** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.458 2008/05/09 16:57:51 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
  if( pBt->pPage1 ) return SQLITE_OK;
  rc = sqlite3BtreeGetPage(pBt, 1, &pPage1, 0);
  if( rc!=SQLITE_OK ) return rc;

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */
  rc = SQLITE_NOTADB;
  nPage = sqlite3PagerPagecount(pBt->pPager);
  if( nPage<0 ){
    rc = SQLITE_IOERR;
    goto page1_init_failed;
  }else if( nPage>0 ){
    int pageSize;
    int usableSize;
    u8 *page1 = pPage1->aData;

    if( memcmp(page1, zMagicHeader, 16)!=0 ){
      goto page1_init_failed;
    }
    if( page1[18]>1 ){
      pBt->readOnly = 1;
    }
    if( page1[19]>1 ){
................................................................................
** Create a new database by initializing the first page of the
** file.
*/
static int newDatabase(BtShared *pBt){
  MemPage *pP1;
  unsigned char *data;
  int rc;


  assert( sqlite3_mutex_held(pBt->mutex) );
  if( sqlite3PagerPagecount(pBt->pPager)>0 ) return SQLITE_OK;



  pP1 = pBt->pPage1;
  assert( pP1!=0 );
  data = pP1->aData;
  rc = sqlite3PagerWrite(pP1->pDbPage);
  if( rc ) return rc;
  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  assert( sizeof(zMagicHeader)==16 );
................................................................................
    releasePage(pPtrPage);
    if( rc==SQLITE_OK ){
      rc = ptrmapPut(pBt, iFreePage, eType, iPtrPage);
    }
  }
  return rc;
}








/* Forward declaration required by incrVacuumStep(). */
static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);

/*
** Perform a single step of an incremental-vacuum. If successful,
** return SQLITE_OK. If there is no work to do (and therefore no
................................................................................
static int incrVacuumStep(BtShared *pBt, Pgno nFin){
  Pgno iLastPg;             /* Last page in the database */
  Pgno nFreeList;           /* Number of pages still on the free-list */

  assert( sqlite3_mutex_held(pBt->mutex) );
  iLastPg = pBt->nTrunc;
  if( iLastPg==0 ){
    iLastPg = sqlite3PagerPagecount(pBt->pPager);
  }

  if( !PTRMAP_ISPAGE(pBt, iLastPg) && iLastPg!=PENDING_BYTE_PAGE(pBt) ){
    int rc;
    u8 eType;
    Pgno iPtrPage;

................................................................................
  if( !pBt->incrVacuum ){
    Pgno nFin = 0;

    if( pBt->nTrunc==0 ){
      Pgno nFree;
      Pgno nPtrmap;
      const int pgsz = pBt->pageSize;
      Pgno nOrig = sqlite3PagerPagecount(pBt->pPager);

      if( PTRMAP_ISPAGE(pBt, nOrig) ){
        return SQLITE_CORRUPT_BKPT;
      }
      if( nOrig==PENDING_BYTE_PAGE(pBt) ){
        nOrig--;
      }
................................................................................
      return rc;
    }
    if( pBt->readOnly && wrFlag ){
      return SQLITE_READONLY;
    }
  }
  pCur->pgnoRoot = (Pgno)iTable;
  if( iTable==1 && sqlite3PagerPagecount(pBt->pPager)==0 ){
    rc = SQLITE_EMPTY;
    goto create_cursor_exception;
  }
  rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->pPage, 0);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
................................................................................
    Pgno iGuess = ovfl+1;
    u8 eType;

    while( PTRMAP_ISPAGE(pBt, iGuess) || iGuess==PENDING_BYTE_PAGE(pBt) ){
      iGuess++;
    }

    if( iGuess<=sqlite3PagerPagecount(pBt->pPager) ){
      rc = ptrmapGet(pBt, iGuess, &eType, &pgno);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      if( eType==PTRMAP_OVERFLOW2 && pgno==ovfl ){
        next = iGuess;
      }
................................................................................
    u8 searchList = 0; /* If the free-list must be searched for 'nearby' */
    
    /* If the 'exact' parameter was true and a query of the pointer-map
    ** shows that the page 'nearby' is somewhere on the free-list, then
    ** the entire-list will be searched for that page.
    */
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( exact && nearby<=sqlite3PagerPagecount(pBt->pPager) ){
      u8 eType;
      assert( nearby>0 );
      assert( pBt->autoVacuum );
      rc = ptrmapGet(pBt, nearby, &eType, 0);
      if( rc ) return rc;
      if( eType==PTRMAP_FREEPAGE ){
        searchList = 1;
................................................................................
        }else{
          closest = 0;
        }

        iPage = get4byte(&aData[8+closest*4]);
        if( !searchList || iPage==nearby ){
          *pPgno = iPage;

          if( *pPgno>sqlite3PagerPagecount(pBt->pPager) ){

            /* Free page off the end of the file */
            rc = SQLITE_CORRUPT_BKPT;
            goto end_allocate_page;
          }
          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
                 ": %d more free pages\n",
                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
................................................................................
      }
      releasePage(pPrevTrunk);
      pPrevTrunk = 0;
    }while( searchList );
  }else{
    /* There are no pages on the freelist, so create a new page at the
    ** end of the file */
    *pPgno = sqlite3PagerPagecount(pBt->pPager) + 1;


