SQLite

  int nStep;                      /* Rows processed for current object */
  int nProgress;                  /* Rows processed for all objects */
  OtaObjIter objiter;             /* Iterator for skipping through tbl/idx */
  const char *zVfsName;           /* Name of automatically created ota vfs */
  ota_file *pTargetFd;            /* File handle open on target db */

  /* The following state variables are used as part of the incremental
  ** checkpoint stage (eStage==OTA_STAGE_CKPT). See comments surrounding
  ** function otaSetupCheckpoint() for details.  */
  u32 iMaxFrame;                  /* Largest iWalFrame value in aFrame[] */
  u32 mLock;
  int nFrame;                     /* Entries in aFrame[] array */
  int nFrameAlloc;                /* Allocated size of aFrame[] array */
  OtaFrame *aFrame;
  int pgsz;
  u8 *aBuf;

    if( p->rc==SQLITE_OK ){
      iRet = ((i64)ptr[10] << 32) + ptr[11];
    }
  }
  return iRet;
}

/*
** This function is called as part of initializing or reinitializing an
** incremental checkpoint. 
**
** It populates the sqlite3ota.aFrame[] array with the set of 
** (wal frame -> db page) copy operations required to checkpoint the 
** current wal file, and obtains the set of shm locks required to safely 
** perform the copy operations directly on the file-system.
**
** If argument pState is not NULL, then the incremental checkpoint is
** being resumed. In this case, if the checksum of the wal-index-header
** following recovery is not the same as the checksum saved in the OtaState
** object, then the ota handle is set to DONE state. This occurs if some
** other client appends a transaction to the wal file in the middle of
** an incremental checkpoint.
*/
static void otaSetupCheckpoint(sqlite3ota *p, OtaState *pState){

  /* If pState is NULL, then the wal file may not have been opened and
  ** recovered. Running a read-statement here to ensure that doing so
  ** does not interfere with the "capture" process below.  */
  if( pState==0 ){
    p->eStage = 0;
    if( p->rc==SQLITE_OK ){
      p->rc = sqlite3_exec(p->db, "SELECT * FROM sqlite_master", 0, 0, 0);
    }
  }

  /* Assuming no error has occurred, run a "restart" checkpoint with the
  ** sqlite3ota.eStage variable set to CAPTURE. This turns on the following
  ** special behaviour in the ota VFS:
  **
  **   * If the exclusive shm WRITER or READ0 lock cannot be obtained,
  **     the checkpoint fails with SQLITE_BUSY (normally SQLite would
  **     proceed with running a passive checkpoint instead of failing).
  **
  **   * Attempts to read from the *-wal file or write to the database file
  **     do not perform any IO. Instead, the frame/page combinations that
  **     would be read/written are recorded in the sqlite3ota.aFrame[]
  **     array.
  **
  **   * Calls to xShmLock(UNLOCK) to release the exclusive shm WRITER, 
  **     READ0 and CHECKPOINT locks taken as part of the checkpoint are
  **     no-ops. These locks will not be released until the connection
  **     is closed.
  **
  **   * Attempting to xSync() the database file causes an SQLITE_INTERNAL 
  **     error.
  **
  ** As a result, unless an error (i.e. OOM or SQLITE_BUSY) occurs, the
  ** checkpoint below fails with SQLITE_INTERNAL, and leaves the aFrame[]
  ** array populated with a set of (frame -> page) mappings. Because the 
  ** WRITER, CHECKPOINT and READ0 locks are still held, it is safe to copy 
  ** data from the wal file into the database file according to the 
  ** contents of aFrame[].
  */
  if( p->rc==SQLITE_OK ){
    int rc2;
    p->eStage = OTA_STAGE_CAPTURE;
    rc2 = sqlite3_exec(p->db, "PRAGMA main.wal_checkpoint=restart", 0, 0, 0);
    if( rc2!=SQLITE_INTERNAL ) p->rc = rc2;
  }

  if( p->rc==SQLITE_OK ){
    p->eStage = OTA_STAGE_CKPT;
    p->nStep = (pState ? pState->nRow : 0);
    p->aBuf = otaMalloc(p, p->pgsz);
    p->iWalCksum = otaShmChecksum(p);
  }

  if( p->rc==SQLITE_OK && pState && pState->iWalCksum!=p->iWalCksum ){
    p->rc = SQLITE_DONE;
    p->eStage = OTA_STAGE_DONE;
  }
}

