsync should occur - passed from sqlite3WalFrames() into
** walWriteToLog().
*/
typedef struct WalWriter {
  Wal *pWal;                   /* The complete WAL information */
  sqlite3_file *pFd;           /* The WAL file to which we write */
  sqlite3_int64 iSyncPoint;    /* Fsync at this offset */
  int syncFlags;               /* Flags for the fsync */
  int szPage;                  /* Size of one page */
} WalWriter;

/*
** Write iAmt bytes of content into the WAL file beginning at iOffset.
** Do a sync when crossing the p->iSyncPoint boundary.
**
** In other words, if iSyncPoint is in between iOffset and iOffset+iAmt,
** first write the part before iSyncPoint, then sync, then write the
** rest.
*/
static int walWriteToLog(
  WalWriter *p,              /* WAL to write to */
  void *pContent,            /* Content to be written */
  int iAmt,                  /* Number of bytes to write */
  sqlite3_int64 iOffset      /* Start writing at this offset */
){
  int rc;
  if( iOffset<p->iSyncPoint && iOffset+iAmt>=p->iSyncPoint ){
    int iFirstAmt = (int)(p->iSyncPoint - iOffset);
    rc = sqlite3OsWrite(p->pFd, pContent, iFirstAmt, iOffset);
    if( rc ) return rc;
    iOffset += iFirstAmt;
    iAmt -= iFirstAmt;
    pContent = (void*)(iFirstAmt + (char*)pContent);
    assert( p->syncFlags & (SQLITE_SYNC_NORMAL|SQLITE_SYNC_FULL) );
    rc = sqlite3OsSync(p->pFd, p->syncFlags & SQLITE_SYNC_MASK);
    if( iAmt==0 || rc ) return rc;
  }
  rc = sqlite3OsWrite(p->pFd, pContent, iAmt, iOffset);
  return rc;
}

/*
** Write out a single frame of the WAL
*/
static int walWriteOneFrame(
  WalWriter *p,               /* Where to write the frame */
  PgHdr *pPage,               /* The page of the frame to be written */
  int nTruncate,              /* The commit flag.  Usually 0.  >0 for commit */
  sqlite3_int64 iOffset       /* Byte offset at which to write */
){
  int rc;                         /* Result code from subfunctions */
  void *pData;                    /* Data actually written */
  u8 aFrame[WAL_FRAME_HDRSIZE];   /* Buffer to assemble frame-header in */
#if defined(SQLITE_HAS_CODEC)
  if( (pData = sqlite3PagerCodec(pPage))==0 ) return SQLITE_NOMEM;
#else
  pData = pPage->pData;
#endif
  walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame);
  rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
  if( rc ) return rc;
  /* Write the page data */
  rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame));
  return rc;
}

/* 
** Write a set of frames to the log. The caller must hold the write-lock
** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
*/
SQLITE_PRIVATE int sqlite3WalFrames(
  Wal *pWal,                      /* Wal handle to write to */
  int szPage,                     /* Database page-size in bytes */
  PgHdr *pList,                   /* List of dirty pages to write */
  Pgno nTruncate,                 /* Database size after this commit */
  int isCommit,                   /* True if this is a commit */
  int sync_flags                  /* Flags to pass to OsSync() (or 0) */
){
  int rc;                         /* Used to catch return codes */
  u32 iFrame;                     /* Next frame address */
  PgHdr *p;                       /* Iterator to run through pList with. */
  PgHdr *pLast = 0;               /* Last frame in list */
  int nExtra = 0;                 /* Number of extra copies of last page */
  int szFrame;                    /* The size of a single frame */
  i64 iOffset;                    /* Next byte to write in WAL file */
  WalWriter w;                    /* The writer */

  assert( pList );
  assert( pWal->writeLock );

  /* If this frame set completes a transaction, then nTruncate>0.  If
  ** nTruncate==0 then this frame set does not complete the transaction. */
  assert( (isCommit!=0)==(nTruncate!=0) );

#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
  { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
    WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n",
              pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill"));
  }
#endif

  /* See if it is possible to write these frames into the start of the
  ** log file, instead of appending to it at pWal->hdr.mxFrame.
  */
  if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){
    return rc;
  }

  /* If this is the first frame written into the log, write the WAL
  ** header to the start of the WAL file. See comments at the top of
  ** this source file for a description of the WAL header format.
  */
  iFrame = pWal->hdr.mxFrame;
  if( iFrame==0 ){
    u8 aWalHdr[WAL_HDRSIZE];      /* Buffer to assemble wal-header in */
    u32 aCksum[2];                /* Checksum for wal-header */

    sqlite3Put4byte(&aWalHdr[0], (WAL_MAGIC | SQLITE_BIGENDIAN));
    sqlite3Put4byte(&aWalHdr[4], WAL_MAX_VERSION);
    sqlite3Put4byte(&aWalHdr[8], szPage);
    sqlite3Put4byte(&aWalHdr[12], pWal->nCkpt);
    if( pWal->nCkpt==0 ) sqlite3_randomness(8, pWal->hdr.aSalt);
    memcpy(&aWalHdr[16], pWal->hdr.aSalt, 8);
    walChecksumBytes(1, aWalHdr, WAL_HDRSIZE-2*4, 0, aCksum);
    sqlite3Put4byte(&aWalHdr[24], aCksum[0]);
    sqlite3Put4byte(&aWalHdr[28], aCksum[1]);
    
    pWal->szPage = szPage;
    pWal->hdr.bigEndCksum = SQLITE_BIGENDIAN;
    pWal->hdr.aFrameCksum[0] = aCksum[0];
    pWal->hdr.aFrameCksum[1] = aCksum[1];
    pWal->truncateOnCommit = 1;

    rc = sqlite3OsWrite(pWal->pWalFd, aWalHdr, sizeof(aWalHdr), 0);
    WALTRACE(("WAL%p: wal-header write %s\n", pWal, rc ? "failed" : "ok"));
    if( rc!=SQLITE_OK ){
      return rc;
    }

    /* Sync the header (unless SQLITE_IOCAP_SEQUENTIAL is true or unless
    ** all syncing is turned off by PRAGMA synchronous=OFF).  Otherwise
    ** an out-of-order write following a WAL restart could result in
    ** database corruption.  See the ticket:
    **
    **     http://localhost:591/sqlite/info/ff5be73dee
    */
    if( pWal->syncHeader && sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags & SQLITE_SYNC_MASK);
      if( rc ) return rc;
    }
  }
  assert( (int)pWal->szPage==szPage );

  /* Setup information needed to write frames into the WAL */
  w.pWal = pWal;
  w.pFd = pWal->pWalFd;
  w.iSyncPoint = 0;
  w.syncFlags = sync_flags;
  w.szPage = szPage;
  iOffset = walFrameOffset(iFrame+1, szPage);
  szFrame = szPage + WAL_FRAME_HDRSIZE;

  /* Write all frames into the log file exactly once */
  for(p=pList; p; p=p->pDirty){
    int nDbSize;   /* 0 normally.  Positive == commit flag */
    iFrame++;
    assert( iOffset==walFrameOffset(iFrame, szPage) );
    nDbSize = (isCommit && p->pDirty==0) ? nTruncate : 0;
    rc = walWriteOneFrame(&w, p, nDbSize, iOffset);
    if( rc ) return rc;
    pLast = p;
    iOffset += szFrame;
  }

  /* If this is the end of a transaction, then we might need to pad
  ** the transaction and/or sync the WAL file.
  **
  ** Padding and syncing only occur if this set of frames complete a
  ** transaction and if PRAGMA synchronous=FULL.  If synchronous==NORMAL
  ** or synchronous==OFF, then no padding or syncing are needed.
  **
  ** If SQLITE_IOCAP_POWERSAFE_OVERWRITE is defined, then padding is not
  ** needed and only the sync is done.  If padding is needed, then the
  ** final frame is repeated (with its commit mark) until the next sector
  ** boundary is crossed.  Only the part of the WAL prior to the last
  ** sector boundary is synced; the part of the last frame that extends
  ** past the sector boundary is written after the sync.
  */
  if( isCommit && (sync_flags & WAL_SYNC_TRANSACTIONS)!=0 ){
    if( pWal->padToSectorBoundary ){
      int sectorSize = sqlite3SectorSize(pWal->pWalFd);
      w.iSyncPoint = ((iOffset+sectorSize-1)/sectorSize)*sectorSize;
      while( iOffset<w.iSyncPoint ){
        rc = walWriteOneFrame(&w, pLast, nTruncate, iOffset);
        if( rc ) return rc;
        iOffset += szFrame;
        nExtra++;
      }
    }else{
      rc = sqlite3OsSync(w.pFd, sync_flags & SQLITE_SYNC_MASK);
    }
  }

  /* If this frame set completes the first transaction in the WAL and
  ** if PRAGMA journal_size_limit is set, then truncate the WAL to the
  ** journal size limit, if possible.
  */
  if( isCommit && pWal->truncateOnCommit && pWal->mxWalSize>=0 ){
    i64 sz = pWal->mxWalSize;
    if( walFrameOffset(iFrame+nExtra+1, szPage)>pWal->mxWalSize ){
      sz = walFrameOffset(iFrame+nExtra+1, szPage);
    }
    walLimitSize(pWal, sz);
    pWal->truncateOnCommit = 0;
  }

  /* Append data to the wal-index. It is not necessary to lock the 
  ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
  ** guarantees that there are no other writers, and no data that may
  ** be in use by existing readers is being overwritten.
  */
  iFrame = pWal->hdr.mxFrame;
  for(p=pList; p && rc==SQLITE_OK; p=p->pDirty){
    iFrame++;
    rc = walIndexAppend(pWal, iFrame, p->pgno);
  }
  while( rc==SQLITE_OK && nExtra>0 ){
    iFrame++;
    nExtra--;
    rc = walIndexAppend(pWal, iFrame, pLast->pgno);
  }

  if( rc==SQLITE_OK ){
    /* Update the private copy of the header. */
    pWal->hdr.szPage = (u16)((szPage&0xff00) | (szPage>>16));
    testcase( szPage<=32768 );
    testcase( szPage>=65536 );
    pWal->hdr.mxFrame = iFrame;
    if( isCommit ){
      pWal->hdr.iChange++;
      pWal->hdr.nPage = nTruncate;
    }
    /* If this is a commit, update the wal-index header too. */
    if( isCommit ){
      walIndexWriteHdr(pWal);
      pWal->iCallback = iFrame;
    }
  }

  WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
  return rc;
}

/* 
** This routine is called to implement sqlite3_wal_checkpoint() and
** related interfaces.
**
** Obtain a CHECKPOINT lock and then backfill as much information as
** we can from WAL into the database.
**
** If parameter xBusy is not NULL, it is a pointer to a busy-handler
** callback. In this case this function runs a blocking checkpoint.
*/
SQLITE_PRIVATE int sqlite3WalCheckpoint(
  Wal *pWal,                      /* Wal connection */
  int eMode,                      /* PASSIVE, FULL, RESTART, or TRUNCATE */
  int (*xBusy)(void*),            /* Function to call when busy */
  void *pBusyArg,                 /* Context argument for xBusyHandler */
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  int nBuf,                       /* Size of temporary buffer */
  u8 *zBuf,                       /* Temporary buffer to use */
  int *pnLog,                     /* OUT: Number of frames in WAL */
  int *pnCkpt                     /* OUT: Number of backfilled frames in WAL */
){
  int rc;                         /* Return code */
  int isChanged = 0;              /* True if a new wal-index header is loaded */
  int eMode2 = eMode;             /* Mode to pass to walCheckpoint() */
  int (*xBusy2)(void*) = xBusy;   /* Busy handler for eMode2 */

  assert( pWal->ckptLock==0 );
  assert( pWal->writeLock==0 );

  /* EVIDENCE-OF: R-62920-47450 The busy-handler callback is never invoked
  ** in the SQLITE_CHECKPOINT_PASSIVE mode. */
  assert( eMode!=SQLITE_CHECKPOINT_PASSIVE || xBusy==0 );

  if( pWal->readOnly ) return SQLITE_READONLY;
  WALTRACE(("WAL%p: checkpoint begins\n", pWal));

  /* IMPLEMENTATION-OF: R-62028-47212 All calls obtain an exclusive 
  ** "checkpoint" lock on the database file. */
  rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1, 0);
  if( rc ){
    /* EVIDENCE-OF: R-10421-19736 If any other process is running a
    ** checkpoint operation at the same time, the lock cannot be obtained and
    ** SQLITE_BUSY is returned.
    ** EVIDENCE-OF: R-53820-33897 Even if there is a busy-handler configured,
    ** it will not be invoked in this case.
    */
    testcase( rc==SQLITE_BUSY );
    testcase( xBusy!=0 );
    return rc;
  }
  pWal->ckptLock = 1;

  /* IMPLEMENTATION-OF: R-59782-36818 The SQLITE_CHECKPOINT_FULL, RESTART and
  ** TRUNCATE modes also obtain the exclusive "writer" lock on the database
  ** file.
  **
  ** EVIDENCE-OF: R-60642-04082 If the writer lock cannot be obtained
  ** immediately, and a busy-handler is configured, it is invoked and the
  ** writer lock retried until either the busy-handler returns 0 or the
  ** lock is successfully obtained.
  */
  if( eMode!=SQLITE_CHECKPOINT_PASSIVE ){
    rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_WRITE_LOCK, 1);
    if( rc==SQLITE_OK ){
      pWal->writeLock = 1;
    }else if( rc==SQLITE_BUSY ){
      eMode2 = SQLITE_CHECKPOINT_PASSIVE;
      xBusy2 = 0;
      rc = SQLITE_OK;
    }
  }

  /* Read the wal-index header. */
  if( rc==SQLITE_OK ){
    rc = walIndexReadHdr(pWal, &isChanged);
    if( isChanged && pWal->pDbFd->pMethods->iVersion>=3 ){
      sqlite3OsUnfetch(pWal->pDbFd, 0, 0);
    }
  }

  /* Copy data from the log to the database file. */
  if( rc==SQLITE_OK ){
    if( pWal->hdr.mxFrame && walPagesize(pWal)!=nBuf ){
      rc = SQLITE_CORRUPT_BKPT;
    }else{
      rc = walCheckpoint(pWal, eMode2, xBusy2, pBusyArg, sync_flags, zBuf);
    }

    /* If no error occurred, set the output variables. */
    if( rc==SQLITE_OK || rc==SQLITE_BUSY ){
      if( pnLog ) *pnLog = (int)pWal->hdr.mxFrame;
      if( pnCkpt ) *pnCkpt = (int)(walCkptInfo(pWal)->nBackfill);
    }
  }

  if( isChanged ){
    /* If a new wal-index header was loaded before the checkpoint was 
    ** performed, then the pager-cache associated with pWal is now
    ** out of date. So zero the cached wal-index header to ensure that
    ** next time the pager opens a snapshot on this database it knows that
    ** the cache needs to be reset.
    */
    memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
  }

  /* Release the locks. */
  sqlite3WalEndWriteTransaction(pWal);
  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
  return (rc==SQLITE_OK && eMode!=eMode2 ? SQLITE_BUSY : rc);
}

#if 0
/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called.  If no commits have occurred since
** the last call, then return 0.
*/
SQLITE_PRIVATE int sqlite3WalCallback(Wal *pWal){
  u32 ret = 0;
  if( pWal ){
    ret = pWal->iCallback;
    pWal->iCallback = 0;
  }
  return (int)ret;
}
#endif

/*
** This function is called to change the WAL subsystem into or out
** of locking_mode=EXCLUSIVE.
**
** If op is zero, then attempt to change from locking_mode=EXCLUSIVE
** into locking_mode=NORMAL.  This means that we must acquire a lock
** on the pWal->readLock byte.  If the WAL is already in locking_mode=NORMAL
** or if the acquisition of the lock fails, then return 0.  If the
** transition out of exclusive-mode is successful, return 1.  This
** operation must occur while the pager is still holding the exclusive
** lock on the main database file.
**
** If op is one, then change from locking_mode=NORMAL into 
** locking_mode=EXCLUSIVE.  This means that the pWal->readLock must
** be released.  Return 1 if the transition is made and 0 if the
** WAL is already in exclusive-locking mode - meaning that this
** routine is a no-op.  The pager must already hold the exclusive lock
** on the main database file before invoking this operation.
**
** If op is negative, then do a dry-run of the op==1 case but do
** not actually change anything. The pager uses this to see if it
** should acquire the database exclusive lock prior to invoking
** the op==1 case.
*/
SQLITE_PRIVATE int sqlite3WalExclusiveMode(Wal *pWal, int op){
  int rc;
  assert( pWal->writeLock==0 );
  assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 );

  /* pWal->readLock is usually set, but might be -1 if there was a 
  ** prior error while attempting to acquire are read-lock. This cannot 
  ** happen if the connection is actually in exclusive mode (as no xShmLock
  ** locks are taken in this case). Nor should the pager attempt to
  ** upgrade to exclusive-mode following such an error.
  */
  assert( pWal->readLock>=0 || pWal->lockError );
  assert( pWal->readLock>=0 || (op<=0 && pWal->exclusiveMode==0) );

  if( op==0 ){
    if( pWal->exclusiveMode ){
      pWal->exclusiveMode = 0;
      if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){
        pWal->exclusiveMode = 1;
      }
      rc = pWal->exclusiveMode==0;
    }else{
      /* Already in locking_mode=NORMAL */
      rc = 0;
    }
  }else if( op>0 ){
    assert( pWal->exclusiveMode==0 );
    assert( pWal->readLock>=0 );
    walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
    pWal->exclusiveMode = 1;
    rc = 1;
  }else{
    rc = pWal->exclusiveMode==0;
  }
  return rc;
}

#if 0
/* 
** Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
SQLITE_PRIVATE int sqlite3WalHeapMemory(Wal *pWal){
  return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}
#endif

#ifdef SQLITE_ENABLE_ZIPVFS
/*
** If the argument is not NULL, it points to a Wal object that holds a
** read-lock. This function returns the database page-size if it is known,
** or zero if it is not (or if pWal is NULL).
*/
SQLITE_PRIVATE int sqlite3WalFramesize(Wal *pWal){
  assert( pWal==0 || pWal->readLock>=0 );
  return (pWal ? pWal->szPage : 0);
}
#endif

#endif /* #ifndef SQLITE_OMIT_WAL */

/************** End of wal.c *************************************************/
/************** Begin file btmutex.c *****************************************/
/*
** 2007 August 27
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains code used to implement mutexes on Btree objects.
** This code really belongs in btree.c.  But btree.c is getting too
** big and we want to break it down some.  This packaged seemed like
** a good breakout.
*/
/* #include "btreeInt.h" */
#ifndef SQLITE_OMIT_SHARED_CACHE
#if SQLITE_THREADSAFE

/*
** Obtain the BtShared mutex associated with B-Tree handle p. Also,
** set BtShared.db to the database handle associated with p and the
** p->locked boolean to true.
*/
static void lockBtreeMutex(Btree *p){
  assert( p->locked==0 );
  assert( sqlite3_mutex_notheld(p->pBt->mutex) );
  assert( sqlite3_mutex_held(p->mutex) );

  sqlite3_mutex_enter(p->pBt->mutex);
  p->pBt->pBt = p;
  p->locked = 1;
}

/*
** Release the BtShared mutex associated with B-Tree handle p and
** clear the p->locked boolean.
*/
static void SQLITE_NOINLINE unlockBtreeMutex(Btree *p){
  BtShared *pBt = p->pBt;
  assert( p->locked==1 );
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( sqlite3_mutex_held(p->db->mutex) );
  assert( p->db==pBt->db );

  sqlite3_mutex_leave(pBt->mutex);
  p->locked = 0;
}

/* Forward reference */
static void SQLITE_NOINLINE btreeLockCarefully(Btree *p);

/*
** Enter a mutex on the given BTree object.
**
** If the object is not sharable, then no mutex is ever required
** and this routine is a no-op.  The underlying mutex is non-recursive.
** But we keep a reference count in Btree.wantToLock so the behavior
** of this interface is recursive.
**
** To avoid deadlocks, multiple Btrees are locked in the same order
** by all database connections.  The p->pNext is a list of other
** Btrees belonging to the same database connection as the p Btree
** which need to be locked after p.  If we cannot get a lock on
** p, then first unlock all of the others on p->pNext, then wait
** for the lock to become available on p, then relock all of the
** subsequent Btrees that desire a lock.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeEnter(Btree *p){
  /* Some basic sanity checking on the Btree.  The list of Btrees
  ** connected by pNext and pPrev should be in sorted order by
  ** Btree.pBt value. All elements of the list should belong to
  ** the same connection. Only shared Btrees are on the list. */
  assert( p->pNext==0 || p->pNext->pBt>p->pBt );
  assert( p->pPrev==0 || p->pPrev->pBt<p->pBt );
  assert( p->pNext==0 || p->pNext->db==p->db );
  assert( p->pPrev==0 || p->pPrev->db==p->db );
  assert( p->sharable || (p->pNext==0 && p->pPrev==0) );

  /* Check for locking consistency */
  assert( !p->locked || p->wantToLock>0 );
  assert( p->sharable || p->wantToLock==0 );

  /* We should already hold a lock on the database connection */
  assert( sqlite3_mutex_held(p->db->mutex) );

  /* Unless the database is sharable and unlocked, then BtShared.db
  ** should already be set correctly. */
  assert( (p->locked==0 && p->sharable) || p->pBt->db==p->db );

  if( !p->sharable ) return;
  p->wantToLock++;
  if( p->locked ) return;
  btreeLockCarefully(p);
}

/* This is a helper function for sqlite3BtreeLock(). By moving
** complex, but seldom used logic, out of sqlite3BtreeLock() and
** into this routine, we avoid unnecessary stack pointer changes
** and thus help the sqlite3BtreeLock() routine to run much faster
** in the common case.
*/
static void SQLITE_NOINLINE btreeLockCarefully(Btree *p){
  Btree *pLater;

  /* In most cases, we should be able to acquire the lock we
  ** want without having to go through the ascending lock
  ** procedure that follows.  Just be sure not to block.
  */
  if( sqlite3_mutex_try(p->pBt->mutex)==SQLITE_OK ){
    p->pBt->pBt = p;
    p->locked = 1;
    return;
  }

  /* To avoid deadlock, first release all locks with a larger
  ** BtShared address.  Then acquire our lock.  Then reacquire
  ** the other BtShared locks that we used to hold in ascending
  ** order.
  */
  for(pLater=p->pNext; pLater; pLater=pLater->pNext){
    assert( pLater->sharable );
    assert( pLater->pNext==0 || pLater->pNext->pBt>pLater->pBt );
    assert( !pLater->locked || pLater->wantToLock>0 );
    if( pLater->locked ){
      unlockBtreeMutex(pLater);
    }
  }
  lockBtreeMutex(p);
  for(pLater=p->pNext; pLater; pLater=pLater->pNext){
    if( pLater->wantToLock ){
      lockBtreeMutex(pLater);
    }
  }
}


/*
** Exit the recursive mutex on a Btree.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeLeave(Btree *p){
  assert( sqlite3_mutex_held(p->db->mutex) );
  if( p->sharable ){
    assert( p->wantToLock>0 );
    p->wantToLock--;
    if( p->wantToLock==0 ){
      unlockBtreeMutex(p);
    }
  }
}

#ifndef NDEBUG
/*
** Return true if the BtShared mutex is held on the btree, or if the
** B-Tree is not marked as sharable.
**
** This routine is used only from within assert() statements.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeHoldsMutex(Btree *p){
  assert( p->sharable==0 || p->locked==0 || p->wantToLock>0 );
  assert( p->sharable==0 || p->locked==0 || p->db==p->pBt->db );
  assert( p->sharable==0 || p->locked==0 || sqlite3_mutex_held(p->pBt->mutex) );
  assert( p->sharable==0 || p->locked==0 || sqlite3_mutex_held(p->db->mutex) );

  return (p->sharable==0 || p->locked);
}
#endif


#ifndef SQLITE_OMIT_INCRBLOB
/*
** Enter and leave a mutex on a Btree given a cursor owned by that
** Btree.  These entry points are used by incremental I/O and can be
** omitted if that module is not used.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeEnterCursor(BtCursor *pCur){
  sqlite3BtreeEnter(pCur->pBtree);
}
SQLITE_API void SQLITE_STDCALL sqlite3BtreeLeaveCursor(BtCursor *pCur){
  sqlite3BtreeLeave(pCur->pBtree);
}
#endif /* SQLITE_OMIT_INCRBLOB */

/*
** Return true if a particular Btree requires a lock.  Return FALSE if
** no lock is ever required since it is not sharable.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSharable(Btree *p){
  return p->sharable;
}

#else /* SQLITE_THREADSAFE>0 above.  SQLITE_THREADSAFE==0 below */
/*
** The following are special cases for mutex enter routines for use
** in single threaded applications that use shared cache.  Except for
** these two routines, all mutex operations are no-ops in that case and
** are null #defines in btree.h.
**
** If shared cache is disabled, then all btree mutex routines, including
** the ones below, are no-ops and are null #defines in btree.h.
*/

SQLITE_API void SQLITE_STDCALL sqlite3BtreeEnter(Btree *p){
  p->pBt->db = p->db;
}
#endif /* if SQLITE_THREADSAFE */
#endif /* ifndef SQLITE_OMIT_SHARED_CACHE */

/************** End of btmutex.c *********************************************/
/************** Begin file btree.c *******************************************/
/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file implements an external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
/* #include "btreeInt.h" */

/*
** The header string that appears at the beginning of every
** SQLite database.
*/
static const char zMagicHeader[] = SQLITE_FILE_HEADER;

/*
** Set this global variable to 1 to enable tracing using the TRACE
** macro.
*/
#if 0
int sqlite3BtreeTrace=1;  /* True to enable tracing */
# define TRACE(X)  if(sqlite3BtreeTrace){printf X;fflush(stdout);}
#else
# define TRACE(X)
#endif

/*
** Extract a 2-byte big-endian integer from an array of unsigned bytes.
** But if the value is zero, make it 65536.
**
** This routine is used to extract the "offset to cell content area" value
** from the header of a btree page.  If the page size is 65536 and the page
** is empty, the offset should be 65536, but the 2-byte value stores zero.
** This routine makes the necessary adjustment to 65536.
*/
#define get2byteNotZero(X)  (((((int)get2byte(X))-1)&0xffff)+1)

/*
** Values passed as the 5th argument to allocateBtreePage()
*/
#define BTALLOC_ANY   0           /* Allocate any page */
#define BTALLOC_EXACT 1           /* Allocate exact page if possible */
#define BTALLOC_LE    2           /* Allocate any page <= the parameter */

/*
** Macro IfNotOmitAV(x) returns (x) if SQLITE_OMIT_AUTOVACUUM is not 
** defined, or 0 if it is. For example:
**
**   bIncrVacuum = IfNotOmitAV(pBtShared->incrVacuum);
*/
#ifndef SQLITE_OMIT_AUTOVACUUM
#define IfNotOmitAV(expr) (expr)
#else
#define IfNotOmitAV(expr) 0
#endif

#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** A list of BtShared objects that are eligible for participation
** in shared cache.  This variable has file scope during normal builds,
** but the test harness needs to access it so we make it global for 
** test builds.
**
** Access to this variable is protected by SQLITE_MUTEX_STATIC_MASTER.
*/
#ifdef SQLITE_TEST
SQLITE_PRIVATE BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#else
static BtShared *SQLITE_WSD sqlite3SharedCacheList = 0;
#endif
#endif /* SQLITE_OMIT_SHARED_CACHE */

#ifdef SQLITE_OMIT_SHARED_CACHE
  /*
  ** The functions querySharedCacheTableLock(), setSharedCacheTableLock(),
  ** and clearAllSharedCacheTableLocks()
  ** manipulate entries in the BtShared.pLock linked list used to store
  ** shared-cache table level locks. If the library is compiled with the
  ** shared-cache feature disabled, then there is only ever one user
  ** of each BtShared structure and so this locking is not necessary. 
  ** So define the lock related functions as no-ops.
  */
  #define querySharedCacheTableLock(a,b,c) SQLITE_OK
  #define setSharedCacheTableLock(a,b,c) SQLITE_OK
  #define clearAllSharedCacheTableLocks(a)
  #define downgradeAllSharedCacheTableLocks(a)
  #define hasSharedCacheTableLock(a,b,c,d) 1
  #define hasReadConflicts(a, b) 0
#endif

#ifndef SQLITE_OMIT_SHARED_CACHE

#ifdef SQLITE_DEBUG
/*
**** This function is only used as part of an assert() statement. ***
**
** Check to see if pBtree holds the required locks to read or write to the 
** table with root page iRoot.   Return 1 if it does and 0 if not.
**
** For example, when writing to a table with root-page iRoot via 
** Btree connection pBtree:
**
**    assert( hasSharedCacheTableLock(pBtree, iRoot, 0, WRITE_LOCK) );
**
** When writing to an index that resides in a sharable database, the 
** caller should have first obtained a lock specifying the root page of
** the corresponding table. This makes things a bit more complicated,
** as this module treats each table as a separate structure. To determine
** the table corresponding to the index being written, this
** function has to search through the database schema.
**
** Instead of a lock on the table/index rooted at page iRoot, the caller may
** hold a write-lock on the schema table (root page 1). This is also
** acceptable.
*/
static int hasSharedCacheTableLock(
  Btree *pBtree,         /* Handle that must hold lock */
  Pgno iRoot,            /* Root page of b-tree */
  int isIndex,           /* True if iRoot is the root of an index b-tree */
  int eLockType          /* Required lock type (READ_LOCK or WRITE_LOCK) */
){
  Schema *pSchema = (Schema *)pBtree->pBt->pSchema;
  Pgno iTab = 0;
  BtLock *pLock;

  /* If this database is not shareable, or if the client is reading
  ** and has the read-uncommitted flag set, then no lock is required. 
  ** Return true immediately.
  */
  if( (pBtree->sharable==0)
   || (eLockType==READ_LOCK && (pBtree->flags & SQLITE_ReadUncommitted))
  ){
    return 1;
  }

  /* If the client is reading  or writing an index and the schema is
  ** not loaded, then it is too difficult to actually check to see if
  ** the correct locks are held.  So do not bother - just return true.
  ** This case does not come up very often anyhow.
  */
  if( isIndex && (!pSchema || (pSchema->schemaFlags&DB_SchemaLoaded)==0) ){
    return 1;
  }

  /* Figure out the root-page that the lock should be held on. For table
  ** b-trees, this is just the root page of the b-tree being read or
  ** written. For index b-trees, it is the root page of the associated
  ** table.  */
  if( isIndex ){
    HashElem *p;
    for(p=sqliteHashFirst(&pSchema->idxHash); p; p=sqliteHashNext(p)){
      Index *pIdx = (Index *)sqliteHashData(p);
      if( pIdx->tnum==(int)iRoot ){
        if( iTab ){
          /* Two or more indexes share the same root page.  There must
          ** be imposter tables.  So just return true.  The assert is not
          ** useful in that case. */
          return 1;
        }
        iTab = pIdx->pTable->tnum;
      }
    }
  }else{
    iTab = iRoot;
  }

  /* Search for the required lock. Either a write-lock on root-page iTab, a 
  ** write-lock on the schema table, or (if the client is reading) a
  ** read-lock on iTab will suffice. Return 1 if any of these are found.  */
  for(pLock=pBtree->pBt->pLock; pLock; pLock=pLock->pNext){
    if( pLock->pBtree==pBtree 
     && (pLock->iTable==iTab || (pLock->eLock==WRITE_LOCK && pLock->iTable==1))
     && pLock->eLock>=eLockType 
    ){
      return 1;
    }
  }

  /* Failed to find the required lock. */
  return 0;
}
#endif /* SQLITE_DEBUG */

#ifdef SQLITE_DEBUG
/*
**** This function may be used as part of assert() statements only. ****
**
** Return true if it would be illegal for pBtree to write into the
** table or index rooted at iRoot because other shared connections are
** simultaneously reading that same table or index.
**
** It is illegal for pBtree to write if some other Btree object that
** shares the same BtShared object is currently reading or writing
** the iRoot table.  Except, if the other Btree object has the
** read-uncommitted flag set, then it is OK for the other object to
** have a read cursor.
**
** For example, before writing to any part of the table or index
** rooted at page iRoot, one should call:
**
**    assert( !hasReadConflicts(pBtree, iRoot) );
*/
static int hasReadConflicts(Btree *pBtree, Pgno iRoot){
  BtCursor *p;
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    if( p->pgnoRoot==iRoot 
     && p->pBtree!=pBtree
     && 0==(p->pBtree->flags & SQLITE_ReadUncommitted)
    ){
      return 1;
    }
  }
  return 0;
}
#endif    /* #ifdef SQLITE_DEBUG */

/*
** Query to see if Btree handle p may obtain a lock of type eLock 
** (READ_LOCK or WRITE_LOCK) on the table with root-page iTab. Return
** SQLITE_OK if the lock may be obtained (by calling
** setSharedCacheTableLock()), or SQLITE_LOCKED if not.
*/
static int querySharedCacheTableLock(Btree *p, Pgno iTab, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pIter;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( !(p->flags&SQLITE_ReadUncommitted)||eLock==WRITE_LOCK||iTab==1 );
  
  /* If requesting a write-lock, then the Btree must have an open write
  ** transaction on this file. And, obviously, for this to be so there 
  ** must be an open write transaction on the file itself.
  */
  assert( eLock==READ_LOCK || (p==pBt->pWriter && p->inTrans==TRANS_WRITE) );
  assert( eLock==READ_LOCK || pBt->inTransaction==TRANS_WRITE );
  
  /* This routine is a no-op if the shared-cache is not enabled */
  if( !p->sharable ){
    return SQLITE_OK;
  }

  /* If some other connection is holding an exclusive lock, the
  ** requested lock may not be obtained.
  */
  if( pBt->pWriter!=p && (pBt->btsFlags & BTS_EXCLUSIVE)!=0 ){
    sqlite3ConnectionBlocked(p->db, pBt->pWriter->db);
    return SQLITE_LOCKED_SHAREDCACHE;
  }

  for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
    /* The condition (pIter->eLock!=eLock) in the following if(...) 
    ** statement is a simplification of:
    **
    **   (eLock==WRITE_LOCK || pIter->eLock==WRITE_LOCK)
    **
    ** since we know that if eLock==WRITE_LOCK, then no other connection
    ** may hold a WRITE_LOCK on any table in this file (since there can
    ** only be a single writer).
    */
    assert( pIter->eLock==READ_LOCK || pIter->eLock==WRITE_LOCK );
    assert( eLock==READ_LOCK || pIter->pBtree==p || pIter->eLock==READ_LOCK);
    if( pIter->pBtree!=p && pIter->iTable==iTab && pIter->eLock!=eLock ){
      sqlite3ConnectionBlocked(p->db, pIter->pBtree->db);
      if( eLock==WRITE_LOCK ){
        assert( p==pBt->pWriter );
        pBt->btsFlags |= BTS_PENDING;
      }
      return SQLITE_LOCKED_SHAREDCACHE;
    }
  }
  return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Add a lock on the table with root-page iTable to the shared-btree used
** by Btree handle p. Parameter eLock must be either READ_LOCK or 
** WRITE_LOCK.
**
** This function assumes the following:
**
**   (a) The specified Btree object p is connected to a sharable
**       database (one with the BtShared.sharable flag set), and
**
**   (b) No other Btree objects hold a lock that conflicts
**       with the requested lock (i.e. querySharedCacheTableLock() has
**       already been called and returned SQLITE_OK).
**
** SQLITE_OK is returned if the lock is added successfully. SQLITE_NOMEM 
** is returned if a malloc attempt fails.
*/
static int setSharedCacheTableLock(Btree *p, Pgno iTable, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pLock = 0;
  BtLock *pIter;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( p->db!=0 );

  /* A connection with the read-uncommitted flag set will never try to
  ** obtain a read-lock using this function. The only read-lock obtained
  ** by a connection in read-uncommitted mode is on the sqlite_master 
  ** table, and that lock is obtained in BtreeBeginTrans().  */
  assert( 0==(p->db->flags&SQLITE_ReadUncommitted) || eLock==WRITE_LOCK );

  /* This function should only be called on a sharable b-tree after it 
  ** has been determined that no other b-tree holds a conflicting lock.  */
  assert( p->sharable );
  assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );

  /* First search the list for an existing lock on this table. */
  for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
    if( pIter->iTable==iTable && pIter->pBtree==p ){
      pLock = pIter;
      break;
    }
  }

  /* If the above search did not find a BtLock struct associating Btree p
  ** with table iTable, allocate one and link it into the list.
  */
  if( !pLock ){
    pLock = (BtLock *)sqlite3MallocZero(sizeof(BtLock));
    if( !pLock ){
      return SQLITE_NOMEM;
    }
    pLock->iTable = iTable;
    pLock->pBtree = p;
    pLock->pNext = pBt->pLock;
    pBt->pLock = pLock;
  }

  /* Set the BtLock.eLock variable to the maximum of the current lock
  ** and the requested lock. This means if a write-lock was already held
  ** and a read-lock requested, we don't incorrectly downgrade the lock.
  */
  assert( WRITE_LOCK>READ_LOCK );
  if( eLock>pLock->eLock ){
    pLock->eLock = eLock;
  }

  return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Release all the table locks (locks obtained via calls to
** the setSharedCacheTableLock() procedure) held by Btree object p.
**
** This function assumes that Btree p has an open read or write 
** transaction. If it does not, then the BTS_PENDING flag
** may be incorrectly cleared.
*/
static void clearAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  BtLock **ppIter = &pBt->pLock;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( p->sharable || 0==*ppIter );
  assert( p->inTrans>0 );

  while( *ppIter ){
    BtLock *pLock = *ppIter;
    assert( (pBt->btsFlags & BTS_EXCLUSIVE)==0 || pBt->pWriter==pLock->pBtree );
    assert( pLock->pBtree->inTrans>=pLock->eLock );
    if( pLock->pBtree==p ){
      *ppIter = pLock->pNext;
      assert( pLock->iTable!=1 || pLock==&p->lock );
      if( pLock->iTable!=1 ){
        sqlite3_free(pLock);
      }
    }else{
      ppIter = &pLock->pNext;
    }
  }

  assert( (pBt->btsFlags & BTS_PENDING)==0 || pBt->pWriter );
  if( pBt->pWriter==p ){
    pBt->pWriter = 0;
    pBt->btsFlags &= ~(BTS_EXCLUSIVE|BTS_PENDING);
  }else if( pBt->nTransaction==2 ){
    /* This function is called when Btree p is concluding its 
    ** transaction. If there currently exists a writer, and p is not
    ** that writer, then the number of locks held by connections other
    ** than the writer must be about to drop to zero. In this case
    ** set the BTS_PENDING flag to 0.
    **
    ** If there is not currently a writer, then BTS_PENDING must
    ** be zero already. So this next line is harmless in that case.
    */
    pBt->btsFlags &= ~BTS_PENDING;
  }
}

/*
** This function changes all write-locks held by Btree p into read-locks.
*/
static void downgradeAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  if( pBt->pWriter==p ){
    BtLock *pLock;
    pBt->pWriter = 0;
    pBt->btsFlags &= ~(BTS_EXCLUSIVE|BTS_PENDING);
    for(pLock=pBt->pLock; pLock; pLock=pLock->pNext){
      assert( pLock->eLock==READ_LOCK || pLock->pBtree==p );
      pLock->eLock = READ_LOCK;
    }
  }
}

#endif /* SQLITE_OMIT_SHARED_CACHE */

static void releasePage(MemPage *pPage);  /* Forward reference */

/*
***** This routine is used inside of assert() only ****
**
** Verify that the cursor holds the mutex on its BtShared
*/
#ifdef SQLITE_DEBUG
static int cursorHoldsMutex(BtCursor *p){
  return sqlite3_mutex_held(p->pBt->mutex);
}
#endif

/*
** Invalidate the overflow cache of the cursor passed as the first argument.
** on the shared btree structure pBt.
*/
#define invalidateOverflowCache(pCur) (pCur->curFlags &= ~BTCF_ValidOvfl)

/*
** Invalidate the overflow page-list cache for all cursors opened
** on the shared btree structure pBt.
*/
static void invalidateAllOverflowCache(BtShared *pBt){
  BtCursor *p;
  assert( sqlite3_mutex_held(pBt->mutex) );
  for(p=pBt->pCursor; p; p=p->pNext){
    invalidateOverflowCache(p);
  }
}

#ifndef SQLITE_OMIT_INCRBLOB
/*
** This function is called before modifying the contents of a table
** to invalidate any incrblob cursors that are open on the
** row or one of the rows being modified.
**
** If argument isClearTable is true, then the entire contents of the
** table is about to be deleted. In this case invalidate all incrblob
** cursors open on any row within the table with root-page pgnoRoot.
**
** Otherwise, if argument isClearTable is false, then the row with
** rowid iRow is being replaced or deleted. In this case invalidate
** only those incrblob cursors open on that specific row.
*/
static void invalidateIncrblobCursors(
  Btree *pBtree,          /* The database file to check */
  i64 iRow,               /* The rowid that might be changing */
  int isClearTable        /* True if all rows are being deleted */
){
  BtCursor *p;
  if( pBtree->hasIncrblobCur==0 ) return;
  assert( sqlite3BtreeHoldsMutex(pBtree) );
  pBtree->hasIncrblobCur = 0;
  for(p=pBtree->pBt->pCursor; p; p=p->pNext){
    if( (p->curFlags & BTCF_Incrblob)!=0 ){
      pBtree->hasIncrblobCur = 1;
      if( isClearTable || p->info.nKey==iRow ){
        p->eState = CURSOR_INVALID;
      }
    }
  }
}

#else
  /* Stub function when INCRBLOB is omitted */
  #define invalidateIncrblobCursors(x,y,z)
#endif /* SQLITE_OMIT_INCRBLOB */

/*
** Set bit pgno of the BtShared.pHasContent bitvec. This is called 
** when a page that previously contained data becomes a free-list leaf 
** page.
**
** The BtShared.pHasContent bitvec exists to work around an obscure
** bug caused by the interaction of two useful IO optimizations surrounding
** free-list leaf pages:
**
**   1) When all data is deleted from a page and the page becomes
**      a free-list leaf page, the page is not written to the database
**      (as free-list leaf pages contain no meaningful data). Sometimes
**      such a page is not even journalled (as it will not be modified,
**      why bother journalling it?).
**
**   2) When a free-list leaf page is reused, its content is not read
**      from the database or written to the journal file (why should it
**      be, if it is not at all meaningful?).
**
** By themselves, these optimizations work fine and provide a handy
** performance boost to bulk delete or insert operations. However, if
** a page is moved to the free-list and then reused within the same
** transaction, a problem comes up. If the page is not journalled when
** it is moved to the free-list and it is also not journalled when it
** is extracted from the free-list and reused, then the original data
** may be lost. In the event of a rollback, it may not be possible
** to restore the database to its original configuration.
**
** The solution is the BtShared.pHasContent bitvec. Whenever a page is 
** moved to become a free-list leaf page, the corresponding bit is
** set in the bitvec. Whenever a leaf page is extracted from the free-list,
** optimization 2 above is omitted if the corresponding bit is already
** set in BtShared.pHasContent. The contents of the bitvec are cleared
** at the end of every transaction.
*/
static int btreeSetHasContent(BtShared *pBt, Pgno pgno){
  int rc = SQLITE_OK;
  if( !pBt->pHasContent ){
    assert( pgno<=pBt->nPage );
    pBt->pHasContent = sqlite3BitvecCreate(pBt->nPage);
    if( !pBt->pHasContent ){
      rc = SQLITE_NOMEM;
    }
  }
  if( rc==SQLITE_OK && pgno<=sqlite3BitvecSize(pBt->pHasContent) ){
    rc = sqlite3BitvecSet(pBt->pHasContent, pgno);
  }
  return rc;
}

/*
** Query the BtShared.pHasContent vector.
**
** This function is called when a free-list leaf page is removed from the
** free-list for reuse. It returns false if it is safe to retrieve the
** page from the pager layer with the 'no-content' flag set. True otherwise.
*/
static int btreeGetHasContent(BtShared *pBt, Pgno pgno){
  Bitvec *p = pBt->pHasContent;
  return (p && (pgno>sqlite3BitvecSize(p) || sqlite3BitvecTest(p, pgno)));
}

/*
** Clear (destroy) the BtShared.pHasContent bitvec. This should be
** invoked at the conclusion of each write-transaction.
*/
static void btreeClearHasContent(BtShared *pBt){
  sqlite3BitvecDestroy(pBt->pHasContent);
  pBt->pHasContent = 0;
}

/*
** Release all of the apPage[] pages for a cursor.
*/
static void btreeReleaseAllCursorPages(BtCursor *pCur){
  int i;
  for(i=0; i<=pCur->iPage; i++){
    releasePage(pCur->apPage[i]);
    pCur->apPage[i] = 0;
  }
  pCur->iPage = -1;
}

/*
** The cursor passed as the only argument must point to a valid entry
** when this function is called (i.e. have eState==CURSOR_VALID). This
** function saves the current cursor key in variables pCur->nKey and
** pCur->pKey. SQLITE_OK is returned if successful or an SQLite error 
** code otherwise.
**
** If the cursor is open on an intkey table, then the integer key
** (the rowid) is stored in pCur->nKey and pCur->pKey is left set to
** NULL. If the cursor is open on a non-intkey table, then pCur->pKey is 
** set to point to a malloced buffer pCur->nKey bytes in size containing 
** the key.
*/
static int saveCursorKey(BtCursor *pCur){
  int rc;
  assert( CURSOR_VALID==pCur->eState );
  assert( 0==pCur->pKey );
  assert( cursorHoldsMutex(pCur) );

  rc = sqlite3BtreeKeySize(pCur, &pCur->nKey);
  assert( rc==SQLITE_OK );  /* KeySize() cannot fail */

  /* If this is an intKey table, then the above call to BtreeKeySize()
  ** stores the integer key in pCur->nKey. In this case this value is
  ** all that is required. Otherwise, if pCur is not open on an intKey
  ** table, then malloc space for and store the pCur->nKey bytes of key 
  ** data.  */
  if( 0==pCur->curIntKey ){
    void *pKey = sqlite3Malloc( pCur->nKey );
    if( pKey ){
      rc = sqlite3BtreeKey(pCur, 0, (int)pCur->nKey, pKey);
      if( rc==SQLITE_OK ){
        pCur->pKey = pKey;
      }else{
        sqlite3_free(pKey);
      }
    }else{
      rc = SQLITE_NOMEM;
    }
  }
  assert( !pCur->curIntKey || !pCur->pKey );
  return rc;
}

/*
** Save the current cursor position in the variables BtCursor.nKey 
** and BtCursor.pKey. The cursor's state is set to CURSOR_REQUIRESEEK.
**
** The caller must ensure that the cursor is valid (has eState==CURSOR_VALID)
** prior to calling this routine.  
*/
static int saveCursorPosition(BtCursor *pCur){
  int rc;

  assert( CURSOR_VALID==pCur->eState || CURSOR_SKIPNEXT==pCur->eState );
  assert( 0==pCur->pKey );
  assert( cursorHoldsMutex(pCur) );

  if( pCur->eState==CURSOR_SKIPNEXT ){
    pCur->eState = CURSOR_VALID;
  }else{
    pCur->skipNext = 0;
  }

  rc = saveCursorKey(pCur);
  if( rc==SQLITE_OK ){
    btreeReleaseAllCursorPages(pCur);
    pCur->eState = CURSOR_REQUIRESEEK;
  }

  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl|BTCF_AtLast);
  return rc;
}

/* Forward reference */
static int SQLITE_NOINLINE saveCursorsOnList(BtCursor*,Pgno,BtCursor*);

/*
** Save the positions of all cursors (except pExcept) that are open on
** the table with root-page iRoot.  "Saving the cursor position" means that
** the location in the btree is remembered in such a way that it can be
** moved back to the same spot after the btree has been modified.  This
** routine is called just before cursor pExcept is used to modify the
** table, for example in BtreeDelete() or BtreeInsert().
**
** If there are two or more cursors on the same btree, then all such 
** cursors should have their BTCF_Multiple flag set.  The btreeCursor()
** routine enforces that rule.  This routine only needs to be called in
** the uncommon case when pExpect has the BTCF_Multiple flag set.
**
** If pExpect!=NULL and if no other cursors are found on the same root-page,
** then the BTCF_Multiple flag on pExpect is cleared, to avoid another
** pointless call to this routine.
**
** Implementation note:  This routine merely checks to see if any cursors
** need to be saved.  It calls out to saveCursorsOnList() in the (unusual)
** event that cursors are in need to being saved.
*/
static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
  BtCursor *p;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pExcept==0 || pExcept->pBt==pBt );
  for(p=pBt->pCursor; p; p=p->pNext){
    if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ) break;
  }
  if( p ) return saveCursorsOnList(p, iRoot, pExcept);
  if( pExcept ) pExcept->curFlags &= ~BTCF_Multiple;
  return SQLITE_OK;
}

/* This helper routine to saveAllCursors does the actual work of saving
** the cursors if and when a cursor is found that actually requires saving.
** The common case is that no cursors need to be saved, so this routine is
** broken out from its caller to avoid unnecessary stack pointer movement.
*/
static int SQLITE_NOINLINE saveCursorsOnList(
  BtCursor *p,         /* The first cursor that needs saving */
  Pgno iRoot,          /* Only save cursor with this iRoot. Save all if zero */
  BtCursor *pExcept    /* Do not save this cursor */
){
  do{
    if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ){
      if( p->eState==CURSOR_VALID || p->eState==CURSOR_SKIPNEXT ){
        int rc = saveCursorPosition(p);
        if( SQLITE_OK!=rc ){
          return rc;
        }
      }else{
        testcase( p->iPage>0 );
        btreeReleaseAllCursorPages(p);
      }
    }
    p = p->pNext;
  }while( p );
  return SQLITE_OK;
}

/*
** Clear the current cursor position.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeClearCursor(BtCursor *pCur){
  assert( cursorHoldsMutex(pCur) );
  sqlite3_free(pCur->pKey);
  pCur->pKey = 0;
  pCur->eState = CURSOR_INVALID;
}

/*
** In this version of BtreeMoveto, pKey is a packed index record
** such as is generated by the OP_MakeRecord opcode.  Unpack the
** record and then call BtreeMovetoUnpacked() to do the work.
*/
static int btreeMoveto(
  BtCursor *pCur,     /* Cursor open on the btree to be searched */
  const void *pKey,   /* Packed key if the btree is an index */
  i64 nKey,           /* Integer key for tables.  Size of pKey for indices */
  int bias,           /* Bias search to the high end */
  int *pRes           /* Write search results here */
){
  int rc;                    /* Status code */
  UnpackedRecord *pIdxKey;   /* Unpacked index key */
  char aSpace[200];          /* Temp space for pIdxKey - to avoid a malloc */
  char *pFree = 0;

  if( pKey ){
    assert( nKey==(i64)(int)nKey );
    pIdxKey = sqlite3VdbeAllocUnpackedRecord(
        pCur->pKeyInfo, aSpace, sizeof(aSpace), &pFree
    );
    if( pIdxKey==0 ) return SQLITE_NOMEM;
    sqlite3VdbeRecordUnpack(pCur->pKeyInfo, (int)nKey, pKey, pIdxKey);
    if( pIdxKey->nField==0 ){
      sqlite3DbFree(pCur->pKeyInfo->pBtree, pFree);
      return SQLITE_CORRUPT_BKPT;
    }
  }else{
    pIdxKey = 0;
  }
  rc = sqlite3BtreeMovetoUnpacked(pCur, pIdxKey, nKey, bias, pRes);
  if( pFree ){
    sqlite3DbFree(pCur->pKeyInfo->pBtree, pFree);
  }
  return rc;
}

/*
** Restore the cursor to the position it was in (or as close to as possible)
** when saveCursorPosition() was called. Note that this call deletes the 
** saved position info stored by saveCursorPosition(), so there can be
** at most one effective restoreCursorPosition() call after each 
** saveCursorPosition().
*/
static int btreeRestoreCursorPosition(BtCursor *pCur){
  int rc;
  int skipNext;
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState>=CURSOR_REQUIRESEEK );
  if( pCur->eState==CURSOR_FAULT ){
    return pCur->skipNext;
  }
  pCur->eState = CURSOR_INVALID;
  rc = btreeMoveto(pCur, pCur->pKey, pCur->nKey, 0, &skipNext);
  if( rc==SQLITE_OK ){
    sqlite3_free(pCur->pKey);
    pCur->pKey = 0;
    assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_INVALID );
    pCur->skipNext |= skipNext;
    if( pCur->skipNext && pCur->eState==CURSOR_VALID ){
      pCur->eState = CURSOR_SKIPNEXT;
    }
  }
  return rc;
}

#define restoreCursorPosition(p) \
  (p->eState>=CURSOR_REQUIRESEEK ? \
         btreeRestoreCursorPosition(p) : \
         SQLITE_OK)

/*
** Determine whether or not a cursor has moved from the position where
** it was last placed, or has been invalidated for any other reason.
** Cursors can move when the row they are pointing at is deleted out
** from under them, for example.  Cursor might also move if a btree
** is rebalanced.
**
** Calling this routine with a NULL cursor pointer returns false.
**
** Use the separate sqlite3BtreeCursorRestore() routine to restore a cursor
** back to where it ought to be if this routine returns true.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursorHasMoved(BtCursor *pCur){
  return pCur->eState!=CURSOR_VALID;
}

/*
** This routine restores a cursor back to its original position after it
** has been moved by some outside activity (such as a btree rebalance or
** a row having been deleted out from under the cursor).  
**
** On success, the *pDifferentRow parameter is false if the cursor is left
** pointing at exactly the same row.  *pDifferntRow is the row the cursor
** was pointing to has been deleted, forcing the cursor to point to some
** nearby row.
**
** This routine should only be called for a cursor that just returned
** TRUE from sqlite3BtreeCursorHasMoved().
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursorRestore(BtCursor *pCur, int *pDifferentRow){
  int rc;

  assert( pCur!=0 );
  assert( pCur->eState!=CURSOR_VALID );
  rc = restoreCursorPosition(pCur);
  if( rc ){
    *pDifferentRow = 1;
    return rc;
  }
  if( pCur->eState!=CURSOR_VALID ){
    *pDifferentRow = 1;
  }else{
    assert( pCur->skipNext==0 );
    *pDifferentRow = 0;
  }
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page
** number for the pointer-map page that contains the entry for the
** input page number.
**
** Return 0 (not a valid page) for pgno==1 since there is
** no pointer map associated with page 1.  The integrity_check logic
** requires that ptrmapPageno(*,1)!=1.
*/
static Pgno ptrmapPageno(BtShared *pBt, Pgno pgno){
  int nPagesPerMapPage;
  Pgno iPtrMap, ret;
  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno<2 ) return 0;
  nPagesPerMapPage = (pBt->usableSize/5)+1;
  iPtrMap = (pgno-2)/nPagesPerMapPage;
  ret = (iPtrMap*nPagesPerMapPage) + 2; 
  if( ret==PENDING_BYTE_PAGE(pBt) ){
    ret++;
  }
  return ret;
}

/*
** Write an entry into the pointer map.
**
** This routine updates the pointer map entry for page number 'key'
** so that it maps to type 'eType' and parent page number 'pgno'.
**
** If *pRC is initially non-zero (non-SQLITE_OK) then this routine is
** a no-op.  If an error occurs, the appropriate error code is written
** into *pRC.
*/
static void ptrmapPut(BtShared *pBt, Pgno key, u8 eType, Pgno parent, int *pRC){
  DbPage *pDbPage;  /* The pointer map page */
  u8 *pPtrmap;      /* The pointer map data */
  Pgno iPtrmap;     /* The pointer map page number */
  int offset;       /* Offset in pointer map page */
  int rc;           /* Return code from subfunctions */

  if( *pRC ) return;

  assert( sqlite3_mutex_held(pBt->mutex) );
  /* The master-journal page number must never be used as a pointer map page */
  assert( 0==PTRMAP_ISPAGE(pBt, PENDING_BYTE_PAGE(pBt)) );

  assert( pBt->autoVacuum );
  if( key==0 ){
    *pRC = SQLITE_CORRUPT_BKPT;
    return;
  }
  iPtrmap = PTRMAP_PAGENO(pBt, key);
  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
  if( rc!=SQLITE_OK ){
    *pRC = rc;
    return;
  }
  offset = PTRMAP_PTROFFSET(iPtrmap, key);
  if( offset<0 ){
    *pRC = SQLITE_CORRUPT_BKPT;
    goto ptrmap_exit;
  }
  assert( offset <= (int)pBt->usableSize-5 );
  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);

  if( eType!=pPtrmap[offset] || get4byte(&pPtrmap[offset+1])!=parent ){
    TRACE(("PTRMAP_UPDATE: %d->(%d,%d)\n", key, eType, parent));
    *pRC= rc = sqlite3PagerWrite(pDbPage);
    if( rc==SQLITE_OK ){
      pPtrmap[offset] = eType;
      put4byte(&pPtrmap[offset+1], parent);
    }
  }

ptrmap_exit:
  sqlite3PagerUnref(pDbPage);
}

/*
** Read an entry from the pointer map.
**
** This routine retrieves the pointer map entry for page 'key', writing
** the type and parent page number to *pEType and *pPgno respectively.
** An error code is returned if something goes wrong, otherwise SQLITE_OK.
*/
static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
  DbPage *pDbPage;   /* The pointer map page */
  int iPtrmap;       /* Pointer map page index */
  u8 *pPtrmap;       /* Pointer map page data */
  int offset;        /* Offset of entry in pointer map */
  int rc;

  assert( sqlite3_mutex_held(pBt->mutex) );

  iPtrmap = PTRMAP_PAGENO(pBt, key);
  rc = sqlite3PagerGet(pBt->pPager, iPtrmap, &pDbPage);
  if( rc!=0 ){
    return rc;
  }
  pPtrmap = (u8 *)sqlite3PagerGetData(pDbPage);

  offset = PTRMAP_PTROFFSET(iPtrmap, key);
  if( offset<0 ){
    sqlite3PagerUnref(pDbPage);
    return SQLITE_CORRUPT_BKPT;
  }
  assert( offset <= (int)pBt->usableSize-5 );
  assert( pEType!=0 );
  *pEType = pPtrmap[offset];
  if( pPgno ) *pPgno = get4byte(&pPtrmap[offset+1]);

  sqlite3PagerUnref(pDbPage);
  if( *pEType<1 || *pEType>5 ) return SQLITE_CORRUPT_BKPT;
  return SQLITE_OK;
}

#else /* if defined SQLITE_OMIT_AUTOVACUUM */
  #define ptrmapPut(w,x,y,z,rc)
  #define ptrmapGet(w,x,y,z) SQLITE_OK
  #define ptrmapPutOvflPtr(x, y, rc)
#endif

/*
** Given a btree page and a cell index (0 means the first cell on
** the page, 1 means the second cell, and so forth) return a pointer
** to the cell content.
**
** findCellPastPtr() does the same except it skips past the initial
** 4-byte child pointer found on interior pages, if there is one.
**
** This routine works only for pages that do not contain overflow cells.
*/
#define findCell(P,I) \
  ((P)->aData + ((P)->maskPage & get2byteAligned(&(P)->aCellIdx[2*(I)])))
#define findCellPastPtr(P,I) \
  ((P)->aDataOfst + ((P)->maskPage & get2byteAligned(&(P)->aCellIdx[2*(I)])))


/*
** This is common tail processing for btreeParseCellPtr() and
** btreeParseCellPtrIndex() for the case when the cell does not fit entirely
** on a single B-tree page.  Make necessary adjustments to the CellInfo
** structure.
*/
static SQLITE_NOINLINE void btreeParseCellAdjustSizeForOverflow(
  MemPage *pPage,         /* Page containing the cell */
  u8 *pCell,              /* Pointer to the cell text. */
  CellInfo *pInfo         /* Fill in this structure */
){
  /* If the payload will not fit completely on the local page, we have
  ** to decide how much to store locally and how much to spill onto
  ** overflow pages.  The strategy is to minimize the amount of unused
  ** space on overflow pages while keeping the amount of local storage
  ** in between minLocal and maxLocal.
  **
  ** Warning:  changing the way overflow payload is distributed in any
  ** way will result in an incompatible file format.
  */
  int minLocal;  /* Minimum amount of payload held locally */
  int maxLocal;  /* Maximum amount of payload held locally */
  int surplus;   /* Overflow payload available for local storage */

  minLocal = pPage->minLocal;
  maxLocal = pPage->maxLocal;
  surplus = minLocal + (pInfo->nPayload - minLocal)%(pPage->pBt->usableSize-4);
  testcase( surplus==maxLocal );
  testcase( surplus==maxLocal+1 );
  if( surplus <= maxLocal ){
    pInfo->nLocal = (u16)surplus;
  }else{
    pInfo->nLocal = (u16)minLocal;
  }
  pInfo->iOverflow = (u16)(&pInfo->pPayload[pInfo->nLocal] - pCell);
  pInfo->nSize = pInfo->iOverflow + 4;
}

/*
** The following routines are implementations of the MemPage.xParseCell()
** method.
**
** Parse a cell content block and fill in the CellInfo structure.
**
** btreeParseCellPtr()        =>   table btree leaf nodes
** btreeParseCellNoPayload()  =>   table btree internal nodes
** btreeParseCellPtrIndex()   =>   index btree nodes
**
** There is also a wrapper function btreeParseCell() that works for
** all MemPage types and that references the cell by index rather than
** by pointer.
*/
static void btreeParseCellPtrNoPayload(
  MemPage *pPage,         /* Page containing the cell */
  u8 *pCell,              /* Pointer to the cell text. */
  CellInfo *pInfo         /* Fill in this structure */
){
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( pPage->leaf==0 );
  assert( pPage->noPayload );
  assert( pPage->childPtrSize==4 );
#ifndef SQLITE_DEBUG
  UNUSED_PARAMETER(pPage);
#endif
  pInfo->nSize = 4 + getVarint(&pCell[4], (u64*)&pInfo->nKey);
  pInfo->nPayload = 0;
  pInfo->nLocal = 0;
  pInfo->iOverflow = 0;
  pInfo->pPayload = 0;
  return;
}
static void btreeParseCellPtr(
  MemPage *pPage,         /* Page containing the cell */
  u8 *pCell,              /* Pointer to the cell text. */
  CellInfo *pInfo         /* Fill in this structure */
){
  u8 *pIter;              /* For scanning through pCell */
  u32 nPayload;           /* Number of bytes of cell payload */
  u64 iKey;               /* Extracted Key value */

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( pPage->leaf==0 || pPage->leaf==1 );
  assert( pPage->intKeyLeaf || pPage->noPayload );
  assert( pPage->noPayload==0 );
  assert( pPage->intKeyLeaf );
  assert( pPage->childPtrSize==0 );
  pIter = pCell;

  /* The next block of code is equivalent to:
  **
  **     pIter += getVarint32(pIter, nPayload);
  **
  ** The code is inlined to avoid a function call.
  */
  nPayload = *pIter;
  if( nPayload>=0x80 ){
    u8 *pEnd = &pIter[8];
    nPayload &= 0x7f;
    do{
      nPayload = (nPayload<<7) | (*++pIter & 0x7f);
    }while( (*pIter)>=0x80 && pIter<pEnd );
  }
  pIter++;

  /* The next block of code is equivalent to:
  **
  **     pIter += getVarint(pIter, (u64*)&pInfo->nKey);
  **
  ** The code is inlined to avoid a function call.
  */
  iKey = *pIter;
  if( iKey>=0x80 ){
    u8 *pEnd = &pIter[7];
    iKey &= 0x7f;
    while(1){
      iKey = (iKey<<7) | (*++pIter & 0x7f);
      if( (*pIter)<0x80 ) break;
      if( pIter>=pEnd ){
        iKey = (iKey<<8) | *++pIter;
        break;
      }
    }
  }
  pIter++;

  pInfo->nKey = *(i64*)&iKey;
  pInfo->nPayload = nPayload;
  pInfo->pPayload = pIter;
  testcase( nPayload==pPage->maxLocal );
  testcase( nPayload==pPage->maxLocal+1 );
  if( nPayload<=pPage->maxLocal ){
    /* This is the (easy) common case where the entire payload fits
    ** on the local page.  No overflow is required.
    */
    pInfo->nSize = nPayload + (u16)(pIter - pCell);
    if( pInfo->nSize<4 ) pInfo->nSize = 4;
    pInfo->nLocal = (u16)nPayload;
    pInfo->iOverflow = 0;
  }else{
    btreeParseCellAdjustSizeForOverflow(pPage, pCell, pInfo);
  }
}
static void btreeParseCellPtrIndex(
  MemPage *pPage,         /* Page containing the cell */
  u8 *pCell,              /* Pointer to the cell text. */
  CellInfo *pInfo         /* Fill in this structure */
){
  u8 *pIter;              /* For scanning through pCell */
  u32 nPayload;           /* Number of bytes of cell payload */

