int rc = SQLITE_OK;

  offset = osTell(pFile);
  for(i=0; i<pFile->nBlk; i++){
    u8 *p = pFile->apBlk[i];
    if( p ){
      int skip = 0;

      if( crash ){
        char random;
        sqlite3Randomness(1, &random);
        if( random & 0x01 ){






          skip = 1;
#ifdef TRACE_WRITECACHE
printf("Not writing block %d of %s\n", i, pFile->zName); 


        }else{

printf("Writing block %d of %s\n", i, pFile->zName); 
#endif
        }
      }
      if( rc==SQLITE_OK ){
        rc = sqlite3RealSeek(&pFile->fd, BLOCK_OFFSET(i));
      }
      if( rc==SQLITE_OK && !skip ){
        int len = BLOCKSIZE;
        if( BLOCK_OFFSET(i+1)>nMax ){
          len = nMax-BLOCK_OFFSET(i);
        }



        rc = sqlite3RealWrite(&pFile->fd, p, len);
      }
      sqliteFree(p);
    }
  }
  sqliteFree(pFile->apBlk);
  pFile->nBlk = 0;

  int rc = SQLITE_OK;

  offset = osTell(pFile);
  for(i=0; i<pFile->nBlk; i++){
    u8 *p = pFile->apBlk[i];
    if( p ){
      int skip = 0;
      int trash = 0;
      if( crash ){
        char random;
        sqlite3Randomness(1, &random);
        if( random & 0x01 ){
          if( 0 && random & 0x02 ){
            trash = 1;
#ifdef TRACE_WRITECACHE
printf("Trashing block %d of %s\n", i, pFile->zName); 
#endif
          }else{
            skip = 1;
#ifdef TRACE_WRITECACHE
printf("Skiping block %d of %s\n", i, pFile->zName); 
#endif
          }
        }else{
#ifdef TRACE_WRITECACHE
printf("Writing block %d of %s\n", i, pFile->zName); 
#endif
        }
      }
      if( rc==SQLITE_OK ){
        rc = sqlite3RealSeek(&pFile->fd, BLOCK_OFFSET(i));
      }
      if( rc==SQLITE_OK && !skip ){
        int len = BLOCKSIZE;
        if( BLOCK_OFFSET(i+1)>nMax ){
          len = nMax-BLOCK_OFFSET(i);
        }
        if( trash ){
          sqlite3Randomness(len, p);
        }
        rc = sqlite3RealWrite(&pFile->fd, p, len);
      }
      sqliteFree(p);
    }
  }
  sqliteFree(pFile->apBlk);
  pFile->nBlk = 0;

** 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.
**
** @(#) $Id: pager.c,v 1.137 2004/06/23 10:43:10 danielk1977 Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
  u8 readOnly;                /* True for a read-only database */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 dirtyCache;              /* True if cached pages have changed */
  u8 alwaysRollback;          /* Disable dont_rollback() for all pages */
  u8 memDb;                   /* True to inhibit all file I/O */
  u8 *aInJournal;             /* One bit for each page in the database file */
  u8 *aInStmt;                /* One bit for each page in the database */
  int nMaster;                /* Number of bytes to reserve for master j.p */
  BusyHandler *pBusyHandler;  /* Pointer to sqlite.busyHandler */
  PgHdr *pFirst, *pLast;      /* List of free pages */
  PgHdr *pFirstSynced;        /* First free page with PgHdr.needSync==0 */
  PgHdr *pAll;                /* List of all pages */
  PgHdr *pStmt;               /* List of pages in the statement subjournal */
  PgHdr *aHash[N_PG_HASH];    /* Hash table to map page number to PgHdr */





};

/*
** These are bits that can be set in Pager.errMask.
*/
#define PAGER_ERR_FULL     0x01  /* a write() failed */
#define PAGER_ERR_MEM      0x02  /* malloc() failed */
................................................................................
  0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
};

/*
** The size of the header and of each page in the journal is determined
** by the following macros.
*/
#define JOURNAL_HDR_SZ(pPager) (24 + (pPager)->nMaster)
#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)



















/*
** Enable reference count tracking (for debugging) here:
*/
#ifdef SQLITE_TEST
  int pager3_refinfo_enable = 0;
  static void pager_refinfo(PgHdr *p){
................................................................................
  if( pPager->errMask & PAGER_ERR_LOCK )    rc = SQLITE_PROTOCOL;
  if( pPager->errMask & PAGER_ERR_DISK )    rc = SQLITE_IOERR;
  if( pPager->errMask & PAGER_ERR_FULL )    rc = SQLITE_FULL;
  if( pPager->errMask & PAGER_ERR_MEM )     rc = SQLITE_NOMEM;
  if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
  return rc;
}















































































































































































































































/*
** Add or remove a page from the list of all pages that are in the
** statement journal.
**
** The Pager keeps a separate list of pages that are currently in
** the statement journal.  This helps the sqlite3pager_stmt_commit()
................................................................................
    pPager->aInJournal = 0;
    for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
      pPg->inJournal = 0;
      pPg->dirty = 0;
      pPg->needSync = 0;
    }
    pPager->dirtyCache = 0;
    pPager->nMaster = 0;
    pPager->nRec = 0;
  }else{
    assert( pPager->dirtyCache==0 || pPager->useJournal==0 );
  }
  sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
  pPager->state = PAGER_SHARED;
  pPager->origDbSize = 0;

  return SQLITE_OK;
}

/*
** Compute and return a checksum for the page of data.
**
** This is not a real checksum.  It is really just the sum of the 
................................................................................
  u32 cksum;                    /* Checksum used for sanity checking */
  u8 aData[SQLITE_PAGE_SIZE];   /* Store data here */

  rc = read32bits(jfd, &pgno);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlite3OsRead(jfd, &aData, pPager->pageSize);
  if( rc!=SQLITE_OK ) return rc;


  /* 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 ){
................................................................................
  }
  if( pgno>(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( useCksum ){
    rc = read32bits(jfd, &cksum);
    if( rc ) return rc;

    if( pager_cksum(pPager, pgno, aData)!=cksum ){
      return SQLITE_DONE;
    }
  }

  assert( pPager->state==PAGER_RESERVED || pPager->state>=PAGER_EXCLUSIVE );

  /* If the pager is in RESERVED 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.
  **
  ** FIX ME: Ideally the page would only be left marked dirty when the
  ** pager is in RESERVED state if it was dirty when this statement
  ** transaction was started. 
  **
  ** If in EXCLUSIVE state, then we update the pager cache if it exists
  ** and the main file. The page is then marked not dirty.
  */
  pPg = pager_lookup(pPager, pgno);
  assert( pPager->state>=PAGER_EXCLUSIVE || pPg );
  TRACE2("PLAYBACK page %d\n", pgno);
  if( pPager->state>=PAGER_EXCLUSIVE ){
................................................................................
  if( rc!=SQLITE_OK ) goto delmaster_out;
  master_open = 1;
  rc = sqlite3OsFileSize(&master, &nMasterJournal);
  if( rc!=SQLITE_OK ) goto delmaster_out;

  if( nMasterJournal>0 ){
    char *zJournal;
    char *zMasterPtr;
    int nMasterPtr;   /* Number of bytes allocated at zMasterPtr */