#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->nTrunc ){
      /* An incr-vacuum has already run within this transaction. So the
      ** page to allocate is not from the physical end of the file, but
      ** at pBt->nTrunc. 
      */
................................................................................
  }
  ovflPgno = get4byte(&pCell[info.iOverflow]);
  ovflPageSize = pBt->usableSize - 4;
  nOvfl = (info.nPayload - info.nLocal + ovflPageSize - 1)/ovflPageSize;
  assert( ovflPgno==0 || nOvfl>0 );
  while( nOvfl-- ){
    MemPage *pOvfl;
    if( ovflPgno==0 || ovflPgno>sqlite3PagerPagecount(pBt->pPager) ){
      return SQLITE_CORRUPT_BKPT;
    }

    rc = getOverflowPage(pBt, ovflPgno, &pOvfl, (nOvfl==0)?0:&ovflPgno);
    if( rc ) return rc;
    rc = freePage(pOvfl);
    sqlite3PagerUnref(pOvfl->pDbPage);
................................................................................
    ** information currently contained in the child.  If this is the 
    ** case, then do not do the transfer.  Leave page 1 empty except
    ** for the right-pointer to the child page.  The child page becomes
    ** the virtual root of the tree.
    */
    pgnoChild = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    assert( pgnoChild>0 );
    assert( pgnoChild<=sqlite3PagerPagecount(pPage->pBt->pPager) );
    rc = sqlite3BtreeGetPage(pPage->pBt, pgnoChild, &pChild, 0);
    if( rc ) goto end_shallow_balance;
    if( pPage->pgno==1 ){
      rc = sqlite3BtreeInitPage(pChild, pPage);
      if( rc ) goto end_shallow_balance;
      assert( pChild->nOverflow==0 );
      if( pChild->nFree>=100 ){
................................................................................
){
  MemPage *pPage = 0;
  int rc;
  unsigned char *pCell;
  int i;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>sqlite3PagerPagecount(pBt->pPager) ){
    return SQLITE_CORRUPT_BKPT;
  }

  rc = getAndInitPage(pBt, pgno, &pPage, pParent);
  if( rc ) goto cleardatabasepage_out;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
................................................................................
  nRef = sqlite3PagerRefcount(pBt->pPager);
  if( lockBtreeWithRetry(p)!=SQLITE_OK ){
    sqlite3BtreeLeave(p);
    return sqlite3StrDup("Unable to acquire a read lock on the database");
  }
  sCheck.pBt = pBt;
  sCheck.pPager = pBt->pPager;
  sCheck.nPage = sqlite3PagerPagecount(sCheck.pPager);
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  *pnErr = 0;
#ifndef SQLITE_OMIT_AUTOVACUUM
  if( pBt->nTrunc!=0 ){
    sCheck.nPage = pBt->nTrunc;
  }
................................................................................
  if( pTo->inTrans!=TRANS_WRITE || pFrom->inTrans!=TRANS_WRITE ){
    return SQLITE_ERROR;
  }
  if( pBtTo->pCursor ){
    return SQLITE_BUSY;
  }

  nToPage = sqlite3PagerPagecount(pBtTo->pPager);
  nFromPage = sqlite3PagerPagecount(pBtFrom->pPager);
  iSkip = PENDING_BYTE_PAGE(pBtTo);

  /* Variable nNewPage is the number of pages required to store the
  ** contents of pFrom using the current page-size of pTo.
  */
  nNewPage = ((i64)nFromPage * (i64)nFromPageSize + (i64)nToPageSize - 1) / 
      (i64)nToPageSize;

** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.459 2008/06/07 08:58:22 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

................................................................................
  if( pBt->pPage1 ) return SQLITE_OK;
  rc = sqlite3BtreeGetPage(pBt, 1, &pPage1, 0);
  if( rc!=SQLITE_OK ) return rc;