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( pPage->leaf==0 || pPage->leaf==1 );
  assert( pPage->intKeyLeaf==0 );
  assert( pPage->noPayload==0 );
  pIter = pCell + pPage->childPtrSize;
  nPayload = *pIter;
  if( nPayload>=0x80 ){
    u8 *pEnd = &pIter[8];
    nPayload &= 0x7f;
    do{
      nPayload = (nPayload<<7) | (*++pIter & 0x7f);
    }while( *(pIter)>=0x80 && pIter<pEnd );
  }
  pIter++;
  pInfo->nKey = nPayload;
  pInfo->nPayload = nPayload;
  pInfo->pPayload = pIter;
  testcase( nPayload==pPage->maxLocal );
  testcase( nPayload==pPage->maxLocal+1 );
  if( nPayload<=pPage->maxLocal ){
    /* This is the (easy) common case where the entire payload fits
    ** on the local page.  No overflow is required.
    */
    pInfo->nSize = nPayload + (u16)(pIter - pCell);
    if( pInfo->nSize<4 ) pInfo->nSize = 4;
    pInfo->nLocal = (u16)nPayload;
    pInfo->iOverflow = 0;
  }else{
    btreeParseCellAdjustSizeForOverflow(pPage, pCell, pInfo);
  }
}
static void btreeParseCell(
  MemPage *pPage,         /* Page containing the cell */
  int iCell,              /* The cell index.  First cell is 0 */
  CellInfo *pInfo         /* Fill in this structure */
){
  pPage->xParseCell(pPage, findCell(pPage, iCell), pInfo);
}

/*
** The following routines are implementations of the MemPage.xCellSize
** method.
**
** Compute the total number of bytes that a Cell needs in the cell
** data area of the btree-page.  The return number includes the cell
** data header and the local payload, but not any overflow page or
** the space used by the cell pointer.
**
** cellSizePtrNoPayload()    =>   table internal nodes
** cellSizePtr()             =>   all index nodes & table leaf nodes
*/
static u16 cellSizePtr(MemPage *pPage, u8 *pCell){
  u8 *pIter = pCell + pPage->childPtrSize; /* For looping over bytes of pCell */
  u8 *pEnd;                                /* End mark for a varint */
  u32 nSize;                               /* Size value to return */

#ifdef SQLITE_DEBUG
  /* The value returned by this function should always be the same as
  ** the (CellInfo.nSize) value found by doing a full parse of the
  ** cell. If SQLITE_DEBUG is defined, an assert() at the bottom of
  ** this function verifies that this invariant is not violated. */
  CellInfo debuginfo;
  pPage->xParseCell(pPage, pCell, &debuginfo);
#endif

  assert( pPage->noPayload==0 );
  nSize = *pIter;
  if( nSize>=0x80 ){
    pEnd = &pIter[8];
    nSize &= 0x7f;
    do{
      nSize = (nSize<<7) | (*++pIter & 0x7f);
    }while( *(pIter)>=0x80 && pIter<pEnd );
  }
  pIter++;
  if( pPage->intKey ){
    /* pIter now points at the 64-bit integer key value, a variable length 
    ** integer. The following block moves pIter to point at the first byte
    ** past the end of the key value. */
    pEnd = &pIter[9];
    while( (*pIter++)&0x80 && pIter<pEnd );
  }
  testcase( nSize==pPage->maxLocal );
  testcase( nSize==pPage->maxLocal+1 );
  if( nSize<=pPage->maxLocal ){
    nSize += (u32)(pIter - pCell);
    if( nSize<4 ) nSize = 4;
  }else{
    int minLocal = pPage->minLocal;
    nSize = minLocal + (nSize - minLocal) % (pPage->pBt->usableSize - 4);
    testcase( nSize==pPage->maxLocal );
    testcase( nSize==pPage->maxLocal+1 );
    if( nSize>pPage->maxLocal ){
      nSize = minLocal;
    }
    nSize += 4 + (u16)(pIter - pCell);
  }
  assert( nSize==debuginfo.nSize || CORRUPT_DB );
  return (u16)nSize;
}
static u16 cellSizePtrNoPayload(MemPage *pPage, u8 *pCell){
  u8 *pIter = pCell + 4; /* For looping over bytes of pCell */
  u8 *pEnd;              /* End mark for a varint */

#ifdef SQLITE_DEBUG
  /* The value returned by this function should always be the same as
  ** the (CellInfo.nSize) value found by doing a full parse of the
  ** cell. If SQLITE_DEBUG is defined, an assert() at the bottom of
  ** this function verifies that this invariant is not violated. */
  CellInfo debuginfo;
  pPage->xParseCell(pPage, pCell, &debuginfo);
#else
  UNUSED_PARAMETER(pPage);
#endif

  assert( pPage->childPtrSize==4 );
  pEnd = pIter + 9;
  while( (*pIter++)&0x80 && pIter<pEnd );
  assert( debuginfo.nSize==(u16)(pIter - pCell) || CORRUPT_DB );
  return (u16)(pIter - pCell);
}


#ifdef SQLITE_DEBUG
/* This variation on cellSizePtr() is used inside of assert() statements
** only. */
static u16 cellSize(MemPage *pPage, int iCell){
  return pPage->xCellSize(pPage, findCell(pPage, iCell));
}
#endif

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static void ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell, int *pRC){
  CellInfo info;
  if( *pRC ) return;
  assert( pCell!=0 );
  pPage->xParseCell(pPage, pCell, &info);
  if( info.iOverflow ){
    Pgno ovfl = get4byte(&pCell[info.iOverflow]);
    ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno, pRC);
  }
}
#endif


/*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
** big FreeBlk that occurs in between the header and cell
** pointer array and the cell content area.
**
** EVIDENCE-OF: R-44582-60138 SQLite may from time to time reorganize a
** b-tree page so that there are no freeblocks or fragment bytes, all
** unused bytes are contained in the unallocated space region, and all
** cells are packed tightly at the end of the page.
*/
static int defragmentPage(MemPage *pPage){
  int i;                     /* Loop counter */
  int pc;                    /* Address of the i-th cell */
  int hdr;                   /* Offset to the page header */
  int size;                  /* Size of a cell */
  int usableSize;            /* Number of usable bytes on a page */
  int cellOffset;            /* Offset to the cell pointer array */
  int cbrk;                  /* Offset to the cell content area */
  int nCell;                 /* Number of cells on the page */
  unsigned char *data;       /* The page data */
  unsigned char *temp;       /* Temp area for cell content */
  unsigned char *src;        /* Source of content */
  int iCellFirst;            /* First allowable cell index */
  int iCellLast;             /* Last possible cell index */


  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( pPage->pBt!=0 );
  assert( pPage->pBt->usableSize <= SQLITE_MAX_PAGE_SIZE );
  assert( pPage->nOverflow==0 );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  temp = 0;
  src = data = pPage->aData;
  hdr = pPage->hdrOffset;
  cellOffset = pPage->cellOffset;
  nCell = pPage->nCell;
  assert( nCell==get2byte(&data[hdr+3]) );
  usableSize = pPage->pBt->usableSize;
  cbrk = usableSize;
  iCellFirst = cellOffset + 2*nCell;
  iCellLast = usableSize - 4;
  for(i=0; i<nCell; i++){
    u8 *pAddr;     /* The i-th cell pointer */
    pAddr = &data[cellOffset + i*2];
    pc = get2byte(pAddr);
    testcase( pc==iCellFirst );
    testcase( pc==iCellLast );
    /* These conditions have already been verified in btreeInitPage()
    ** if PRAGMA cell_size_check=ON.
    */
    if( pc<iCellFirst || pc>iCellLast ){
      return SQLITE_CORRUPT_BKPT;
    }
    assert( pc>=iCellFirst && pc<=iCellLast );
    size = pPage->xCellSize(pPage, &src[pc]);
    cbrk -= size;
    if( cbrk<iCellFirst || pc+size>usableSize ){
      return SQLITE_CORRUPT_BKPT;
    }
    assert( cbrk+size<=usableSize && cbrk>=iCellFirst );
    testcase( cbrk+size==usableSize );
    testcase( pc+size==usableSize );
    put2byte(pAddr, cbrk);
    if( temp==0 ){
      int x;
      if( cbrk==pc ) continue;
      temp = sqlite3PagerTempSpace(pPage->pBt->pPager);
      x = get2byte(&data[hdr+5]);
      memcpy(&temp[x], &data[x], (cbrk+size) - x);
      src = temp;
    }
    memcpy(&data[cbrk], &src[pc], size);
  }
  assert( cbrk>=iCellFirst );
  put2byte(&data[hdr+5], cbrk);
  data[hdr+1] = 0;
  data[hdr+2] = 0;
  data[hdr+7] = 0;
  memset(&data[iCellFirst], 0, cbrk-iCellFirst);
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  if( cbrk-iCellFirst!=pPage->nFree ){
    return SQLITE_CORRUPT_BKPT;
  }
  return SQLITE_OK;
}

/*
** Search the free-list on page pPg for space to store a cell nByte bytes in
** size. If one can be found, return a pointer to the space and remove it
** from the free-list.
**
** If no suitable space can be found on the free-list, return NULL.
**
** This function may detect corruption within pPg.  If corruption is
** detected then *pRc is set to SQLITE_CORRUPT and NULL is returned.
**
** Slots on the free list that are between 1 and 3 bytes larger than nByte
** will be ignored if adding the extra space to the fragmentation count
** causes the fragmentation count to exceed 60.
*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
  const int hdr = pPg->hdrOffset;
  u8 * const aData = pPg->aData;
  int iAddr = hdr + 1;
  int pc = get2byte(&aData[iAddr]);
  int x;
  int usableSize = pPg->pBt->usableSize;

  assert( pc>0 );
  do{
    int size;            /* Size of the free slot */
    /* EVIDENCE-OF: R-06866-39125 Freeblocks are always connected in order of
    ** increasing offset. */
    if( pc>usableSize-4 || pc<iAddr+4 ){
      *pRc = SQLITE_CORRUPT_BKPT;
      return 0;
    }
    /* EVIDENCE-OF: R-22710-53328 The third and fourth bytes of each
    ** freeblock form a big-endian integer which is the size of the freeblock
    ** in bytes, including the 4-byte header. */
    size = get2byte(&aData[pc+2]);
    if( (x = size - nByte)>=0 ){
      testcase( x==4 );
      testcase( x==3 );
      if( pc < pPg->cellOffset+2*pPg->nCell || size+pc > usableSize ){
        *pRc = SQLITE_CORRUPT_BKPT;
        return 0;
      }else if( x<4 ){
        /* EVIDENCE-OF: R-11498-58022 In a well-formed b-tree page, the total
        ** number of bytes in fragments may not exceed 60. */
        if( aData[hdr+7]>57 ) return 0;

        /* Remove the slot from the free-list. Update the number of
        ** fragmented bytes within the page. */
        memcpy(&aData[iAddr], &aData[pc], 2);
        aData[hdr+7] += (u8)x;
      }else{
        /* The slot remains on the free-list. Reduce its size to account
         ** for the portion used by the new allocation. */
        put2byte(&aData[pc+2], x);
      }
      return &aData[pc + x];
    }
    iAddr = pc;
    pc = get2byte(&aData[pc]);
  }while( pc );

  return 0;
}

/*
** Allocate nByte bytes of space from within the B-Tree page passed
** as the first argument. Write into *pIdx the index into pPage->aData[]
** of the first byte of allocated space. Return either SQLITE_OK or
** an error code (usually SQLITE_CORRUPT).
**
** The caller guarantees that there is sufficient space to make the
** allocation.  This routine might need to defragment in order to bring
** all the space together, however.  This routine will avoid using
** the first two bytes past the cell pointer area since presumably this
** allocation is being made in order to insert a new cell, so we will
** also end up needing a new cell pointer.
*/
static int allocateSpace(MemPage *pPage, int nByte, int *pIdx){
  const int hdr = pPage->hdrOffset;    /* Local cache of pPage->hdrOffset */
  u8 * const data = pPage->aData;      /* Local cache of pPage->aData */
  int top;                             /* First byte of cell content area */
  int rc = SQLITE_OK;                  /* Integer return code */
  int gap;        /* First byte of gap between cell pointers and cell content */
  
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( pPage->pBt );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( nByte>=0 );  /* Minimum cell size is 4 */
  assert( pPage->nFree>=nByte );
  assert( pPage->nOverflow==0 );
  assert( nByte < (int)(pPage->pBt->usableSize-8) );

  assert( pPage->cellOffset == hdr + 12 - 4*pPage->leaf );
  gap = pPage->cellOffset + 2*pPage->nCell;
  assert( gap<=65536 );
  /* EVIDENCE-OF: R-29356-02391 If the database uses a 65536-byte page size
  ** and the reserved space is zero (the usual value for reserved space)
  ** then the cell content offset of an empty page wants to be 65536.
  ** However, that integer is too large to be stored in a 2-byte unsigned
  ** integer, so a value of 0 is used in its place. */
  top = get2byte(&data[hdr+5]);
  assert( top<=(int)pPage->pBt->usableSize ); /* Prevent by getAndInitPage() */
  if( gap>top ){
    if( top==0 && pPage->pBt->usableSize==65536 ){
      top = 65536;
    }else{
      return SQLITE_CORRUPT_BKPT;
    }
  }

  /* If there is enough space between gap and top for one more cell pointer
  ** array entry offset, and if the freelist is not empty, then search the
  ** freelist looking for a free slot big enough to satisfy the request.
  */
  testcase( gap+2==top );
  testcase( gap+1==top );
  testcase( gap==top );
  if( (data[hdr+2] || data[hdr+1]) && gap+2<=top ){
    u8 *pSpace = pageFindSlot(pPage, nByte, &rc);
    if( pSpace ){
      assert( pSpace>=data && (pSpace - data)<65536 );
      *pIdx = (int)(pSpace - data);
      return SQLITE_OK;
    }else if( rc ){
      return rc;
    }
  }

  /* The request could not be fulfilled using a freelist slot.  Check
  ** to see if defragmentation is necessary.
  */
  testcase( gap+2+nByte==top );
  if( gap+2+nByte>top ){
    assert( pPage->nCell>0 || CORRUPT_DB );
    rc = defragmentPage(pPage);
    if( rc ) return rc;
    top = get2byteNotZero(&data[hdr+5]);
    assert( gap+nByte<=top );
  }


  /* Allocate memory from the gap in between the cell pointer array
  ** and the cell content area.  The btreeInitPage() call has already
  ** validated the freelist.  Given that the freelist is valid, there
  ** is no way that the allocation can extend off the end of the page.
  ** The assert() below verifies the previous sentence.
  */
  top -= nByte;
  put2byte(&data[hdr+5], top);
  assert( top+nByte <= (int)pPage->pBt->usableSize );
  *pIdx = top;
  return SQLITE_OK;
}

/*
** Return a section of the pPage->aData to the freelist.
** The first byte of the new free block is pPage->aData[iStart]
** and the size of the block is iSize bytes.
**
** Adjacent freeblocks are coalesced.
**
** Note that even though the freeblock list was checked by btreeInitPage(),
** that routine will not detect overlap between cells or freeblocks.  Nor
** does it detect cells or freeblocks that encrouch into the reserved bytes
** at the end of the page.  So do additional corruption checks inside this
** routine and return SQLITE_CORRUPT if any problems are found.
*/
static int freeSpace(MemPage *pPage, u16 iStart, u16 iSize){
  u16 iPtr;                             /* Address of ptr to next freeblock */
  u16 iFreeBlk;                         /* Address of the next freeblock */
  u8 hdr;                               /* Page header size.  0 or 100 */
  u8 nFrag = 0;                         /* Reduction in fragmentation */
  u16 iOrigSize = iSize;                /* Original value of iSize */
  u32 iLast = pPage->pBt->usableSize-4; /* Largest possible freeblock offset */
  u32 iEnd = iStart + iSize;            /* First byte past the iStart buffer */
  unsigned char *data = pPage->aData;   /* Page content */

  assert( pPage->pBt!=0 );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( CORRUPT_DB || iStart>=pPage->hdrOffset+6+pPage->childPtrSize );
  assert( CORRUPT_DB || iEnd <= pPage->pBt->usableSize );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( iSize>=4 );   /* Minimum cell size is 4 */
  assert( iStart<=iLast );

  /* Overwrite deleted information with zeros when the secure_delete
  ** option is enabled */
  if( pPage->pBt->btsFlags & BTS_SECURE_DELETE ){
    memset(&data[iStart], 0, iSize);
  }

  /* The list of freeblocks must be in ascending order.  Find the 
  ** spot on the list where iStart should be inserted.
  */
  hdr = pPage->hdrOffset;
  iPtr = hdr + 1;
  if( data[iPtr+1]==0 && data[iPtr]==0 ){
    iFreeBlk = 0;  /* Shortcut for the case when the freelist is empty */
  }else{
    while( (iFreeBlk = get2byte(&data[iPtr]))>0 && iFreeBlk<iStart ){
      if( iFreeBlk<iPtr+4 ) return SQLITE_CORRUPT_BKPT;
      iPtr = iFreeBlk;
    }
    if( iFreeBlk>iLast ) return SQLITE_CORRUPT_BKPT;
    assert( iFreeBlk>iPtr || iFreeBlk==0 );
  
    /* At this point:
    **    iFreeBlk:   First freeblock after iStart, or zero if none
    **    iPtr:       The address of a pointer to iFreeBlk
    **
    ** Check to see if iFreeBlk should be coalesced onto the end of iStart.
    */
    if( iFreeBlk && iEnd+3>=iFreeBlk ){
      nFrag = iFreeBlk - iEnd;
      if( iEnd>iFreeBlk ) return SQLITE_CORRUPT_BKPT;
      iEnd = iFreeBlk + get2byte(&data[iFreeBlk+2]);
      if( iEnd > pPage->pBt->usableSize ) return SQLITE_CORRUPT_BKPT;
      iSize = iEnd - iStart;
      iFreeBlk = get2byte(&data[iFreeBlk]);
    }
  
    /* If iPtr is another freeblock (that is, if iPtr is not the freelist
    ** pointer in the page header) then check to see if iStart should be
    ** coalesced onto the end of iPtr.
    */
    if( iPtr>hdr+1 ){
      int iPtrEnd = iPtr + get2byte(&data[iPtr+2]);
      if( iPtrEnd+3>=iStart ){
        if( iPtrEnd>iStart ) return SQLITE_CORRUPT_BKPT;
        nFrag += iStart - iPtrEnd;
        iSize = iEnd - iPtr;
        iStart = iPtr;
      }
    }
    if( nFrag>data[hdr+7] ) return SQLITE_CORRUPT_BKPT;
    data[hdr+7] -= nFrag;
  }
  if( iStart==get2byte(&data[hdr+5]) ){
    /* The new freeblock is at the beginning of the cell content area,
    ** so just extend the cell content area rather than create another
    ** freelist entry */
    if( iPtr!=hdr+1 ) return SQLITE_CORRUPT_BKPT;
    put2byte(&data[hdr+1], iFreeBlk);
    put2byte(&data[hdr+5], iEnd);
  }else{
    /* Insert the new freeblock into the freelist */
    put2byte(&data[iPtr], iStart);
    put2byte(&data[iStart], iFreeBlk);
    put2byte(&data[iStart+2], iSize);
  }
  pPage->nFree += iOrigSize;
  return SQLITE_OK;
}

/*
** Decode the flags byte (the first byte of the header) for a page
** and initialize fields of the MemPage structure accordingly.
**
** Only the following combinations are supported.  Anything different
** indicates a corrupt database files:
**
**         PTF_ZERODATA
**         PTF_ZERODATA | PTF_LEAF
**         PTF_LEAFDATA | PTF_INTKEY
**         PTF_LEAFDATA | PTF_INTKEY | PTF_LEAF
*/
static int decodeFlags(MemPage *pPage, int flagByte){
  BtShared *pBt;     /* A copy of pPage->pBt */

  assert( pPage->hdrOffset==(pPage->pgno==1 ? 100 : 0) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  pPage->leaf = (u8)(flagByte>>3);  assert( PTF_LEAF == 1<<3 );
  flagByte &= ~PTF_LEAF;
  pPage->childPtrSize = 4-4*pPage->leaf;
  pPage->xCellSize = cellSizePtr;
  pBt = pPage->pBt;
  if( flagByte==(PTF_LEAFDATA | PTF_INTKEY) ){
    /* EVIDENCE-OF: R-03640-13415 A value of 5 means the page is an interior
    ** table b-tree page. */
    assert( (PTF_LEAFDATA|PTF_INTKEY)==5 );
    /* EVIDENCE-OF: R-20501-61796 A value of 13 means the page is a leaf
    ** table b-tree page. */
    assert( (PTF_LEAFDATA|PTF_INTKEY|PTF_LEAF)==13 );
    pPage->intKey = 1;
    if( pPage->leaf ){
      pPage->intKeyLeaf = 1;
      pPage->noPayload = 0;
      pPage->xParseCell = btreeParseCellPtr;
    }else{
      pPage->intKeyLeaf = 0;
      pPage->noPayload = 1;
      pPage->xCellSize = cellSizePtrNoPayload;
      pPage->xParseCell = btreeParseCellPtrNoPayload;
    }
    pPage->maxLocal = pBt->maxLeaf;
    pPage->minLocal = pBt->minLeaf;
  }else if( flagByte==PTF_ZERODATA ){
    /* EVIDENCE-OF: R-27225-53936 A value of 2 means the page is an interior
    ** index b-tree page. */
    assert( (PTF_ZERODATA)==2 );
    /* EVIDENCE-OF: R-16571-11615 A value of 10 means the page is a leaf
    ** index b-tree page. */
    assert( (PTF_ZERODATA|PTF_LEAF)==10 );
    pPage->intKey = 0;
    pPage->intKeyLeaf = 0;
    pPage->noPayload = 0;
    pPage->xParseCell = btreeParseCellPtrIndex;
    pPage->maxLocal = pBt->maxLocal;
    pPage->minLocal = pBt->minLocal;
  }else{
    /* EVIDENCE-OF: R-47608-56469 Any other value for the b-tree page type is
    ** an error. */
    return SQLITE_CORRUPT_BKPT;
  }
  pPage->max1bytePayload = pBt->max1bytePayload;
  return SQLITE_OK;
}

/*
** Initialize the auxiliary information for a disk block.
**
** Return SQLITE_OK on success.  If we see that the page does
** not contain a well-formed database page, then return 
** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
** guarantee that the page is well-formed.  It only shows that
** we failed to detect any corruption.
*/
static int btreeInitPage(MemPage *pPage){

  assert( pPage->pBt!=0 );
  assert( pPage->pBt->db!=0 );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( pPage->pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
  assert( pPage == sqlite3PagerGetExtra(pPage->pDbPage) );
  assert( pPage->aData == sqlite3PagerGetData(pPage->pDbPage) );

  if( !pPage->isInit ){
    u16 pc;            /* Address of a freeblock within pPage->aData[] */
    u8 hdr;            /* Offset to beginning of page header */
    u8 *data;          /* Equal to pPage->aData */
    BtShared *pBt;        /* The main btree structure */
    int usableSize;    /* Amount of usable space on each page */
    u16 cellOffset;    /* Offset from start of page to first cell pointer */
    int nFree;         /* Number of unused bytes on the page */
    int top;           /* First byte of the cell content area */
    int iCellFirst;    /* First allowable cell or freeblock offset */
    int iCellLast;     /* Last possible cell or freeblock offset */

    pBt = pPage->pBt;

    hdr = pPage->hdrOffset;
    data = pPage->aData;
    /* EVIDENCE-OF: R-28594-02890 The one-byte flag at offset 0 indicating
    ** the b-tree page type. */
    if( decodeFlags(pPage, data[hdr]) ) return SQLITE_CORRUPT_BKPT;
    assert( pBt->pageSize>=512 && pBt->pageSize<=65536 );
    pPage->maskPage = (u16)(pBt->pageSize - 1);
    pPage->nOverflow = 0;
    usableSize = pBt->usableSize;
    pPage->cellOffset = cellOffset = hdr + 8 + pPage->childPtrSize;
    pPage->aDataEnd = &data[usableSize];
    pPage->aCellIdx = &data[cellOffset];
    pPage->aDataOfst = &data[pPage->childPtrSize];
    /* EVIDENCE-OF: R-58015-48175 The two-byte integer at offset 5 designates
    ** the start of the cell content area. A zero value for this integer is
    ** interpreted as 65536. */
    top = get2byteNotZero(&data[hdr+5]);
    /* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
    ** number of cells on the page. */
    pPage->nCell = get2byte(&data[hdr+3]);
    if( pPage->nCell>MX_CELL(pBt) ){
      /* To many cells for a single page.  The page must be corrupt */
      return SQLITE_CORRUPT_BKPT;
    }
    testcase( pPage->nCell==MX_CELL(pBt) );
    /* EVIDENCE-OF: R-24089-57979 If a page contains no cells (which is only
    ** possible for a root page of a table that contains no rows) then the
    ** offset to the cell content area will equal the page size minus the
    ** bytes of reserved space. */
    assert( pPage->nCell>0 || top==usableSize || CORRUPT_DB );

    /* A malformed database page might cause us to read past the end
    ** of page when parsing a cell.  
    **
    ** The following block of code checks early to see if a cell extends
    ** past the end of a page boundary and causes SQLITE_CORRUPT to be 
    ** returned if it does.
    */
    iCellFirst = cellOffset + 2*pPage->nCell;
    iCellLast = usableSize - 4;
    if( pBt->pBt->flags & SQLITE_CellSizeCk ){
      int i;            /* Index into the cell pointer array */
      int sz;           /* Size of a cell */

      if( !pPage->leaf ) iCellLast--;
      for(i=0; i<pPage->nCell; i++){
        pc = get2byteAligned(&data[cellOffset+i*2]);
        testcase( pc==iCellFirst );
        testcase( pc==iCellLast );
        if( pc<iCellFirst || pc>iCellLast ){
          return SQLITE_CORRUPT_BKPT;
        }
        sz = pPage->xCellSize(pPage, &data[pc]);
        testcase( pc+sz==usableSize );
        if( pc+sz>usableSize ){
          return SQLITE_CORRUPT_BKPT;
        }
      }
      if( !pPage->leaf ) iCellLast++;
    }  

    /* Compute the total free space on the page
    ** EVIDENCE-OF: R-23588-34450 The two-byte integer at offset 1 gives the
    ** start of the first freeblock on the page, or is zero if there are no
    ** freeblocks. */
    pc = get2byte(&data[hdr+1]);
    nFree = data[hdr+7] + top;  /* Init nFree to non-freeblock free space */
    while( pc>0 ){
      u16 next, size;
      if( pc<iCellFirst || pc>iCellLast ){
        /* EVIDENCE-OF: R-55530-52930 In a well-formed b-tree page, there will
        ** always be at least one cell before the first freeblock.
        **
        ** Or, the freeblock is off the end of the page
        */
        return SQLITE_CORRUPT_BKPT; 
      }
      next = get2byte(&data[pc]);
      size = get2byte(&data[pc+2]);
      if( (next>0 && next<=pc+size+3) || pc+size>usableSize ){
        /* Free blocks must be in ascending order. And the last byte of
        ** the free-block must lie on the database page.  */
        return SQLITE_CORRUPT_BKPT; 
      }
      nFree = nFree + size;
      pc = next;
    }

    /* At this point, nFree contains the sum of the offset to the start
    ** of the cell-content area plus the number of free bytes within
    ** the cell-content area. If this is greater than the usable-size
    ** of the page, then the page must be corrupted. This check also
    ** serves to verify that the offset to the start of the cell-content
    ** area, according to the page header, lies within the page.
    */
    if( nFree>usableSize ){
      return SQLITE_CORRUPT_BKPT; 
    }
    pPage->nFree = (u16)(nFree - iCellFirst);
    pPage->isInit = 1;
  }
  return SQLITE_OK;
}

/*
** Set up a raw page so that it looks like a database page holding
** no entries.
*/
static void zeroPage(MemPage *pPage, int flags){
  unsigned char *data = pPage->aData;
  BtShared *pBt = pPage->pBt;
  u8 hdr = pPage->hdrOffset;
  u16 first;

  assert( sqlite3PagerPagenumber(pPage->pDbPage)==pPage->pgno );
  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
  assert( sqlite3PagerGetData(pPage->pDbPage) == data );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pBt->btsFlags & BTS_SECURE_DELETE ){
    memset(&data[hdr], 0, pBt->usableSize - hdr);
  }
  data[hdr] = (char)flags;
  first = hdr + ((flags&PTF_LEAF)==0 ? 12 : 8);
  memset(&data[hdr+1], 0, 4);
  data[hdr+7] = 0;
  put2byte(&data[hdr+5], pBt->usableSize);
  pPage->nFree = (u16)(pBt->usableSize - first);
  decodeFlags(pPage, flags);
  pPage->cellOffset = first;
  pPage->aDataEnd = &data[pBt->usableSize];
  pPage->aCellIdx = &data[first];
  pPage->aDataOfst = &data[pPage->childPtrSize];
  pPage->nOverflow = 0;
  assert( pBt->pageSize>=512 && pBt->pageSize<=65536 );
  pPage->maskPage = (u16)(pBt->pageSize - 1);
  pPage->nCell = 0;
  pPage->isInit = 1;
}


/*
** Convert a DbPage obtained from the pager into a MemPage used by
** the btree layer.
*/
static MemPage *btreePageFromDbPage(DbPage *pDbPage, Pgno pgno, BtShared *pBt){
  MemPage *pPage = (MemPage*)sqlite3PagerGetExtra(pDbPage);
  pPage->aData = sqlite3PagerGetData(pDbPage);
  pPage->pDbPage = pDbPage;
  pPage->pBt = pBt;
  pPage->pgno = pgno;
  pPage->hdrOffset = pgno==1 ? 100 : 0;
  return pPage; 
}

/*
** Get a page from the pager.  Initialize the MemPage.pBt and
** MemPage.aData elements if needed.  See also: btreeGetUnusedPage().
**
** If the PAGER_GET_NOCONTENT flag is set, it means that we do not care
** about the content of the page at this time.  So do not go to the disk
** to fetch the content.  Just fill in the content with zeros for now.
** If in the future we call sqlite3PagerWrite() on this page, that
** means we have started to be concerned about content and the disk
** read should occur at that point.
*/
static int btreeGetPage(
  BtShared *pBt,       /* The btree */
  Pgno pgno,           /* Number of the page to fetch */
  MemPage **ppPage,    /* Return the page in this parameter */
  int flags            /* PAGER_GET_NOCONTENT or PAGER_GET_READONLY */
){
  int rc;
  DbPage *pDbPage;

  assert( flags==0 || flags==PAGER_GET_NOCONTENT || flags==PAGER_GET_READONLY );
  assert( sqlite3_mutex_held(pBt->mutex) );
  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, flags);
  if( rc ) return rc;
  *ppPage = btreePageFromDbPage(pDbPage, pgno, pBt);
  return SQLITE_OK;
}

/*
** Retrieve a page from the pager cache. If the requested page is not
** already in the pager cache return NULL. Initialize the MemPage.pBt and
** MemPage.aData elements if needed.
*/
static MemPage *btreePageLookup(BtShared *pBt, Pgno pgno){
  DbPage *pDbPage;
  assert( sqlite3_mutex_held(pBt->mutex) );
  pDbPage = sqlite3PagerLookup(pBt->pPager, pgno);
  if( pDbPage ){
    return btreePageFromDbPage(pDbPage, pgno, pBt);
  }
  return 0;
}

/*
** Return the size of the database file in pages. If there is any kind of
** error, return ((unsigned int)-1).
*/
static Pgno btreePagecount(BtShared *pBt){
  return pBt->nPage;
}
SQLITE_API u32 SQLITE_STDCALL sqlite3BtreeLastPage(Btree *p){
  assert( sqlite3BtreeHoldsMutex(p) );
  assert( ((p->pBt->nPage)&0x8000000)==0 );
  return btreePagecount(p->pBt);
}

/*
** Get a page from the pager and initialize it.
**
** If pCur!=0 then the page is being fetched as part of a moveToChild()
** call.  Do additional sanity checking on the page in this case.
** And if the fetch fails, this routine must decrement pCur->iPage.
**
** The page is fetched as read-write unless pCur is not NULL and is
** a read-only cursor.
**
** If an error occurs, then *ppPage is undefined. It
** may remain unchanged, or it may be set to an invalid value.
*/
static int getAndInitPage(
  BtShared *pBt,                  /* The database file */
  Pgno pgno,                      /* Number of the page to get */
  MemPage **ppPage,               /* Write the page pointer here */
  BtCursor *pCur,                 /* Cursor to receive the page, or NULL */
  int bReadOnly                   /* True for a read-only page */
){
  int rc;
  DbPage *pDbPage;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pCur==0 || ppPage==&pCur->apPage[pCur->iPage] );
  assert( pCur==0 || bReadOnly==pCur->curPagerFlags );
  assert( pCur==0 || pCur->iPage>0 );

  if( pgno>btreePagecount(pBt) ){
    rc = SQLITE_CORRUPT_BKPT;
    goto getAndInitPage_error;
  }
  rc = sqlite3PagerAcquire(pBt->pPager, pgno, (DbPage**)&pDbPage, bReadOnly);
  if( rc ){
    goto getAndInitPage_error;
  }
  *ppPage = btreePageFromDbPage(pDbPage, pgno, pBt);
  if( (*ppPage)->isInit==0 ){
    rc = btreeInitPage(*ppPage);
    if( rc!=SQLITE_OK ){
      releasePage(*ppPage);
      goto getAndInitPage_error;
    }
  }

  /* If obtaining a child page for a cursor, we must verify that the page is
  ** compatible with the root page. */
  if( pCur
   && ((*ppPage)->nCell<1 || (*ppPage)->intKey!=pCur->curIntKey)
  ){
    rc = SQLITE_CORRUPT_BKPT;
    releasePage(*ppPage);
    goto getAndInitPage_error;
  }
  return SQLITE_OK;

getAndInitPage_error:
  if( pCur ) pCur->iPage--;
  testcase( pgno==0 );
  assert( pgno!=0 || rc==SQLITE_CORRUPT );
  return rc;
}

/*
** Release a MemPage.  This should be called once for each prior
** call to btreeGetPage.
*/
static void releasePageNotNull(MemPage *pPage){
  assert( pPage->aData );
  assert( pPage->pBt );
  assert( pPage->pDbPage!=0 );
  assert( sqlite3PagerGetExtra(pPage->pDbPage) == (void*)pPage );
  assert( sqlite3PagerGetData(pPage->pDbPage)==pPage->aData );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  sqlite3PagerUnrefNotNull(pPage->pDbPage);
}
static void releasePage(MemPage *pPage){
  if( pPage ) releasePageNotNull(pPage);
}

/*
** Get an unused page.
**
** This works just like btreeGetPage() with the addition:
**
**   *  If the page is already in use for some other purpose, immediately
**      release it and return an SQLITE_CURRUPT error.
**   *  Make sure the isInit flag is clear
*/
static int btreeGetUnusedPage(
  BtShared *pBt,       /* The btree */
  Pgno pgno,           /* Number of the page to fetch */
  MemPage **ppPage,    /* Return the page in this parameter */
  int flags            /* PAGER_GET_NOCONTENT or PAGER_GET_READONLY */
){
  int rc = btreeGetPage(pBt, pgno, ppPage, flags);
  if( rc==SQLITE_OK ){
    if( sqlite3PagerPageRefcount((*ppPage)->pDbPage)>1 ){
      releasePage(*ppPage);
      *ppPage = 0;
      return SQLITE_CORRUPT_BKPT;
    }
    (*ppPage)->isInit = 0;
  }else{
    *ppPage = 0;
  }
  return rc;
}


/*
** During a rollback, when the pager reloads information into the cache
** so that the cache is restored to its original state at the start of
** the transaction, for each page restored this routine is called.
**
** This routine needs to reset the extra data section at the end of the
** page to agree with the restored data.
*/
static void pageReinit(DbPage *pData){
  MemPage *pPage;
  pPage = (MemPage *)sqlite3PagerGetExtra(pData);
  assert( sqlite3PagerPageRefcount(pData)>0 );
  if( pPage->isInit ){
    assert( sqlite3_mutex_held(pPage->pBt->mutex) );
    pPage->isInit = 0;
    if( sqlite3PagerPageRefcount(pData)>1 ){
      /* pPage might not be a btree page;  it might be an overflow page
      ** or ptrmap page or a free page.  In those cases, the following
      ** call to btreeInitPage() will likely return SQLITE_CORRUPT.
      ** But no harm is done by this.  And it is very important that
      ** btreeInitPage() be called on every btree page so we make
      ** the call for every page that comes in for re-initing. */
      btreeInitPage(pPage);
    }
  }
}

/*
** Invoke the busy handler for a btree.
*/
static int btreeInvokeBusyHandler(void *pArg){
  BtShared *pBt = (BtShared*)pArg;
  assert( pBt->pBt );
  assert( sqlite3_mutex_held(pBt->pBt->mutex) );
  return sqlite3InvokeBusyHandler(&pBt->pBt->busyHandler);
}

/*
** Open a database file.
** 
** zFilename is the name of the database file.  If zFilename is NULL
** then an ephemeral database is created.  The ephemeral database might
** be exclusively in memory, or it might use a disk-based memory cache.
** Either way, the ephemeral database will be automatically deleted 
** when sqlite3BtreeClose() is called.
**
** If zFilename is ":memory:" then an in-memory database is created
** that is automatically destroyed when it is closed.
**
** The "flags" parameter is a bitmask that might contain bits like
** BTREE_OMIT_JOURNAL and/or BTREE_MEMORY.
**
** If the database is already opened in the same database connection
** and we are in shared cache mode, then the open will fail with an
** SQLITE_CONSTRAINT error.  We cannot allow two or more BtShared
** objects in the same database connection since doing so will lead
** to problems with locking.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeOpen(
  const char *zVfs,       /* VFS to use for this b-tree */
  const char *zFilename,  /* Name of the file containing the BTree database */
  Btree **ppBtree,        /* Pointer to new Btree object written here */
  int flags,              /* Options */
  int vfsFlags            /* Flags passed through to sqlite3_vfs.xOpen() */
){
  BtShared *pBt = 0;             /* Shared part of btree structure */
  Btree *p;                      /* Handle to return */
  sqlite3_mutex *mutexOpen = 0;  /* Prevents a race condition. Ticket #3537 */
  int rc = SQLITE_OK;            /* Result code from this function */
  u8 nReserve;                   /* Byte of unused space on each page */
  unsigned char zDbHeader[100];  /* Database header content */
  int isThreadsafe;              /* True for threadsafe connections */

#ifdef SQLITE_ENABLE_API_ARMOR
  if( ppBtree==0 ) return SQLITE_MISUSE_BKPT;
#endif
  *ppBtree = 0;
#ifndef SQLITE_OMIT_AUTOINIT
  rc = sqlite3BtreeInitialize();
  if( rc ) return rc;
#endif

  /* Only allow sensible combinations of bits in the vfsFlags argument.  
  ** Throw an error if any non-sense combination is used.  If we
  ** do not block illegal combinations here, it could trigger
  ** assert() statements in deeper layers.  Sensible combinations
  ** are:
  **
  **  1:  SQLITE_OPEN_READONLY
  **  2:  SQLITE_OPEN_READWRITE
  **  6:  SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE
  */
  assert( SQLITE_OPEN_READONLY  == 0x01 );
  assert( SQLITE_OPEN_READWRITE == 0x02 );
  assert( SQLITE_OPEN_CREATE    == 0x04 );
  testcase( (1<<(vfsFlags&7))==0x02 ); /* READONLY */
  testcase( (1<<(vfsFlags&7))==0x04 ); /* READWRITE */
  testcase( (1<<(vfsFlags&7))==0x40 ); /* READWRITE | CREATE */
  if( ((1<<(vfsFlags&7)) & 0x46)==0 ){
    return SQLITE_MISUSE_BKPT;  /* IMP: R-65497-44594 */
  }

  if( sqlite3GlobalConfig.bCoreMutex==0 ){
    isThreadsafe = 0;
  }else if( vfsFlags & SQLITE_OPEN_NOMUTEX ){
    isThreadsafe = 0;
  }else if( vfsFlags & SQLITE_OPEN_FULLMUTEX ){
    isThreadsafe = 1;
  }else{
    isThreadsafe = sqlite3GlobalConfig.bFullMutex;
  }
  if( vfsFlags & SQLITE_OPEN_PRIVATECACHE ){
    vfsFlags &= ~SQLITE_OPEN_SHAREDCACHE;
  }else if( sqlite3GlobalConfig.sharedCacheEnabled ){
    vfsFlags |= SQLITE_OPEN_SHAREDCACHE;
  }

  /* Remove harmful bits from the vfsFlags parameter
  **
  ** The SQLITE_OPEN_NOMUTEX and SQLITE_OPEN_FULLMUTEX vfsFlags were
  ** dealt with in the previous code block.  Besides these, the only
  ** valid input vfsFlags for sqlite3_open_v2() are SQLITE_OPEN_READONLY,
  ** SQLITE_OPEN_READWRITE, SQLITE_OPEN_CREATE, SQLITE_OPEN_SHAREDCACHE,
  ** SQLITE_OPEN_PRIVATECACHE, and some reserved bits.  Silently mask
  ** off all other vfsFlags.
  */
  vfsFlags &=  ~( SQLITE_OPEN_DELETEONCLOSE |
                  SQLITE_OPEN_EXCLUSIVE |
                  SQLITE_OPEN_MAIN_DB |
                  SQLITE_OPEN_TEMP_DB | 
                  SQLITE_OPEN_TRANSIENT_DB | 
                  SQLITE_OPEN_MAIN_JOURNAL | 
                  SQLITE_OPEN_TEMP_JOURNAL | 
                  SQLITE_OPEN_SUBJOURNAL | 
                  SQLITE_OPEN_MASTER_JOURNAL |
                  SQLITE_OPEN_NOMUTEX |
                  SQLITE_OPEN_FULLMUTEX |
                  SQLITE_OPEN_WAL
                );

  assert( (vfsFlags&0xff)==vfsFlags );   /* flags fit in 8 bits */

  /* Only a BTREE_SINGLE database can be BTREE_UNORDERED */
  assert( (vfsFlags & BTREE_UNORDERED)==0 || (vfsFlags & BTREE_SINGLE)!=0 );

  sqlite3_vfs *pVfs =
    sqlite3_vfs_find(zVfs);
  if( pVfs==0 ){
    return SQLITE_ERROR;
  }

  p = sqlite3MallocZero(sizeof(Btree));
  if( !p ){
    return SQLITE_NOMEM;
  }
  p->inTrans = TRANS_NONE;
#ifndef SQLITE_OMIT_SHARED_CACHE
  p->lock.pBtree = p;
  p->lock.iTable = 1;
#endif
  p->magic = SQLITE_MAGIC_BUSY;

  if( isThreadsafe ){
    p->mutex = sqlite3MutexAlloc(SQLITE_MUTEX_RECURSIVE);
    if( p->mutex==0 ){
      sqlite3_free(p);
      p = 0;
      goto btree_open_out;
    }
  }
  sqlite3_mutex_enter(p->mutex);

  p->enc    = SQLITE_UTF8;
  p->szMmap = sqlite3GlobalConfig.szMmap;
  p->flags |= 0
#if SQLITE_DEFAULT_CKPTFULLFSYNC
                 | SQLITE_CkptFullFSync
#endif
#if defined(SQLITE_ENABLE_OVERSIZE_CELL_CHECK)
                 | SQLITE_CellSizeCk
#endif
;

#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
  /*
  ** If this Btree is a candidate for shared cache, try to find an
  ** existing BtShared object that we can share with
  */
  if( (vfsFlags&SQLITE_OPEN_URI)!=0 ){
    if( vfsFlags & SQLITE_OPEN_SHAREDCACHE ){
      int nFilename = sqlite3Strlen30(zFilename)+1;
      int nFullPathname = pVfs->mxPathname+1;
      char *zFullPathname = sqlite3Malloc(MAX(nFullPathname,nFilename));
      MUTEX_LOGIC( sqlite3_mutex *mutexShared; )

      p->sharable = 1;
      if( !zFullPathname ){
        sqlite3_free(p);
        return SQLITE_NOMEM;
      }
      rc = sqlite3OsFullPathname(pVfs, zFilename,
                                 nFullPathname, zFullPathname);
      if( rc ){
        sqlite3_free(zFullPathname);
        sqlite3_free(p);
        return rc;
      }
#if SQLITE_THREADSAFE
      mutexOpen = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_OPEN);
      sqlite3_mutex_enter(mutexOpen);
      mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
      sqlite3_mutex_enter(mutexShared);
#endif
      for(pBt=GLOBAL(BtShared*,sqlite3SharedCacheList); pBt; pBt=pBt->pNext){
        assert( pBt->nRef>0 );
        if( 0==strcmp(zFullPathname, sqlite3PagerFilename(pBt->pPager, 0))
                 && sqlite3PagerVfs(pBt->pPager)==pVfs ){
          p->pBt = pBt;
          pBt->nRef++;
          break;
        }
      }
      sqlite3_mutex_leave(mutexShared);
      sqlite3_free(zFullPathname);
    }
#ifdef SQLITE_DEBUG
    else{
      /* In debug mode, we mark all persistent databases as sharable
      ** even when they are not.  This exercises the locking code and
      ** gives more opportunity for asserts(sqlite3_mutex_held())
      ** statements to find locking problems.
      */
      p->sharable = 1;
    }
#endif
  }
#endif
  if( pBt==0 ){
    /*
    ** The following asserts make sure that structures used by the btree are
    ** the right size.  This is to guard against size changes that result
    ** when compiling on a different architecture.
    */
    assert( sizeof(i64)==8 );
    assert( sizeof(u64)==8 );
    assert( sizeof(u32)==4 );
    assert( sizeof(u16)==2 );
    assert( sizeof(Pgno)==4 );
  
    pBt = sqlite3MallocZero( sizeof(*pBt) );
    if( pBt==0 ){
      rc = SQLITE_NOMEM;
      goto btree_open_out;
    }
    rc = sqlite3PagerOpen(pVfs, &pBt->pPager, zFilename,
                          EXTRA_SIZE, flags, vfsFlags, pageReinit);
    if( rc==SQLITE_OK ){
      sqlite3PagerSetMmapLimit(pBt->pPager, p->szMmap);
      rc = sqlite3PagerReadFileheader(pBt->pPager,sizeof(zDbHeader),zDbHeader);
    }
    if( rc!=SQLITE_OK ){
      goto btree_open_out;
    }
    pBt->openFlags = (u8)flags;
    pBt->pBt = p;
    sqlite3PagerSetBusyhandler(pBt->pPager, btreeInvokeBusyHandler, pBt);
    p->pBt = pBt;

    pBt->pCursor = 0;
    pBt->pPage1 = 0;
    if( sqlite3PagerIsreadonly(pBt->pPager) ) pBt->btsFlags |= BTS_READ_ONLY;
#ifdef SQLITE_SECURE_DELETE
    pBt->btsFlags |= BTS_SECURE_DELETE;
#endif
    /* EVIDENCE-OF: R-51873-39618 The page size for a database file is
    ** determined by the 2-byte integer located at an offset of 16 bytes from
    ** the beginning of the database file. */
    pBt->pageSize = (zDbHeader[16]<<8) | (zDbHeader[17]<<16);
    if( pBt->pageSize<512 || pBt->pageSize>SQLITE_MAX_PAGE_SIZE
         || ((pBt->pageSize-1)&pBt->pageSize)!=0 ){
      pBt->pageSize = 0;
#ifndef SQLITE_OMIT_AUTOVACUUM
      /* If the magic name ":memory:" will create an in-memory database, then
      ** leave the autoVacuum mode at 0 (do not auto-vacuum), even if
      ** SQLITE_DEFAULT_AUTOVACUUM is true.
      */
      if( zFilename ){
        pBt->autoVacuum = (SQLITE_DEFAULT_AUTOVACUUM ? 1 : 0);
        pBt->incrVacuum = (SQLITE_DEFAULT_AUTOVACUUM==2 ? 1 : 0);
      }
#endif
      nReserve = 0;
    }else{
      /* EVIDENCE-OF: R-37497-42412 The size of the reserved region is
      ** determined by the one-byte unsigned integer found at an offset of 20
      ** into the database file header. */
      nReserve = zDbHeader[20];
      pBt->btsFlags |= BTS_PAGESIZE_FIXED;
#ifndef SQLITE_OMIT_AUTOVACUUM
      pBt->autoVacuum = (get4byte(&zDbHeader[36 + 4*4])?1:0);
      pBt->incrVacuum = (get4byte(&zDbHeader[36 + 7*4])?1:0);
#endif
    }
    rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize, nReserve);
    if( rc ) goto btree_open_out;
    pBt->usableSize = pBt->pageSize - nReserve;
    assert( (pBt->pageSize & 7)==0 );  /* 8-byte alignment of pageSize */

    /*
    ** file_format==1    Version 3.0.0.
    ** file_format==2    Version 3.1.3.  // ALTER TABLE ADD COLUMN
    ** file_format==3    Version 3.1.4.  // ditto but with non-NULL defaults
    ** file_format==4    Version 3.3.0.  // DESC indices.  Boolean constants
    */
    pBt->file_format = zDbHeader[18];
    if( pBt->file_format==0 ){
      pBt->file_format = 1;
    }
    if( pBt->file_format>SQLITE_MAX_FILE_FORMAT ){
      rc = SQLITE_ERROR;
      goto btree_open_out;
    }
   
#if !defined(SQLITE_OMIT_SHARED_CACHE) && !defined(SQLITE_OMIT_DISKIO)
    /* Add the new BtShared object to the linked list sharable BtShareds.
    */
    if( p->sharable ){
      MUTEX_LOGIC( sqlite3_mutex *mutexShared; )
      pBt->nRef = 1;
      MUTEX_LOGIC( mutexShared = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER);)
      if( SQLITE_THREADSAFE && sqlite3GlobalConfig.bCoreMutex ){
        pBt->mutex = sqlite3MutexAlloc(SQLITE_MUTEX_FAST);
        if( pBt->mutex==0 ){
          rc = SQLITE_NOMEM;
          p->mallocFailed = 0;
          goto btree_open_out;
        }
      }
      sqlite3_mutex_enter(mutexShared);
      pBt->pNext = GLOBAL(BtShared*,sqlite3SharedCacheList);
      GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt;
      sqlite3_mutex_leave(mutexShared);
    }
#endif
  }

  sqlite3PagerSetCachesize(pBt->pPager, SQLITE_DEFAULT_CACHE_SIZE);

  p->magic = SQLITE_MAGIC_OPEN;

  /* -DSQLITE_DEFAULT_LOCKING_MODE=1 makes EXCLUSIVE the default locking
  ** mode.  -DSQLITE_DEFAULT_LOCKING_MODE=0 make NORMAL the default locking
  ** mode.  Doing nothing at all also makes NORMAL the default.
  */
#ifdef SQLITE_DEFAULT_LOCKING_MODE
  sqlite3PagerLockingMode(sqlite3BtreePager(db->aDb[0].pBt),
                          SQLITE_DEFAULT_LOCKING_MODE);
#endif

  *ppBtree = p;

btree_open_out:
  if( rc!=SQLITE_OK ){
    if( pBt && pBt->pPager ){
      sqlite3PagerClose(pBt->pPager);
    }
    sqlite3_free(pBt);
    sqlite3_free(p);
    *ppBtree = 0;
  }else{
    if (p) {
      assert( p->mutex!=0 || isThreadsafe==0
             || sqlite3GlobalConfig.bFullMutex==0 );
      sqlite3_mutex_leave(p->mutex);
    }

    /* If the B-Tree was successfully opened, set the pager-cache size to the
    ** default value. Except, when opening on an existing shared pager-cache,
    ** do not change the pager-cache size.
    */
    if( sqlite3BtreeSchema(p, 0, 0)==0 ){
      sqlite3PagerSetCachesize(pBt->pPager, SQLITE_DEFAULT_CACHE_SIZE);
    }
  }
  if( mutexOpen ){
    assert( sqlite3_mutex_held(mutexOpen) );
    sqlite3_mutex_leave(mutexOpen);
  }
  return rc;
}

/*
** Decrement the BtShared.nRef counter.  When it reaches zero,
** remove the BtShared structure from the sharing list.  Return
** true if the BtShared.nRef counter reaches zero and return
** false if it is still positive.
*/
static int removeFromSharingList(BtShared *pBt){
#ifndef SQLITE_OMIT_SHARED_CACHE
  MUTEX_LOGIC( sqlite3_mutex *pMaster; )
  BtShared *pList;
  int removed = 0;

  assert( sqlite3_mutex_notheld(pBt->mutex) );
  MUTEX_LOGIC( pMaster = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER); )
  sqlite3_mutex_enter(pMaster);
  pBt->nRef--;
  if( pBt->nRef<=0 ){
    if( GLOBAL(BtShared*,sqlite3SharedCacheList)==pBt ){
      GLOBAL(BtShared*,sqlite3SharedCacheList) = pBt->pNext;
    }else{
      pList = GLOBAL(BtShared*,sqlite3SharedCacheList);
      while( ALWAYS(pList) && pList->pNext!=pBt ){
        pList=pList->pNext;
      }
      if( ALWAYS(pList) ){
        pList->pNext = pBt->pNext;
      }
    }
    if( SQLITE_THREADSAFE ){
      sqlite3_mutex_free(pBt->mutex);
    }
    removed = 1;
  }
  sqlite3_mutex_leave(pMaster);
  return removed;
#else
  return 1;
#endif
}

/*
** Make sure pBt->pTmpSpace points to an allocation of 
** MX_CELL_SIZE(pBt) bytes with a 4-byte prefix for a left-child
** pointer.
*/
static void allocateTempSpace(BtShared *pBt){
  if( !pBt->pTmpSpace ){
    pBt->pTmpSpace = sqlite3PageMalloc( pBt->pageSize );

    /* One of the uses of pBt->pTmpSpace is to format cells before
    ** inserting them into a leaf page (function fillInCell()). If
    ** a cell is less than 4 bytes in size, it is rounded up to 4 bytes
    ** by the various routines that manipulate binary cells. Which
    ** can mean that fillInCell() only initializes the first 2 or 3
    ** bytes of pTmpSpace, but that the first 4 bytes are copied from
    ** it into a database page. This is not actually a problem, but it
    ** does cause a valgrind error when the 1 or 2 bytes of unitialized 
    ** data is passed to system call write(). So to avoid this error,
    ** zero the first 4 bytes of temp space here.
    **
    ** Also:  Provide four bytes of initialized space before the
    ** beginning of pTmpSpace as an area available to prepend the
    ** left-child pointer to the beginning of a cell.
    */
    if( pBt->pTmpSpace ){
      memset(pBt->pTmpSpace, 0, 8);
      pBt->pTmpSpace += 4;
    }
  }
}

/*
** Free the pBt->pTmpSpace allocation
*/
static void freeTempSpace(BtShared *pBt){
  if( pBt->pTmpSpace ){
    pBt->pTmpSpace -= 4;
    sqlite3PageFree(pBt->pTmpSpace);
    pBt->pTmpSpace = 0;
  }
}

/*
** Close an open database and invalidate all cursors.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeClose(Btree *p){
  if( !p ){
    /* EVIDENCE-OF: R-63257-11740 Calling sqlite3BtreeClose()
    ** with a NULL pointer argument is a harmless no-op. */
    return SQLITE_OK;
  }

  if( !sqlite3SafetyCheckSickOrOk(p) ){
    return SQLITE_MISUSE_BKPT;
  }

  sqlite3_mutex_enter(p->mutex);

  p->magic = SQLITE_MAGIC_ZOMBIE;

  BtShared *pBt = p->pBt;
  BtCursor *pCur;

  /* Close all cursors opened via this handle.  */
  sqlite3BtreeEnter(p);
  pCur = pBt->pCursor;
  while( pCur ){
    BtCursor *pTmp = pCur;
    pCur = pCur->pNext;
    if( pTmp->pBtree==p ){
      sqlite3BtreeCloseCursor(pTmp);
    }
  }

  /* Rollback any active transaction and free the handle structure.
  ** The call to sqlite3BtreeRollback() drops any table-locks held by
  ** this handle.
  */
  sqlite3BtreeRollback(p, SQLITE_OK, 0);
  sqlite3BtreeLeave(p);

  /* If there are still other outstanding references to the shared-btree
  ** structure, return now. The remainder of this procedure cleans 
  ** up the shared-btree.
  */
  assert( p->wantToLock==0 && p->locked==0 );
  if( !p->sharable || removeFromSharingList(pBt) ){
    /* The pBt is no longer on the sharing list, so we can access
    ** it without having to hold the mutex.
    **
    ** Clean out and delete the BtShared object.
    */
    assert( !pBt->pCursor );
    sqlite3PagerClose(pBt->pPager);
    if( pBt->xFreeSchema && pBt->pSchema ){
      pBt->xFreeSchema(pBt->pSchema);
    }
    sqlite3DbFree(0, pBt->pSchema);
    freeTempSpace(pBt);
    sqlite3_free(pBt);
  }

#ifndef SQLITE_OMIT_SHARED_CACHE
  assert( p->wantToLock==0 );
  assert( p->locked==0 );
  if( p->pPrev ) p->pPrev->pNext = p->pNext;
  if( p->pNext ) p->pNext->pPrev = p->pPrev;
#endif

  sqlite3_mutex_leave(p->mutex);
  sqlite3_mutex_free(p->mutex);

  p->magic = SQLITE_MAGIC_CLOSED;

  sqlite3_free(p);
  return SQLITE_OK;
}

/*
** Change the limit on the number of pages allowed in the cache.
**
** The maximum number of cache pages is set to the absolute
** value of mxPage.  If mxPage is negative, the pager will
** operate asynchronously - it will not stop to do fsync()s
** to insure data is written to the disk surface before
** continuing.  Transactions still work if synchronous is off,
** and the database cannot be corrupted if this program
** crashes.  But if the operating system crashes or there is
** an abrupt power failure when synchronous is off, the database
** could be left in an inconsistent and unrecoverable state.
** Synchronous is on by default so database corruption is not
** normally a worry.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetCacheSize(Btree *p, int mxPage){
  BtShared *pBt = p->pBt;
  assert( sqlite3_mutex_held(p->db->mutex) );
  sqlite3BtreeEnter(p);
  sqlite3PagerSetCachesize(pBt->pPager, mxPage);
  sqlite3BtreeLeave(p);
  return SQLITE_OK;
}

#if SQLITE_MAX_MMAP_SIZE>0
/*
** Change the limit on the amount of the database file that may be
** memory mapped.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetMmapLimit(Btree *p, sqlite3_int64 szMmap){
  BtShared *pBt = p->pBt;
  assert( sqlite3_mutex_held(p->db->mutex) );
  sqlite3BtreeEnter(p);
  sqlite3PagerSetMmapLimit(pBt->pPager, szMmap);
  sqlite3BtreeLeave(p);
  return SQLITE_OK;
}
#endif /* SQLITE_MAX_MMAP_SIZE>0 */

/*
** Change the way data is synced to disk in order to increase or decrease
** how well the database resists damage due to OS crashes and power
** failures.  Level 1 is the same as asynchronous (no syncs() occur and
** there is a high probability of damage)  Level 2 is the default.  There
** is a very low but non-zero probability of damage.  Level 3 reduces the
** probability of damage to near zero but with a write performance reduction.
*/
#ifndef SQLITE_OMIT_PAGER_PRAGMAS
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetPagerFlags(
  Btree *p,              /* The btree to set the safety level on */
  unsigned pgFlags       /* Various PAGER_* flags */
){
  BtShared *pBt = p->pBt;
  assert( sqlite3_mutex_held(p->db->mutex) );
  sqlite3BtreeEnter(p);
  sqlite3PagerSetFlags(pBt->pPager, pgFlags);
  sqlite3BtreeLeave(p);
  return SQLITE_OK;
}
#endif

/*
** Return TRUE if the given btree is set to safety level 1.  In other
** words, return TRUE if no sync() occurs on the disk files.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSyncDisabled(Btree *p){
  BtShared *pBt = p->pBt;
  int rc;
  assert( sqlite3_mutex_held(p->db->mutex) );  
  sqlite3BtreeEnter(p);
  assert( pBt && pBt->pPager );
  rc = sqlite3PagerNosync(pBt->pPager);
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Change the default pages size and the number of reserved bytes per page.
** Or, if the page size has already been fixed, return SQLITE_READONLY 
** without changing anything.
**
** The page size must be a power of 2 between 512 and 65536.  If the page
** size supplied does not meet this constraint then the page size is not
** changed.
**
** Page sizes are constrained to be a power of two so that the region
** of the database file used for locking (beginning at PENDING_BYTE,
** the first byte past the 1GB boundary, 0x40000000) needs to occur
** at the beginning of a page.
**
** If parameter nReserve is less than zero, then the number of reserved
** bytes per page is left unchanged.
**
** If the iFix!=0 then the BTS_PAGESIZE_FIXED flag is set so that the page size
** and autovacuum mode can no longer be changed.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetPageSize(Btree *p, int pageSize, int nReserve, int iFix){
  int rc = SQLITE_OK;
  BtShared *pBt = p->pBt;
  assert( nReserve>=-1 && nReserve<=255 );
  sqlite3BtreeEnter(p);
#if SQLITE_HAS_CODEC
  if( nReserve>pBt->optimalReserve ) pBt->optimalReserve = (u8)nReserve;
#endif
  if( pBt->btsFlags & BTS_PAGESIZE_FIXED ){
    sqlite3BtreeLeave(p);
    return SQLITE_READONLY;
  }
  if( nReserve<0 ){
    nReserve = pBt->pageSize - pBt->usableSize;
  }
  assert( nReserve>=0 && nReserve<=255 );
  if( pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE &&
        ((pageSize-1)&pageSize)==0 ){
    assert( (pageSize & 7)==0 );
    assert( !pBt->pCursor );
    pBt->pageSize = (u32)pageSize;
    freeTempSpace(pBt);
  }
  rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize, nReserve);
  pBt->usableSize = pBt->pageSize - (u16)nReserve;
  if( iFix ) pBt->btsFlags |= BTS_PAGESIZE_FIXED;
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Return the currently defined page size
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeGetPageSize(Btree *p){
  return p->pBt->pageSize;
}

/*
** This function is similar to sqlite3BtreeGetReserve(), except that it
** may only be called if it is guaranteed that the b-tree mutex is already
** held.
**
** This is useful in one special case in the backup API code where it is
** known that the shared b-tree mutex is held, but the mutex on the 
** database handle that owns *p is not. In this case if sqlite3BtreeEnter()
** were to be called, it might collide with some other operation on the
** database handle that owns *p, causing undefined behavior.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeGetReserveNoMutex(Btree *p){
  int n;
  assert( sqlite3_mutex_held(p->pBt->mutex) );
  n = p->pBt->pageSize - p->pBt->usableSize;
  return n;
}

/*
** Return the number of bytes of space at the end of every page that
** are intentually left unused.  This is the "reserved" space that is
** sometimes used by extensions.
**
** If SQLITE_HAS_MUTEX is defined then the number returned is the
** greater of the current reserved space and the maximum requested
** reserve space.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeGetOptimalReserve(Btree *p){
  int n;
  sqlite3BtreeEnter(p);
  n = sqlite3BtreeGetReserveNoMutex(p);
#ifdef SQLITE_HAS_CODEC
  if( n<p->pBt->optimalReserve ) n = p->pBt->optimalReserve;
#endif
  sqlite3BtreeLeave(p);
  return n;
}