    /* Load the entire master journal file into space obtained from
    ** sqliteMalloc() and pointed to by zMasterJournal. 
    **
    ** Also allocate an extra (strlen(zMaster)+1) bytes. This space is used
    ** to load a master-journal filename from some other journal file to
    ** check if it points at this master journal file.
    */
    nMasterPtr = strlen(zMaster) + 1;
    zMasterJournal = (char *)sqliteMalloc(nMasterJournal) + nMasterPtr;
    if( !zMasterJournal ){
      rc = SQLITE_NOMEM;
      goto delmaster_out;
    }
    zMasterPtr = &zMasterJournal[nMasterJournal];
    rc = sqlite3OsRead(&master, zMasterJournal, nMasterJournal);
    if( rc!=SQLITE_OK ) goto delmaster_out;

    zJournal = zMasterJournal;
    while( (zJournal-zMasterJournal)<nMasterJournal ){
      if( sqlite3OsFileExists(zJournal) ){
        /* 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.
        */
        OsFile journal;
        int nMaster;
        off_t jsz;

        memset(&journal, 0, sizeof(journal));
        rc = sqlite3OsOpenReadOnly(zJournal, &journal);
        if( rc!=SQLITE_OK ){




          sqlite3OsClose(&journal);

          goto delmaster_out;
        }

	/* Check if the file is big enough to be a journal file
        ** with the required master journal name. If not, ignore it.
        */
        rc = sqlite3OsFileSize(&journal, &jsz);
        if( rc!=SQLITE_OK ){
          sqlite3OsClose(&journal);
          goto delmaster_out;
        }
        if( jsz<(25+strlen(zMaster)) ){
          sqlite3OsClose(&journal);
          continue;
        }
        
        /* Seek to the point in the journal where the master journal name
        ** is stored. Read the master journal name into memory obtained
        ** from malloc.
        */
        rc = sqlite3OsSeek(&journal, 20);
        if( rc!=SQLITE_OK ) goto delmaster_out;
        rc = read32bits(&journal, (u32*)&nMaster);
        if( rc!=SQLITE_OK ) goto delmaster_out;
        if( nMaster>=nMasterPtr ){
          rc = sqlite3OsRead(&journal, zMasterPtr, nMasterPtr);
          if( rc!=SQLITE_OK ){
            goto delmaster_out;
          }
          if( zMasterPtr[nMasterPtr-1]=='\0' && !strcmp(zMasterPtr, zMaster) ){
            /* We have a match. Do not delete the master journal file. */
            goto delmaster_out;
          }
        }
      }
      zJournal += (strlen(zJournal)+1);
    }
  }
  
  sqlite3OsDelete(zMaster);

................................................................................
    }
    pPg->needSync = 0;
    pPg->dirty = 0;
  }
  return rc;
}


/*
** 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[].
................................................................................
** 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.
*/
static int pager_playback(Pager *pPager, int useJournalSize){
  off_t szJ;               /* Size of the journal file in bytes */
  int nRec;                /* Number of Records in the journal */
  int i;                   /* Loop counter */
  Pgno mxPg = 0;           /* Size of the original file in pages */
  unsigned char aMagic[8]; /* A buffer to hold the magic header */
  int rc;                  /* Result code of a subroutine */
  int nMaster;             /* Number of bytes in the name of master journal */
  char *zMaster = 0;       /* Name of master journal file if any */

  /* Figure out how many records are in the journal.  Abort early if
  ** the journal is empty.
  */
  assert( pPager->journalOpen );
  sqlite3OsSeek(&pPager->jfd, 0);
  rc = sqlite3OsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_playback;
  }

  /* If the journal file is too small to contain a complete header,
  ** it must mean that the process that created the journal was just
  ** beginning to write the journal file when it died.  In that case,
  ** the database file should have still been completely unchanged.
  ** Nothing needs to be rolled back.  We can safely ignore this journal.
  */

  if( szJ < 24 ){
    goto end_playback;
  }



  /* (1) Read the beginning of the journal and verify the magic string
  ** at the beginning of the journal. */
  rc = sqlite3OsRead(&pPager->jfd, aMagic, sizeof(aMagic));
  if( rc!=SQLITE_OK || memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
    goto end_playback;
  }

  /* (2) Read the number of pages stored in the journal.  */
  rc = read32bits(&pPager->jfd, (u32*)&nRec);
  if( rc ) goto end_playback;
  if( nRec==0xffffffff || useJournalSize || 
      nRec>(szJ - JOURNAL_HDR_SZ(pPager))/JOURNAL_PG_SZ(pPager)
  ){
    nRec = (szJ - JOURNAL_HDR_SZ(pPager))/JOURNAL_PG_SZ(pPager);

  }




  /* (3) Read the initial value for the sanity checksum */
  rc = read32bits(&pPager->jfd, &pPager->cksumInit);
  if( rc ) goto end_playback;

  /* (4) Read the number of pages in the database file prior to the
  ** start of the transaction */
  rc = read32bits(&pPager->jfd, &mxPg);






  if( rc!=SQLITE_OK ){
    goto end_playback;


  }

  /* (5) and (6): Check if a master journal file is specified. If one is
  ** specified, only proceed with the playback if it still exists. */
  rc = read32bits(&pPager->jfd, &nMaster);
  if( rc ) goto end_playback;
  if( szJ < 24+nMaster ) goto end_playback;
  if( nMaster>0 ){
    zMaster = sqliteMalloc(nMaster);
    if( !zMaster ){
      rc = SQLITE_NOMEM;
      goto end_playback;
    }
    rc = sqlite3OsRead(&pPager->jfd, zMaster, nMaster);
    if( rc!=SQLITE_OK || (zMaster[0] && !sqlite3OsFileExists(zMaster)) ){
      goto end_playback;
    }








  }


  /* Truncate the database file back to it's original size */


  assert( pPager->origDbSize==0 || pPager->origDbSize==mxPg );
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)mxPg);
  if( rc!=SQLITE_OK ){
    goto end_playback;
  }
  pPager->dbSize = mxPg;
  




  /* Copy original pages out of the journal and back into the database file.
  */
  for(i=0; i<nRec; i++){
    rc = pager_playback_one_page(pPager, &pPager->jfd, 1);
    if( rc!=SQLITE_OK ){
      if( rc==SQLITE_DONE ){
        rc = SQLITE_OK;
      }

      break;




    }
  }

  /* Pages that have been written to the journal but never synced
  ** where not restored by the loop above.  We have to restore those
  ** pages by reading them back from the original database.
  */
  if( rc==SQLITE_OK ){
    pager_reload_cache(pPager);
  }

end_playback:
  if( zMaster ){
    /* If there was a master journal and this routine will return true,
    ** see if it is possible to delete the master journal. If errors 
    ** occur during this process, ignore them.
    */
................................................................................
      pager_delmaster(zMaster);
    }
    sqliteFree(zMaster);
  }
  if( rc==SQLITE_OK ){
    rc = pager_unwritelock(pPager);
  }






  return rc;
}

/*
** Playback the statement journal.
**
** This is similar to playing back the transaction journal but with
................................................................................
**
**    (2)  In addition to playing back the statement journal, also
**         playback all pages of the transaction journal beginning
**         at offset pPager->stmtJSize.
*/
static int pager_stmt_playback(Pager *pPager){
  off_t szJ;               /* Size of the full journal */

  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;






















  /* Truncate the database back to its original size.
  */
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->stmtSize);
  pPager->dbSize = pPager->stmtSize;

  /* Figure out how many records are in the statement journal.
................................................................................
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->stfd, 0);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  /* Figure out how many pages need to be copied out of the transaction
  ** journal.





