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 1.417 2008/03/17 13:50:58 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*

  int readOnly = 0;
  int useJournal = (flags & PAGER_OMIT_JOURNAL)==0;
  int noReadlock = (flags & PAGER_NO_READLOCK)!=0;
  int journalFileSize = sqlite3JournalSize(pVfs);
  int nDefaultPage = SQLITE_DEFAULT_PAGE_SIZE;
  char *zPathname;
  int nPathname;
  char *zStmtJrnl;
  int nStmtJrnl;

  /* The default return is a NULL pointer */
  *ppPager = 0;

  /* Compute the full pathname */
  nPathname = pVfs->mxPathname+1;
  zPathname = sqlite3_malloc(nPathname*2);
  if( zPathname==0 ){
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){
#ifndef SQLITE_OMIT_MEMORYDB
    if( strcmp(zFilename,":memory:")==0 ){
      memDb = 1;

    rc = sqlite3OsGetTempname(pVfs, nPathname, zPathname);
  }
  if( rc!=SQLITE_OK ){
    sqlite3_free(zPathname);
    return rc;
  }
  nPathname = strlen(zPathname);

  /* Put the statement journal in temporary disk space since this is
  ** sometimes RAM disk or other optimized storage.  Unlikely the main
  ** main journal file, the statement journal does not need to be 
  ** colocated with the database nor does it need to be persistent.
  */
  zStmtJrnl = &zPathname[nPathname+1];
  rc = sqlite3OsGetTempname(pVfs, pVfs->mxPathname+1, zStmtJrnl);
  if( rc!=SQLITE_OK ){
    sqlite3_free(zPathname);
    return rc;
  }
  nStmtJrnl = strlen(zStmtJrnl);

  /* Allocate memory for the pager structure */
  pPager = sqlite3MallocZero(
    sizeof(*pPager) +           /* Pager structure */
    journalFileSize +           /* The journal file structure */ 
    pVfs->szOsFile * 3 +        /* The main db and two journal files */ 
    3*nPathname + 40 +          /* zFilename, zDirectory, zJournal */
    nStmtJrnl                   /* zStmtJrnl */
  );
  if( !pPager ){
    sqlite3_free(zPathname);
    return SQLITE_NOMEM;
  }
  pPtr = (u8 *)&pPager[1];
  pPager->vfsFlags = vfsFlags;
  pPager->fd = (sqlite3_file*)&pPtr[pVfs->szOsFile*0];
  pPager->stfd = (sqlite3_file*)&pPtr[pVfs->szOsFile*1];
  pPager->jfd = (sqlite3_file*)&pPtr[pVfs->szOsFile*2];
  pPager->zFilename = (char*)&pPtr[pVfs->szOsFile*2+journalFileSize];
  pPager->zDirectory = &pPager->zFilename[nPathname+1];
  pPager->zJournal = &pPager->zDirectory[nPathname+1];
  pPager->zStmtJrnl = &pPager->zJournal[nPathname+10];
  pPager->pVfs = pVfs;
  memcpy(pPager->zFilename, zPathname, nPathname+1);
  memcpy(pPager->zStmtJrnl, zStmtJrnl, nStmtJrnl+1);
  sqlite3_free(zPathname);

  /* Open the pager file.
  */
  if( zFilename && zFilename[0] && !memDb ){
    if( nPathname>(pVfs->mxPathname - sizeof("-journal")) ){
      rc = SQLITE_CANTOPEN;

  IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))

  /* Fill in Pager.zDirectory[] */
  memcpy(pPager->zDirectory, pPager->zFilename, nPathname+1);
  for(i=strlen(pPager->zDirectory); i>0 && pPager->zDirectory[i-1]!='/'; i--){}
  if( i>0 ) pPager->zDirectory[i-1] = 0;

  /* Fill in Pager.zJournal[] */
  memcpy(pPager->zJournal, pPager->zFilename, nPathname);
  memcpy(&pPager->zJournal[nPathname], "-journal", 9);



  /* pPager->journalOpen = 0; */
  pPager->useJournal = useJournal && !memDb;
  pPager->noReadlock = noReadlock && readOnly;
  /* pPager->stmtOpen = 0; */
  /* pPager->stmtInUse = 0; */
  /* pPager->nRef = 0; */