/*
** Set the maximum page count for a database if mxPage is positive.
** No changes are made if mxPage is 0 or negative.
** Regardless of the value of mxPage, return the maximum page count.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeMaxPageCount(Btree *p, int mxPage){
  int n;
  sqlite3BtreeEnter(p);
  n = sqlite3PagerMaxPageCount(p->pBt->pPager, mxPage);
  sqlite3BtreeLeave(p);
  return n;
}

/*
** Set the BTS_SECURE_DELETE flag if newFlag is 0 or 1.  If newFlag is -1,
** then make no changes.  Always return the value of the BTS_SECURE_DELETE
** setting after the change.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSecureDelete(Btree *p, int newFlag){
  int b;
  if( p==0 ) return 0;
  sqlite3BtreeEnter(p);
  if( newFlag>=0 ){
    p->pBt->btsFlags &= ~BTS_SECURE_DELETE;
    if( newFlag ) p->pBt->btsFlags |= BTS_SECURE_DELETE;
  } 
  b = (p->pBt->btsFlags & BTS_SECURE_DELETE)!=0;
  sqlite3BtreeLeave(p);
  return b;
}

/*
** Change the 'auto-vacuum' property of the database. If the 'autoVacuum'
** parameter is non-zero, then auto-vacuum mode is enabled. If zero, it
** is disabled. The default value for the auto-vacuum property is 
** determined by the SQLITE_DEFAULT_AUTOVACUUM macro.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetAutoVacuum(Btree *p, int autoVacuum){
#ifdef SQLITE_OMIT_AUTOVACUUM
  return SQLITE_READONLY;
#else
  BtShared *pBt = p->pBt;
  int rc = SQLITE_OK;
  u8 av = (u8)autoVacuum;

  sqlite3BtreeEnter(p);
  if( (pBt->btsFlags & BTS_PAGESIZE_FIXED)!=0 && (av ?1:0)!=pBt->autoVacuum ){
    rc = SQLITE_READONLY;
  }else{
    pBt->autoVacuum = av ?1:0;
    pBt->incrVacuum = av==2 ?1:0;
  }
  sqlite3BtreeLeave(p);
  return rc;
#endif
}

/*
** Return the value of the 'auto-vacuum' property. If auto-vacuum is 
** enabled 1 is returned. Otherwise 0.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeGetAutoVacuum(Btree *p){
#ifdef SQLITE_OMIT_AUTOVACUUM
  return BTREE_AUTOVACUUM_NONE;
#else
  int rc;
  sqlite3BtreeEnter(p);
  rc = (
    (!p->pBt->autoVacuum)?BTREE_AUTOVACUUM_NONE:
    (!p->pBt->incrVacuum)?BTREE_AUTOVACUUM_FULL:
    BTREE_AUTOVACUUM_INCR
  );
  sqlite3BtreeLeave(p);
  return rc;
#endif
}


/*
** Get a reference to pPage1 of the database file.  This will
** also acquire a readlock on that file.
**
** SQLITE_OK is returned on success.  If the file is not a
** well-formed database file, then SQLITE_CORRUPT is returned.
** SQLITE_BUSY is returned if the database is locked.  SQLITE_NOMEM
** is returned if we run out of memory. 
*/
static int lockBtree(BtShared *pBt){
  int rc;              /* Result code from subfunctions */
  MemPage *pPage1;     /* Page 1 of the database file */
  int nPage;           /* Number of pages in the database */
  int nPageFile = 0;   /* Number of pages in the database file */
  int nPageHeader;     /* Number of pages in the database according to hdr */

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pBt->pPage1==0 );
  rc = sqlite3PagerSharedLock(pBt->pPager);
  if( rc!=SQLITE_OK ) return rc;
  rc = btreeGetPage(pBt, 1, &pPage1, 0);
  if( rc!=SQLITE_OK ) return rc;

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  nPage = nPageHeader = get4byte(28+(u8*)pPage1->aData);
  sqlite3PagerPagecount(pBt->pPager, &nPageFile);
  if( nPage==0 || memcmp(24+(u8*)pPage1->aData, 92+(u8*)pPage1->aData,4)!=0 ){
    nPage = nPageFile;
  }
  if( nPage>0 ){
    u32 pageSize;
    u32 usableSize;
    u8 *page1 = pPage1->aData;
    rc = SQLITE_NOTADB;
    /* EVIDENCE-OF: R-43737-39999 Every valid SQLite database file begins
    ** with the following 16 bytes (in hex): 53 51 4c 69 74 65 20 66 6f 72 6d
    ** 61 74 20 33 00. */
    if( memcmp(page1, zMagicHeader, 16)!=0 ){
      goto page1_init_failed;
    }

#ifdef SQLITE_OMIT_WAL
    if( page1[18]>1 ){
      pBt->btsFlags |= BTS_READ_ONLY;
    }
    if( page1[19]>1 ){
      goto page1_init_failed;
    }
#else
    if( page1[18]>2 ){
      pBt->btsFlags |= BTS_READ_ONLY;
    }
    if( page1[19]>2 ){
      goto page1_init_failed;
    }

    /* If the write version is set to 2, this database should be accessed
    ** in WAL mode. If the log is not already open, open it now. Then 
    ** return SQLITE_OK and return without populating BtShared.pPage1.
    ** The caller detects this and calls this function again. This is
    ** required as the version of page 1 currently in the page1 buffer
    ** may not be the latest version - there may be a newer one in the log
    ** file.
    */
    if( page1[19]==2 && (pBt->btsFlags & BTS_NO_WAL)==0 ){
      int isOpen = 0;
      rc = sqlite3PagerOpenWal(pBt->pPager, &isOpen);
      if( rc!=SQLITE_OK ){
        goto page1_init_failed;
      }else if( isOpen==0 ){
        releasePage(pPage1);
        return SQLITE_OK;
      }
      rc = SQLITE_NOTADB;
    }
#endif

    /* EVIDENCE-OF: R-15465-20813 The maximum and minimum embedded payload
    ** fractions and the leaf payload fraction values must be 64, 32, and 32.
    **
    ** The original design allowed these amounts to vary, but as of
    ** version 3.6.0, we require them to be fixed.
    */
    if( memcmp(&page1[21], "\100\040\040",3)!=0 ){
      goto page1_init_failed;
    }
    /* EVIDENCE-OF: R-51873-39618 The page size for a database file is
    ** determined by the 2-byte integer located at an offset of 16 bytes from
    ** the beginning of the database file. */
    pageSize = (page1[16]<<8) | (page1[17]<<16);
    /* EVIDENCE-OF: R-25008-21688 The size of a page is a power of two
    ** between 512 and 65536 inclusive. */
    if( ((pageSize-1)&pageSize)!=0
     || pageSize>SQLITE_MAX_PAGE_SIZE 
     || pageSize<=256 
    ){
      goto page1_init_failed;
    }
    assert( (pageSize & 7)==0 );
    /* EVIDENCE-OF: R-59310-51205 The "reserved space" size in the 1-byte
    ** integer at offset 20 is the number of bytes of space at the end of
    ** each page to reserve for extensions. 
    **
    ** EVIDENCE-OF: R-37497-42412 The size of the reserved region is
    ** determined by the one-byte unsigned integer found at an offset of 20
    ** into the database file header. */
    usableSize = pageSize - page1[20];
    if( (u32)pageSize!=pBt->pageSize ){
      /* After reading the first page of the database assuming a page size
      ** of BtShared.pageSize, we have discovered that the page-size is
      ** actually pageSize. Unlock the database, leave pBt->pPage1 at
      ** zero and return SQLITE_OK. The caller will call this function
      ** again with the correct page-size.
      */
      releasePage(pPage1);
      pBt->usableSize = usableSize;
      pBt->pageSize = pageSize;
      freeTempSpace(pBt);
      rc = sqlite3PagerSetPagesize(pBt->pPager, &pBt->pageSize,
                                   pageSize-usableSize);
      return rc;
    }
    if( (pBt->pBt->flags & SQLITE_RecoveryMode)==0 && nPage>nPageFile ){
      rc = SQLITE_CORRUPT_BKPT;
      goto page1_init_failed;
    }
    /* EVIDENCE-OF: R-28312-64704 However, the usable size is not allowed to
    ** be less than 480. In other words, if the page size is 512, then the
    ** reserved space size cannot exceed 32. */
    if( usableSize<480 ){
      goto page1_init_failed;
    }
    pBt->pageSize = pageSize;
    pBt->usableSize = usableSize;
#ifndef SQLITE_OMIT_AUTOVACUUM
    pBt->autoVacuum = (get4byte(&page1[36 + 4*4])?1:0);
    pBt->incrVacuum = (get4byte(&page1[36 + 7*4])?1:0);
#endif
  }

  /* maxLocal is the maximum amount of payload to store locally for
  ** a cell.  Make sure it is small enough so that at least minFanout
  ** cells can will fit on one page.  We assume a 10-byte page header.
  ** Besides the payload, the cell must store:
  **     2-byte pointer to the cell
  **     4-byte child pointer
  **     9-byte nKey value
  **     4-byte nData value
  **     4-byte overflow page pointer
  ** So a cell consists of a 2-byte pointer, a header which is as much as
  ** 17 bytes long, 0 to N bytes of payload, and an optional 4 byte overflow
  ** page pointer.
  */
  pBt->maxLocal = (u16)((pBt->usableSize-12)*64/255 - 23);
  pBt->minLocal = (u16)((pBt->usableSize-12)*32/255 - 23);
  pBt->maxLeaf = (u16)(pBt->usableSize - 35);
  pBt->minLeaf = (u16)((pBt->usableSize-12)*32/255 - 23);
  if( pBt->maxLocal>127 ){
    pBt->max1bytePayload = 127;
  }else{
    pBt->max1bytePayload = (u8)pBt->maxLocal;
  }
  assert( pBt->maxLeaf + 23 <= MX_CELL_SIZE(pBt) );
  pBt->pPage1 = pPage1;
  pBt->nPage = nPage;
  return SQLITE_OK;

page1_init_failed:
  releasePage(pPage1);
  pBt->pPage1 = 0;
  return rc;
}

#ifndef NDEBUG
/*
** Return the number of cursors open on pBt. This is for use
** in assert() expressions, so it is only compiled if NDEBUG is not
** defined.
**
** Only write cursors are counted if wrOnly is true.  If wrOnly is
** false then all cursors are counted.
**
** For the purposes of this routine, a cursor is any cursor that
** is capable of reading or writing to the database.  Cursors that
** have been tripped into the CURSOR_FAULT state are not counted.
*/
static int countValidCursors(BtShared *pBt, int wrOnly){
  BtCursor *pCur;
  int r = 0;
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( (wrOnly==0 || (pCur->curFlags & BTCF_WriteFlag)!=0)
     && pCur->eState!=CURSOR_FAULT ) r++; 
  }
  return r;
}
#endif

/*
** If there are no outstanding cursors and we are not in the middle
** of a transaction but there is a read lock on the database, then
** this routine unrefs the first page of the database file which 
** has the effect of releasing the read lock.
**
** If there is a transaction in progress, this routine is a no-op.
*/
static void unlockBtreeIfUnused(BtShared *pBt){
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( countValidCursors(pBt,0)==0 || pBt->inTransaction>TRANS_NONE );
  if( pBt->inTransaction==TRANS_NONE && pBt->pPage1!=0 ){
    MemPage *pPage1 = pBt->pPage1;
    assert( pPage1->aData );
    assert( sqlite3PagerRefcount(pBt->pPager)==1 );
    pBt->pPage1 = 0;
    releasePageNotNull(pPage1);
  }
}

/*
** If pBt points to an empty file then convert that empty file
** into a new empty database by initializing the first page of
** the database.
*/
static int newDatabase(BtShared *pBt){
  MemPage *pP1;
  unsigned char *data;
  int rc;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pBt->nPage>0 ){
    return SQLITE_OK;
  }
  pP1 = pBt->pPage1;
  assert( pP1!=0 );
  data = pP1->aData;
  rc = sqlite3PagerWrite(pP1->pDbPage);
  if( rc ) return rc;
  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  assert( sizeof(zMagicHeader)==16 );
  data[16] = (u8)((pBt->pageSize>>8)&0xff);
  data[17] = (u8)((pBt->pageSize>>16)&0xff);
  data[18] = 1;
  data[19] = 1;
  assert( pBt->usableSize<=pBt->pageSize && pBt->usableSize+255>=pBt->pageSize);
  data[20] = (u8)(pBt->pageSize - pBt->usableSize);
  data[21] = 64;
  data[22] = 32;
  data[23] = 32;
  memset(&data[24], 0, 100-24);
  zeroPage(pP1, PTF_INTKEY|PTF_LEAF|PTF_LEAFDATA );
  pBt->btsFlags |= BTS_PAGESIZE_FIXED;
#ifndef SQLITE_OMIT_AUTOVACUUM
  assert( pBt->autoVacuum==1 || pBt->autoVacuum==0 );
  assert( pBt->incrVacuum==1 || pBt->incrVacuum==0 );
  put4byte(&data[36 + 4*4], pBt->autoVacuum);
  put4byte(&data[36 + 7*4], pBt->incrVacuum);
#endif
  pBt->nPage = 1;
  data[31] = 1;
  return SQLITE_OK;
}

/*
** Initialize the first page of the database file (creating a database
** consisting of a single page and no schema objects). Return SQLITE_OK
** if successful, or an SQLite error code otherwise.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeNewDb(Btree *p){
  int rc;
  sqlite3BtreeEnter(p);
  p->pBt->nPage = 0;
  rc = newDatabase(p->pBt);
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Attempt to start a new transaction. A write-transaction
** is started if the second argument is nonzero, otherwise a read-
** transaction.  If the second argument is 2 or more and exclusive
** transaction is started, meaning that no other process is allowed
** to access the database.  A preexisting transaction may not be
** upgraded to exclusive by calling this routine a second time - the
** exclusivity flag only works for a new transaction.
**
** A write-transaction must be started before attempting any 
** changes to the database.  None of the following routines 
** will work unless a transaction is started first:
**
**      sqlite3BtreeCreateTable()
**      sqlite3BtreeCreateIndex()
**      sqlite3BtreeClearTable()
**      sqlite3BtreeDropTable()
**      sqlite3BtreeInsert()
**      sqlite3BtreeDelete()
**      sqlite3BtreeUpdateMeta()
**
** If an initial attempt to acquire the lock fails because of lock contention
** and the database was previously unlocked, then invoke the busy handler
** if there is one.  But if there was previously a read-lock, do not
** invoke the busy handler - just return SQLITE_BUSY.  SQLITE_BUSY is 
** returned when there is already a read-lock in order to avoid a deadlock.
**
** Suppose there are two processes A and B.  A has a read lock and B has
** a reserved lock.  B tries to promote to exclusive but is blocked because
** of A's read lock.  A tries to promote to reserved but is blocked by B.
** One or the other of the two processes must give way or there can be
** no progress.  By returning SQLITE_BUSY and not invoking the busy callback
** when A already has a read lock, we encourage A to give up and let B
** proceed.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeBeginTrans(Btree *p, int wrflag){
  Btree *pBlock = 0;
  BtShared *pBt = p->pBt;
  int rc = SQLITE_OK;

  sqlite3BtreeEnter(p);
  btreeIntegrity(p);

  /* If the btree is already in a write-transaction, or it
  ** is already in a read-transaction and a read-transaction
  ** is requested, this is a no-op.
  */
  if( p->inTrans==TRANS_WRITE || (p->inTrans==TRANS_READ && !wrflag) ){
    goto trans_begun;
  }
  assert( pBt->inTransaction==TRANS_WRITE || IfNotOmitAV(pBt->bDoTruncate)==0 );

  /* Write transactions are not possible on a read-only database */
  if( (pBt->btsFlags & BTS_READ_ONLY)!=0 && wrflag ){
    rc = SQLITE_READONLY;
    goto trans_begun;
  }

#ifndef SQLITE_OMIT_SHARED_CACHE
  /* If another database handle has already opened a write transaction 
  ** on this shared-btree structure and a second write transaction is
  ** requested, return SQLITE_LOCKED.
  */
  if( (wrflag && pBt->inTransaction==TRANS_WRITE)
   || (pBt->btsFlags & BTS_PENDING)!=0
  ){
    pBlock = pBt->pWriter;
  }else if( wrflag>1 ){
    BtLock *pIter;
    for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
      if( pIter->pBtree!=p ){
        pBlock = pIter->pBtree;
        break;
      }
    }
  }
  if( pBlock ){
    sqlite3ConnectionBlocked(p, pBlock);
    rc = SQLITE_LOCKED_SHAREDCACHE;
    goto trans_begun;
  }
#endif

  /* Any read-only or read-write transaction implies a read-lock on 
  ** page 1. So if some other shared-cache client already has a write-lock 
  ** on page 1, the transaction cannot be opened. */
  rc = querySharedCacheTableLock(p, MASTER_ROOT, READ_LOCK);
  if( SQLITE_OK!=rc ) goto trans_begun;

  pBt->btsFlags &= ~BTS_INITIALLY_EMPTY;
  if( pBt->nPage==0 ) pBt->btsFlags |= BTS_INITIALLY_EMPTY;
  do {
    /* Call lockBtree() until either pBt->pPage1 is populated or
    ** lockBtree() returns something other than SQLITE_OK. lockBtree()
    ** may return SQLITE_OK but leave pBt->pPage1 set to 0 if after
    ** reading page 1 it discovers that the page-size of the database 
    ** file is not pBt->pageSize. In this case lockBtree() will update
    ** pBt->pageSize to the page-size of the file on disk.
    */
    while( pBt->pPage1==0 && SQLITE_OK==(rc = lockBtree(pBt)) );

    if( rc==SQLITE_OK && wrflag ){
      if( (pBt->btsFlags & BTS_READ_ONLY)!=0 ){
        rc = SQLITE_READONLY;
      }else{
        rc = sqlite3PagerBegin(pBt->pPager,wrflag>1,0);
        if( rc==SQLITE_OK ){
          rc = newDatabase(pBt);
        }
      }
    }
  
    if( rc!=SQLITE_OK ){
      unlockBtreeIfUnused(pBt);
    }
  }while( (rc&0xFF)==SQLITE_BUSY && pBt->inTransaction==TRANS_NONE &&
          btreeInvokeBusyHandler(pBt) );

  if( rc==SQLITE_OK ){
    if( p->inTrans==TRANS_NONE ){
      pBt->nTransaction++;
#ifndef SQLITE_OMIT_SHARED_CACHE
      if( p->sharable ){
        assert( p->lock.pBtree==p && p->lock.iTable==1 );
        p->lock.eLock = READ_LOCK;
        p->lock.pNext = pBt->pLock;
        pBt->pLock = &p->lock;
      }
#endif
    }
    p->inTrans = (wrflag?TRANS_WRITE:TRANS_READ);
    if( p->inTrans>pBt->inTransaction ){
      pBt->inTransaction = p->inTrans;
    }
    if( wrflag ){
      MemPage *pPage1 = pBt->pPage1;
#ifndef SQLITE_OMIT_SHARED_CACHE
      assert( !pBt->pWriter );
      pBt->pWriter = p;
      pBt->btsFlags &= ~BTS_EXCLUSIVE;
      if( wrflag>1 ) pBt->btsFlags |= BTS_EXCLUSIVE;
#endif

      /* If the db-size header field is incorrect (as it may be if an old
      ** client has been writing the database file), update it now. Doing
      ** this sooner rather than later means the database size can safely 
      ** re-read the database size from page 1 if a savepoint or transaction
      ** rollback occurs within the transaction.
      */
      if( pBt->nPage!=get4byte(&pPage1->aData[28]) ){
        rc = sqlite3PagerWrite(pPage1->pDbPage);
        if( rc==SQLITE_OK ){
          put4byte(&pPage1->aData[28], pBt->nPage);
        }
      }
    }
  }


trans_begun:
  if( rc==SQLITE_OK && wrflag ){
    /* This call makes sure that the pager has the correct number of
    ** open savepoints. If the second parameter is greater than 0 and
    ** the sub-journal is not already open, then it will be opened here.
    */
    rc = sqlite3PagerOpenSavepoint(pBt->pPager, p->nSavepoint);
  }

  btreeIntegrity(p);
  sqlite3BtreeLeave(p);
  return rc;
}

#ifndef SQLITE_OMIT_AUTOVACUUM

/*
** Set the pointer-map entries for all children of page pPage. Also, if
** pPage contains cells that point to overflow pages, set the pointer
** map entries for the overflow pages as well.
*/
static int setChildPtrmaps(MemPage *pPage){
  int i;                             /* Counter variable */
  int nCell;                         /* Number of cells in page pPage */
  int rc;                            /* Return code */
  BtShared *pBt = pPage->pBt;
  u8 isInitOrig = pPage->isInit;
  Pgno pgno = pPage->pgno;

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  rc = btreeInitPage(pPage);
  if( rc!=SQLITE_OK ){
    goto set_child_ptrmaps_out;
  }
  nCell = pPage->nCell;

  for(i=0; i<nCell; i++){
    u8 *pCell = findCell(pPage, i);

    ptrmapPutOvflPtr(pPage, pCell, &rc);

    if( !pPage->leaf ){
      Pgno childPgno = get4byte(pCell);
      ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno, &rc);
    }
  }

  if( !pPage->leaf ){
    Pgno childPgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    ptrmapPut(pBt, childPgno, PTRMAP_BTREE, pgno, &rc);
  }

set_child_ptrmaps_out:
  pPage->isInit = isInitOrig;
  return rc;
}

/*
** Somewhere on pPage is a pointer to page iFrom.  Modify this pointer so
** that it points to iTo. Parameter eType describes the type of pointer to
** be modified, as  follows:
**
** PTRMAP_BTREE:     pPage is a btree-page. The pointer points at a child 
**                   page of pPage.
**
** PTRMAP_OVERFLOW1: pPage is a btree-page. The pointer points at an overflow
**                   page pointed to by one of the cells on pPage.
**
** PTRMAP_OVERFLOW2: pPage is an overflow-page. The pointer points at the next
**                   overflow page in the list.
*/
static int modifyPagePointer(MemPage *pPage, Pgno iFrom, Pgno iTo, u8 eType){
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  if( eType==PTRMAP_OVERFLOW2 ){
    /* The pointer is always the first 4 bytes of the page in this case.  */
    if( get4byte(pPage->aData)!=iFrom ){
      return SQLITE_CORRUPT_BKPT;
    }
    put4byte(pPage->aData, iTo);
  }else{
    u8 isInitOrig = pPage->isInit;
    int i;
    int nCell;
    int rc;

    rc = btreeInitPage(pPage);
    if( rc ) return rc;
    nCell = pPage->nCell;

    for(i=0; i<nCell; i++){
      u8 *pCell = findCell(pPage, i);
      if( eType==PTRMAP_OVERFLOW1 ){
        CellInfo info;
        pPage->xParseCell(pPage, pCell, &info);
        if( info.iOverflow
         && pCell+info.iOverflow+3<=pPage->aData+pPage->maskPage
         && iFrom==get4byte(&pCell[info.iOverflow])
        ){
          put4byte(&pCell[info.iOverflow], iTo);
          break;
        }
      }else{
        if( get4byte(pCell)==iFrom ){
          put4byte(pCell, iTo);
          break;
        }
      }
    }
  
    if( i==nCell ){
      if( eType!=PTRMAP_BTREE || 
          get4byte(&pPage->aData[pPage->hdrOffset+8])!=iFrom ){
        return SQLITE_CORRUPT_BKPT;
      }
      put4byte(&pPage->aData[pPage->hdrOffset+8], iTo);
    }

    pPage->isInit = isInitOrig;
  }
  return SQLITE_OK;
}


/*
** Move the open database page pDbPage to location iFreePage in the 
** database. The pDbPage reference remains valid.
**
** The isCommit flag indicates that there is no need to remember that
** the journal needs to be sync()ed before database page pDbPage->pgno 
** can be written to. The caller has already promised not to write to that
** page.
*/
static int relocatePage(
  BtShared *pBt,           /* Btree */
  MemPage *pDbPage,        /* Open page to move */
  u8 eType,                /* Pointer map 'type' entry for pDbPage */
  Pgno iPtrPage,           /* Pointer map 'page-no' entry for pDbPage */
  Pgno iFreePage,          /* The location to move pDbPage to */
  int isCommit             /* isCommit flag passed to sqlite3PagerMovepage */
){
  MemPage *pPtrPage;   /* The page that contains a pointer to pDbPage */
  Pgno iDbPage = pDbPage->pgno;
  Pager *pPager = pBt->pPager;
  int rc;

  assert( eType==PTRMAP_OVERFLOW2 || eType==PTRMAP_OVERFLOW1 || 
      eType==PTRMAP_BTREE || eType==PTRMAP_ROOTPAGE );
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( pDbPage->pBt==pBt );

  /* Move page iDbPage from its current location to page number iFreePage */
  TRACE(("AUTOVACUUM: Moving %d to free page %d (ptr page %d type %d)\n", 
      iDbPage, iFreePage, iPtrPage, eType));
  rc = sqlite3PagerMovepage(pPager, pDbPage->pDbPage, iFreePage, isCommit);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  pDbPage->pgno = iFreePage;

  /* If pDbPage was a btree-page, then it may have child pages and/or cells
  ** that point to overflow pages. The pointer map entries for all these
  ** pages need to be changed.
  **
  ** If pDbPage is an overflow page, then the first 4 bytes may store a
  ** pointer to a subsequent overflow page. If this is the case, then
  ** the pointer map needs to be updated for the subsequent overflow page.
  */
  if( eType==PTRMAP_BTREE || eType==PTRMAP_ROOTPAGE ){
    rc = setChildPtrmaps(pDbPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }else{
    Pgno nextOvfl = get4byte(pDbPage->aData);
    if( nextOvfl!=0 ){
      ptrmapPut(pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage, &rc);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
  ** that it points at iFreePage. Also fix the pointer map entry for
  ** iPtrPage.
  */
  if( eType!=PTRMAP_ROOTPAGE ){
    rc = btreeGetPage(pBt, iPtrPage, &pPtrPage, 0);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    rc = sqlite3PagerWrite(pPtrPage->pDbPage);
    if( rc!=SQLITE_OK ){
      releasePage(pPtrPage);
      return rc;
    }
    rc = modifyPagePointer(pPtrPage, iDbPage, iFreePage, eType);
    releasePage(pPtrPage);
    if( rc==SQLITE_OK ){
      ptrmapPut(pBt, iFreePage, eType, iPtrPage, &rc);
    }
  }
  return rc;
}

/* Forward declaration required by incrVacuumStep(). */
static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);

/*
** Perform a single step of an incremental-vacuum. If successful, return
** SQLITE_OK. If there is no work to do (and therefore no point in 
** calling this function again), return SQLITE_DONE. Or, if an error 
** occurs, return some other error code.
**
** More specifically, this function attempts to re-organize the database so 
** that the last page of the file currently in use is no longer in use.
**
** Parameter nFin is the number of pages that this database would contain
** were this function called until it returns SQLITE_DONE.
**
** If the bCommit parameter is non-zero, this function assumes that the 
** caller will keep calling incrVacuumStep() until it returns SQLITE_DONE 
** or an error. bCommit is passed true for an auto-vacuum-on-commit 
** operation, or false for an incremental vacuum.
*/
static int incrVacuumStep(BtShared *pBt, Pgno nFin, Pgno iLastPg, int bCommit){
  Pgno nFreeList;           /* Number of pages still on the free-list */
  int rc;

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( iLastPg>nFin );

  if( !PTRMAP_ISPAGE(pBt, iLastPg) && iLastPg!=PENDING_BYTE_PAGE(pBt) ){
    u8 eType;
    Pgno iPtrPage;

    nFreeList = get4byte(&pBt->pPage1->aData[36]);
    if( nFreeList==0 ){
      return SQLITE_DONE;
    }

    rc = ptrmapGet(pBt, iLastPg, &eType, &iPtrPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    if( eType==PTRMAP_ROOTPAGE ){
      return SQLITE_CORRUPT_BKPT;
    }

    if( eType==PTRMAP_FREEPAGE ){
      if( bCommit==0 ){
        /* Remove the page from the files free-list. This is not required
        ** if bCommit is non-zero. In that case, the free-list will be
        ** truncated to zero after this function returns, so it doesn't 
        ** matter if it still contains some garbage entries.
        */
        Pgno iFreePg;
        MemPage *pFreePg;
        rc = allocateBtreePage(pBt, &pFreePg, &iFreePg, iLastPg, BTALLOC_EXACT);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        assert( iFreePg==iLastPg );
        releasePage(pFreePg);
      }
    } else {
      Pgno iFreePg;             /* Index of free page to move pLastPg to */
      MemPage *pLastPg;
      u8 eMode = BTALLOC_ANY;   /* Mode parameter for allocateBtreePage() */
      Pgno iNear = 0;           /* nearby parameter for allocateBtreePage() */

      rc = btreeGetPage(pBt, iLastPg, &pLastPg, 0);
      if( rc!=SQLITE_OK ){
        return rc;
      }

      /* If bCommit is zero, this loop runs exactly once and page pLastPg
      ** is swapped with the first free page pulled off the free list.
      **
      ** On the other hand, if bCommit is greater than zero, then keep
      ** looping until a free-page located within the first nFin pages
      ** of the file is found.
      */
      if( bCommit==0 ){
        eMode = BTALLOC_LE;
        iNear = nFin;
      }
      do {
        MemPage *pFreePg;
        rc = allocateBtreePage(pBt, &pFreePg, &iFreePg, iNear, eMode);
        if( rc!=SQLITE_OK ){
          releasePage(pLastPg);
          return rc;
        }
        releasePage(pFreePg);
      }while( bCommit && iFreePg>nFin );
      assert( iFreePg<iLastPg );
      
      rc = relocatePage(pBt, pLastPg, eType, iPtrPage, iFreePg, bCommit);
      releasePage(pLastPg);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }

  if( bCommit==0 ){
    do {
      iLastPg--;
    }while( iLastPg==PENDING_BYTE_PAGE(pBt) || PTRMAP_ISPAGE(pBt, iLastPg) );
    pBt->bDoTruncate = 1;
    pBt->nPage = iLastPg;
  }
  return SQLITE_OK;
}

/*
** The database opened by the first argument is an auto-vacuum database
** nOrig pages in size containing nFree free pages. Return the expected 
** size of the database in pages following an auto-vacuum operation.
*/
static Pgno finalDbSize(BtShared *pBt, Pgno nOrig, Pgno nFree){
  int nEntry;                     /* Number of entries on one ptrmap page */
  Pgno nPtrmap;                   /* Number of PtrMap pages to be freed */
  Pgno nFin;                      /* Return value */

  nEntry = pBt->usableSize/5;
  nPtrmap = (nFree-nOrig+PTRMAP_PAGENO(pBt, nOrig)+nEntry)/nEntry;
  nFin = nOrig - nFree - nPtrmap;
  if( nOrig>PENDING_BYTE_PAGE(pBt) && nFin<PENDING_BYTE_PAGE(pBt) ){
    nFin--;
  }
  while( PTRMAP_ISPAGE(pBt, nFin) || nFin==PENDING_BYTE_PAGE(pBt) ){
    nFin--;
  }

  return nFin;
}

/*
** A write-transaction must be opened before calling this function.
** It performs a single unit of work towards an incremental vacuum.
**
** If the incremental vacuum is finished after this function has run,
** SQLITE_DONE is returned. If it is not finished, but no error occurred,
** SQLITE_OK is returned. Otherwise an SQLite error code. 
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeIncrVacuum(Btree *p){
  int rc;
  BtShared *pBt = p->pBt;

  sqlite3BtreeEnter(p);
  assert( pBt->inTransaction==TRANS_WRITE && p->inTrans==TRANS_WRITE );
  if( !pBt->autoVacuum ){
    rc = SQLITE_DONE;
  }else{
    Pgno nOrig = btreePagecount(pBt);
    Pgno nFree = get4byte(&pBt->pPage1->aData[36]);
    Pgno nFin = finalDbSize(pBt, nOrig, nFree);

    if( nOrig<nFin ){
      rc = SQLITE_CORRUPT_BKPT;
    }else if( nFree>0 ){
      rc = saveAllCursors(pBt, 0, 0);
      if( rc==SQLITE_OK ){
        invalidateAllOverflowCache(pBt);
        rc = incrVacuumStep(pBt, nFin, nOrig, 0);
      }
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
        put4byte(&pBt->pPage1->aData[28], pBt->nPage);
      }
    }else{
      rc = SQLITE_DONE;
    }
  }
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** This routine is called prior to sqlite3PagerCommit when a transaction
** is committed for an auto-vacuum database.
**
** If SQLITE_OK is returned, then *pnTrunc is set to the number of pages
** the database file should be truncated to during the commit process. 
** i.e. the database has been reorganized so that only the first *pnTrunc
** pages are in use.
*/
static int autoVacuumCommit(BtShared *pBt){
  int rc = SQLITE_OK;
  Pager *pPager = pBt->pPager;
  VVA_ONLY( int nRef = sqlite3PagerRefcount(pPager); )

  assert( sqlite3_mutex_held(pBt->mutex) );
  invalidateAllOverflowCache(pBt);
  assert(pBt->autoVacuum);
  if( !pBt->incrVacuum ){
    Pgno nFin;         /* Number of pages in database after autovacuuming */
    Pgno nFree;        /* Number of pages on the freelist initially */
    Pgno iFree;        /* The next page to be freed */
    Pgno nOrig;        /* Database size before freeing */

    nOrig = btreePagecount(pBt);
    if( PTRMAP_ISPAGE(pBt, nOrig) || nOrig==PENDING_BYTE_PAGE(pBt) ){
      /* It is not possible to create a database for which the final page
      ** is either a pointer-map page or the pending-byte page. If one
      ** is encountered, this indicates corruption.
      */
      return SQLITE_CORRUPT_BKPT;
    }

    nFree = get4byte(&pBt->pPage1->aData[36]);
    nFin = finalDbSize(pBt, nOrig, nFree);
    if( nFin>nOrig ) return SQLITE_CORRUPT_BKPT;
    if( nFin<nOrig ){
      rc = saveAllCursors(pBt, 0, 0);
    }
    for(iFree=nOrig; iFree>nFin && rc==SQLITE_OK; iFree--){
      rc = incrVacuumStep(pBt, nFin, iFree, 1);
    }
    if( (rc==SQLITE_DONE || rc==SQLITE_OK) && nFree>0 ){
      rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
      put4byte(&pBt->pPage1->aData[32], 0);
      put4byte(&pBt->pPage1->aData[36], 0);
      put4byte(&pBt->pPage1->aData[28], nFin);
      pBt->bDoTruncate = 1;
      pBt->nPage = nFin;
    }
    if( rc!=SQLITE_OK ){
      sqlite3PagerRollback(pPager);
    }
  }

  assert( nRef>=sqlite3PagerRefcount(pPager) );
  return rc;
}

#else /* ifndef SQLITE_OMIT_AUTOVACUUM */
# define setChildPtrmaps(x) SQLITE_OK
#endif

/*
** This routine does the first phase of a two-phase commit.  This routine
** causes a rollback journal to be created (if it does not already exist)
** and populated with enough information so that if a power loss occurs
** the database can be restored to its original state by playing back
** the journal.  Then the contents of the journal are flushed out to
** the disk.  After the journal is safely on oxide, the changes to the
** database are written into the database file and flushed to oxide.
** At the end of this call, the rollback journal still exists on the
** disk and we are still holding all locks, so the transaction has not
** committed.  See sqlite3BtreeCommitPhaseTwo() for the second phase of the
** commit process.
**
** This call is a no-op if no write-transaction is currently active on pBt.
**
** Otherwise, sync the database file for the btree pBt. zMaster points to
** the name of a master journal file that should be written into the
** individual journal file, or is NULL, indicating no master journal file 
** (single database transaction).
**
** When this is called, the master journal should already have been
** created, populated with this journal pointer and synced to disk.
**
** Once this is routine has returned, the only thing required to commit
** the write-transaction for this database file is to delete the journal.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCommitPhaseOne(Btree *p, const char *zMaster){
  int rc = SQLITE_OK;
  if( p->inTrans==TRANS_WRITE ){
    BtShared *pBt = p->pBt;
    sqlite3BtreeEnter(p);
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum ){
      rc = autoVacuumCommit(pBt);
      if( rc!=SQLITE_OK ){
        sqlite3BtreeLeave(p);
        return rc;
      }
    }
    if( pBt->bDoTruncate ){
      sqlite3PagerTruncateImage(pBt->pPager, pBt->nPage);
    }
#endif
    rc = sqlite3PagerCommitPhaseOne(pBt->pPager, zMaster, 0);
    sqlite3BtreeLeave(p);
  }
  return rc;
}

/*
** This function is called from both BtreeCommitPhaseTwo() and BtreeRollback()
** at the conclusion of a transaction.
*/
static void btreeEndTransaction(Btree *p){
  BtShared *pBt = p->pBt;
  assert( sqlite3BtreeHoldsMutex(p) );

#ifndef SQLITE_OMIT_AUTOVACUUM
  pBt->bDoTruncate = 0;
#endif
  if( p->inTrans>TRANS_NONE && p->nVdbeRead>1 ){
    /* If there are other active statements that belong to this database
    ** handle, downgrade to a read-only transaction. The other statements
    ** may still be reading from the database.  */
    downgradeAllSharedCacheTableLocks(p);
    p->inTrans = TRANS_READ;
  }else{
    /* If the handle had any kind of transaction open, decrement the 
    ** transaction count of the shared btree. If the transaction count 
    ** reaches 0, set the shared state to TRANS_NONE. The unlockBtreeIfUnused()
    ** call below will unlock the pager.  */
    if( p->inTrans!=TRANS_NONE ){
      clearAllSharedCacheTableLocks(p);
      pBt->nTransaction--;
      if( 0==pBt->nTransaction ){
        pBt->inTransaction = TRANS_NONE;
      }
    }

    /* Set the current transaction state to TRANS_NONE and unlock the 
    ** pager if this call closed the only read or write transaction.  */
    p->inTrans = TRANS_NONE;
    unlockBtreeIfUnused(pBt);
  }

  btreeIntegrity(p);
}

/*
** Commit the transaction currently in progress.
**
** This routine implements the second phase of a 2-phase commit.  The
** sqlite3BtreeCommitPhaseOne() routine does the first phase and should
** be invoked prior to calling this routine.  The sqlite3BtreeCommitPhaseOne()
** routine did all the work of writing information out to disk and flushing the
** contents so that they are written onto the disk platter.  All this
** routine has to do is delete or truncate or zero the header in the
** the rollback journal (which causes the transaction to commit) and
** drop locks.
**
** Normally, if an error occurs while the pager layer is attempting to 
** finalize the underlying journal file, this function returns an error and
** the upper layer will attempt a rollback. However, if the second argument
** is non-zero then this b-tree transaction is part of a multi-file 
** transaction. In this case, the transaction has already been committed 
** (by deleting a master journal file) and the caller will ignore this 
** functions return code. So, even if an error occurs in the pager layer,
** reset the b-tree objects internal state to indicate that the write
** transaction has been closed. This is quite safe, as the pager will have
** transitioned to the error state.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCommitPhaseTwo(Btree *p, int bCleanup){

  if( p->inTrans==TRANS_NONE ) return SQLITE_OK;
  sqlite3BtreeEnter(p);
  btreeIntegrity(p);

  /* If the handle has a write-transaction open, commit the shared-btrees 
  ** transaction and set the shared state to TRANS_READ.
  */
  if( p->inTrans==TRANS_WRITE ){
    int rc;
    BtShared *pBt = p->pBt;
    assert( pBt->inTransaction==TRANS_WRITE );
    assert( pBt->nTransaction>0 );
    rc = sqlite3PagerCommitPhaseTwo(pBt->pPager);
    if( rc!=SQLITE_OK && bCleanup==0 ){
      sqlite3BtreeLeave(p);
      return rc;
    }
    p->iDataVersion--;  /* Compensate for pPager->iDataVersion++; */
    pBt->inTransaction = TRANS_READ;
    btreeClearHasContent(pBt);
  }

  btreeEndTransaction(p);
  sqlite3BtreeLeave(p);
  return SQLITE_OK;
}

/*
** Do both phases of a commit.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCommit(Btree *p){
  int rc;
  sqlite3BtreeEnter(p);
  rc = sqlite3BtreeCommitPhaseOne(p, 0);
  if( rc==SQLITE_OK ){
    rc = sqlite3BtreeCommitPhaseTwo(p, 0);
  }
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** This routine sets the state to CURSOR_FAULT and the error
** code to errCode for every cursor on any BtShared that pBtree
** references.  Or if the writeOnly flag is set to 1, then only
** trip write cursors and leave read cursors unchanged.
**
** Every cursor is a candidate to be tripped, including cursors
** that belong to other database connections that happen to be
** sharing the cache with pBtree.
**
** This routine gets called when a rollback occurs. If the writeOnly
** flag is true, then only write-cursors need be tripped - read-only
** cursors save their current positions so that they may continue 
** following the rollback. Or, if writeOnly is false, all cursors are 
** tripped. In general, writeOnly is false if the transaction being
** rolled back modified the database schema. In this case b-tree root
** pages may be moved or deleted from the database altogether, making
** it unsafe for read cursors to continue.
**
** If the writeOnly flag is true and an error is encountered while 
** saving the current position of a read-only cursor, all cursors, 
** including all read-cursors are tripped.
**
** SQLITE_OK is returned if successful, or if an error occurs while
** saving a cursor position, an SQLite error code.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeTripAllCursors(Btree *pBtree, int errCode, int writeOnly){
  BtCursor *p;
  int rc = SQLITE_OK;

  assert( (writeOnly==0 || writeOnly==1) && BTCF_WriteFlag==1 );
  if( pBtree ){
    sqlite3BtreeEnter(pBtree);
    for(p=pBtree->pBt->pCursor; p; p=p->pNext){
      int i;
      if( writeOnly && (p->curFlags & BTCF_WriteFlag)==0 ){
        if( p->eState==CURSOR_VALID || p->eState==CURSOR_SKIPNEXT ){
          rc = saveCursorPosition(p);
          if( rc!=SQLITE_OK ){
            (void)sqlite3BtreeTripAllCursors(pBtree, rc, 0);
            break;
          }
        }
      }else{
        sqlite3BtreeClearCursor(p);
        p->eState = CURSOR_FAULT;
        p->skipNext = errCode;
      }
      for(i=0; i<=p->iPage; i++){
        releasePage(p->apPage[i]);
        p->apPage[i] = 0;
      }
    }
    sqlite3BtreeLeave(pBtree);
  }
  return rc;
}

/*
** Rollback the transaction in progress.
**
** If tripCode is not SQLITE_OK then cursors will be invalidated (tripped).
** Only write cursors are tripped if writeOnly is true but all cursors are
** tripped if writeOnly is false.  Any attempt to use
** a tripped cursor will result in an error.
**
** This will release the write lock on the database file.  If there
** are no active cursors, it also releases the read lock.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeRollback(Btree *p, int tripCode, int writeOnly){
  int rc;
  BtShared *pBt = p->pBt;
  MemPage *pPage1;

  assert( writeOnly==1 || writeOnly==0 );
  assert( tripCode==SQLITE_ABORT_ROLLBACK || tripCode==SQLITE_OK );
  sqlite3BtreeEnter(p);
  if( tripCode==SQLITE_OK ){
    rc = tripCode = saveAllCursors(pBt, 0, 0);
    if( rc ) writeOnly = 0;
  }else{
    rc = SQLITE_OK;
  }
  if( tripCode ){
    int rc2 = sqlite3BtreeTripAllCursors(p, tripCode, writeOnly);
    assert( rc==SQLITE_OK || (writeOnly==0 && rc2==SQLITE_OK) );
    if( rc2!=SQLITE_OK ) rc = rc2;
  }
  btreeIntegrity(p);

  if( p->inTrans==TRANS_WRITE ){
    int rc2;

    assert( TRANS_WRITE==pBt->inTransaction );
    rc2 = sqlite3PagerRollback(pBt->pPager);
    if( rc2!=SQLITE_OK ){
      rc = rc2;
    }

    /* The rollback may have destroyed the pPage1->aData value.  So
    ** call btreeGetPage() on page 1 again to make
    ** sure pPage1->aData is set correctly. */
    if( btreeGetPage(pBt, 1, &pPage1, 0)==SQLITE_OK ){
      int nPage = get4byte(28+(u8*)pPage1->aData);
      testcase( nPage==0 );
      if( nPage==0 ) sqlite3PagerPagecount(pBt->pPager, &nPage);
      testcase( pBt->nPage!=nPage );
      pBt->nPage = nPage;
      releasePage(pPage1);
    }
    assert( countValidCursors(pBt, 1)==0 );
    pBt->inTransaction = TRANS_READ;
    btreeClearHasContent(pBt);
  }

  btreeEndTransaction(p);
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Start a statement subtransaction. The subtransaction can be rolled
** back independently of the main transaction. You must start a transaction 
** before starting a subtransaction. The subtransaction is ended automatically 
** if the main transaction commits or rolls back.
**
** Statement subtransactions are used around individual SQL statements
** that are contained within a BEGIN...COMMIT block.  If a constraint
** error occurs within the statement, the effect of that one statement
** can be rolled back without having to rollback the entire transaction.
**
** A statement sub-transaction is implemented as an anonymous savepoint. The
** value passed as the second parameter is the total number of savepoints,
** including the new anonymous savepoint, open on the B-Tree. i.e. if there
** are no active savepoints and no other statement-transactions open,
** iStatement is 1. This anonymous savepoint can be released or rolled back
** using the sqlite3BtreeSavepoint() function.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeBeginStmt(Btree *p, int iStatement){
  int rc;
  BtShared *pBt = p->pBt;
  sqlite3BtreeEnter(p);
  assert( p->inTrans==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( iStatement>0 );
  assert( iStatement>p->nSavepoint );
  assert( pBt->inTransaction==TRANS_WRITE );
  /* At the pager level, a statement transaction is a savepoint with
  ** an index greater than all savepoints created explicitly using
  ** SQL statements. It is illegal to open, release or rollback any
  ** such savepoints while the statement transaction savepoint is active.
  */
  rc = sqlite3PagerOpenSavepoint(pBt->pPager, iStatement);
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** The second argument to this function, op, is always SAVEPOINT_ROLLBACK
** or SAVEPOINT_RELEASE. This function either releases or rolls back the
** savepoint identified by parameter iSavepoint, depending on the value 
** of op.
**
** Normally, iSavepoint is greater than or equal to zero. However, if op is
** SAVEPOINT_ROLLBACK, then iSavepoint may also be -1. In this case the 
** contents of the entire transaction are rolled back. This is different
** from a normal transaction rollback, as no locks are released and the
** transaction remains open.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSavepoint(Btree *p, int op, int iSavepoint){
  int rc = SQLITE_OK;
  if( p && p->inTrans==TRANS_WRITE ){
    BtShared *pBt = p->pBt;
    assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
    assert( iSavepoint>=0 || (iSavepoint==-1 && op==SAVEPOINT_ROLLBACK) );
    sqlite3BtreeEnter(p);
    rc = sqlite3PagerSavepoint(pBt->pPager, op, iSavepoint);
    if( rc==SQLITE_OK ){
      if( iSavepoint<0 && (pBt->btsFlags & BTS_INITIALLY_EMPTY)!=0 ){
        pBt->nPage = 0;
      }
      rc = newDatabase(pBt);
      pBt->nPage = get4byte(28 + pBt->pPage1->aData);

      /* The database size was written into the offset 28 of the header
      ** when the transaction started, so we know that the value at offset
      ** 28 is nonzero. */
      assert( pBt->nPage>0 );
    }
    sqlite3BtreeLeave(p);
  }
  return rc;
}

/*
** Create a new cursor for the BTree whose root is on the page
** iTable. If a read-only cursor is requested, it is assumed that
** the caller already has at least a read-only transaction open
** on the database already. If a write-cursor is requested, then
** the caller is assumed to have an open write transaction.
**
** If wrFlag==0, then the cursor can only be used for reading.
** If wrFlag==1, then the cursor can be used for reading or for
** writing if other conditions for writing are also met.  These
** are the conditions that must be met in order for writing to
** be allowed:
**
** 1:  The cursor must have been opened with wrFlag==1
**
** 2:  Other database connections that share the same pager cache
**     but which are not in the READ_UNCOMMITTED state may not have
**     cursors open with wrFlag==0 on the same table.  Otherwise
**     the changes made by this write cursor would be visible to
**     the read cursors in the other database connection.
**
** 3:  The database must be writable (not on read-only media)
**
** 4:  There must be an active transaction.
**
** No checking is done to make sure that page iTable really is the
** root page of a b-tree.  If it is not, then the cursor acquired
** will not work correctly.
*/
static int btreeCursor(
  Btree *p,                              /* The btree */
  int iTable,                            /* Root page of table to open */
  int wrFlag,                            /* 1 to write. 0 read-only */
  struct KeyInfo *pKeyInfo,              /* First arg to comparison function */
  BtCursor *pCur                         /* Space for new cursor */
){
  BtShared *pBt = p->pBt;                /* Shared b-tree handle */
  BtCursor *pX;                          /* Looping over other all cursors */

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( wrFlag==0 || wrFlag==1 );

  /* The following assert statements verify that if this is a sharable 
  ** b-tree database, the connection is holding the required table locks, 
  ** and that no other connection has any open cursor that conflicts with 
  ** this lock.  */
  assert( hasSharedCacheTableLock(p, iTable, pKeyInfo!=0, wrFlag+1) );
  assert( wrFlag==0 || !hasReadConflicts(p, iTable) );

  /* Assert that the caller has opened the required transaction. */
  assert( p->inTrans>TRANS_NONE );
  assert( wrFlag==0 || p->inTrans==TRANS_WRITE );
  assert( pBt->pPage1 && pBt->pPage1->aData );
  assert( wrFlag==0 || (pBt->btsFlags & BTS_READ_ONLY)==0 );

  if( wrFlag ){
    allocateTempSpace(pBt);
    if( pBt->pTmpSpace==0 ) return SQLITE_NOMEM;
  }
  if( iTable==1 && btreePagecount(pBt)==0 ){
    assert( wrFlag==0 );
    iTable = 0;
  }

  /* Now that no other errors can occur, finish filling in the BtCursor
  ** variables and link the cursor into the BtShared list.  */
  pCur->pgnoRoot = (Pgno)iTable;
  pCur->iPage = -1;
  pCur->pKeyInfo = pKeyInfo;
  pCur->pBtree = p;
  pCur->pBt = pBt;
  assert( wrFlag==0 || wrFlag==BTCF_WriteFlag );
  pCur->curFlags = wrFlag;
  pCur->curPagerFlags = wrFlag ? 0 : PAGER_GET_READONLY;
  /* If there are two or more cursors on the same btree, then all such
  ** cursors *must* have the BTCF_Multiple flag set. */
  for(pX=pBt->pCursor; pX; pX=pX->pNext){
    if( pX->pgnoRoot==(Pgno)iTable ){
      pX->curFlags |= BTCF_Multiple;
      pCur->curFlags |= BTCF_Multiple;
    }
  }
  pCur->pNext = pBt->pCursor;
  pBt->pCursor = pCur;
  pCur->eState = CURSOR_INVALID;
  return SQLITE_OK;
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursor(
  Btree *p,                                   /* The btree */
  int iTable,                                 /* Root page of table to open */
  int wrFlag,                                 /* 1 to write. 0 read-only */
  int N, int X,                               /* index of N key columns and X extra columns */
  BtCursor **ppCur                            /* Write new cursor here */
){
  int rc;
  
  *ppCur = 0;
  if( iTable<1 ){
    rc = SQLITE_CORRUPT_BKPT;
  }else{
    KeyInfo *pKeyInfo = NULL;
    if (N > 0 || X > 0) {
      pKeyInfo = sqlite3DbMallocZero(0, 
          	                   sizeof(KeyInfo) + (N+X)*(sizeof(CollSeq*)+1));
      if( pKeyInfo ){
        pKeyInfo->aSortOrder = (u8*)&pKeyInfo->aColl[N+X];
        pKeyInfo->nField = (u16)N;
        pKeyInfo->nXField = (u16)X;
        pKeyInfo->enc = p->enc;
        pKeyInfo->pBtree = p;
        pKeyInfo->nRef = 1;
      }else{
        p->mallocFailed = 1;
        return SQLITE_NOMEM;
      }
    }

	BtCursor *pCur = sqlite3MallocZero(sizeof(BtCursor));
	if (!pCur) {
	  p->mallocFailed = 1;
	  sqlite3_free(pKeyInfo);
	  return SQLITE_NOMEM;
	}

    sqlite3BtreeEnter(p);
    rc = btreeCursor(p, iTable, wrFlag, pKeyInfo, pCur);
    sqlite3BtreeLeave(p);
    
    if (rc != SQLITE_OK) {
		sqlite3_free(pKeyInfo);
		sqlite3_free(pCur);
		return rc;
	}

	*ppCur = pCur;
  }
  return rc;
}

/*
** Return the size of a BtCursor object in bytes.
**
** This interfaces is needed so that users of cursors can preallocate
** sufficient storage to hold a cursor.  The BtCursor object is opaque
** to users so they cannot do the sizeof() themselves - they must call
** this routine.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursorSize(void){
  return ROUND8(sizeof(BtCursor));
}

/*
** Close a cursor.  The read lock on the database file is released
** when the last cursor is closed.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCloseCursor(BtCursor *pCur){
  Btree *pBtree = pCur->pBtree;
  if( pBtree ){
    int i;
    BtShared *pBt = pCur->pBt;
    sqlite3BtreeEnter(pBtree);
    sqlite3BtreeClearCursor(pCur);
    assert( pBt->pCursor!=0 );
    if( pBt->pCursor==pCur ){
      pBt->pCursor = pCur->pNext;
    }else{
      BtCursor *pPrev = pBt->pCursor;
      do{
        if( pPrev->pNext==pCur ){
          pPrev->pNext = pCur->pNext;
          break;
        }
        pPrev = pPrev->pNext;
      }while( ALWAYS(pPrev) );
    }
    for(i=0; i<=pCur->iPage; i++){
      releasePage(pCur->apPage[i]);
    }
    unlockBtreeIfUnused(pBt);
    sqlite3_free(pCur->aOverflow);
    /* sqlite3_free(pCur); */
    sqlite3BtreeLeave(pBtree);
  }
  
  if( pCur->pKeyInfo ) {
    assert( pCur->pKeyInfo->nRef>0 );
    pCur->pKeyInfo->nRef--;
    if( pCur->pKeyInfo->nRef==0 ) sqlite3DbFree(0, pCur->pKeyInfo);
  }

  sqlite3_free(pCur);
  return SQLITE_OK;
}

/*
** Make sure the BtCursor* given in the argument has a valid
** BtCursor.info structure.  If it is not already valid, call
** btreeParseCell() to fill it in.
**
** BtCursor.info is a cache of the information in the current cell.
** Using this cache reduces the number of calls to btreeParseCell().
*/
#ifndef NDEBUG
  static void assertCellInfo(BtCursor *pCur){
    CellInfo info;
    int iPage = pCur->iPage;
    memset(&info, 0, sizeof(info));
    btreeParseCell(pCur->apPage[iPage], pCur->aiIdx[iPage], &info);
    assert( CORRUPT_DB || memcmp(&info, &pCur->info, sizeof(info))==0 );
  }
#else
  #define assertCellInfo(x)
#endif
static SQLITE_NOINLINE void getCellInfo(BtCursor *pCur){
  if( pCur->info.nSize==0 ){
    int iPage = pCur->iPage;
    pCur->curFlags |= BTCF_ValidNKey;
    btreeParseCell(pCur->apPage[iPage],pCur->aiIdx[iPage],&pCur->info);
  }else{
    assertCellInfo(pCur);
  }
}

#ifndef NDEBUG  /* The next routine used only within assert() statements */
/*
** Return true if the given BtCursor is valid.  A valid cursor is one
** that is currently pointing to a row in a (non-empty) table.
** This is a verification routine is used only within assert() statements.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursorIsValid(BtCursor *pCur){
  return pCur && pCur->eState==CURSOR_VALID;
}
#endif /* NDEBUG */

/*
** Set *pSize to the size of the buffer needed to hold the value of
** the key for the current entry.  If the cursor is not pointing
** to a valid entry, *pSize is set to 0. 
**
** For a table with the INTKEY flag set, this routine returns the key
** itself, not the number of bytes in the key.
**
** The caller must position the cursor prior to invoking this routine.
** 
** This routine cannot fail.  It always returns SQLITE_OK.  
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeKeySize(BtCursor *pCur, i64 *pSize){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  getCellInfo(pCur);
  *pSize = pCur->info.nKey;
  return SQLITE_OK;
}

/*
** Set *pSize to the number of bytes of data in the entry the
** cursor currently points to.
**
** The caller must guarantee that the cursor is pointing to a non-NULL
** valid entry.  In other words, the calling procedure must guarantee
** that the cursor has Cursor.eState==CURSOR_VALID.
**
** Failure is not possible.  This function always returns SQLITE_OK.
** It might just as well be a procedure (returning void) but we continue
** to return an integer result code for historical reasons.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeDataSize(BtCursor *pCur, u32 *pSize){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage>=0 );
  assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
  assert( pCur->apPage[pCur->iPage]->intKeyLeaf==1 );
  getCellInfo(pCur);
  *pSize = pCur->info.nPayload;
  return SQLITE_OK;
}

/*
** Given the page number of an overflow page in the database (parameter
** ovfl), this function finds the page number of the next page in the 
** linked list of overflow pages. If possible, it uses the auto-vacuum
** pointer-map data instead of reading the content of page ovfl to do so. 
**
** If an error occurs an SQLite error code is returned. Otherwise:
**
** The page number of the next overflow page in the linked list is 
** written to *pPgnoNext. If page ovfl is the last page in its linked 
** list, *pPgnoNext is set to zero. 
**
** If ppPage is not NULL, and a reference to the MemPage object corresponding
** to page number pOvfl was obtained, then *ppPage is set to point to that
** reference. It is the responsibility of the caller to call releasePage()
** on *ppPage to free the reference. In no reference was obtained (because
** the pointer-map was used to obtain the value for *pPgnoNext), then
** *ppPage is set to zero.
*/
static int getOverflowPage(
  BtShared *pBt,               /* The database file */
  Pgno ovfl,                   /* Current overflow page number */
  MemPage **ppPage,            /* OUT: MemPage handle (may be NULL) */
  Pgno *pPgnoNext              /* OUT: Next overflow page number */
){
  Pgno next = 0;
  MemPage *pPage = 0;
  int rc = SQLITE_OK;

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert(pPgnoNext);

#ifndef SQLITE_OMIT_AUTOVACUUM
  /* Try to find the next page in the overflow list using the
  ** autovacuum pointer-map pages. Guess that the next page in 
  ** the overflow list is page number (ovfl+1). If that guess turns 
  ** out to be wrong, fall back to loading the data of page 
  ** number ovfl to determine the next page number.
  */
  if( pBt->autoVacuum ){
    Pgno pgno;
    Pgno iGuess = ovfl+1;
    u8 eType;

    while( PTRMAP_ISPAGE(pBt, iGuess) || iGuess==PENDING_BYTE_PAGE(pBt) ){
      iGuess++;
    }

    if( iGuess<=btreePagecount(pBt) ){
      rc = ptrmapGet(pBt, iGuess, &eType, &pgno);
      if( rc==SQLITE_OK && eType==PTRMAP_OVERFLOW2 && pgno==ovfl ){
        next = iGuess;
        rc = SQLITE_DONE;
      }
    }
  }
#endif

  assert( next==0 || rc==SQLITE_DONE );
  if( rc==SQLITE_OK ){
    rc = btreeGetPage(pBt, ovfl, &pPage, (ppPage==0) ? PAGER_GET_READONLY : 0);
    assert( rc==SQLITE_OK || pPage==0 );
    if( rc==SQLITE_OK ){
      next = get4byte(pPage->aData);
    }
  }

  *pPgnoNext = next;
  if( ppPage ){
    *ppPage = pPage;
  }else{
    releasePage(pPage);
  }
  return (rc==SQLITE_DONE ? SQLITE_OK : rc);
}

/*
** Copy data from a buffer to a page, or from a page to a buffer.
**
** pPayload is a pointer to data stored on database page pDbPage.
** If argument eOp is false, then nByte bytes of data are copied
** from pPayload to the buffer pointed at by pBuf. If eOp is true,
** then sqlite3PagerWrite() is called on pDbPage and nByte bytes
** of data are copied from the buffer pBuf to pPayload.
**
** SQLITE_OK is returned on success, otherwise an error code.
*/
static int copyPayload(
  void *pPayload,           /* Pointer to page data */
  void *pBuf,               /* Pointer to buffer */
  int nByte,                /* Number of bytes to copy */
  int eOp,                  /* 0 -> copy from page, 1 -> copy to page */
  DbPage *pDbPage           /* Page containing pPayload */
){
  if( eOp ){
    /* Copy data from buffer to page (a write operation) */
    int rc = sqlite3PagerWrite(pDbPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    memcpy(pPayload, pBuf, nByte);
  }else{
    /* Copy data from page to buffer (a read operation) */
    memcpy(pBuf, pPayload, nByte);
  }
  return SQLITE_OK;
}

/*
** This function is used to read or overwrite payload information
** for the entry that the pCur cursor is pointing to. The eOp
** argument is interpreted as follows:
**
**   0: The operation is a read. Populate the overflow cache.
**   1: The operation is a write. Populate the overflow cache.
**   2: The operation is a read. Do not populate the overflow cache.
**
** A total of "amt" bytes are read or written beginning at "offset".
** Data is read to or from the buffer pBuf.
**
** The content being read or written might appear on the main page
** or be scattered out on multiple overflow pages.
**
** If the current cursor entry uses one or more overflow pages and the
** eOp argument is not 2, this function may allocate space for and lazily 
** populates the overflow page-list cache array (BtCursor.aOverflow). 
** Subsequent calls use this cache to make seeking to the supplied offset 
** more efficient.
**
** Once an overflow page-list cache has been allocated, it may be
** invalidated if some other cursor writes to the same table, or if
** the cursor is moved to a different row. Additionally, in auto-vacuum
** mode, the following events may invalidate an overflow page-list cache.
**
**   * An incremental vacuum,
**   * A commit in auto_vacuum="full" mode,
**   * Creating a table (may require moving an overflow page).
*/
static int accessPayload(
  BtCursor *pCur,      /* Cursor pointing to entry to read from */
  u32 offset,          /* Begin reading this far into payload */
  u32 amt,             /* Read this many bytes */
  unsigned char *pBuf, /* Write the bytes into this buffer */ 
  int eOp              /* zero to read. non-zero to write. */
){
  unsigned char *aPayload;
  int rc = SQLITE_OK;
  int iIdx = 0;
  MemPage *pPage = pCur->apPage[pCur->iPage]; /* Btree page of current entry */
  BtShared *pBt = pCur->pBt;                  /* Btree this cursor belongs to */
#ifdef SQLITE_DIRECT_OVERFLOW_READ
  unsigned char * const pBufStart = pBuf;
  int bEnd;                                 /* True if reading to end of data */
#endif

  assert( pPage );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
  assert( cursorHoldsMutex(pCur) );
  assert( eOp!=2 || offset==0 );    /* Always start from beginning for eOp==2 */

  getCellInfo(pCur);
  aPayload = pCur->info.pPayload;
#ifdef SQLITE_DIRECT_OVERFLOW_READ
  bEnd = offset+amt==pCur->info.nPayload;
#endif
  assert( offset+amt <= pCur->info.nPayload );

  if( &aPayload[pCur->info.nLocal] > &pPage->aData[pBt->usableSize] ){
    /* Trying to read or write past the end of the data is an error */
    return SQLITE_CORRUPT_BKPT;
  }

  /* Check if data must be read/written to/from the btree page itself. */
  if( offset<pCur->info.nLocal ){
    int a = amt;
    if( a+offset>pCur->info.nLocal ){
      a = pCur->info.nLocal - offset;
    }
    rc = copyPayload(&aPayload[offset], pBuf, a, (eOp & 0x01), pPage->pDbPage);
    offset = 0;
    pBuf += a;
    amt -= a;
  }else{
    offset -= pCur->info.nLocal;
  }


  if( rc==SQLITE_OK && amt>0 ){
    const u32 ovflSize = pBt->usableSize - 4;  /* Bytes content per ovfl page */
    Pgno nextPage;

    nextPage = get4byte(&aPayload[pCur->info.nLocal]);