  */
  rc = sqlite3OsSeek(&pPager->jfd, pPager->stmtJSize);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  rc = sqlite3OsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  nRec = (szJ - pPager->stmtJSize)/JOURNAL_PG_SZ(pPager);
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->jfd, 1);




    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_stmt_playback;
    }




  }



  
end_stmt_playback:
  if( rc!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_CORRUPT;
    rc = SQLITE_CORRUPT;
  }
  return rc;
................................................................................
  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->nExtra = nExtra;

  pPager->pBusyHandler = (BusyHandler *)pBusyHandler;
  memset(pPager->aHash, 0, sizeof(pPager->aHash));
  *ppPager = pPager;
  return SQLITE_OK;
}

/*
................................................................................
  }
  return n;
}

/*
** Forward declaration
*/
static int syncJournal(Pager*, const char*);


/*
** Unlink a page from the free list (the list of all pages where nRef==0)
** and from its hash collision chain.
*/
static void unlinkPage(PgHdr *pPg){
................................................................................
    return SQLITE_OK;
  }
  if( pPager->memDb ){
    pPager->dbSize = nPage;
    memoryTruncate(pPager);
    return SQLITE_OK;
  }
  rc = syncJournal(pPager, 0);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)nPage);
  if( rc==SQLITE_OK ){
    pPager->dbSize = nPage;
  }
................................................................................
**
** For temporary databases, we do not care if we are able to rollback
** after a power failure, so sync occurs.
**
** This routine clears the needSync field of every page current held in
** memory.
*/
static int syncJournal(Pager *pPager, const char *zMaster){
  PgHdr *pPg;
  int rc = SQLITE_OK;

  /* Sync the journal before modifying the main database
  ** (assuming there is a journal and it needs to be synced.)
  */
  if( pPager->needSync || zMaster ){
    if( !pPager->tempFile ){
      assert( pPager->journalOpen );
      /* assert( !pPager->noSync ); // noSync might be set if synchronous
      ** was turned off after the transaction was started.  Ticket #615 */
#ifndef NDEBUG
      {
        /* Make sure the pPager->nRec counter we are keeping agrees
        ** with the nRec computed from the size of the journal file.
        */
        off_t hdrSz, pgSz, jSz;
        hdrSz = JOURNAL_HDR_SZ(pPager);
        pgSz = JOURNAL_PG_SZ(pPager);
        rc = sqlite3OsFileSize(&pPager->jfd, &jSz);
        if( rc!=0 ) return rc;
        assert( pPager->nRec*pgSz+hdrSz==jSz );
      }
#endif
      {
        /* Write the nRec value into the journal file header */
        off_t szJ;



        if( pPager->fullSync ){
          TRACE2("SYNC journal of %d\n", pPager->fd.h);
          rc = sqlite3OsSync(&pPager->jfd);
          if( rc!=0 ) return rc;
        }
        sqlite3OsSeek(&pPager->jfd, sizeof(aJournalMagic));
        rc = write32bits(&pPager->jfd, pPager->nRec);
        if( rc ) return rc;

        /* Write the name of the master journal file if one is specified */
        if( zMaster ){
          assert( strlen(zMaster)<pPager->nMaster );
          rc = sqlite3OsSeek(&pPager->jfd, 20);
          if( rc ) return rc;
          rc = sqlite3OsWrite(&pPager->jfd, zMaster, strlen(zMaster)+1);
          if( rc ) return rc;
        }

        szJ = JOURNAL_HDR_SZ(pPager) +  pPager->nRec*JOURNAL_PG_SZ(pPager);
        sqlite3OsSeek(&pPager->jfd, szJ);
      }
      TRACE2("SYNC journal of %d\n", pPager->fd.h);
      rc = sqlite3OsSync(&pPager->jfd);
      if( rc!=0 ) return rc;
      pPager->journalStarted = 1;
    }
    pPager->needSync = 0;
................................................................................
       if( rc!=SQLITE_OK ){
         sqlite3OsUnlock(&pPager->fd, NO_LOCK);
         pPager->state = PAGER_UNLOCK;
         return SQLITE_BUSY;
       }
       pPager->journalOpen = 1;
       pPager->journalStarted = 0;




       /* Playback and delete the journal.  Drop the database write
       ** lock and reacquire the read lock.
       */
       rc = pager_playback(pPager, 0);
       if( rc!=SQLITE_OK ){
         return rc;
       }
    }
    pPg = 0;
  }else{
    /* Search for page in cache */
................................................................................

      /* If we could not find a page that does not require an fsync()
      ** on the journal file then fsync the journal file.  This is a
      ** very slow operation, so we work hard to avoid it.  But sometimes
      ** it can't be helped.
      */
      if( pPg==0 ){
        int rc = syncJournal(pPager, 0);
        if( rc!=0 ){
          sqlite3pager_rollback(pPager);
          return SQLITE_IOERR;














        }
        pPg = pPager->pFirst;
      }
      assert( pPg->nRef==0 );

      /* Write the page to the database file if it is dirty.
      */
................................................................................
  pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInJournal==0 ){
    sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    return SQLITE_NOMEM;
  }
  rc = sqlite3OsOpenExclusive(pPager->zJournal, &pPager->jfd,pPager->tempFile);



  if( rc!=SQLITE_OK ){
    sqliteFree(pPager->aInJournal);
    pPager->aInJournal = 0;
    sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    return SQLITE_CANTOPEN;
  }
................................................................................
  pPager->nRec = 0;
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  pPager->origDbSize = pPager->dbSize;

