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 1.143 2004/06/26 01:48:19 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>

  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 */
  off_t stmtCksum;            /* cksumInit when statement was started */
  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.
*/

  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 || pgno==PAGER_MJ_PGNO(pPager) ){
    return SQLITE_DONE;
  }
  if( pgno>(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( useCksum ){
    rc = read32bits(jfd, &cksum);

  ** 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;
  pPager->cksumInit = pPager->stmtCksum;
  assert( JOURNAL_HDR_SZ(pPager)<(pPager->pageSize+8) );
  while( pPager->journalOff <= (hdrOff-(pPager->pageSize+8)) ){
    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;
    }
    if( nRec==0 ){
      nRec = (szJ - pPager->journalOff) / (pPager->pageSize+8);
    }
    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;
  }else{
    pPager->journalOff = szJ;
    /* pager_reload_cache(pPager); */
  }
  return rc;
}

/*
** Change the maximum number of in-memory pages that are allowed.
**

  pPager->state = PAGER_UNLOCK;
  pPager->errMask = 0;
  pPager->tempFile = tempFile;
  pPager->memDb = memDb;
  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->fullSync = (pPager->noSync?0:1);
  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));

  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;
  pPager->stmtCksum = pPager->cksumInit;
  if( !pPager->stmtOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->stfd);
    if( rc ) goto stmt_begin_failed;
    pPager->stmtOpen = 1;
    pPager->stmtNRec = 0;
  }
  pPager->stmtInUse = 1;