    /* If the BtCursor.aOverflow[] has not been allocated, allocate it now.
    ** Except, do not allocate aOverflow[] for eOp==2.
    **
    ** The aOverflow[] array is sized at one entry for each overflow page
    ** in the overflow chain. The page number of the first overflow page is
    ** stored in aOverflow[0], etc. A value of 0 in the aOverflow[] array
    ** means "not yet known" (the cache is lazily populated).
    */
    if( eOp!=2 && (pCur->curFlags & BTCF_ValidOvfl)==0 ){
      int nOvfl = (pCur->info.nPayload-pCur->info.nLocal+ovflSize-1)/ovflSize;
      if( nOvfl>pCur->nOvflAlloc ){
        Pgno *aNew = (Pgno*)sqlite3Realloc(
            pCur->aOverflow, nOvfl*2*sizeof(Pgno)
        );
        if( aNew==0 ){
          rc = SQLITE_NOMEM;
        }else{
          pCur->nOvflAlloc = nOvfl*2;
          pCur->aOverflow = aNew;
        }
      }
      if( rc==SQLITE_OK ){
        memset(pCur->aOverflow, 0, nOvfl*sizeof(Pgno));
        pCur->curFlags |= BTCF_ValidOvfl;
      }
    }

    /* If the overflow page-list cache has been allocated and the
    ** entry for the first required overflow page is valid, skip
    ** directly to it.
    */
    if( (pCur->curFlags & BTCF_ValidOvfl)!=0
     && pCur->aOverflow[offset/ovflSize]
    ){
      iIdx = (offset/ovflSize);
      nextPage = pCur->aOverflow[iIdx];
      offset = (offset%ovflSize);
    }

    for( ; rc==SQLITE_OK && amt>0 && nextPage; iIdx++){

      /* If required, populate the overflow page-list cache. */
      if( (pCur->curFlags & BTCF_ValidOvfl)!=0 ){
        assert(!pCur->aOverflow[iIdx] || pCur->aOverflow[iIdx]==nextPage);
        pCur->aOverflow[iIdx] = nextPage;
      }

      if( offset>=ovflSize ){
        /* The only reason to read this page is to obtain the page
        ** number for the next page in the overflow chain. The page
        ** data is not required. So first try to lookup the overflow
        ** page-list cache, if any, then fall back to the getOverflowPage()
        ** function.
        **
        ** Note that the aOverflow[] array must be allocated because eOp!=2
        ** here.  If eOp==2, then offset==0 and this branch is never taken.
        */
        assert( eOp!=2 );
        assert( pCur->curFlags & BTCF_ValidOvfl );
        assert( pCur->pBtree->db==pBt->db );
        if( pCur->aOverflow[iIdx+1] ){
          nextPage = pCur->aOverflow[iIdx+1];
        }else{
          rc = getOverflowPage(pBt, nextPage, 0, &nextPage);
        }
        offset -= ovflSize;
      }else{
        /* Need to read this page properly. It contains some of the
        ** range of data that is being read (eOp==0) or written (eOp!=0).
        */
#ifdef SQLITE_DIRECT_OVERFLOW_READ
        sqlite3_file *fd;
#endif
        int a = amt;
        if( a + offset > ovflSize ){
          a = ovflSize - offset;
        }

#ifdef SQLITE_DIRECT_OVERFLOW_READ
        /* If all the following are true:
        **
        **   1) this is a read operation, and 
        **   2) data is required from the start of this overflow page, and
        **   3) the database is file-backed, and
        **   4) there is no open write-transaction, and
        **   5) the database is not a WAL database,
        **   6) all data from the page is being read.
        **   7) at least 4 bytes have already been read into the output buffer 
        **
        ** then data can be read directly from the database file into the
        ** output buffer, bypassing the page-cache altogether. This speeds
        ** up loading large records that span many overflow pages.
        */
        if( (eOp&0x01)==0                                      /* (1) */
         && offset==0                                          /* (2) */
         && (bEnd || a==ovflSize)                              /* (6) */
         && pBt->inTransaction==TRANS_READ                     /* (4) */
         && (fd = sqlite3PagerFile(pBt->pPager))->pMethods     /* (3) */
         && pBt->pPage1->aData[19]==0x01                       /* (5) */
         && &pBuf[-4]>=pBufStart                               /* (7) */
        ){
          u8 aSave[4];
          u8 *aWrite = &pBuf[-4];
          assert( aWrite>=pBufStart );                         /* hence (7) */
          memcpy(aSave, aWrite, 4);
          rc = sqlite3OsRead(fd, aWrite, a+4, (i64)pBt->pageSize*(nextPage-1));
          nextPage = get4byte(aWrite);
          memcpy(aWrite, aSave, 4);
        }else
#endif

        {
          DbPage *pDbPage;
          rc = sqlite3PagerAcquire(pBt->pPager, nextPage, &pDbPage,
              ((eOp&0x01)==0 ? PAGER_GET_READONLY : 0)
          );
          if( rc==SQLITE_OK ){
            aPayload = sqlite3PagerGetData(pDbPage);
            nextPage = get4byte(aPayload);
            rc = copyPayload(&aPayload[offset+4], pBuf, a, (eOp&0x01), pDbPage);
            sqlite3PagerUnref(pDbPage);
            offset = 0;
          }
        }
        amt -= a;
        pBuf += a;
      }
    }
  }

  if( rc==SQLITE_OK && amt>0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  return rc;
}

/*
** Read part of the key associated with cursor pCur.  Exactly
** "amt" bytes will be transferred into pBuf[].  The transfer
** begins at "offset".
**
** The caller must ensure that pCur is pointing to a valid row
** in the table.
**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeKey(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage>=0 && pCur->apPage[pCur->iPage] );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  return accessPayload(pCur, offset, amt, (unsigned char*)pBuf, 0);
}

/*
** Read part of the data associated with cursor pCur.  Exactly
** "amt" bytes will be transfered into pBuf[].  The transfer
** begins at "offset".
**
** Return SQLITE_OK on success or an error code if anything goes
** wrong.  An error is returned if "offset+amt" is larger than
** the available payload.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeData(BtCursor *pCur, u32 offset, u32 amt, void *pBuf){
  int rc;

#ifndef SQLITE_OMIT_INCRBLOB
  if ( pCur->eState==CURSOR_INVALID ){
    return SQLITE_ABORT;
  }
#endif

  assert( cursorHoldsMutex(pCur) );
  rc = restoreCursorPosition(pCur);
  if( rc==SQLITE_OK ){
    assert( pCur->eState==CURSOR_VALID );
    assert( pCur->iPage>=0 && pCur->apPage[pCur->iPage] );
    assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
    rc = accessPayload(pCur, offset, amt, pBuf, 0);
  }
  return rc;
}

/*
** Return a pointer to payload information from the entry that the 
** pCur cursor is pointing to.  The pointer is to the beginning of
** the key if index btrees (pPage->intKey==0) and is the data for
** table btrees (pPage->intKey==1). The number of bytes of available
** key/data is written into *pAmt.  If *pAmt==0, then the value
** returned will not be a valid pointer.
**
** This routine is an optimization.  It is common for the entire key
** and data to fit on the local page and for there to be no overflow
** pages.  When that is so, this routine can be used to access the
** key and data without making a copy.  If the key and/or data spills
** onto overflow pages, then accessPayload() must be used to reassemble
** the key/data and copy it into a preallocated buffer.
**
** The pointer returned by this routine looks directly into the cached
** page of the database.  The data might change or move the next time
** any btree routine is called.
*/
static const void *fetchPayload(
  BtCursor *pCur,      /* Cursor pointing to entry to read from */
  u32 *pAmt            /* Write the number of available bytes here */
){
  u32 amt;
  assert( pCur!=0 && pCur->iPage>=0 && pCur->apPage[pCur->iPage]);
  assert( pCur->eState==CURSOR_VALID );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  assert( pCur->info.nSize>0 );
  assert( pCur->info.pPayload>pCur->apPage[pCur->iPage]->aData || CORRUPT_DB );
  assert( pCur->info.pPayload<pCur->apPage[pCur->iPage]->aDataEnd ||CORRUPT_DB);
  amt = (int)(pCur->apPage[pCur->iPage]->aDataEnd - pCur->info.pPayload);
  if( pCur->info.nLocal<amt ) amt = pCur->info.nLocal;
  *pAmt = amt;
  return (void*)pCur->info.pPayload;
}


/*
** For the entry that cursor pCur is point to, return as
** many bytes of the key or data as are available on the local
** b-tree page.  Write the number of available bytes into *pAmt.
**
** The pointer returned is ephemeral.  The key/data may move
** or be destroyed on the next call to any Btree routine,
** including calls from other threads against the same cache.
** Hence, a mutex on the BtShared should be held prior to calling
** this routine.
**
** These routines is used to get quick access to key and data
** in the common case where no overflow pages are used.
*/
SQLITE_API const void *SQLITE_STDCALL sqlite3BtreeKeyFetch(BtCursor *pCur, u32 *pAmt){
  return fetchPayload(pCur, pAmt);
}
SQLITE_API const void *SQLITE_STDCALL sqlite3BtreeDataFetch(BtCursor *pCur, u32 *pAmt){
  return fetchPayload(pCur, pAmt);
}


/*
** Move the cursor down to a new child page.  The newPgno argument is the
** page number of the child page to move to.
**
** This function returns SQLITE_CORRUPT if the page-header flags field of
** the new child page does not match the flags field of the parent (i.e.
** if an intkey page appears to be the parent of a non-intkey page, or
** vice-versa).
*/
static int moveToChild(BtCursor *pCur, u32 newPgno){
  BtShared *pBt = pCur->pBt;

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage<BTCURSOR_MAX_DEPTH );
  assert( pCur->iPage>=0 );
  if( pCur->iPage>=(BTCURSOR_MAX_DEPTH-1) ){
    return SQLITE_CORRUPT_BKPT;
  }
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  pCur->iPage++;
  pCur->aiIdx[pCur->iPage] = 0;
  return getAndInitPage(pBt, newPgno, &pCur->apPage[pCur->iPage],
                        pCur, pCur->curPagerFlags);
}

#if SQLITE_DEBUG
/*
** Page pParent is an internal (non-leaf) tree page. This function 
** asserts that page number iChild is the left-child if the iIdx'th
** cell in page pParent. Or, if iIdx is equal to the total number of
** cells in pParent, that page number iChild is the right-child of
** the page.
*/
static void assertParentIndex(MemPage *pParent, int iIdx, Pgno iChild){
  if( CORRUPT_DB ) return;  /* The conditions tested below might not be true
                            ** in a corrupt database */
  assert( iIdx<=pParent->nCell );
  if( iIdx==pParent->nCell ){
    assert( get4byte(&pParent->aData[pParent->hdrOffset+8])==iChild );
  }else{
    assert( get4byte(findCell(pParent, iIdx))==iChild );
  }
}
#else
#  define assertParentIndex(x,y,z) 
#endif

/*
** Move the cursor up to the parent page.
**
** pCur->idx is set to the cell index that contains the pointer
** to the page we are coming from.  If we are coming from the
** right-most child page then pCur->idx is set to one more than
** the largest cell index.
*/
static void moveToParent(BtCursor *pCur){
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  assert( pCur->iPage>0 );
  assert( pCur->apPage[pCur->iPage] );
  assertParentIndex(
    pCur->apPage[pCur->iPage-1], 
    pCur->aiIdx[pCur->iPage-1], 
    pCur->apPage[pCur->iPage]->pgno
  );
  testcase( pCur->aiIdx[pCur->iPage-1] > pCur->apPage[pCur->iPage-1]->nCell );
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  releasePageNotNull(pCur->apPage[pCur->iPage--]);
}

/*
** Move the cursor to point to the root page of its b-tree structure.
**
** If the table has a virtual root page, then the cursor is moved to point
** to the virtual root page instead of the actual root page. A table has a
** virtual root page when the actual root page contains no cells and a 
** single child page. This can only happen with the table rooted at page 1.
**
** If the b-tree structure is empty, the cursor state is set to 
** CURSOR_INVALID. Otherwise, the cursor is set to point to the first
** cell located on the root (or virtual root) page and the cursor state
** is set to CURSOR_VALID.
**
** If this function returns successfully, it may be assumed that the
** page-header flags indicate that the [virtual] root-page is the expected 
** kind of b-tree page (i.e. if when opening the cursor the caller did not
** specify a KeyInfo structure the flags byte is set to 0x05 or 0x0D,
** indicating a table b-tree, or if the caller did specify a KeyInfo 
** structure the flags byte is set to 0x02 or 0x0A, indicating an index
** b-tree).
*/
static int moveToRoot(BtCursor *pCur){
  MemPage *pRoot;
  int rc = SQLITE_OK;

  assert( cursorHoldsMutex(pCur) );
  assert( CURSOR_INVALID < CURSOR_REQUIRESEEK );
  assert( CURSOR_VALID   < CURSOR_REQUIRESEEK );
  assert( CURSOR_FAULT   > CURSOR_REQUIRESEEK );
  if( pCur->eState>=CURSOR_REQUIRESEEK ){
    if( pCur->eState==CURSOR_FAULT ){
      assert( pCur->skipNext!=SQLITE_OK );
      return pCur->skipNext;
    }
    sqlite3BtreeClearCursor(pCur);
  }

  if( pCur->iPage>=0 ){
    while( pCur->iPage ){
      assert( pCur->apPage[pCur->iPage]!=0 );
      releasePageNotNull(pCur->apPage[pCur->iPage--]);
    }
  }else if( pCur->pgnoRoot==0 ){
    pCur->eState = CURSOR_INVALID;
    return SQLITE_OK;
  }else{
    assert( pCur->iPage==(-1) );
    rc = getAndInitPage(pCur->pBtree->pBt, pCur->pgnoRoot, &pCur->apPage[0],
                        0, pCur->curPagerFlags);
    if( rc!=SQLITE_OK ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    pCur->iPage = 0;
    pCur->curIntKey = pCur->apPage[0]->intKey;
  }
  pRoot = pCur->apPage[0];
  assert( pRoot->pgno==pCur->pgnoRoot );

  /* If pCur->pKeyInfo is not NULL, then the caller that opened this cursor
  ** expected to open it on an index b-tree. Otherwise, if pKeyInfo is
  ** NULL, the caller expects a table b-tree. If this is not the case,
  ** return an SQLITE_CORRUPT error. 
  **
  ** Earlier versions of SQLite assumed that this test could not fail
  ** if the root page was already loaded when this function was called (i.e.
  ** if pCur->iPage>=0). But this is not so if the database is corrupted 
  ** in such a way that page pRoot is linked into a second b-tree table 
  ** (or the freelist).  */
  assert( pRoot->intKey==1 || pRoot->intKey==0 );
  if( pRoot->isInit==0 || (pCur->pKeyInfo==0)!=pRoot->intKey ){
    return SQLITE_CORRUPT_BKPT;
  }

  pCur->aiIdx[0] = 0;
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidNKey|BTCF_ValidOvfl);

  if( pRoot->nCell>0 ){
    pCur->eState = CURSOR_VALID;
  }else if( !pRoot->leaf ){
    Pgno subpage;
    if( pRoot->pgno!=1 ) return SQLITE_CORRUPT_BKPT;
    subpage = get4byte(&pRoot->aData[pRoot->hdrOffset+8]);
    pCur->eState = CURSOR_VALID;
    rc = moveToChild(pCur, subpage);
  }else{
    pCur->eState = CURSOR_INVALID;
  }
  return rc;
}

/*
** Move the cursor down to the left-most leaf entry beneath the
** entry to which it is currently pointing.
**
** The left-most leaf is the one with the smallest key - the first
** in ascending order.
*/
static int moveToLeftmost(BtCursor *pCur){
  Pgno pgno;
  int rc = SQLITE_OK;
  MemPage *pPage;

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  while( rc==SQLITE_OK && !(pPage = pCur->apPage[pCur->iPage])->leaf ){
    assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
    pgno = get4byte(findCell(pPage, pCur->aiIdx[pCur->iPage]));
    rc = moveToChild(pCur, pgno);
  }
  return rc;
}

/*
** Move the cursor down to the right-most leaf entry beneath the
** page to which it is currently pointing.  Notice the difference
** between moveToLeftmost() and moveToRightmost().  moveToLeftmost()
** finds the left-most entry beneath the *entry* whereas moveToRightmost()
** finds the right-most entry beneath the *page*.
**
** The right-most entry is the one with the largest key - the last
** key in ascending order.
*/
static int moveToRightmost(BtCursor *pCur){
  Pgno pgno;
  int rc = SQLITE_OK;
  MemPage *pPage = 0;

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState==CURSOR_VALID );
  while( !(pPage = pCur->apPage[pCur->iPage])->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    pCur->aiIdx[pCur->iPage] = pPage->nCell;
    rc = moveToChild(pCur, pgno);
    if( rc ) return rc;
  }
  pCur->aiIdx[pCur->iPage] = pPage->nCell-1;
  assert( pCur->info.nSize==0 );
  assert( (pCur->curFlags & BTCF_ValidNKey)==0 );
  return SQLITE_OK;
}

/* Move the cursor to the first entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeFirst(BtCursor *pCur, int *pRes){
  int rc;

  assert( cursorHoldsMutex(pCur) );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  rc = moveToRoot(pCur);
  if( rc==SQLITE_OK ){
    if( pCur->eState==CURSOR_INVALID ){
      assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
      *pRes = 1;
    }else{
      assert( pCur->apPage[pCur->iPage]->nCell>0 );
      *pRes = 0;
      rc = moveToLeftmost(pCur);
    }
  }
  return rc;
}

/* Move the cursor to the last entry in the table.  Return SQLITE_OK
** on success.  Set *pRes to 0 if the cursor actually points to something
** or set *pRes to 1 if the table is empty.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeLast(BtCursor *pCur, int *pRes){
  int rc;
 
  assert( cursorHoldsMutex(pCur) );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );

  /* If the cursor already points to the last entry, this is a no-op. */
  if( CURSOR_VALID==pCur->eState && (pCur->curFlags & BTCF_AtLast)!=0 ){
#ifdef SQLITE_DEBUG
    /* This block serves to assert() that the cursor really does point 
    ** to the last entry in the b-tree. */
    int ii;
    for(ii=0; ii<pCur->iPage; ii++){
      assert( pCur->aiIdx[ii]==pCur->apPage[ii]->nCell );
    }
    assert( pCur->aiIdx[pCur->iPage]==pCur->apPage[pCur->iPage]->nCell-1 );
    assert( pCur->apPage[pCur->iPage]->leaf );
#endif
    return SQLITE_OK;
  }

  rc = moveToRoot(pCur);
  if( rc==SQLITE_OK ){
    if( CURSOR_INVALID==pCur->eState ){
      assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
      *pRes = 1;
    }else{
      assert( pCur->eState==CURSOR_VALID );
      *pRes = 0;
      rc = moveToRightmost(pCur);
      if( rc==SQLITE_OK ){
        pCur->curFlags |= BTCF_AtLast;
      }else{
        pCur->curFlags &= ~BTCF_AtLast;
      }
   
    }
  }
  return rc;
}

SQLITE_API void SQLITE_STDCALL sqlite3BtreeInitUnpackedRecord(
  UnpackedRecord *pUnKey,
  BtCursor* pCur,
  int nField,
  int default_rc,
  Mem* pMem)
{
	pUnKey->pKeyInfo = pCur->pKeyInfo;
	pUnKey->nField = nField;
	pUnKey->default_rc = default_rc;
	pUnKey->aMem = pMem;
}

/* Move the cursor so that it points to an entry near the key 
** specified by pIdxKey or intKey.   Return a success code.
**
** For INTKEY tables, the intKey parameter is used.  pIdxKey 
** must be NULL.  For index tables, pIdxKey is used and intKey
** is ignored.
**
** If an exact match is not found, then the cursor is always
** left pointing at a leaf page which would hold the entry if it
** were present.  The cursor might point to an entry that comes
** before or after the key.
**
** An integer is written into *pRes which is the result of
** comparing the key with the entry to which the cursor is 
** pointing.  The meaning of the integer written into
** *pRes is as follows:
**
**     *pRes<0      The cursor is left pointing at an entry that
**                  is smaller than intKey/pIdxKey or if the table is empty
**                  and the cursor is therefore left point to nothing.
**
**     *pRes==0     The cursor is left pointing at an entry that
**                  exactly matches intKey/pIdxKey.
**
**     *pRes>0      The cursor is left pointing at an entry that
**                  is larger than intKey/pIdxKey.
**
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeMovetoUnpacked(
  BtCursor *pCur,          /* The cursor to be moved */
  UnpackedRecord *pIdxKey, /* Unpacked index key */
  i64 intKey,              /* The table key */
  int biasRight,           /* If true, bias the search to the high end */
  int *pRes                /* Write search results here */
){
  int rc;
  RecordCompare xRecordCompare;

  assert( cursorHoldsMutex(pCur) );
  assert( sqlite3_mutex_held(pCur->pBtree->db->mutex) );
  assert( pRes );
  assert( (pIdxKey==0)==(pCur->pKeyInfo==0) );

  /* If the cursor is already positioned at the point we are trying
  ** to move to, then just return without doing any work */
  if( pCur->eState==CURSOR_VALID && (pCur->curFlags & BTCF_ValidNKey)!=0
   && pCur->curIntKey 
  ){
    if( pCur->info.nKey==intKey ){
      *pRes = 0;
      return SQLITE_OK;
    }
    if( (pCur->curFlags & BTCF_AtLast)!=0 && pCur->info.nKey<intKey ){
      *pRes = -1;
      return SQLITE_OK;
    }
  }

  if( pIdxKey ){
    xRecordCompare = sqlite3VdbeFindCompare(pIdxKey);
    pIdxKey->errCode = 0;
    assert( pIdxKey->default_rc==1 
         || pIdxKey->default_rc==0 
         || pIdxKey->default_rc==-1
    );
  }else{
    xRecordCompare = 0; /* All keys are integers */
  }

  rc = moveToRoot(pCur);
  if( rc ){
    return rc;
  }
  assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage] );
  assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->isInit );
  assert( pCur->eState==CURSOR_INVALID || pCur->apPage[pCur->iPage]->nCell>0 );
  if( pCur->eState==CURSOR_INVALID ){
    *pRes = -1;
    assert( pCur->pgnoRoot==0 || pCur->apPage[pCur->iPage]->nCell==0 );
    return SQLITE_OK;
  }
  assert( pCur->apPage[0]->intKey==pCur->curIntKey );
  assert( pCur->curIntKey || pIdxKey );
  for(;;){
    int lwr, upr, idx, c;
    Pgno chldPg;
    MemPage *pPage = pCur->apPage[pCur->iPage];
    u8 *pCell;                          /* Pointer to current cell in pPage */

    /* pPage->nCell must be greater than zero. If this is the root-page
    ** the cursor would have been INVALID above and this for(;;) loop
    ** not run. If this is not the root-page, then the moveToChild() routine
    ** would have already detected db corruption. Similarly, pPage must
    ** be the right kind (index or table) of b-tree page. Otherwise
    ** a moveToChild() or moveToRoot() call would have detected corruption.  */
    assert( pPage->nCell>0 );
    assert( pPage->intKey==(pIdxKey==0) );
    lwr = 0;
    upr = pPage->nCell-1;
    assert( biasRight==0 || biasRight==1 );
    idx = upr>>(1-biasRight); /* idx = biasRight ? upr : (lwr+upr)/2; */
    pCur->aiIdx[pCur->iPage] = (u16)idx;
    if( xRecordCompare==0 ){
      for(;;){
        i64 nCellKey;
        pCell = findCellPastPtr(pPage, idx);
        if( pPage->intKeyLeaf ){
          while( 0x80 <= *(pCell++) ){
            if( pCell>=pPage->aDataEnd ) return SQLITE_CORRUPT_BKPT;
          }
        }
        getVarint(pCell, (u64*)&nCellKey);
        if( nCellKey<intKey ){
          lwr = idx+1;
          if( lwr>upr ){ c = -1; break; }
        }else if( nCellKey>intKey ){
          upr = idx-1;
          if( lwr>upr ){ c = +1; break; }
        }else{
          assert( nCellKey==intKey );
          pCur->curFlags |= BTCF_ValidNKey;
          pCur->info.nKey = nCellKey;
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          if( !pPage->leaf ){
            lwr = idx;
            goto moveto_next_layer;
          }else{
            *pRes = 0;
            rc = SQLITE_OK;
            goto moveto_finish;
          }
        }
        assert( lwr+upr>=0 );
        idx = (lwr+upr)>>1;  /* idx = (lwr+upr)/2; */
      }
    }else{
      for(;;){
        int nCell;  /* Size of the pCell cell in bytes */
        pCell = findCellPastPtr(pPage, idx);

        /* The maximum supported page-size is 65536 bytes. This means that
        ** the maximum number of record bytes stored on an index B-Tree
        ** page is less than 16384 bytes and may be stored as a 2-byte
        ** varint. This information is used to attempt to avoid parsing 
        ** the entire cell by checking for the cases where the record is 
        ** stored entirely within the b-tree page by inspecting the first 
        ** 2 bytes of the cell.
        */
        nCell = pCell[0];
        if( nCell<=pPage->max1bytePayload ){
          /* This branch runs if the record-size field of the cell is a
          ** single byte varint and the record fits entirely on the main
          ** b-tree page.  */
          testcase( pCell+nCell+1==pPage->aDataEnd );
          c = xRecordCompare(nCell, (void*)&pCell[1], pIdxKey);
        }else if( !(pCell[1] & 0x80) 
          && (nCell = ((nCell&0x7f)<<7) + pCell[1])<=pPage->maxLocal
        ){
          /* The record-size field is a 2 byte varint and the record 
          ** fits entirely on the main b-tree page.  */
          testcase( pCell+nCell+2==pPage->aDataEnd );
          c = xRecordCompare(nCell, (void*)&pCell[2], pIdxKey);
        }else{
          /* The record flows over onto one or more overflow pages. In
          ** this case the whole cell needs to be parsed, a buffer allocated
          ** and accessPayload() used to retrieve the record into the
          ** buffer before VdbeRecordCompare() can be called. 
          **
          ** If the record is corrupt, the xRecordCompare routine may read
          ** up to two varints past the end of the buffer. An extra 18 
          ** bytes of padding is allocated at the end of the buffer in
          ** case this happens.  */
          void *pCellKey;
          u8 * const pCellBody = pCell - pPage->childPtrSize;
          pPage->xParseCell(pPage, pCellBody, &pCur->info);
          nCell = (int)pCur->info.nKey;
          testcase( nCell<0 );   /* True if key size is 2^32 or more */
          testcase( nCell==0 );  /* Invalid key size:  0x80 0x80 0x00 */
          testcase( nCell==1 );  /* Invalid key size:  0x80 0x80 0x01 */
          testcase( nCell==2 );  /* Minimum legal index key size */
          if( nCell<2 ){
            rc = SQLITE_CORRUPT_BKPT;
            goto moveto_finish;
          }
          pCellKey = sqlite3Malloc( nCell+18 );
          if( pCellKey==0 ){
            rc = SQLITE_NOMEM;
            goto moveto_finish;
          }
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          rc = accessPayload(pCur, 0, nCell, (unsigned char*)pCellKey, 2);
          if( rc ){
            sqlite3_free(pCellKey);
            goto moveto_finish;
          }
          c = xRecordCompare(nCell, pCellKey, pIdxKey);
          sqlite3_free(pCellKey);
        }
        assert( 
            (pIdxKey->errCode!=SQLITE_CORRUPT || c==0)
         && (pIdxKey->errCode!=SQLITE_NOMEM || pCur->pBtree->mallocFailed)
        );
        if( c<0 ){
          lwr = idx+1;
        }else if( c>0 ){
          upr = idx-1;
        }else{
          assert( c==0 );
          *pRes = 0;
          rc = SQLITE_OK;
          pCur->aiIdx[pCur->iPage] = (u16)idx;
          if( pIdxKey->errCode ) rc = SQLITE_CORRUPT;
          goto moveto_finish;
        }
        if( lwr>upr ) break;
        assert( lwr+upr>=0 );
        idx = (lwr+upr)>>1;  /* idx = (lwr+upr)/2 */
      }
    }
    assert( lwr==upr+1 || (pPage->intKey && !pPage->leaf) );
    assert( pPage->isInit );
    if( pPage->leaf ){
      assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
      pCur->aiIdx[pCur->iPage] = (u16)idx;
      *pRes = c;
      rc = SQLITE_OK;
      goto moveto_finish;
    }
moveto_next_layer:
    if( lwr>=pPage->nCell ){
      chldPg = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    }else{
      chldPg = get4byte(findCell(pPage, lwr));
    }
    pCur->aiIdx[pCur->iPage] = (u16)lwr;
    rc = moveToChild(pCur, chldPg);
    if( rc ) break;
  }
moveto_finish:
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  return rc;
}


/*
** Return TRUE if the cursor is not pointing at an entry of the table.
**
** TRUE will be returned after a call to sqlite3BtreeNext() moves
** past the last entry in the table or sqlite3BtreePrev() moves past
** the first entry.  TRUE is also returned if the table is empty.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeEof(BtCursor *pCur){
  /* TODO: What if the cursor is in CURSOR_REQUIRESEEK but all table entries
  ** have been deleted? This API will need to change to return an error code
  ** as well as the boolean result value.
  */
  return (CURSOR_VALID!=pCur->eState);
}

/*
** Advance the cursor to the next entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the last entry in the database before
** this routine was called, then set *pRes=1.
**
** The main entry point is sqlite3BtreeNext().  That routine is optimized
** for the common case of merely incrementing the cell counter BtCursor.aiIdx
** to the next cell on the current page.  The (slower) btreeNext() helper
** routine is called when it is necessary to move to a different page or
** to restore the cursor.
**
** The calling function will set *pRes to 0 or 1.  The initial *pRes value
** will be 1 if the cursor being stepped corresponds to an SQL index and
** if this routine could have been skipped if that SQL index had been
** a unique index.  Otherwise the caller will have set *pRes to zero.
** Zero is the common case. The btree implementation is free to use the
** initial *pRes value as a hint to improve performance, but the current
** SQLite btree implementation does not. (Note that the comdb2 btree
** implementation does use this hint, however.)
*/
static SQLITE_NOINLINE int btreeNext(BtCursor *pCur, int *pRes){
  int rc;
  int idx;
  MemPage *pPage;

  assert( cursorHoldsMutex(pCur) );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  assert( *pRes==0 );
  if( pCur->eState!=CURSOR_VALID ){
    assert( (pCur->curFlags & BTCF_ValidOvfl)==0 );
    rc = restoreCursorPosition(pCur);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    if( CURSOR_INVALID==pCur->eState ){
      *pRes = 1;
      return SQLITE_OK;
    }
    if( pCur->skipNext ){
      assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_SKIPNEXT );
      pCur->eState = CURSOR_VALID;
      if( pCur->skipNext>0 ){
        pCur->skipNext = 0;
        return SQLITE_OK;
      }
      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  idx = ++pCur->aiIdx[pCur->iPage];
  assert( pPage->isInit );

  /* If the database file is corrupt, it is possible for the value of idx 
  ** to be invalid here. This can only occur if a second cursor modifies
  ** the page while cursor pCur is holding a reference to it. Which can
  ** only happen if the database is corrupt in such a way as to link the
  ** page into more than one b-tree structure. */
  testcase( idx>pPage->nCell );

  if( idx>=pPage->nCell ){
    if( !pPage->leaf ){
      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
      if( rc ) return rc;
      return moveToLeftmost(pCur);
    }
    do{
      if( pCur->iPage==0 ){
        *pRes = 1;
        pCur->eState = CURSOR_INVALID;
        return SQLITE_OK;
      }
      moveToParent(pCur);
      pPage = pCur->apPage[pCur->iPage];
    }while( pCur->aiIdx[pCur->iPage]>=pPage->nCell );
    if( pPage->intKey ){
      return sqlite3BtreeNext(pCur, pRes);
    }else{
      return SQLITE_OK;
    }
  }
  if( pPage->leaf ){
    return SQLITE_OK;
  }else{
    return moveToLeftmost(pCur);
  }
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreeNext(BtCursor *pCur, int *pRes){
  MemPage *pPage;
  assert( cursorHoldsMutex(pCur) );
  assert( pRes!=0 );
  assert( *pRes==0 || *pRes==1 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  pCur->info.nSize = 0;
  pCur->curFlags &= ~(BTCF_ValidNKey|BTCF_ValidOvfl);
  *pRes = 0;
  if( pCur->eState!=CURSOR_VALID ) return btreeNext(pCur, pRes);
  pPage = pCur->apPage[pCur->iPage];
  if( (++pCur->aiIdx[pCur->iPage])>=pPage->nCell ){
    pCur->aiIdx[pCur->iPage]--;
    return btreeNext(pCur, pRes);
  }
  if( pPage->leaf ){
    return SQLITE_OK;
  }else{
    return moveToLeftmost(pCur);
  }
}

/*
** Step the cursor to the back to the previous entry in the database.  If
** successful then set *pRes=0.  If the cursor
** was already pointing to the first entry in the database before
** this routine was called, then set *pRes=1.
**
** The main entry point is sqlite3BtreePrevious().  That routine is optimized
** for the common case of merely decrementing the cell counter BtCursor.aiIdx
** to the previous cell on the current page.  The (slower) btreePrevious()
** helper routine is called when it is necessary to move to a different page
** or to restore the cursor.
**
** The calling function will set *pRes to 0 or 1.  The initial *pRes value
** will be 1 if the cursor being stepped corresponds to an SQL index and
** if this routine could have been skipped if that SQL index had been
** a unique index.  Otherwise the caller will have set *pRes to zero.
** Zero is the common case. The btree implementation is free to use the
** initial *pRes value as a hint to improve performance, but the current
** SQLite btree implementation does not. (Note that the comdb2 btree
** implementation does use this hint, however.)
*/
static SQLITE_NOINLINE int btreePrevious(BtCursor *pCur, int *pRes){
  int rc;
  MemPage *pPage;

  assert( cursorHoldsMutex(pCur) );
  assert( pRes!=0 );
  assert( *pRes==0 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  assert( (pCur->curFlags & (BTCF_AtLast|BTCF_ValidOvfl|BTCF_ValidNKey))==0 );
  assert( pCur->info.nSize==0 );
  if( pCur->eState!=CURSOR_VALID ){
    rc = restoreCursorPosition(pCur);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    if( CURSOR_INVALID==pCur->eState ){
      *pRes = 1;
      return SQLITE_OK;
    }
    if( pCur->skipNext ){
      assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_SKIPNEXT );
      pCur->eState = CURSOR_VALID;
      if( pCur->skipNext<0 ){
        pCur->skipNext = 0;
        return SQLITE_OK;
      }
      pCur->skipNext = 0;
    }
  }

  pPage = pCur->apPage[pCur->iPage];
  assert( pPage->isInit );
  if( !pPage->leaf ){
    int idx = pCur->aiIdx[pCur->iPage];
    rc = moveToChild(pCur, get4byte(findCell(pPage, idx)));
    if( rc ) return rc;
    rc = moveToRightmost(pCur);
  }else{
    while( pCur->aiIdx[pCur->iPage]==0 ){
      if( pCur->iPage==0 ){
        pCur->eState = CURSOR_INVALID;
        *pRes = 1;
        return SQLITE_OK;
      }
      moveToParent(pCur);
    }
    assert( pCur->info.nSize==0 );
    assert( (pCur->curFlags & (BTCF_ValidNKey|BTCF_ValidOvfl))==0 );

    pCur->aiIdx[pCur->iPage]--;
    pPage = pCur->apPage[pCur->iPage];
    if( pPage->intKey && !pPage->leaf ){
      rc = sqlite3BtreePrevious(pCur, pRes);
    }else{
      rc = SQLITE_OK;
    }
  }
  return rc;
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreePrevious(BtCursor *pCur, int *pRes){
  assert( cursorHoldsMutex(pCur) );
  assert( pRes!=0 );
  assert( *pRes==0 || *pRes==1 );
  assert( pCur->skipNext==0 || pCur->eState!=CURSOR_VALID );
  *pRes = 0;
  pCur->curFlags &= ~(BTCF_AtLast|BTCF_ValidOvfl|BTCF_ValidNKey);
  pCur->info.nSize = 0;
  if( pCur->eState!=CURSOR_VALID
   || pCur->aiIdx[pCur->iPage]==0
   || pCur->apPage[pCur->iPage]->leaf==0
  ){
    return btreePrevious(pCur, pRes);
  }
  pCur->aiIdx[pCur->iPage]--;
  return SQLITE_OK;
}

/*
** Allocate a new page from the database file.
**
** The new page is marked as dirty.  (In other words, sqlite3PagerWrite()
** has already been called on the new page.)  The new page has also
** been referenced and the calling routine is responsible for calling
** sqlite3PagerUnref() on the new page when it is done.
**
** SQLITE_OK is returned on success.  Any other return value indicates
** an error.  *ppPage is set to NULL in the event of an error.
**
** If the "nearby" parameter is not 0, then an effort is made to 
** locate a page close to the page number "nearby".  This can be used in an
** attempt to keep related pages close to each other in the database file,
** which in turn can make database access faster.
**
** If the eMode parameter is BTALLOC_EXACT and the nearby page exists
** anywhere on the free-list, then it is guaranteed to be returned.  If
** eMode is BTALLOC_LT then the page returned will be less than or equal
** to nearby if any such page exists.  If eMode is BTALLOC_ANY then there
** are no restrictions on which page is returned.
*/
static int allocateBtreePage(
  BtShared *pBt,         /* The btree */
  MemPage **ppPage,      /* Store pointer to the allocated page here */
  Pgno *pPgno,           /* Store the page number here */
  Pgno nearby,           /* Search for a page near this one */
  u8 eMode               /* BTALLOC_EXACT, BTALLOC_LT, or BTALLOC_ANY */
){
  MemPage *pPage1;
  int rc;
  u32 n;     /* Number of pages on the freelist */
  u32 k;     /* Number of leaves on the trunk of the freelist */
  MemPage *pTrunk = 0;
  MemPage *pPrevTrunk = 0;
  Pgno mxPage;     /* Total size of the database file */

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( eMode==BTALLOC_ANY || (nearby>0 && IfNotOmitAV(pBt->autoVacuum)) );
  pPage1 = pBt->pPage1;
  mxPage = btreePagecount(pBt);
  /* EVIDENCE-OF: R-05119-02637 The 4-byte big-endian integer at offset 36
  ** stores stores the total number of pages on the freelist. */
  n = get4byte(&pPage1->aData[36]);
  testcase( n==mxPage-1 );
  if( n>=mxPage ){
    return SQLITE_CORRUPT_BKPT;
  }
  if( n>0 ){
    /* There are pages on the freelist.  Reuse one of those pages. */
    Pgno iTrunk;
    u8 searchList = 0; /* If the free-list must be searched for 'nearby' */
    u32 nSearch = 0;   /* Count of the number of search attempts */
    
    /* If eMode==BTALLOC_EXACT and a query of the pointer-map
    ** shows that the page 'nearby' is somewhere on the free-list, then
    ** the entire-list will be searched for that page.
    */
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( eMode==BTALLOC_EXACT ){
      if( nearby<=mxPage ){
        u8 eType;
        assert( nearby>0 );
        assert( pBt->autoVacuum );
        rc = ptrmapGet(pBt, nearby, &eType, 0);
        if( rc ) return rc;
        if( eType==PTRMAP_FREEPAGE ){
          searchList = 1;
        }
      }
    }else if( eMode==BTALLOC_LE ){
      searchList = 1;
    }
#endif

    /* Decrement the free-list count by 1. Set iTrunk to the index of the
    ** first free-list trunk page. iPrevTrunk is initially 1.
    */
    rc = sqlite3PagerWrite(pPage1->pDbPage);
    if( rc ) return rc;
    put4byte(&pPage1->aData[36], n-1);

    /* The code within this loop is run only once if the 'searchList' variable
    ** is not true. Otherwise, it runs once for each trunk-page on the
    ** free-list until the page 'nearby' is located (eMode==BTALLOC_EXACT)
    ** or until a page less than 'nearby' is located (eMode==BTALLOC_LT)
    */
    do {
      pPrevTrunk = pTrunk;
      if( pPrevTrunk ){
        /* EVIDENCE-OF: R-01506-11053 The first integer on a freelist trunk page
        ** is the page number of the next freelist trunk page in the list or
        ** zero if this is the last freelist trunk page. */
        iTrunk = get4byte(&pPrevTrunk->aData[0]);
      }else{
        /* EVIDENCE-OF: R-59841-13798 The 4-byte big-endian integer at offset 32
        ** stores the page number of the first page of the freelist, or zero if
        ** the freelist is empty. */
        iTrunk = get4byte(&pPage1->aData[32]);
      }
      testcase( iTrunk==mxPage );
      if( iTrunk>mxPage || nSearch++ > n ){
        rc = SQLITE_CORRUPT_BKPT;
      }else{
        rc = btreeGetUnusedPage(pBt, iTrunk, &pTrunk, 0);
      }
      if( rc ){
        pTrunk = 0;
        goto end_allocate_page;
      }
      assert( pTrunk!=0 );
      assert( pTrunk->aData!=0 );
      /* EVIDENCE-OF: R-13523-04394 The second integer on a freelist trunk page
      ** is the number of leaf page pointers to follow. */
      k = get4byte(&pTrunk->aData[4]);
      if( k==0 && !searchList ){
        /* The trunk has no leaves and the list is not being searched. 
        ** So extract the trunk page itself and use it as the newly 
        ** allocated page */
        assert( pPrevTrunk==0 );
        rc = sqlite3PagerWrite(pTrunk->pDbPage);
        if( rc ){
          goto end_allocate_page;
        }
        *pPgno = iTrunk;
        memcpy(&pPage1->aData[32], &pTrunk->aData[0], 4);
        *ppPage = pTrunk;
        pTrunk = 0;
        TRACE(("ALLOCATE: %d trunk - %d free pages left\n", *pPgno, n-1));
      }else if( k>(u32)(pBt->usableSize/4 - 2) ){
        /* Value of k is out of range.  Database corruption */
        rc = SQLITE_CORRUPT_BKPT;
        goto end_allocate_page;
#ifndef SQLITE_OMIT_AUTOVACUUM
      }else if( searchList 
            && (nearby==iTrunk || (iTrunk<nearby && eMode==BTALLOC_LE)) 
      ){
        /* The list is being searched and this trunk page is the page
        ** to allocate, regardless of whether it has leaves.
        */
        *pPgno = iTrunk;
        *ppPage = pTrunk;
        searchList = 0;
        rc = sqlite3PagerWrite(pTrunk->pDbPage);
        if( rc ){
          goto end_allocate_page;
        }
        if( k==0 ){
          if( !pPrevTrunk ){
            memcpy(&pPage1->aData[32], &pTrunk->aData[0], 4);
          }else{
            rc = sqlite3PagerWrite(pPrevTrunk->pDbPage);
            if( rc!=SQLITE_OK ){
              goto end_allocate_page;
            }
            memcpy(&pPrevTrunk->aData[0], &pTrunk->aData[0], 4);
          }
        }else{
          /* The trunk page is required by the caller but it contains 
          ** pointers to free-list leaves. The first leaf becomes a trunk
          ** page in this case.
          */
          MemPage *pNewTrunk;
          Pgno iNewTrunk = get4byte(&pTrunk->aData[8]);
          if( iNewTrunk>mxPage ){ 
            rc = SQLITE_CORRUPT_BKPT;
            goto end_allocate_page;
          }
          testcase( iNewTrunk==mxPage );
          rc = btreeGetUnusedPage(pBt, iNewTrunk, &pNewTrunk, 0);
          if( rc!=SQLITE_OK ){
            goto end_allocate_page;
          }
          rc = sqlite3PagerWrite(pNewTrunk->pDbPage);
          if( rc!=SQLITE_OK ){
            releasePage(pNewTrunk);
            goto end_allocate_page;
          }
          memcpy(&pNewTrunk->aData[0], &pTrunk->aData[0], 4);
          put4byte(&pNewTrunk->aData[4], k-1);
          memcpy(&pNewTrunk->aData[8], &pTrunk->aData[12], (k-1)*4);
          releasePage(pNewTrunk);
          if( !pPrevTrunk ){
            assert( sqlite3PagerIswriteable(pPage1->pDbPage) );
            put4byte(&pPage1->aData[32], iNewTrunk);
          }else{
            rc = sqlite3PagerWrite(pPrevTrunk->pDbPage);
            if( rc ){
              goto end_allocate_page;
            }
            put4byte(&pPrevTrunk->aData[0], iNewTrunk);
          }
        }
        pTrunk = 0;
        TRACE(("ALLOCATE: %d trunk - %d free pages left\n", *pPgno, n-1));
#endif
      }else if( k>0 ){
        /* Extract a leaf from the trunk */
        u32 closest;
        Pgno iPage;
        unsigned char *aData = pTrunk->aData;
        if( nearby>0 ){
          u32 i;
          closest = 0;
          if( eMode==BTALLOC_LE ){
            for(i=0; i<k; i++){
              iPage = get4byte(&aData[8+i*4]);
              if( iPage<=nearby ){
                closest = i;
                break;
              }
            }
          }else{
            int dist;
            dist = sqlite3AbsInt32(get4byte(&aData[8]) - nearby);
            for(i=1; i<k; i++){
              int d2 = sqlite3AbsInt32(get4byte(&aData[8+i*4]) - nearby);
              if( d2<dist ){
                closest = i;
                dist = d2;
              }
            }
          }
        }else{
          closest = 0;
        }

        iPage = get4byte(&aData[8+closest*4]);
        testcase( iPage==mxPage );
        if( iPage>mxPage ){
          rc = SQLITE_CORRUPT_BKPT;
          goto end_allocate_page;
        }
        testcase( iPage==mxPage );
        if( !searchList 
         || (iPage==nearby || (iPage<nearby && eMode==BTALLOC_LE)) 
        ){
          int noContent;
          *pPgno = iPage;
          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
                 ": %d more free pages\n",
                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
          rc = sqlite3PagerWrite(pTrunk->pDbPage);
          if( rc ) goto end_allocate_page;
          if( closest<k-1 ){
            memcpy(&aData[8+closest*4], &aData[4+k*4], 4);
          }
          put4byte(&aData[4], k-1);
          noContent = !btreeGetHasContent(pBt, *pPgno)? PAGER_GET_NOCONTENT : 0;
          rc = btreeGetUnusedPage(pBt, *pPgno, ppPage, noContent);
          if( rc==SQLITE_OK ){
            rc = sqlite3PagerWrite((*ppPage)->pDbPage);
            if( rc!=SQLITE_OK ){
              releasePage(*ppPage);
              *ppPage = 0;
            }
          }
          searchList = 0;
        }
      }
      releasePage(pPrevTrunk);
      pPrevTrunk = 0;
    }while( searchList );
  }else{
    /* There are no pages on the freelist, so append a new page to the
    ** database image.
    **
    ** Normally, new pages allocated by this block can be requested from the
    ** pager layer with the 'no-content' flag set. This prevents the pager
    ** from trying to read the pages content from disk. However, if the
    ** current transaction has already run one or more incremental-vacuum
    ** steps, then the page we are about to allocate may contain content
    ** that is required in the event of a rollback. In this case, do
    ** not set the no-content flag. This causes the pager to load and journal
    ** the current page content before overwriting it.
    **
    ** Note that the pager will not actually attempt to load or journal 
    ** content for any page that really does lie past the end of the database
    ** file on disk. So the effects of disabling the no-content optimization
    ** here are confined to those pages that lie between the end of the
    ** database image and the end of the database file.
    */
    int bNoContent = (0==IfNotOmitAV(pBt->bDoTruncate))? PAGER_GET_NOCONTENT:0;

    rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
    if( rc ) return rc;
    pBt->nPage++;
    if( pBt->nPage==PENDING_BYTE_PAGE(pBt) ) pBt->nPage++;

#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum && PTRMAP_ISPAGE(pBt, pBt->nPage) ){
      /* If *pPgno refers to a pointer-map page, allocate two new pages
      ** at the end of the file instead of one. The first allocated page
      ** becomes a new pointer-map page, the second is used by the caller.
      */
      MemPage *pPg = 0;
      TRACE(("ALLOCATE: %d from end of file (pointer-map page)\n", pBt->nPage));
      assert( pBt->nPage!=PENDING_BYTE_PAGE(pBt) );
      rc = btreeGetUnusedPage(pBt, pBt->nPage, &pPg, bNoContent);
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerWrite(pPg->pDbPage);
        releasePage(pPg);
      }
      if( rc ) return rc;
      pBt->nPage++;
      if( pBt->nPage==PENDING_BYTE_PAGE(pBt) ){ pBt->nPage++; }
    }
#endif
    put4byte(28 + (u8*)pBt->pPage1->aData, pBt->nPage);
    *pPgno = pBt->nPage;

    assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );
    rc = btreeGetUnusedPage(pBt, *pPgno, ppPage, bNoContent);
    if( rc ) return rc;
    rc = sqlite3PagerWrite((*ppPage)->pDbPage);
    if( rc!=SQLITE_OK ){
      releasePage(*ppPage);
      *ppPage = 0;
    }
    TRACE(("ALLOCATE: %d from end of file\n", *pPgno));
  }

  assert( *pPgno!=PENDING_BYTE_PAGE(pBt) );

end_allocate_page:
  releasePage(pTrunk);
  releasePage(pPrevTrunk);
  assert( rc!=SQLITE_OK || sqlite3PagerPageRefcount((*ppPage)->pDbPage)<=1 );
  assert( rc!=SQLITE_OK || (*ppPage)->isInit==0 );
  return rc;
}

/*
** This function is used to add page iPage to the database file free-list. 
** It is assumed that the page is not already a part of the free-list.
**
** The value passed as the second argument to this function is optional.
** If the caller happens to have a pointer to the MemPage object 
** corresponding to page iPage handy, it may pass it as the second value. 
** Otherwise, it may pass NULL.
**
** If a pointer to a MemPage object is passed as the second argument,
** its reference count is not altered by this function.
*/
static int freePage2(BtShared *pBt, MemPage *pMemPage, Pgno iPage){
  MemPage *pTrunk = 0;                /* Free-list trunk page */
  Pgno iTrunk = 0;                    /* Page number of free-list trunk page */ 
  MemPage *pPage1 = pBt->pPage1;      /* Local reference to page 1 */
  MemPage *pPage;                     /* Page being freed. May be NULL. */
  int rc;                             /* Return Code */
  int nFree;                          /* Initial number of pages on free-list */

  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( CORRUPT_DB || iPage>1 );
  assert( !pMemPage || pMemPage->pgno==iPage );

  if( iPage<2 ) return SQLITE_CORRUPT_BKPT;
  if( pMemPage ){
    pPage = pMemPage;
    sqlite3PagerRef(pPage->pDbPage);
  }else{
    pPage = btreePageLookup(pBt, iPage);
  }

  /* Increment the free page count on pPage1 */
  rc = sqlite3PagerWrite(pPage1->pDbPage);
  if( rc ) goto freepage_out;
  nFree = get4byte(&pPage1->aData[36]);
  put4byte(&pPage1->aData[36], nFree+1);

  if( pBt->btsFlags & BTS_SECURE_DELETE ){
    /* If the secure_delete option is enabled, then
    ** always fully overwrite deleted information with zeros.
    */
    if( (!pPage && ((rc = btreeGetPage(pBt, iPage, &pPage, 0))!=0) )
     ||            ((rc = sqlite3PagerWrite(pPage->pDbPage))!=0)
    ){
      goto freepage_out;
    }
    memset(pPage->aData, 0, pPage->pBt->pageSize);
  }

  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free.
  */
  if( ISAUTOVACUUM ){
    ptrmapPut(pBt, iPage, PTRMAP_FREEPAGE, 0, &rc);
    if( rc ) goto freepage_out;
  }

  /* Now manipulate the actual database free-list structure. There are two
  ** possibilities. If the free-list is currently empty, or if the first
  ** trunk page in the free-list is full, then this page will become a
  ** new free-list trunk page. Otherwise, it will become a leaf of the
  ** first trunk page in the current free-list. This block tests if it
  ** is possible to add the page as a new free-list leaf.
  */
  if( nFree!=0 ){
    u32 nLeaf;                /* Initial number of leaf cells on trunk page */

    iTrunk = get4byte(&pPage1->aData[32]);
    rc = btreeGetPage(pBt, iTrunk, &pTrunk, 0);
    if( rc!=SQLITE_OK ){
      goto freepage_out;
    }

    nLeaf = get4byte(&pTrunk->aData[4]);
    assert( pBt->usableSize>32 );
    if( nLeaf > (u32)pBt->usableSize/4 - 2 ){
      rc = SQLITE_CORRUPT_BKPT;
      goto freepage_out;
    }
    if( nLeaf < (u32)pBt->usableSize/4 - 8 ){
      /* In this case there is room on the trunk page to insert the page
      ** being freed as a new leaf.
      **
      ** Note that the trunk page is not really full until it contains
      ** usableSize/4 - 2 entries, not usableSize/4 - 8 entries as we have
      ** coded.  But due to a coding error in versions of SQLite prior to
      ** 3.6.0, databases with freelist trunk pages holding more than
      ** usableSize/4 - 8 entries will be reported as corrupt.  In order
      ** to maintain backwards compatibility with older versions of SQLite,
      ** we will continue to restrict the number of entries to usableSize/4 - 8
      ** for now.  At some point in the future (once everyone has upgraded
      ** to 3.6.0 or later) we should consider fixing the conditional above
      ** to read "usableSize/4-2" instead of "usableSize/4-8".
      **
      ** EVIDENCE-OF: R-19920-11576 However, newer versions of SQLite still
      ** avoid using the last six entries in the freelist trunk page array in
      ** order that database files created by newer versions of SQLite can be
      ** read by older versions of SQLite.
      */
      rc = sqlite3PagerWrite(pTrunk->pDbPage);
      if( rc==SQLITE_OK ){
        put4byte(&pTrunk->aData[4], nLeaf+1);
        put4byte(&pTrunk->aData[8+nLeaf*4], iPage);
        if( pPage && (pBt->btsFlags & BTS_SECURE_DELETE)==0 ){
          sqlite3PagerDontWrite(pPage->pDbPage);
        }
        rc = btreeSetHasContent(pBt, iPage);
      }
      TRACE(("FREE-PAGE: %d leaf on trunk page %d\n",pPage->pgno,pTrunk->pgno));
      goto freepage_out;
    }
  }

  /* If control flows to this point, then it was not possible to add the
  ** the page being freed as a leaf page of the first trunk in the free-list.
  ** Possibly because the free-list is empty, or possibly because the 
  ** first trunk in the free-list is full. Either way, the page being freed
  ** will become the new first trunk page in the free-list.
  */
  if( pPage==0 && SQLITE_OK!=(rc = btreeGetPage(pBt, iPage, &pPage, 0)) ){
    goto freepage_out;
  }
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc!=SQLITE_OK ){
    goto freepage_out;
  }
  put4byte(pPage->aData, iTrunk);
  put4byte(&pPage->aData[4], 0);
  put4byte(&pPage1->aData[32], iPage);
  TRACE(("FREE-PAGE: %d new trunk page replacing %d\n", pPage->pgno, iTrunk));

freepage_out:
  if( pPage ){
    pPage->isInit = 0;
  }
  releasePage(pPage);
  releasePage(pTrunk);
  return rc;
}
static void freePage(MemPage *pPage, int *pRC){
  if( (*pRC)==SQLITE_OK ){
    *pRC = freePage2(pPage->pBt, pPage, pPage->pgno);
  }
}

/*
** Free any overflow pages associated with the given Cell.  Write the
** local Cell size (the number of bytes on the original page, omitting
** overflow) into *pnSize.
*/
static int clearCell(
  MemPage *pPage,          /* The page that contains the Cell */
  unsigned char *pCell,    /* First byte of the Cell */
  u16 *pnSize              /* Write the size of the Cell here */
){
  BtShared *pBt = pPage->pBt;
  CellInfo info;
  Pgno ovflPgno;
  int rc;
  int nOvfl;
  u32 ovflPageSize;

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  pPage->xParseCell(pPage, pCell, &info);
  *pnSize = info.nSize;
  if( info.iOverflow==0 ){
    return SQLITE_OK;  /* No overflow pages. Return without doing anything */
  }
  if( pCell+info.iOverflow+3 > pPage->aData+pPage->maskPage ){
    return SQLITE_CORRUPT_BKPT;  /* Cell extends past end of page */
  }
  ovflPgno = get4byte(&pCell[info.iOverflow]);
  assert( pBt->usableSize > 4 );
  ovflPageSize = pBt->usableSize - 4;
  nOvfl = (info.nPayload - info.nLocal + ovflPageSize - 1)/ovflPageSize;
  assert( nOvfl>0 || 
    (CORRUPT_DB && (info.nPayload + ovflPageSize)<ovflPageSize)
  );
  while( nOvfl-- ){
    Pgno iNext = 0;
    MemPage *pOvfl = 0;
    if( ovflPgno<2 || ovflPgno>btreePagecount(pBt) ){
      /* 0 is not a legal page number and page 1 cannot be an 
      ** overflow page. Therefore if ovflPgno<2 or past the end of the 
      ** file the database must be corrupt. */
      return SQLITE_CORRUPT_BKPT;
    }
    if( nOvfl ){
      rc = getOverflowPage(pBt, ovflPgno, &pOvfl, &iNext);
      if( rc ) return rc;
    }

    if( ( pOvfl || ((pOvfl = btreePageLookup(pBt, ovflPgno))!=0) )
     && sqlite3PagerPageRefcount(pOvfl->pDbPage)!=1
    ){
      /* There is no reason any cursor should have an outstanding reference 
      ** to an overflow page belonging to a cell that is being deleted/updated.
      ** So if there exists more than one reference to this page, then it 
      ** must not really be an overflow page and the database must be corrupt. 
      ** It is helpful to detect this before calling freePage2(), as 
      ** freePage2() may zero the page contents if secure-delete mode is
      ** enabled. If this 'overflow' page happens to be a page that the
      ** caller is iterating through or using in some other way, this
      ** can be problematic.
      */
      rc = SQLITE_CORRUPT_BKPT;
    }else{
      rc = freePage2(pBt, pOvfl, ovflPgno);
    }

    if( pOvfl ){
      sqlite3PagerUnref(pOvfl->pDbPage);
    }
    if( rc ) return rc;
    ovflPgno = iNext;
  }
  return SQLITE_OK;
}

/*
** Create the byte sequence used to represent a cell on page pPage
** and write that byte sequence into pCell[].  Overflow pages are
** allocated and filled in as necessary.  The calling procedure
** is responsible for making sure sufficient space has been allocated
** for pCell[].
**
** Note that pCell does not necessary need to point to the pPage->aData
** area.  pCell might point to some temporary storage.  The cell will
** be constructed in this temporary area then copied into pPage->aData
** later.
*/
static int fillInCell(
  MemPage *pPage,                /* The page that contains the cell */
  unsigned char *pCell,          /* Complete text of the cell */
  const void *pKey, i64 nKey,    /* The key */
  const void *pData,int nData,   /* The data */
  int nZero,                     /* Extra zero bytes to append to pData */
  int *pnSize                    /* Write cell size here */
){
  int nPayload;
  const u8 *pSrc;
  int nSrc, n, rc;
  int spaceLeft;
  MemPage *pOvfl = 0;
  MemPage *pToRelease = 0;
  unsigned char *pPrior;
  unsigned char *pPayload;
  BtShared *pBt = pPage->pBt;
  Pgno pgnoOvfl = 0;
  int nHeader;

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );

  /* pPage is not necessarily writeable since pCell might be auxiliary
  ** buffer space that is separate from the pPage buffer area */
  assert( pCell<pPage->aData || pCell>=&pPage->aData[pBt->pageSize]
            || sqlite3PagerIswriteable(pPage->pDbPage) );

  /* Fill in the header. */
  nHeader = pPage->childPtrSize;
  nPayload = nData + nZero;
  if( pPage->intKeyLeaf ){
    nHeader += putVarint32(&pCell[nHeader], nPayload);
  }else{
    assert( nData==0 );
    assert( nZero==0 );
  }
  nHeader += putVarint(&pCell[nHeader], *(u64*)&nKey);
  
  /* Fill in the payload size */
  if( pPage->intKey ){
    pSrc = pData;
    nSrc = nData;
    nData = 0;
  }else{ 
    assert( nKey<=0x7fffffff && pKey!=0 );
    nPayload = (int)nKey;
    pSrc = pKey;
    nSrc = (int)nKey;
  }
  if( nPayload<=pPage->maxLocal ){
    n = nHeader + nPayload;
    testcase( n==3 );
    testcase( n==4 );
    if( n<4 ) n = 4;
    *pnSize = n;
    spaceLeft = nPayload;
    pPrior = pCell;
  }else{
    int mn = pPage->minLocal;
    n = mn + (nPayload - mn) % (pPage->pBt->usableSize - 4);
    testcase( n==pPage->maxLocal );
    testcase( n==pPage->maxLocal+1 );
    if( n > pPage->maxLocal ) n = mn;
    spaceLeft = n;
    *pnSize = n + nHeader + 4;
    pPrior = &pCell[nHeader+n];
  }
  pPayload = &pCell[nHeader];

  /* At this point variables should be set as follows:
  **
  **   nPayload           Total payload size in bytes
  **   pPayload           Begin writing payload here
  **   spaceLeft          Space available at pPayload.  If nPayload>spaceLeft,
  **                      that means content must spill into overflow pages.
  **   *pnSize            Size of the local cell (not counting overflow pages)
  **   pPrior             Where to write the pgno of the first overflow page
  **
  ** Use a call to btreeParseCellPtr() to verify that the values above
  ** were computed correctly.
  */
#if SQLITE_DEBUG
  {
    CellInfo info;
    pPage->xParseCell(pPage, pCell, &info);
    assert( nHeader=(int)(info.pPayload - pCell) );
    assert( info.nKey==nKey );
    assert( *pnSize == info.nSize );
    assert( spaceLeft == info.nLocal );
    assert( pPrior == &pCell[info.iOverflow] );
  }
#endif

  /* Write the payload into the local Cell and any extra into overflow pages */
  while( nPayload>0 ){
    if( spaceLeft==0 ){
#ifndef SQLITE_OMIT_AUTOVACUUM
      Pgno pgnoPtrmap = pgnoOvfl; /* Overflow page pointer-map entry page */
      if( pBt->autoVacuum ){
        do{
          pgnoOvfl++;
        } while( 
          PTRMAP_ISPAGE(pBt, pgnoOvfl) || pgnoOvfl==PENDING_BYTE_PAGE(pBt) 
        );
      }
#endif
      rc = allocateBtreePage(pBt, &pOvfl, &pgnoOvfl, pgnoOvfl, 0);
#ifndef SQLITE_OMIT_AUTOVACUUM
      /* If the database supports auto-vacuum, and the second or subsequent
      ** overflow page is being allocated, add an entry to the pointer-map
      ** for that page now. 
      **
      ** If this is the first overflow page, then write a partial entry 
      ** to the pointer-map. If we write nothing to this pointer-map slot,
      ** then the optimistic overflow chain processing in clearCell()
      ** may misinterpret the uninitialized values and delete the
      ** wrong pages from the database.
      */
      if( pBt->autoVacuum && rc==SQLITE_OK ){
        u8 eType = (pgnoPtrmap?PTRMAP_OVERFLOW2:PTRMAP_OVERFLOW1);
        ptrmapPut(pBt, pgnoOvfl, eType, pgnoPtrmap, &rc);
        if( rc ){
          releasePage(pOvfl);
        }
      }
#endif
      if( rc ){
        releasePage(pToRelease);
        return rc;
      }

      /* If pToRelease is not zero than pPrior points into the data area
      ** of pToRelease.  Make sure pToRelease is still writeable. */
      assert( pToRelease==0 || sqlite3PagerIswriteable(pToRelease->pDbPage) );

