Intermediate Driver Network Data Management

An intermediate driver receives NET_BUFFER_LIST structures with one or more associated MDLs from a higher-level driver to send over the network. The intermediate driver can pass the data through to the underlying driver by calling NdisSendNetBufferLists if the driver has a connectionless lower edge, or by calling NdisCoSendNetBufferLists if the driver has a connection-oriented lower edge. Alternatively, the intermediate driver can take some actions to modify either the contents of the chained buffers or the ordering or timing of the incoming data relative to other transmissions.

Depending on the purpose of the intermediate driver, such a driver can repackage buffers that are chained to incoming NET_BUFFER_LIST structures. For example, an intermediate driver repackages network data in the following circumstances:

• The intermediate driver receives a larger data buffer from an overlying protocol driver than can be sent in a single buffer over the underlying medium. Consequently, the intermediate driver must divide the incoming data into smaller buffers.

• The intermediate driver changes the length or content of the network data by compressing or encrypting the data before forwarding each send to the underlying driver.

For information about creating network data management, see Protocol Driver Buffer Management.

NDIS provides interfaces to clone and fragment NET_BUFFER_LIST structures. For more information about cloning and fragmenting structures, see Derived NET_BUFFER_LIST Structures.

NET_BUFFER_LIST structures can be allocated as needed, at driver initialization time, or in the ProtocolBindAdapterEx function. An intermediate driver developer can, if necessary and for performance reasons, allocate a number of structures at initialization time so that ProtocolReceiveNetBufferLists has preallocated resources into which to copy incoming data for indicating to a higher-level driver, and so that MiniportSendNetBufferLists has available NET_BUFFER_LIST structures (and possibly buffers) to pass incoming send network data on to the next lower driver.

If an intermediate driver copies send data or received data to a new buffer or buffers, and the length of actual data in the last buffer is less than the allocated length of the buffer, the intermediate driver can call NdisAdjustMdlLength to adjust the buffer to the actual length of the data.

An intermediate driver with a connectionless lower edge always receives incoming data from an underlying miniport adapter from its ProtocolReceiveNetBufferLists function.

An intermediate driver with a connection-oriented lower edge always receives incoming data from an underlying miniport adapter from its ProtocolCoReceiveNetBufferLists function.