  /* Do some checking to help insure the file we opened really is
  ** a valid database file. 
  */

  rc = sqlite3PagerPagecount(pBt->pPager, &nPage);

  if( rc!=SQLITE_OK ){
    goto page1_init_failed;
  }else if( nPage>0 ){
    int pageSize;
    int usableSize;
    u8 *page1 = pPage1->aData;
    rc = SQLITE_NOTADB;
    if( memcmp(page1, zMagicHeader, 16)!=0 ){
      goto page1_init_failed;
    }
    if( page1[18]>1 ){
      pBt->readOnly = 1;
    }
    if( page1[19]>1 ){
................................................................................
** Create a new database by initializing the first page of the
** file.
*/
static int newDatabase(BtShared *pBt){
  MemPage *pP1;
  unsigned char *data;
  int rc;
  int nPage;

  assert( sqlite3_mutex_held(pBt->mutex) );
  rc = sqlite3PagerPagecount(pBt->pPager, &nPage);
  if( rc!=SQLITE_OK || nPage>0 ){
    return rc;
  }
  pP1 = pBt->pPage1;
  assert( pP1!=0 );
  data = pP1->aData;
  rc = sqlite3PagerWrite(pP1->pDbPage);
  if( rc ) return rc;
  memcpy(data, zMagicHeader, sizeof(zMagicHeader));
  assert( sizeof(zMagicHeader)==16 );
................................................................................
    releasePage(pPtrPage);
    if( rc==SQLITE_OK ){
      rc = ptrmapPut(pBt, iFreePage, eType, iPtrPage);
    }
  }
  return rc;
}

static int pagerPagecount(Pager *pPager){
  int rc;
  int nPage;
  rc = sqlite3PagerPagecount(pPager, &nPage);
  return (rc==SQLITE_OK?nPage:-1);
}

/* Forward declaration required by incrVacuumStep(). */
static int allocateBtreePage(BtShared *, MemPage **, Pgno *, Pgno, u8);

/*
** Perform a single step of an incremental-vacuum. If successful,
** return SQLITE_OK. If there is no work to do (and therefore no
................................................................................
static int incrVacuumStep(BtShared *pBt, Pgno nFin){
  Pgno iLastPg;             /* Last page in the database */
  Pgno nFreeList;           /* Number of pages still on the free-list */

  assert( sqlite3_mutex_held(pBt->mutex) );
  iLastPg = pBt->nTrunc;
  if( iLastPg==0 ){
    iLastPg = pagerPagecount(pBt->pPager);
  }

  if( !PTRMAP_ISPAGE(pBt, iLastPg) && iLastPg!=PENDING_BYTE_PAGE(pBt) ){
    int rc;
    u8 eType;
    Pgno iPtrPage;

................................................................................
  if( !pBt->incrVacuum ){
    Pgno nFin = 0;

    if( pBt->nTrunc==0 ){
      Pgno nFree;
      Pgno nPtrmap;
      const int pgsz = pBt->pageSize;
      int nOrig = pagerPagecount(pBt->pPager);

      if( PTRMAP_ISPAGE(pBt, nOrig) ){
        return SQLITE_CORRUPT_BKPT;
      }
      if( nOrig==PENDING_BYTE_PAGE(pBt) ){
        nOrig--;
      }
................................................................................
      return rc;
    }
    if( pBt->readOnly && wrFlag ){
      return SQLITE_READONLY;
    }
  }
  pCur->pgnoRoot = (Pgno)iTable;
  if( iTable==1 && pagerPagecount(pBt->pPager)==0 ){
    rc = SQLITE_EMPTY;
    goto create_cursor_exception;
  }
  rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->pPage, 0);
  if( rc!=SQLITE_OK ){
    goto create_cursor_exception;
  }
................................................................................
    Pgno iGuess = ovfl+1;
    u8 eType;

    while( PTRMAP_ISPAGE(pBt, iGuess) || iGuess==PENDING_BYTE_PAGE(pBt) ){
      iGuess++;
    }

    if( iGuess<=pagerPagecount(pBt->pPager) ){
      rc = ptrmapGet(pBt, iGuess, &eType, &pgno);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      if( eType==PTRMAP_OVERFLOW2 && pgno==ovfl ){
        next = iGuess;
      }
................................................................................
    u8 searchList = 0; /* If the free-list must be searched for 'nearby' */
    
    /* If the 'exact' parameter was true and a query of the pointer-map
    ** shows that the page 'nearby' is somewhere on the free-list, then
    ** the entire-list will be searched for that page.
    */
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( exact && nearby<=pagerPagecount(pBt->pPager) ){
      u8 eType;
      assert( nearby>0 );
      assert( pBt->autoVacuum );
      rc = ptrmapGet(pBt, nearby, &eType, 0);
      if( rc ) return rc;
      if( eType==PTRMAP_FREEPAGE ){
        searchList = 1;
................................................................................
        }else{
          closest = 0;
        }

        iPage = get4byte(&aData[8+closest*4]);
        if( !searchList || iPage==nearby ){
          *pPgno = iPage;
          int nPage;
          nPage = pagerPagecount(pBt->pPager);
          if( *pPgno>nPage ){
            /* Free page off the end of the file */
            rc = SQLITE_CORRUPT_BKPT;
            goto end_allocate_page;
          }
          TRACE(("ALLOCATE: %d was leaf %d of %d on trunk %d"
                 ": %d more free pages\n",
                 *pPgno, closest+1, k, pTrunk->pgno, n-1));
................................................................................
      }
      releasePage(pPrevTrunk);
      pPrevTrunk = 0;
    }while( searchList );
  }else{
    /* There are no pages on the freelist, so create a new page at the
    ** end of the file */
    int nPage = pagerPagecount(pBt->pPager);
    *pPgno = nPage + 1;

