Responds to notification that an exclusive opportunistic lock on a file is about to be broken. Use this operation to indicate that the file should receive a level 2 opportunistic lock.

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

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

Major code


Input buffer

Input buffer length

Output buffer

Output buffer length

Input / Output buffer

Input / Output buffer length

Status block

Irp->IoStatus.Status is set to STATUS_SUCCESS if the request is successful.

Otherwise, Status to the appropriate error condition as a NTSTATUS code.

For more information, see NTSTATUS Values.


This operation is used only by client applications that have requested an opportunistic lock from a local server. Client applications requesting opportunistic locks from remote servers must not request them directly—the network redirector transparently requests opportunistic locks for the application.

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

FSCTL_OPLOCK_BREAK_ACKNOWLEDGE is a response to notification that a level 1, batch, or filter opportunistic lock on an application's file has been broken. It indicates to the server that the application should receive a level 2 opportunistic lock. If the operation returns the error code ERROR_IO_PENDING, the server has granted the application a level 2 lock on the file.

One alternative to using FSCTL_OPLOCK_BREAK_ACKNOWLEDGE is to indicate that the application is about to close the file anyway. Use the FSCTL_OPBATCH_ACK_CLOSE_PENDING control code for this response.

Another alternative is to request to keep the file open but loose all locking, by means of the FSCTL_OPLOCK_BREAK_ACK_NO_2 control code.

Applications are notified that an opportunistic lock is broken by using the hEvent member of the OVERLAPPED structure associated with the file on which the opportunistic lock is broken. Applications may also use functions such as GetOverlappedResult and HasOverlappedIoCompleted.

IIn Windows 8 and Windows Server 2012, this code is supported by the following technologies.

Technology Supported
Server Message Block (SMB) 3.0 protocol No
SMB 3.0 Transparent Failover (TFO) No
SMB 3.0 with Scale-out File Shares (SO) No
Cluster Shared Volume File System (CsvFS) Yes
Resilient File System (ReFS) Yes


Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header winioctl.h (include Windows.h)

See also








Oplock Semantics

Opportunistic Locks