FSCTL_REQUEST_OPLOCK_LEVEL_2

The FSCTL_REQUEST_OPLOCK_LEVEL_2 operation requests a level 2 opportunistic lock on a file.

To perform this operation, call the DeviceIoControl function using the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,              // handle to file
  FSCTL_REQUEST_OPLOCK_LEVEL_2,  // dwIoControlCode operation
  NULL,                          // lpInBuffer; must be NULL
  0,                             // nInBufferSize; must be zero
  NULL,                          // lpOutBuffer; must be NULL
  0,                             // nOutBufferSize; must be zero
  (LPDWORD) lpBytesReturned,     // number of bytes returned
  (LPOVERLAPPED) lpOverlapped    // OVERLAPPED structure
);

Parameters

hDevice

[in] Handle to the file or alternate stream on which the opportunistic lock is requested. To obtain a handle, call the CreateFile function. The file or alternate stream must have been opened with the flag FILE_FLAG_OVERLAPPED.

dwIoControlCode

[in] Control code for the operation. This value identifies the specific operation to be performed and the type of device on which to perform it. Use FSCTL_REQUEST_OPLOCK_LEVEL_2 for this operation.

lpInBuffer

[in] Pointer to the input buffer. Not used; must be NULL.

nInBufferSize

[in] Size, in bytes, of the input buffer. Not used; must be zero.

lpOutBuffer

[out] Pointer to the output buffer. Not used; must be NULL.

nOutBufferSize

[in] Size, in bytes, of the output buffer. Not used; must be zero.

lpBytesReturned

[out] Pointer to a variable that receives the actual count of bytes returned by the function in the output buffer. The lpBytesReturned value is meaningless until the operation is complete or if there is no output buffer. With an asynchronous call, the programmer must provide a pointer to a valid value.

If lpOverlapped is NULL (nonoverlapped I/O), lpBytesReturned is used internally and cannot be NULL.

If lpOverlapped is not NULL (overlapped I/O), lpBytesReturned can be NULL.

lpOverlapped

[in] Pointer to an OVERLAPPED structure.

If hDevice was opened with the FILE_FLAG_OVERLAPPED flag, lpOverlapped must point to a valid OVERLAPPED structure. In this case, DeviceIoControl is performed as an overlapped (asynchronous) operation. If the device was opened with the FILE_FLAG_OVERLAPPED flag and lpOverlapped is NULL, the function fails in unpredictable ways.

If hDevice was opened without specifying the FILE_FLAG_OVERLAPPED flag, lpOverlapped is ignored and the DeviceIoControl function does not return until the operation has been completed, or until an error occurs.

Return Values

If the operation succeeds, DeviceIoControl returns a nonzero value. To determine if the opportunistic lock is granted, call GetLastError. The code ERROR_IO_PENDING indicates that the opportunistic lock was granted. Any other code indicates that the request was denied.

If the operation fails, DeviceIoControl returns zero. To get extended error information, call GetLastError.

Remarks

For the implications of overlapped I/O on this operation, see the Remarks section of the DeviceIoControl topic.

Use FSCTL_REQUEST_OPLOCK_LEVEL_2 to request a level 2 opportunistic lock on a file. A client file system can cache read data (but not write data) locally as long as the level 2 lock is held.

The file system provides no acknowledgment to the application that requested the level 2 opportunistic lock when the lock is broken. After the lock is broken, the network redirector is notified not to regard as valid any cached data from the file.

An FSCTL_REQUEST_OPLOCK_LEVEL_2 operation fails if the file is opened in nonoverlapped (synchronous) mode.

Requirements

  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Unsupported.
  Header: Declared in Winioctl.h.

See Also

Device Input and Output Overview, Device Input and Output Control Codes, CreateFile, DeviceIoControl, Opportunistic Locks, OVERLAPPED