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NdisAllocateFragmentNetBufferList (Compact 7)

  • Article

3/12/2014

Call this function to create a new fragmented NET_BUFFER_LIST structure based on the data in an existing NET_BUFFER_LIST structure.

Syntax

PNET_BUFFER_LIST
  NdisAllocateFragmentNetBufferList(
    IN PNET_BUFFER_LIST  OriginalNetBufferList,
    IN PNDIS_HANDLE  NetBufferListPoolHandle OPTIONAL,
    IN PNDIS_HANDLE  NetBufferPoolHandle OPTIONAL,
    IN ULONG  StartOffset,
    IN ULONG  MaximumLength,
    IN ULONG  DataOffsetDelta,
    IN ULONG  DataBackFill,
    IN ULONG  AllocateFragmentFlags
    );

Parameters

  • OriginalNetBufferList
    A pointer to an existing NET_BUFFER_LIST structure.
  • NetBufferPoolHandle
    A NET_BUFFER structure pool handle that was previously returned from a call to NdisAllocateNetBufferPool.
  • StartOffset
    An additional byte offset from the start of the data in each NET_BUFFER structure. This offset is in addition to the value of the DataOffset member that is specified in each NET_BUFFER structure.
  • MaximumLength
    The maximum length, in bytes, for each fragment in the new NET_BUFFER_LIST structure. Each fragment is described by a NET_BUFFER structure.
  • DataOffsetDelta
    The additional amount of used data space that NDIS should make available in the new NET_BUFFER structures.
  • DataBackFill
    The data space in addition to the value of the DataOffsetDelta parameter to allocate if allocation is necessary. If NDIS must allocate memory to supply the data space requested in DataOffsetDelta, it should also allocate the additional space that DataBackFill specifies.
  • AllocateFragmentFlags
    NDIS flags that can be combined with an OR operation. Set this parameter to zero. There are currently no flags defined for this function.

Return Value

NdisAllocateFragmentNetBufferList returns a pointer to a new fragmented NET_BUFFER_LIST structure. If the allocation failed, the return value is NULL.

Remarks

NdisAllocateFragmentNetBufferList allocates and initializes a new fragment NET_BUFFER_LIST structure and NET_BUFFER structures that describe the same data that is described by the NET_BUFFER_LIST structure that the caller passed to NdisAllocateFragmentNetBufferList.

If the fragment NET_BUFFER_LIST structure should have attributes that are associated with a given pool, the caller must specify the pool handle in the NetBufferListPoolHandle or NetBufferPoolHandle parameter. For example, the ProtocolType member of the NET_BUFFER_LIST structure is associated with the pool.

For each NET_BUFFER structure in the specified source NET_BUFFER_LIST structure, NDIS creates the fragment NET_BUFFER structures as follows:

  • NDIS creates the fragments starting at the beginning of the used data space in the source NET_BUFFER structure and offset by the value specified in the StartOffset parameter.
  • NDIS divides the used data space (after accounting for the StartOffset) in the source NET_BUFFER structure into fragments.
  • The length of the used data space of each fragment is less than or equal to the value specified in the MaximumLength parameter. The used data space of the last fragment can be less than MaximumLength.
  • Each fragment is described by a new NET_BUFFER structure and a new set of MDL chains.
  • The data offset of the new NET_BUFFER structures is retreated (the value of the DataOffset member is reduced) by the number of bytes specified in the DataOffsetDelta parameter.
  • If NDIS must allocate memory to supply the data space requested in DataOffsetDelta, it should also allocate the additional space that DataBackFill specifies.

The new fragment NET_BUFFER_LIST structure that NdisAllocateFragmentNetBufferList creates does not include an initial NET_BUFFER_LIST_CONTEXT structure.

Call the NdisFreeFragmentNetBufferList function to free a NET_BUFFER_LIST structure and all associated NET_BUFFER structures and MDL chains that were previously allocated by calling NdisAllocateFragmentNetBufferList.

Requirements

Header

ndis.h

See Also

Reference

NDIS NET_BUFFER Functions
NdisAllocateNetBufferListPool
NdisAllocateNetBufferPool
NdisFreeFragmentNetBufferList
NET_BUFFER
NET_BUFFER_LIST
NET_BUFFER_LIST_CONTEXT