      /* If pPrior is part of the data area of pPage, then make sure pPage
      ** is still writeable */
      assert( pPrior<pPage->aData || pPrior>=&pPage->aData[pBt->pageSize]
            || sqlite3PagerIswriteable(pPage->pDbPage) );

      put4byte(pPrior, pgnoOvfl);
      releasePage(pToRelease);
      pToRelease = pOvfl;
      pPrior = pOvfl->aData;
      put4byte(pPrior, 0);
      pPayload = &pOvfl->aData[4];
      spaceLeft = pBt->usableSize - 4;
    }
    n = nPayload;
    if( n>spaceLeft ) n = spaceLeft;

    /* If pToRelease is not zero than pPayload points into the data area
    ** of pToRelease.  Make sure pToRelease is still writeable. */
    assert( pToRelease==0 || sqlite3PagerIswriteable(pToRelease->pDbPage) );

    /* If pPayload is part of the data area of pPage, then make sure pPage
    ** is still writeable */
    assert( pPayload<pPage->aData || pPayload>=&pPage->aData[pBt->pageSize]
            || sqlite3PagerIswriteable(pPage->pDbPage) );

    if( nSrc>0 ){
      if( n>nSrc ) n = nSrc;
      assert( pSrc );
      memcpy(pPayload, pSrc, n);
    }else{
      memset(pPayload, 0, n);
    }
    nPayload -= n;
    pPayload += n;
    pSrc += n;
    nSrc -= n;
    spaceLeft -= n;
    if( nSrc==0 ){
      nSrc = nData;
      pSrc = pData;
    }
  }
  releasePage(pToRelease);
  return SQLITE_OK;
}

/*
** Remove the i-th cell from pPage.  This routine effects pPage only.
** The cell content is not freed or deallocated.  It is assumed that
** the cell content has been copied someplace else.  This routine just
** removes the reference to the cell from pPage.
**
** "sz" must be the number of bytes in the cell.
*/
static void dropCell(MemPage *pPage, int idx, int sz, int *pRC){
  u32 pc;         /* Offset to cell content of cell being deleted */
  u8 *data;       /* pPage->aData */
  u8 *ptr;        /* Used to move bytes around within data[] */
  int rc;         /* The return code */
  int hdr;        /* Beginning of the header.  0 most pages.  100 page 1 */

  if( *pRC ) return;

  assert( idx>=0 && idx<pPage->nCell );
  assert( CORRUPT_DB || sz==cellSize(pPage, idx) );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  data = pPage->aData;
  ptr = &pPage->aCellIdx[2*idx];
  pc = get2byte(ptr);
  hdr = pPage->hdrOffset;
  testcase( pc==get2byte(&data[hdr+5]) );
  testcase( pc+sz==pPage->pBt->usableSize );
  if( pc < (u32)get2byte(&data[hdr+5]) || pc+sz > pPage->pBt->usableSize ){
    *pRC = SQLITE_CORRUPT_BKPT;
    return;
  }
  rc = freeSpace(pPage, pc, sz);
  if( rc ){
    *pRC = rc;
    return;
  }
  pPage->nCell--;
  if( pPage->nCell==0 ){
    memset(&data[hdr+1], 0, 4);
    data[hdr+7] = 0;
    put2byte(&data[hdr+5], pPage->pBt->usableSize);
    pPage->nFree = pPage->pBt->usableSize - pPage->hdrOffset
                       - pPage->childPtrSize - 8;
  }else{
    memmove(ptr, ptr+2, 2*(pPage->nCell - idx));
    put2byte(&data[hdr+3], pPage->nCell);
    pPage->nFree += 2;
  }
}

/*
** Insert a new cell on pPage at cell index "i".  pCell points to the
** content of the cell.
**
** If the cell content will fit on the page, then put it there.  If it
** will not fit, then make a copy of the cell content into pTemp if
** pTemp is not null.  Regardless of pTemp, allocate a new entry
** in pPage->apOvfl[] and make it point to the cell content (either
** in pTemp or the original pCell) and also record its index. 
** Allocating a new entry in pPage->aCell[] implies that 
** pPage->nOverflow is incremented.
*/
static void insertCell(
  MemPage *pPage,   /* Page into which we are copying */
  int i,            /* New cell becomes the i-th cell of the page */
  u8 *pCell,        /* Content of the new cell */
  int sz,           /* Bytes of content in pCell */
  u8 *pTemp,        /* Temp storage space for pCell, if needed */
  Pgno iChild,      /* If non-zero, replace first 4 bytes with this value */
  int *pRC          /* Read and write return code from here */
){
  int idx = 0;      /* Where to write new cell content in data[] */
  int j;            /* Loop counter */
  u8 *data;         /* The content of the whole page */
  u8 *pIns;         /* The point in pPage->aCellIdx[] where no cell inserted */

  if( *pRC ) return;

  assert( i>=0 && i<=pPage->nCell+pPage->nOverflow );
  assert( MX_CELL(pPage->pBt)<=10921 );
  assert( pPage->nCell<=MX_CELL(pPage->pBt) || CORRUPT_DB );
  assert( pPage->nOverflow<=ArraySize(pPage->apOvfl) );
  assert( ArraySize(pPage->apOvfl)==ArraySize(pPage->aiOvfl) );
  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  /* The cell should normally be sized correctly.  However, when moving a
  ** malformed cell from a leaf page to an interior page, if the cell size
  ** wanted to be less than 4 but got rounded up to 4 on the leaf, then size
  ** might be less than 8 (leaf-size + pointer) on the interior node.  Hence
  ** the term after the || in the following assert(). */
  assert( sz==pPage->xCellSize(pPage, pCell) || (sz==8 && iChild>0) );
  if( pPage->nOverflow || sz+2>pPage->nFree ){
    if( pTemp ){
      memcpy(pTemp, pCell, sz);
      pCell = pTemp;
    }
    if( iChild ){
      put4byte(pCell, iChild);
    }
    j = pPage->nOverflow++;
    assert( j<(int)(sizeof(pPage->apOvfl)/sizeof(pPage->apOvfl[0])) );
    pPage->apOvfl[j] = pCell;
    pPage->aiOvfl[j] = (u16)i;

    /* When multiple overflows occur, they are always sequential and in
    ** sorted order.  This invariants arise because multiple overflows can
    ** only occur when inserting divider cells into the parent page during
    ** balancing, and the dividers are adjacent and sorted.
    */
    assert( j==0 || pPage->aiOvfl[j-1]<(u16)i ); /* Overflows in sorted order */
    assert( j==0 || i==pPage->aiOvfl[j-1]+1 );   /* Overflows are sequential */
  }else{
    int rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc!=SQLITE_OK ){
      *pRC = rc;
      return;
    }
    assert( sqlite3PagerIswriteable(pPage->pDbPage) );
    data = pPage->aData;
    assert( &data[pPage->cellOffset]==pPage->aCellIdx );
    rc = allocateSpace(pPage, sz, &idx);
    if( rc ){ *pRC = rc; return; }
    /* The allocateSpace() routine guarantees the following properties
    ** if it returns successfully */
    assert( idx >= 0 );
    assert( idx >= pPage->cellOffset+2*pPage->nCell+2 || CORRUPT_DB );
    assert( idx+sz <= (int)pPage->pBt->usableSize );
    pPage->nFree -= (u16)(2 + sz);
    memcpy(&data[idx], pCell, sz);
    if( iChild ){
      put4byte(&data[idx], iChild);
    }
    pIns = pPage->aCellIdx + i*2;
    memmove(pIns+2, pIns, 2*(pPage->nCell - i));
    put2byte(pIns, idx);
    pPage->nCell++;
    /* increment the cell count */
    if( (++data[pPage->hdrOffset+4])==0 ) data[pPage->hdrOffset+3]++;
    assert( get2byte(&data[pPage->hdrOffset+3])==pPage->nCell );
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pPage->pBt->autoVacuum ){
      /* The cell may contain a pointer to an overflow page. If so, write
      ** the entry for the overflow page into the pointer map.
      */
      ptrmapPutOvflPtr(pPage, pCell, pRC);
    }
#endif
  }
}

/*
** A CellArray object contains a cache of pointers and sizes for a
** consecutive sequence of cells that might be held multiple pages.
*/
typedef struct CellArray CellArray;
struct CellArray {
  int nCell;              /* Number of cells in apCell[] */
  MemPage *pRef;          /* Reference page */
  u8 **apCell;            /* All cells begin balanced */
  u16 *szCell;            /* Local size of all cells in apCell[] */
};

/*
** Make sure the cell sizes at idx, idx+1, ..., idx+N-1 have been
** computed.
*/
static void populateCellCache(CellArray *p, int idx, int N){
  assert( idx>=0 && idx+N<=p->nCell );
  while( N>0 ){
    assert( p->apCell[idx]!=0 );
    if( p->szCell[idx]==0 ){
      p->szCell[idx] = p->pRef->xCellSize(p->pRef, p->apCell[idx]);
    }else{
      assert( CORRUPT_DB ||
              p->szCell[idx]==p->pRef->xCellSize(p->pRef, p->apCell[idx]) );
    }
    idx++;
    N--;
  }
}

/*
** Return the size of the Nth element of the cell array
*/
static SQLITE_NOINLINE u16 computeCellSize(CellArray *p, int N){
  assert( N>=0 && N<p->nCell );
  assert( p->szCell[N]==0 );
  p->szCell[N] = p->pRef->xCellSize(p->pRef, p->apCell[N]);
  return p->szCell[N];
}
static u16 cachedCellSize(CellArray *p, int N){
  assert( N>=0 && N<p->nCell );
  if( p->szCell[N] ) return p->szCell[N];
  return computeCellSize(p, N);
}

/*
** Array apCell[] contains pointers to nCell b-tree page cells. The 
** szCell[] array contains the size in bytes of each cell. This function
** replaces the current contents of page pPg with the contents of the cell
** array.
**
** Some of the cells in apCell[] may currently be stored in pPg. This
** function works around problems caused by this by making a copy of any 
** such cells before overwriting the page data.
**
** The MemPage.nFree field is invalidated by this function. It is the 
** responsibility of the caller to set it correctly.
*/
static int rebuildPage(
  MemPage *pPg,                   /* Edit this page */
  int nCell,                      /* Final number of cells on page */
  u8 **apCell,                    /* Array of cells */
  u16 *szCell                     /* Array of cell sizes */
){
  const int hdr = pPg->hdrOffset;          /* Offset of header on pPg */
  u8 * const aData = pPg->aData;           /* Pointer to data for pPg */
  const int usableSize = pPg->pBt->usableSize;
  u8 * const pEnd = &aData[usableSize];
  int i;
  u8 *pCellptr = pPg->aCellIdx;
  u8 *pTmp = sqlite3PagerTempSpace(pPg->pBt->pPager);
  u8 *pData;

  i = get2byte(&aData[hdr+5]);
  memcpy(&pTmp[i], &aData[i], usableSize - i);

  pData = pEnd;
  for(i=0; i<nCell; i++){
    u8 *pCell = apCell[i];
    if( pCell>aData && pCell<pEnd ){
      pCell = &pTmp[pCell - aData];
    }
    pData -= szCell[i];
    put2byte(pCellptr, (pData - aData));
    pCellptr += 2;
    if( pData < pCellptr ) return SQLITE_CORRUPT_BKPT;
    memcpy(pData, pCell, szCell[i]);
    assert( szCell[i]==pPg->xCellSize(pPg, pCell) || CORRUPT_DB );
    testcase( szCell[i]!=pPg->xCellSize(pPg,pCell) );
  }

  /* The pPg->nFree field is now set incorrectly. The caller will fix it. */
  pPg->nCell = nCell;
  pPg->nOverflow = 0;

  put2byte(&aData[hdr+1], 0);
  put2byte(&aData[hdr+3], pPg->nCell);
  put2byte(&aData[hdr+5], pData - aData);
  aData[hdr+7] = 0x00;
  return SQLITE_OK;
}

/*
** Array apCell[] contains nCell pointers to b-tree cells. Array szCell
** contains the size in bytes of each such cell. This function attempts to 
** add the cells stored in the array to page pPg. If it cannot (because 
** the page needs to be defragmented before the cells will fit), non-zero
** is returned. Otherwise, if the cells are added successfully, zero is
** returned.
**
** Argument pCellptr points to the first entry in the cell-pointer array
** (part of page pPg) to populate. After cell apCell[0] is written to the
** page body, a 16-bit offset is written to pCellptr. And so on, for each
** cell in the array. It is the responsibility of the caller to ensure
** that it is safe to overwrite this part of the cell-pointer array.
**
** When this function is called, *ppData points to the start of the 
** content area on page pPg. If the size of the content area is extended,
** *ppData is updated to point to the new start of the content area
** before returning.
**
** Finally, argument pBegin points to the byte immediately following the
** end of the space required by this page for the cell-pointer area (for
** all cells - not just those inserted by the current call). If the content
** area must be extended to before this point in order to accomodate all
** cells in apCell[], then the cells do not fit and non-zero is returned.
*/
static int pageInsertArray(
  MemPage *pPg,                   /* Page to add cells to */
  u8 *pBegin,                     /* End of cell-pointer array */
  u8 **ppData,                    /* IN/OUT: Page content -area pointer */
  u8 *pCellptr,                   /* Pointer to cell-pointer area */
  int iFirst,                     /* Index of first cell to add */
  int nCell,                      /* Number of cells to add to pPg */
  CellArray *pCArray              /* Array of cells */
){
  int i;
  u8 *aData = pPg->aData;
  u8 *pData = *ppData;
  int iEnd = iFirst + nCell;
  assert( CORRUPT_DB || pPg->hdrOffset==0 );    /* Never called on page 1 */
  for(i=iFirst; i<iEnd; i++){
    int sz, rc;
    u8 *pSlot;
    sz = cachedCellSize(pCArray, i);
    if( (aData[1]==0 && aData[2]==0) || (pSlot = pageFindSlot(pPg,sz,&rc))==0 ){
      pData -= sz;
      if( pData<pBegin ) return 1;
      pSlot = pData;
    }
    /* pSlot and pCArray->apCell[i] will never overlap on a well-formed
    ** database.  But they might for a corrupt database.  Hence use memmove()
    ** since memcpy() sends SIGABORT with overlapping buffers on OpenBSD */
    assert( (pSlot+sz)<=pCArray->apCell[i]
         || pSlot>=(pCArray->apCell[i]+sz)
         || CORRUPT_DB );
    memmove(pSlot, pCArray->apCell[i], sz);
    put2byte(pCellptr, (pSlot - aData));
    pCellptr += 2;
  }
  *ppData = pData;
  return 0;
}

/*
** Array apCell[] contains nCell pointers to b-tree cells. Array szCell 
** contains the size in bytes of each such cell. This function adds the
** space associated with each cell in the array that is currently stored 
** within the body of pPg to the pPg free-list. The cell-pointers and other
** fields of the page are not updated.
**
** This function returns the total number of cells added to the free-list.
*/
static int pageFreeArray(
  MemPage *pPg,                   /* Page to edit */
  int iFirst,                     /* First cell to delete */
  int nCell,                      /* Cells to delete */
  CellArray *pCArray              /* Array of cells */
){
  u8 * const aData = pPg->aData;
  u8 * const pEnd = &aData[pPg->pBt->usableSize];
  u8 * const pStart = &aData[pPg->hdrOffset + 8 + pPg->childPtrSize];
  int nRet = 0;
  int i;
  int iEnd = iFirst + nCell;
  u8 *pFree = 0;
  int szFree = 0;

  for(i=iFirst; i<iEnd; i++){
    u8 *pCell = pCArray->apCell[i];
    if( pCell>=pStart && pCell<pEnd ){
      int sz;
      /* No need to use cachedCellSize() here.  The sizes of all cells that
      ** are to be freed have already been computing while deciding which
      ** cells need freeing */
      sz = pCArray->szCell[i];  assert( sz>0 );
      if( pFree!=(pCell + sz) ){
        if( pFree ){
          assert( pFree>aData && (pFree - aData)<65536 );
          freeSpace(pPg, (u16)(pFree - aData), szFree);
        }
        pFree = pCell;
        szFree = sz;
        if( pFree+sz>pEnd ) return 0;
      }else{
        pFree = pCell;
        szFree += sz;
      }
      nRet++;
    }
  }
  if( pFree ){
    assert( pFree>aData && (pFree - aData)<65536 );
    freeSpace(pPg, (u16)(pFree - aData), szFree);
  }
  return nRet;
}

/*
** apCell[] and szCell[] contains pointers to and sizes of all cells in the
** pages being balanced.  The current page, pPg, has pPg->nCell cells starting
** with apCell[iOld].  After balancing, this page should hold nNew cells
** starting at apCell[iNew].
**
** This routine makes the necessary adjustments to pPg so that it contains
** the correct cells after being balanced.
**
** The pPg->nFree field is invalid when this function returns. It is the
** responsibility of the caller to set it correctly.
*/
static int editPage(
  MemPage *pPg,                   /* Edit this page */
  int iOld,                       /* Index of first cell currently on page */
  int iNew,                       /* Index of new first cell on page */
  int nNew,                       /* Final number of cells on page */
  CellArray *pCArray              /* Array of cells and sizes */
){
  u8 * const aData = pPg->aData;
  const int hdr = pPg->hdrOffset;
  u8 *pBegin = &pPg->aCellIdx[nNew * 2];
  int nCell = pPg->nCell;       /* Cells stored on pPg */
  u8 *pData;
  u8 *pCellptr;
  int i;
  int iOldEnd = iOld + pPg->nCell + pPg->nOverflow;
  int iNewEnd = iNew + nNew;

#ifdef SQLITE_DEBUG
  u8 *pTmp = sqlite3PagerTempSpace(pPg->pBt->pPager);
  memcpy(pTmp, aData, pPg->pBt->usableSize);
#endif

  /* Remove cells from the start and end of the page */
  if( iOld<iNew ){
    int nShift = pageFreeArray(pPg, iOld, iNew-iOld, pCArray);
    memmove(pPg->aCellIdx, &pPg->aCellIdx[nShift*2], nCell*2);
    nCell -= nShift;
  }
  if( iNewEnd < iOldEnd ){
    nCell -= pageFreeArray(pPg, iNewEnd, iOldEnd - iNewEnd, pCArray);
  }

  pData = &aData[get2byteNotZero(&aData[hdr+5])];
  if( pData<pBegin ) goto editpage_fail;

  /* Add cells to the start of the page */
  if( iNew<iOld ){
    int nAdd = MIN(nNew,iOld-iNew);
    assert( (iOld-iNew)<nNew || nCell==0 || CORRUPT_DB );
    pCellptr = pPg->aCellIdx;
    memmove(&pCellptr[nAdd*2], pCellptr, nCell*2);
    if( pageInsertArray(
          pPg, pBegin, &pData, pCellptr,
          iNew, nAdd, pCArray
    ) ) goto editpage_fail;
    nCell += nAdd;
  }

  /* Add any overflow cells */
  for(i=0; i<pPg->nOverflow; i++){
    int iCell = (iOld + pPg->aiOvfl[i]) - iNew;
    if( iCell>=0 && iCell<nNew ){
      pCellptr = &pPg->aCellIdx[iCell * 2];
      memmove(&pCellptr[2], pCellptr, (nCell - iCell) * 2);
      nCell++;
      if( pageInsertArray(
            pPg, pBegin, &pData, pCellptr,
            iCell+iNew, 1, pCArray
      ) ) goto editpage_fail;
    }
  }

  /* Append cells to the end of the page */
  pCellptr = &pPg->aCellIdx[nCell*2];
  if( pageInsertArray(
        pPg, pBegin, &pData, pCellptr,
        iNew+nCell, nNew-nCell, pCArray
  ) ) goto editpage_fail;

  pPg->nCell = nNew;
  pPg->nOverflow = 0;

  put2byte(&aData[hdr+3], pPg->nCell);
  put2byte(&aData[hdr+5], pData - aData);

#ifdef SQLITE_DEBUG
  for(i=0; i<nNew && !CORRUPT_DB; i++){
    u8 *pCell = pCArray->apCell[i+iNew];
    int iOff = get2byteAligned(&pPg->aCellIdx[i*2]);
    if( pCell>=aData && pCell<&aData[pPg->pBt->usableSize] ){
      pCell = &pTmp[pCell - aData];
    }
    assert( 0==memcmp(pCell, &aData[iOff],
            pCArray->pRef->xCellSize(pCArray->pRef, pCArray->apCell[i+iNew])) );
  }
#endif

  return SQLITE_OK;
 editpage_fail:
  /* Unable to edit this page. Rebuild it from scratch instead. */
  populateCellCache(pCArray, iNew, nNew);
  return rebuildPage(pPg, nNew, &pCArray->apCell[iNew], &pCArray->szCell[iNew]);
}

/*
** The following parameters determine how many adjacent pages get involved
** in a balancing operation.  NN is the number of neighbors on either side
** of the page that participate in the balancing operation.  NB is the
** total number of pages that participate, including the target page and
** NN neighbors on either side.
**
** The minimum value of NN is 1 (of course).  Increasing NN above 1
** (to 2 or 3) gives a modest improvement in SELECT and DELETE performance
** in exchange for a larger degradation in INSERT and UPDATE performance.
** The value of NN appears to give the best results overall.
*/
#define NN 1             /* Number of neighbors on either side of pPage */
#define NB (NN*2+1)      /* Total pages involved in the balance */


#ifndef SQLITE_OMIT_QUICKBALANCE
/*
** This version of balance() handles the common special case where
** a new entry is being inserted on the extreme right-end of the
** tree, in other words, when the new entry will become the largest
** entry in the tree.
**
** Instead of trying to balance the 3 right-most leaf pages, just add
** a new page to the right-hand side and put the one new entry in
** that page.  This leaves the right side of the tree somewhat
** unbalanced.  But odds are that we will be inserting new entries
** at the end soon afterwards so the nearly empty page will quickly
** fill up.  On average.
**
** pPage is the leaf page which is the right-most page in the tree.
** pParent is its parent.  pPage must have a single overflow entry
** which is also the right-most entry on the page.
**
** The pSpace buffer is used to store a temporary copy of the divider
** cell that will be inserted into pParent. Such a cell consists of a 4
** byte page number followed by a variable length integer. In other
** words, at most 13 bytes. Hence the pSpace buffer must be at
** least 13 bytes in size.
*/
static int balance_quick(MemPage *pParent, MemPage *pPage, u8 *pSpace){
  BtShared *const pBt = pPage->pBt;    /* B-Tree Database */
  MemPage *pNew;                       /* Newly allocated page */
  int rc;                              /* Return Code */
  Pgno pgnoNew;                        /* Page number of pNew */

  assert( sqlite3_mutex_held(pPage->pBt->mutex) );
  assert( sqlite3PagerIswriteable(pParent->pDbPage) );
  assert( pPage->nOverflow==1 );

  /* This error condition is now caught prior to reaching this function */
  if( NEVER(pPage->nCell==0) ) return SQLITE_CORRUPT_BKPT;

  /* Allocate a new page. This page will become the right-sibling of 
  ** pPage. Make the parent page writable, so that the new divider cell
  ** may be inserted. If both these operations are successful, proceed.
  */
  rc = allocateBtreePage(pBt, &pNew, &pgnoNew, 0, 0);

  if( rc==SQLITE_OK ){

    u8 *pOut = &pSpace[4];
    u8 *pCell = pPage->apOvfl[0];
    u16 szCell = pPage->xCellSize(pPage, pCell);
    u8 *pStop;

    assert( sqlite3PagerIswriteable(pNew->pDbPage) );
    assert( pPage->aData[0]==(PTF_INTKEY|PTF_LEAFDATA|PTF_LEAF) );
    zeroPage(pNew, PTF_INTKEY|PTF_LEAFDATA|PTF_LEAF);
    rc = rebuildPage(pNew, 1, &pCell, &szCell);
    if( NEVER(rc) ) return rc;
    pNew->nFree = pBt->usableSize - pNew->cellOffset - 2 - szCell;

    /* If this is an auto-vacuum database, update the pointer map
    ** with entries for the new page, and any pointer from the 
    ** cell on the page to an overflow page. If either of these
    ** operations fails, the return code is set, but the contents
    ** of the parent page are still manipulated by thh code below.
    ** That is Ok, at this point the parent page is guaranteed to
    ** be marked as dirty. Returning an error code will cause a
    ** rollback, undoing any changes made to the parent page.
    */
    if( ISAUTOVACUUM ){
      ptrmapPut(pBt, pgnoNew, PTRMAP_BTREE, pParent->pgno, &rc);
      if( szCell>pNew->minLocal ){
        ptrmapPutOvflPtr(pNew, pCell, &rc);
      }
    }
  
    /* Create a divider cell to insert into pParent. The divider cell
    ** consists of a 4-byte page number (the page number of pPage) and
    ** a variable length key value (which must be the same value as the
    ** largest key on pPage).
    **
    ** To find the largest key value on pPage, first find the right-most 
    ** cell on pPage. The first two fields of this cell are the 
    ** record-length (a variable length integer at most 32-bits in size)
    ** and the key value (a variable length integer, may have any value).
    ** The first of the while(...) loops below skips over the record-length
    ** field. The second while(...) loop copies the key value from the
    ** cell on pPage into the pSpace buffer.
    */
    pCell = findCell(pPage, pPage->nCell-1);
    pStop = &pCell[9];
    while( (*(pCell++)&0x80) && pCell<pStop );
    pStop = &pCell[9];
    while( ((*(pOut++) = *(pCell++))&0x80) && pCell<pStop );

    /* Insert the new divider cell into pParent. */
    insertCell(pParent, pParent->nCell, pSpace, (int)(pOut-pSpace),
               0, pPage->pgno, &rc);

    /* Set the right-child pointer of pParent to point to the new page. */
    put4byte(&pParent->aData[pParent->hdrOffset+8], pgnoNew);
  
    /* Release the reference to the new page. */
    releasePage(pNew);
  }

  return rc;
}
#endif /* SQLITE_OMIT_QUICKBALANCE */

#if 0
/*
** This function does not contribute anything to the operation of SQLite.
** it is sometimes activated temporarily while debugging code responsible 
** for setting pointer-map entries.
*/
static int ptrmapCheckPages(MemPage **apPage, int nPage){
  int i, j;
  for(i=0; i<nPage; i++){
    Pgno n;
    u8 e;
    MemPage *pPage = apPage[i];
    BtShared *pBt = pPage->pBt;
    assert( pPage->isInit );

    for(j=0; j<pPage->nCell; j++){
      CellInfo info;
      u8 *z;
     
      z = findCell(pPage, j);
      pPage->xParseCell(pPage, z, &info);
      if( info.iOverflow ){
        Pgno ovfl = get4byte(&z[info.iOverflow]);
        ptrmapGet(pBt, ovfl, &e, &n);
        assert( n==pPage->pgno && e==PTRMAP_OVERFLOW1 );
      }
      if( !pPage->leaf ){
        Pgno child = get4byte(z);
        ptrmapGet(pBt, child, &e, &n);
        assert( n==pPage->pgno && e==PTRMAP_BTREE );
      }
    }
    if( !pPage->leaf ){
      Pgno child = get4byte(&pPage->aData[pPage->hdrOffset+8]);
      ptrmapGet(pBt, child, &e, &n);
      assert( n==pPage->pgno && e==PTRMAP_BTREE );
    }
  }
  return 1;
}
#endif

/*
** This function is used to copy the contents of the b-tree node stored 
** on page pFrom to page pTo. If page pFrom was not a leaf page, then
** the pointer-map entries for each child page are updated so that the
** parent page stored in the pointer map is page pTo. If pFrom contained
** any cells with overflow page pointers, then the corresponding pointer
** map entries are also updated so that the parent page is page pTo.
**
** If pFrom is currently carrying any overflow cells (entries in the
** MemPage.apOvfl[] array), they are not copied to pTo. 
**
** Before returning, page pTo is reinitialized using btreeInitPage().
**
** The performance of this function is not critical. It is only used by 
** the balance_shallower() and balance_deeper() procedures, neither of
** which are called often under normal circumstances.
*/
static void copyNodeContent(MemPage *pFrom, MemPage *pTo, int *pRC){
  if( (*pRC)==SQLITE_OK ){
    BtShared * const pBt = pFrom->pBt;
    u8 * const aFrom = pFrom->aData;
    u8 * const aTo = pTo->aData;
    int const iFromHdr = pFrom->hdrOffset;
    int const iToHdr = ((pTo->pgno==1) ? 100 : 0);
    int rc;
    int iData;
  
  
    assert( pFrom->isInit );
    assert( pFrom->nFree>=iToHdr );
    assert( get2byte(&aFrom[iFromHdr+5]) <= (int)pBt->usableSize );
  
    /* Copy the b-tree node content from page pFrom to page pTo. */
    iData = get2byte(&aFrom[iFromHdr+5]);
    memcpy(&aTo[iData], &aFrom[iData], pBt->usableSize-iData);
    memcpy(&aTo[iToHdr], &aFrom[iFromHdr], pFrom->cellOffset + 2*pFrom->nCell);
  
    /* Reinitialize page pTo so that the contents of the MemPage structure
    ** match the new data. The initialization of pTo can actually fail under
    ** fairly obscure circumstances, even though it is a copy of initialized 
    ** page pFrom.
    */
    pTo->isInit = 0;
    rc = btreeInitPage(pTo);
    if( rc!=SQLITE_OK ){
      *pRC = rc;
      return;
    }
  
    /* If this is an auto-vacuum database, update the pointer-map entries
    ** for any b-tree or overflow pages that pTo now contains the pointers to.
    */
    if( ISAUTOVACUUM ){
      *pRC = setChildPtrmaps(pTo);
    }
  }
}

/*
** This routine redistributes cells on the iParentIdx'th child of pParent
** (hereafter "the page") and up to 2 siblings so that all pages have about the
** same amount of free space. Usually a single sibling on either side of the
** page are used in the balancing, though both siblings might come from one
** side if the page is the first or last child of its parent. If the page 
** has fewer than 2 siblings (something which can only happen if the page
** is a root page or a child of a root page) then all available siblings
** participate in the balancing.
**
** The number of siblings of the page might be increased or decreased by 
** one or two in an effort to keep pages nearly full but not over full. 
**
** Note that when this routine is called, some of the cells on the page
** might not actually be stored in MemPage.aData[]. This can happen
** if the page is overfull. This routine ensures that all cells allocated
** to the page and its siblings fit into MemPage.aData[] before returning.
**
** In the course of balancing the page and its siblings, cells may be
** inserted into or removed from the parent page (pParent). Doing so
** may cause the parent page to become overfull or underfull. If this
** happens, it is the responsibility of the caller to invoke the correct
** balancing routine to fix this problem (see the balance() routine). 
**
** If this routine fails for any reason, it might leave the database
** in a corrupted state. So if this routine fails, the database should
** be rolled back.
**
** The third argument to this function, aOvflSpace, is a pointer to a
** buffer big enough to hold one page. If while inserting cells into the parent
** page (pParent) the parent page becomes overfull, this buffer is
** used to store the parent's overflow cells. Because this function inserts
** a maximum of four divider cells into the parent page, and the maximum
** size of a cell stored within an internal node is always less than 1/4
** of the page-size, the aOvflSpace[] buffer is guaranteed to be large
** enough for all overflow cells.
**
** If aOvflSpace is set to a null pointer, this function returns 
** SQLITE_NOMEM.
*/
#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM)
#pragma optimize("", off)
#endif
static int balance_nonroot(
  MemPage *pParent,               /* Parent page of siblings being balanced */
  int iParentIdx,                 /* Index of "the page" in pParent */
  u8 *aOvflSpace,                 /* page-size bytes of space for parent ovfl */
  int isRoot,                     /* True if pParent is a root-page */
  int bBulk                       /* True if this call is part of a bulk load */
){
  BtShared *pBt;               /* The whole database */
  int nMaxCells = 0;           /* Allocated size of apCell, szCell, aFrom. */
  int nNew = 0;                /* Number of pages in apNew[] */
  int nOld;                    /* Number of pages in apOld[] */
  int i, j, k;                 /* Loop counters */
  int nxDiv;                   /* Next divider slot in pParent->aCell[] */
  int rc = SQLITE_OK;          /* The return code */
  u16 leafCorrection;          /* 4 if pPage is a leaf.  0 if not */
  int leafData;                /* True if pPage is a leaf of a LEAFDATA tree */
  int usableSpace;             /* Bytes in pPage beyond the header */
  int pageFlags;               /* Value of pPage->aData[0] */
  int iSpace1 = 0;             /* First unused byte of aSpace1[] */
  int iOvflSpace = 0;          /* First unused byte of aOvflSpace[] */
  int szScratch;               /* Size of scratch memory requested */
  MemPage *apOld[NB];          /* pPage and up to two siblings */
  MemPage *apNew[NB+2];        /* pPage and up to NB siblings after balancing */
  u8 *pRight;                  /* Location in parent of right-sibling pointer */
  u8 *apDiv[NB-1];             /* Divider cells in pParent */
  int cntNew[NB+2];            /* Index in b.paCell[] of cell after i-th page */
  int cntOld[NB+2];            /* Old index in b.apCell[] */
  int szNew[NB+2];             /* Combined size of cells placed on i-th page */
  u8 *aSpace1;                 /* Space for copies of dividers cells */
  Pgno pgno;                   /* Temp var to store a page number in */
  u8 abDone[NB+2];             /* True after i'th new page is populated */
  Pgno aPgno[NB+2];            /* Page numbers of new pages before shuffling */
  Pgno aPgOrder[NB+2];         /* Copy of aPgno[] used for sorting pages */
  u16 aPgFlags[NB+2];          /* flags field of new pages before shuffling */
  CellArray b;                  /* Parsed information on cells being balanced */

  memset(abDone, 0, sizeof(abDone));
  b.nCell = 0;
  b.apCell = 0;
  pBt = pParent->pBt;
  assert( sqlite3_mutex_held(pBt->mutex) );
  assert( sqlite3PagerIswriteable(pParent->pDbPage) );

#if 0
  TRACE(("BALANCE: begin page %d child of %d\n", pPage->pgno, pParent->pgno));
#endif

  /* At this point pParent may have at most one overflow cell. And if
  ** this overflow cell is present, it must be the cell with 
  ** index iParentIdx. This scenario comes about when this function
  ** is called (indirectly) from sqlite3BtreeDelete().
  */
  assert( pParent->nOverflow==0 || pParent->nOverflow==1 );
  assert( pParent->nOverflow==0 || pParent->aiOvfl[0]==iParentIdx );

  if( !aOvflSpace ){
    return SQLITE_NOMEM;
  }

  /* Find the sibling pages to balance. Also locate the cells in pParent 
  ** that divide the siblings. An attempt is made to find NN siblings on 
  ** either side of pPage. More siblings are taken from one side, however, 
  ** if there are fewer than NN siblings on the other side. If pParent
  ** has NB or fewer children then all children of pParent are taken.  
  **
  ** This loop also drops the divider cells from the parent page. This
  ** way, the remainder of the function does not have to deal with any
  ** overflow cells in the parent page, since if any existed they will
  ** have already been removed.
  */
  i = pParent->nOverflow + pParent->nCell;
  if( i<2 ){
    nxDiv = 0;
  }else{
    assert( bBulk==0 || bBulk==1 );
    if( iParentIdx==0 ){                 
      nxDiv = 0;
    }else if( iParentIdx==i ){
      nxDiv = i-2+bBulk;
    }else{
      nxDiv = iParentIdx-1;
    }
    i = 2-bBulk;
  }
  nOld = i+1;
  if( (i+nxDiv-pParent->nOverflow)==pParent->nCell ){
    pRight = &pParent->aData[pParent->hdrOffset+8];
  }else{
    pRight = findCell(pParent, i+nxDiv-pParent->nOverflow);
  }
  pgno = get4byte(pRight);
  while( 1 ){
    rc = getAndInitPage(pBt, pgno, &apOld[i], 0, 0);
    if( rc ){
      memset(apOld, 0, (i+1)*sizeof(MemPage*));
      goto balance_cleanup;
    }
    nMaxCells += 1+apOld[i]->nCell+apOld[i]->nOverflow;
    if( (i--)==0 ) break;

    if( i+nxDiv==pParent->aiOvfl[0] && pParent->nOverflow ){
      apDiv[i] = pParent->apOvfl[0];
      pgno = get4byte(apDiv[i]);
      szNew[i] = pParent->xCellSize(pParent, apDiv[i]);
      pParent->nOverflow = 0;
    }else{
      apDiv[i] = findCell(pParent, i+nxDiv-pParent->nOverflow);
      pgno = get4byte(apDiv[i]);
      szNew[i] = pParent->xCellSize(pParent, apDiv[i]);

      /* Drop the cell from the parent page. apDiv[i] still points to
      ** the cell within the parent, even though it has been dropped.
      ** This is safe because dropping a cell only overwrites the first
      ** four bytes of it, and this function does not need the first
      ** four bytes of the divider cell. So the pointer is safe to use
      ** later on.  
      **
      ** But not if we are in secure-delete mode. In secure-delete mode,
      ** the dropCell() routine will overwrite the entire cell with zeroes.
      ** In this case, temporarily copy the cell into the aOvflSpace[]
      ** buffer. It will be copied out again as soon as the aSpace[] buffer
      ** is allocated.  */
      if( pBt->btsFlags & BTS_SECURE_DELETE ){
        int iOff;

        iOff = SQLITE_PTR_TO_INT(apDiv[i]) - SQLITE_PTR_TO_INT(pParent->aData);
        if( (iOff+szNew[i])>(int)pBt->usableSize ){
          rc = SQLITE_CORRUPT_BKPT;
          memset(apOld, 0, (i+1)*sizeof(MemPage*));
          goto balance_cleanup;
        }else{
          memcpy(&aOvflSpace[iOff], apDiv[i], szNew[i]);
          apDiv[i] = &aOvflSpace[apDiv[i]-pParent->aData];
        }
      }
      dropCell(pParent, i+nxDiv-pParent->nOverflow, szNew[i], &rc);
    }
  }

  /* Make nMaxCells a multiple of 4 in order to preserve 8-byte
  ** alignment */
  nMaxCells = (nMaxCells + 3)&~3;

  /*
  ** Allocate space for memory structures
  */
  szScratch =
       nMaxCells*sizeof(u8*)                       /* b.apCell */
     + nMaxCells*sizeof(u16)                       /* b.szCell */
     + pBt->pageSize;                              /* aSpace1 */

  /* EVIDENCE-OF: R-28375-38319 SQLite will never request a scratch buffer
  ** that is more than 6 times the database page size. */
  assert( szScratch<=6*(int)pBt->pageSize );
  b.apCell = sqlite3ScratchMalloc( szScratch ); 
  if( b.apCell==0 ){
    rc = SQLITE_NOMEM;
    goto balance_cleanup;
  }
  b.szCell = (u16*)&b.apCell[nMaxCells];
  aSpace1 = (u8*)&b.szCell[nMaxCells];
  assert( EIGHT_BYTE_ALIGNMENT(aSpace1) );

  /*
  ** Load pointers to all cells on sibling pages and the divider cells
  ** into the local b.apCell[] array.  Make copies of the divider cells
  ** into space obtained from aSpace1[]. The divider cells have already
  ** been removed from pParent.
  **
  ** If the siblings are on leaf pages, then the child pointers of the
  ** divider cells are stripped from the cells before they are copied
  ** into aSpace1[].  In this way, all cells in b.apCell[] are without
  ** child pointers.  If siblings are not leaves, then all cell in
  ** b.apCell[] include child pointers.  Either way, all cells in b.apCell[]
  ** are alike.
  **
  ** leafCorrection:  4 if pPage is a leaf.  0 if pPage is not a leaf.
  **       leafData:  1 if pPage holds key+data and pParent holds only keys.
  */
  b.pRef = apOld[0];
  leafCorrection = b.pRef->leaf*4;
  leafData = b.pRef->intKeyLeaf;
  for(i=0; i<nOld; i++){
    MemPage *pOld = apOld[i];
    int limit = pOld->nCell;
    u8 *aData = pOld->aData;
    u16 maskPage = pOld->maskPage;
    u8 *piCell = aData + pOld->cellOffset;
    u8 *piEnd;

    /* Verify that all sibling pages are of the same "type" (table-leaf,
    ** table-interior, index-leaf, or index-interior).
    */
    if( pOld->aData[0]!=apOld[0]->aData[0] ){
      rc = SQLITE_CORRUPT_BKPT;
      goto balance_cleanup;
    }

    /* Load b.apCell[] with pointers to all cells in pOld.  If pOld
    ** constains overflow cells, include them in the b.apCell[] array
    ** in the correct spot.
    **
    ** Note that when there are multiple overflow cells, it is always the
    ** case that they are sequential and adjacent.  This invariant arises
    ** because multiple overflows can only occurs when inserting divider
    ** cells into a parent on a prior balance, and divider cells are always
    ** adjacent and are inserted in order.  There is an assert() tagged
    ** with "NOTE 1" in the overflow cell insertion loop to prove this
    ** invariant.
    **
    ** This must be done in advance.  Once the balance starts, the cell
    ** offset section of the btree page will be overwritten and we will no
    ** long be able to find the cells if a pointer to each cell is not saved
    ** first.
    */
    memset(&b.szCell[b.nCell], 0, sizeof(b.szCell[0])*limit);
    if( pOld->nOverflow>0 ){
      memset(&b.szCell[b.nCell+limit], 0, sizeof(b.szCell[0])*pOld->nOverflow);
      limit = pOld->aiOvfl[0];
      for(j=0; j<limit; j++){
        b.apCell[b.nCell] = aData + (maskPage & get2byteAligned(piCell));
        piCell += 2;
        b.nCell++;
      }
      for(k=0; k<pOld->nOverflow; k++){
        assert( k==0 || pOld->aiOvfl[k-1]+1==pOld->aiOvfl[k] );/* NOTE 1 */
        b.apCell[b.nCell] = pOld->apOvfl[k];
        b.nCell++;
      }
    }
    piEnd = aData + pOld->cellOffset + 2*pOld->nCell;
    while( piCell<piEnd ){
      assert( b.nCell<nMaxCells );
      b.apCell[b.nCell] = aData + (maskPage & get2byteAligned(piCell));
      piCell += 2;
      b.nCell++;
    }

    cntOld[i] = b.nCell;
    if( i<nOld-1 && !leafData){
      u16 sz = (u16)szNew[i];
      u8 *pTemp;
      assert( b.nCell<nMaxCells );
      b.szCell[b.nCell] = sz;
      pTemp = &aSpace1[iSpace1];
      iSpace1 += sz;
      assert( sz<=pBt->maxLocal+23 );
      assert( iSpace1 <= (int)pBt->pageSize );
      memcpy(pTemp, apDiv[i], sz);
      b.apCell[b.nCell] = pTemp+leafCorrection;
      assert( leafCorrection==0 || leafCorrection==4 );
      b.szCell[b.nCell] = b.szCell[b.nCell] - leafCorrection;
      if( !pOld->leaf ){
        assert( leafCorrection==0 );
        assert( pOld->hdrOffset==0 );
        /* The right pointer of the child page pOld becomes the left
        ** pointer of the divider cell */
        memcpy(b.apCell[b.nCell], &pOld->aData[8], 4);
      }else{
        assert( leafCorrection==4 );
        while( b.szCell[b.nCell]<4 ){
          /* Do not allow any cells smaller than 4 bytes. If a smaller cell
          ** does exist, pad it with 0x00 bytes. */
          assert( b.szCell[b.nCell]==3 || CORRUPT_DB );
          assert( b.apCell[b.nCell]==&aSpace1[iSpace1-3] || CORRUPT_DB );
          aSpace1[iSpace1++] = 0x00;
          b.szCell[b.nCell]++;
        }
      }
      b.nCell++;
    }
  }

  /*
  ** Figure out the number of pages needed to hold all b.nCell cells.
  ** Store this number in "k".  Also compute szNew[] which is the total
  ** size of all cells on the i-th page and cntNew[] which is the index
  ** in b.apCell[] of the cell that divides page i from page i+1.  
  ** cntNew[k] should equal b.nCell.
  **
  ** Values computed by this block:
  **
  **           k: The total number of sibling pages
  **    szNew[i]: Spaced used on the i-th sibling page.
  **   cntNew[i]: Index in b.apCell[] and b.szCell[] for the first cell to
  **              the right of the i-th sibling page.
  ** usableSpace: Number of bytes of space available on each sibling.
  ** 
  */
  usableSpace = pBt->usableSize - 12 + leafCorrection;
  for(i=0; i<nOld; i++){
    MemPage *p = apOld[i];
    szNew[i] = usableSpace - p->nFree;
    if( szNew[i]<0 ){ rc = SQLITE_CORRUPT_BKPT; goto balance_cleanup; }
    for(j=0; j<p->nOverflow; j++){
      szNew[i] += 2 + p->xCellSize(p, p->apOvfl[j]);
    }
    cntNew[i] = cntOld[i];
  }
  k = nOld;
  for(i=0; i<k; i++){
    int sz;
    while( szNew[i]>usableSpace ){
      if( i+1>=k ){
        k = i+2;
        if( k>NB+2 ){ rc = SQLITE_CORRUPT_BKPT; goto balance_cleanup; }
        szNew[k-1] = 0;
        cntNew[k-1] = b.nCell;
      }
      sz = 2 + cachedCellSize(&b, cntNew[i]-1);
      szNew[i] -= sz;
      if( !leafData ){
        if( cntNew[i]<b.nCell ){
          sz = 2 + cachedCellSize(&b, cntNew[i]);
        }else{
          sz = 0;
        }
      }
      szNew[i+1] += sz;
      cntNew[i]--;
    }
    while( cntNew[i]<b.nCell ){
      sz = 2 + cachedCellSize(&b, cntNew[i]);
      if( szNew[i]+sz>usableSpace ) break;
      szNew[i] += sz;
      cntNew[i]++;
      if( !leafData ){
        if( cntNew[i]<b.nCell ){
          sz = 2 + cachedCellSize(&b, cntNew[i]);
        }else{
          sz = 0;
        }
      }
      szNew[i+1] -= sz;
    }
    if( cntNew[i]>=b.nCell ){
      k = i+1;
    }else if( cntNew[i] <= (i>0 ? cntNew[i-1] : 0) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto balance_cleanup;
    }
  }

  /*
  ** The packing computed by the previous block is biased toward the siblings
  ** on the left side (siblings with smaller keys). The left siblings are
  ** always nearly full, while the right-most sibling might be nearly empty.
  ** The next block of code attempts to adjust the packing of siblings to
  ** get a better balance.
  **
  ** This adjustment is more than an optimization.  The packing above might
  ** be so out of balance as to be illegal.  For example, the right-most
  ** sibling might be completely empty.  This adjustment is not optional.
  */
  for(i=k-1; i>0; i--){
    int szRight = szNew[i];  /* Size of sibling on the right */
    int szLeft = szNew[i-1]; /* Size of sibling on the left */
    int r;              /* Index of right-most cell in left sibling */
    int d;              /* Index of first cell to the left of right sibling */

    r = cntNew[i-1] - 1;
    d = r + 1 - leafData;
    (void)cachedCellSize(&b, d);
    do{
      assert( d<nMaxCells );
      assert( r<nMaxCells );
      (void)cachedCellSize(&b, r);
      if( szRight!=0
       && (bBulk || szRight+b.szCell[d]+2 > szLeft-(b.szCell[r]+2)) ){
        break;
      }
      szRight += b.szCell[d] + 2;
      szLeft -= b.szCell[r] + 2;
      cntNew[i-1] = r;
      r--;
      d--;
    }while( r>=0 );
    szNew[i] = szRight;
    szNew[i-1] = szLeft;
    if( cntNew[i-1] <= (i>1 ? cntNew[i-2] : 0) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto balance_cleanup;
    }
  }

  /* Sanity check:  For a non-corrupt database file one of the follwing
  ** must be true:
  **    (1) We found one or more cells (cntNew[0])>0), or
  **    (2) pPage is a virtual root page.  A virtual root page is when
  **        the real root page is page 1 and we are the only child of
  **        that page.
  */
  assert( cntNew[0]>0 || (pParent->pgno==1 && pParent->nCell==0) || CORRUPT_DB);
  TRACE(("BALANCE: old: %d(nc=%d) %d(nc=%d) %d(nc=%d)\n",
    apOld[0]->pgno, apOld[0]->nCell,
    nOld>=2 ? apOld[1]->pgno : 0, nOld>=2 ? apOld[1]->nCell : 0,
    nOld>=3 ? apOld[2]->pgno : 0, nOld>=3 ? apOld[2]->nCell : 0
  ));

  /*
  ** Allocate k new pages.  Reuse old pages where possible.
  */
  pageFlags = apOld[0]->aData[0];
  for(i=0; i<k; i++){
    MemPage *pNew;
    if( i<nOld ){
      pNew = apNew[i] = apOld[i];
      apOld[i] = 0;
      rc = sqlite3PagerWrite(pNew->pDbPage);
      nNew++;
      if( rc ) goto balance_cleanup;
    }else{
      assert( i>0 );
      rc = allocateBtreePage(pBt, &pNew, &pgno, (bBulk ? 1 : pgno), 0);
      if( rc ) goto balance_cleanup;
      zeroPage(pNew, pageFlags);
      apNew[i] = pNew;
      nNew++;
      cntOld[i] = b.nCell;

      /* Set the pointer-map entry for the new sibling page. */
      if( ISAUTOVACUUM ){
        ptrmapPut(pBt, pNew->pgno, PTRMAP_BTREE, pParent->pgno, &rc);
        if( rc!=SQLITE_OK ){
          goto balance_cleanup;
        }
      }
    }
  }

  /*
  ** Reassign page numbers so that the new pages are in ascending order. 
  ** This helps to keep entries in the disk file in order so that a scan
  ** of the table is closer to a linear scan through the file. That in turn 
  ** helps the operating system to deliver pages from the disk more rapidly.
  **
  ** An O(n^2) insertion sort algorithm is used, but since n is never more 
  ** than (NB+2) (a small constant), that should not be a problem.
  **
  ** When NB==3, this one optimization makes the database about 25% faster 
  ** for large insertions and deletions.
  */
  for(i=0; i<nNew; i++){
    aPgOrder[i] = aPgno[i] = apNew[i]->pgno;
    aPgFlags[i] = apNew[i]->pDbPage->flags;
    for(j=0; j<i; j++){
      if( aPgno[j]==aPgno[i] ){
        /* This branch is taken if the set of sibling pages somehow contains
        ** duplicate entries. This can happen if the database is corrupt. 
        ** It would be simpler to detect this as part of the loop below, but
        ** we do the detection here in order to avoid populating the pager
        ** cache with two separate objects associated with the same
        ** page number.  */
        assert( CORRUPT_DB );
        rc = SQLITE_CORRUPT_BKPT;
        goto balance_cleanup;
      }
    }
  }
  for(i=0; i<nNew; i++){
    int iBest = 0;                /* aPgno[] index of page number to use */
    for(j=1; j<nNew; j++){
      if( aPgOrder[j]<aPgOrder[iBest] ) iBest = j;
    }
    pgno = aPgOrder[iBest];
    aPgOrder[iBest] = 0xffffffff;
    if( iBest!=i ){
      if( iBest>i ){
        sqlite3PagerRekey(apNew[iBest]->pDbPage, pBt->nPage+iBest+1, 0);
      }
      sqlite3PagerRekey(apNew[i]->pDbPage, pgno, aPgFlags[iBest]);
      apNew[i]->pgno = pgno;
    }
  }

  TRACE(("BALANCE: new: %d(%d nc=%d) %d(%d nc=%d) %d(%d nc=%d) "
         "%d(%d nc=%d) %d(%d nc=%d)\n",
    apNew[0]->pgno, szNew[0], cntNew[0],
    nNew>=2 ? apNew[1]->pgno : 0, nNew>=2 ? szNew[1] : 0,
    nNew>=2 ? cntNew[1] - cntNew[0] - !leafData : 0,
    nNew>=3 ? apNew[2]->pgno : 0, nNew>=3 ? szNew[2] : 0,
    nNew>=3 ? cntNew[2] - cntNew[1] - !leafData : 0,
    nNew>=4 ? apNew[3]->pgno : 0, nNew>=4 ? szNew[3] : 0,
    nNew>=4 ? cntNew[3] - cntNew[2] - !leafData : 0,
    nNew>=5 ? apNew[4]->pgno : 0, nNew>=5 ? szNew[4] : 0,
    nNew>=5 ? cntNew[4] - cntNew[3] - !leafData : 0
  ));

  assert( sqlite3PagerIswriteable(pParent->pDbPage) );
  put4byte(pRight, apNew[nNew-1]->pgno);

  /* If the sibling pages are not leaves, ensure that the right-child pointer
  ** of the right-most new sibling page is set to the value that was 
  ** originally in the same field of the right-most old sibling page. */
  if( (pageFlags & PTF_LEAF)==0 && nOld!=nNew ){
    MemPage *pOld = (nNew>nOld ? apNew : apOld)[nOld-1];
    memcpy(&apNew[nNew-1]->aData[8], &pOld->aData[8], 4);
  }

  /* Make any required updates to pointer map entries associated with 
  ** cells stored on sibling pages following the balance operation. Pointer
  ** map entries associated with divider cells are set by the insertCell()
  ** routine. The associated pointer map entries are:
  **
  **   a) if the cell contains a reference to an overflow chain, the
  **      entry associated with the first page in the overflow chain, and
  **
  **   b) if the sibling pages are not leaves, the child page associated
  **      with the cell.
  **
  ** If the sibling pages are not leaves, then the pointer map entry 
  ** associated with the right-child of each sibling may also need to be 
  ** updated. This happens below, after the sibling pages have been 
  ** populated, not here.
  */
  if( ISAUTOVACUUM ){
    MemPage *pNew = apNew[0];
    u8 *aOld = pNew->aData;
    int cntOldNext = pNew->nCell + pNew->nOverflow;
    int usableSize = pBt->usableSize;
    int iNew = 0;
    int iOld = 0;

    for(i=0; i<b.nCell; i++){
      u8 *pCell = b.apCell[i];
      if( i==cntOldNext ){
        MemPage *pOld = (++iOld)<nNew ? apNew[iOld] : apOld[iOld];
        cntOldNext += pOld->nCell + pOld->nOverflow + !leafData;
        aOld = pOld->aData;
      }
      if( i==cntNew[iNew] ){
        pNew = apNew[++iNew];
        if( !leafData ) continue;
      }

      /* Cell pCell is destined for new sibling page pNew. Originally, it
      ** was either part of sibling page iOld (possibly an overflow cell), 
      ** or else the divider cell to the left of sibling page iOld. So,
      ** if sibling page iOld had the same page number as pNew, and if
      ** pCell really was a part of sibling page iOld (not a divider or
      ** overflow cell), we can skip updating the pointer map entries.  */
      if( iOld>=nNew
       || pNew->pgno!=aPgno[iOld]
       || pCell<aOld
       || pCell>=&aOld[usableSize]
      ){
        if( !leafCorrection ){
          ptrmapPut(pBt, get4byte(pCell), PTRMAP_BTREE, pNew->pgno, &rc);
        }
        if( cachedCellSize(&b,i)>pNew->minLocal ){
          ptrmapPutOvflPtr(pNew, pCell, &rc);
        }
        if( rc ) goto balance_cleanup;
      }
    }
  }

  /* Insert new divider cells into pParent. */
  for(i=0; i<nNew-1; i++){
    u8 *pCell;
    u8 *pTemp;
    int sz;
    MemPage *pNew = apNew[i];
    j = cntNew[i];

    assert( j<nMaxCells );
    assert( b.apCell[j]!=0 );
    pCell = b.apCell[j];
    sz = b.szCell[j] + leafCorrection;
    pTemp = &aOvflSpace[iOvflSpace];
    if( !pNew->leaf ){
      memcpy(&pNew->aData[8], pCell, 4);
    }else if( leafData ){
      /* If the tree is a leaf-data tree, and the siblings are leaves, 
      ** then there is no divider cell in b.apCell[]. Instead, the divider 
      ** cell consists of the integer key for the right-most cell of 
      ** the sibling-page assembled above only.
      */
      CellInfo info;
      j--;
      pNew->xParseCell(pNew, b.apCell[j], &info);
      pCell = pTemp;
      sz = 4 + putVarint(&pCell[4], info.nKey);
      pTemp = 0;
    }else{
      pCell -= 4;
      /* Obscure case for non-leaf-data trees: If the cell at pCell was
      ** previously stored on a leaf node, and its reported size was 4
      ** bytes, then it may actually be smaller than this 
      ** (see btreeParseCellPtr(), 4 bytes is the minimum size of
      ** any cell). But it is important to pass the correct size to 
      ** insertCell(), so reparse the cell now.
      **
      ** Note that this can never happen in an SQLite data file, as all
      ** cells are at least 4 bytes. It only happens in b-trees used
      ** to evaluate "IN (SELECT ...)" and similar clauses.
      */
      if( b.szCell[j]==4 ){
        assert(leafCorrection==4);
        sz = pParent->xCellSize(pParent, pCell);
      }
    }
    iOvflSpace += sz;
    assert( sz<=pBt->maxLocal+23 );
    assert( iOvflSpace <= (int)pBt->pageSize );
    insertCell(pParent, nxDiv+i, pCell, sz, pTemp, pNew->pgno, &rc);
    if( rc!=SQLITE_OK ) goto balance_cleanup;
    assert( sqlite3PagerIswriteable(pParent->pDbPage) );
  }

  /* Now update the actual sibling pages. The order in which they are updated
  ** is important, as this code needs to avoid disrupting any page from which
  ** cells may still to be read. In practice, this means:
  **
  **  (1) If cells are moving left (from apNew[iPg] to apNew[iPg-1])
  **      then it is not safe to update page apNew[iPg] until after
  **      the left-hand sibling apNew[iPg-1] has been updated.
  **
  **  (2) If cells are moving right (from apNew[iPg] to apNew[iPg+1])
  **      then it is not safe to update page apNew[iPg] until after
  **      the right-hand sibling apNew[iPg+1] has been updated.
  **
  ** If neither of the above apply, the page is safe to update.
  **
  ** The iPg value in the following loop starts at nNew-1 goes down
  ** to 0, then back up to nNew-1 again, thus making two passes over
  ** the pages.  On the initial downward pass, only condition (1) above
  ** needs to be tested because (2) will always be true from the previous
  ** step.  On the upward pass, both conditions are always true, so the
  ** upwards pass simply processes pages that were missed on the downward
  ** pass.
  */
  for(i=1-nNew; i<nNew; i++){
    int iPg = i<0 ? -i : i;
    assert( iPg>=0 && iPg<nNew );
    if( abDone[iPg] ) continue;         /* Skip pages already processed */
    if( i>=0                            /* On the upwards pass, or... */
     || cntOld[iPg-1]>=cntNew[iPg-1]    /* Condition (1) is true */
    ){
      int iNew;
      int iOld;
      int nNewCell;

      /* Verify condition (1):  If cells are moving left, update iPg
      ** only after iPg-1 has already been updated. */
      assert( iPg==0 || cntOld[iPg-1]>=cntNew[iPg-1] || abDone[iPg-1] );

      /* Verify condition (2):  If cells are moving right, update iPg
      ** only after iPg+1 has already been updated. */
      assert( cntNew[iPg]>=cntOld[iPg] || abDone[iPg+1] );

      if( iPg==0 ){
        iNew = iOld = 0;
        nNewCell = cntNew[0];
      }else{
        iOld = iPg<nOld ? (cntOld[iPg-1] + !leafData) : b.nCell;
        iNew = cntNew[iPg-1] + !leafData;
        nNewCell = cntNew[iPg] - iNew;
      }

      rc = editPage(apNew[iPg], iOld, iNew, nNewCell, &b);
      if( rc ) goto balance_cleanup;
      abDone[iPg]++;
      apNew[iPg]->nFree = usableSpace-szNew[iPg];
      assert( apNew[iPg]->nOverflow==0 );
      assert( apNew[iPg]->nCell==nNewCell );
    }
  }

  /* All pages have been processed exactly once */
  assert( memcmp(abDone, "\01\01\01\01\01", nNew)==0 );

  assert( nOld>0 );
  assert( nNew>0 );

  if( isRoot && pParent->nCell==0 && pParent->hdrOffset<=apNew[0]->nFree ){
    /* The root page of the b-tree now contains no cells. The only sibling
    ** page is the right-child of the parent. Copy the contents of the
    ** child page into the parent, decreasing the overall height of the
    ** b-tree structure by one. This is described as the "balance-shallower"
    ** sub-algorithm in some documentation.
    **
    ** If this is an auto-vacuum database, the call to copyNodeContent() 
    ** sets all pointer-map entries corresponding to database image pages 
    ** for which the pointer is stored within the content being copied.
    **
    ** It is critical that the child page be defragmented before being
    ** copied into the parent, because if the parent is page 1 then it will
    ** by smaller than the child due to the database header, and so all the
    ** free space needs to be up front.
    */
    assert( nNew==1 || CORRUPT_DB );
    rc = defragmentPage(apNew[0]);
    testcase( rc!=SQLITE_OK );
    assert( apNew[0]->nFree == 
        (get2byte(&apNew[0]->aData[5])-apNew[0]->cellOffset-apNew[0]->nCell*2)
      || rc!=SQLITE_OK
    );
    copyNodeContent(apNew[0], pParent, &rc);
    freePage(apNew[0], &rc);
  }else if( ISAUTOVACUUM && !leafCorrection ){
    /* Fix the pointer map entries associated with the right-child of each
    ** sibling page. All other pointer map entries have already been taken
    ** care of.  */
    for(i=0; i<nNew; i++){
      u32 key = get4byte(&apNew[i]->aData[8]);
      ptrmapPut(pBt, key, PTRMAP_BTREE, apNew[i]->pgno, &rc);
    }
  }

  assert( pParent->isInit );
  TRACE(("BALANCE: finished: old=%d new=%d cells=%d\n",
          nOld, nNew, b.nCell));

  /* Free any old pages that were not reused as new pages.
  */
  for(i=nNew; i<nOld; i++){
    freePage(apOld[i], &rc);
  }

#if 0
  if( ISAUTOVACUUM && rc==SQLITE_OK && apNew[0]->isInit ){
    /* The ptrmapCheckPages() contains assert() statements that verify that
    ** all pointer map pages are set correctly. This is helpful while 
    ** debugging. This is usually disabled because a corrupt database may
    ** cause an assert() statement to fail.  */
    ptrmapCheckPages(apNew, nNew);
    ptrmapCheckPages(&pParent, 1);
  }
#endif

  /*
  ** Cleanup before returning.
  */
balance_cleanup:
  sqlite3ScratchFree(b.apCell);
  for(i=0; i<nOld; i++){
    releasePage(apOld[i]);
  }
  for(i=0; i<nNew; i++){
    releasePage(apNew[i]);
  }

  return rc;
}
#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM)
#pragma optimize("", on)
#endif


/*
** This function is called when the root page of a b-tree structure is
** overfull (has one or more overflow pages).
**
** A new child page is allocated and the contents of the current root
** page, including overflow cells, are copied into the child. The root
** page is then overwritten to make it an empty page with the right-child 
** pointer pointing to the new page.
**
** Before returning, all pointer-map entries corresponding to pages 
** that the new child-page now contains pointers to are updated. The
** entry corresponding to the new right-child pointer of the root
** page is also updated.
**
** If successful, *ppChild is set to contain a reference to the child 
** page and SQLITE_OK is returned. In this case the caller is required
** to call releasePage() on *ppChild exactly once. If an error occurs,
** an error code is returned and *ppChild is set to 0.
*/
static int balance_deeper(MemPage *pRoot, MemPage **ppChild){
  int rc;                        /* Return value from subprocedures */
  MemPage *pChild = 0;           /* Pointer to a new child page */
  Pgno pgnoChild = 0;            /* Page number of the new child page */
  BtShared *pBt = pRoot->pBt;    /* The BTree */

  assert( pRoot->nOverflow>0 );
  assert( sqlite3_mutex_held(pBt->mutex) );

  /* Make pRoot, the root page of the b-tree, writable. Allocate a new 
  ** page that will become the new right-child of pPage. Copy the contents
  ** of the node stored on pRoot into the new child page.
  */
  rc = sqlite3PagerWrite(pRoot->pDbPage);
  if( rc==SQLITE_OK ){
    rc = allocateBtreePage(pBt,&pChild,&pgnoChild,pRoot->pgno,0);
    copyNodeContent(pRoot, pChild, &rc);
    if( ISAUTOVACUUM ){
      ptrmapPut(pBt, pgnoChild, PTRMAP_BTREE, pRoot->pgno, &rc);
    }
  }
  if( rc ){
    *ppChild = 0;
    releasePage(pChild);
    return rc;
  }
  assert( sqlite3PagerIswriteable(pChild->pDbPage) );
  assert( sqlite3PagerIswriteable(pRoot->pDbPage) );
  assert( pChild->nCell==pRoot->nCell );