  /* Create the header for the journal:
  ** - 8 bytes: Magic identifying journal format.
  ** - 4 bytes: Number of records in journal, or -1 no-sync mode is on.
  ** - 4 bytes: Magic used for page checksums.
  ** - 4 bytes: Initial database page count.
  ** - 4 bytes: Number of bytes reserved for master journal ptr (nMaster)
  ** - nMaster bytes: Space for a master journal pointer.
  */
  rc = sqlite3OsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->noSync ? 0xffffffff : 0);
  }
  if( rc==SQLITE_OK ){
    sqlite3Randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
    rc = write32bits(&pPager->jfd, pPager->cksumInit);
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->nMaster);
  }
  if( rc==SQLITE_OK ){
    sqlite3OsSeek(&pPager->jfd, 24 + pPager->nMaster - 1);
    rc = sqlite3OsWrite(&pPager->jfd, "\000", 1);
  }
  if( pPager->stmtAutoopen && rc==SQLITE_OK ){
    rc = sqlite3pager_stmt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
................................................................................
**
** A journal file is opened if this is not a temporary file.  For temporary
** files, the opening of the journal file is deferred until there is an
** actual need to write to the journal.
**
** If the database is already reserved for writing, this routine is a no-op.
*/
int sqlite3pager_begin(void *pData, int nMaster){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( nMaster>=0 );
  assert( pPager->state!=PAGER_UNLOCK );
  if( pPager->state==PAGER_SHARED ){
    assert( pPager->aInJournal==0 );
    if( pPager->memDb ){
      pPager->state = PAGER_EXCLUSIVE;
      pPager->origDbSize = pPager->dbSize;
    }else{
................................................................................
          pPager->pBusyHandler && 
          pPager->pBusyHandler->xFunc && 
          pPager->pBusyHandler->xFunc(pPager->pBusyHandler->pArg, busy++)
      );
      if( rc!=SQLITE_OK ){
        return rc;
      }
      pPager->nMaster = nMaster;
      pPager->state = PAGER_RESERVED;
      pPager->dirtyCache = 0;
      TRACE3("TRANSACTION %d nMaster=%d\n", pPager->fd.h, nMaster);
      if( pPager->useJournal && !pPager->tempFile ){
        rc = pager_open_journal(pPager);
      }
    }
  }
  return rc;
}
................................................................................
  */
  if( pPager->errMask ){ 
    return pager_errcode(pPager);
  }
  if( pPager->readOnly ){
    return SQLITE_PERM;
  }



  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  pPg->dirty = 1;
  if( pPg->inJournal && (pPg->inStmt || pPager->stmtInUse==0) ){
    pPager->dirtyCache = 1;
................................................................................
        u32 cksum = pager_cksum(pPager, pPg->pgno, pData);
        saved = *(u32*)PGHDR_TO_EXTRA(pPg);
        store32bits(cksum, pPg, SQLITE_PAGE_SIZE);
        szPg = SQLITE_PAGE_SIZE+8;
        store32bits(pPg->pgno, pPg, -4);
        CODEC(pPager, pData, pPg->pgno, 7);
        rc = sqlite3OsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);

        TRACE3("JOURNAL page %d needSync=%d\n", pPg->pgno, pPg->needSync);
        CODEC(pPager, pData, pPg->pgno, 0);
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
        if( rc!=SQLITE_OK ){
          sqlite3pager_rollback(pPager);
          pPager->errMask |= PAGER_ERR_FULL;
          return rc;
................................................................................
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }

  if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
    if( pPager->state>=PAGER_EXCLUSIVE ){
      pager_playback(pPager, 1);
    }
    return pager_errcode(pPager);
  }
  if( pPager->state==PAGER_RESERVED ){
    int rc2;
    rc = pager_reload_cache(pPager);
    rc2 = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = rc2;
    }
  }else{
    rc = pager_playback(pPager, 1);
  }
  if( rc!=SQLITE_OK ){
    rc = SQLITE_CORRUPT;
    pPager->errMask |= PAGER_ERR_CORRUPT;
  }
  pPager->dbSize = -1;
  return rc;
................................................................................
  if( pPager->aInStmt==0 ){
    sqlite3OsLock(&pPager->fd, SHARED_LOCK);
    return SQLITE_NOMEM;
  }
#ifndef NDEBUG
  rc = sqlite3OsFileSize(&pPager->jfd, &pPager->stmtJSize);
  if( rc ) goto stmt_begin_failed;
  assert( pPager->stmtJSize == 
    pPager->nRec*JOURNAL_PG_SZ(pPager) + JOURNAL_HDR_SZ(pPager) );
#endif
  pPager->stmtJSize =
     pPager->nRec*JOURNAL_PG_SZ(pPager) + JOURNAL_HDR_SZ(pPager);
  pPager->stmtSize = pPager->dbSize;

  if( !pPager->stmtOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->stfd);
    if( rc ) goto stmt_begin_failed;
    pPager->stmtOpen = 1;
    pPager->stmtNRec = 0;
  }
  pPager->stmtInUse = 1;
................................................................................
  /* If this is an in-memory db, or no pages have been written to, or this
  ** function has already been called, it is a no-op.
  */
  if( pPager->state!=PAGER_SYNCED && !pPager->memDb && pPager->dirtyCache ){
    PgHdr *pPg;
    assert( pPager->journalOpen );








    rc = pager_incr_changecounter(pPager);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Sync the journal file */


    rc = syncJournal(pPager, zMaster);
    if( rc!=SQLITE_OK ) goto sync_exit;


    /* Write all dirty pages to the database file */
    pPg = pager_get_all_dirty_pages(pPager);
    rc = pager_write_pagelist(pPg);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Sync the database file. */

** 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.
**
** @(#) $Id: pager.c,v 1.138 2004/06/25 02:38:55 danielk1977 Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
  u8 readOnly;                /* True for a read-only database */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 dirtyCache;              /* True if cached pages have changed */
  u8 alwaysRollback;          /* Disable dont_rollback() for all pages */
  u8 memDb;                   /* True to inhibit all file I/O */
  u8 *aInJournal;             /* One bit for each page in the database file */
  u8 *aInStmt;                /* One bit for each page in the database */

  BusyHandler *pBusyHandler;  /* Pointer to sqlite.busyHandler */
  PgHdr *pFirst, *pLast;      /* List of free pages */
  PgHdr *pFirstSynced;        /* First free page with PgHdr.needSync==0 */
  PgHdr *pAll;                /* List of all pages */
  PgHdr *pStmt;               /* List of pages in the statement subjournal */
  PgHdr *aHash[N_PG_HASH];    /* Hash table to map page number to PgHdr */
  off_t journalOff;           /* Current byte offset in the journal file */
  off_t journalHdr;           /* Byte offset to previous journal header */
  off_t stmtHdrOff;           /* First journal header written this statement */
  int sectorSize;             /* Assumed sector size during rollback */
  u8 setMaster;               /* True if a m-j name has been written to jrnl */
};

/*
** These are bits that can be set in Pager.errMask.
*/
#define PAGER_ERR_FULL     0x01  /* a write() failed */
#define PAGER_ERR_MEM      0x02  /* malloc() failed */
................................................................................
  0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
};

/*
** The size of the header and of each page in the journal is determined
** by the following macros.
*/

#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)

/*
** The journal header size for this pager. In the future, this could be
** set to some value read from the disk controller. The important
** characteristic is that it is the same size as a disk sector.
*/
#define JOURNAL_HDR_SZ(pPager) (pPager->sectorSize)

#define PAGER_SECTOR_SIZE 512

/*
** 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() for details.
*/
#define PAGER_MJ_PGNO(x) (PENDING_BYTE/((x)->pageSize))

