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Artifact 573911e274738b3fda813d4f0a6e319f8a9ecd36:


/*
** 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.
**
*************************************************************************
**
** @(#) $Id: journal.c,v 1.3 2007/08/24 08:15:54 danielk1977 Exp $
*/

#ifdef SQLITE_ENABLE_ATOMIC_WRITE

/*
** 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 xSync() method is called.
*/

#include "sqliteInt.h"

struct JournalFile {
  sqlite3_io_methods *pMethod;

  int nBuf;
  char *zBuf;
  int iSize;

  int flags;
  sqlite3_vfs *pVfs;
  sqlite3_file *pReal;
  const char *zJournal;
};
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);
      }
    }
  }
  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, 
  void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  int rc = SQLITE_OK;
  JournalFile *p = (JournalFile *)pJfd;
  if( p->pReal ){
    rc = sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
  }else{
    int n = iAmt;
    memset(zBuf, 0, n);
    if( n+iOfst>p->iSize ){
      rc = SQLITE_IOERR_SHORT_READ;
    }else{
      memcpy(zBuf, &p->zBuf[iOfst], n);
    }
  }
  return rc;
}

/*
** Write data to the file.
*/
static int jrnlWrite(
  sqlite3_file *pJfd, 
  const void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  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;
  rc = createFile(p);
  if( rc==SQLITE_OK ){
    rc = sqlite3OsSync(p->pReal, flags);
  }
  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,             /* xBreakLock */
  0,             /* xLockState */
  0,             /* xSectorSize */
  0              /* xDeviceCharacteristics */
};

/* 
** Open a journal file.
*/
int sqlite3JournalOpen(
  sqlite3_vfs *pVfs, 
  const char *zName, 
  sqlite3_file *pJfd,
  int flags,
  int nBuf
){
  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.
*/
int sqlite3JournalCreate(sqlite3_file *p){
  if( p->pMethods!=&JournalFileMethods ){
    return SQLITE_OK;
  }
  return createFile((JournalFile *)p);
}

/* 
** Return the number of bytes required to store a JournalFile that uses vfs
** pVfs to create the underlying on-disk files.
*/
int sqlite3JournalSize(sqlite3_vfs *pVfs){
  return (pVfs->szOsFile+sizeof(JournalFile));
}
#endif