NdisRetreatNetBufferDataStart function (ndis/nblapi.h)

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


  [in]           NET_BUFFER              *NetBuffer,
  [in]           ULONG                   DataOffsetDelta,
  [in]           ULONG                   DataBackFill,
  [in, optional] NET_BUFFER_ALLOCATE_MDL *AllocateMdlHandler


[in] NetBuffer

A pointer to a previously allocated NET_BUFFER structure.

[in] DataOffsetDelta

The amount of 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.

[in] DataBackFill

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

[in, optional] 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:

Return code Description
NdisRetreatNetBufferDataStart successfully allocated used data space either by using the unused data space or by allocating new storage.
NdisRetreatNetBufferDataStart failed due to insufficient resources.
NdisRetreatNetBufferDataStart failed for reasons other than insufficient resources.


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

If there isn't 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.


Minimum supported client Supported in NDIS 6.0 and later.
Target Platform Universal
Header ndis/nblapi.h (include ndis.h)
Library Ndis.lib
DDI compliance rules Irql_NetBuffer_Function

See also