** 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 1.253 2006/01/23 15:39:59 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>
................................................................................
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        i64 fileSize;
        int rc2 = sqlite3OsFileSize(pPager->fd, &fileSize);
        if( rc2!=SQLITE_OK || fileSize>=pgno*pPager->pageSize ){
	  /* An IO error occured in one of the the sqlite3OsSeek() or
          ** sqlite3OsRead() calls above. */

          sqlite3pager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          clear_simulated_io_error();
          memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
        }
      }else{
................................................................................
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3pager_write().  In other words, return TRUE if it is ok
** to change the content of the page.
*/

int sqlite3pager_iswriteable(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  return pPg->dirty;
}


#ifndef SQLITE_OMIT_VACUUM
/*
** Replace the content of a single page with the information in the third
** argument.
*/
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void *pData){

** 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 1.254 2006/01/23 16:21:06 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>
................................................................................
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        i64 fileSize;
        int rc2 = sqlite3OsFileSize(pPager->fd, &fileSize);
        if( rc2!=SQLITE_OK || fileSize>=pgno*pPager->pageSize ){
	  /* An IO error occured in one of the the sqlite3OsSeek() or
          ** sqlite3OsRead() calls above. */
          pPg->pgno = 0;
          sqlite3pager_unref(PGHDR_TO_DATA(pPg));
          return rc;
        }else{
          clear_simulated_io_error();
          memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
        }
      }else{
................................................................................
}

/*
** Return TRUE if the page given in the argument was previously passed
** to sqlite3pager_write().  In other words, return TRUE if it is ok
** to change the content of the page.
*/
#ifndef NDEBUG
int sqlite3pager_iswriteable(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  return pPg->dirty;
}
#endif

#ifndef SQLITE_OMIT_VACUUM
/*
** Replace the content of a single page with the information in the third
** argument.
*/
int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void *pData){