  TRACE(("BALANCE: copy root %d into %d\n", pRoot->pgno, pChild->pgno));

  /* Copy the overflow cells from pRoot to pChild */
  memcpy(pChild->aiOvfl, pRoot->aiOvfl,
         pRoot->nOverflow*sizeof(pRoot->aiOvfl[0]));
  memcpy(pChild->apOvfl, pRoot->apOvfl,
         pRoot->nOverflow*sizeof(pRoot->apOvfl[0]));
  pChild->nOverflow = pRoot->nOverflow;

  /* Zero the contents of pRoot. Then install pChild as the right-child. */
  zeroPage(pRoot, pChild->aData[0] & ~PTF_LEAF);
  put4byte(&pRoot->aData[pRoot->hdrOffset+8], pgnoChild);

  *ppChild = pChild;
  return SQLITE_OK;
}

/*
** The page that pCur currently points to has just been modified in
** some way. This function figures out if this modification means the
** tree needs to be balanced, and if so calls the appropriate balancing 
** routine. Balancing routines are:
**
**   balance_quick()
**   balance_deeper()
**   balance_nonroot()
*/
static int balance(BtCursor *pCur){
  int rc = SQLITE_OK;
  const int nMin = pCur->pBt->usableSize * 2 / 3;
  u8 aBalanceQuickSpace[13];
  u8 *pFree = 0;

  TESTONLY( int balance_quick_called = 0 );
  TESTONLY( int balance_deeper_called = 0 );

  do {
    int iPage = pCur->iPage;
    MemPage *pPage = pCur->apPage[iPage];

    if( iPage==0 ){
      if( pPage->nOverflow ){
        /* The root page of the b-tree is overfull. In this case call the
        ** balance_deeper() function to create a new child for the root-page
        ** and copy the current contents of the root-page to it. The
        ** next iteration of the do-loop will balance the child page.
        */ 
        assert( (balance_deeper_called++)==0 );
        rc = balance_deeper(pPage, &pCur->apPage[1]);
        if( rc==SQLITE_OK ){
          pCur->iPage = 1;
          pCur->aiIdx[0] = 0;
          pCur->aiIdx[1] = 0;
          assert( pCur->apPage[1]->nOverflow );
        }
      }else{
        break;
      }
    }else if( pPage->nOverflow==0 && pPage->nFree<=nMin ){
      break;
    }else{
      MemPage * const pParent = pCur->apPage[iPage-1];
      int const iIdx = pCur->aiIdx[iPage-1];

      rc = sqlite3PagerWrite(pParent->pDbPage);
      if( rc==SQLITE_OK ){
#ifndef SQLITE_OMIT_QUICKBALANCE
        if( pPage->intKeyLeaf
         && pPage->nOverflow==1
         && pPage->aiOvfl[0]==pPage->nCell
         && pParent->pgno!=1
         && pParent->nCell==iIdx
        ){
          /* Call balance_quick() to create a new sibling of pPage on which
          ** to store the overflow cell. balance_quick() inserts a new cell
          ** into pParent, which may cause pParent overflow. If this
          ** happens, the next iteration of the do-loop will balance pParent 
          ** use either balance_nonroot() or balance_deeper(). Until this
          ** happens, the overflow cell is stored in the aBalanceQuickSpace[]
          ** buffer. 
          **
          ** The purpose of the following assert() is to check that only a
          ** single call to balance_quick() is made for each call to this
          ** function. If this were not verified, a subtle bug involving reuse
          ** of the aBalanceQuickSpace[] might sneak in.
          */
          assert( (balance_quick_called++)==0 );
          rc = balance_quick(pParent, pPage, aBalanceQuickSpace);
        }else
#endif
        {
          /* In this case, call balance_nonroot() to redistribute cells
          ** between pPage and up to 2 of its sibling pages. This involves
          ** modifying the contents of pParent, which may cause pParent to
          ** become overfull or underfull. The next iteration of the do-loop
          ** will balance the parent page to correct this.
          ** 
          ** If the parent page becomes overfull, the overflow cell or cells
          ** are stored in the pSpace buffer allocated immediately below. 
          ** A subsequent iteration of the do-loop will deal with this by
          ** calling balance_nonroot() (balance_deeper() may be called first,
          ** but it doesn't deal with overflow cells - just moves them to a
          ** different page). Once this subsequent call to balance_nonroot() 
          ** has completed, it is safe to release the pSpace buffer used by
          ** the previous call, as the overflow cell data will have been 
          ** copied either into the body of a database page or into the new
          ** pSpace buffer passed to the latter call to balance_nonroot().
          */
          u8 *pSpace = sqlite3PageMalloc(pCur->pBt->pageSize);
          rc = balance_nonroot(pParent, iIdx, pSpace, iPage==1,
                               pCur->hints&BTREE_BULKLOAD);
          if( pFree ){
            /* If pFree is not NULL, it points to the pSpace buffer used 
            ** by a previous call to balance_nonroot(). Its contents are
            ** now stored either on real database pages or within the 
            ** new pSpace buffer, so it may be safely freed here. */
            sqlite3PageFree(pFree);
          }

          /* The pSpace buffer will be freed after the next call to
          ** balance_nonroot(), or just before this function returns, whichever
          ** comes first. */
          pFree = pSpace;
        }
      }

      pPage->nOverflow = 0;

      /* The next iteration of the do-loop balances the parent page. */
      releasePage(pPage);
      pCur->iPage--;
      assert( pCur->iPage>=0 );
    }
  }while( rc==SQLITE_OK );

  if( pFree ){
    sqlite3PageFree(pFree);
  }
  return rc;
}


/*
** Insert a new record into the BTree.  The key is given by (pKey,nKey)
** and the data is given by (pData,nData).  The cursor is used only to
** define what table the record should be inserted into.  The cursor
** is left pointing at a random location.
**
** For an INTKEY table, only the nKey value of the key is used.  pKey is
** ignored.  For a ZERODATA table, the pData and nData are both ignored.
**
** If the seekResult parameter is non-zero, then a successful call to
** MovetoUnpacked() to seek cursor pCur to (pKey, nKey) has already
** been performed. seekResult is the search result returned (a negative
** number if pCur points at an entry that is smaller than (pKey, nKey), or
** a positive value if pCur points at an entry that is larger than 
** (pKey, nKey)). 
**
** If the seekResult parameter is non-zero, then the caller guarantees that
** cursor pCur is pointing at the existing copy of a row that is to be
** overwritten.  If the seekResult parameter is 0, then cursor pCur may
** point to any entry or to no entry at all and so this function has to seek
** the cursor before the new key can be inserted.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeInsert(
  BtCursor *pCur,                /* Insert data into the table of this cursor */
  const void *pKey, i64 nKey,    /* The key of the new record */
  const void *pData, int nData,  /* The data of the new record */
  int nZero,                     /* Number of extra 0 bytes to append to data */
  int appendBias,                /* True if this is likely an append */
  int seekResult                 /* Result of prior MovetoUnpacked() call */
){
  int rc;
  int loc = seekResult;          /* -1: before desired location  +1: after */
  int szNew = 0;
  int idx;
  MemPage *pPage;
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;
  unsigned char *oldCell;
  unsigned char *newCell = 0;

  if( pCur->eState==CURSOR_FAULT ){
    assert( pCur->skipNext!=SQLITE_OK );
    return pCur->skipNext;
  }

  assert( cursorHoldsMutex(pCur) );
  assert( (pCur->curFlags & BTCF_WriteFlag)!=0
              && pBt->inTransaction==TRANS_WRITE
              && (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );

  /* Assert that the caller has been consistent. If this cursor was opened
  ** expecting an index b-tree, then the caller should be inserting blob
  ** keys with no associated data. If the cursor was opened expecting an
  ** intkey table, the caller should be inserting integer keys with a
  ** blob of associated data.  */
  assert( (pKey==0)==(pCur->pKeyInfo==0) );

  /* Save the positions of any other cursors open on this table.
  **
  ** In some cases, the call to btreeMoveto() below is a no-op. For
  ** example, when inserting data into a table with auto-generated integer
  ** keys, the VDBE layer invokes sqlite3BtreeLast() to figure out the 
  ** integer key to use. It then calls this function to actually insert the 
  ** data into the intkey B-Tree. In this case btreeMoveto() recognizes
  ** that the cursor is already where it needs to be and returns without
  ** doing any work. To avoid thwarting these optimizations, it is important
  ** not to clear the cursor here.
  */
  if( pCur->curFlags & BTCF_Multiple ){
    rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
    if( rc ) return rc;
  }

  if( pCur->pKeyInfo==0 ){
    assert( pKey==0 );
    /* If this is an insert into a table b-tree, invalidate any incrblob 
    ** cursors open on the row being replaced */
    invalidateIncrblobCursors(p, nKey, 0);

    /* If the cursor is currently on the last row and we are appending a
    ** new row onto the end, set the "loc" to avoid an unnecessary
    ** btreeMoveto() call */
    if( (pCur->curFlags&BTCF_ValidNKey)!=0 && nKey>0
      && pCur->info.nKey==nKey-1 ){
       loc = -1;
    }else if( loc==0 ){
      rc = sqlite3BtreeMovetoUnpacked(pCur, 0, nKey, appendBias, &loc);
      if( rc ) return rc;
    }
  }else if( loc==0 ){
    rc = btreeMoveto(pCur, pKey, nKey, appendBias, &loc);
    if( rc ) return rc;
  }
  assert( pCur->eState==CURSOR_VALID || (pCur->eState==CURSOR_INVALID && loc) );

  pPage = pCur->apPage[pCur->iPage];
  assert( pPage->intKey || nKey>=0 );
  assert( pPage->leaf || !pPage->intKey );

  TRACE(("INSERT: table=%d nkey=%lld ndata=%d page=%d %s\n",
          pCur->pgnoRoot, nKey, nData, pPage->pgno,
          loc==0 ? "overwrite" : "new entry"));
  assert( pPage->isInit );
  newCell = pBt->pTmpSpace;
  assert( newCell!=0 );
  rc = fillInCell(pPage, newCell, pKey, nKey, pData, nData, nZero, &szNew);
  if( rc ) goto end_insert;
  assert( szNew==pPage->xCellSize(pPage, newCell) );
  assert( szNew <= MX_CELL_SIZE(pBt) );
  idx = pCur->aiIdx[pCur->iPage];
  if( loc==0 ){
    u16 szOld;
    assert( idx<pPage->nCell );
    rc = sqlite3PagerWrite(pPage->pDbPage);
    if( rc ){
      goto end_insert;
    }
    oldCell = findCell(pPage, idx);
    if( !pPage->leaf ){
      memcpy(newCell, oldCell, 4);
    }
    rc = clearCell(pPage, oldCell, &szOld);
    dropCell(pPage, idx, szOld, &rc);
    if( rc ) goto end_insert;
  }else if( loc<0 && pPage->nCell>0 ){
    assert( pPage->leaf );
    idx = ++pCur->aiIdx[pCur->iPage];
  }else{
    assert( pPage->leaf );
  }
  insertCell(pPage, idx, newCell, szNew, 0, 0, &rc);
  assert( rc!=SQLITE_OK || pPage->nCell>0 || pPage->nOverflow>0 );

  /* If no error has occurred and pPage has an overflow cell, call balance() 
  ** to redistribute the cells within the tree. Since balance() may move
  ** the cursor, zero the BtCursor.info.nSize and BTCF_ValidNKey
  ** variables.
  **
  ** Previous versions of SQLite called moveToRoot() to move the cursor
  ** back to the root page as balance() used to invalidate the contents
  ** of BtCursor.apPage[] and BtCursor.aiIdx[]. Instead of doing that,
  ** set the cursor state to "invalid". This makes common insert operations
  ** slightly faster.
  **
  ** There is a subtle but important optimization here too. When inserting
  ** multiple records into an intkey b-tree using a single cursor (as can
  ** happen while processing an "INSERT INTO ... SELECT" statement), it
  ** is advantageous to leave the cursor pointing to the last entry in
  ** the b-tree if possible. If the cursor is left pointing to the last
  ** entry in the table, and the next row inserted has an integer key
  ** larger than the largest existing key, it is possible to insert the
  ** row without seeking the cursor. This can be a big performance boost.
  */
  pCur->info.nSize = 0;
  if( rc==SQLITE_OK && pPage->nOverflow ){
    pCur->curFlags &= ~(BTCF_ValidNKey);
    rc = balance(pCur);

    /* Must make sure nOverflow is reset to zero even if the balance()
    ** fails. Internal data structure corruption will result otherwise. 
    ** Also, set the cursor state to invalid. This stops saveCursorPosition()
    ** from trying to save the current position of the cursor.  */
    pCur->apPage[pCur->iPage]->nOverflow = 0;
    pCur->eState = CURSOR_INVALID;
  }
  assert( pCur->apPage[pCur->iPage]->nOverflow==0 );

end_insert:
  return rc;
}

/*
** Delete the entry that the cursor is pointing to. 
**
** If the second parameter is zero, then the cursor is left pointing at an
** arbitrary location after the delete. If it is non-zero, then the cursor 
** is left in a state such that the next call to BtreeNext() or BtreePrev()
** moves it to the same row as it would if the call to BtreeDelete() had
** been omitted.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeDelete(BtCursor *pCur, int bPreserve){
  Btree *p = pCur->pBtree;
  BtShared *pBt = p->pBt;              
  int rc;                              /* Return code */
  MemPage *pPage;                      /* Page to delete cell from */
  unsigned char *pCell;                /* Pointer to cell to delete */
  int iCellIdx;                        /* Index of cell to delete */
  int iCellDepth;                      /* Depth of node containing pCell */ 
  u16 szCell;                          /* Size of the cell being deleted */
  int bSkipnext = 0;                   /* Leaf cursor in SKIPNEXT state */

  assert( cursorHoldsMutex(pCur) );
  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );
  assert( pCur->curFlags & BTCF_WriteFlag );
  assert( hasSharedCacheTableLock(p, pCur->pgnoRoot, pCur->pKeyInfo!=0, 2) );
  assert( !hasReadConflicts(p, pCur->pgnoRoot) );
  assert( pCur->aiIdx[pCur->iPage]<pCur->apPage[pCur->iPage]->nCell );
  assert( pCur->eState==CURSOR_VALID );

  iCellDepth = pCur->iPage;
  iCellIdx = pCur->aiIdx[iCellDepth];
  pPage = pCur->apPage[iCellDepth];
  pCell = findCell(pPage, iCellIdx);

  /* If the page containing the entry to delete is not a leaf page, move
  ** the cursor to the largest entry in the tree that is smaller than
  ** the entry being deleted. This cell will replace the cell being deleted
  ** from the internal node. The 'previous' entry is used for this instead
  ** of the 'next' entry, as the previous entry is always a part of the
  ** sub-tree headed by the child page of the cell being deleted. This makes
  ** balancing the tree following the delete operation easier.  */
  if( !pPage->leaf ){
    int notUsed = 0;
    rc = sqlite3BtreePrevious(pCur, &notUsed);
    if( rc ) return rc;
  }

  /* Save the positions of any other cursors open on this table before
  ** making any modifications.  */
  if( pCur->curFlags & BTCF_Multiple ){
    rc = saveAllCursors(pBt, pCur->pgnoRoot, pCur);
    if( rc ) return rc;
  }

  /* If this is a delete operation to remove a row from a table b-tree,
  ** invalidate any incrblob cursors open on the row being deleted.  */
  if( pCur->pKeyInfo==0 ){
    invalidateIncrblobCursors(p, pCur->info.nKey, 0);
  }

  /* If the bPreserve flag is set to true, then the cursor position must
  ** be preserved following this delete operation. If the current delete
  ** will cause a b-tree rebalance, then this is done by saving the cursor
  ** key and leaving the cursor in CURSOR_REQUIRESEEK state before 
  ** returning. 
  **
  ** Or, if the current delete will not cause a rebalance, then the cursor
  ** will be left in CURSOR_SKIPNEXT state pointing to the entry immediately
  ** before or after the deleted entry. In this case set bSkipnext to true.  */
  if( bPreserve ){
    if( !pPage->leaf 
     || (pPage->nFree+cellSizePtr(pPage,pCell)+2)>(int)(pBt->usableSize*2/3)
    ){
      /* A b-tree rebalance will be required after deleting this entry.
      ** Save the cursor key.  */
      rc = saveCursorKey(pCur);
      if( rc ) return rc;
    }else{
      bSkipnext = 1;
    }
  }

  /* Make the page containing the entry to be deleted writable. Then free any
  ** overflow pages associated with the entry and finally remove the cell
  ** itself from within the page.  */
  rc = sqlite3PagerWrite(pPage->pDbPage);
  if( rc ) return rc;
  rc = clearCell(pPage, pCell, &szCell);
  dropCell(pPage, iCellIdx, szCell, &rc);
  if( rc ) return rc;

  /* If the cell deleted was not located on a leaf page, then the cursor
  ** is currently pointing to the largest entry in the sub-tree headed
  ** by the child-page of the cell that was just deleted from an internal
  ** node. The cell from the leaf node needs to be moved to the internal
  ** node to replace the deleted cell.  */
  if( !pPage->leaf ){
    MemPage *pLeaf = pCur->apPage[pCur->iPage];
    int nCell;
    Pgno n = pCur->apPage[iCellDepth+1]->pgno;
    unsigned char *pTmp;

    pCell = findCell(pLeaf, pLeaf->nCell-1);
    if( pCell<&pLeaf->aData[4] ) return SQLITE_CORRUPT_BKPT;
    nCell = pLeaf->xCellSize(pLeaf, pCell);
    assert( MX_CELL_SIZE(pBt) >= nCell );
    pTmp = pBt->pTmpSpace;
    assert( pTmp!=0 );
    rc = sqlite3PagerWrite(pLeaf->pDbPage);
    insertCell(pPage, iCellIdx, pCell-4, nCell+4, pTmp, n, &rc);
    dropCell(pLeaf, pLeaf->nCell-1, nCell, &rc);
    if( rc ) return rc;
  }

  /* Balance the tree. If the entry deleted was located on a leaf page,
  ** then the cursor still points to that page. In this case the first
  ** call to balance() repairs the tree, and the if(...) condition is
  ** never true.
  **
  ** Otherwise, if the entry deleted was on an internal node page, then
  ** pCur is pointing to the leaf page from which a cell was removed to
  ** replace the cell deleted from the internal node. This is slightly
  ** tricky as the leaf node may be underfull, and the internal node may
  ** be either under or overfull. In this case run the balancing algorithm
  ** on the leaf node first. If the balance proceeds far enough up the
  ** tree that we can be sure that any problem in the internal node has
  ** been corrected, so be it. Otherwise, after balancing the leaf node,
  ** walk the cursor up the tree to the internal node and balance it as 
  ** well.  */
  rc = balance(pCur);
  if( rc==SQLITE_OK && pCur->iPage>iCellDepth ){
    while( pCur->iPage>iCellDepth ){
      releasePage(pCur->apPage[pCur->iPage--]);
    }
    rc = balance(pCur);
  }

  if( rc==SQLITE_OK ){
    if( bSkipnext ){
      assert( bPreserve && pCur->iPage==iCellDepth );
      assert( pPage==pCur->apPage[pCur->iPage] );
      assert( (pPage->nCell>0 || CORRUPT_DB) && iCellIdx<=pPage->nCell );
      pCur->eState = CURSOR_SKIPNEXT;
      if( iCellIdx>=pPage->nCell ){
        pCur->skipNext = -1;
        pCur->aiIdx[iCellDepth] = pPage->nCell-1;
      }else{
        pCur->skipNext = 1;
      }
    }else{
      rc = moveToRoot(pCur);
      if( bPreserve ){
        pCur->eState = CURSOR_REQUIRESEEK;
      }
    }
  }
  return rc;
}

/*
** Create a new BTree table.  Write into *piTable the page
** number for the root page of the new table.
**
** The type of type is determined by the flags parameter.  Only the
** following values of flags are currently in use.  Other values for
** flags might not work:
**
**     BTREE_INTKEY|BTREE_LEAFDATA     Used for SQL tables with rowid keys
**     BTREE_ZERODATA                  Used for SQL indices
*/
static int btreeCreateTable(Btree *p, int *piTable, int createTabFlags){
  BtShared *pBt = p->pBt;
  MemPage *pRoot;
  Pgno pgnoRoot;
  int rc;
  int ptfFlags;          /* Page-type flage for the root page of new table */

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( pBt->inTransaction==TRANS_WRITE );
  assert( (pBt->btsFlags & BTS_READ_ONLY)==0 );

#ifdef SQLITE_OMIT_AUTOVACUUM
  rc = allocateBtreePage(pBt, &pRoot, &pgnoRoot, 1, 0);
  if( rc ){
    return rc;
  }
#else
  if( pBt->autoVacuum ){
    Pgno pgnoMove;      /* Move a page here to make room for the root-page */
    MemPage *pPageMove; /* The page to move to. */

    /* Creating a new table may probably require moving an existing database
    ** to make room for the new tables root page. In case this page turns
    ** out to be an overflow page, delete all overflow page-map caches
    ** held by open cursors.
    */
    invalidateAllOverflowCache(pBt);

    /* Read the value of meta[3] from the database to determine where the
    ** root page of the new table should go. meta[3] is the largest root-page
    ** created so far, so the new root-page is (meta[3]+1).
    */
    sqlite3BtreeGetMeta(p, BTREE_LARGEST_ROOT_PAGE, &pgnoRoot);
    pgnoRoot++;

    /* The new root-page may not be allocated on a pointer-map page, or the
    ** PENDING_BYTE page.
    */
    while( pgnoRoot==PTRMAP_PAGENO(pBt, pgnoRoot) ||
        pgnoRoot==PENDING_BYTE_PAGE(pBt) ){
      pgnoRoot++;
    }
    assert( pgnoRoot>=3 || CORRUPT_DB );
    testcase( pgnoRoot<3 );

    /* Allocate a page. The page that currently resides at pgnoRoot will
    ** be moved to the allocated page (unless the allocated page happens
    ** to reside at pgnoRoot).
    */
    rc = allocateBtreePage(pBt, &pPageMove, &pgnoMove, pgnoRoot, BTALLOC_EXACT);
    if( rc!=SQLITE_OK ){
      return rc;
    }

    if( pgnoMove!=pgnoRoot ){
      /* pgnoRoot is the page that will be used for the root-page of
      ** the new table (assuming an error did not occur). But we were
      ** allocated pgnoMove. If required (i.e. if it was not allocated
      ** by extending the file), the current page at position pgnoMove
      ** is already journaled.
      */
      u8 eType = 0;
      Pgno iPtrPage = 0;

      /* Save the positions of any open cursors. This is required in
      ** case they are holding a reference to an xFetch reference
      ** corresponding to page pgnoRoot.  */
      rc = saveAllCursors(pBt, 0, 0);
      releasePage(pPageMove);
      if( rc!=SQLITE_OK ){
        return rc;
      }

      /* Move the page currently at pgnoRoot to pgnoMove. */
      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
      if( eType==PTRMAP_ROOTPAGE || eType==PTRMAP_FREEPAGE ){
        rc = SQLITE_CORRUPT_BKPT;
      }
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
      assert( eType!=PTRMAP_ROOTPAGE );
      assert( eType!=PTRMAP_FREEPAGE );
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove, 0);
      releasePage(pRoot);

      /* Obtain the page at pgnoRoot */
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = btreeGetPage(pBt, pgnoRoot, &pRoot, 0);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = sqlite3PagerWrite(pRoot->pDbPage);
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
    }else{
      pRoot = pPageMove;
    } 

    /* Update the pointer-map and meta-data with the new root-page number. */
    ptrmapPut(pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0, &rc);
    if( rc ){
      releasePage(pRoot);
      return rc;
    }

    /* When the new root page was allocated, page 1 was made writable in
    ** order either to increase the database filesize, or to decrement the
    ** freelist count.  Hence, the sqlite3BtreeUpdateMeta() call cannot fail.
    */
    assert( sqlite3PagerIswriteable(pBt->pPage1->pDbPage) );
    rc = sqlite3BtreeUpdateMeta(p, 4, pgnoRoot);
    if( NEVER(rc) ){
      releasePage(pRoot);
      return rc;
    }

  }else{
    rc = allocateBtreePage(pBt, &pRoot, &pgnoRoot, 1, 0);
    if( rc ) return rc;
  }
#endif
  assert( sqlite3PagerIswriteable(pRoot->pDbPage) );
  if( createTabFlags & BTREE_INTKEY ){
    ptfFlags = PTF_INTKEY | PTF_LEAFDATA | PTF_LEAF;
  }else{
    ptfFlags = PTF_ZERODATA | PTF_LEAF;
  }
  zeroPage(pRoot, ptfFlags);
  sqlite3PagerUnref(pRoot->pDbPage);
  assert( (pBt->openFlags & BTREE_SINGLE)==0 || pgnoRoot==2 );
  *piTable = (int)pgnoRoot;
  return SQLITE_OK;
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCreateTable(Btree *p, int *piTable, int flags){
  int rc;
  sqlite3BtreeEnter(p);
  rc = btreeCreateTable(p, piTable, flags);
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Erase the given database page and all its children.  Return
** the page to the freelist.
*/
static int clearDatabasePage(
  BtShared *pBt,           /* The BTree that contains the table */
  Pgno pgno,               /* Page number to clear */
  int freePageFlag,        /* Deallocate page if true */
  int *pnChange            /* Add number of Cells freed to this counter */
){
  MemPage *pPage;
  int rc;
  unsigned char *pCell;
  int i;
  int hdr;
  u16 szCell;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>btreePagecount(pBt) ){
    return SQLITE_CORRUPT_BKPT;
  }
  rc = getAndInitPage(pBt, pgno, &pPage, 0, 0);
  if( rc ) return rc;
  if( pPage->bBusy ){
    rc = SQLITE_CORRUPT_BKPT;
    goto cleardatabasepage_out;
  }
  pPage->bBusy = 1;
  hdr = pPage->hdrOffset;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
    if( !pPage->leaf ){
      rc = clearDatabasePage(pBt, get4byte(pCell), 1, pnChange);
      if( rc ) goto cleardatabasepage_out;
    }
    rc = clearCell(pPage, pCell, &szCell);
    if( rc ) goto cleardatabasepage_out;
  }
  if( !pPage->leaf ){
    rc = clearDatabasePage(pBt, get4byte(&pPage->aData[hdr+8]), 1, pnChange);
    if( rc ) goto cleardatabasepage_out;
  }else if( pnChange ){
    assert( pPage->intKey || CORRUPT_DB );
    testcase( !pPage->intKey );
    *pnChange += pPage->nCell;
  }
  if( freePageFlag ){
    freePage(pPage, &rc);
  }else if( (rc = sqlite3PagerWrite(pPage->pDbPage))==0 ){
    zeroPage(pPage, pPage->aData[hdr] | PTF_LEAF);
  }

cleardatabasepage_out:
  pPage->bBusy = 0;
  releasePage(pPage);
  return rc;
}

/*
** Delete all information from a single table in the database.  iTable is
** the page number of the root of the table.  After this routine returns,
** the root page is empty, but still exists.
**
** This routine will fail with SQLITE_LOCKED if there are any open
** read cursors on the table.  Open write cursors are moved to the
** root of the table.
**
** If pnChange is not NULL, then table iTable must be an intkey table. The
** integer value pointed to by pnChange is incremented by the number of
** entries in the table.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeClearTable(Btree *p, int iTable, int *pnChange){
  int rc;
  BtShared *pBt = p->pBt;
  sqlite3BtreeEnter(p);
  assert( p->inTrans==TRANS_WRITE );

  rc = saveAllCursors(pBt, (Pgno)iTable, 0);

  if( SQLITE_OK==rc ){
    /* Invalidate all incrblob cursors open on table iTable (assuming iTable
    ** is the root of a table b-tree - if it is not, the following call is
    ** a no-op).  */
    invalidateIncrblobCursors(p, 0, 1);
    rc = clearDatabasePage(pBt, (Pgno)iTable, 0, pnChange);
  }
  sqlite3BtreeLeave(p);
  return rc;
}

/*
** Delete all information from the single table that pCur is open on.
**
** This routine only work for pCur on an ephemeral table.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeClearTableOfCursor(BtCursor *pCur){
  return sqlite3BtreeClearTable(pCur->pBtree, pCur->pgnoRoot, 0);
}

/*
** Erase all information in a table and add the root of the table to
** the freelist.  Except, the root of the principle table (the one on
** page 1) is never added to the freelist.
**
** This routine will fail with SQLITE_LOCKED if there are any open
** cursors on the table.
**
** If AUTOVACUUM is enabled and the page at iTable is not the last
** root page in the database file, then the last root page 
** in the database file is moved into the slot formerly occupied by
** iTable and that last slot formerly occupied by the last root page
** is added to the freelist instead of iTable.  In this say, all
** root pages are kept at the beginning of the database file, which
** is necessary for AUTOVACUUM to work right.  *piMoved is set to the 
** page number that used to be the last root page in the file before
** the move.  If no page gets moved, *piMoved is set to 0.
** The last root page is recorded in meta[3] and the value of
** meta[3] is updated by this procedure.
*/
static int btreeDropTable(Btree *p, Pgno iTable, int *piMoved){
  int rc;
  MemPage *pPage = 0;
  BtShared *pBt = p->pBt;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( p->inTrans==TRANS_WRITE );

  /* It is illegal to drop a table if any cursors are open on the
  ** database. This is because in auto-vacuum mode the backend may
  ** need to move another root-page to fill a gap left by the deleted
  ** root page. If an open cursor was using this page a problem would 
  ** occur.
  **
  ** This error is caught long before control reaches this point.
  */
  if( NEVER(pBt->pCursor) ){
    sqlite3ConnectionBlocked(p->db, pBt->pCursor->pBtree->db);
    return SQLITE_LOCKED_SHAREDCACHE;
  }

  rc = btreeGetPage(pBt, (Pgno)iTable, &pPage, 0);
  if( rc ) return rc;
  rc = sqlite3BtreeClearTable(p, iTable, 0);
  if( rc ){
    releasePage(pPage);
    return rc;
  }

  *piMoved = 0;

  if( iTable>1 ){
#ifdef SQLITE_OMIT_AUTOVACUUM
    freePage(pPage, &rc);
    releasePage(pPage);
#else
    if( pBt->autoVacuum ){
      Pgno maxRootPgno;
      sqlite3BtreeGetMeta(p, BTREE_LARGEST_ROOT_PAGE, &maxRootPgno);

      if( iTable==maxRootPgno ){
        /* If the table being dropped is the table with the largest root-page
        ** number in the database, put the root page on the free list. 
        */
        freePage(pPage, &rc);
        releasePage(pPage);
        if( rc!=SQLITE_OK ){
          return rc;
        }
      }else{
        /* The table being dropped does not have the largest root-page
        ** number in the database. So move the page that does into the 
        ** gap left by the deleted root-page.
        */
        MemPage *pMove;
        releasePage(pPage);
        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        rc = relocatePage(pBt, pMove, PTRMAP_ROOTPAGE, 0, iTable, 0);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        pMove = 0;
        rc = btreeGetPage(pBt, maxRootPgno, &pMove, 0);
        freePage(pMove, &rc);
        releasePage(pMove);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        *piMoved = maxRootPgno;
      }

      /* Set the new 'max-root-page' value in the database header. This
      ** is the old value less one, less one more if that happens to
      ** be a root-page number, less one again if that is the
      ** PENDING_BYTE_PAGE.
      */
      maxRootPgno--;
      while( maxRootPgno==PENDING_BYTE_PAGE(pBt)
             || PTRMAP_ISPAGE(pBt, maxRootPgno) ){
        maxRootPgno--;
      }
      assert( maxRootPgno!=PENDING_BYTE_PAGE(pBt) );

      rc = sqlite3BtreeUpdateMeta(p, 4, maxRootPgno);
    }else{
      freePage(pPage, &rc);
      releasePage(pPage);
    }
#endif
  }else{
    /* If sqlite3BtreeDropTable was called on page 1.
    ** This really never should happen except in a corrupt
    ** database. 
    */
    zeroPage(pPage, PTF_INTKEY|PTF_LEAF );
    releasePage(pPage);
  }
  return rc;  
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreeDropTable(Btree *p, int iTable, int *piMoved){
  int rc;
  sqlite3BtreeEnter(p);
  rc = btreeDropTable(p, iTable, piMoved);
  sqlite3BtreeLeave(p);
  return rc;
}


/*
** This function may only be called if the b-tree connection already
** has a read or write transaction open on the database.
**
** Read the meta-information out of a database file.  Meta[0]
** is the number of free pages currently in the database.  Meta[1]
** through meta[15] are available for use by higher layers.  Meta[0]
** is read-only, the others are read/write.
** 
** The schema layer numbers meta values differently.  At the schema
** layer (and the SetCookie and ReadCookie opcodes) the number of
** free pages is not visible.  So Cookie[0] is the same as Meta[1].
**
** This routine treats Meta[BTREE_DATA_VERSION] as a special case.  Instead
** of reading the value out of the header, it instead loads the "DataVersion"
** from the pager.  The BTREE_DATA_VERSION value is not actually stored in the
** database file.  It is a number computed by the pager.  But its access
** pattern is the same as header meta values, and so it is convenient to
** read it from this routine.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeGetMeta(Btree *p, int idx, u32 *pMeta){
  BtShared *pBt = p->pBt;

  sqlite3BtreeEnter(p);
  assert( p->inTrans>TRANS_NONE );
  assert( SQLITE_OK==querySharedCacheTableLock(p, MASTER_ROOT, READ_LOCK) );
  assert( pBt->pPage1 );
  assert( idx>=0 && idx<=15 );

  if( idx==BTREE_DATA_VERSION ){
    *pMeta = sqlite3PagerDataVersion(pBt->pPager) + p->iDataVersion;
  }else{
    *pMeta = get4byte(&pBt->pPage1->aData[36 + idx*4]);
  }

  /* If auto-vacuum is disabled in this build and this is an auto-vacuum
  ** database, mark the database as read-only.  */
#ifdef SQLITE_OMIT_AUTOVACUUM
  if( idx==BTREE_LARGEST_ROOT_PAGE && *pMeta>0 ){
    pBt->btsFlags |= BTS_READ_ONLY;
  }
#endif

  sqlite3BtreeLeave(p);
}

/*
** Write meta-information back into the database.  Meta[0] is
** read-only and may not be written.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeUpdateMeta(Btree *p, int idx, u32 iMeta){
  BtShared *pBt = p->pBt;
  unsigned char *pP1;
  int rc;
  assert( idx>=1 && idx<=15 );
  sqlite3BtreeEnter(p);
  assert( p->inTrans==TRANS_WRITE );
  assert( pBt->pPage1!=0 );
  pP1 = pBt->pPage1->aData;
  rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
  if( rc==SQLITE_OK ){
    put4byte(&pP1[36 + idx*4], iMeta);
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( idx==BTREE_INCR_VACUUM ){
      assert( pBt->autoVacuum || iMeta==0 );
      assert( iMeta==0 || iMeta==1 );
      pBt->incrVacuum = (u8)iMeta;
    }
#endif
  }
  sqlite3BtreeLeave(p);
  return rc;
}

#ifndef SQLITE_OMIT_BTREECOUNT
/*
** The first argument, pCur, is a cursor opened on some b-tree. Count the
** number of entries in the b-tree and write the result to *pnEntry.
**
** SQLITE_OK is returned if the operation is successfully executed. 
** Otherwise, if an error is encountered (i.e. an IO error or database
** corruption) an SQLite error code is returned.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCount(BtCursor *pCur, i64 *pnEntry){
  i64 nEntry = 0;                      /* Value to return in *pnEntry */
  int rc;                              /* Return code */

  if( pCur->pgnoRoot==0 ){
    *pnEntry = 0;
    return SQLITE_OK;
  }
  rc = moveToRoot(pCur);

  /* Unless an error occurs, the following loop runs one iteration for each
  ** page in the B-Tree structure (not including overflow pages). 
  */
  while( rc==SQLITE_OK ){
    int iIdx;                          /* Index of child node in parent */
    MemPage *pPage;                    /* Current page of the b-tree */

    /* If this is a leaf page or the tree is not an int-key tree, then 
    ** this page contains countable entries. Increment the entry counter
    ** accordingly.
    */
    pPage = pCur->apPage[pCur->iPage];
    if( pPage->leaf || !pPage->intKey ){
      nEntry += pPage->nCell;
    }

    /* pPage is a leaf node. This loop navigates the cursor so that it 
    ** points to the first interior cell that it points to the parent of
    ** the next page in the tree that has not yet been visited. The
    ** pCur->aiIdx[pCur->iPage] value is set to the index of the parent cell
    ** of the page, or to the number of cells in the page if the next page
    ** to visit is the right-child of its parent.
    **
    ** If all pages in the tree have been visited, return SQLITE_OK to the
    ** caller.
    */
    if( pPage->leaf ){
      do {
        if( pCur->iPage==0 ){
          /* All pages of the b-tree have been visited. Return successfully. */
          *pnEntry = nEntry;
          return moveToRoot(pCur);
        }
        moveToParent(pCur);
      }while ( pCur->aiIdx[pCur->iPage]>=pCur->apPage[pCur->iPage]->nCell );

      pCur->aiIdx[pCur->iPage]++;
      pPage = pCur->apPage[pCur->iPage];
    }

    /* Descend to the child node of the cell that the cursor currently 
    ** points at. This is the right-child if (iIdx==pPage->nCell).
    */
    iIdx = pCur->aiIdx[pCur->iPage];
    if( iIdx==pPage->nCell ){
      rc = moveToChild(pCur, get4byte(&pPage->aData[pPage->hdrOffset+8]));
    }else{
      rc = moveToChild(pCur, get4byte(findCell(pPage, iIdx)));
    }
  }

  /* An error has occurred. Return an error code. */
  return rc;
}
#endif

/*
** Return the pager associated with a BTree.  This routine is used for
** testing and debugging only.
*/
SQLITE_API Pager *SQLITE_STDCALL sqlite3BtreePager(Btree *p){
  return p->pBt->pPager;
}

#ifndef SQLITE_OMIT_INTEGRITY_CHECK
/*
** Append a message to the error message string.
*/
static void checkAppendMsg(
  IntegrityCk *pCheck,
  const char *zFormat,
  ...
){
  va_list ap;
  if( !pCheck->mxErr ) return;
  pCheck->mxErr--;
  pCheck->nErr++;
  va_start(ap, zFormat);
  if( pCheck->errMsg.nChar ){
    sqlite3StrAccumAppend(&pCheck->errMsg, "\n", 1);
  }
  if( pCheck->zPfx ){
    sqlite3XPrintf(&pCheck->errMsg, 0, pCheck->zPfx, pCheck->v1, pCheck->v2);
  }
  sqlite3VXPrintf(&pCheck->errMsg, 1, zFormat, ap);
  va_end(ap);
  if( pCheck->errMsg.accError==STRACCUM_NOMEM ){
    pCheck->mallocFailed = 1;
  }
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

#ifndef SQLITE_OMIT_INTEGRITY_CHECK

/*
** Return non-zero if the bit in the IntegrityCk.aPgRef[] array that
** corresponds to page iPg is already set.
*/
static int getPageReferenced(IntegrityCk *pCheck, Pgno iPg){
  assert( iPg<=pCheck->nPage && sizeof(pCheck->aPgRef[0])==1 );
  return (pCheck->aPgRef[iPg/8] & (1 << (iPg & 0x07)));
}

/*
** Set the bit in the IntegrityCk.aPgRef[] array that corresponds to page iPg.
*/
static void setPageReferenced(IntegrityCk *pCheck, Pgno iPg){
  assert( iPg<=pCheck->nPage && sizeof(pCheck->aPgRef[0])==1 );
  pCheck->aPgRef[iPg/8] |= (1 << (iPg & 0x07));
}


/*
** Add 1 to the reference count for page iPage.  If this is the second
** reference to the page, add an error message to pCheck->zErrMsg.
** Return 1 if there are 2 or more references to the page and 0 if
** if this is the first reference to the page.
**
** Also check that the page number is in bounds.
*/
static int checkRef(IntegrityCk *pCheck, Pgno iPage){
  if( iPage==0 ) return 1;
  if( iPage>pCheck->nPage ){
    checkAppendMsg(pCheck, "invalid page number %d", iPage);
    return 1;
  }
  if( getPageReferenced(pCheck, iPage) ){
    checkAppendMsg(pCheck, "2nd reference to page %d", iPage);
    return 1;
  }
  setPageReferenced(pCheck, iPage);
  return 0;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Check that the entry in the pointer-map for page iChild maps to 
** page iParent, pointer type ptrType. If not, append an error message
** to pCheck.
*/
static void checkPtrmap(
  IntegrityCk *pCheck,   /* Integrity check context */
  Pgno iChild,           /* Child page number */
  u8 eType,              /* Expected pointer map type */
  Pgno iParent           /* Expected pointer map parent page number */
){
  int rc;
  u8 ePtrmapType;
  Pgno iPtrmapParent;

  rc = ptrmapGet(pCheck->pBt, iChild, &ePtrmapType, &iPtrmapParent);
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_NOMEM || rc==SQLITE_IOERR_NOMEM ) pCheck->mallocFailed = 1;
    checkAppendMsg(pCheck, "Failed to read ptrmap key=%d", iChild);
    return;
  }

  if( ePtrmapType!=eType || iPtrmapParent!=iParent ){
    checkAppendMsg(pCheck,
      "Bad ptr map entry key=%d expected=(%d,%d) got=(%d,%d)", 
      iChild, eType, iParent, ePtrmapType, iPtrmapParent);
  }
}
#endif

/*
** Check the integrity of the freelist or of an overflow page list.
** Verify that the number of pages on the list is N.
*/
static void checkList(
  IntegrityCk *pCheck,  /* Integrity checking context */
  int isFreeList,       /* True for a freelist.  False for overflow page list */
  int iPage,            /* Page number for first page in the list */
  int N                 /* Expected number of pages in the list */
){
  int i;
  int expected = N;
  int iFirst = iPage;
  while( N-- > 0 && pCheck->mxErr ){
    DbPage *pOvflPage;
    unsigned char *pOvflData;
    if( iPage<1 ){
      checkAppendMsg(pCheck,
         "%d of %d pages missing from overflow list starting at %d",
          N+1, expected, iFirst);
      break;
    }
    if( checkRef(pCheck, iPage) ) break;
    if( sqlite3PagerGet(pCheck->pPager, (Pgno)iPage, &pOvflPage) ){
      checkAppendMsg(pCheck, "failed to get page %d", iPage);
      break;
    }
    pOvflData = (unsigned char *)sqlite3PagerGetData(pOvflPage);
    if( isFreeList ){
      int n = get4byte(&pOvflData[4]);
#ifndef SQLITE_OMIT_AUTOVACUUM
      if( pCheck->pBt->autoVacuum ){
        checkPtrmap(pCheck, iPage, PTRMAP_FREEPAGE, 0);
      }
#endif
      if( n>(int)pCheck->pBt->usableSize/4-2 ){
        checkAppendMsg(pCheck,
           "freelist leaf count too big on page %d", iPage);
        N--;
      }else{
        for(i=0; i<n; i++){
          Pgno iFreePage = get4byte(&pOvflData[8+i*4]);
#ifndef SQLITE_OMIT_AUTOVACUUM
          if( pCheck->pBt->autoVacuum ){
            checkPtrmap(pCheck, iFreePage, PTRMAP_FREEPAGE, 0);
          }
#endif
          checkRef(pCheck, iFreePage);
        }
        N -= n;
      }
    }
#ifndef SQLITE_OMIT_AUTOVACUUM
    else{
      /* If this database supports auto-vacuum and iPage is not the last
      ** page in this overflow list, check that the pointer-map entry for
      ** the following page matches iPage.
      */
      if( pCheck->pBt->autoVacuum && N>0 ){
        i = get4byte(pOvflData);
        checkPtrmap(pCheck, i, PTRMAP_OVERFLOW2, iPage);
      }
    }
#endif
    iPage = get4byte(pOvflData);
    sqlite3PagerUnref(pOvflPage);

    if( isFreeList && N<(iPage!=0) ){
      checkAppendMsg(pCheck, "free-page count in header is too small");
    }
  }
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

/*
** An implementation of a min-heap.
**
** aHeap[0] is the number of elements on the heap.  aHeap[1] is the
** root element.  The daughter nodes of aHeap[N] are aHeap[N*2]
** and aHeap[N*2+1].
**
** The heap property is this:  Every node is less than or equal to both
** of its daughter nodes.  A consequence of the heap property is that the
** root node aHeap[1] is always the minimum value currently in the heap.
**
** The btreeHeapInsert() routine inserts an unsigned 32-bit number onto
** the heap, preserving the heap property.  The btreeHeapPull() routine
** removes the root element from the heap (the minimum value in the heap)
** and then moves other nodes around as necessary to preserve the heap
** property.
**
** This heap is used for cell overlap and coverage testing.  Each u32
** entry represents the span of a cell or freeblock on a btree page.  
** The upper 16 bits are the index of the first byte of a range and the
** lower 16 bits are the index of the last byte of that range.
*/
static void btreeHeapInsert(u32 *aHeap, u32 x){
  u32 j, i = ++aHeap[0];
  aHeap[i] = x;
  while( (j = i/2)>0 && aHeap[j]>aHeap[i] ){
    x = aHeap[j];
    aHeap[j] = aHeap[i];
    aHeap[i] = x;
    i = j;
  }
}
static int btreeHeapPull(u32 *aHeap, u32 *pOut){
  u32 j, i, x;
  if( (x = aHeap[0])==0 ) return 0;
  *pOut = aHeap[1];
  aHeap[1] = aHeap[x];
  aHeap[x] = 0xffffffff;
  aHeap[0]--;
  i = 1;
  while( (j = i*2)<=aHeap[0] ){
    if( aHeap[j]>aHeap[j+1] ) j++;
    if( aHeap[i]<aHeap[j] ) break;
    x = aHeap[i];
    aHeap[i] = aHeap[j];
    aHeap[j] = x;
    i = j;
  }
  return 1;  
}

#ifndef SQLITE_OMIT_INTEGRITY_CHECK
/*
** Do various sanity checks on a single page of a tree.  Return
** the tree depth.  Root pages return 0.  Parents of root pages
** return 1, and so forth.
** 
** These checks are done:
**
**      1.  Make sure that cells and freeblocks do not overlap
**          but combine to completely cover the page.
**      2.  Make sure integer cell keys are in order.
**      3.  Check the integrity of overflow pages.
**      4.  Recursively call checkTreePage on all children.
**      5.  Verify that the depth of all children is the same.
*/
static int checkTreePage(
  IntegrityCk *pCheck,  /* Context for the sanity check */
  int iPage,            /* Page number of the page to check */
  i64 *piMinKey,        /* Write minimum integer primary key here */
  i64 maxKey            /* Error if integer primary key greater than this */
){
  MemPage *pPage = 0;      /* The page being analyzed */
  int i;                   /* Loop counter */
  int rc;                  /* Result code from subroutine call */
  int depth = -1, d2;      /* Depth of a subtree */
  int pgno;                /* Page number */
  int nFrag;               /* Number of fragmented bytes on the page */
  int hdr;                 /* Offset to the page header */
  int cellStart;           /* Offset to the start of the cell pointer array */
  int nCell;               /* Number of cells */
  int doCoverageCheck = 1; /* True if cell coverage checking should be done */
  int keyCanBeEqual = 1;   /* True if IPK can be equal to maxKey
                           ** False if IPK must be strictly less than maxKey */
  u8 *data;                /* Page content */
  u8 *pCell;               /* Cell content */
  u8 *pCellIdx;            /* Next element of the cell pointer array */
  BtShared *pBt;           /* The BtShared object that owns pPage */
  u32 pc;                  /* Address of a cell */
  u32 usableSize;          /* Usable size of the page */
  u32 contentOffset;       /* Offset to the start of the cell content area */
  u32 *heap = 0;           /* Min-heap used for checking cell coverage */
  u32 x, prev = 0;         /* Next and previous entry on the min-heap */
  const char *saved_zPfx = pCheck->zPfx;
  int saved_v1 = pCheck->v1;
  int saved_v2 = pCheck->v2;
  u8 savedIsInit = 0;

  /* Check that the page exists
  */
  pBt = pCheck->pBt;
  usableSize = pBt->usableSize;
  if( iPage==0 ) return 0;
  if( checkRef(pCheck, iPage) ) return 0;
  pCheck->zPfx = "Page %d: ";
  pCheck->v1 = iPage;
  if( (rc = btreeGetPage(pBt, (Pgno)iPage, &pPage, 0))!=0 ){
    checkAppendMsg(pCheck,
       "unable to get the page. error code=%d", rc);
    goto end_of_check;
  }

  /* Clear MemPage.isInit to make sure the corruption detection code in
  ** btreeInitPage() is executed.  */
  savedIsInit = pPage->isInit;
  pPage->isInit = 0;
  if( (rc = btreeInitPage(pPage))!=0 ){
    assert( rc==SQLITE_CORRUPT );  /* The only possible error from InitPage */
    checkAppendMsg(pCheck,
                   "btreeInitPage() returns error code %d", rc);
    goto end_of_check;
  }
  data = pPage->aData;
  hdr = pPage->hdrOffset;

  /* Set up for cell analysis */
  pCheck->zPfx = "On tree page %d cell %d: ";
  contentOffset = get2byteNotZero(&data[hdr+5]);
  assert( contentOffset<=usableSize );  /* Enforced by btreeInitPage() */

  /* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
  ** number of cells on the page. */
  nCell = get2byte(&data[hdr+3]);
  assert( pPage->nCell==nCell );

  /* EVIDENCE-OF: R-23882-45353 The cell pointer array of a b-tree page
  ** immediately follows the b-tree page header. */
  cellStart = hdr + 12 - 4*pPage->leaf;
  assert( pPage->aCellIdx==&data[cellStart] );
  pCellIdx = &data[cellStart + 2*(nCell-1)];

  if( !pPage->leaf ){
    /* Analyze the right-child page of internal pages */
    pgno = get4byte(&data[hdr+8]);
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum ){
      pCheck->zPfx = "On page %d at right child: ";
      checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage);
    }
#endif
    depth = checkTreePage(pCheck, pgno, &maxKey, maxKey);
    keyCanBeEqual = 0;
  }else{
    /* For leaf pages, the coverage check will occur in the same loop
    ** as the other cell checks, so initialize the heap.  */
    heap = pCheck->heap;
    heap[0] = 0;
  }

  /* EVIDENCE-OF: R-02776-14802 The cell pointer array consists of K 2-byte
  ** integer offsets to the cell contents. */
  for(i=nCell-1; i>=0 && pCheck->mxErr; i--){
    CellInfo info;

    /* Check cell size */
    pCheck->v2 = i;
    assert( pCellIdx==&data[cellStart + i*2] );
    pc = get2byteAligned(pCellIdx);
    pCellIdx -= 2;
    if( pc<contentOffset || pc>usableSize-4 ){
      checkAppendMsg(pCheck, "Offset %d out of range %d..%d",
                             pc, contentOffset, usableSize-4);
      doCoverageCheck = 0;
      continue;
    }
    pCell = &data[pc];
    pPage->xParseCell(pPage, pCell, &info);
    if( pc+info.nSize>usableSize ){
      checkAppendMsg(pCheck, "Extends off end of page");
      doCoverageCheck = 0;
      continue;
    }

    /* Check for integer primary key out of range */
    if( pPage->intKey ){
      if( keyCanBeEqual ? (info.nKey > maxKey) : (info.nKey >= maxKey) ){
        checkAppendMsg(pCheck, "Rowid %lld out of order", info.nKey);
      }
      maxKey = info.nKey;
    }

    /* Check the content overflow list */
    if( info.nPayload>info.nLocal ){
      int nPage;       /* Number of pages on the overflow chain */
      Pgno pgnoOvfl;   /* First page of the overflow chain */
      assert( pc + info.iOverflow <= usableSize );
      nPage = (info.nPayload - info.nLocal + usableSize - 5)/(usableSize - 4);
      pgnoOvfl = get4byte(&pCell[info.iOverflow]);
#ifndef SQLITE_OMIT_AUTOVACUUM
      if( pBt->autoVacuum ){
        checkPtrmap(pCheck, pgnoOvfl, PTRMAP_OVERFLOW1, iPage);
      }
#endif
      checkList(pCheck, 0, pgnoOvfl, nPage);
    }

    if( !pPage->leaf ){
      /* Check sanity of left child page for internal pages */
      pgno = get4byte(pCell);
#ifndef SQLITE_OMIT_AUTOVACUUM
      if( pBt->autoVacuum ){
        checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage);
      }
#endif
      d2 = checkTreePage(pCheck, pgno, &maxKey, maxKey);
      keyCanBeEqual = 0;
      if( d2!=depth ){
        checkAppendMsg(pCheck, "Child page depth differs");
        depth = d2;
      }
    }else{
      /* Populate the coverage-checking heap for leaf pages */
      btreeHeapInsert(heap, (pc<<16)|(pc+info.nSize-1));
    }
  }
  *piMinKey = maxKey;

  /* Check for complete coverage of the page
  */
  pCheck->zPfx = 0;
  if( doCoverageCheck && pCheck->mxErr>0 ){
    /* For leaf pages, the min-heap has already been initialized and the
    ** cells have already been inserted.  But for internal pages, that has
    ** not yet been done, so do it now */
    if( !pPage->leaf ){
      heap = pCheck->heap;
      heap[0] = 0;
      for(i=nCell-1; i>=0; i--){
        u32 size;
        pc = get2byteAligned(&data[cellStart+i*2]);
        size = pPage->xCellSize(pPage, &data[pc]);
        btreeHeapInsert(heap, (pc<<16)|(pc+size-1));
      }
    }
    /* Add the freeblocks to the min-heap
    **
    ** EVIDENCE-OF: R-20690-50594 The second field of the b-tree page header
    ** is the offset of the first freeblock, or zero if there are no
    ** freeblocks on the page. 
    */
    i = get2byte(&data[hdr+1]);
    while( i>0 ){
      int size, j;
      assert( (u32)i<=usableSize-4 );     /* Enforced by btreeInitPage() */
      size = get2byte(&data[i+2]);
      assert( (u32)(i+size)<=usableSize );  /* Enforced by btreeInitPage() */
      btreeHeapInsert(heap, (((u32)i)<<16)|(i+size-1));
      /* EVIDENCE-OF: R-58208-19414 The first 2 bytes of a freeblock are a
      ** big-endian integer which is the offset in the b-tree page of the next
      ** freeblock in the chain, or zero if the freeblock is the last on the
      ** chain. */
      j = get2byte(&data[i]);
      /* EVIDENCE-OF: R-06866-39125 Freeblocks are always connected in order of
      ** increasing offset. */
      assert( j==0 || j>i+size );  /* Enforced by btreeInitPage() */
      assert( (u32)j<=usableSize-4 );   /* Enforced by btreeInitPage() */
      i = j;
    }
    /* Analyze the min-heap looking for overlap between cells and/or 
    ** freeblocks, and counting the number of untracked bytes in nFrag.
    ** 
    ** Each min-heap entry is of the form:    (start_address<<16)|end_address.
    ** There is an implied first entry the covers the page header, the cell
    ** pointer index, and the gap between the cell pointer index and the start
    ** of cell content.  
    **
    ** The loop below pulls entries from the min-heap in order and compares
    ** the start_address against the previous end_address.  If there is an
    ** overlap, that means bytes are used multiple times.  If there is a gap,
    ** that gap is added to the fragmentation count.
    */
    nFrag = 0;
    prev = contentOffset - 1;   /* Implied first min-heap entry */
    while( btreeHeapPull(heap,&x) ){
      if( (prev&0xffff)>=(x>>16) ){
        checkAppendMsg(pCheck,
          "Multiple uses for byte %u of page %d", x>>16, iPage);
        break;
      }else{
        nFrag += (x>>16) - (prev&0xffff) - 1;
        prev = x;
      }
    }
    nFrag += usableSize - (prev&0xffff) - 1;
    /* EVIDENCE-OF: R-43263-13491 The total number of bytes in all fragments
    ** is stored in the fifth field of the b-tree page header.
    ** EVIDENCE-OF: R-07161-27322 The one-byte integer at offset 7 gives the
    ** number of fragmented free bytes within the cell content area.
    */
    if( heap[0]==0 && nFrag!=data[hdr+7] ){
      checkAppendMsg(pCheck,
          "Fragmentation of %d bytes reported as %d on page %d",
          nFrag, data[hdr+7], iPage);
    }
  }

end_of_check:
  if( !doCoverageCheck ) pPage->isInit = savedIsInit;
  releasePage(pPage);
  pCheck->zPfx = saved_zPfx;
  pCheck->v1 = saved_v1;
  pCheck->v2 = saved_v2;
  return depth+1;
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

#ifndef SQLITE_OMIT_INTEGRITY_CHECK
/*
** This routine does a complete check of the given BTree file.  aRoot[] is
** an array of pages numbers were each page number is the root page of
** a table.  nRoot is the number of entries in aRoot.
**
** A read-only or read-write transaction must be opened before calling
** this function.
**
** Write the number of error seen in *pnErr.  Except for some memory
** allocation errors,  an error message held in memory obtained from
** malloc is returned if *pnErr is non-zero.  If *pnErr==0 then NULL is
** returned.  If a memory allocation error occurs, NULL is returned.
*/
SQLITE_API char *SQLITE_STDCALL sqlite3BtreeIntegrityCheck(
  Btree *p,     /* The btree to be checked */
  int *aRoot,   /* An array of root pages numbers for individual trees */
  int nRoot,    /* Number of entries in aRoot[] */
  int mxErr,    /* Stop reporting errors after this many */
  int *pnErr    /* Write number of errors seen to this variable */
){
  Pgno i;
  IntegrityCk sCheck;
  BtShared *pBt = p->pBt;
  int savedDbFlags = pBt->pBt->flags;
  char zErr[100];
  VVA_ONLY( int nRef );

  sqlite3BtreeEnter(p);
  assert( p->inTrans>TRANS_NONE && pBt->inTransaction>TRANS_NONE );
  assert( (nRef = sqlite3PagerRefcount(pBt->pPager))>=0 );
  sCheck.pBt = pBt;
  sCheck.pPager = pBt->pPager;
  sCheck.nPage = btreePagecount(sCheck.pBt);
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  sCheck.mallocFailed = 0;
  sCheck.zPfx = 0;
  sCheck.v1 = 0;
  sCheck.v2 = 0;
  sCheck.aPgRef = 0;
  sCheck.heap = 0;
  sqlite3StrAccumInit(&sCheck.errMsg, 0, zErr, sizeof(zErr), SQLITE_MAX_LENGTH);
  if( sCheck.nPage==0 ){
    goto integrity_ck_cleanup;
  }

  sCheck.aPgRef = sqlite3MallocZero((sCheck.nPage / 8)+ 1);
  if( !sCheck.aPgRef ){
    sCheck.mallocFailed = 1;
    goto integrity_ck_cleanup;
  }
  sCheck.heap = (u32*)sqlite3PageMalloc( pBt->pageSize );
  if( sCheck.heap==0 ){
    sCheck.mallocFailed = 1;
    goto integrity_ck_cleanup;
  }

  i = PENDING_BYTE_PAGE(pBt);
  if( i<=sCheck.nPage ) setPageReferenced(&sCheck, i);

  /* Check the integrity of the freelist
  */
  sCheck.zPfx = "Main freelist: ";
  checkList(&sCheck, 1, get4byte(&pBt->pPage1->aData[32]),
            get4byte(&pBt->pPage1->aData[36]));
  sCheck.zPfx = 0;

  /* Check all the tables.
  */
  testcase( pBt->pBt->flags & SQLITE_CellSizeCk );
  pBt->pBt->flags &= ~SQLITE_CellSizeCk;
  for(i=0; (int)i<nRoot && sCheck.mxErr; i++){
    i64 notUsed;
    if( aRoot[i]==0 ) continue;
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum && aRoot[i]>1 ){
      checkPtrmap(&sCheck, aRoot[i], PTRMAP_ROOTPAGE, 0);
    }
#endif
    checkTreePage(&sCheck, aRoot[i], &notUsed, LARGEST_INT64);
  }
  pBt->pBt->flags = savedDbFlags;

  /* Make sure every page in the file is referenced
  */
  for(i=1; i<=sCheck.nPage && sCheck.mxErr; i++){
#ifdef SQLITE_OMIT_AUTOVACUUM
    if( getPageReferenced(&sCheck, i)==0 ){
      checkAppendMsg(&sCheck, "Page %d is never used", i);
    }
#else
    /* If the database supports auto-vacuum, make sure no tables contain
    ** references to pointer-map pages.
    */
    if( getPageReferenced(&sCheck, i)==0 && 
       (PTRMAP_PAGENO(pBt, i)!=i || !pBt->autoVacuum) ){
      checkAppendMsg(&sCheck, "Page %d is never used", i);
    }
    if( getPageReferenced(&sCheck, i)!=0 && 
       (PTRMAP_PAGENO(pBt, i)==i && pBt->autoVacuum) ){
      checkAppendMsg(&sCheck, "Pointer map page %d is referenced", i);
    }
#endif
  }

  /* Clean  up and report errors.
  */
integrity_ck_cleanup:
  sqlite3PageFree(sCheck.heap);
  sqlite3_free(sCheck.aPgRef);
  if( sCheck.mallocFailed ){
    sqlite3StrAccumReset(&sCheck.errMsg);
    sCheck.nErr++;
  }
  *pnErr = sCheck.nErr;
  if( sCheck.nErr==0 ) sqlite3StrAccumReset(&sCheck.errMsg);
  /* Make sure this analysis did not leave any unref() pages. */
  assert( nRef==sqlite3PagerRefcount(pBt->pPager) );
  sqlite3BtreeLeave(p);
  return sqlite3StrAccumFinish(&sCheck.errMsg);
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

SQLITE_API int SQLITE_STDCALL sqlite3BtreeFileFormat(Btree *p){
	return p->pBt->file_format;
}

/*
** Return the full pathname of the underlying database file.  Return
** an empty string if the database is in-memory or a TEMP database.
**
** The pager filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
SQLITE_API const char *SQLITE_STDCALL sqlite3BtreeGetFilename(Btree *p){
  assert( p->pBt->pPager!=0 );
  return sqlite3PagerFilename(p->pBt->pPager, 1);
}

/*
** Return the pathname of the journal file for this database. The return
** value of this routine is the same regardless of whether the journal file
** has been created or not.
**
** The pager journal filename is invariant as long as the pager is
** open so it is safe to access without the BtShared mutex.
*/
SQLITE_API const char *SQLITE_STDCALL sqlite3BtreeGetJournalname(Btree *p){
  assert( p->pBt->pPager!=0 );
  return sqlite3PagerJournalname(p->pBt->pPager);
}

/*
** Return non-zero if a transaction is active.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeIsInTrans(Btree *p){
  assert( p==0 || sqlite3_mutex_held(p->db->mutex) );
  return (p && (p->inTrans==TRANS_WRITE));
}

#ifndef SQLITE_OMIT_WAL
/*
** Run a checkpoint on the Btree passed as the first argument.
**
** Return SQLITE_LOCKED if this or any other connection has an open 
** transaction on the shared-cache the argument Btree is connected to.
**
** Parameter eMode is one of SQLITE_CHECKPOINT_PASSIVE, FULL or RESTART.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCheckpoint(Btree *p, int eMode, int *pnLog, int *pnCkpt){
  int rc = SQLITE_OK;
  if( p ){
    BtShared *pBt = p->pBt;
    sqlite3BtreeEnter(p);
    if( pBt->inTransaction!=TRANS_NONE ){
      rc = SQLITE_LOCKED;
    }else{
      rc = sqlite3PagerCheckpoint(pBt->pPager, eMode, pnLog, pnCkpt);
    }
    sqlite3BtreeLeave(p);
  }
  return rc;
}
#endif