#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->nTrunc ){
      /* An incr-vacuum has already run within this transaction. So the
      ** page to allocate is not from the physical end of the file, but
      ** at pBt->nTrunc. 
      */
................................................................................
  }
  ovflPgno = get4byte(&pCell[info.iOverflow]);
  ovflPageSize = pBt->usableSize - 4;
  nOvfl = (info.nPayload - info.nLocal + ovflPageSize - 1)/ovflPageSize;
  assert( ovflPgno==0 || nOvfl>0 );
  while( nOvfl-- ){
    MemPage *pOvfl;
    if( ovflPgno==0 || ovflPgno>pagerPagecount(pBt->pPager) ){
      return SQLITE_CORRUPT_BKPT;
    }

    rc = getOverflowPage(pBt, ovflPgno, &pOvfl, (nOvfl==0)?0:&ovflPgno);
    if( rc ) return rc;
    rc = freePage(pOvfl);
    sqlite3PagerUnref(pOvfl->pDbPage);
................................................................................
    ** information currently contained in the child.  If this is the 
    ** case, then do not do the transfer.  Leave page 1 empty except
    ** for the right-pointer to the child page.  The child page becomes
    ** the virtual root of the tree.
    */
    pgnoChild = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    assert( pgnoChild>0 );
    assert( pgnoChild<=pagerPagecount(pPage->pBt->pPager) );
    rc = sqlite3BtreeGetPage(pPage->pBt, pgnoChild, &pChild, 0);
    if( rc ) goto end_shallow_balance;
    if( pPage->pgno==1 ){
      rc = sqlite3BtreeInitPage(pChild, pPage);
      if( rc ) goto end_shallow_balance;
      assert( pChild->nOverflow==0 );
      if( pChild->nFree>=100 ){
................................................................................
){
  MemPage *pPage = 0;
  int rc;
  unsigned char *pCell;
  int i;

  assert( sqlite3_mutex_held(pBt->mutex) );
  if( pgno>pagerPagecount(pBt->pPager) ){
    return SQLITE_CORRUPT_BKPT;
  }

  rc = getAndInitPage(pBt, pgno, &pPage, pParent);
  if( rc ) goto cleardatabasepage_out;
  for(i=0; i<pPage->nCell; i++){
    pCell = findCell(pPage, i);
................................................................................
  nRef = sqlite3PagerRefcount(pBt->pPager);
  if( lockBtreeWithRetry(p)!=SQLITE_OK ){
    sqlite3BtreeLeave(p);
    return sqlite3StrDup("Unable to acquire a read lock on the database");
  }
  sCheck.pBt = pBt;
  sCheck.pPager = pBt->pPager;
  sCheck.nPage = pagerPagecount(sCheck.pPager);
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  *pnErr = 0;
#ifndef SQLITE_OMIT_AUTOVACUUM
  if( pBt->nTrunc!=0 ){
    sCheck.nPage = pBt->nTrunc;
  }
................................................................................
  if( pTo->inTrans!=TRANS_WRITE || pFrom->inTrans!=TRANS_WRITE ){
    return SQLITE_ERROR;
  }
  if( pBtTo->pCursor ){
    return SQLITE_BUSY;
  }

  nToPage = pagerPagecount(pBtTo->pPager);
  nFromPage = pagerPagecount(pBtFrom->pPager);
  iSkip = PENDING_BYTE_PAGE(pBtTo);

  /* Variable nNewPage is the number of pages required to store the
  ** contents of pFrom using the current page-size of pTo.
  */
  nNewPage = ((i64)nFromPage * (i64)nFromPageSize + (i64)nToPageSize - 1) / 
      (i64)nToPageSize;

** 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 1.455 2008/06/07 05:19:38 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*
................................................................................
**
** Regardless of mxPage, return the current maximum page count.
*/
int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
  if( mxPage>0 ){
    pPager->mxPgno = mxPage;
  }
  sqlite3PagerPagecount(pPager);
  return pPager->mxPgno;
}

