NdisRetreatNetBufferDataStart (Compact 2013)

3/26/2014

Call this function to access more used data space in the MDL chain of a NET_BUFFER structure.

Syntax

NDIS_STATUS
  NdisRetreatNetBufferDataStart(
    IN PNET_BUFFER  NetBuffer,
    IN ULONG  DataOffsetDelta,
    IN ULONG  DataBackFill,
    IN NET_BUFFER_ALLOCATE_MDL_HANDLER  AllocateMdlHandler OPTIONAL
    );

Parameters

• NetBuffer
  A pointer to a previously allocated NET_BUFFER structure.

• DataOffsetDelta
  The used data space to add. NDIS adjusts the DataOffset member of the NET_BUFFER structure accordingly. If there is not enough unused data space to satisfy the request, NDIS allocates additional memory.

• DataBackFill
  If NDIS must allocate memory, this parameter specifies the data space, in addition to the value of the DataOffsetDelta parameter, to allocate.

• AllocateMdlHandler
  An optional entry point for an NetAllocateMdl function. If the caller specifies an entry point for the NetAllocateMdl function, NDIS calls NetAllocateMdl to allocate an MDL and memory.

Return Value

NdisRetreatNetBufferDataStart returns one of the following:

Value	Description
NDIS_STATUS_SUCCESS	NdisRetreatNetBufferDataStart successfully allocated used data space either by using the unused data space or by allocating new storage.
NDIS_STATUS_RESOURCES	NdisRetreatNetBufferDataStart failed because of insufficient resources.
NDIS_STATUS_FAILURE	NdisRetreatNetBufferDataStart failed for reasons other than insufficient resources.

Remarks

NdisRetreatNetBufferDataStart tries to satisfy the request by reducing the value of the DataOffset member of the NET_BUFFER structure.

If there is not enough unused data space, this function allocates a new buffer and an MDL to describe the new buffer and chains the new MDL to the beginning of the MDL chain. NDIS calls the NetAllocateMdl function specified at AllocateMdl to allocate the MDL and memory. The NetAllocateMdl function can use any allocation method that meets the driver's design requirements.

Call the NdisAdvanceNetBufferDataStart function to release the used data space that was added with NdisRetreatNetBufferDataStart.

Requirements

Header

ndis.h

See Also

Reference

NDIS NET_BUFFER Functions
NdisAdvanceNetBufferDataStart
NetAllocateMdl
NET_BUFFER