/*
** Enable reference count tracking (for debugging) here:
*/
#ifdef SQLITE_TEST
  int pager3_refinfo_enable = 0;
  static void pager_refinfo(PgHdr *p){
................................................................................
  if( pPager->errMask & PAGER_ERR_LOCK )    rc = SQLITE_PROTOCOL;
  if( pPager->errMask & PAGER_ERR_DISK )    rc = SQLITE_IOERR;
  if( pPager->errMask & PAGER_ERR_FULL )    rc = SQLITE_FULL;
  if( pPager->errMask & PAGER_ERR_MEM )     rc = SQLITE_NOMEM;
  if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
  return rc;
}

/*
** When this is called the journal file for pager pPager must be open.
** The master journal file name is read from the end of the file and 
** written into memory obtained from sqliteMalloc(). *pzMaster is
** set to point at the memory and SQLITE_OK returned. The caller must
** sqliteFree() *pzMaster.
**
** If no master journal file name is present *pzMaster is set to 0 and
** SQLITE_OK returned.
*/
static int readMasterJournal(OsFile *pJrnl, char **pzMaster){
  int rc;
  u32 len;
  off_t szJ;
  unsigned char aMagic[8]; /* A buffer to hold the magic header */

  *pzMaster = 0;

  rc = sqlite3OsFileSize(pJrnl, &szJ);
  if( rc!=SQLITE_OK || szJ<12 ) return rc;

  rc = sqlite3OsSeek(pJrnl, szJ-12);
  if( rc!=SQLITE_OK ) return rc;
 
  rc = read32bits(pJrnl, &len);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3OsRead(pJrnl, aMagic, 8);
  if( rc!=SQLITE_OK || memcmp(aMagic, aJournalMagic, 8) ) return rc;

  rc = sqlite3OsSeek(pJrnl, szJ-12-len);
  if( rc!=SQLITE_OK ) return rc;

  *pzMaster = (char *)sqliteMalloc(len);
  if( !*pzMaster ){
    return SQLITE_NOMEM;
  }
  rc = sqlite3OsRead(pJrnl, *pzMaster, len);
  if( rc!=SQLITE_OK ){
    sqliteFree(*pzMaster);
    *pzMaster = 0;
    return rc;
  }
   
  return SQLITE_OK;
}

/*
** Seek the journal file descriptor to the next sector boundary where a
** journal header may be read or written. Pager.journalOff is updated with
** the new seek offset.
**
** i.e for a sector size of 512:
**
** Input Offset              Output Offset
** ---------------------------------------
** 0                         0
** 512                       512
** 100                       512
** 2000                      2048
** 
*/
static int seekJournalHdr(Pager *pPager){
  off_t offset = 0;
  off_t 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) );
  pPager->journalOff = offset;
  return sqlite3OsSeek(&pPager->jfd, pPager->journalOff);
}

/*
** 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.
** 
** Followed by (JOURNAL_HDR_SZ - 20) bytes of unused space.
*/
static int writeJournalHdr(Pager *pPager){

  int rc = seekJournalHdr(pPager);
  if( rc ) return rc;

  pPager->journalHdr = pPager->journalOff;
  if( pPager->stmtHdrOff==0 ){
    pPager->stmtHdrOff = pPager->journalHdr;
  }
  pPager->journalOff += JOURNAL_HDR_SZ(pPager);

  /* FIX ME: 
  **
  ** Possibly for a pager not in no-sync mode, the journal magic should not
  ** be written until nRec is filled in as part of next syncJournal(). 
  **
  ** Actually maybe the whole journal header should be delayed until that
  ** point. Think about this.
  */
  rc = sqlite3OsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));

  if( rc==SQLITE_OK ){
    /* The nRec Field. 0xFFFFFFFF for no-sync journals. */
    rc = write32bits(&pPager->jfd, pPager->noSync ? 0xffffffff : 0);
  }
  if( rc==SQLITE_OK ){
    /* The random check-hash initialiser */ 
    sqlite3Randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
    rc = write32bits(&pPager->jfd, pPager->cksumInit);
  }
  if( rc==SQLITE_OK ){
    /* The initial database size */
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( rc==SQLITE_OK ){
    /* The assumed sector size for this process */
    rc = write32bits(&pPager->jfd, pPager->sectorSize);
  }

  /* The journal header has been written successfully. Seek the journal
  ** file descriptor to the end of the journal header sector.
  */
  if( rc==SQLITE_OK ){
    sqlite3OsSeek(&pPager->jfd, pPager->journalOff-1);
    rc = sqlite3OsWrite(&pPager->jfd, "\000", 1);
  }
  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. See comments above function writeJournalHdr() for a description of
** the journal header format.
**
** If the header is read successfully, *nRec is set to the number of
** page records following this header and *dbSize 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 *nRec and *dbSize are not set.  If JOURNAL_HDR_SZ bytes
** cannot be read from the journal file an error code is returned.
*/
static int readJournalHdr(
  Pager *pPager, 
  off_t journalSize,
  u32 *pNRec, 
  u32 *pDbSize
){
  int rc;
  unsigned char aMagic[8]; /* A buffer to hold the magic header */

  rc = seekJournalHdr(pPager);
  if( rc ) return rc;

  if( pPager->journalOff+JOURNAL_HDR_SZ(pPager) > journalSize ){
    return SQLITE_DONE;
  }

  rc = sqlite3OsRead(&pPager->jfd, aMagic, sizeof(aMagic));
  if( rc ) return rc;

  if( memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
    return SQLITE_DONE;
  }

  rc = read32bits(&pPager->jfd, pNRec);
  if( rc ) return rc;

  rc = read32bits(&pPager->jfd, &pPager->cksumInit);
  if( rc ) return rc;

  rc = read32bits(&pPager->jfd, pDbSize);
  if( rc ) return rc;

  /* 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.
  */
  rc = read32bits(&pPager->jfd, &pPager->sectorSize);
  if( rc ) return rc;

  pPager->journalOff += JOURNAL_HDR_SZ(pPager);
  rc = sqlite3OsSeek(&pPager->jfd, pPager->journalOff);
  return rc;
}


/*
** Write the supplied master journal name into the journal file for pager
** pPager at the current location.
*/
static int writeMasterJournal(Pager *pPager, const char *zMaster){
  int rc;
  int len; 

  if( !zMaster || pPager->setMaster) return SQLITE_OK;
  pPager->setMaster = 1;

  len = strlen(zMaster);

  /* 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 ){
    rc = seekJournalHdr(pPager);
    if( rc!=SQLITE_OK ) return rc;
  }

  pPager->journalOff += (len+16);

  rc = write32bits(&pPager->jfd, PAGER_MJ_PGNO(pPager));
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3OsWrite(&pPager->jfd, zMaster, len);
  if( rc!=SQLITE_OK ) return rc;

  rc = write32bits(&pPager->jfd, len);
  if( rc!=SQLITE_OK ) return rc;

  rc = sqlite3OsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));
  return rc;
}

