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Attaching a Filter Module

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To initiate the process of inserting a filter module into a driver stack, NDIS calls a filter driver's FilterAttach function. At the start of execution in the FilterAttach function, the filter module enters the Attaching state. For more information about attaching a filter module to a driver stack, see Starting a Driver Stack.

A filter driver uses the handle, that NDIS passes at the NdisFilterHandle parameter of FilterAttach in all future NdisXxx function calls that refer to this filter module. Such functions include status indications, send requests, receive indications, and OID requests.

While a filter module is in the Attaching state, the driver:

  • Creates a context area for the filter module and allocates buffer pools and other filter module-specific resources. For more information about buffer pools, see Filter Driver Buffer Management.

  • Calls the NdisFSetAttributes function by using the NdisFilterHandle value that NDIS passed to FilterAttach. The FilterModuleContext parameter of NdisFSetAttributes specifies the filter driver's context area for this filter module. NDIS passes this context area to the filter driver's FilterXxx functions.

  • Optionally, reads configuration parameters for this filter module from the registry. For more information, see Accessing Configuration Information for a Filter Driver.

  • If the preceding operations completed successfully, the filter module is in the Paused state.

  • If the preceding operations failed, the filter driver must release any resources that it allocated in the FilterAttach function and return the filter module to the Detached state.

  • Returns NDIS_STATUS_SUCCESS or an appropriate failure code. If the driver returns a failure code, NDIS terminates the driver stack.

Note  The registry can contain a flag, which specifies that a filter module is optional. If an optional filter module does not attach, NDIS does not terminate the rest of the driver stack.

A filter driver cannot make send requests, indicate received data, make OID requests, or make status indications from the Attaching state. Send and receive operations are supported in the Running and Pausing states. OID requests and status indications are supported in the Paused, Restarting, Running, and Pausing states.

NDIS calls the FilterDetach function to detach a filter module that NDIS attached with FilterAttach. For more information, see Detaching a Filter Module.