/*
** The following set of routines are used to disable the simulated
** I/O error mechanism.  These routines are used to avoid simulated
** errors in places where we do not care about errors.
................................................................................
** pPager. 
**
** If the PENDING_BYTE lies on the page directly after the end of the
** file, then consider this page part of the file too. For example, if
** PENDING_BYTE is byte 4096 (the first byte of page 5) and the size of the
** file is 4096 bytes, 5 is returned instead of 4.
*/
int sqlite3PagerPagecount(Pager *pPager){
  i64 n = 0;
  int rc;
  assert( pPager!=0 );
  if( pPager->errCode ){
    return -1;
  }
  if( pPager->dbSize>=0 ){
    n = pPager->dbSize;
  } else {
    assert(pPager->fd->pMethods||pPager->tempFile);
    if( (pPager->fd->pMethods)
     && (rc = sqlite3OsFileSize(pPager->fd, &n))!=SQLITE_OK ){
      pPager->nRef++;
      pager_error(pPager, rc);
      pPager->nRef--;
      return -1;
    }
    if( n>0 && n<pPager->pageSize ){
      n = 1;
    }else{
      n /= pPager->pageSize;
    }
    if( pPager->state!=PAGER_UNLOCK ){
................................................................................
  }
  if( n==(PENDING_BYTE/pPager->pageSize) ){
    n++;
  }
  if( n>pPager->mxPgno ){
    pPager->mxPgno = n;
  }



  return n;
}


#ifndef SQLITE_OMIT_MEMORYDB
/*
** Clear a PgHistory block
*/
................................................................................

/*
** Truncate the file to the number of pages specified.
*/
int sqlite3PagerTruncate(Pager *pPager, Pgno nPage){
  int rc;
  assert( pPager->state>=PAGER_SHARED || MEMDB );
  sqlite3PagerPagecount(pPager);
  if( pPager->errCode ){
    rc = pPager->errCode;
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
................................................................................

    rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
    if( rc==SQLITE_OK && exists ){
      rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    }

    if( rc==SQLITE_OK && exists && !locked ){

      int nPage = sqlite3PagerPagecount(pPager);
      if( nPage==0 ){
        sqlite3OsDelete(pVfs, pPager->zJournal, 0);
        exists = 0;
      }else if( nPage<0 ){
        rc = SQLITE_IOERR;
      }
    }

    res = (rc!=SQLITE_OK ? -1 : (exists && !locked));
  }

  return res;
................................................................................
        ** a codec is in use.
        ** 
        ** There is a vanishingly small chance that a change will not be 
        ** detected.  The chance of an undetected change is so small that
        ** it can be neglected.
        */
        char dbFileVers[sizeof(pPager->dbFileVers)];
        sqlite3PagerPagecount(pPager);

        if( pPager->errCode ){
          rc = pPager->errCode;
          goto failed;
        }

        if( pPager->dbSize>0 ){
................................................................................
    makeClean(pPg);
    pPg->nRef = 1;

    pPager->nRef++;
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
    }
    nMax = sqlite3PagerPagecount(pPager);
    if( pPager->errCode ){
      rc = pPager->errCode;
      sqlite3PagerUnref(pPg);
      return rc;
    }

    /* Populate the page with data, either by reading from the database
    ** file, or by setting the entire page to zero.
    */
................................................................................
  int flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_EXCLUSIVE|SQLITE_OPEN_CREATE);

  int rc;
  assert( !MEMDB );
  assert( pPager->state>=PAGER_RESERVED );
  assert( pPager->useJournal );
  assert( pPager->pInJournal==0 );
  sqlite3PagerPagecount(pPager);
  pagerLeave(pPager);
  pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
  pagerEnter(pPager);
  if( pPager->pInJournal==0 ){
    rc = SQLITE_NOMEM;
    goto failed_to_open_journal;
  }
................................................................................
    ** by this connection. Instead of deleting the journal file it was 
    ** kept open and either was truncated to 0 bytes or its header was
    ** overwritten with zeros.
    */
    assert( pPager->nRec==0 );
    assert( pPager->origDbSize==0 );
    assert( pPager->pInJournal==0 );
    sqlite3PagerPagecount(pPager);
    pagerLeave(pPager);
    pPager->pInJournal = sqlite3BitvecCreate( pPager->dbSize );
    pagerEnter(pPager);
    if( !pPager->pInJournal ){
      rc = SQLITE_NOMEM;
    }else{
      pPager->origDbSize = pPager->dbSize;
................................................................................

    /* This trick assumes that both the page-size and sector-size are
    ** an integer power of 2. It sets variable pg1 to the identifier
    ** of the first page of the sector pPg is located on.
    */
    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

    nPageCount = sqlite3PagerPagecount(pPager);
    if( pPg->pgno>nPageCount ){
      nPage = (pPg->pgno - pg1)+1;
    }else if( (pg1+nPagePerSector-1)>nPageCount ){
      nPage = nPageCount+1-pg1;
    }else{
      nPage = nPagePerSector;
    }

** 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 1.456 2008/06/07 08:58:22 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include <assert.h>
#include <string.h>

/*
................................................................................
**
** Regardless of mxPage, return the current maximum page count.
*/
int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
  if( mxPage>0 ){
    pPager->mxPgno = mxPage;
  }
  sqlite3PagerPagecount(pPager, 0);
  return pPager->mxPgno;
}