/*
** Called when iAmt bytes are read from offset iOff of the wal file while
** the ota object is in capture mode. Record the frame number of the frame
** being read in the aFrame[] array.
*/
static int otaCaptureWalRead(sqlite3ota *pOta, i64 iOff, int iAmt){
  const u32 mReq = (1<<WAL_LOCK_WRITE)|(1<<WAL_LOCK_CKPT)|(1<<WAL_LOCK_READ0);
  u32 iFrame;

  if( pOta->mLock!=mReq ){
    pOta->rc = SQLITE_BUSY;
    return SQLITE_INTERNAL;

  if( pOta->iMaxFrame<iFrame ) pOta->iMaxFrame = iFrame;
  pOta->aFrame[pOta->nFrame].iWalFrame = iFrame;
  pOta->aFrame[pOta->nFrame].iDbPage = 0;
  pOta->nFrame++;
  return SQLITE_OK;
}

/*
** Called when a page of data is written to offset iOff of the database
** file while the ota handle is in capture mode. Record the page number 
** of the page being written in the aFrame[] array.
*/
static int otaCaptureDbWrite(sqlite3ota *pOta, i64 iOff){
  pOta->aFrame[pOta->nFrame-1].iDbPage = (u32)(iOff / pOta->pgsz) + 1;
  return SQLITE_OK;
}

/*
** This is called as part of an incremental checkpoint operation. Copy
** a single frame of data from the wal file into the database file, as
** indicated by the OtaFrame object.
*/
static void otaCheckpointFrame(sqlite3ota *p, OtaFrame *pFrame){
  sqlite3_file *pWal = p->pTargetFd->pWalFd->pReal;
  sqlite3_file *pDb = p->pTargetFd->pReal;
  i64 iOff;

  assert( p->rc==SQLITE_OK );
  iOff = (i64)(pFrame->iWalFrame-1) * (p->pgsz + 24) + 32 + 24;

  if( res==0 ){
    otaBadControlError(p);
  }
  return res;
}

#ifdef SQLITE_DEBUG
/*
** Assert that column iCol of statement pStmt is named zName.
*/
static void assertColumnName(sqlite3_stmt *pStmt, int iCol, const char *zName){
  const char *zCol = sqlite3_column_name(pStmt, iCol);
  assert( 0==sqlite3_stricmp(zName, zCol) );
}
#else
# define assertColumnName(x,y,z)
#endif

    }
    if( p->rc==SQLITE_OK ){
      otaMPrintfExec(p, "PRAGMA schema_version = %d", iCookie+1);
    }
  }
}

/*
** Update the contents of the ota_state table within the ota database. The
** value stored in the OTA_STATE_STAGE column is eStage. All other values
** are determined by inspecting the ota handle passed as the first argument.
*/
static void otaSaveState(sqlite3ota *p, int eStage){
  if( p->rc==SQLITE_OK || p->rc==SQLITE_DONE ){
    sqlite3_stmt *pInsert = 0;
    int rc;

    assert( p->zErrmsg==0 );
    rc = prepareFreeAndCollectError(p->db, &pInsert, &p->zErrmsg, 