/*
** Return non-zero if a read (or write) transaction is active.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeIsInReadTrans(Btree *p){
  assert( p );
  assert( sqlite3_mutex_held(p->db->mutex) );
  return p->inTrans!=TRANS_NONE;
}

SQLITE_API int SQLITE_STDCALL sqlite3BtreeIsInBackup(Btree *p){
  assert( p );
  assert( sqlite3_mutex_held(p->db->mutex) );
  return p->nBackup!=0;
}

/*
** This function returns a pointer to a blob of memory associated with
** a single shared-btree. The memory is used by client code for its own
** purposes (for example, to store a high-level schema associated with 
** the shared-btree). The btree layer manages reference counting issues.
**
** The first time this is called on a shared-btree, nBytes bytes of memory
** are allocated, zeroed, and returned to the caller. For each subsequent 
** call the nBytes parameter is ignored and a pointer to the same blob
** of memory returned. 
**
** If the nBytes parameter is 0 and the blob of memory has not yet been
** allocated, a null pointer is returned. If the blob has already been
** allocated, it is returned as normal.
**
** Just before the shared-btree is closed, the function passed as the 
** xFree argument when the memory allocation was made is invoked on the 
** blob of allocated memory. The xFree function should not call sqlite3_free()
** on the memory, the btree layer does that.
*/
SQLITE_API void *SQLITE_STDCALL sqlite3BtreeSchema(Btree *p, int nBytes, void(*xFree)(void *)){
  BtShared *pBt = p->pBt;
  sqlite3BtreeEnter(p);
  if( !pBt->pSchema && nBytes ){
    pBt->pSchema = sqlite3DbMallocZero(0, nBytes);
    pBt->xFreeSchema = xFree;
  }
  sqlite3BtreeLeave(p);
  return pBt->pSchema;
}

/*
** Return SQLITE_LOCKED_SHAREDCACHE if another user of the same shared 
** btree as the argument handle holds an exclusive lock on the 
** sqlite_master table. Otherwise SQLITE_OK.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSchemaLocked(Btree *p){
  int rc;
  assert( sqlite3_mutex_held(p->db->mutex) );
  sqlite3BtreeEnter(p);
  rc = querySharedCacheTableLock(p, MASTER_ROOT, READ_LOCK);
  assert( rc==SQLITE_OK || rc==SQLITE_LOCKED_SHAREDCACHE );
  sqlite3BtreeLeave(p);
  return rc;
}


#ifndef SQLITE_OMIT_SHARED_CACHE
/*
** Obtain a lock on the table whose root page is iTab.  The
** lock is a write lock if isWritelock is true or a read lock
** if it is false.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeLockTable(Btree *p, int iTab, u8 isWriteLock){
  int rc = SQLITE_OK;
  assert( p->inTrans!=TRANS_NONE );
  if( p->sharable ){
    u8 lockType = READ_LOCK + isWriteLock;
    assert( READ_LOCK+1==WRITE_LOCK );
    assert( isWriteLock==0 || isWriteLock==1 );

    sqlite3BtreeEnter(p);
    rc = querySharedCacheTableLock(p, iTab, lockType);
    if( rc==SQLITE_OK ){
      rc = setSharedCacheTableLock(p, iTab, lockType);
    }
    sqlite3BtreeLeave(p);
  }
  return rc;
}
#endif

#ifndef SQLITE_OMIT_INCRBLOB
/*
** Argument pCsr must be a cursor opened for writing on an 
** INTKEY table currently pointing at a valid table entry. 
** This function modifies the data stored as part of that entry.
**
** Only the data content may only be modified, it is not possible to 
** change the length of the data stored. If this function is called with
** parameters that attempt to write past the end of the existing data,
** no modifications are made and SQLITE_CORRUPT is returned.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreePutData(BtCursor *pCsr, u32 offset, u32 amt, void *z){
  int rc;
  assert( cursorHoldsMutex(pCsr) );
  assert( sqlite3_mutex_held(pCsr->pBtree->db->mutex) );
  assert( pCsr->curFlags & BTCF_Incrblob );

  rc = restoreCursorPosition(pCsr);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pCsr->eState!=CURSOR_REQUIRESEEK );
  if( pCsr->eState!=CURSOR_VALID ){
    return SQLITE_ABORT;
  }

  /* Save the positions of all other cursors open on this table. This is
  ** required in case any of them are holding references to an xFetch
  ** version of the b-tree page modified by the accessPayload call below.
  **
  ** Note that pCsr must be open on a INTKEY table and saveCursorPosition()
  ** and hence saveAllCursors() cannot fail on a BTREE_INTKEY table, hence
  ** saveAllCursors can only return SQLITE_OK.
  */
  VVA_ONLY(rc =) saveAllCursors(pCsr->pBt, pCsr->pgnoRoot, pCsr);
  assert( rc==SQLITE_OK );

  /* Check some assumptions: 
  **   (a) the cursor is open for writing,
  **   (b) there is a read/write transaction open,
  **   (c) the connection holds a write-lock on the table (if required),
  **   (d) there are no conflicting read-locks, and
  **   (e) the cursor points at a valid row of an intKey table.
  */
  if( (pCsr->curFlags & BTCF_WriteFlag)==0 ){
    return SQLITE_READONLY;
  }
  assert( (pCsr->pBt->btsFlags & BTS_READ_ONLY)==0
              && pCsr->pBt->inTransaction==TRANS_WRITE );
  assert( hasSharedCacheTableLock(pCsr->pBtree, pCsr->pgnoRoot, 0, 2) );
  assert( !hasReadConflicts(pCsr->pBtree, pCsr->pgnoRoot) );
  assert( pCsr->apPage[pCsr->iPage]->intKey );

  return accessPayload(pCsr, offset, amt, (unsigned char *)z, 1);
}

/* 
** Mark this cursor as an incremental blob cursor.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeIncrblobCursor(BtCursor *pCur){
  pCur->curFlags |= BTCF_Incrblob;
  pCur->pBtree->hasIncrblobCur = 1;
}
#endif

/*
** Set both the "read version" (single byte at byte offset 18) and 
** "write version" (single byte at byte offset 19) fields in the database
** header to iVersion.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeSetVersion(Btree *pBtree, int iVersion){
  BtShared *pBt = pBtree->pBt;
  int rc;                         /* Return code */
 
  assert( iVersion==1 || iVersion==2 );

  /* If setting the version fields to 1, do not automatically open the
  ** WAL connection, even if the version fields are currently set to 2.
  */
  pBt->btsFlags &= ~BTS_NO_WAL;
  if( iVersion==1 ) pBt->btsFlags |= BTS_NO_WAL;

  rc = sqlite3BtreeBeginTrans(pBtree, 0);
  if( rc==SQLITE_OK ){
    u8 *aData = pBt->pPage1->aData;
    if( aData[18]!=(u8)iVersion || aData[19]!=(u8)iVersion ){
      rc = sqlite3BtreeBeginTrans(pBtree, 2);
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
        if( rc==SQLITE_OK ){
          aData[18] = (u8)iVersion;
          aData[19] = (u8)iVersion;
        }
      }
    }
  }

  pBt->btsFlags &= ~BTS_NO_WAL;
  return rc;
}

/*
** set the mask of hint flags for cursor pCsr.
*/
SQLITE_API void SQLITE_STDCALL sqlite3BtreeCursorHints(BtCursor *pCsr, unsigned int mask){
  assert( mask==BTREE_BULKLOAD || mask==BTREE_SEEK_EQ || mask==0 );
  pCsr->hints = mask;
}

#ifdef SQLITE_DEBUG
/*
** Return true if the cursor has a hint specified.  This routine is
** only used from within assert() statements
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeCursorHasHint(BtCursor *pCsr, unsigned int mask){
  return (pCsr->hints & mask)!=0;
}
#endif

/*
** Return true if the given Btree is read-only.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeIsReadonly(Btree *p){
  return (p->pBt->btsFlags & BTS_READ_ONLY)!=0;
}

/*
** Return the size of the header added to each page by this module.
*/
SQLITE_PRIVATE int sqlite3HeaderSizeBtree(void){ return ROUND8(sizeof(MemPage)); }

SQLITE_API const char *SQLITE_STDCALL sqlite3BtreeErrName(int rc){
  const char *zName = 0;
  int i, origRc = rc;
  for(i=0; i<2 && zName==0; i++, rc &= 0xff){
    switch( rc ){
      case SQLITE_OK:                 zName = "SQLITE_OK";                break;
      case SQLITE_ERROR:              zName = "SQLITE_ERROR";             break;
      case SQLITE_INTERNAL:           zName = "SQLITE_INTERNAL";          break;
      case SQLITE_PERM:               zName = "SQLITE_PERM";              break;
      case SQLITE_ABORT:              zName = "SQLITE_ABORT";             break;
      case SQLITE_ABORT_ROLLBACK:     zName = "SQLITE_ABORT_ROLLBACK";    break;
      case SQLITE_BUSY:               zName = "SQLITE_BUSY";              break;
      case SQLITE_BUSY_RECOVERY:      zName = "SQLITE_BUSY_RECOVERY";     break;
      case SQLITE_BUSY_SNAPSHOT:      zName = "SQLITE_BUSY_SNAPSHOT";     break;
      case SQLITE_LOCKED:             zName = "SQLITE_LOCKED";            break;
      case SQLITE_LOCKED_SHAREDCACHE: zName = "SQLITE_LOCKED_SHAREDCACHE";break;
      case SQLITE_NOMEM:              zName = "SQLITE_NOMEM";             break;
      case SQLITE_READONLY:           zName = "SQLITE_READONLY";          break;
      case SQLITE_READONLY_RECOVERY:  zName = "SQLITE_READONLY_RECOVERY"; break;
      case SQLITE_READONLY_CANTLOCK:  zName = "SQLITE_READONLY_CANTLOCK"; break;
      case SQLITE_READONLY_ROLLBACK:  zName = "SQLITE_READONLY_ROLLBACK"; break;
      case SQLITE_READONLY_DBMOVED:   zName = "SQLITE_READONLY_DBMOVED";  break;
      case SQLITE_INTERRUPT:          zName = "SQLITE_INTERRUPT";         break;
      case SQLITE_IOERR:              zName = "SQLITE_IOERR";             break;
      case SQLITE_IOERR_READ:         zName = "SQLITE_IOERR_READ";        break;
      case SQLITE_IOERR_SHORT_READ:   zName = "SQLITE_IOERR_SHORT_READ";  break;
      case SQLITE_IOERR_WRITE:        zName = "SQLITE_IOERR_WRITE";       break;
      case SQLITE_IOERR_FSYNC:        zName = "SQLITE_IOERR_FSYNC";       break;
      case SQLITE_IOERR_DIR_FSYNC:    zName = "SQLITE_IOERR_DIR_FSYNC";   break;
      case SQLITE_IOERR_TRUNCATE:     zName = "SQLITE_IOERR_TRUNCATE";    break;
      case SQLITE_IOERR_FSTAT:        zName = "SQLITE_IOERR_FSTAT";       break;
      case SQLITE_IOERR_UNLOCK:       zName = "SQLITE_IOERR_UNLOCK";      break;
      case SQLITE_IOERR_RDLOCK:       zName = "SQLITE_IOERR_RDLOCK";      break;
      case SQLITE_IOERR_DELETE:       zName = "SQLITE_IOERR_DELETE";      break;
      case SQLITE_IOERR_NOMEM:        zName = "SQLITE_IOERR_NOMEM";       break;
      case SQLITE_IOERR_ACCESS:       zName = "SQLITE_IOERR_ACCESS";      break;
      case SQLITE_IOERR_CHECKRESERVEDLOCK:
                                zName = "SQLITE_IOERR_CHECKRESERVEDLOCK"; break;
      case SQLITE_IOERR_LOCK:         zName = "SQLITE_IOERR_LOCK";        break;
      case SQLITE_IOERR_CLOSE:        zName = "SQLITE_IOERR_CLOSE";       break;
      case SQLITE_IOERR_DIR_CLOSE:    zName = "SQLITE_IOERR_DIR_CLOSE";   break;
      case SQLITE_IOERR_SHMOPEN:      zName = "SQLITE_IOERR_SHMOPEN";     break;
      case SQLITE_IOERR_SHMSIZE:      zName = "SQLITE_IOERR_SHMSIZE";     break;
      case SQLITE_IOERR_SHMLOCK:      zName = "SQLITE_IOERR_SHMLOCK";     break;
      case SQLITE_IOERR_SHMMAP:       zName = "SQLITE_IOERR_SHMMAP";      break;
      case SQLITE_IOERR_SEEK:         zName = "SQLITE_IOERR_SEEK";        break;
      case SQLITE_IOERR_DELETE_NOENT: zName = "SQLITE_IOERR_DELETE_NOENT";break;
      case SQLITE_IOERR_MMAP:         zName = "SQLITE_IOERR_MMAP";        break;
      case SQLITE_IOERR_GETTEMPPATH:  zName = "SQLITE_IOERR_GETTEMPPATH"; break;
      case SQLITE_IOERR_CONVPATH:     zName = "SQLITE_IOERR_CONVPATH";    break;
      case SQLITE_CORRUPT:            zName = "SQLITE_CORRUPT";           break;
      case SQLITE_CORRUPT_VTAB:       zName = "SQLITE_CORRUPT_VTAB";      break;
      case SQLITE_NOTFOUND:           zName = "SQLITE_NOTFOUND";          break;
      case SQLITE_FULL:               zName = "SQLITE_FULL";              break;
      case SQLITE_CANTOPEN:           zName = "SQLITE_CANTOPEN";          break;
      case SQLITE_CANTOPEN_NOTEMPDIR: zName = "SQLITE_CANTOPEN_NOTEMPDIR";break;
      case SQLITE_CANTOPEN_ISDIR:     zName = "SQLITE_CANTOPEN_ISDIR";    break;
      case SQLITE_CANTOPEN_FULLPATH:  zName = "SQLITE_CANTOPEN_FULLPATH"; break;
      case SQLITE_CANTOPEN_CONVPATH:  zName = "SQLITE_CANTOPEN_CONVPATH"; break;
      case SQLITE_PROTOCOL:           zName = "SQLITE_PROTOCOL";          break;
      case SQLITE_EMPTY:              zName = "SQLITE_EMPTY";             break;
      case SQLITE_SCHEMA:             zName = "SQLITE_SCHEMA";            break;
      case SQLITE_TOOBIG:             zName = "SQLITE_TOOBIG";            break;
      case SQLITE_CONSTRAINT:         zName = "SQLITE_CONSTRAINT";        break;
      case SQLITE_CONSTRAINT_UNIQUE:  zName = "SQLITE_CONSTRAINT_UNIQUE"; break;
      case SQLITE_CONSTRAINT_TRIGGER: zName = "SQLITE_CONSTRAINT_TRIGGER";break;
      case SQLITE_CONSTRAINT_FOREIGNKEY:
                                  zName = "SQLITE_CONSTRAINT_FOREIGNKEY"; break;
      case SQLITE_CONSTRAINT_CHECK:   zName = "SQLITE_CONSTRAINT_CHECK";  break;
      case SQLITE_CONSTRAINT_PRIMARYKEY:
                                   zName = "SQLITE_CONSTRAINT_PRIMARYKEY";break;
      case SQLITE_CONSTRAINT_NOTNULL: zName = "SQLITE_CONSTRAINT_NOTNULL";break;
      case SQLITE_CONSTRAINT_COMMITHOOK:
                                   zName = "SQLITE_CONSTRAINT_COMMITHOOK";break;
      case SQLITE_CONSTRAINT_VTAB:    zName = "SQLITE_CONSTRAINT_VTAB";   break;
      case SQLITE_CONSTRAINT_FUNCTION:
                                     zName = "SQLITE_CONSTRAINT_FUNCTION";break;
      case SQLITE_CONSTRAINT_ROWID:   zName = "SQLITE_CONSTRAINT_ROWID";  break;
      case SQLITE_MISMATCH:           zName = "SQLITE_MISMATCH";          break;
      case SQLITE_MISUSE:             zName = "SQLITE_MISUSE";            break;
      case SQLITE_NOLFS:              zName = "SQLITE_NOLFS";             break;
      case SQLITE_AUTH:               zName = "SQLITE_AUTH";              break;
      case SQLITE_FORMAT:             zName = "SQLITE_FORMAT";            break;
      case SQLITE_RANGE:              zName = "SQLITE_RANGE";             break;
      case SQLITE_NOTADB:             zName = "SQLITE_NOTADB";            break;
      case SQLITE_ROW:                zName = "SQLITE_ROW";               break;
      case SQLITE_NOTICE:             zName = "SQLITE_NOTICE";            break;
      case SQLITE_NOTICE_RECOVER_WAL: zName = "SQLITE_NOTICE_RECOVER_WAL";break;
      case SQLITE_NOTICE_RECOVER_ROLLBACK:
                                zName = "SQLITE_NOTICE_RECOVER_ROLLBACK"; break;
      case SQLITE_WARNING:            zName = "SQLITE_WARNING";           break;
      case SQLITE_WARNING_AUTOINDEX:  zName = "SQLITE_WARNING_AUTOINDEX"; break;
      case SQLITE_DONE:               zName = "SQLITE_DONE";              break;
    }
  }
  if( zName==0 ){
    static char zBuf[50];
    sqlite3_snprintf(sizeof(zBuf), zBuf, "SQLITE_UNKNOWN(%d)", origRc);
    zName = zBuf;
  }
  return zName;
}

/*
** The following functions:
**
** sqlite3BtreeSerialType()
** sqlite3BtreeSerialTypeLen()
** sqlite3BtreeSerialLen()
** sqlite3BtreeSerialPut()
** sqlite3BtreeSerialGet()
**
** encapsulate the code that serializes values for storage in SQLite
** data and index records. Each serialized value consists of a
** 'serial-type' and a blob of data. The serial type is an 8-byte unsigned
** integer, stored as a varint.
**
** In an SQLite index record, the serial type is stored directly before
** the blob of data that it corresponds to. In a table record, all serial
** types are stored at the start of the record, and the blobs of data at
** the end. Hence these functions allow the caller to handle the
** serial-type and data blob separately.
**
** The following table describes the various storage classes for data:
**
**   serial type        bytes of data      type
**   --------------     ---------------    ---------------
**      0                     0            NULL
**      1                     1            signed integer
**      2                     2            signed integer
**      3                     3            signed integer
**      4                     4            signed integer
**      5                     6            signed integer
**      6                     8            signed integer
**      7                     8            IEEE float
**      8                     0            Integer constant 0
**      9                     0            Integer constant 1
**     10,11                               reserved for expansion
**    N>=12 and even       (N-12)/2        BLOB
**    N>=13 and odd        (N-13)/2        text
**
** The 8 and 9 types were added in 3.3.0, file format 4.  Prior versions
** of SQLite will not understand those serial types.
*/

/*
** Return the serial-type for the value stored in pMem.
*/
SQLITE_API u32 SQLITE_STDCALL sqlite3BtreeSerialType(Mem *pMem, int file_format){
  int flags = pMem->flags;
  u32 n;

  if( flags&MEM_Null ){
    return 0;
  }
  if( flags&MEM_Int ){
    /* Figure out whether to use 1, 2, 4, 6 or 8 bytes. */
#   define MAX_6BYTE ((((i64)0x00008000)<<32)-1)
    i64 i = pMem->u.i;
    u64 u;
    if( i<0 ){
      u = ~i;
    }else{
      u = i;
    }
    if( u<=127 ){
      return ((i&1)==i && file_format>=4) ? 8+(u32)u : 1;
    }
    if( u<=32767 ) return 2;
    if( u<=8388607 ) return 3;
    if( u<=2147483647 ) return 4;
    if( u<=MAX_6BYTE ) return 5;
    return 6;
  }
  if( flags&MEM_Real ){
    return 7;
  }
  assert( pMem->pBtree->mallocFailed || flags&(MEM_Str|MEM_Blob) );
  assert( pMem->n>=0 );
  n = (u32)pMem->n;
  if( flags & MEM_Zero ){
    n += pMem->u.nZero;
  }
  return ((n*2) + 12 + ((flags&MEM_Str)!=0));
}

/*
** The sizes for serial types less than 12
*/
static const u8 sqlite3SmallTypeSizes[] = {
  0, 1, 2, 3, 4, 6, 8, 8, 0, 0, 0, 0
};

/*
** Return the length of the data corresponding to the supplied serial-type.
*/
SQLITE_API u32 SQLITE_STDCALL sqlite3BtreeSerialTypeLen(u32 serial_type){
  if( serial_type>=12 ){
    return (serial_type-12)/2;
  }else{
    return sqlite3SmallTypeSizes[serial_type];
  }
}

/*
** If we are on an architecture with mixed-endian floating 
** points (ex: ARM7) then swap the lower 4 bytes with the 
** upper 4 bytes.  Return the result.
**
** For most architectures, this is a no-op.
**
** (later):  It is reported to me that the mixed-endian problem
** on ARM7 is an issue with GCC, not with the ARM7 chip.  It seems
** that early versions of GCC stored the two words of a 64-bit
** float in the wrong order.  And that error has been propagated
** ever since.  The blame is not necessarily with GCC, though.
** GCC might have just copying the problem from a prior compiler.
** I am also told that newer versions of GCC that follow a different
** ABI get the byte order right.
**
** Developers using SQLite on an ARM7 should compile and run their
** application using -DSQLITE_DEBUG=1 at least once.  With DEBUG
** enabled, some asserts below will ensure that the byte order of
** floating point values is correct.
**
** (2007-08-30)  Frank van Vugt has studied this problem closely
** and has send his findings to the SQLite developers.  Frank
** writes that some Linux kernels offer floating point hardware
** emulation that uses only 32-bit mantissas instead of a full 
** 48-bits as required by the IEEE standard.  (This is the
** CONFIG_FPE_FASTFPE option.)  On such systems, floating point
** byte swapping becomes very complicated.  To avoid problems,
** the necessary byte swapping is carried out using a 64-bit integer
** rather than a 64-bit float.  Frank assures us that the code here
** works for him.  We, the developers, have no way to independently
** verify this, but Frank seems to know what he is talking about
** so we trust him.
*/
#ifdef SQLITE_MIXED_ENDIAN_64BIT_FLOAT
static u64 floatSwap(u64 in){
  union {
    u64 r;
    u32 i[2];
  } u;
  u32 t;

  u.r = in;
  t = u.i[0];
  u.i[0] = u.i[1];
  u.i[1] = t;
  return u.r;
}
# define swapMixedEndianFloat(X)  X = floatSwap(X)
#else
# define swapMixedEndianFloat(X)
#endif

/*
** Write the serialized data blob for the value stored in pMem into 
** buf. It is assumed that the caller has allocated sufficient space.
** Return the number of bytes written.
**
** nBuf is the amount of space left in buf[].  The caller is responsible
** for allocating enough space to buf[] to hold the entire field, exclusive
** of the pMem->u.nZero bytes for a MEM_Zero value.
**
** Return the number of bytes actually written into buf[].  The number
** of bytes in the zero-filled tail is included in the return value only
** if those bytes were zeroed in buf[].
*/ 
SQLITE_API u32 SQLITE_STDCALL sqlite3BtreeSerialPut(u8 *buf, Mem *pMem, u32 serial_type){
  u32 len;

  /* Integer and Real */
  if( serial_type<=7 && serial_type>0 ){
    u64 v;
    u32 i;
    if( serial_type==7 ){
      assert( sizeof(v)==sizeof(pMem->u.r) );
      memcpy(&v, &pMem->u.r, sizeof(v));
      swapMixedEndianFloat(v);
    }else{
      v = pMem->u.i;
    }
    len = i = sqlite3SmallTypeSizes[serial_type];
    assert( i>0 );
    do{
      buf[--i] = (u8)(v&0xFF);
      v >>= 8;
    }while( i );
    return len;
  }

  /* String or blob */
  if( serial_type>=12 ){
    assert( pMem->n + ((pMem->flags & MEM_Zero)?pMem->u.nZero:0)
             == (int)sqlite3BtreeSerialTypeLen(serial_type) );
    len = pMem->n;
    memcpy(buf, pMem->z, len);
    return len;
  }

  /* NULL or constants 0 or 1 */
  return 0;
}

/* Input "x" is a sequence of unsigned characters that represent a
** big-endian integer.  Return the equivalent native integer
*/
#define ONE_BYTE_INT(x)    ((i8)(x)[0])
#define TWO_BYTE_INT(x)    (256*(i8)((x)[0])|(x)[1])
#define THREE_BYTE_INT(x)  (65536*(i8)((x)[0])|((x)[1]<<8)|(x)[2])
#define FOUR_BYTE_UINT(x)  (((u32)(x)[0]<<24)|((x)[1]<<16)|((x)[2]<<8)|(x)[3])
#define FOUR_BYTE_INT(x) (16777216*(i8)((x)[0])|((x)[1]<<16)|((x)[2]<<8)|(x)[3])

/*
** Size of struct Mem not including the Mem.zMalloc member or anything that
** follows.
*/
#define MEMCELLSIZE offsetof(Mem,zMalloc)

#define VdbeMemDynamic(X)  \
  (((X)->flags&MEM_Dyn)!=0)

/*
** Initialize bulk memory to be a consistent Mem object.
**
** The minimum amount of initialization feasible is performed.
*/
SQLITE_PRIVATE void sqlite3VdbeMemInit(Mem *pMem, Btree *pBtree, u16 flags){
  assert( (flags & ~MEM_TypeMask)==0 );
  pMem->flags = flags;
  pMem->pBtree = pBtree;
  pMem->szMalloc = 0;
}

/*
** If pMem is an object with a valid string representation, this routine
** ensures the internal encoding for the string representation is
** 'desiredEnc', one of SQLITE_UTF8, SQLITE_UTF16LE or SQLITE_UTF16BE.
**
** If pMem is not a string object, or the encoding of the string
** representation is already stored using the requested encoding, then this
** routine is a no-op.
**
** SQLITE_OK is returned if the conversion is successful (or not required).
** SQLITE_NOMEM may be returned if a malloc() fails during conversion
** between formats.
*/
SQLITE_PRIVATE int sqlite3VdbeChangeEncoding(Mem *pMem, int desiredEnc){
  assert( (pMem->flags&MEM_RowSet)==0 );
  assert( desiredEnc==SQLITE_UTF8 || desiredEnc==SQLITE_UTF16LE
           || desiredEnc==SQLITE_UTF16BE );
  if( !(pMem->flags&MEM_Str) || pMem->enc==desiredEnc ){
    return SQLITE_OK;
  }
  assert( pMem->db==0 || sqlite3_mutex_held(pMem->db->mutex) );
  return SQLITE_ERROR;
}

/*
** If the memory cell contains a value that must be freed by
** invoking the external callback in Mem.xDel, then this routine
** will free that value.  It also sets Mem.flags to MEM_Null.
**
** This is a helper routine for sqlite3VdbeMemSetNull() and
** for sqlite3VdbeMemRelease().  Use those other routines as the
** entry point for releasing Mem resources.
*/
static SQLITE_NOINLINE void vdbeMemClearExternAndSetNull(Mem *p){
  assert( p->db==0 || sqlite3_mutex_held(p->db->mutex) );
  assert( VdbeMemDynamic(p) );
  if( p->flags&MEM_Dyn ){
    assert( p->xDel!=SQLITE_DYNAMIC && p->xDel!=0 );
    p->xDel((void *)p->z);
  }
  p->flags = MEM_Null;
}

/*
** Delete any previous value and set the value stored in *pMem to NULL.
**
** This routine calls the Mem.xDel destructor to dispose of values that
** require the destructor.  But it preserves the Mem.zMalloc memory allocation.
** To free all resources, use sqlite3VdbeMemRelease(), which both calls this
** routine to invoke the destructor and deallocates Mem.zMalloc.
**
** Use this routine to reset the Mem prior to insert a new value.
**
** Use sqlite3VdbeMemRelease() to complete erase the Mem prior to abandoning it.
*/
SQLITE_PRIVATE void sqlite3VdbeMemSetNull(Mem *pMem){
  if( VdbeMemDynamic(pMem) ){
    vdbeMemClearExternAndSetNull(pMem);
  }else{
    pMem->flags = MEM_Null;
  }
}

/*
** Make sure pMem->z points to a writable allocation of at least 
** min(n,32) bytes.
**
** If the bPreserve argument is true, then copy of the content of
** pMem->z into the new allocation.  pMem must be either a string or
** blob if bPreserve is true.  If bPreserve is false, any prior content
** in pMem->z is discarded.
*/
SQLITE_PRIVATE SQLITE_NOINLINE int sqlite3VdbeMemGrow(Mem *pMem, int n, int bPreserve){
  assert( sqlite3VdbeCheckMemInvariants(pMem) );
  assert( (pMem->flags&MEM_RowSet)==0 );

  /* If the bPreserve flag is set to true, then the memory cell must already
  ** contain a valid string or blob value.  */
  assert( bPreserve==0 || pMem->flags&(MEM_Blob|MEM_Str) );
  testcase( bPreserve && pMem->z==0 );

  assert( pMem->szMalloc==0
       || pMem->szMalloc==sqlite3DbMallocSize(pMem->pBtree, pMem->zMalloc) );
  if( pMem->szMalloc<n ){
    if( n<32 ) n = 32;
    if( bPreserve && pMem->szMalloc>0 && pMem->z==pMem->zMalloc ){
      pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->pBtree, pMem->z, n);
      bPreserve = 0;
    }else{
      if( pMem->szMalloc>0 ) sqlite3DbFree(pMem->pBtree, pMem->zMalloc);
      pMem->zMalloc = sqlite3DbMallocRaw(pMem->pBtree, n);
    }
    if( pMem->zMalloc==0 ){
      sqlite3VdbeMemSetNull(pMem);
      pMem->z = 0;
      pMem->szMalloc = 0;
      return SQLITE_NOMEM;
    }else{
      pMem->szMalloc = sqlite3DbMallocSize(pMem->pBtree, pMem->zMalloc);
    }
  }

  if( bPreserve && pMem->z && pMem->z!=pMem->zMalloc ){
    memcpy(pMem->zMalloc, pMem->z, pMem->n);
  }
  if( (pMem->flags&MEM_Dyn)!=0 ){
    assert( pMem->xDel!=0 && pMem->xDel!=SQLITE_DYNAMIC );
    pMem->xDel((void *)(pMem->z));
  }

  pMem->z = pMem->zMalloc;
  pMem->flags &= ~(MEM_Dyn|MEM_Ephem|MEM_Static);
  return SQLITE_OK;
}

/*
** Change the pMem->zMalloc allocation to be at least szNew bytes.
** If pMem->zMalloc already meets or exceeds the requested size, this
** routine is a no-op.
**
** Any prior string or blob content in the pMem object may be discarded.
** The pMem->xDel destructor is called, if it exists.  Though MEM_Str
** and MEM_Blob values may be discarded, MEM_Int, MEM_Real, and MEM_Null
** values are preserved.
**
** Return SQLITE_OK on success or an error code (probably SQLITE_NOMEM)
** if unable to complete the resizing.
*/
SQLITE_PRIVATE int sqlite3VdbeMemClearAndResize(Mem *pMem, int szNew){
  assert( szNew>0 );
  assert( (pMem->flags & MEM_Dyn)==0 || pMem->szMalloc==0 );
  if( pMem->szMalloc<szNew ){
    return sqlite3VdbeMemGrow(pMem, szNew, 0);
  }
  assert( (pMem->flags & MEM_Dyn)==0 );
  pMem->z = pMem->zMalloc;
  pMem->flags &= (MEM_Null|MEM_Int|MEM_Real);
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_INCRBLOB
  int sqlite3VdbeMemExpandBlob(Mem *);
  #define ExpandBlob(P) (((P)->flags&MEM_Zero)?sqlite3VdbeMemExpandBlob(P):0)
#else
  #define sqlite3VdbeMemExpandBlob(x) SQLITE_OK
  #define ExpandBlob(P) SQLITE_OK
#endif

/*
** Change pMem so that its MEM_Str or MEM_Blob value is stored in
** MEM.zMalloc, where it can be safely written.
**
** Return SQLITE_OK on success or SQLITE_NOMEM if malloc fails.
*/
SQLITE_PRIVATE int sqlite3VdbeMemMakeWriteable(Mem *pMem){
  int f;
  assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );
  assert( (pMem->flags&MEM_RowSet)==0 );
  ExpandBlob(pMem);
  f = pMem->flags;
  if( (f&(MEM_Str|MEM_Blob)) && (pMem->szMalloc==0 || pMem->z!=pMem->zMalloc) ){
    if( sqlite3VdbeMemGrow(pMem, pMem->n + 2, 1) ){
      return SQLITE_NOMEM;
    }
    pMem->z[pMem->n] = 0;
    pMem->z[pMem->n+1] = 0;
    pMem->flags |= MEM_Term;
  }
  pMem->flags &= ~MEM_Ephem;
#ifdef SQLITE_DEBUG
  pMem->pScopyFrom = 0;
#endif

  return SQLITE_OK;
}

/*
** It is already known that pMem contains an unterminated string.
** Add the zero terminator.
*/
static SQLITE_NOINLINE int vdbeMemAddTerminator(Mem *pMem){
  if( sqlite3VdbeMemGrow(pMem, pMem->n+2, 1) ){
    return SQLITE_NOMEM;
  }
  pMem->z[pMem->n] = 0;
  pMem->z[pMem->n+1] = 0;
  pMem->flags |= MEM_Term;
  return SQLITE_OK;
}

/*
** Make sure the given Mem is \u0000 terminated.
*/
SQLITE_PRIVATE int sqlite3VdbeMemNulTerminate(Mem *pMem){
  assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );
  testcase( (pMem->flags & (MEM_Term|MEM_Str))==(MEM_Term|MEM_Str) );
  testcase( (pMem->flags & (MEM_Term|MEM_Str))==0 );
  if( (pMem->flags & (MEM_Term|MEM_Str))!=MEM_Str ){
    return SQLITE_OK;   /* Nothing to do */
  }else{
    return vdbeMemAddTerminator(pMem);
  }
}

/*
** Add MEM_Str to the set of representations for the given Mem.  Numbers
** are converted using sqlite3_snprintf().  Converting a BLOB to a string
** is a no-op.
**
** Existing representations MEM_Int and MEM_Real are invalidated if
** bForce is true but are retained if bForce is false.
**
** A MEM_Null value will never be passed to this function. This function is
** used for converting values to text for returning to the user (i.e. via
** sqlite3_value_text()), or for ensuring that values to be used as btree
** keys are strings. In the former case a NULL pointer is returned the
** user and the latter is an internal programming error.
*/
SQLITE_PRIVATE int sqlite3VdbeMemStringify(Mem *pMem, u8 enc, u8 bForce){
  int fg = pMem->flags;
  const int nByte = 32;

  assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );
  assert( !(fg&MEM_Zero) );
  assert( !(fg&(MEM_Str|MEM_Blob)) );
  assert( fg&(MEM_Int|MEM_Real) );
  assert( (pMem->flags&MEM_RowSet)==0 );
  assert( EIGHT_BYTE_ALIGNMENT(pMem) );


  if( sqlite3VdbeMemClearAndResize(pMem, nByte) ){
    return SQLITE_NOMEM;
  }

  /* For a Real or Integer, use sqlite3_snprintf() to produce the UTF-8
  ** string representation of the value. Then, if the required encoding
  ** is UTF-16le or UTF-16be do a translation.
  ** 
  ** FIX ME: It would be better if sqlite3_snprintf() could do UTF-16.
  */
  if( fg & MEM_Int ){
    sqlite3_snprintf(nByte, pMem->z, "%lld", pMem->u.i);
  }else{
    assert( fg & MEM_Real );
    sqlite3_snprintf(nByte, pMem->z, "%!.15g", pMem->u.r);
  }
  pMem->n = sqlite3Strlen30(pMem->z);
  pMem->enc = SQLITE_UTF8;
  pMem->flags |= MEM_Str|MEM_Term;
  if( bForce ) pMem->flags &= ~(MEM_Int|MEM_Real);
  sqlite3VdbeChangeEncoding(pMem, enc);
  return SQLITE_OK;
}

/*
** Release memory held by the Mem p, both external memory cleared
** by p->xDel and memory in p->zMalloc.
**
** This is a helper routine invoked by sqlite3VdbeMemRelease() in
** the unusual case where there really is memory in p that needs
** to be freed.
*/
static SQLITE_NOINLINE void vdbeMemClear(Mem *p){
  if( VdbeMemDynamic(p) ){
    vdbeMemClearExternAndSetNull(p);
  }
  if( p->szMalloc ){
    sqlite3DbFree(p->pBtree, p->zMalloc);
    p->szMalloc = 0;
  }
  p->z = 0;
}

/*
** Release any memory resources held by the Mem.  Both the memory that is
** free by Mem.xDel and the Mem.zMalloc allocation are freed.
**
** Use this routine prior to clean up prior to abandoning a Mem, or to
** reset a Mem back to its minimum memory utilization.
**
** Use sqlite3VdbeMemSetNull() to release just the Mem.xDel space
** prior to inserting new content into the Mem.
*/
SQLITE_PRIVATE void sqlite3VdbeMemRelease(Mem *p){
  assert( sqlite3VdbeCheckMemInvariants(p) );
  if( VdbeMemDynamic(p) || p->szMalloc ){
    vdbeMemClear(p);
  }
}

/*
** Make an shallow copy of pFrom into pTo.  Prior contents of
** pTo are freed.  The pFrom->z field is not duplicated.  If
** pFrom->z is used, then pTo->z points to the same thing as pFrom->z
** and flags gets srcType (either MEM_Ephem or MEM_Static).
*/
static void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType);
static SQLITE_NOINLINE void vdbeClrCopy(Mem *pTo, const Mem *pFrom, int eType){
  vdbeMemClearExternAndSetNull(pTo);
  assert( !VdbeMemDynamic(pTo) );
  sqlite3VdbeMemShallowCopy(pTo, pFrom, eType);
}
static void sqlite3VdbeMemShallowCopy(Mem *pTo, const Mem *pFrom, int srcType){
  assert( (pFrom->flags & MEM_RowSet)==0 );
  assert( pTo->pBtree==pFrom->pBtree );
  if( VdbeMemDynamic(pTo) ){ vdbeClrCopy(pTo,pFrom,srcType); return; }
  memcpy(pTo, pFrom, MEMCELLSIZE);
  if( (pFrom->flags&MEM_Static)==0 ){
    pTo->flags &= ~(MEM_Dyn|MEM_Static|MEM_Ephem);
    assert( srcType==MEM_Ephem || srcType==MEM_Static );
    pTo->flags |= srcType;
  }
}

/*
** Deserialize the data blob pointed to by buf as serial type serial_type
** and store the result in pMem.  Return the number of bytes read.
**
** This function is implemented as two separate routines for performance.
** The few cases that require local variables are broken out into a separate
** routine so that in most cases the overhead of moving the stack pointer
** is avoided.
*/ 
static u32 SQLITE_NOINLINE serialGet(
  const unsigned char *buf,     /* Buffer to deserialize from */
  u32 serial_type,              /* Serial type to deserialize */
  Mem *pMem                     /* Memory cell to write value into */
){
  u64 x = FOUR_BYTE_UINT(buf);
  u32 y = FOUR_BYTE_UINT(buf+4);
  x = (x<<32) + y;
  if( serial_type==6 ){
    /* EVIDENCE-OF: R-29851-52272 Value is a big-endian 64-bit
    ** twos-complement integer. */
    pMem->u.i = *(i64*)&x;
    pMem->flags = MEM_Int;
    testcase( pMem->u.i<0 );
  }else{
    /* EVIDENCE-OF: R-57343-49114 Value is a big-endian IEEE 754-2008 64-bit
    ** floating point number. */
#if !defined(NDEBUG) && !defined(SQLITE_OMIT_FLOATING_POINT)
    /* Verify that integers and floating point values use the same
    ** byte order.  Or, that if SQLITE_MIXED_ENDIAN_64BIT_FLOAT is
    ** defined that 64-bit floating point values really are mixed
    ** endian.
    */
    static const u64 t1 = ((u64)0x3ff00000)<<32;
    static const double r1 = 1.0;
    u64 t2 = t1;
    swapMixedEndianFloat(t2);
    assert( sizeof(r1)==sizeof(t2) && memcmp(&r1, &t2, sizeof(r1))==0 );
#endif
    assert( sizeof(x)==8 && sizeof(pMem->u.r)==8 );
    swapMixedEndianFloat(x);
    memcpy(&pMem->u.r, &x, sizeof(x));
    pMem->flags = sqlite3IsNaN(pMem->u.r) ? MEM_Null : MEM_Real;
  }
  return 8;
}
SQLITE_API u32 SQLITE_STDCALL sqlite3BtreeSerialGet(
  const unsigned char *buf,     /* Buffer to deserialize from */
  u32 serial_type,              /* Serial type to deserialize */
  Mem *pMem                     /* Memory cell to write value into */
){
  switch( serial_type ){
    case 10:   /* Reserved for future use */
    case 11:   /* Reserved for future use */
    case 0: {  /* Null */
      /* EVIDENCE-OF: R-24078-09375 Value is a NULL. */
      pMem->flags = MEM_Null;
      break;
    }
    case 1: {
      /* EVIDENCE-OF: R-44885-25196 Value is an 8-bit twos-complement
      ** integer. */
      pMem->u.i = ONE_BYTE_INT(buf);
      pMem->flags = MEM_Int;
      testcase( pMem->u.i<0 );
      return 1;
    }
    case 2: { /* 2-byte signed integer */
      /* EVIDENCE-OF: R-49794-35026 Value is a big-endian 16-bit
      ** twos-complement integer. */
      pMem->u.i = TWO_BYTE_INT(buf);
      pMem->flags = MEM_Int;
      testcase( pMem->u.i<0 );
      return 2;
    }
    case 3: { /* 3-byte signed integer */
      /* EVIDENCE-OF: R-37839-54301 Value is a big-endian 24-bit
      ** twos-complement integer. */
      pMem->u.i = THREE_BYTE_INT(buf);
      pMem->flags = MEM_Int;
      testcase( pMem->u.i<0 );
      return 3;
    }
    case 4: { /* 4-byte signed integer */
      /* EVIDENCE-OF: R-01849-26079 Value is a big-endian 32-bit
      ** twos-complement integer. */
      pMem->u.i = FOUR_BYTE_INT(buf);
      pMem->flags = MEM_Int;
      testcase( pMem->u.i<0 );
      return 4;
    }
    case 5: { /* 6-byte signed integer */
      /* EVIDENCE-OF: R-50385-09674 Value is a big-endian 48-bit
      ** twos-complement integer. */
      pMem->u.i = FOUR_BYTE_UINT(buf+2) + (((i64)1)<<32)*TWO_BYTE_INT(buf);
      pMem->flags = MEM_Int;
      testcase( pMem->u.i<0 );
      return 6;
    }
    case 6:   /* 8-byte signed integer */
    case 7: { /* IEEE floating point */
      /* These use local variables, so do them in a separate routine
      ** to avoid having to move the frame pointer in the common case */
      return serialGet(buf,serial_type,pMem);
    }
    case 8:    /* Integer 0 */
    case 9: {  /* Integer 1 */
      /* EVIDENCE-OF: R-12976-22893 Value is the integer 0. */
      /* EVIDENCE-OF: R-18143-12121 Value is the integer 1. */
      pMem->u.i = serial_type-8;
      pMem->flags = MEM_Int;
      return 0;
    }
    default: {
      /* EVIDENCE-OF: R-14606-31564 Value is a BLOB that is (N-12)/2 bytes in
      ** length.
      ** EVIDENCE-OF: R-28401-00140 Value is a string in the text encoding and
      ** (N-13)/2 bytes in length. */
      static const u16 aFlag[] = { MEM_Blob|MEM_Ephem, MEM_Str|MEM_Ephem };
      pMem->z = (char *)buf;
      pMem->n = (serial_type-12)/2;
      pMem->flags = aFlag[serial_type&1];
      return pMem->n;
    }
  }
  return 0;
}

/*
** This routine is used to allocate sufficient space for an UnpackedRecord
** structure large enough to be used with sqlite3VdbeRecordUnpack() if
** the first argument is a pointer to KeyInfo structure pKeyInfo.
**
** The space is either allocated using sqlite3DbMallocRaw() or from within
** the unaligned buffer passed via the second and third arguments (presumably
** stack space). If the former, then *ppFree is set to a pointer that should
** be eventually freed by the caller using sqlite3DbFree(). Or, if the 
** allocation comes from the pSpace/szSpace buffer, *ppFree is set to NULL
** before returning.
**
** If an OOM error occurs, NULL is returned.
*/
SQLITE_PRIVATE UnpackedRecord *sqlite3VdbeAllocUnpackedRecord(
  KeyInfo *pKeyInfo,              /* Description of the record */
  char *pSpace,                   /* Unaligned space available */
  int szSpace,                    /* Size of pSpace[] in bytes */
  char **ppFree                   /* OUT: Caller should free this pointer */
){
  UnpackedRecord *p;              /* Unpacked record to return */
  int nOff;                       /* Increment pSpace by nOff to align it */
  int nByte;                      /* Number of bytes required for *p */

  /* We want to shift the pointer pSpace up such that it is 8-byte aligned.
  ** Thus, we need to calculate a value, nOff, between 0 and 7, to shift 
  ** it by.  If pSpace is already 8-byte aligned, nOff should be zero.
  */
  nOff = (8 - (SQLITE_PTR_TO_INT(pSpace) & 7)) & 7;
  nByte = ROUND8(sizeof(UnpackedRecord)) + sizeof(Mem)*(pKeyInfo->nField+1);
  if( nByte>szSpace+nOff ){
    p = (UnpackedRecord *)sqlite3DbMallocRaw(pKeyInfo->pBtree, nByte);
    *ppFree = (char *)p;
    if( !p ) return 0;
  }else{
    p = (UnpackedRecord*)&pSpace[nOff];
    *ppFree = 0;
  }

  p->aMem = (Mem*)&((char*)p)[ROUND8(sizeof(UnpackedRecord))];
  assert( pKeyInfo->aSortOrder!=0 );
  p->pKeyInfo = pKeyInfo;
  p->nField = pKeyInfo->nField + 1;
  return p;
}

/*
** Given the nKey-byte encoding of a record in pKey[], populate the 
** UnpackedRecord structure indicated by the fourth argument with the
** contents of the decoded record.
*/ 
SQLITE_PRIVATE void sqlite3VdbeRecordUnpack(
  KeyInfo *pKeyInfo,     /* Information about the record format */
  int nKey,              /* Size of the binary record */
  const void *pKey,      /* The binary record */
  UnpackedRecord *p      /* Populate this structure before returning. */
){
  const unsigned char *aKey = (const unsigned char *)pKey;
  int d; 
  u32 idx;                        /* Offset in aKey[] to read from */
  u16 u;                          /* Unsigned loop counter */
  u32 szHdr;
  Mem *pMem = p->aMem;

  p->default_rc = 0;
  assert( EIGHT_BYTE_ALIGNMENT(pMem) );
  idx = getVarint32(aKey, szHdr);
  d = szHdr;
  u = 0;
  while( idx<szHdr && d<=nKey ){
    u32 serial_type;

    idx += getVarint32(&aKey[idx], serial_type);
    pMem->enc = pKeyInfo->enc;
    pMem->pBtree = pKeyInfo->pBtree;
    /* pMem->flags = 0; // sqlite3BtreeSerialGet() will set this for us */
    pMem->szMalloc = 0;
    d += sqlite3BtreeSerialGet(&aKey[d], serial_type, pMem);
    pMem++;
    if( (++u)>=p->nField ) break;
  }
  assert( u<=pKeyInfo->nField + 1 );
  p->nField = u;
}

#if SQLITE_DEBUG
/*
** Count the number of fields (a.k.a. columns) in the record given by
** pKey,nKey.  The verify that this count is less than or equal to the
** limit given by pKeyInfo->nField + pKeyInfo->nXField.
**
** If this constraint is not satisfied, it means that the high-speed
** vdbeRecordCompareInt() and vdbeRecordCompareString() routines will
** not work correctly.  If this assert() ever fires, it probably means
** that the KeyInfo.nField or KeyInfo.nXField values were computed
** incorrectly.
*/
static void vdbeAssertFieldCountWithinLimits(
  int nKey, const void *pKey,   /* The record to verify */ 
  const KeyInfo *pKeyInfo       /* Compare size with this KeyInfo */
){
  int nField = 0;
  u32 szHdr;
  u32 idx;
  u32 notUsed;
  const unsigned char *aKey = (const unsigned char*)pKey;

  if( CORRUPT_DB ) return;
  idx = getVarint32(aKey, szHdr);
  assert( nKey>=0 );
  assert( szHdr<=(u32)nKey );
  while( idx<szHdr ){
    idx += getVarint32(aKey+idx, notUsed);
    nField++;
  }
  assert( nField <= pKeyInfo->nField+pKeyInfo->nXField );
}
#else
# define vdbeAssertFieldCountWithinLimits(A,B,C)
#endif

/*
** This function is an optimized version of sqlite3BtreeRecordCompare() 
** that (a) the first field of pPKey2 is an integer, and (b) the 
** size-of-header varint at the start of (pKey1/nKey1) fits in a single
** byte (i.e. is less than 128).
**
** To avoid concerns about buffer overreads, this routine is only used
** on schemas where the maximum valid header size is 63 bytes or less.
*/
static int vdbeRecordCompareInt(
  int nKey1, const void *pKey1, /* Left key */
  UnpackedRecord *pPKey2        /* Right key */
){
  const u8 *aKey = &((const u8*)pKey1)[*(const u8*)pKey1 & 0x3F];
  int serial_type = ((const u8*)pKey1)[1];
  int res;
  u32 y;
  u64 x;
  i64 v = pPKey2->aMem[0].u.i;
  i64 lhs;

  vdbeAssertFieldCountWithinLimits(nKey1, pKey1, pPKey2->pKeyInfo);
  assert( (*(u8*)pKey1)<=0x3F || CORRUPT_DB );
  switch( serial_type ){
    case 1: { /* 1-byte signed integer */
      lhs = ONE_BYTE_INT(aKey);
      testcase( lhs<0 );
      break;
    }
    case 2: { /* 2-byte signed integer */
      lhs = TWO_BYTE_INT(aKey);
      testcase( lhs<0 );
      break;
    }
    case 3: { /* 3-byte signed integer */
      lhs = THREE_BYTE_INT(aKey);
      testcase( lhs<0 );
      break;
    }
    case 4: { /* 4-byte signed integer */
      y = FOUR_BYTE_UINT(aKey);
      lhs = (i64)*(int*)&y;
      testcase( lhs<0 );
      break;
    }
    case 5: { /* 6-byte signed integer */
      lhs = FOUR_BYTE_UINT(aKey+2) + (((i64)1)<<32)*TWO_BYTE_INT(aKey);
      testcase( lhs<0 );
      break;
    }
    case 6: { /* 8-byte signed integer */
      x = FOUR_BYTE_UINT(aKey);
      x = (x<<32) | FOUR_BYTE_UINT(aKey+4);
      lhs = *(i64*)&x;
      testcase( lhs<0 );
      break;
    }
    case 8: 
      lhs = 0;
      break;
    case 9:
      lhs = 1;
      break;

    /* This case could be removed without changing the results of running
    ** this code. Including it causes gcc to generate a faster switch 
    ** statement (since the range of switch targets now starts at zero and
    ** is contiguous) but does not cause any duplicate code to be generated
    ** (as gcc is clever enough to combine the two like cases). Other 
    ** compilers might be similar.  */ 
    case 0: case 7:
      return sqlite3BtreeRecordCompare(nKey1, pKey1, pPKey2);

    default:
      return sqlite3BtreeRecordCompare(nKey1, pKey1, pPKey2);
  }

  if( v>lhs ){
    res = pPKey2->r1;
  }else if( v<lhs ){
    res = pPKey2->r2;
  }else if( pPKey2->nField>1 ){
    /* The first fields of the two keys are equal. Compare the trailing 
    ** fields.  */
    res = sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
  }else{
    /* The first fields of the two keys are equal and there are no trailing
    ** fields. Return pPKey2->default_rc in this case. */
    res = pPKey2->default_rc;
  }

  assert( vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, res) );
  return res;
}

/*
** This function is an optimized version of sqlite3BtreeRecordCompare() 
** that (a) the first field of pPKey2 is a string, that (b) the first field
** uses the collation sequence BINARY and (c) that the size-of-header varint 
** at the start of (pKey1/nKey1) fits in a single byte.
*/
static int vdbeRecordCompareString(
  int nKey1, const void *pKey1, /* Left key */
  UnpackedRecord *pPKey2        /* Right key */
){
  const u8 *aKey1 = (const u8*)pKey1;
  int serial_type;
  int res;

  vdbeAssertFieldCountWithinLimits(nKey1, pKey1, pPKey2->pKeyInfo);
  getVarint32(&aKey1[1], serial_type);
  if( serial_type<12 ){
    res = pPKey2->r1;      /* (pKey1/nKey1) is a number or a null */
  }else if( !(serial_type & 0x01) ){ 
    res = pPKey2->r2;      /* (pKey1/nKey1) is a blob */
  }else{
    int nCmp;
    int nStr;
    int szHdr = aKey1[0];

    nStr = (serial_type-12) / 2;
    if( (szHdr + nStr) > nKey1 ){
      pPKey2->errCode = (u8)SQLITE_CORRUPT_BKPT;
      return 0;    /* Corruption */
    }
    nCmp = MIN( pPKey2->aMem[0].n, nStr );
    res = memcmp(&aKey1[szHdr], pPKey2->aMem[0].z, nCmp);

    if( res==0 ){
      res = nStr - pPKey2->aMem[0].n;
      if( res==0 ){
        if( pPKey2->nField>1 ){
          res = sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 1);
        }else{
          res = pPKey2->default_rc;
        }
      }else if( res>0 ){
        res = pPKey2->r2;
      }else{
        res = pPKey2->r1;
      }
    }else if( res>0 ){
      res = pPKey2->r2;
    }else{
      res = pPKey2->r1;
    }
  }

  assert( vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, res)
       || CORRUPT_DB
       || pPKey2->pKeyInfo->pBtree->mallocFailed
  );
  return res;
}

/*
** If the given Mem* has a zero-filled tail, turn it into an ordinary
** blob stored in dynamically allocated space.
*/
#ifndef SQLITE_OMIT_INCRBLOB
SQLITE_PRIVATE int sqlite3VdbeMemExpandBlob(Mem *pMem){
  if( pMem->flags & MEM_Zero ){
    int nByte;
    assert( pMem->flags&MEM_Blob );
    assert( (pMem->flags&MEM_RowSet)==0 );
    assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );

    /* Set nByte to the number of bytes required to store the expanded blob. */
    nByte = pMem->n + pMem->u.nZero;
    if( nByte<=0 ){
      nByte = 1;
    }
    if( sqlite3VdbeMemGrow(pMem, nByte, 1) ){
      return SQLITE_NOMEM;
    }

    memset(&pMem->z[pMem->n], 0, pMem->u.nZero);
    pMem->n += pMem->u.nZero;
    pMem->flags &= ~MEM_Zero;
  }
  return SQLITE_OK;
}
#endif

/*
** Convert a 64-bit IEEE double into a 64-bit signed integer.
** If the double is out of range of a 64-bit signed integer then
** return the closest available 64-bit signed integer.
*/
static i64 doubleToInt64(double r){
#ifdef SQLITE_OMIT_FLOATING_POINT
  /* When floating-point is omitted, double and int64 are the same thing */
  return r;
#else
  /*
  ** Many compilers we encounter do not define constants for the
  ** minimum and maximum 64-bit integers, or they define them
  ** inconsistently.  And many do not understand the "LL" notation.
  ** So we define our own static constants here using nothing
  ** larger than a 32-bit integer constant.
  */
  static const i64 maxInt = LARGEST_INT64;
  static const i64 minInt = SMALLEST_INT64;

  if( r<=(double)minInt ){
    return minInt;
  }else if( r>=(double)maxInt ){
    return maxInt;
  }else{
    return (i64)r;
  }
#endif
}

/*
** Return some kind of integer value which is the best we can do
** at representing the value that *pMem describes as an integer.
** If pMem is an integer, then the value is exact.  If pMem is
** a floating-point then the value returned is the integer part.
** If pMem is a string or blob, then we make an attempt to convert
** it into an integer and return that.  If pMem represents an
** an SQL-NULL value, return 0.
**
** If pMem represents a string value, its encoding might be changed.
*/
SQLITE_PRIVATE i64 sqlite3VdbeIntValue(Mem *pMem){
  int flags;
  assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );
  assert( EIGHT_BYTE_ALIGNMENT(pMem) );
  flags = pMem->flags;
  if( flags & MEM_Int ){
    return pMem->u.i;
  }else if( flags & MEM_Real ){
    return doubleToInt64(pMem->u.r);
  }else if( flags & (MEM_Str|MEM_Blob) ){
    i64 value = 0;
    assert( pMem->z || pMem->n==0 );
    sqlite3Atoi64(pMem->z, &value, pMem->n, pMem->enc);
    return value;
  }else{
    return 0;
  }
}

/*
** Return the best representation of pMem that we can get into a
** double.  If pMem is already a double or an integer, return its
** value.  If it is a string or blob, try to convert it to a double.
** If it is a NULL, return 0.0.
*/
SQLITE_PRIVATE double sqlite3VdbeRealValue(Mem *pMem){
  assert( pMem->pBtree==0 || sqlite3_mutex_held(pMem->pBtree->mutex) );
  assert( EIGHT_BYTE_ALIGNMENT(pMem) );
  if( pMem->flags & MEM_Real ){
    return pMem->u.r;
  }else if( pMem->flags & MEM_Int ){
    return (double)pMem->u.i;
  }else if( pMem->flags & (MEM_Str|MEM_Blob) ){
    /* (double)0 In case of SQLITE_OMIT_FLOATING_POINT... */
    double val = (double)0;
    sqlite3AtoF(pMem->z, &val, pMem->n, pMem->enc);
    return val;
  }else{
    /* (double)0 In case of SQLITE_OMIT_FLOATING_POINT... */
    return (double)0;
  }
}

/*
** The pVal argument is known to be a value other than NULL.
** Convert it into a string with encoding enc and return a pointer
** to a zero-terminated version of that string.
*/
static SQLITE_NOINLINE const void *valueToText(Mem* pVal, u8 enc){
  assert( pVal!=0 );
  assert( pVal->pBtree==0 || sqlite3_mutex_held(pVal->pBtree->mutex) );
  assert( (enc&3)==(enc&~SQLITE_UTF16_ALIGNED) );
  assert( (pVal->flags & MEM_RowSet)==0 );
  assert( (pVal->flags & (MEM_Null))==0 );
  if( pVal->flags & (MEM_Blob|MEM_Str) ){
    pVal->flags |= MEM_Str;
    if( pVal->flags & MEM_Zero ){
      sqlite3VdbeMemExpandBlob(pVal);
    }
    if( pVal->enc != (enc & ~SQLITE_UTF16_ALIGNED) ){
      sqlite3VdbeChangeEncoding(pVal, enc & ~SQLITE_UTF16_ALIGNED);
    }
    if( (enc & SQLITE_UTF16_ALIGNED)!=0 && 1==(1&SQLITE_PTR_TO_INT(pVal->z)) ){
      assert( (pVal->flags & (MEM_Ephem|MEM_Static))!=0 );
      if( sqlite3VdbeMemMakeWriteable(pVal)!=SQLITE_OK ){
        return 0;
      }
    }
    sqlite3VdbeMemNulTerminate(pVal); /* IMP: R-31275-44060 */
  }else{
    sqlite3VdbeMemStringify(pVal, enc, 0);
    assert( 0==(1&SQLITE_PTR_TO_INT(pVal->z)) );
  }
  assert(pVal->enc==(enc & ~SQLITE_UTF16_ALIGNED) || pVal->pBtree==0
              || pVal->pBtree->mallocFailed );
  if( pVal->enc==(enc & ~SQLITE_UTF16_ALIGNED) ){
    return pVal->z;
  }else{
    return 0;
  }
}

/* This function is only available internally, it is not part of the
** external API. It works in a similar way to sqlite3_value_text(),
** except the data returned is in the encoding specified by the second
** parameter, which must be one of SQLITE_UTF16BE, SQLITE_UTF16LE or
** SQLITE_UTF8.
**
** (2006-02-16:)  The enc value can be or-ed with SQLITE_UTF16_ALIGNED.
** If that is the case, then the result must be aligned on an even byte
** boundary.
*/
SQLITE_PRIVATE const void *sqlite3ValueText(Mem* pVal, u8 enc){
  if( !pVal ) return 0;
  assert( pVal->pBtree==0 || sqlite3_mutex_held(pVal->pBtree->mutex) );
  assert( (enc&3)==(enc&~SQLITE_UTF16_ALIGNED) );
  assert( (pVal->flags & MEM_RowSet)==0 );
  if( (pVal->flags&MEM_Str)==MEM_Str && pVal->enc==enc ){
    return pVal->z;
  }
  if( pVal->flags&MEM_Null ){
    return 0;
  }
  return valueToText(pVal, enc);
}

/*
** Both *pMem1 and *pMem2 contain string values. Compare the two values
** using the collation sequence pColl. As usual, return a negative , zero
** or positive value if *pMem1 is less than, equal to or greater than 
** *pMem2, respectively. Similar in spirit to "rc = (*pMem1) - (*pMem2);".
*/
static int vdbeCompareMemString(
  const Mem *pMem1,
  const Mem *pMem2,
  const CollSeq *pColl,
  u8 *prcErr                      /* If an OOM occurs, set to SQLITE_NOMEM */
){
  if( pMem1->enc==pColl->enc ){
    /* The strings are already in the correct encoding.  Call the
     ** comparison function directly */
    return pColl->xCmp(pColl->pUser,pMem1->n,pMem1->z,pMem2->n,pMem2->z);
  }else{
    int rc;
    const void *v1, *v2;
    int n1, n2;
    Mem c1;
    Mem c2;
    sqlite3VdbeMemInit(&c1, pMem1->pBtree, MEM_Null);
    sqlite3VdbeMemInit(&c2, pMem1->pBtree, MEM_Null);
    sqlite3VdbeMemShallowCopy(&c1, pMem1, MEM_Ephem);
    sqlite3VdbeMemShallowCopy(&c2, pMem2, MEM_Ephem);
    v1 = sqlite3ValueText(&c1, pColl->enc);
    n1 = v1==0 ? 0 : c1.n;
    v2 = sqlite3ValueText(&c2, pColl->enc);
    n2 = v2==0 ? 0 : c2.n;
    rc = pColl->xCmp(pColl->pUser, n1, v1, n2, v2);
    sqlite3VdbeMemRelease(&c1);
    sqlite3VdbeMemRelease(&c2);
    if( (v1==0 || v2==0) && prcErr ) *prcErr = SQLITE_NOMEM;
    return rc;
  }
}

