SQLite

  u32 mLock;                      /* Mask of locks */
};

struct Log {
  LogSummary *pSummary;           /* Log file summary data */
  sqlite3_vfs *pVfs;              /* The VFS used to create pFd */
  sqlite3_file *pFd;              /* File handle for log file */
  int sync_flags;                 /* Flags to use with OsSync() */
  int isLocked;                   /* Non-zero if a snapshot is held open */
  int isWriteLocked;              /* True if this is the writer connection */
  LogSummaryHdr hdr;              /* Log summary header for current snapshot */
  LogLock lock;                   /* Lock held by this connection (if any) */
};

      }
    }
    z[j++] = z[i];
  }
  z[j] = 0;
}

/*
** Lock the summary file pSummary->fd.
*/
static int logSummaryLock(LogSummary *pSummary){
  int rc;
  struct flock f;
  memset(&f, 0, sizeof(f));
  f.l_type = F_WRLCK;
  f.l_whence = SEEK_SET;
  f.l_start = 0;
  f.l_len = 1;
  rc = fcntl(pSummary->fd, F_SETLKW, &f);
  if( rc!=0 ){
    return SQLITE_IOERR;
  }
  return SQLITE_OK;
}

/*
** Unlock the summary file pSummary->fd.
*/
static int logSummaryUnlock(LogSummary *pSummary){
  int rc;
  struct flock f;
  memset(&f, 0, sizeof(f));
  f.l_type = F_UNLCK;
  f.l_whence = SEEK_SET;
  f.l_start = 0;
  f.l_len = 1;
  rc = fcntl(pSummary->fd, F_SETLK, &f);
  if( rc!=0 ){
    return SQLITE_IOERR;
  }
  return SQLITE_OK;
}

/*
** Memory map the first nByte bytes of the summary file opened with 
** pSummary->fd at pSummary->aData. If the summary file is smaller than
** nByte bytes in size when this function is called, ftruncate() is
** used to expand it before it is mapped.
**
** It is assumed that an exclusive lock is held on the summary file

  /* Allocate an instance of struct Log to return. */
  *ppLog = 0;
  pRet = (Log *)sqlite3MallocZero(sizeof(Log) + pVfs->szOsFile);
  if( !pRet ) goto out;
  pRet->pVfs = pVfs;
  pRet->pFd = (sqlite3_file *)&pRet[1];
  pRet->sync_flags = SQLITE_SYNC_NORMAL;

  /* Normalize the path name. */
  zWal = sqlite3_mprintf("%s-wal", zDb);
  if( !zWal ) goto out;
  logNormalizePath(zWal);
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_MAIN_JOURNAL);
  nWal = sqlite3Strlen30(zWal);

/*
** Checkpoint the contents of the log file.
*/
static int logCheckpoint(
  Log *pLog,                      /* Log connection */
  sqlite3_file *pFd,              /* File descriptor open on db file */

  u8 *zBuf                        /* Temporary buffer to use */
){
  int rc;                         /* Return code */
  int pgsz = pLog->hdr.pgsz;      /* Database page-size */
  LogIterator *pIter = 0;         /* Log iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Log frame containing data for iDbpage */

  if( pLog->hdr.iLastPg==0 ){
    return SQLITE_OK;
  }

  /* Allocate the iterator */
  pIter = logIteratorInit(pLog);
  if( !pIter ) return SQLITE_NOMEM;

  /* Sync the log file to disk */

  rc = sqlite3OsSync(pLog->pFd, pLog->sync_flags);
  if( rc!=SQLITE_OK ) goto out;


  /* Iterate through the contents of the log, copying data to the db file. */
  while( 0==logIteratorNext(pIter, &iDbpage, &iFrame) ){
    rc = sqlite3OsRead(pLog->pFd, zBuf, pgsz, 
        logFrameOffset(iFrame, pgsz) + LOG_FRAME_HDRSIZE
    );
    if( rc!=SQLITE_OK ) goto out;
    rc = sqlite3OsWrite(pFd, zBuf, pgsz, (iDbpage-1)*pgsz);
    if( rc!=SQLITE_OK ) goto out;
  }