/*
** Add or remove a page from the list of all pages that are in the
** statement journal.
**
** The Pager keeps a separate list of pages that are currently in
** the statement journal.  This helps the sqlite3pager_stmt_commit()
................................................................................
    pPager->aInJournal = 0;
    for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
      pPg->inJournal = 0;
      pPg->dirty = 0;
      pPg->needSync = 0;
    }
    pPager->dirtyCache = 0;

    pPager->nRec = 0;
  }else{
    assert( pPager->dirtyCache==0 || pPager->useJournal==0 );
  }
  sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
  pPager->state = PAGER_SHARED;
  pPager->origDbSize = 0;
  pPager->setMaster = 0;
  return SQLITE_OK;
}

/*
** Compute and return a checksum for the page of data.
**
** This is not a real checksum.  It is really just the sum of the 
................................................................................
  u32 cksum;                    /* Checksum used for sanity checking */
  u8 aData[SQLITE_PAGE_SIZE];   /* Store data here */

  rc = read32bits(jfd, &pgno);
  if( rc!=SQLITE_OK ) return rc;
  rc = sqlite3OsRead(jfd, &aData, pPager->pageSize);
  if( rc!=SQLITE_OK ) return rc;
  pPager->journalOff += pPager->pageSize + 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 ){
................................................................................
  }
  if( pgno>(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( useCksum ){
    rc = read32bits(jfd, &cksum);
    if( rc ) return rc;
    pPager->journalOff += 4;
    if( pager_cksum(pPager, pgno, aData)!=cksum ){
      return SQLITE_DONE;
    }
  }

  assert( pPager->state==PAGER_RESERVED || pPager->state>=PAGER_EXCLUSIVE );

  /* If the pager is in RESERVED 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.
  **




  ** If in EXCLUSIVE state, then we update the pager cache if it exists
  ** and the main file. The page is then marked not dirty.
  */
  pPg = pager_lookup(pPager, pgno);
  assert( pPager->state>=PAGER_EXCLUSIVE || pPg );
  TRACE2("PLAYBACK page %d\n", pgno);
  if( pPager->state>=PAGER_EXCLUSIVE ){
................................................................................
  if( rc!=SQLITE_OK ) goto delmaster_out;
  master_open = 1;
  rc = sqlite3OsFileSize(&master, &nMasterJournal);
  if( rc!=SQLITE_OK ) goto delmaster_out;

  if( nMasterJournal>0 ){
    char *zJournal;
    char *zMasterPtr = 0;


    /* Load the entire master journal file into space obtained from
    ** sqliteMalloc() and pointed to by zMasterJournal. 




    */

    zMasterJournal = (char *)sqliteMalloc(nMasterJournal);
    if( !zMasterJournal ){
      rc = SQLITE_NOMEM;
      goto delmaster_out;
    }

    rc = sqlite3OsRead(&master, zMasterJournal, nMasterJournal);
    if( rc!=SQLITE_OK ) goto delmaster_out;

    zJournal = zMasterJournal;
    while( (zJournal-zMasterJournal)<nMasterJournal ){
      if( sqlite3OsFileExists(zJournal) ){
        /* 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.
        */
        OsFile journal;



        memset(&journal, 0, sizeof(journal));
        rc = sqlite3OsOpenReadOnly(zJournal, &journal);
        if( rc!=SQLITE_OK ){
          goto delmaster_out;
        }

        rc = readMasterJournal(&journal, &zMasterPtr);
        sqlite3OsClose(&journal);
        if( rc!=SQLITE_OK ){
          goto delmaster_out;
        }



























        if( zMasterPtr && !strcmp(zMasterPtr, zMaster) ){
          /* We have a match. Do not delete the master journal file. */
          goto delmaster_out;
        }

      }
      zJournal += (strlen(zJournal)+1);
    }
  }
  
  sqlite3OsDelete(zMaster);

................................................................................
    }
    pPg->needSync = 0;
    pPg->dirty = 0;
  }
  return rc;
}


/*
** 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[].
................................................................................
** 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.
*/
static int pager_playback(Pager *pPager){
  off_t szJ;               /* Size of the journal file in bytes */
  int nRec;                /* Number of Records in the journal */
  int i;                   /* Loop counter */
  Pgno mxPg = 0;           /* Size of the original file in pages */

  int rc;                  /* Result code of a subroutine */

  char *zMaster = 0;       /* Name of master journal file if any */

  /* Figure out how many records are in the journal.  Abort early if
  ** the journal is empty.
  */
  assert( pPager->journalOpen );

  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.

  */
  rc = readMasterJournal(&pPager->jfd, &zMaster);
  assert( rc!=SQLITE_DONE );
  if( rc!=SQLITE_OK || (zMaster && !sqlite3OsFileExists(zMaster)) ){


    sqliteFree(zMaster);
    zMaster = 0;
    if( rc==SQLITE_DONE ) rc = SQLITE_OK;



    goto end_playback;
  }


  sqlite3OsSeek(&pPager->jfd, 0);





  pPager->journalOff = 0;

  /* This loop terminates either when the readJournalHdr() 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 of failed while writing it.
    ** This indicates nothing more needs to be rolled back.
    */
    rc = readJournalHdr(pPager, 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 = (szJ - JOURNAL_HDR_SZ(pPager))/JOURNAL_PG_SZ(pPager);
    }

    /* If this is the first header read from the journal, truncate the
    ** database file back to it's original size.
    */
    if( pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){
      assert( pPager->origDbSize==0 || pPager->origDbSize==mxPg );
      rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)mxPg);
      if( rc!=SQLITE_OK ){
        goto end_playback;
      }
      pPager->dbSize = mxPg;
    }

    /* rc = sqlite3OsSeek(&pPager->jfd, JOURNAL_HDR_SZ(pPager)); */
    if( rc!=SQLITE_OK ) goto end_playback;
  
    /* Copy original pages out of the journal and back into the database file.
    */
    for(i=0; i<nRec; i++){
      rc = pager_playback_one_page(pPager, &pPager->jfd, 1);
      if( rc!=SQLITE_OK ){
        if( rc==SQLITE_DONE ){
          rc = SQLITE_OK;

          pPager->journalOff = szJ;
          break;
        }else{
          goto end_playback;
        }
      }
    }
  }

  /* Pages that have been written to the journal but never synced
  ** where not restored by the loop above.  We have to restore those
  ** pages by reading them back from the original database.
  */
  assert( rc==SQLITE_OK );
  pager_reload_cache(pPager);


end_playback:
  if( zMaster ){
    /* If there was a master journal and this routine will return true,
    ** see if it is possible to delete the master journal. If errors 
    ** occur during this process, ignore them.
    */
................................................................................
      pager_delmaster(zMaster);
    }
    sqliteFree(zMaster);
  }
  if( rc==SQLITE_OK ){
    rc = pager_unwritelock(pPager);
  }

  /* The Pager.sectorSize variable may have been updated while rolling
  ** back a journal created by a process with a different PAGER_SECTOR_SIZE
  ** value. Reset it to the correct value for this process.
  */
  pPager->sectorSize = PAGER_SECTOR_SIZE;
  return rc;
}