/*
** The first argument passed to this function is a serial-type that
** corresponds to an integer - all values between 1 and 9 inclusive 
** except 7. The second points to a buffer containing an integer value
** serialized according to serial_type. This function deserializes
** and returns the value.
*/
static i64 vdbeRecordDecodeInt(u32 serial_type, const u8 *aKey){
  u32 y;
  assert( CORRUPT_DB || (serial_type>=1 && serial_type<=9 && serial_type!=7) );
  switch( serial_type ){
    case 0:
    case 1:
      testcase( aKey[0]&0x80 );
      return ONE_BYTE_INT(aKey);
    case 2:
      testcase( aKey[0]&0x80 );
      return TWO_BYTE_INT(aKey);
    case 3:
      testcase( aKey[0]&0x80 );
      return THREE_BYTE_INT(aKey);
    case 4: {
      testcase( aKey[0]&0x80 );
      y = FOUR_BYTE_UINT(aKey);
      return (i64)*(int*)&y;
    }
    case 5: {
      testcase( aKey[0]&0x80 );
      return FOUR_BYTE_UINT(aKey+2) + (((i64)1)<<32)*TWO_BYTE_INT(aKey);
    }
    case 6: {
      u64 x = FOUR_BYTE_UINT(aKey);
      testcase( aKey[0]&0x80 );
      x = (x<<32) | FOUR_BYTE_UINT(aKey+4);
      return (i64)*(i64*)&x;
    }
  }

  return (serial_type - 8);
}

/*
** This function compares the two table rows or index records
** specified by {nKey1, pKey1} and pPKey2.  It returns a negative, zero
** or positive integer if key1 is less than, equal to or 
** greater than key2.  The {nKey1, pKey1} key must be a blob
** created by the OP_MakeRecord opcode of the VDBE.  The pPKey2
** key must be a parsed key such as obtained from
** sqlite3VdbeParseRecord.
**
** If argument bSkip is non-zero, it is assumed that the caller has already
** determined that the first fields of the keys are equal.
**
** Key1 and Key2 do not have to contain the same number of fields. If all 
** fields that appear in both keys are equal, then pPKey2->default_rc is 
** returned.
**
** If database corruption is discovered, set pPKey2->errCode to 
** SQLITE_CORRUPT and return 0. If an OOM error is encountered, 
** pPKey2->errCode is set to SQLITE_NOMEM and, if it is not NULL, the
** malloc-failed flag set on database handle (pPKey2->pKeyInfo->pBtree).
*/
SQLITE_PRIVATE int sqlite3VdbeRecordCompareWithSkip(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2,         /* Right key */
  int bSkip                       /* If true, skip the first field */
){
  u32 d1;                         /* Offset into aKey[] of next data element */
  int i;                          /* Index of next field to compare */
  u32 szHdr1;                     /* Size of record header in bytes */
  u32 idx1;                       /* Offset of first type in header */
  int rc = 0;                     /* Return value */
  Mem *pRhs = pPKey2->aMem;       /* Next field of pPKey2 to compare */
  KeyInfo *pKeyInfo = pPKey2->pKeyInfo;
  const unsigned char *aKey1 = (const unsigned char *)pKey1;
  Mem mem1;

  /* If bSkip is true, then the caller has already determined that the first
  ** two elements in the keys are equal. Fix the various stack variables so
  ** that this routine begins comparing at the second field. */
  if( bSkip ){
    u32 s1;
    idx1 = 1 + getVarint32(&aKey1[1], s1);
    szHdr1 = aKey1[0];
    d1 = szHdr1 + sqlite3BtreeSerialTypeLen(s1);
    i = 1;
    pRhs++;
  }else{
    idx1 = getVarint32(aKey1, szHdr1);
    d1 = szHdr1;
    if( d1>(unsigned)nKey1 ){ 
      pPKey2->errCode = (u8)SQLITE_CORRUPT_BKPT;
      return 0;  /* Corruption */
    }
    i = 0;
  }

  VVA_ONLY( mem1.szMalloc = 0; ) /* Only needed by assert() statements */
  assert( pPKey2->pKeyInfo->nField+pPKey2->pKeyInfo->nXField>=pPKey2->nField 
       || CORRUPT_DB );
  assert( pPKey2->pKeyInfo->aSortOrder!=0 );
  assert( pPKey2->pKeyInfo->nField>0 );
  assert( idx1<=szHdr1 || CORRUPT_DB );
  do{
    u32 serial_type;

    /* RHS is an integer */
    if( pRhs->flags & MEM_Int ){
      serial_type = aKey1[idx1];
      testcase( serial_type==12 );
      if( serial_type>=10 ){
        rc = +1;
      }else if( serial_type==0 ){
        rc = -1;
      }else if( serial_type==7 ){
        double rhs = (double)pRhs->u.i;
        sqlite3BtreeSerialGet(&aKey1[d1], serial_type, &mem1);
        if( mem1.u.r<rhs ){
          rc = -1;
        }else if( mem1.u.r>rhs ){
          rc = +1;
        }
      }else{
        i64 lhs = vdbeRecordDecodeInt(serial_type, &aKey1[d1]);
        i64 rhs = pRhs->u.i;
        if( lhs<rhs ){
          rc = -1;
        }else if( lhs>rhs ){
          rc = +1;
        }
      }
    }

    /* RHS is real */
    else if( pRhs->flags & MEM_Real ){
      serial_type = aKey1[idx1];
      if( serial_type>=10 ){
        /* Serial types 12 or greater are strings and blobs (greater than
        ** numbers). Types 10 and 11 are currently "reserved for future 
        ** use", so it doesn't really matter what the results of comparing
        ** them to numberic values are.  */
        rc = +1;
      }else if( serial_type==0 ){
        rc = -1;
      }else{
        double rhs = pRhs->u.r;
        double lhs;
        sqlite3BtreeSerialGet(&aKey1[d1], serial_type, &mem1);
        if( serial_type==7 ){
          lhs = mem1.u.r;
        }else{
          lhs = (double)mem1.u.i;
        }
        if( lhs<rhs ){
          rc = -1;
        }else if( lhs>rhs ){
          rc = +1;
        }
      }
    }

    /* RHS is a string */
    else if( pRhs->flags & MEM_Str ){
      getVarint32(&aKey1[idx1], serial_type);
      testcase( serial_type==12 );
      if( serial_type<12 ){
        rc = -1;
      }else if( !(serial_type & 0x01) ){
        rc = +1;
      }else{
        mem1.n = (serial_type - 12) / 2;
        testcase( (d1+mem1.n)==(unsigned)nKey1 );
        testcase( (d1+mem1.n+1)==(unsigned)nKey1 );
        if( (d1+mem1.n) > (unsigned)nKey1 ){
          pPKey2->errCode = (u8)SQLITE_CORRUPT_BKPT;
          return 0;                /* Corruption */
        }else if( pKeyInfo->aColl[i] ){
          mem1.enc = pKeyInfo->enc;
          mem1.pBtree = pKeyInfo->pBtree;
          mem1.flags = MEM_Str;
          mem1.z = (char*)&aKey1[d1];
          rc = vdbeCompareMemString(
              &mem1, pRhs, pKeyInfo->aColl[i], &pPKey2->errCode
          );
        }else{
          int nCmp = MIN(mem1.n, pRhs->n);
          rc = memcmp(&aKey1[d1], pRhs->z, nCmp);
          if( rc==0 ) rc = mem1.n - pRhs->n; 
        }
      }
    }

    /* RHS is a blob */
    else if( pRhs->flags & MEM_Blob ){
      getVarint32(&aKey1[idx1], serial_type);
      testcase( serial_type==12 );
      if( serial_type<12 || (serial_type & 0x01) ){
        rc = -1;
      }else{
        int nStr = (serial_type - 12) / 2;
        testcase( (d1+nStr)==(unsigned)nKey1 );
        testcase( (d1+nStr+1)==(unsigned)nKey1 );
        if( (d1+nStr) > (unsigned)nKey1 ){
          pPKey2->errCode = (u8)SQLITE_CORRUPT_BKPT;
          return 0;                /* Corruption */
        }else{
          int nCmp = MIN(nStr, pRhs->n);
          rc = memcmp(&aKey1[d1], pRhs->z, nCmp);
          if( rc==0 ) rc = nStr - pRhs->n;
        }
      }
    }

    /* RHS is null */
    else{
      serial_type = aKey1[idx1];
      rc = (serial_type!=0);
    }

    if( rc!=0 ){
      if( pKeyInfo->aSortOrder[i] ){
        rc = -rc;
      }
      assert( vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, rc) );
      assert( mem1.szMalloc==0 );  /* See comment below */
      return rc;
    }

    i++;
    pRhs++;
    d1 += sqlite3BtreeSerialTypeLen(serial_type);
    idx1 += sqlite3BtreeVarintLen(serial_type);
  }while( idx1<(unsigned)szHdr1 && i<pPKey2->nField && d1<=(unsigned)nKey1 );

  /* No memory allocation is ever used on mem1.  Prove this using
  ** the following assert().  If the assert() fails, it indicates a
  ** memory leak and a need to call sqlite3VdbeMemRelease(&mem1).  */
  assert( mem1.szMalloc==0 );

  /* rc==0 here means that one or both of the keys ran out of fields and
  ** all the fields up to that point were equal. Return the default_rc
  ** value.  */
  assert( CORRUPT_DB 
       || vdbeRecordCompareDebug(nKey1, pKey1, pPKey2, pPKey2->default_rc) 
       || pKeyInfo->pBtree->mallocFailed
  );
  return pPKey2->default_rc;
}
SQLITE_API int SQLITE_STDCALL sqlite3BtreeRecordCompare(
  int nKey1, const void *pKey1,   /* Left key */
  UnpackedRecord *pPKey2          /* Right key */
){
  return sqlite3VdbeRecordCompareWithSkip(nKey1, pKey1, pPKey2, 0);
}

/*
** Return a pointer to an sqlite3BtreeRecordCompare() compatible function
** suitable for comparing serialized records to the unpacked record passed
** as the only argument.
*/
SQLITE_PRIVATE RecordCompare sqlite3VdbeFindCompare(UnpackedRecord *p){
  /* varintRecordCompareInt() and varintRecordCompareString() both assume
  ** that the size-of-header varint that occurs at the start of each record
  ** fits in a single byte (i.e. is 127 or less). varintRecordCompareInt()
  ** also assumes that it is safe to overread a buffer by at least the 
  ** maximum possible legal header size plus 8 bytes. Because there is
  ** guaranteed to be at least 74 (but not 136) bytes of padding following each
  ** buffer passed to varintRecordCompareInt() this makes it convenient to
  ** limit the size of the header to 64 bytes in cases where the first field
  ** is an integer.
  **
  ** The easiest way to enforce this limit is to consider only records with
  ** 13 fields or less. If the first field is an integer, the maximum legal
  ** header size is (12*5 + 1 + 1) bytes.  */
  if( (p->pKeyInfo->nField + p->pKeyInfo->nXField)<=13 ){
    int flags = p->aMem[0].flags;
    if( p->pKeyInfo->aSortOrder[0] ){
      p->r1 = 1;
      p->r2 = -1;
    }else{
      p->r1 = -1;
      p->r2 = 1;
    }
    if( (flags & MEM_Int) ){
      return vdbeRecordCompareInt;
    }
    testcase( flags & MEM_Real );
    testcase( flags & MEM_Null );
    testcase( flags & MEM_Blob );
    if( (flags & (MEM_Real|MEM_Null|MEM_Blob))==0 && p->pKeyInfo->aColl[0]==0 ){
      assert( flags & MEM_Str );
      return vdbeRecordCompareString;
    }
  }

  return sqlite3BtreeRecordCompare;
}

/*
** Move data out of a btree key or data field and into a Mem structure.
** The data or key is taken from the entry that pCur is currently pointing
** to.  offset and amt determine what portion of the data or key to retrieve.
** key is true to get the key or false to get data.  The result is written
** into the pMem element.
**
** The pMem object must have been initialized.  This routine will use
** pMem->zMalloc to hold the content from the btree, if possible.  New
** pMem->zMalloc space will be allocated if necessary.  The calling routine
** is responsible for making sure that the pMem object is eventually
** destroyed.
**
** If this routine fails for any reason (malloc returns NULL or unable
** to read from the disk) then the pMem is left in an inconsistent state.
*/
static SQLITE_NOINLINE int vdbeMemFromBtreeResize(
  BtCursor *pCur,   /* Cursor pointing at record to retrieve. */
  u32 offset,       /* Offset from the start of data to return bytes from. */
  u32 amt,          /* Number of bytes to return. */
  int key,          /* If true, retrieve from the btree key, not data. */
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  int rc;
  pMem->flags = MEM_Null;
  if( SQLITE_OK==(rc = sqlite3VdbeMemClearAndResize(pMem, amt+2)) ){
    if( key ){
      rc = sqlite3BtreeKey(pCur, offset, amt, pMem->z);
    }else{
      rc = sqlite3BtreeData(pCur, offset, amt, pMem->z);
    }
    if( rc==SQLITE_OK ){
      pMem->z[amt] = 0;
      pMem->z[amt+1] = 0;
      pMem->flags = MEM_Blob|MEM_Term;
      pMem->n = (int)amt;
    }else{
      sqlite3VdbeMemRelease(pMem);
    }
  }
  return rc;
}

SQLITE_PRIVATE int sqlite3VdbeMemFromBtree(
  BtCursor *pCur,   /* Cursor pointing at record to retrieve. */
  u32 offset,       /* Offset from the start of data to return bytes from. */
  u32 amt,          /* Number of bytes to return. */
  int key,          /* If true, retrieve from the btree key, not data. */
  Mem *pMem         /* OUT: Return data in this Mem structure. */
){
  char *zData;        /* Data from the btree layer */
  u32 available = 0;  /* Number of bytes available on the local btree page */
  int rc = SQLITE_OK; /* Return code */

  assert( sqlite3BtreeCursorIsValid(pCur) );
  assert( !VdbeMemDynamic(pMem) );

  /* Note: the calls to BtreeKeyFetch() and DataFetch() below assert() 
  ** that both the BtShared and database handle mutexes are held. */
  assert( (pMem->flags & MEM_RowSet)==0 );
  if( key ){
    zData = (char *)sqlite3BtreeKeyFetch(pCur, &available);
  }else{
    zData = (char *)sqlite3BtreeDataFetch(pCur, &available);
  }
  assert( zData!=0 );

  if( offset+amt<=available ){
    pMem->z = &zData[offset];
    pMem->flags = MEM_Blob|MEM_Ephem;
    pMem->n = (int)amt;
  }else{
    rc = vdbeMemFromBtreeResize(pCur, offset, amt, key, pMem);
  }

  return rc;
}

/*
** pCur points at an index entry created using the OP_MakeRecord opcode.
** Read the rowid (the last field in the record) and store it in *rowid.
** Return SQLITE_OK if everything works, or an error code otherwise.
**
** pCur might be pointing to text obtained from a corrupt database file.
** So the content cannot be trusted.  Do appropriate checks on the content.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeIdxRowid(Btree* pBtree, BtCursor *pCur, i64 *rowid){
  i64 nCellKey = 0;
  int rc;
  u32 szHdr;        /* Size of the header */
  u32 typeRowid;    /* Serial type of the rowid */
  u32 lenRowid;     /* Size of the rowid */
  Mem m, v;

  /* Get the size of the index entry.  Only indices entries of less
  ** than 2GiB are support - anything large must be database corruption.
  ** Any corruption is detected in sqlite3BtreeParseCellPtr(), though, so
  ** this code can safely assume that nCellKey is 32-bits  
  */
  assert( sqlite3BtreeCursorIsValid(pCur) );
  VVA_ONLY(rc =) sqlite3BtreeKeySize(pCur, &nCellKey);
  assert( rc==SQLITE_OK );     /* pCur is always valid so KeySize cannot fail */
  assert( (nCellKey & SQLITE_MAX_U32)==(u64)nCellKey );

  /* Read in the complete content of the index entry */
  sqlite3VdbeMemInit(&m, pBtree, 0);
  rc = sqlite3VdbeMemFromBtree(pCur, 0, (u32)nCellKey, 1, &m);
  if( rc ){
    return rc;
  }

  /* The index entry must begin with a header size */
  (void)getVarint32((u8*)m.z, szHdr);
  testcase( szHdr==3 );
  testcase( szHdr==m.n );
  if( unlikely(szHdr<3 || (int)szHdr>m.n) ){
    goto idx_rowid_corruption;
  }

  /* The last field of the index should be an integer - the ROWID.
  ** Verify that the last entry really is an integer. */
  (void)getVarint32((u8*)&m.z[szHdr-1], typeRowid);
  testcase( typeRowid==1 );
  testcase( typeRowid==2 );
  testcase( typeRowid==3 );
  testcase( typeRowid==4 );
  testcase( typeRowid==5 );
  testcase( typeRowid==6 );
  testcase( typeRowid==8 );
  testcase( typeRowid==9 );
  if( unlikely(typeRowid<1 || typeRowid>9 || typeRowid==7) ){
    goto idx_rowid_corruption;
  }
  lenRowid = sqlite3SmallTypeSizes[typeRowid];
  testcase( (u32)m.n==szHdr+lenRowid );
  if( unlikely((u32)m.n<szHdr+lenRowid) ){
    goto idx_rowid_corruption;
  }

  /* Fetch the integer off the end of the index record */
  sqlite3BtreeSerialGet((u8*)&m.z[m.n-lenRowid], typeRowid, &v);
  *rowid = v.u.i;
  sqlite3VdbeMemRelease(&m);
  return SQLITE_OK;

  /* Jump here if database corruption is detected after m has been
  ** allocated.  Free the m object and return SQLITE_CORRUPT. */
idx_rowid_corruption:
  testcase( m.szMalloc!=0 );
  sqlite3VdbeMemRelease(&m);
  return SQLITE_CORRUPT_BKPT;
}

/************** End of btree.c ***********************************************/
/************** Begin file backup.c ******************************************/
/*
** 2009 January 28
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the implementation of the sqlite3_backup_XXX() 
** API functions and the related features.
*/
/* #include "sqliteInt.h" */
/* #include "btreeInt.h" */

/*
** Structure allocated for each backup operation.
*/
struct sqlite3_backup {
  Btree *pDest;            /* Destination b-tree file */
  u32 iDestSchema;         /* Original schema cookie in destination */
  int bDestLocked;         /* True once a write-transaction is open on pDest */

  Pgno iNext;              /* Page number of the next source page to copy */
  Btree *pSrc;             /* Source b-tree file */

  int rc;                  /* Backup process error code */

  /* These two variables are set by every call to backup_step(). They are
  ** read by calls to backup_remaining() and backup_pagecount().
  */
  Pgno nRemaining;         /* Number of pages left to copy */
  Pgno nPagecount;         /* Total number of pages to copy */

  int isAttached;          /* True once backup has been registered with pager */
  sqlite3_backup *pNext;   /* Next backup associated with source pager */
};

/*
** Argument rc is an SQLite error code. Return true if this error is 
** considered fatal if encountered during a backup operation. All errors
** are considered fatal except for SQLITE_BUSY and SQLITE_LOCKED.
*/
static int isFatalError(int rc){
  return (rc!=SQLITE_OK && rc!=SQLITE_BUSY && ALWAYS(rc!=SQLITE_LOCKED));
}

/*
** Parameter zSrcData points to a buffer containing the data for 
** page iSrcPg from the source database. Copy this data into the 
** destination database.
*/
static int backupOnePage(
  sqlite3_backup *p,              /* Backup handle */
  Pgno iSrcPg,                    /* Source database page to backup */
  const u8 *zSrcData,             /* Source database page data */
  int bUpdate                     /* True for an update, false otherwise */
){
  Pager * const pDestPager = sqlite3BtreePager(p->pDest);
  const int nSrcPgsz = sqlite3BtreeGetPageSize(p->pSrc);
  int nDestPgsz = sqlite3BtreeGetPageSize(p->pDest);
  const int nCopy = MIN(nSrcPgsz, nDestPgsz);
  const i64 iEnd = (i64)iSrcPg*(i64)nSrcPgsz;
#ifdef SQLITE_HAS_CODEC
  /* Use BtreeGetReserveNoMutex() for the source b-tree, as although it is
  ** guaranteed that the shared-mutex is held by this thread, handle
  ** p->pSrc may not actually be the owner.  */
  int nSrcReserve = sqlite3BtreeGetReserveNoMutex(p->pSrc);
  int nDestReserve = sqlite3BtreeGetOptimalReserve(p->pDest);
#endif
  int rc = SQLITE_OK;
  i64 iOff;

  assert( sqlite3BtreeGetReserveNoMutex(p->pSrc)>=0 );
  assert( p->bDestLocked );
  assert( !isFatalError(p->rc) );
  assert( iSrcPg!=PENDING_BYTE_PAGE(p->pSrc->pBt) );
  assert( zSrcData );

#ifdef SQLITE_HAS_CODEC
  /* Backup is not possible if the page size of the destination is changing
  ** and a codec is in use.
  */
  if( nSrcPgsz!=nDestPgsz && sqlite3PagerGetCodec(pDestPager)!=0 ){
    rc = SQLITE_READONLY;
  }

  /* Backup is not possible if the number of bytes of reserve space differ
  ** between source and destination.  If there is a difference, try to
  ** fix the destination to agree with the source.  If that is not possible,
  ** then the backup cannot proceed.
  */
  if( nSrcReserve!=nDestReserve ){
    u32 newPgsz = nSrcPgsz;
    rc = sqlite3PagerSetPagesize(pDestPager, &newPgsz, nSrcReserve);
    if( rc==SQLITE_OK && newPgsz!=nSrcPgsz ) rc = SQLITE_READONLY;
  }
#endif

  /* This loop runs once for each destination page spanned by the source 
  ** page. For each iteration, variable iOff is set to the byte offset
  ** of the destination page.
  */
  for(iOff=iEnd-(i64)nSrcPgsz; rc==SQLITE_OK && iOff<iEnd; iOff+=nDestPgsz){
    DbPage *pDestPg = 0;
    Pgno iDest = (Pgno)(iOff/nDestPgsz)+1;
    if( iDest==PENDING_BYTE_PAGE(p->pDest->pBt) ) continue;
    if( SQLITE_OK==(rc = sqlite3PagerGet(pDestPager, iDest, &pDestPg))
     && SQLITE_OK==(rc = sqlite3PagerWrite(pDestPg))
    ){
      const u8 *zIn = &zSrcData[iOff%nSrcPgsz];
      u8 *zDestData = sqlite3PagerGetData(pDestPg);
      u8 *zOut = &zDestData[iOff%nDestPgsz];

      /* Copy the data from the source page into the destination page.
      ** Then clear the Btree layer MemPage.isInit flag. Both this module
      ** and the pager code use this trick (clearing the first byte
      ** of the page 'extra' space to invalidate the Btree layers
      ** cached parse of the page). MemPage.isInit is marked 
      ** "MUST BE FIRST" for this purpose.
      */
      memcpy(zOut, zIn, nCopy);
      ((u8 *)sqlite3PagerGetExtra(pDestPg))[0] = 0;
      if( iOff==0 && bUpdate==0 ){
        sqlite3Put4byte(&zOut[28], sqlite3BtreeLastPage(p->pSrc));
      }
    }
    sqlite3PagerUnref(pDestPg);
  }

  return rc;
}

/*
** This function is called after the contents of page iPage of the
** source database have been modified. If page iPage has already been 
** copied into the destination database, then the data written to the
** destination is now invalidated. The destination copy of iPage needs
** to be updated with the new data before the backup operation is
** complete.
**
** It is assumed that the mutex associated with the BtShared object
** corresponding to the source database is held when this function is
** called.
*/
static SQLITE_NOINLINE void backupUpdate(
  sqlite3_backup *p,
  Pgno iPage,
  const u8 *aData
){
  assert( p!=0 );
  do{
    assert( sqlite3_mutex_held(p->pSrc->pBt->mutex) );
    if( !isFatalError(p->rc) && iPage<p->iNext ){
      /* The backup process p has already copied page iPage. But now it
      ** has been modified by a transaction on the source pager. Copy
      ** the new data into the backup.
      */
      int rc;
      assert( p->pDest );
      sqlite3_mutex_enter(p->pDest->mutex);
      rc = backupOnePage(p, iPage, aData, 1);
      sqlite3_mutex_leave(p->pDest->mutex);
      assert( rc!=SQLITE_BUSY && rc!=SQLITE_LOCKED );
      if( rc!=SQLITE_OK ){
        p->rc = rc;
      }
    }
  }while( (p = p->pNext)!=0 );
}
SQLITE_PRIVATE void sqlite3BackupUpdate(sqlite3_backup *pBackup, Pgno iPage, const u8 *aData){
  if( pBackup ) backupUpdate(pBackup, iPage, aData);
}

/*
** Restart the backup process. This is called when the pager layer
** detects that the database has been modified by an external database
** connection. In this case there is no way of knowing which of the
** pages that have been copied into the destination database are still 
** valid and which are not, so the entire process needs to be restarted.
**
** It is assumed that the mutex associated with the BtShared object
** corresponding to the source database is held when this function is
** called.
*/
SQLITE_PRIVATE void sqlite3BackupRestart(sqlite3_backup *pBackup){
  sqlite3_backup *p;                   /* Iterator variable */
  for(p=pBackup; p; p=p->pNext){
    assert( sqlite3_mutex_held(p->pSrc->pBt->mutex) );
    p->iNext = 1;
  }
}

/************** End of backup.c **********************************************/
/************** Begin file journal.c *****************************************/
/*
** 2007 August 22
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file implements a special kind of sqlite3_file object used
** by SQLite to create journal files if the atomic-write optimization
** is enabled.
**
** The distinctive characteristic of this sqlite3_file is that the
** actual on disk file is created lazily. When the file is created,
** the caller specifies a buffer size for an in-memory buffer to
** be used to service read() and write() requests. The actual file
** on disk is not created or populated until either:
**
**   1) The in-memory representation grows too large for the allocated 
**      buffer, or
**   2) The sqlite3JournalCreate() function is called.
*/
#ifdef SQLITE_ENABLE_ATOMIC_WRITE
/* #include "sqliteInt.h" */


/*
** A JournalFile object is a subclass of sqlite3_file used by
** as an open file handle for journal files.
*/
struct JournalFile {
  sqlite3_io_methods *pMethod;    /* I/O methods on journal files */
  int nBuf;                       /* Size of zBuf[] in bytes */
  char *zBuf;                     /* Space to buffer journal writes */
  int iSize;                      /* Amount of zBuf[] currently used */
  int flags;                      /* xOpen flags */
  sqlite3_vfs *pVfs;              /* The "real" underlying VFS */
  sqlite3_file *pReal;            /* The "real" underlying file descriptor */
  const char *zJournal;           /* Name of the journal file */
};
typedef struct JournalFile JournalFile;

/*
** If it does not already exists, create and populate the on-disk file 
** for JournalFile p.
*/
static int createFile(JournalFile *p){
  int rc = SQLITE_OK;
  if( !p->pReal ){
    sqlite3_file *pReal = (sqlite3_file *)&p[1];
    rc = sqlite3OsOpen(p->pVfs, p->zJournal, pReal, p->flags, 0);
    if( rc==SQLITE_OK ){
      p->pReal = pReal;
      if( p->iSize>0 ){
        assert(p->iSize<=p->nBuf);
        rc = sqlite3OsWrite(p->pReal, p->zBuf, p->iSize, 0);
      }
      if( rc!=SQLITE_OK ){
        /* If an error occurred while writing to the file, close it before
        ** returning. This way, SQLite uses the in-memory journal data to 
        ** roll back changes made to the internal page-cache before this
        ** function was called.  */
        sqlite3OsClose(pReal);
        p->pReal = 0;
      }
    }
  }
  return rc;
}

/*
** Close the file.
*/
static int jrnlClose(sqlite3_file *pJfd){
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    sqlite3OsClose(p->pReal);
  }
  sqlite3_free(p->zBuf);
  return SQLITE_OK;
}

/*
** Read data from the file.
*/
static int jrnlRead(
  sqlite3_file *pJfd,    /* The journal file from which to read */
  void *zBuf,            /* Put the results here */
  int iAmt,              /* Number of bytes to read */
  sqlite_int64 iOfst     /* Begin reading at this offset */
){
  int rc = SQLITE_OK;
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
  }else if( (iAmt+iOfst)>p->iSize ){
    rc = SQLITE_IOERR_SHORT_READ;
  }else{
    memcpy(zBuf, &p->zBuf[iOfst], iAmt);
  }
  return rc;
}

/*
** Write data to the file.
*/
static int jrnlWrite(
  sqlite3_file *pJfd,    /* The journal file into which to write */
  const void *zBuf,      /* Take data to be written from here */
  int iAmt,              /* Number of bytes to write */
  sqlite_int64 iOfst     /* Begin writing at this offset into the file */
){
  int rc = SQLITE_OK;
  JournalFile *p = (JournalFile *)pJfd;
  if( !p->pReal && (iOfst+iAmt)>p->nBuf ){
    rc = createFile(p);
  }
  if( rc==SQLITE_OK ){
    if( p->pReal ){
      rc = sqlite3OsWrite(p->pReal, zBuf, iAmt, iOfst);
    }else{
      memcpy(&p->zBuf[iOfst], zBuf, iAmt);
      if( p->iSize<(iOfst+iAmt) ){
        p->iSize = (iOfst+iAmt);
      }
    }
  }
  return rc;
}

/*
** Truncate the file.
*/
static int jrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
  int rc = SQLITE_OK;
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    rc = sqlite3OsTruncate(p->pReal, size);
  }else if( size<p->iSize ){
    p->iSize = size;
  }
  return rc;
}

/*
** Sync the file.
*/
static int jrnlSync(sqlite3_file *pJfd, int flags){
  int rc;
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    rc = sqlite3OsSync(p->pReal, flags);
  }else{
    rc = SQLITE_OK;
  }
  return rc;
}

/*
** Query the size of the file in bytes.
*/
static int jrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
  int rc = SQLITE_OK;
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    rc = sqlite3OsFileSize(p->pReal, pSize);
  }else{
    *pSize = (sqlite_int64) p->iSize;
  }
  return rc;
}

/*
** Table of methods for JournalFile sqlite3_file object.
*/
static struct sqlite3_io_methods JournalFileMethods = {
  1,             /* iVersion */
  jrnlClose,     /* xClose */
  jrnlRead,      /* xRead */
  jrnlWrite,     /* xWrite */
  jrnlTruncate,  /* xTruncate */
  jrnlSync,      /* xSync */
  jrnlFileSize,  /* xFileSize */
  0,             /* xLock */
  0,             /* xUnlock */
  0,             /* xCheckReservedLock */
  0,             /* xFileControl */
  0,             /* xSectorSize */
  0,             /* xDeviceCharacteristics */
  0,             /* xShmMap */
  0,             /* xShmLock */
  0,             /* xShmBarrier */
  0              /* xShmUnmap */
};

/* 
** Open a journal file.
*/
SQLITE_PRIVATE int sqlite3JournalOpen(
  sqlite3_vfs *pVfs,         /* The VFS to use for actual file I/O */
  const char *zName,         /* Name of the journal file */
  sqlite3_file *pJfd,        /* Preallocated, blank file handle */
  int flags,                 /* Opening flags */
  int nBuf                   /* Bytes buffered before opening the file */
){
  JournalFile *p = (JournalFile *)pJfd;
  memset(p, 0, sqlite3JournalSize(pVfs));
  if( nBuf>0 ){
    p->zBuf = sqlite3MallocZero(nBuf);
    if( !p->zBuf ){
      return SQLITE_NOMEM;
    }
  }else{
    return sqlite3OsOpen(pVfs, zName, pJfd, flags, 0);
  }
  p->pMethod = &JournalFileMethods;
  p->nBuf = nBuf;
  p->flags = flags;
  p->zJournal = zName;
  p->pVfs = pVfs;
  return SQLITE_OK;
}

/*
** If the argument p points to a JournalFile structure, and the underlying
** file has not yet been created, create it now.
*/
SQLITE_PRIVATE int sqlite3JournalCreate(sqlite3_file *p){
  if( p->pMethods!=&JournalFileMethods ){
    return SQLITE_OK;
  }
  return createFile((JournalFile *)p);
}

/*
** The file-handle passed as the only argument is guaranteed to be an open
** file. It may or may not be of class JournalFile. If the file is a
** JournalFile, and the underlying file on disk has not yet been opened,
** return 0. Otherwise, return 1.
*/
SQLITE_PRIVATE int sqlite3JournalExists(sqlite3_file *p){
  return (p->pMethods!=&JournalFileMethods || ((JournalFile *)p)->pReal!=0);
}

/* 
** Return the number of bytes required to store a JournalFile that uses vfs
** pVfs to create the underlying on-disk files.
*/
SQLITE_PRIVATE int sqlite3JournalSize(sqlite3_vfs *pVfs){
  return (pVfs->szOsFile+sizeof(JournalFile));
}
#endif

/************** End of journal.c *********************************************/
/************** Begin file memjournal.c **************************************/
/*
** 2008 October 7
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains code use to implement an in-memory rollback journal.
** The in-memory rollback journal is used to journal transactions for
** ":memory:" databases and when the journal_mode=MEMORY pragma is used.
*/
/* #include "sqliteInt.h" */

/* Forward references to internal structures */
typedef struct MemJournal MemJournal;
typedef struct FilePoint FilePoint;
typedef struct FileChunk FileChunk;

/* Space to hold the rollback journal is allocated in increments of
** this many bytes.
**
** The size chosen is a little less than a power of two.  That way,
** the FileChunk object will have a size that almost exactly fills
** a power-of-two allocation.  This minimizes wasted space in power-of-two
** memory allocators.
*/
#define JOURNAL_CHUNKSIZE ((int)(1024-sizeof(FileChunk*)))

/*
** The rollback journal is composed of a linked list of these structures.
*/
struct FileChunk {
  FileChunk *pNext;               /* Next chunk in the journal */
  u8 zChunk[JOURNAL_CHUNKSIZE];   /* Content of this chunk */
};

/*
** An instance of this object serves as a cursor into the rollback journal.
** The cursor can be either for reading or writing.
*/
struct FilePoint {
  sqlite3_int64 iOffset;          /* Offset from the beginning of the file */
  FileChunk *pChunk;              /* Specific chunk into which cursor points */
};

/*
** This subclass is a subclass of sqlite3_file.  Each open memory-journal
** is an instance of this class.
*/
struct MemJournal {
  sqlite3_io_methods *pMethod;    /* Parent class. MUST BE FIRST */
  FileChunk *pFirst;              /* Head of in-memory chunk-list */
  FilePoint endpoint;             /* Pointer to the end of the file */
  FilePoint readpoint;            /* Pointer to the end of the last xRead() */
};

/*
** Read data from the in-memory journal file.  This is the implementation
** of the sqlite3_vfs.xRead method.
*/
static int memjrnlRead(
  sqlite3_file *pJfd,    /* The journal file from which to read */
  void *zBuf,            /* Put the results here */
  int iAmt,              /* Number of bytes to read */
  sqlite_int64 iOfst     /* Begin reading at this offset */
){
  MemJournal *p = (MemJournal *)pJfd;
  u8 *zOut = zBuf;
  int nRead = iAmt;
  int iChunkOffset;
  FileChunk *pChunk;

  /* SQLite never tries to read past the end of a rollback journal file */
  assert( iOfst+iAmt<=p->endpoint.iOffset );

  if( p->readpoint.iOffset!=iOfst || iOfst==0 ){
    sqlite3_int64 iOff = 0;
    for(pChunk=p->pFirst; 
        ALWAYS(pChunk) && (iOff+JOURNAL_CHUNKSIZE)<=iOfst;
        pChunk=pChunk->pNext
    ){
      iOff += JOURNAL_CHUNKSIZE;
    }
  }else{
    pChunk = p->readpoint.pChunk;
  }

  iChunkOffset = (int)(iOfst%JOURNAL_CHUNKSIZE);
  do {
    int iSpace = JOURNAL_CHUNKSIZE - iChunkOffset;
    int nCopy = MIN(nRead, (JOURNAL_CHUNKSIZE - iChunkOffset));
    memcpy(zOut, &pChunk->zChunk[iChunkOffset], nCopy);
    zOut += nCopy;
    nRead -= iSpace;
    iChunkOffset = 0;
  } while( nRead>=0 && (pChunk=pChunk->pNext)!=0 && nRead>0 );
  p->readpoint.iOffset = iOfst+iAmt;
  p->readpoint.pChunk = pChunk;

  return SQLITE_OK;
}

/*
** Write data to the file.
*/
static int memjrnlWrite(
  sqlite3_file *pJfd,    /* The journal file into which to write */
  const void *zBuf,      /* Take data to be written from here */
  int iAmt,              /* Number of bytes to write */
  sqlite_int64 iOfst     /* Begin writing at this offset into the file */
){
  MemJournal *p = (MemJournal *)pJfd;
  int nWrite = iAmt;
  u8 *zWrite = (u8 *)zBuf;

  /* An in-memory journal file should only ever be appended to. Random
  ** access writes are not required by sqlite.
  */
  assert( iOfst==p->endpoint.iOffset );
  UNUSED_PARAMETER(iOfst);

  while( nWrite>0 ){
    FileChunk *pChunk = p->endpoint.pChunk;
    int iChunkOffset = (int)(p->endpoint.iOffset%JOURNAL_CHUNKSIZE);
    int iSpace = MIN(nWrite, JOURNAL_CHUNKSIZE - iChunkOffset);

    if( iChunkOffset==0 ){
      /* New chunk is required to extend the file. */
      FileChunk *pNew = sqlite3_malloc(sizeof(FileChunk));
      if( !pNew ){
        return SQLITE_IOERR_NOMEM;
      }
      pNew->pNext = 0;
      if( pChunk ){
        assert( p->pFirst );
        pChunk->pNext = pNew;
      }else{
        assert( !p->pFirst );
        p->pFirst = pNew;
      }
      p->endpoint.pChunk = pNew;
    }

    memcpy(&p->endpoint.pChunk->zChunk[iChunkOffset], zWrite, iSpace);
    zWrite += iSpace;
    nWrite -= iSpace;
    p->endpoint.iOffset += iSpace;
  }

  return SQLITE_OK;
}

/*
** Truncate the file.
*/
static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
  MemJournal *p = (MemJournal *)pJfd;
  FileChunk *pChunk;
  assert(size==0);
  UNUSED_PARAMETER(size);
  pChunk = p->pFirst;
  while( pChunk ){
    FileChunk *pTmp = pChunk;
    pChunk = pChunk->pNext;
    sqlite3_free(pTmp);
  }
  sqlite3MemJournalOpen(pJfd);
  return SQLITE_OK;
}

/*
** Close the file.
*/
static int memjrnlClose(sqlite3_file *pJfd){
  memjrnlTruncate(pJfd, 0);
  return SQLITE_OK;
}


/*
** Sync the file.
**
** Syncing an in-memory journal is a no-op.  And, in fact, this routine
** is never called in a working implementation.  This implementation
** exists purely as a contingency, in case some malfunction in some other
** part of SQLite causes Sync to be called by mistake.
*/
static int memjrnlSync(sqlite3_file *NotUsed, int NotUsed2){
  UNUSED_PARAMETER2(NotUsed, NotUsed2);
  return SQLITE_OK;
}

/*
** Query the size of the file in bytes.
*/
static int memjrnlFileSize(sqlite3_file *pJfd, sqlite_int64 *pSize){
  MemJournal *p = (MemJournal *)pJfd;
  *pSize = (sqlite_int64) p->endpoint.iOffset;
  return SQLITE_OK;
}

/*
** Table of methods for MemJournal sqlite3_file object.
*/
static const struct sqlite3_io_methods MemJournalMethods = {
  1,                /* iVersion */
  memjrnlClose,     /* xClose */
  memjrnlRead,      /* xRead */
  memjrnlWrite,     /* xWrite */
  memjrnlTruncate,  /* xTruncate */
  memjrnlSync,      /* xSync */
  memjrnlFileSize,  /* xFileSize */
  0,                /* xLock */
  0,                /* xUnlock */
  0,                /* xCheckReservedLock */
  0,                /* xFileControl */
  0,                /* xSectorSize */
  0,                /* xDeviceCharacteristics */
  0,                /* xShmMap */
  0,                /* xShmLock */
  0,                /* xShmBarrier */
  0,                /* xShmUnmap */
  0,                /* xFetch */
  0                 /* xUnfetch */
};

/* 
** Open a journal file.
*/
SQLITE_PRIVATE void sqlite3MemJournalOpen(sqlite3_file *pJfd){
  MemJournal *p = (MemJournal *)pJfd;
  assert( EIGHT_BYTE_ALIGNMENT(p) );
  memset(p, 0, sqlite3MemJournalSize());
  p->pMethod = (sqlite3_io_methods*)&MemJournalMethods;
}

/*
** Return true if the file-handle passed as an argument is 
** an in-memory journal 
*/
SQLITE_PRIVATE int sqlite3IsMemJournal(sqlite3_file *pJfd){
  return pJfd->pMethods==&MemJournalMethods;
}

/* 
** Return the number of bytes required to store a MemJournal file descriptor.
*/
SQLITE_PRIVATE int sqlite3MemJournalSize(void){
  return sizeof(MemJournal);
}

/************** End of memjournal.c ******************************************/
/************** Begin file main.c ********************************************/
/* #include "sqliteInt.h" */

/* IMPLEMENTATION-OF: R-63124-39300 The sqlite3_sourceid() function returns a
** pointer to a string constant whose value is the same as the
** SQLITE_SOURCE_ID C preprocessor macro. 
*/
SQLITE_PRIVATE const char *sqlite3_sourceid(void){ return SQLITE_SOURCE_ID; }

/*
** If the following global variable points to a string which is the
** name of a directory, then that directory will be used to store
** temporary files.
**
** See also the "PRAGMA temp_store_directory" SQL command.
*/
SQLITE_PRIVATE char *sqlite3_temp_directory = 0;

/*
** Initialize SQLite.  
**
** This routine must be called to initialize the memory allocation,
** VFS, and mutex subsystems prior to doing any serious work with
** SQLite.  But as long as you do not compile with SQLITE_OMIT_AUTOINIT
** this routine will be called automatically by key routines such as
** sqlite3_open().  
**
** This routine is a no-op except on its very first call for the process,
** or for the first call after a call to sqlite3BtreeShutdown.
**
** The first thread to call this routine runs the initialization to
** completion.  If subsequent threads call this routine before the first
** thread has finished the initialization process, then the subsequent
** threads must block until the first thread finishes with the initialization.
**
** The first thread might call this routine recursively.  Recursive
** calls to this routine should not block, of course.  Otherwise the
** initialization process would never complete.
**
** Let X be the first thread to enter this routine.  Let Y be some other
** thread.  Then while the initial invocation of this routine by X is
** incomplete, it is required that:
**
**    *  Calls to this routine from Y must block until the outer-most
**       call by X completes.
**
**    *  Recursive calls to this routine from thread X return immediately
**       without blocking.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeInitialize(void){
  MUTEX_LOGIC( sqlite3_mutex *pMaster; )       /* The main static mutex */
  int rc;                                      /* Result code */
#ifdef SQLITE_EXTRA_INIT
  int bRunExtraInit = 0;                       /* Extra initialization needed */
#endif

#ifdef SQLITE_OMIT_WSD
  rc = sqlite3_wsd_init(4096, 24);
  if( rc!=SQLITE_OK ){
    return rc;
  }
#endif

  /* If the following assert() fails on some obscure processor/compiler
  ** combination, the work-around is to set the correct pointer
  ** size at compile-time using -DSQLITE_PTRSIZE=n compile-time option */
  assert( SQLITE_PTRSIZE==sizeof(char*) );

  /* If SQLite is already completely initialized, then this call
  ** to sqlite3BtreeInitialize() should be a no-op.  But the initialization
  ** must be complete.  So isInit must not be set until the very end
  ** of this routine.
  */
  if( sqlite3GlobalConfig.isInit ) return SQLITE_OK;

  /* Make sure the mutex subsystem is initialized.  If unable to 
  ** initialize the mutex subsystem, return early with the error.
  ** If the system is so sick that we are unable to allocate a mutex,
  ** there is not much SQLite is going to be able to do.
  **
  ** The mutex subsystem must take care of serializing its own
  ** initialization.
  */
  rc = sqlite3MutexInit();
  if( rc ) return rc;

  /* Initialize the malloc() system and the recursive pInitMutex mutex.
  ** This operation is protected by the STATIC_MASTER mutex.  Note that
  ** MutexAlloc() is called for a static mutex prior to initializing the
  ** malloc subsystem - this implies that the allocation of a static
  ** mutex must not require support from the malloc subsystem.
  */
  MUTEX_LOGIC( pMaster = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER); )
  sqlite3_mutex_enter(pMaster);
  sqlite3GlobalConfig.isMutexInit = 1;
  if( !sqlite3GlobalConfig.isMallocInit ){
    rc = sqlite3MallocInit();
  }
  if( rc==SQLITE_OK ){
    sqlite3GlobalConfig.isMallocInit = 1;
    if( !sqlite3GlobalConfig.pInitMutex ){
      sqlite3GlobalConfig.pInitMutex =
           sqlite3MutexAlloc(SQLITE_MUTEX_RECURSIVE);
      if( sqlite3GlobalConfig.bCoreMutex && !sqlite3GlobalConfig.pInitMutex ){
        rc = SQLITE_NOMEM;
      }
    }
  }
  if( rc==SQLITE_OK ){
    sqlite3GlobalConfig.nRefInitMutex++;
  }
  sqlite3_mutex_leave(pMaster);

  /* If rc is not SQLITE_OK at this point, then either the malloc
  ** subsystem could not be initialized or the system failed to allocate
  ** the pInitMutex mutex. Return an error in either case.  */
  if( rc!=SQLITE_OK ){
    return rc;
  }

  /* Do the rest of the initialization under the recursive mutex so
  ** that we will be able to handle recursive calls into
  ** sqlite3BtreeInitialize().  The recursive calls normally come through
  ** sqlite3_os_init() when it invokes sqlite3_vfs_register(), but other
  ** recursive calls might also be possible.
  **
  ** IMPLEMENTATION-OF: R-00140-37445 SQLite automatically serializes calls
  ** to the xInit method, so the xInit method need not be threadsafe.
  **
  ** The following mutex is what serializes access to the appdef pcache xInit
  ** methods.  The sqlite3_pcache_methods.xInit() all is embedded in the
  ** call to sqlite3PcacheInitialize().
  */
  sqlite3_mutex_enter(sqlite3GlobalConfig.pInitMutex);
  if( sqlite3GlobalConfig.isInit==0 && sqlite3GlobalConfig.inProgress==0 ){
    sqlite3GlobalConfig.inProgress = 1;
    if( sqlite3GlobalConfig.isPCacheInit==0 ){
      rc = sqlite3PcacheInitialize();
    }
    if( rc==SQLITE_OK ){
      sqlite3GlobalConfig.isPCacheInit = 1;
      rc = sqlite3OsInit();
    }
    if( rc==SQLITE_OK ){
      sqlite3PCacheBufferSetup( sqlite3GlobalConfig.pPage, 
          sqlite3GlobalConfig.szPage, sqlite3GlobalConfig.nPage);
      sqlite3GlobalConfig.isInit = 1;
#ifdef SQLITE_EXTRA_INIT
      bRunExtraInit = 1;
#endif
    }
    sqlite3GlobalConfig.inProgress = 0;
  }
  sqlite3_mutex_leave(sqlite3GlobalConfig.pInitMutex);

  /* Go back under the static mutex and clean up the recursive
  ** mutex to prevent a resource leak.
  */
  sqlite3_mutex_enter(pMaster);
  sqlite3GlobalConfig.nRefInitMutex--;
  if( sqlite3GlobalConfig.nRefInitMutex<=0 ){
    assert( sqlite3GlobalConfig.nRefInitMutex==0 );
    sqlite3_mutex_free(sqlite3GlobalConfig.pInitMutex);
    sqlite3GlobalConfig.pInitMutex = 0;
  }
  sqlite3_mutex_leave(pMaster);

  /* The following is just a sanity check to make sure SQLite has
  ** been compiled correctly.  It is important to run this code, but
  ** we don't want to run it too often and soak up CPU cycles for no
  ** reason.  So we run it once during initialization.
  */
#ifndef NDEBUG
#ifndef SQLITE_OMIT_FLOATING_POINT
  /* This section of code's only "output" is via assert() statements. */
  if ( rc==SQLITE_OK ){
    u64 x = (((u64)1)<<63)-1;
    double y;
    assert(sizeof(x)==8);
    assert(sizeof(x)==sizeof(y));
    memcpy(&y, &x, 8);
    assert( sqlite3IsNaN(y) );
  }
#endif
#endif

  /* Do extra initialization steps requested by the SQLITE_EXTRA_INIT
  ** compile-time option.
  */
#ifdef SQLITE_EXTRA_INIT
  if( bRunExtraInit ){
    int SQLITE_EXTRA_INIT(const char*);
    rc = SQLITE_EXTRA_INIT(0);
  }
#endif

  return rc;
}

/*
** Undo the effects of sqlite3BtreeInitialize().  Must not be called while
** there are outstanding database connections or memory allocations or
** while any part of SQLite is otherwise in use in any thread.  This
** routine is not threadsafe.  But it is safe to invoke this routine
** on when SQLite is already shut down.  If SQLite is already shut down
** when this routine is invoked, then this routine is a harmless no-op.
*/
SQLITE_API int SQLITE_STDCALL sqlite3BtreeShutdown(void){
#ifdef SQLITE_OMIT_WSD
  int rc = sqlite3_wsd_init(4096, 24);
  if( rc!=SQLITE_OK ){
    return rc;
  }
#endif

  if( sqlite3GlobalConfig.isInit ){
#ifdef SQLITE_EXTRA_SHUTDOWN
    void SQLITE_EXTRA_SHUTDOWN(void);
    SQLITE_EXTRA_SHUTDOWN();
#endif
    sqlite3_os_end();
    sqlite3GlobalConfig.isInit = 0;
  }
  if( sqlite3GlobalConfig.isPCacheInit ){
    sqlite3PcacheShutdown();
    sqlite3GlobalConfig.isPCacheInit = 0;
  }
  if( sqlite3GlobalConfig.isMallocInit ){
    sqlite3MallocEnd();
    sqlite3GlobalConfig.isMallocInit = 0;
  }
  if( sqlite3GlobalConfig.isMutexInit ){
    sqlite3MutexEnd();
    sqlite3GlobalConfig.isMutexInit = 0;
  }

  return SQLITE_OK;
}

/*
** The following routines are substitutes for constants SQLITE_CORRUPT,
** SQLITE_MISUSE, SQLITE_CANTOPEN, SQLITE_IOERR and possibly other error
** constants.  They serve two purposes:
**
**   1.  Serve as a convenient place to set a breakpoint in a debugger
**       to detect when version error conditions occurs.
**
**   2.  Invoke sqlite3_log() to provide the source code location where
**       a low-level error is first detected.
*/
SQLITE_PRIVATE int sqlite3CorruptError(int lineno){
  testcase( sqlite3GlobalConfig.xLog!=0 );
  sqlite3_log(SQLITE_CORRUPT,
              "database corruption at line %d of [%.10s]",
              lineno, 20+sqlite3_sourceid());
  return SQLITE_CORRUPT;
}
SQLITE_PRIVATE int sqlite3MisuseError(int lineno){
  testcase( sqlite3GlobalConfig.xLog!=0 );
  sqlite3_log(SQLITE_MISUSE, 
              "misuse at line %d of [%.10s]",
              lineno, 20+sqlite3_sourceid());
  return SQLITE_MISUSE;
}
SQLITE_PRIVATE int sqlite3CantopenError(int lineno){
  testcase( sqlite3GlobalConfig.xLog!=0 );
  sqlite3_log(SQLITE_CANTOPEN, 
              "cannot open file at line %d of [%.10s]",
              lineno, 20+sqlite3_sourceid());
  return SQLITE_CANTOPEN;
}

/*
** Invoke the given busy handler.
**
** This routine is called when an operation failed with a lock.
** If this routine returns non-zero, the lock is retried.  If it
** returns 0, the operation aborts with an SQLITE_BUSY error.
*/
SQLITE_PRIVATE int sqlite3InvokeBusyHandler(BusyHandler *p){
  int rc;
  if( NEVER(p==0) || p->xFunc==0 || p->nBusy<0 ) return 0;
  rc = p->xFunc(p->pArg, p->nBusy);
  if( rc==0 ){
    p->nBusy = -1;
  }else{
    p->nBusy++;
  }
  return rc; 
}

/*
** This API allows applications to modify the global configuration of
** the SQLite library at run-time.
**
** This routine should only be called when there are no outstanding
** database connections or memory allocations.  This routine is not
** threadsafe.  Failure to heed these warnings can lead to unpredictable
** behavior.
*/
SQLITE_PRIVATE int sqlite3_config(int op, ...){
  va_list ap;
  int rc = SQLITE_OK;

  /* sqlite3_config() shall return SQLITE_MISUSE if it is invoked while
  ** the SQLite library is in use. */
  if( sqlite3GlobalConfig.isInit ) return SQLITE_MISUSE_BKPT;

  va_start(ap, op);
  switch( op ){

    /* Mutex configuration options are only available in a threadsafe
    ** compile.
    */
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0  /* IMP: R-54466-46756 */
    case SQLITE_CONFIG_SINGLETHREAD: {
      /* EVIDENCE-OF: R-02748-19096 This option sets the threading mode to
      ** Single-thread. */
      sqlite3GlobalConfig.bCoreMutex = 0;  /* Disable mutex on core */
      sqlite3GlobalConfig.bFullMutex = 0;  /* Disable mutex on connections */
      break;
    }
#endif
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-20520-54086 */
    case SQLITE_CONFIG_MULTITHREAD: {
      /* EVIDENCE-OF: R-14374-42468 This option sets the threading mode to
      ** Multi-thread. */
      sqlite3GlobalConfig.bCoreMutex = 1;  /* Enable mutex on core */
      sqlite3GlobalConfig.bFullMutex = 0;  /* Disable mutex on connections */
      break;
    }
#endif
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-59593-21810 */
    case SQLITE_CONFIG_SERIALIZED: {
      /* EVIDENCE-OF: R-41220-51800 This option sets the threading mode to
      ** Serialized. */
      sqlite3GlobalConfig.bCoreMutex = 1;  /* Enable mutex on core */
      sqlite3GlobalConfig.bFullMutex = 1;  /* Enable mutex on connections */
      break;
    }
#endif
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-63666-48755 */
    case SQLITE_CONFIG_MUTEX: {
      /* Specify an alternative mutex implementation */
      sqlite3GlobalConfig.mutex = *va_arg(ap, sqlite3_mutex_methods*);
      break;
    }
#endif
#if defined(SQLITE_THREADSAFE) && SQLITE_THREADSAFE>0 /* IMP: R-14450-37597 */
    case SQLITE_CONFIG_GETMUTEX: {
      /* Retrieve the current mutex implementation */
      *va_arg(ap, sqlite3_mutex_methods*) = sqlite3GlobalConfig.mutex;
      break;
    }
#endif

    case SQLITE_CONFIG_MALLOC: {
      /* EVIDENCE-OF: R-55594-21030 The SQLITE_CONFIG_MALLOC option takes a
      ** single argument which is a pointer to an instance of the
      ** sqlite3_mem_methods structure. The argument specifies alternative
      ** low-level memory allocation routines to be used in place of the memory
      ** allocation routines built into SQLite. */
      sqlite3GlobalConfig.m = *va_arg(ap, sqlite3_mem_methods*);
      break;
    }
    case SQLITE_CONFIG_GETMALLOC: {
      /* EVIDENCE-OF: R-51213-46414 The SQLITE_CONFIG_GETMALLOC option takes a
      ** single argument which is a pointer to an instance of the
      ** sqlite3_mem_methods structure. The sqlite3_mem_methods structure is
      ** filled with the currently defined memory allocation routines. */
      if( sqlite3GlobalConfig.m.xMalloc==0 ) sqlite3MemSetDefault();
      *va_arg(ap, sqlite3_mem_methods*) = sqlite3GlobalConfig.m;
      break;
    }
    case SQLITE_CONFIG_MEMSTATUS: {
      /* EVIDENCE-OF: R-61275-35157 The SQLITE_CONFIG_MEMSTATUS option takes
      ** single argument of type int, interpreted as a boolean, which enables
      ** or disables the collection of memory allocation statistics. */
      sqlite3GlobalConfig.bMemstat = va_arg(ap, int);
      break;
    }
    case SQLITE_CONFIG_SCRATCH: {
      /* EVIDENCE-OF: R-08404-60887 There are three arguments to
      ** SQLITE_CONFIG_SCRATCH: A pointer an 8-byte aligned memory buffer from
      ** which the scratch allocations will be drawn, the size of each scratch
      ** allocation (sz), and the maximum number of scratch allocations (N). */
      sqlite3GlobalConfig.pScratch = va_arg(ap, void*);
      sqlite3GlobalConfig.szScratch = va_arg(ap, int);
      sqlite3GlobalConfig.nScratch = va_arg(ap, int);
      break;
    }
    case SQLITE_CONFIG_PAGECACHE: {
      /* EVIDENCE-OF: R-31408-40510 There are three arguments to
      ** SQLITE_CONFIG_PAGECACHE: A pointer to 8-byte aligned memory, the size
      ** of each page buffer (sz), and the number of pages (N). */
      sqlite3GlobalConfig.pPage = va_arg(ap, void*);
      sqlite3GlobalConfig.szPage = va_arg(ap, int);
      sqlite3GlobalConfig.nPage = va_arg(ap, int);
      break;
    }
    case SQLITE_CONFIG_PCACHE_HDRSZ: {
      /* EVIDENCE-OF: R-39100-27317 The SQLITE_CONFIG_PCACHE_HDRSZ option takes
      ** a single parameter which is a pointer to an integer and writes into
      ** that integer the number of extra bytes per page required for each page
      ** in SQLITE_CONFIG_PAGECACHE. */
      *va_arg(ap, int*) = 
          sqlite3HeaderSizeBtree() +
          sqlite3HeaderSizePcache() +
          sqlite3HeaderSizePcache1();
      break;
    }

    case SQLITE_CONFIG_PCACHE: {
      /* no-op */
      break;
    }
    case SQLITE_CONFIG_GETPCACHE: {
      /* now an error */
      rc = SQLITE_ERROR;
      break;
    }

    case SQLITE_CONFIG_PCACHE2: {
      /* EVIDENCE-OF: R-63325-48378 The SQLITE_CONFIG_PCACHE2 option takes a
      ** single argument which is a pointer to an sqlite3_pcache_methods2
      ** object. This object specifies the interface to a custom page cache
      ** implementation. */
      sqlite3GlobalConfig.pcache2 = *va_arg(ap, sqlite3_pcache_methods2*);
      break;
    }
    case SQLITE_CONFIG_GETPCACHE2: {
      /* EVIDENCE-OF: R-22035-46182 The SQLITE_CONFIG_GETPCACHE2 option takes a
      ** single argument which is a pointer to an sqlite3_pcache_methods2
      ** object. SQLite copies of the current page cache implementation into
      ** that object. */
      if( sqlite3GlobalConfig.pcache2.xInit==0 ){
        sqlite3PCacheSetDefault();
      }
      *va_arg(ap, sqlite3_pcache_methods2*) = sqlite3GlobalConfig.pcache2;
      break;
    }

/* EVIDENCE-OF: R-06626-12911 The SQLITE_CONFIG_HEAP option is only
** available if SQLite is compiled with either SQLITE_ENABLE_MEMSYS3 or
** SQLITE_ENABLE_MEMSYS5 and returns SQLITE_ERROR if invoked otherwise. */
#if defined(SQLITE_ENABLE_MEMSYS3) || defined(SQLITE_ENABLE_MEMSYS5)
    case SQLITE_CONFIG_HEAP: {
      /* EVIDENCE-OF: R-19854-42126 There are three arguments to
      ** SQLITE_CONFIG_HEAP: An 8-byte aligned pointer to the memory, the
      ** number of bytes in the memory buffer, and the minimum allocation size.
      */
      sqlite3GlobalConfig.pHeap = va_arg(ap, void*);
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      sqlite3GlobalConfig.mnReq = va_arg(ap, int);

      if( sqlite3GlobalConfig.mnReq<1 ){
        sqlite3GlobalConfig.mnReq = 1;
      }else if( sqlite3GlobalConfig.mnReq>(1<<12) ){
        /* cap min request size at 2^12 */
        sqlite3GlobalConfig.mnReq = (1<<12);
      }

      if( sqlite3GlobalConfig.pHeap==0 ){
        /* EVIDENCE-OF: R-49920-60189 If the first pointer (the memory pointer)
        ** is NULL, then SQLite reverts to using its default memory allocator
        ** (the system malloc() implementation), undoing any prior invocation of
        ** SQLITE_CONFIG_MALLOC.
        **
        ** Setting sqlite3GlobalConfig.m to all zeros will cause malloc to
        ** revert to its default implementation when sqlite3BtreeInitialize() is run
        */
        memset(&sqlite3GlobalConfig.m, 0, sizeof(sqlite3GlobalConfig.m));
      }else{
        /* EVIDENCE-OF: R-61006-08918 If the memory pointer is not NULL then the
        ** alternative memory allocator is engaged to handle all of SQLites
        ** memory allocation needs. */
#ifdef SQLITE_ENABLE_MEMSYS3
        sqlite3GlobalConfig.m = *sqlite3MemGetMemsys3();
#endif
#ifdef SQLITE_ENABLE_MEMSYS5
        sqlite3GlobalConfig.m = *sqlite3MemGetMemsys5();
#endif
      }
      break;
    }
#endif

    case SQLITE_CONFIG_LOOKASIDE: {
      sqlite3GlobalConfig.szLookaside = va_arg(ap, int);
      sqlite3GlobalConfig.nLookaside = va_arg(ap, int);
      break;
    }
    
    /* Record a pointer to the logger function and its first argument.
    ** The default is NULL.  Logging is disabled if the function pointer is
    ** NULL.
    */
    case SQLITE_CONFIG_LOG: {
      /* MSVC is picky about pulling func ptrs from va lists.
      ** http://support.microsoft.com/kb/47961
      ** sqlite3GlobalConfig.xLog = va_arg(ap, void(*)(void*,int,const char*));
      */
      typedef void(*LOGFUNC_t)(void*,int,const char*);
      sqlite3GlobalConfig.xLog = va_arg(ap, LOGFUNC_t);
      sqlite3GlobalConfig.pLogArg = va_arg(ap, void*);
      break;
    }

    /* EVIDENCE-OF: R-55548-33817 The compile-time setting for URI filenames
    ** can be changed at start-time using the
    ** sqlite3_config(SQLITE_CONFIG_URI,1) or
    ** sqlite3_config(SQLITE_CONFIG_URI,0) configuration calls.
    */
    case SQLITE_CONFIG_URI: {
      /* EVIDENCE-OF: R-25451-61125 The SQLITE_CONFIG_URI option takes a single
      ** argument of type int. If non-zero, then URI handling is globally
      ** enabled. If the parameter is zero, then URI handling is globally
      ** disabled. */
      sqlite3GlobalConfig.bOpenUri = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_COVERING_INDEX_SCAN: {
      /* EVIDENCE-OF: R-36592-02772 The SQLITE_CONFIG_COVERING_INDEX_SCAN
      ** option takes a single integer argument which is interpreted as a
      ** boolean in order to enable or disable the use of covering indices for
      ** full table scans in the query optimizer. */
      sqlite3GlobalConfig.bUseCis = va_arg(ap, int);
      break;
    }

    case SQLITE_CONFIG_MMAP_SIZE: {
      /* EVIDENCE-OF: R-58063-38258 SQLITE_CONFIG_MMAP_SIZE takes two 64-bit
      ** integer (sqlite3_int64) values that are the default mmap size limit
      ** (the default setting for PRAGMA mmap_size) and the maximum allowed
      ** mmap size limit. */
      sqlite3_int64 szMmap = va_arg(ap, sqlite3_int64);
      sqlite3_int64 mxMmap = va_arg(ap, sqlite3_int64);
      /* EVIDENCE-OF: R-53367-43190 If either argument to this option is
      ** negative, then that argument is changed to its compile-time default.
      **
      ** EVIDENCE-OF: R-34993-45031 The maximum allowed mmap size will be
      ** silently truncated if necessary so that it does not exceed the
      ** compile-time maximum mmap size set by the SQLITE_MAX_MMAP_SIZE
      ** compile-time option.
      */
      if( mxMmap<0 || mxMmap>SQLITE_MAX_MMAP_SIZE ){
        mxMmap = SQLITE_MAX_MMAP_SIZE;
      }
      if( szMmap<0 ) szMmap = SQLITE_DEFAULT_MMAP_SIZE;
      if( szMmap>mxMmap) szMmap = mxMmap;
      sqlite3GlobalConfig.mxMmap = mxMmap;
      sqlite3GlobalConfig.szMmap = szMmap;
      break;
    }

#if SQLITE_OS_WIN && defined(SQLITE_WIN32_MALLOC) /* IMP: R-04780-55815 */
    case SQLITE_CONFIG_WIN32_HEAPSIZE: {
      /* EVIDENCE-OF: R-34926-03360 SQLITE_CONFIG_WIN32_HEAPSIZE takes a 32-bit
      ** unsigned integer value that specifies the maximum size of the created
      ** heap. */
      sqlite3GlobalConfig.nHeap = va_arg(ap, int);
      break;
    }
#endif

    case SQLITE_CONFIG_PMASZ: {
      sqlite3GlobalConfig.szPma = va_arg(ap, unsigned int);
      break;
    }

    default: {
      rc = SQLITE_ERROR;
      break;
    }
  }
  va_end(ap);
  return rc;
}

/************** End of main.c ************************************************/