VOID
NpLockUserBuffer(
  IN OUT PIRP Irp,
  IN  LOCK_OPERATION Operation,
  IN  ULONG BufferLength
  );

Routine Description:

    This routine locks the specified buffer for the specified type of
    access.  The file system requires this routine since it does not
    ask the I/O system to lock its buffers for direct I/O.  This routine
    may only be called from the Fsd while still in the user context.

Arguments:

    Irp - Pointer to the Irp for which the buffer is to be locked.

    Operation - IoWriteAccess for read operations, or IoReadAccess for
                write operations.

    BufferLength - Length of user buffer.

Return Value:

    None