Registering Callouts with the Filter Engine

After a callout driver has created a device object, it can then register its callouts with the filter engine. A callout driver can register its callouts with the filter engine at any time, even if the filter engine is currently not running. To register a callout with the filter engine, a callout driver calls the FwpsCalloutRegister0 function. For example:

// Prototypes for the callout's callout functions
VOID NTAPI
 ClassifyFn(
    IN const FWPS_INCOMING_VALUES0  *inFixedValues,
    IN const FWPS_INCOMING_METADATA_VALUES0  *inMetaValues,
    IN OUT VOID  *layerData,
    IN const FWPS_FILTER0  *filter,
    IN UINT64  flowContext,
    IN OUT FWPS_CLASSIFY_OUT0  *classifyOut
    );

NTSTATUS NTAPI
 NotifyFn(
 IN FWPS_CALLOUT_NOTIFY_TYPE notifyType,
    IN const GUID  *filterKey,
    IN const FWPS_FILTER0  *filter
    );

VOID NTAPI
 FlowDeleteFn(
    IN UINT16  layerId,
    IN UINT32  calloutId,
    IN UINT64  flowContext
    );

// Callout registration structure
const FWPS_CALLOUT0 Callout =
{
 { ... }, // GUID key identifying the callout
  0,       // Callout-specific flags (none set here)
 ClassifyFn,
 NotifyFn,
 FlowDeleteFn
};

// Variable for the run-time callout identifier
UINT32 CalloutId;

NTSTATUS
 DriverEntry(
    IN PDRIVER_OBJECT DriverObject,
    IN PUNICODE_STRING RegistryPath
    )
{
  PDEVICE_OBJECT deviceObject;
  NTSTATUS status;

  ...

 status =
 FwpsCalloutRegister0(
 deviceObject,
      &Callout,
      &CalloutId
      );

  ...

 return status;
}

If the call to the FwpsCalloutRegister0 function is successful, the variable pointed to by the last parameter contains the run-time identifier for the callout. This run-time identifier corresponds to the GUID that was specified for the callout key.

A single callout driver can implement more than one callout. If a callout driver implements more than one callout, it calls the FwpsCalloutRegister0 function one time for each callout that it supports to register each callout with the filter engine.

Related topics

classifyFn