/*
** Playback the statement journal.
**
** This is similar to playing back the transaction journal but with
................................................................................
**
**    (2)  In addition to playing back the statement journal, also
**         playback all pages of the transaction journal beginning
**         at offset pPager->stmtJSize.
*/
static int pager_stmt_playback(Pager *pPager){
  off_t szJ;               /* Size of the full journal */
  off_t hdrOff;
  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;

  szJ = pPager->journalOff;
#ifndef NDEBUG 
  {
    off_t os_szJ;
    rc = sqlite3OsFileSize(&pPager->jfd, &os_szJ);
    if( rc!=SQLITE_OK ) return rc;
    assert( szJ==os_szJ );
  }
#endif

  /* Set hdrOff to be the offset to the first journal header written
  ** this statement transaction, or the end of the file if no journal
  ** header was written.
  */
  hdrOff = pPager->stmtHdrOff;
  assert( pPager->fullSync || !hdrOff );
  if( !hdrOff ){
    hdrOff = szJ;
  }
  

  /* Truncate the database back to its original size.
  */
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->stmtSize);
  pPager->dbSize = pPager->stmtSize;

  /* Figure out how many records are in the statement journal.
................................................................................
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->stfd, 0);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  /* Now roll some pages back from the transaction journal. Pager.stmtJSize
  ** was the size of the journal file when this statement was started, so
  ** everything after that needs to be rolled back, either into the
  ** database, the memory cache, or both.
  **
  ** If it is not zero, then Pager.stmtHdrOff is the offset to the start
  ** of the first journal header written during this statement transaction.
  */
  rc = sqlite3OsSeek(&pPager->jfd, pPager->stmtJSize);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  pPager->journalOff = pPager->stmtJSize;
  while( pPager->journalOff < hdrOff ){
    rc = pager_playback_one_page(pPager, &pPager->jfd, 1);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  while( pPager->journalOff < szJ ){
    u32 nRec;
    u32 dummy;
    rc = readJournalHdr(pPager, szJ, &nRec, &dummy);
    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_stmt_playback;
    }
    for(i=nRec-1; i>=0 && pPager->journalOff < szJ; i--){
      rc = pager_playback_one_page(pPager, &pPager->jfd, 1);
      assert( rc!=SQLITE_DONE );
      if( rc!=SQLITE_OK ) goto end_stmt_playback;
    }
  }

  pPager->journalOff = szJ;
  
end_stmt_playback:
  if( rc!=SQLITE_OK ){
    pPager->errMask |= PAGER_ERR_CORRUPT;
    rc = SQLITE_CORRUPT;
  }
  return rc;
................................................................................
  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->nExtra = nExtra;
  pPager->sectorSize = PAGER_SECTOR_SIZE;
  pPager->pBusyHandler = (BusyHandler *)pBusyHandler;
  memset(pPager->aHash, 0, sizeof(pPager->aHash));
  *ppPager = pPager;
  return SQLITE_OK;
}

/*
................................................................................
  }
  return n;
}

/*
** Forward declaration
*/
static int syncJournal(Pager*);


/*
** Unlink a page from the free list (the list of all pages where nRef==0)
** and from its hash collision chain.
*/
static void unlinkPage(PgHdr *pPg){
................................................................................
    return SQLITE_OK;
  }
  if( pPager->memDb ){
    pPager->dbSize = nPage;
    memoryTruncate(pPager);
    return SQLITE_OK;
  }
  rc = syncJournal(pPager);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)nPage);
  if( rc==SQLITE_OK ){
    pPager->dbSize = nPage;
  }
................................................................................
**
** For temporary databases, we do not care if we are able to rollback
** after a power failure, so sync occurs.
**
** This routine clears the needSync field of every page current held in
** memory.
*/
static int syncJournal(Pager *pPager){
  PgHdr *pPg;
  int rc = SQLITE_OK;

  /* Sync the journal before modifying the main database
  ** (assuming there is a journal and it needs to be synced.)
  */
  if( pPager->needSync ){
    if( !pPager->tempFile ){
      assert( pPager->journalOpen );
      /* assert( !pPager->noSync ); // noSync might be set if synchronous
      ** was turned off after the transaction was started.  Ticket #615 */
#ifndef NDEBUG
      {
        /* Make sure the pPager->nRec counter we are keeping agrees
        ** with the nRec computed from the size of the journal file.
        */
        off_t jSz;


        rc = sqlite3OsFileSize(&pPager->jfd, &jSz);
        if( rc!=0 ) return rc;
        assert( pPager->journalOff==jSz );
      }
#endif
      {
        /* 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. 
        */
        if( pPager->fullSync ){
          TRACE2("SYNC journal of %d\n", pPager->fd.h);
          rc = sqlite3OsSync(&pPager->jfd);
          if( rc!=0 ) return rc;
        }
        sqlite3OsSeek(&pPager->jfd, pPager->journalHdr + sizeof(aJournalMagic));
        rc = write32bits(&pPager->jfd, pPager->nRec);
        if( rc ) return rc;











        sqlite3OsSeek(&pPager->jfd, pPager->journalOff);
      }
      TRACE2("SYNC journal of %d\n", pPager->fd.h);
      rc = sqlite3OsSync(&pPager->jfd);
      if( rc!=0 ) return rc;
      pPager->journalStarted = 1;
    }
    pPager->needSync = 0;
................................................................................
       if( rc!=SQLITE_OK ){
         sqlite3OsUnlock(&pPager->fd, NO_LOCK);
         pPager->state = PAGER_UNLOCK;
         return SQLITE_BUSY;
       }
       pPager->journalOpen = 1;
       pPager->journalStarted = 0;
       pPager->journalOff = 0;
       pPager->setMaster = 0;
       pPager->journalHdr = 0;

       /* Playback and delete the journal.  Drop the database write
       ** lock and reacquire the read lock.
       */
       rc = pager_playback(pPager);
       if( rc!=SQLITE_OK ){
         return rc;
       }
    }
    pPg = 0;
  }else{
    /* Search for page in cache */
................................................................................

      /* If we could not find a page that does not require an fsync()
      ** on the journal file then fsync the journal file.  This is a
      ** very slow operation, so we work hard to avoid it.  But sometimes
      ** it can't be helped.
      */
      if( pPg==0 ){
        int rc = syncJournal(pPager);
        if( rc!=0 ){
          sqlite3pager_rollback(pPager);
          return SQLITE_IOERR;
        }
        if( pPager->fullSync ){
          /* If in full-sync mode, write a new journal header into the
	  ** journal file. This is done to avoid ever modifying a journal
	  ** header that is involved in the rollback of pages that have
	  ** already been written to the database (in case the header is
	  ** trashed when the nRec field is updated).
          */
          pPager->nRec = 0;
          rc = writeJournalHdr(pPager);
          if( rc!=0 ){
            sqlite3pager_rollback(pPager);
            return SQLITE_IOERR;
          }
        }
        pPg = pPager->pFirst;
      }
      assert( pPg->nRef==0 );