/*
** The following set of routines are used to disable the simulated
** I/O error mechanism.  These routines are used to avoid simulated
** errors in places where we do not care about errors.
................................................................................
** pPager. 
**
** If the PENDING_BYTE lies on the page directly after the end of the
** file, then consider this page part of the file too. For example, if
** PENDING_BYTE is byte 4096 (the first byte of page 5) and the size of the
** file is 4096 bytes, 5 is returned instead of 4.
*/
int sqlite3PagerPagecount(Pager *pPager, int *pnPage){
  i64 n = 0;
  int rc;
  assert( pPager!=0 );
  if( pPager->errCode ){
    return pPager->errCode;
  }
  if( pPager->dbSize>=0 ){
    n = pPager->dbSize;
  } else {
    assert(pPager->fd->pMethods||pPager->tempFile);
    if( (pPager->fd->pMethods)
     && (rc = sqlite3OsFileSize(pPager->fd, &n))!=SQLITE_OK ){
      pPager->nRef++;
      pager_error(pPager, rc);
      pPager->nRef--;
      return rc;
    }
    if( n>0 && n<pPager->pageSize ){
      n = 1;
    }else{
      n /= pPager->pageSize;
    }
    if( pPager->state!=PAGER_UNLOCK ){
................................................................................
  }
  if( n==(PENDING_BYTE/pPager->pageSize) ){
    n++;
  }
  if( n>pPager->mxPgno ){
    pPager->mxPgno = n;
  }
  if( pnPage ){
    *pnPage = n;
  }
  return SQLITE_OK;
}


#ifndef SQLITE_OMIT_MEMORYDB
/*
** Clear a PgHistory block
*/
................................................................................

/*
** Truncate the file to the number of pages specified.
*/
int sqlite3PagerTruncate(Pager *pPager, Pgno nPage){
  int rc;
  assert( pPager->state>=PAGER_SHARED || MEMDB );
  sqlite3PagerPagecount(pPager, 0);
  if( pPager->errCode ){
    rc = pPager->errCode;
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
................................................................................

    rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
    if( rc==SQLITE_OK && exists ){
      rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    }

    if( rc==SQLITE_OK && exists && !locked ){
      int nPage;
      rc = sqlite3PagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK && nPage==0 ){
        sqlite3OsDelete(pVfs, pPager->zJournal, 0);
        exists = 0;


      }
    }

    res = (rc!=SQLITE_OK ? -1 : (exists && !locked));
  }

  return res;
................................................................................
        ** a codec is in use.
        ** 
        ** There is a vanishingly small chance that a change will not be 
        ** detected.  The chance of an undetected change is so small that
        ** it can be neglected.
        */
        char dbFileVers[sizeof(pPager->dbFileVers)];
        sqlite3PagerPagecount(pPager, 0);

        if( pPager->errCode ){
          rc = pPager->errCode;
          goto failed;
        }

        if( pPager->dbSize>0 ){
................................................................................
    makeClean(pPg);
    pPg->nRef = 1;

    pPager->nRef++;
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
    }
    rc = sqlite3PagerPagecount(pPager, &nMax);
    if( rc!=SQLITE_OK ){

      sqlite3PagerUnref(pPg);
      return rc;
    }

    /* Populate the page with data, either by reading from the database
    ** file, or by setting the entire page to zero.
    */
................................................................................
  int flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_EXCLUSIVE|SQLITE_OPEN_CREATE);

  int rc;
  assert( !MEMDB );
  assert( pPager->state>=PAGER_RESERVED );
  assert( pPager->useJournal );
  assert( pPager->pInJournal==0 );
  sqlite3PagerPagecount(pPager, 0);
  pagerLeave(pPager);
  pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
  pagerEnter(pPager);
  if( pPager->pInJournal==0 ){
    rc = SQLITE_NOMEM;
    goto failed_to_open_journal;
  }
................................................................................
    ** by this connection. Instead of deleting the journal file it was 
    ** kept open and either was truncated to 0 bytes or its header was
    ** overwritten with zeros.
    */
    assert( pPager->nRec==0 );
    assert( pPager->origDbSize==0 );
    assert( pPager->pInJournal==0 );
    sqlite3PagerPagecount(pPager, 0);
    pagerLeave(pPager);
    pPager->pInJournal = sqlite3BitvecCreate( pPager->dbSize );
    pagerEnter(pPager);
    if( !pPager->pInJournal ){
      rc = SQLITE_NOMEM;
    }else{
      pPager->origDbSize = pPager->dbSize;
................................................................................

