SQLite

** 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 1.320 2007/04/05 11:54:43 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

  char *zMasterJournal = 0; /* Contents of master journal file */
  i64 nMasterJournal;       /* Size of master journal file */

  /* Open the master journal file exclusively in case some other process
  ** is running this routine also. Not that it makes too much difference.
  */
  rc = sqlite3OsOpenReadOnly(zMaster, &master);
  assert( rc!=SQLITE_OK || master );
  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;

        ** Open it and check if it points at the master journal. If
        ** so, return without deleting the master journal file.
        */
        OsFile *journal = 0;
        int c;

        rc = sqlite3OsOpenReadOnly(zJournal, &journal);
        assert( rc!=SQLITE_OK || journal );
        if( rc!=SQLITE_OK ){
          goto delmaster_out;
        }

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

#ifdef SQLITE_TEST
  sqlite3_opentemp_count++;  /* Used for testing and analysis only */
#endif
  do{
    cnt--;
    sqlite3OsTempFileName(zFile);
    rc = sqlite3OsOpenExclusive(zFile, pFd, 1);
    assert( rc!=SQLITE_OK || *pFd );
  }while( cnt>0 && rc!=SQLITE_OK && rc!=SQLITE_NOMEM );
  return rc;
}

/*
** Create a new page cache and put a pointer to the page cache in *ppPager.
** The file to be cached need not exist.  The file is not locked until

      zFullPathname = sqliteStrDup("");
    }else
#endif
    {
      zFullPathname = sqlite3OsFullPathname(zFilename);
      if( zFullPathname ){
        rc = sqlite3OsOpenReadWrite(zFullPathname, &fd, &readOnly);
        assert( rc!=SQLITE_OK || fd );
      }
    }
  }else{
    rc = sqlite3PagerOpentemp(&fd);
    sqlite3OsTempFileName(zTemp);
    zFilename = zTemp;
    zFullPathname = sqlite3OsFullPathname(zFilename);

  assert( pPg->nRef==0 );

  /* Write the page to the database file if it is dirty.
  */
  if( pPg->dirty ){
    int rc;
    assert( pPg->needSync==0 );
    assert( !MEMDB );
    makeClean(pPg);
    pPg->dirty = 1;
    pPg->pDirty = 0;
    rc = pager_write_pagelist( pPg );
    if( rc!=SQLITE_OK ){
      return rc;
    }

        ** a read/write file handle.
        */
        rc = SQLITE_BUSY;
        if( sqlite3OsFileExists(pPager->zJournal) ){
          int ro;
          assert( !pPager->tempFile );
          rc = sqlite3OsOpenReadWrite(pPager->zJournal, &pPager->jfd, &ro);
          assert( rc!=SQLITE_OK || pPager->jfd );
          if( ro ){
            rc = SQLITE_BUSY;
            sqlite3OsClose(&pPager->jfd);
          }
        }
        if( rc!=SQLITE_OK ){
          pager_unlock(pPager);

  pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInJournal==0 ){
    rc = SQLITE_NOMEM;
    goto failed_to_open_journal;
  }
  rc = sqlite3OsOpenExclusive(pPager->zJournal, &pPager->jfd,
                                 pPager->tempFile);
  assert( rc!=SQLITE_OK || pPager->jfd );
  pPager->journalOff = 0;
  pPager->setMaster = 0;
  pPager->journalHdr = 0;
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_NOMEM ){
      sqlite3OsDelete(pPager->zJournal);
    }