  /* Truncate the database file */
  rc = sqlite3OsTruncate(pFd, ((i64)pLog->hdr.nPage*(i64)pgsz));
  if( rc!=SQLITE_OK ) goto out;

  /* Sync the database file. If successful, update the log-summary. */

  rc = sqlite3OsSync(pFd, pLog->sync_flags);
  if( rc!=SQLITE_OK ) goto out;

  pLog->hdr.iLastPg = 0;
  pLog->hdr.iCheck1 = 2;
  pLog->hdr.iCheck2 = 3;
  logSummaryWriteHdr(pLog->pSummary, &pLog->hdr);

  /* TODO: If a crash occurs and the current log is copied into the 
  ** database there is no problem. However, if a crash occurs while

/*
** Close a connection to a log file.
*/
int sqlite3LogClose(
  Log *pLog,                      /* Log to close */
  sqlite3_file *pFd,              /* Database file */

  u8 *zBuf                        /* Buffer of at least page-size bytes */
){
  int rc = SQLITE_OK;
  if( pLog ){
    LogLock **ppL;
    LogSummary *pSummary = pLog->pSummary;
    sqlite3_mutex *mutex = 0;

        /* This is the last connection to the database (including other
        ** processes). Do three things:
        **
        **   1. Checkpoint the db.
        **   2. Truncate the log file.
        **   3. Unlink the log-summary file.
        */
        rc = logCheckpoint(pLog, pFd, zBuf);
        if( rc==SQLITE_OK ){
          rc = sqlite3OsDelete(pLog->pVfs, pSummary->zPath, 0);
        }

        logSummaryUnmap(pSummary, 1);
      }else{
        if( rc==SQLITE_BUSY ){

    /* Close the connection to the log file and free the Log handle. */
    sqlite3OsClose(pLog->pFd);
    sqlite3_free(pLog);
  }
  return rc;
}

/*
** Set the flags to pass to the sqlite3OsSync() function when syncing
** the log file.
*/
#if 0
void sqlite3LogSetSyncflags(Log *pLog, int sync_flags){
  assert( sync_flags==SQLITE_SYNC_NORMAL || sync_flags==SQLITE_SYNC_FULL );
  pLog->sync_flags = sync_flags;
}
#endif

/*
** Enter and leave the log-summary mutex. In this context, entering the
** log-summary mutex means:
**
**   1. Obtaining mutex pLog->pSummary->mutex, and
**   2. Taking an exclusive lock on the log-summary file.
**

*/
int sqlite3LogFrames(
  Log *pLog,                      /* Log handle to write to */
  int nPgsz,                      /* 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 isSync                      /* True to sync the log file */
){
  int rc;                         /* Used to catch return codes */
  u32 iFrame;                     /* Next frame address */
  u8 aFrame[LOG_FRAME_HDRSIZE];   /* Buffer to assemble frame-header in */
  PgHdr *p;                       /* Iterator to run through pList with. */
  u32 aCksum[2];                  /* Checksums */
  PgHdr *pLast;                   /* Last frame in list */

    if( rc!=SQLITE_OK ){
      return rc;
    }
    pLast = p;
  }

  /* Sync the log file if the 'isSync' flag was specified. */
  if( isSync ){
    i64 iSegment = sqlite3OsSectorSize(pLog->pFd);
    i64 iOffset = logFrameOffset(iFrame+1, nPgsz);

    assert( isCommit );

    if( iSegment<SQLITE_DEFAULT_SECTOR_SIZE ){
      iSegment = SQLITE_DEFAULT_SECTOR_SIZE;

      if( rc!=SQLITE_OK ){
        return rc;
      }
      nLast++;
      iOffset += nPgsz;
    }

    rc = sqlite3OsSync(pLog->pFd, pLog->sync_flags);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }

  /* Append data to the log summary. It is not necessary to lock the 
  ** log-summary to do this as the RESERVED lock held on the db file