    /* This trick assumes that both the page-size and sector-size are
    ** an integer power of 2. It sets variable pg1 to the identifier
    ** of the first page of the sector pPg is located on.
    */
    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;

    sqlite3PagerPagecount(pPager, (int *)&nPageCount);
    if( pPg->pgno>nPageCount ){
      nPage = (pPg->pgno - pg1)+1;
    }else if( (pg1+nPagePerSector-1)>nPageCount ){
      nPage = nPageCount+1-pg1;
    }else{
      nPage = nPagePerSector;
    }

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.75 2008/06/06 11:11:26 danielk1977 Exp $
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** If defined as non-zero, auto-vacuum is enabled by default. Otherwise
................................................................................
int sqlite3PagerClose(Pager *pPager);
int sqlite3PagerAcquire(Pager *pPager, Pgno pgno, DbPage **ppPage, int clrFlag);
#define sqlite3PagerGet(A,B,C) sqlite3PagerAcquire(A,B,C,0)
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno);
int sqlite3PagerRef(DbPage*);
int sqlite3PagerUnref(DbPage*);
int sqlite3PagerWrite(DbPage*);
int sqlite3PagerPagecount(Pager*);
int sqlite3PagerTruncate(Pager*,Pgno);
int sqlite3PagerBegin(DbPage*, int exFlag);
int sqlite3PagerCommitPhaseOne(Pager*,const char *zMaster, Pgno, int);
int sqlite3PagerCommitPhaseTwo(Pager*);
int sqlite3PagerRollback(Pager*);
int sqlite3PagerIsreadonly(Pager*);
int sqlite3PagerStmtBegin(Pager*);

**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the sqlite page cache
** subsystem.  The page cache subsystem reads and writes a file a page
** at a time and provides a journal for rollback.
**
** @(#) $Id: pager.h,v 1.76 2008/06/07 08:58:22 danielk1977 Exp $
*/

#ifndef _PAGER_H_
#define _PAGER_H_

/*
** If defined as non-zero, auto-vacuum is enabled by default. Otherwise
................................................................................
int sqlite3PagerClose(Pager *pPager);
int sqlite3PagerAcquire(Pager *pPager, Pgno pgno, DbPage **ppPage, int clrFlag);
#define sqlite3PagerGet(A,B,C) sqlite3PagerAcquire(A,B,C,0)
DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno);
int sqlite3PagerRef(DbPage*);
int sqlite3PagerUnref(DbPage*);
int sqlite3PagerWrite(DbPage*);
int sqlite3PagerPagecount(Pager*, int*);
int sqlite3PagerTruncate(Pager*,Pgno);
int sqlite3PagerBegin(DbPage*, int exFlag);
int sqlite3PagerCommitPhaseOne(Pager*,const char *zMaster, Pgno, int);
int sqlite3PagerCommitPhaseTwo(Pager*);
int sqlite3PagerRollback(Pager*);
int sqlite3PagerIsreadonly(Pager*);
int sqlite3PagerStmtBegin(Pager*);

**    May you share freely, never taking more than you give.
**
*************************************************************************
** Code for testing the pager.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library.
**
** $Id: test2.c,v 1.57 2008/03/21 16:45:48 drh Exp $
*/
#include "sqliteInt.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

................................................................................
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  char zBuf[100];

  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  pPager = sqlite3TextToPtr(argv[1]);
  sqlite3_snprintf(sizeof(zBuf),zBuf,"%d",sqlite3PagerPagecount(pPager));

  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_get ID PGNO
**

**    May you share freely, never taking more than you give.
**
*************************************************************************
** Code for testing the pager.c module in SQLite.  This code
** is not included in the SQLite library.  It is used for automated
** testing of the SQLite library.
**
** $Id: test2.c,v 1.58 2008/06/07 08:58:22 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "tcl.h"
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

................................................................................
  void *NotUsed,
  Tcl_Interp *interp,    /* The TCL interpreter that invoked this command */
  int argc,              /* Number of arguments */
  const char **argv      /* Text of each argument */
){
  Pager *pPager;
  char zBuf[100];
  int nPage;
  if( argc!=2 ){
    Tcl_AppendResult(interp, "wrong # args: should be \"", argv[0],
       " ID\"", 0);
    return TCL_ERROR;
  }
  pPager = sqlite3TextToPtr(argv[1]);
  sqlite3PagerPagecount(pPager, &nPage);
  sqlite3_snprintf(sizeof(zBuf), zBuf, "%d", nPage);
  Tcl_AppendResult(interp, zBuf, 0);
  return TCL_OK;
}

/*
** Usage:   page_get ID PGNO
**

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.747 2008/06/06 15:04:37 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>
#include "vdbeInt.h"

/*
** The following global variable is incremented every time a cursor
................................................................................
** flag on jump instructions, we get a (small) speed improvement.
*/
#define CHECK_FOR_INTERRUPT \
   if( db->u1.isInterrupted ) goto abort_due_to_interrupt;

#ifdef SQLITE_DEBUG
static int fileExists(sqlite3 *db, const char *zFile){
  int res;









  int rc = sqlite3OsAccess(db->pVfs, zFile, SQLITE_ACCESS_EXISTS, &res);
  return (res && rc==SQLITE_OK);
}
#endif