    }
    return p->rc;
  }else{
    return SQLITE_NOMEM;
  }
}

/*
** Free an OtaState object allocated by otaLoadState().
*/
static void otaFreeState(OtaState *p){
  if( p ){
    sqlite3_free(p->zTbl);
    sqlite3_free(p->zIdx);
    sqlite3_free(p);
  }
}

  rc2 = sqlite3_finalize(pStmt);
  if( rc==SQLITE_OK ) rc = rc2;

  p->rc = rc;
  return pRet;
}

/*
** Compare strings z1 and z2, returning 0 if they are identical, or non-zero
** otherwise. Either or both argument may be NULL. Two NULL values are
** considered equal, and NULL is considered distinct from all other values.
*/
static int otaStrCompare(const char *z1, const char *z2){
  if( z1==0 && z2==0 ) return 0;
  if( z1==0 || z2==0 ) return 1;
  return (sqlite3_stricmp(z1, z2)!=0);
}

/*
** This function is called as part of sqlite3ota_open() when initializing
** an ota handle in OAL stage. If the ota update has not started (i.e.
** the ota_state table was empty) it is a no-op. Otherwise, it arranges
** things so that the next call to sqlite3ota_step() continues on from
** where the previous ota handle left off.
**
** If an error occurs, an error code and error message are left in the
** ota handle passed as the first argument.
*/
static void otaSetupOal(sqlite3ota *p, OtaState *pState){
  assert( p->rc==SQLITE_OK );
  if( pState->zTbl ){
    OtaObjIter *pIter = &p->objiter;
    int rc = SQLITE_OK;

    while( rc==SQLITE_OK && pIter->zTbl && (pIter->bCleanup 
       || otaStrCompare(pIter->zIdx, pState->zIdx)

static void otaDeleteOalFile(sqlite3ota *p){
  char *zOal = sqlite3_mprintf("%s-oal", p->zTarget);
  assert( p->rc==SQLITE_OK && p->zErrmsg==0 );
  unlink(zOal);
  sqlite3_free(zOal);
}

/*
** Allocate a private ota VFS for the ota handle passed as the only
** argument. This VFS will be used unless the call to sqlite3ota_open()
** specified a URI with a vfs=? option in place of a target database
** file name.
*/
static void otaCreateVfs(sqlite3ota *p){
  int rnd;
  char zRnd[64];

  assert( p->rc==SQLITE_OK );
  sqlite3_randomness(sizeof(int), (void*)&rnd);
  sprintf(zRnd, "ota_vfs_%d", rnd);
  p->rc = sqlite3ota_create_vfs(zRnd, 0);
  if( p->rc==SQLITE_OK ){
    sqlite3_vfs *pVfs = sqlite3_vfs_find(zRnd);
    assert( pVfs );
    p->zVfsName = pVfs->zName;
  }
}

/*
** Destroy the private VFS created for the ota handle passed as the only
** argument by an earlier call to otaCreateVfs().
*/
static void otaDeleteVfs(sqlite3ota *p){
  if( p->zVfsName ){
    sqlite3ota_destroy_vfs(p->zVfsName);
    p->zVfsName = 0;
  }
}

  
        /* Point the object iterator at the first object */
        if( p->rc==SQLITE_OK ){
          p->rc = otaObjIterFirst(p, &p->objiter);
        }
  
        if( p->rc==SQLITE_OK ){
          otaSetupOal(p, pState);
        }
      }else if( p->eStage==OTA_STAGE_MOVE ){
        /* no-op */
      }else if( p->eStage==OTA_STAGE_CKPT ){
        otaSetupCheckpoint(p, pState);

      }else if( p->eStage==OTA_STAGE_DONE ){
        p->rc = SQLITE_DONE;
      }else{
        p->rc = SQLITE_CORRUPT;
      }
    }

*/
static int otaVfsDeviceCharacteristics(sqlite3_file *pFile){
  ota_file *p = (ota_file *)pFile;
  return p->pReal->pMethods->xDeviceCharacteristics(p->pReal);
}

/*
** Take or release a shared-memory lock.
*/
static int otaVfsShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  ota_file *p = (ota_file*)pFile;
  sqlite3ota *pOta = p->pOta;
  int rc = SQLITE_OK;

