SQLite

/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** 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 1.516 2008/09/19 16:39:38 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( pCur->eState>=CURSOR_REQUIRESEEK ){
    if( pCur->eState==CURSOR_FAULT ){
      return pCur->skip;
    }
    clearCursorPosition(pCur);
  }
  pRoot = pCur->pPage;
  if( pRoot && pRoot->isInit ){
    /* If the page the cursor is currently pointing to is fully initialized,
    ** then the root page can be found by following the MemPage.pParent
    ** pointers. This is faster than requesting a reference to the root
    ** page from the pager layer.
    */
    while( pRoot->pParent ){
      assert( pRoot->isInit==PAGE_ISINIT_FULL );
      pRoot = pRoot->pParent;
    }
    assert( pRoot->isInit==PAGE_ISINIT_FULL );
    if( pRoot!=pCur->pPage ){
      sqlite3PagerRef(pRoot->pDbPage);
      releasePage(pCur->pPage);
      pCur->pPage = pRoot;
    }
  }else{
    if( 
      SQLITE_OK!=(rc = getAndInitPage(pBt, pCur->pgnoRoot, &pRoot, 0))
    ){
      pCur->eState = CURSOR_INVALID;
      return rc;
    }
    releasePage(pCur->pPage);
    pCur->pPage = pRoot;
  }
  assert( pCur->pPage->pgno==pCur->pgnoRoot );
  pCur->idx = 0;
  pCur->info.nSize = 0;
  pCur->atLast = 0;
  pCur->validNKey = 0;
  if( pRoot->nCell==0 && !pRoot->leaf ){
    Pgno subpage;
    assert( pRoot->pgno==1 );

      return SQLITE_OK;
    }
    if( pCur->atLast && pCur->info.nKey<intKey ){
      *pRes = -1;
      return SQLITE_OK;
    }
  }


  rc = moveToRoot(pCur);
  if( rc ){
    return rc;
  }
  assert( pCur->pPage );
  assert( pCur->pPage->isInit==PAGE_ISINIT_FULL );

  rc = queryTableLock(p, 1, READ_LOCK);
  if( rc!=SQLITE_OK ){
    sqlite3BtreeLeave(p);
    return rc;
  }

  assert( idx>=0 && idx<=15 );
  if( pBt->pPage1 ){
    /* The b-tree is already holding a reference to page 1 of the database
    ** file. In this case the required meta-data value can be read directly
    ** from the page data of this reference. This is slightly faster than
    ** requesting a new reference from the pager layer.
    */
    pP1 = (unsigned char *)pBt->pPage1->aData;
  }else{
    /* The b-tree does not have a reference to page 1 of the database file.
    ** Obtain one from the pager layer.
    */
    rc = sqlite3PagerGet(pBt->pPager, 1, &pDbPage);
    if( rc ){
      sqlite3BtreeLeave(p);
      return rc;
    }
    pP1 = (unsigned char *)sqlite3PagerGetData(pDbPage);


  }
  *pMeta = get4byte(&pP1[36 + idx*4]);

  /* If the b-tree is not holding a reference to page 1, then one was 
  ** requested from the pager layer in the above block. Release it now.
  */
  if( !pBt->pPage1 ){
    sqlite3PagerUnref(pDbPage);
  }

  /* If autovacuumed is disabled in this build but we are trying to 
  ** access an autovacuumed database, then make the database readonly. 
  */