/*
** Execute as much of a VDBE program as we can then return.
**
................................................................................
      p->pc = pc;
      p->rc = rc = SQLITE_BUSY;
      goto vdbe_return;
    }
    case SQLITE_OK: {
      int flags = sqlite3BtreeFlags(pCur->pCursor);
      /* Sanity checking.  Only the lower four bits of the flags byte should
      ** be used.  Bit 3 (mask 0x08) is unpreditable.  The lower 3 bits
      ** (mask 0x07) should be either 5 (intkey+leafdata for tables) or
      ** 2 (zerodata for indices).  If these conditions are not met it can
      ** only mean that we are dealing with a corrupt database file
      */
      if( (flags & 0xf0)!=0 || ((flags & 0x07)!=5 && (flags & 0x07)!=2) ){
        rc = SQLITE_CORRUPT_BKPT;
        goto abort_due_to_error;
................................................................................
** Write the current number of pages in database P1 to memory cell P2.
*/
case OP_Pagecount: {            /* out2-prerelease */
  int p1 = pOp->p1; 
  int nPage;
  Pager *pPager = sqlite3BtreePager(db->aDb[p1].pBt);

  nPage = sqlite3PagerPagecount(pPager);
  if( nPage<0 ){
    rc = SQLITE_IOERR;
  }else{
    pOut->flags = MEM_Int;
    pOut->u.i = nPage;
  }
  break;
}
#endif

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.748 2008/06/07 08:58:22 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>
#include "vdbeInt.h"

/*
** The following global variable is incremented every time a cursor
................................................................................
** flag on jump instructions, we get a (small) speed improvement.
*/
#define CHECK_FOR_INTERRUPT \
   if( db->u1.isInterrupted ) goto abort_due_to_interrupt;

#ifdef SQLITE_DEBUG
static int fileExists(sqlite3 *db, const char *zFile){
  int res = 0;
  int rc = SQLITE_OK;
#ifdef SQLITE_TEST
  /* If we are currently testing IO errors, then do not call OsAccess() to
  ** test for the presence of zFile. This is because any IO error that
  ** occurs here will not be reported, causing the test to fail.
  */
  extern int sqlite3_io_error_pending;
  if( sqlite3_io_error_pending<=0 )
#endif
    rc = sqlite3OsAccess(db->pVfs, zFile, SQLITE_ACCESS_EXISTS, &res);
  return (res && rc==SQLITE_OK);
}
#endif

/*
** Execute as much of a VDBE program as we can then return.
**
................................................................................
      p->pc = pc;
      p->rc = rc = SQLITE_BUSY;
      goto vdbe_return;
    }
    case SQLITE_OK: {
      int flags = sqlite3BtreeFlags(pCur->pCursor);
      /* Sanity checking.  Only the lower four bits of the flags byte should
      ** be used.  Bit 3 (mask 0x08) is unpredictable.  The lower 3 bits
      ** (mask 0x07) should be either 5 (intkey+leafdata for tables) or
      ** 2 (zerodata for indices).  If these conditions are not met it can
      ** only mean that we are dealing with a corrupt database file
      */
      if( (flags & 0xf0)!=0 || ((flags & 0x07)!=5 && (flags & 0x07)!=2) ){
        rc = SQLITE_CORRUPT_BKPT;
        goto abort_due_to_error;
................................................................................
** Write the current number of pages in database P1 to memory cell P2.
*/
case OP_Pagecount: {            /* out2-prerelease */
  int p1 = pOp->p1; 
  int nPage;
  Pager *pPager = sqlite3BtreePager(db->aDb[p1].pBt);

  rc = sqlite3PagerPagecount(pPager, &nPage);

  if( rc==SQLITE_OK ){

    pOut->flags = MEM_Int;
    pOut->u.i = nPage;
  }
  break;
}
#endif

# This file implements regression tests for SQLite library.  The
# focus of this file is testing for correct handling of I/O errors
# such as writes failing because the disk is full.
# 
# The tests in this file use special facilities that are only
# available in the SQLite test fixture.
#
# $Id: ioerr.test,v 1.36 2008/06/05 11:39:12 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl


# If SQLITE_DEFAULT_AUTOVACUUM is set to true, then a simulated IO error
# on the 8th IO operation in the SQL script below doesn't report an error.
#
# This is because the 8th IO call attempts to read page 2 of the database
# file when the file on disk is only 1 page. The pager layer detects that
# this has happened and suppresses the error returned by the OS layer.

# This file implements regression tests for SQLite library.  The
# focus of this file is testing for correct handling of I/O errors
# such as writes failing because the disk is full.
# 
# The tests in this file use special facilities that are only
# available in the SQLite test fixture.
#
# $Id: ioerr.test,v 1.37 2008/06/07 08:58:23 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl


# If SQLITE_DEFAULT_AUTOVACUUM is set to true, then a simulated IO error
# on the 8th IO operation in the SQL script below doesn't report an error.
#
# This is because the 8th IO call attempts to read page 2 of the database
# file when the file on disk is only 1 page. The pager layer detects that
# this has happened and suppresses the error returned by the OS layer.