** 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 1.97 2004/02/10 01:54:28 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>

................................................................................
    */
    assert( pPg->nRef==0 || pPg->pgno==1 );
    memcpy(PGHDR_TO_DATA(pPg), pgRec.aData, SQLITE_PAGE_SIZE);
    memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
    pPg->dirty = 0;
    pPg->needSync = 0;
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pPg), 2);
    }
  }
  return rc;
}

/*
** Playback the journal and thus restore the database file to
................................................................................
      char zBuf[SQLITE_PAGE_SIZE];
      if( !pPg->dirty ) continue;
      if( (int)pPg->pgno <= pPager->origDbSize ){
        sqliteOsSeek(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)(pPg->pgno-1));
        rc = sqliteOsRead(&pPager->fd, zBuf, SQLITE_PAGE_SIZE);
        if( rc ) break;
        if( pPager->xCodec ){
          pPager->xCodec(pPager->pCodecArg, zBuf, 0);
        }
      }else{
        memset(zBuf, 0, SQLITE_PAGE_SIZE);
      }
      if( pPg->nRef==0 || memcmp(zBuf, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE) ){
        memcpy(PGHDR_TO_DATA(pPg), zBuf, SQLITE_PAGE_SIZE);
        memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
................................................................................

  if( pList==0 ) return SQLITE_OK;
  pPager = pList->pPager;
  while( pList ){
    assert( pList->dirty );
    sqliteOsSeek(&pPager->fd, (pList->pgno-1)*(off_t)SQLITE_PAGE_SIZE);
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pList), 1);
    }
    rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pList), SQLITE_PAGE_SIZE);
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pList), 0);
    }
    if( rc ) return rc;
    pList->dirty = 0;
................................................................................
               || fileSize>=pgno*SQLITE_PAGE_SIZE ){
          sqlitepager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
        }
      }else if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pPg), 0);
      }
    }
  }else{
    /* The requested page is in the page cache. */
    pPager->nHit++;
    page_ref(pPg);
  }
................................................................................
      }
      store32bits(pPg->pgno, pPg, -4);
      if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, pData, 3);
      }
      rc = sqliteOsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, pData, 2);
      }
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlitepager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;

** 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 1.98 2004/02/10 23:51:06 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>

................................................................................
    */
    assert( pPg->nRef==0 || pPg->pgno==1 );
    memcpy(PGHDR_TO_DATA(pPg), pgRec.aData, SQLITE_PAGE_SIZE);
    memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
    pPg->dirty = 0;
    pPg->needSync = 0;
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pPg), 3);
    }
  }
  return rc;
}

/*
** Playback the journal and thus restore the database file to
................................................................................
      char zBuf[SQLITE_PAGE_SIZE];
      if( !pPg->dirty ) continue;
      if( (int)pPg->pgno <= pPager->origDbSize ){
        sqliteOsSeek(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)(pPg->pgno-1));
        rc = sqliteOsRead(&pPager->fd, zBuf, SQLITE_PAGE_SIZE);
        if( rc ) break;
        if( pPager->xCodec ){
          pPager->xCodec(pPager->pCodecArg, zBuf, 2);
        }
      }else{
        memset(zBuf, 0, SQLITE_PAGE_SIZE);
      }
      if( pPg->nRef==0 || memcmp(zBuf, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE) ){
        memcpy(PGHDR_TO_DATA(pPg), zBuf, SQLITE_PAGE_SIZE);
        memset(PGHDR_TO_EXTRA(pPg), 0, pPager->nExtra);
................................................................................

  if( pList==0 ) return SQLITE_OK;
  pPager = pList->pPager;
  while( pList ){
    assert( pList->dirty );
    sqliteOsSeek(&pPager->fd, (pList->pgno-1)*(off_t)SQLITE_PAGE_SIZE);
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pList), 6);
    }
    rc = sqliteOsWrite(&pPager->fd, PGHDR_TO_DATA(pList), SQLITE_PAGE_SIZE);
    if( pPager->xCodec ){
      pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pList), 0);
    }
    if( rc ) return rc;
    pList->dirty = 0;
................................................................................
               || fileSize>=pgno*SQLITE_PAGE_SIZE ){
          sqlitepager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
        }
      }else if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, PGHDR_TO_DATA(pPg), 3);
      }
    }
  }else{
    /* The requested page is in the page cache. */
    pPager->nHit++;
    page_ref(pPg);
  }
................................................................................
      }
      store32bits(pPg->pgno, pPg, -4);
      if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, pData, 3);
      }
      rc = sqliteOsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      if( pPager->xCodec ){
        pPager->xCodec(pPager->pCodecArg, pData, 0);
      }
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlitepager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;