NET_BUFFER structure (ndis/nbl.h)

Article
09/01/2022

The NET_BUFFER structure specifies data that is transmitted or received over the network.

Syntax

typedef struct _NET_BUFFER {
  union {
    struct {
      NET_BUFFER *Next;
      MDL        *CurrentMdl;
      ULONG      CurrentMdlOffset;
      union {
        ULONG  DataLength;
        SIZE_T stDataLength;
      };
      MDL        *MdlChain;
      ULONG      DataOffset;
    };
    SLIST_HEADER      Link;
    NET_BUFFER_HEADER NetBufferHeader;
  };
  USHORT           ChecksumBias;
  USHORT           Reserved;
  NDIS_HANDLE      NdisPoolHandle;
  PVOID            NdisReserved[2];
  PVOID            ProtocolReserved[6];
  PVOID            MiniportReserved[4];
  PHYSICAL_ADDRESS DataPhysicalAddress;
  union {
    NET_BUFFER_SHARED_MEMORY *SharedMemoryInfo;
    SCATTER_GATHER_LIST      *ScatterGatherList;
  };
} NET_BUFFER, *PNET_BUFFER;

Members

Next

A pointer to the next NET_BUFFER structure in a linked list of NET_BUFFER structures. If this structure is the last NET_BUFFER structure in the list, this member is NULL.

CurrentMdl

A pointer to the first MDL that the current driver is using. This member provides an optimization that improves performance by skipping over any MDLs that the current driver is not using.

CurrentMdlOffset

The offset, in bytes, to the beginning of the used data space in the MDL that is specified by the CurrentMdl member.

DataLength

The length, in bytes, of the used data space in the MDL chain. The maximum length is 0xFFFFFFFF bytes.

stDataLength

The length, in bytes, of the used data space in the MDL chain. The maximum length is 0xFFFFFFFF bytes. This member is the same as DataLength, but its type is SIZE_T instead of ULONG.

MdlChain

A pointer to a linked list of MDLs that map a data buffer. The data buffer stores the network data.

DataOffset

The offset, in bytes, from the beginning of the MDL chain to the beginning of the network data in the MDL chain. This offset is also the size, in bytes, of the unused data space.

Link

Reserved for NDIS.

NetBufferHeader

A NET_BUFFER_HEADER structure. This is a duplicate of the above union, for compatibility reasons.

ChecksumBias

The number of bytes to skip over from the beginning of the data buffer when computing a checksum. This member is used by the TCP/IP protocol.

Reserved

Reserved for future use.

NdisPoolHandle

A pool handle that identifies the NET_BUFFER pool from which the NET_BUFFER structure was allocated.

NdisReserved[2]

Reserved for NDIS.

ProtocolReserved[6]

Reserved for use by protocol drivers. Protocol drivers and NDIS intermediate drivers can use this area for their own purposes. Intermediate drivers can use this member only if it is not already in use.

MiniportReserved[4]

Reserved for use by miniport drivers. Miniport drivers and NDIS intermediate drivers can use this area for their own purposes.

DataPhysicalAddress

Note The name of this member is NdisReserved1 for NDIS 6.0 drivers and is DataPhysicalAddress for NDIS 6.1 and later drivers. For NDIS 6.0 drivers, this member is reserved for NDIS.

The physical address of the data portion of a frame. This member should be to zero if the driver that allocated NET_BUFFER does not specify the address. This member is valid only if the NDIS_NBL_FLAGS_SPLIT_AT_UPPER_LAYER_PROTOCOL_HEADER or NDIS_NBL_FLAGS_SPLIT_AT_UPPER_LAYER_PROTOCOL_PAYLOAD flag is set in the NblFlags member of the NET_BUFFER_LIST structure that is associated with the NET_BUFFER.

Note A miniport driver can set the DataPhysicalAddress member of the NET_BUFFER structure, even if the structure is not associated with a split frame. In this case, DataPhysicalAddress contains the physical address of the header MDL.

SharedMemoryInfo

A pointer to an NET_BUFFER_SHARED_MEMORY structure.

ScatterGatherList

The SCATTER_GATHER_LIST structure describes a scatter/gather list for DMA.

Remarks

NDIS drivers can call the following functions to allocate and initialize a NET_BUFFER structure:

NDIS drivers can call the NdisAllocateNetBufferListPool function and then set the fAllocateNetBuffer member of the NET_BUFFER_LIST_POOL_PARAMETERS structure to TRUE when allocating a NET_BUFFER_LIST structure pool. In this case, a NET_BUFFER structure is preallocated with each NET_BUFFER_LIST structure that the driver allocates from the pool.

Chained to each NET_BUFFER structure are one or more buffer descriptors that map buffers that contain network packet data. These buffer descriptors are specified as an MDL chain in the NetBufferHeader member. Such network packet data either was received or will be transmitted.

To access additional data space in the MDL chain, NDIS drivers can call the following functions:

NDIS drivers typically use the MiniportReserved or ProtocolReserved members of the NET_BUFFER structure to maintain NET_BUFFER structure context information.

Note Only one driver can use MiniportReserved or ProtocolReserved members. Therefore, if another driver has used either of these members, an intermediate driver cannot use them.

To access members of the NET_BUFFER structure, use the following macros and functions:

NET_BUFFER_NEXT_NB

NET_BUFFER_FIRST_MDL

NET_BUFFER_DATA_OFFSET

NET_BUFFER_DATA_LENGTH

NET_BUFFER_PROTOCOL_RESERVED

NET_BUFFER_MINIPORT_RESERVED

NET_BUFFER_CHECKSUM_BIAS

NET_BUFFER_CURRENT_MDL

NET_BUFFER_CURRENT_MDL_OFFSET

NdisGetPoolFromNetBuffer

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