This topic has not yet been rated - Rate this topic

FsRtlPrepareMdlWriteDev routine

The FsRtlPrepareMdlWriteDev routine returns a linked list of memory descriptor lists (MDLs) that point to the specified range of cached file data to write data directly to the cache.

Syntax

C++


BOOLEAN FsRtlPrepareMdlWriteDev(
  _In_   PFILE_OBJECT FileObject,
  _In_   PLARGE_INTEGER FileOffset,
  _In_   ULONG Length,
  _In_   ULONG LockKey,
  _Out_  PMDL *MdlChain,
  _Out_  PIO_STATUS_BLOCK IoStatus,
  _In_   PDEVICE_OBJECT DeviceObject
);

Parameters

FileObject [in]: A pointer to the file object.
FileOffset [in]: A pointer to a value that specifies the starting byte offset within the cache that holds the data.
Length [in]: The length in bytes of the data to read from the cache.
LockKey [in]: A value that is associated with the byte range to lock. If the range to lock overlaps another range that is already locked with a nonexclusive lock, or if the range to read is a subrange of another range that is already locked nonexclusively, the value in this parameter must be the key for that nonexclusive lock. The lock must be held by the parent process of the calling thread. Otherwise, this parameter has no effect.
MdlChain [out]: On output, a pointer to a linked list of memory descriptor lists (MDLs) that point to the byte range within the cached data.
IoStatus [out]: A pointer to an IO_STATUS_BLOCK structure that, on output, contains the status of the transfer. If the operation succeeds, IoStatus.Status is set to STATUS_SUCCESS. Otherwise, it is set to an appropriate NTSTATUS error code. IoStatus.Information is set to the actual number of bytes that the routine successfully locked.
DeviceObject [in]: The device object for the device that holds the file data.

Return value

The FsRtlPrepareMdlWriteDev routine returns TRUE if the operation succeeds and FALSE if the operation fails.

Remarks

FsRtlPrepareMdlWriteDev is similar to FsRtlCopyWrite, except that FsRtlPrepareMdlWriteDev does not copy data to the cache. Instead, the physical pages that the caller will overwrite are locked in memory, and FsRtlPrepareMdlWriteDev returns one or more memory descriptor lists (MDLs) that point to the specified byte range. The locked pages remain locked until the caller calls FsRtlMdlWriteCompleteDev. Thus each call to FsRtlPrepareMdlWriteDev must be followed by a call to FsRtlMdlWriteCompleteDev.

The pages that the MDLs point to are locked in memory, but are not mapped in system space. The caller can perform this mapping by calling MmGetSystemAddressForMdlSafe.

Requirements