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 1.93 2004/02/08 00:40:52 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( pPager->journalOpen );
  sqliteOsSeek(&pPager->jfd, 0);
  rc = sqliteOsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_playback;
  }

  /* If the journal file is too small to contain a complete header,
  ** then ignore the journal completely.
  */
  if( szJ < sizeof(aMagic)+sizeof(Pgno) ){
    goto end_playback;
  }

  /* Read the beginning of the journal and truncate the
  ** database file back to its original size.
  */

  }else if( memcmp(aMagic, aJournalMagic1, sizeof(aMagic))==0 ){
    format = JOURNAL_FORMAT_1;
  }else{
    rc = SQLITE_PROTOCOL;
    goto end_playback;
  }
  if( format>=JOURNAL_FORMAT_3 ){
    if( szJ < sizeof(aMagic) + 3*sizeof(u32) ){
      /* Ignore the journal if it is too small to contain a complete
      ** header.  We already did this test once above, but at the prior
      ** test, we did not know the journal format and so we had to assume
      ** the smallest possible header.  Now we know the header is bigger
      ** than that so we test again.
      */
      goto end_playback;
    }
    rc = read32bits(format, &pPager->jfd, (u32*)&nRec);
    if( rc ) goto end_playback;
    rc = read32bits(format, &pPager->jfd, &pPager->cksumInit);
    if( rc ) goto end_playback;
    if( nRec==0xffffffff || useJournalSize ){
      nRec = (szJ - JOURNAL_HDR_SZ(3))/JOURNAL_PG_SZ(3);
    }

      }
      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 ){
    PgHdr *pPg;
    for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
      char zBuf[SQLITE_PAGE_SIZE];
      if( !pPg->dirty ) continue;
      if( (int)pPg->pgno <= pPager->origDbSize ){

    ** if there have been no changes to the database file. */
    assert( pPager->needSync==0 );
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }
  assert( pPager->journalOpen );
  rc = syncAllPages(pPager);
  if( rc!=SQLITE_OK ){
    goto commit_abort;
  }
  pPg = pager_get_all_dirty_pages(pPager);
  if( pPg ){
    rc = pager_write_pagelist(pPg);
    if( rc || (!pPager->noSync && sqliteOsSync(&pPager->fd)!=SQLITE_OK) ){
      goto commit_abort;

  free(aData);
}

int main(int argc, char **argv){
  struct stat sbuf;
  unsigned int u;
  int rc;
  unsigned char zBuf[10];
  unsigned char zBuf2[sizeof(u)];
  if( argc!=2 ){
    fprintf(stderr,"Usage: %s FILENAME\n", argv[0]);
    exit(1);
  }
  db = open(argv[1], O_RDONLY);
  if( db<0 ){
    fprintf(stderr,"%s: can't open %s\n", argv[0], argv[1]);
    exit(1);
  }
  read(db, zBuf, 8);
  if( zBuf[7]==0xd6 ){
    read(db, &u, sizeof(u));
    printf("Records in Journal: %u\n", u);
    read(db, &u, sizeof(u));
    printf("Magic Number: 0x%08x\n", u);
  }
  read(db, zBuf2, sizeof(zBuf2));
  u = zBuf2[0]<<24 | zBuf2[1]<<16 | zBuf2[2]<<8 | zBuf2[3];
  printf("Database Size: %u\n", u);
  while( read(db, zBuf2, sizeof(zBuf2))==sizeof(zBuf2) ){
    u = zBuf2[0]<<24 | zBuf2[1]<<16 | zBuf2[2]<<8 | zBuf2[3];
    print_page(u);
    if( zBuf[7]==0xd6 ){
      read(db, &u, sizeof(u));
      printf("Checksum: 0x%08x\n", u);
    }
  }
  close(db);
}