**   3. Copy the contents of the log into the database file.
**   4. Zero the log-summary header (so new readers will ignore the log).
**   5. Drop the locks obtained in steps 1 and 2.
*/
int sqlite3LogCheckpoint(
  Log *pLog,                      /* Log connection */
  sqlite3_file *pFd,              /* File descriptor open on db file */

  u8 *zBuf,                       /* Temporary buffer to use */
  int (*xBusyHandler)(void *),    /* Pointer to busy-handler function */
  void *pBusyHandlerArg           /* Argument to pass to xBusyHandler */
){
  int rc;                         /* Return code */

  assert( !pLog->isLocked );

    logLockRegion(pLog, LOG_REGION_B|LOG_REGION_C, LOG_UNLOCK);
    return rc;
  }

  /* Copy data from the log to the database file. */
  rc = logSummaryReadHdr(pLog, 0);
  if( rc==SQLITE_OK ){
    rc = logCheckpoint(pLog, pFd, zBuf);
  }

  /* Release the locks. */
  logLockRegion(pLog, LOG_REGION_A|LOG_REGION_B|LOG_REGION_C, LOG_UNLOCK);
  return rc;
}

*/

#ifndef _LOG_H_
#define _LOG_H_

#include "sqliteInt.h"

/* Flags that may be set in the 'flags' argument to sqlite3LogWrite(): */
#define LOG_MASK_COMMIT        0x08
#define LOG_MASK_MASTERJOURNAL 0x10
#define LOG_MASK_TRUNCATE      0x20


#define LOG_TRUNCATE_BIT       0x80000000 

/* Connection to a log file. There is one object of this type for each pager. */
typedef struct Log Log;

/* Open and close a connection to a log file. */
int sqlite3LogOpen(sqlite3_vfs*, const char *zDb, Log **ppLog);
int sqlite3LogClose(Log *pLog, sqlite3_file *pFd, u8 *zBuf);

/* Configure the log connection. */
void sqlite3LogSetSyncflags(Log *, int sync_flags);

/* Used by readers to open (lock) and close (unlock) a database snapshot. */
int sqlite3LogOpenSnapshot(Log *pLog, int *);
void sqlite3LogCloseSnapshot(Log *pLog);

/* Read a page from the log, if it is present. */
int sqlite3LogRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut);
void sqlite3LogMaxpgno(Log *pLog, Pgno *pPgno);

/* Obtain or release the WRITER lock. */
int sqlite3LogWriteLock(Log *pLog, int op);

/* Write a segment to the log. */
int sqlite3LogFrames(Log *pLog, int, PgHdr *, Pgno, int, int);

/* Copy pages from the log to the database file */ 
int sqlite3LogCheckpoint(
  Log *pLog,                      /* Log connection */
  sqlite3_file *pFd,              /* File descriptor open on db file */

  u8 *zBuf,                       /* Temporary buffer to use */
  int (*xBusyHandler)(void *),    /* Pointer to busy-handler function */
  void *pBusyHandlerArg           /* Argument to pass to xBusyHandler */
);

#endif /* _LOG_H_ */

int sqlite3PagerClose(Pager *pPager){
  u8 *pTmp = (u8 *)pPager->pTmpSpace;

  disable_simulated_io_errors();
  sqlite3BeginBenignMalloc();
  pPager->errCode = 0;
  pPager->exclusiveMode = 0;
  sqlite3LogClose(pPager->pLog, pPager->fd, pTmp);


  pPager->pLog = 0;
  pager_reset(pPager);
  if( MEMDB ){
    pager_unlock(pPager);
  }else{
    /* Set Pager.journalHdr to -1 for the benefit of the pager_playback() 
    ** call which may be made from within pagerUnlockAndRollback(). If it

    */
    sqlite3BackupRestart(pPager->pBackup);
  }else if( pPager->state!=PAGER_SYNCED && pPager->dbModified ){
    if( pagerUseLog(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
        rc = sqlite3LogFrames(pPager->pLog, pPager->pageSize, pList,
            pPager->dbSize, 1, pPager->fullSync
        );
      }
      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 

** This function is called when the user invokes "PRAGMA checkpoint".
*/
int sqlite3PagerCheckpoint(Pager *pPager){
  int rc = SQLITE_OK;
  if( pPager->pLog ){
    u8 *zBuf = (u8 *)pPager->pTmpSpace;
    rc = sqlite3LogCheckpoint(pPager->pLog, pPager->fd, 

        zBuf, pPager->xBusyHandler, pPager->pBusyHandlerArg
    );
  }
  return rc;
}

#endif /* SQLITE_OMIT_DISKIO */