NET_BUFFER_LIST_CONTEXT structure (ndis/nbl.h)

The NET_BUFFER_LIST_CONTEXT structure stores context information for a NET_BUFFER_LIST structure.

Syntax

typedef struct _NET_BUFFER_LIST_CONTEXT {
  NET_BUFFER_LIST_CONTEXT *Next;
  USHORT                  Size;
  USHORT                  Offset;
  UCHAR                   ContextData[];
} NET_BUFFER_LIST_CONTEXT, *PNET_BUFFER_LIST_CONTEXT;

Members

Next

A pointer to the next NET_BUFFER_LIST_CONTEXT structure in a linked list of NET_BUFFER_LIST_CONTEXT structures.

Size

The size, in bytes, of the entire context space in the NET_BUFFER_LIST_CONTEXT structure, including the used and unused context space.

Offset

The offset, in bytes, from the beginning of the context data buffer to the start of the context data in the NET_BUFFER_LIST_CONTEXT structure. The Offset member also specifies the size in bytes of the unused context space in the NET_BUFFER_LIST_CONTEXT structure.

ContextData

The context data buffer. The context data can include any information that a driver requires.

Remarks

Every NET_BUFFER_LIST structure can include a preallocated NET_BUFFER_LIST_CONTEXT structure. As a NET_BUFFER_LIST structure travels through the driver stack, the linked list of NET_BUFFER_LIST_CONTEXT structures can expand to accommodate additional data space for each driver.

Drivers should use the following NDIS macros and functions to access and manipulate members in a NET_BUFFER_LIST_CONTEXT structure:

• NdisAllocateNetBufferListContext
• NdisFreeNetBufferListContext
• NET_BUFFER_LIST_CONTEXT_DATA_START
• NET_BUFFER_LIST_CONTEXT_DATA_SIZE

The ContextData member of the NET_BUFFER_LIST_CONTEXT structure specifies the data portion of the NET_BUFFER_LIST_CONTEXT structure. To improve system performance, a driver should preallocate any required context data space when the driver allocates a NET_BUFFER_LIST structure pool. To preallocate this data space, a driver calls the NdisAllocateNetBufferListPool function and then specifies the amount of data space required in the ContextSize parameter. Preallocation of this data space saves NDIS from allocating memory in the receive and send paths.

Note  NDIS estimates the required context data space and, if necessary, adjusts the allocated data space to meet the requirements for the entire driver stack.

 

The Offset member specifies the amount of unused context space in the NET_BUFFER_LIST_CONTEXT structure. The Offset member also indicates the offset from the beginning of the ContextData member to the start of the used context data space.

NDIS drivers call the NdisAllocateNetBufferListContext function to allocate contiguous buffer space in the NET_BUFFER_LIST_CONTEXT structure. If necessary, NDIS allocates a new NET_BUFFER_LIST_CONTEXT structure with additional space to honor the request. NDIS drivers call the NdisFreeNetBufferListContext function to free the buffer space.

Use the NET_BUFFER_LIST_CONTEXT_DATA_SIZE macro to obtain the size of the used context space. Use the NET_BUFFER_LIST_CONTEXT_DATA_START macro to get the starting address of the used context space.

For more information on how to use net buffers, see NET_BUFFER Architecture.

Requirements

Requirement	Value
Minimum supported client	Supported in NDIS 6.0 and later.
Header	ndis/nbl.h (include ndis.h)

See also

NET_BUFFER

NET_BUFFER_LIST

NET_BUFFER_LIST_CONTEXT_DATA_SIZE NET_BUFFER_LIST_CONTEXT_DATA_START NdisAllocateNetBufferListContext NdisAllocateNetBufferListPool

NdisFreeNetBufferListContext