** 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 1.84 2003/06/04 16:24:40 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
      return rc;
    }
    pPager->state = SQLITE_READLOCK;

    /* If a journal file exists, try to play it back.
    */
    if( pPager->useJournal && sqliteOsFileExists(pPager->zJournal) ){
       int rc, dummy;

       /* Get a write lock on the database
       */
       rc = sqliteOsWriteLock(&pPager->fd);
       if( rc!=SQLITE_OK ){
         if( sqliteOsUnlock(&pPager->fd)!=SQLITE_OK ){
           /* This should never happen! */
           rc = SQLITE_INTERNAL;
         }
         return rc;
       }
       pPager->state = SQLITE_WRITELOCK;

       /* Open the journal for exclusive access.  Return SQLITE_BUSY if
       ** we cannot get exclusive access to the journal file. 
       **
       ** Even though we will only be reading from the journal, not writing,
       ** we have to open the journal for writing in order to obtain an
       ** exclusive access lock.

       */
       rc = sqliteOsOpenReadWrite(pPager->zJournal, &pPager->jfd, &dummy);
       if( rc!=SQLITE_OK ){
         rc = sqliteOsUnlock(&pPager->fd);
         assert( rc==SQLITE_OK );
         return SQLITE_BUSY;
       }
       pPager->journalOpen = 1;
       pPager->journalStarted = 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 1.85 2003/06/14 11:42:58 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
      return rc;
    }
    pPager->state = SQLITE_READLOCK;

    /* If a journal file exists, try to play it back.
    */
    if( pPager->useJournal && sqliteOsFileExists(pPager->zJournal) ){
       int rc;

       /* Get a write lock on the database
       */
       rc = sqliteOsWriteLock(&pPager->fd);
       if( rc!=SQLITE_OK ){
         if( sqliteOsUnlock(&pPager->fd)!=SQLITE_OK ){
           /* This should never happen! */
           rc = SQLITE_INTERNAL;
         }
         return rc;
       }
       pPager->state = SQLITE_WRITELOCK;

       /* Open the journal for reading only.  Return SQLITE_BUSY if
       ** we are unable to open the journal file. 
       **
       ** The journal file does not need to be locked itself.  The
       ** journal file is never open unless the main database file holds
       ** a write lock, so there is never any chance of two or more
       ** processes opening the journal at the same time.
       */
       rc = sqliteOsOpenReadOnly(pPager->zJournal, &pPager->jfd);
       if( rc!=SQLITE_OK ){
         rc = sqliteOsUnlock(&pPager->fd);
         assert( rc==SQLITE_OK );
         return SQLITE_BUSY;
       }
       pPager->journalOpen = 1;
       pPager->journalStarted = 0;