      /* Write the page to the database file if it is dirty.
      */
................................................................................
  pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInJournal==0 ){
    sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    return SQLITE_NOMEM;
  }
  rc = sqlite3OsOpenExclusive(pPager->zJournal, &pPager->jfd,pPager->tempFile);
  pPager->journalOff = 0;
  pPager->setMaster = 0;
  pPager->journalHdr = 0;
  if( rc!=SQLITE_OK ){
    sqliteFree(pPager->aInJournal);
    pPager->aInJournal = 0;
    sqlite3OsUnlock(&pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    return SQLITE_CANTOPEN;
  }
................................................................................
  pPager->nRec = 0;
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  pPager->origDbSize = pPager->dbSize;

  rc = writeJournalHdr(pPager);

























  if( pPager->stmtAutoopen && rc==SQLITE_OK ){
    rc = sqlite3pager_stmt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
................................................................................
**
** A journal file is opened if this is not a temporary file.  For temporary
** files, the opening of the journal file is deferred until there is an
** actual need to write to the journal.
**
** If the database is already reserved for writing, this routine is a no-op.
*/
int sqlite3pager_begin(void *pData, int dummy_fixme){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );

  assert( pPager->state!=PAGER_UNLOCK );
  if( pPager->state==PAGER_SHARED ){
    assert( pPager->aInJournal==0 );
    if( pPager->memDb ){
      pPager->state = PAGER_EXCLUSIVE;
      pPager->origDbSize = pPager->dbSize;
    }else{
................................................................................
          pPager->pBusyHandler && 
          pPager->pBusyHandler->xFunc && 
          pPager->pBusyHandler->xFunc(pPager->pBusyHandler->pArg, busy++)
      );
      if( rc!=SQLITE_OK ){
        return rc;
      }

      pPager->state = PAGER_RESERVED;
      pPager->dirtyCache = 0;
      TRACE2("TRANSACTION %d\n", pPager->fd.h);
      if( pPager->useJournal && !pPager->tempFile ){
        rc = pager_open_journal(pPager);
      }
    }
  }
  return rc;
}
................................................................................
  */
  if( pPager->errMask ){ 
    return pager_errcode(pPager);
  }
  if( pPager->readOnly ){
    return SQLITE_PERM;
  }

  assert( !pPager->setMaster );

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  pPg->dirty = 1;
  if( pPg->inJournal && (pPg->inStmt || pPager->stmtInUse==0) ){
    pPager->dirtyCache = 1;
................................................................................
        u32 cksum = pager_cksum(pPager, pPg->pgno, pData);
        saved = *(u32*)PGHDR_TO_EXTRA(pPg);
        store32bits(cksum, pPg, SQLITE_PAGE_SIZE);
        szPg = SQLITE_PAGE_SIZE+8;
        store32bits(pPg->pgno, pPg, -4);
        CODEC(pPager, pData, pPg->pgno, 7);
        rc = sqlite3OsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
        pPager->journalOff += szPg;
        TRACE3("JOURNAL page %d needSync=%d\n", pPg->pgno, pPg->needSync);
        CODEC(pPager, pData, pPg->pgno, 0);
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
        if( rc!=SQLITE_OK ){
          sqlite3pager_rollback(pPager);
          pPager->errMask |= PAGER_ERR_FULL;
          return rc;
................................................................................
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }

  if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
    if( pPager->state>=PAGER_EXCLUSIVE ){
      pager_playback(pPager);
    }
    return pager_errcode(pPager);
  }
  if( pPager->state==PAGER_RESERVED ){
    int rc2;
    rc = pager_reload_cache(pPager);
    rc2 = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = rc2;
    }
  }else{
    rc = pager_playback(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = SQLITE_CORRUPT;
    pPager->errMask |= PAGER_ERR_CORRUPT;
  }
  pPager->dbSize = -1;
  return rc;
................................................................................
  if( pPager->aInStmt==0 ){
    sqlite3OsLock(&pPager->fd, SHARED_LOCK);
    return SQLITE_NOMEM;
  }
#ifndef NDEBUG
  rc = sqlite3OsFileSize(&pPager->jfd, &pPager->stmtJSize);
  if( rc ) goto stmt_begin_failed;
  assert( pPager->stmtJSize == pPager->journalOff );

#endif
  pPager->stmtJSize = pPager->journalOff;

  pPager->stmtSize = pPager->dbSize;
  pPager->stmtHdrOff = 0;
  if( !pPager->stmtOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->stfd);
    if( rc ) goto stmt_begin_failed;
    pPager->stmtOpen = 1;
    pPager->stmtNRec = 0;
  }
  pPager->stmtInUse = 1;
................................................................................
  /* If this is an in-memory db, or no pages have been written to, or this
  ** function has already been called, it is a no-op.
  */
  if( pPager->state!=PAGER_SYNCED && !pPager->memDb && pPager->dirtyCache ){
    PgHdr *pPg;
    assert( pPager->journalOpen );

    /* If a master journal file name has already been written to the
    ** journal file, then no sync is required. This happens when it is
    ** written, then the process fails to upgrade from a RESERVED to an
    ** EXCLUSIVE lock. The next time the process tries to commit the
    ** transaction the m-j name will have already been written.
    */
    if( !pPager->setMaster ){
      rc = pager_incr_changecounter(pPager);
      if( rc!=SQLITE_OK ) goto sync_exit;


      rc = writeMasterJournal(pPager, zMaster);
      if( rc!=SQLITE_OK ) goto sync_exit;
      rc = syncJournal(pPager);
      if( rc!=SQLITE_OK ) goto sync_exit;
    }

    /* Write all dirty pages to the database file */
    pPg = pager_get_all_dirty_pages(pPager);
    rc = pager_write_pagelist(pPg);
    if( rc!=SQLITE_OK ) goto sync_exit;

    /* Sync the database file. */

*************************************************************************
** Code for testing the utf.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library. Specifically, the code in this file
** is used for testing the SQLite routines for converting between
** the various supported unicode encodings.
**
** $Id: test5.c,v 1.12 2004/06/23 13:46:32 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "vdbeInt.h"
#include "os.h"         /* to get SQLITE_BIGENDIAN */
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
................................................................................
      char *zTmp = z;
      z = sqliteMalloc(len);
      memcpy(z, zTmp, len);
    }
    sqlite3ValueSetStr(pVal, -1, z, enc_from, xDel);
  }

  z = sqlite3ValueText(pVal, enc_to);
  len = sqlite3ValueBytes(pVal, enc_to) + (enc_to==SQLITE_UTF8?1:2);
  Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(z, len));

  sqlite3ValueFree(pVal);

  return TCL_OK;
}

*************************************************************************
** Code for testing the utf.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library. Specifically, the code in this file
** is used for testing the SQLite routines for converting between
** the various supported unicode encodings.
**
** $Id: test5.c,v 1.13 2004/06/25 02:38:55 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "vdbeInt.h"
#include "os.h"         /* to get SQLITE_BIGENDIAN */
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
................................................................................
      char *zTmp = z;
      z = sqliteMalloc(len);
      memcpy(z, zTmp, len);
    }
    sqlite3ValueSetStr(pVal, -1, z, enc_from, xDel);
  }

  z = (char *)sqlite3ValueText(pVal, enc_to);
  len = sqlite3ValueBytes(pVal, enc_to) + (enc_to==SQLITE_UTF8?1:2);
  Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(z, len));

  sqlite3ValueFree(pVal);

  return TCL_OK;
}