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 1.652 2009/07/04 17:16:01 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"

    sqlite3BtreeLeave(p);
  }
  return rc;
}

/*
** Create a new cursor for the BTree whose root is on the page
** iTable. If a read-only cursor is requested, it is assumed that
** the caller already has at least a read-only transaction open
** on the database already. If a write-cursor is requested, then
** the caller is assumed to have an open write transaction.
**
** If wrFlag==0, then the cursor can only be used for reading.
** If wrFlag==1, then the cursor can be used for reading or for
** writing if other conditions for writing are also met.  These
** are the conditions that must be met in order for writing to
** be allowed:
**

static int btreeCursor(
  Btree *p,                              /* The btree */
  int iTable,                            /* Root page of table to open */
  int wrFlag,                            /* 1 to write. 0 read-only */
  struct KeyInfo *pKeyInfo,              /* First arg to comparison function */
  BtCursor *pCur                         /* Space for new cursor */
){
  int rc;                                /* Return code */

  BtShared *pBt = p->pBt;                /* Shared b-tree handle */

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( wrFlag==0 || wrFlag==1 );

  /* The following assert statements verify that if this is a sharable 
  ** b-tree database, the connection is holding the required table locks, 
  ** and that no other connection has any open cursor that conflicts with 
  ** this lock.  */
  assert( hasSharedCacheTableLock(p, iTable, pKeyInfo!=0, wrFlag+1) );
  assert( wrFlag==0 || !hasReadConflicts(p, iTable) );

  /* Assert that the caller has opened the required transaction. */
  assert( p->inTrans>TRANS_NONE );
  assert( wrFlag==0 || p->inTrans==TRANS_WRITE );
  assert( pBt->pPage1 && pBt->pPage1->aData );

  if( NEVER(wrFlag && pBt->readOnly) ){
    return SQLITE_READONLY;
  }
  if( iTable==1 && pagerPagecount(pBt)==0 ){



    return SQLITE_EMPTY;
  }

  pCur->pgnoRoot = (Pgno)iTable;








  rc = getAndInitPage(pBt, pCur->pgnoRoot, &pCur->apPage[0]);
  if( rc!=SQLITE_OK ){
    assert( pCur->apPage[0]==0 );
    return rc;
  }

  /* Now that no other errors can occur, finish filling in the BtCursor
  ** variables and link the cursor into the BtShared list.  */


  pCur->pKeyInfo = pKeyInfo;
  pCur->pBtree = p;
  pCur->pBt = pBt;
  pCur->wrFlag = (u8)wrFlag;
  pCur->pNext = pBt->pCursor;
  if( pCur->pNext ){
    pCur->pNext->pPrev = pCur;
  }
  pBt->pCursor = pCur;
  pCur->eState = CURSOR_INVALID;
  pCur->cachedRowid = 0;

  return SQLITE_OK;





}
int sqlite3BtreeCursor(
  Btree *p,                                   /* The btree */
  int iTable,                                 /* Root page of table to open */
  int wrFlag,                                 /* 1 to write. 0 read-only */
  struct KeyInfo *pKeyInfo,                   /* First arg to xCompare() */
  BtCursor *pCur                              /* Write new cursor here */