#ifdef SQLITE_AMALGAMATION

      }
    }
  }

  return rc;
}

/*
** Obtain a pointer to a mapping of a single 32KiB page of the *-shm file.
*/
static int otaVfsShmMap(
  sqlite3_file *pFile, 
  int iRegion, 
  int szRegion, 
  int isWrite, 
  void volatile **pp
){

** Memory barrier.
*/
static void otaVfsShmBarrier(sqlite3_file *pFile){
  ota_file *p = (ota_file *)pFile;
  p->pReal->pMethods->xShmBarrier(p->pReal);
}

/*
** The xShmUnmap method.
*/
static int otaVfsShmUnmap(sqlite3_file *pFile, int delFlag){
  ota_file *p = (ota_file*)pFile;
  int rc = SQLITE_OK;
  int eStage = (p->pOta ? p->pOta->eStage : 0);

  assert( p->openFlags & (SQLITE_OPEN_MAIN_DB|SQLITE_OPEN_TEMP_DB) );
  if( eStage==OTA_STAGE_OAL || eStage==OTA_STAGE_MOVE ){
    /* no-op */
  }else{
    rc = p->pReal->pMethods->xShmUnmap(p->pReal, delFlag);
  }
  return rc;
}

/*
** Given that zWal points to a buffer containing a wal file name passed to 
** either the xOpen() or xAccess() VFS method, return a pointer to the
** file-handle opened by the same database connection on the corresponding
** database file.
*/
static ota_file *otaFindMaindb(ota_vfs *pOtaVfs, const char *zWal){
  ota_file *pDb;
  sqlite3_mutex_enter(pOtaVfs->mutex);
  for(pDb=pOtaVfs->pMain; pDb && pDb->zWal!=zWal; pDb=pDb->pMainNext);
  sqlite3_mutex_leave(pOtaVfs->mutex);
  return pDb;
}

** Return the current time as a Julian Day number in *pTimeOut.
*/
static int otaVfsCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
  sqlite3_vfs *pRealVfs = ((ota_vfs*)pVfs)->pRealVfs;
  return pRealVfs->xCurrentTime(pRealVfs, pTimeOut);
}

/*
** No-op.
*/
static int otaVfsGetLastError(sqlite3_vfs *pVfs, int a, char *b){
  return 0;
}

/*
** Deregister and destroy an OTA vfs created by an earlier call to
** sqlite3ota_create_vfs().
*/
void sqlite3ota_destroy_vfs(const char *zName){
  sqlite3_vfs *pVfs = sqlite3_vfs_find(zName);
  if( pVfs && pVfs->xOpen==otaVfsOpen ){
    sqlite3_mutex_free(((ota_vfs*)pVfs)->mutex);
    sqlite3_vfs_unregister(pVfs);
    sqlite3_free(pVfs);
  }
}

/*
** Create an OTA VFS named zName that accesses the underlying file-system
** via existing VFS zParent. The new object is registered as a non-default
** VFS with SQLite before returning.
*/
int sqlite3ota_create_vfs(const char *zName, const char *zParent){

  /* Template for VFS */
  static sqlite3_vfs vfs_template = {
    1,                            /* iVersion */
    0,                            /* szOsFile */
    0,                            /* mxPathname */

** Return the total number of key-value operations (inserts, deletes or 
** updates) that have been performed on the target database since the
** current OTA update was started.
*/
sqlite3_int64 sqlite3ota_progress(sqlite3ota *pOta);

/*
** Create an OTA VFS named zName that accesses the underlying file-system
** via existing VFS zParent. The new object is registered as a non-default
** VFS with SQLite before returning.
**
** Part of the OTA implementation uses a custom VFS object. Usually, this
** object is created and deleted automatically by OTA. 
**
** The exception is for applications that also use zipvfs. In this case,
** the custom VFS must be explicitly created by the user before the OTA
** handle is opened. The OTA VFS should be installed so that the zipvfs
** VFS uses the OTA VFS, which in turn uses any other VFS layers in use