WdfIoQueueAssignForwardProgressPolicy function

Description

[Applies to KMDF only]

The WdfIoQueueAssignForwardProgressPolicy method enables the framework's ability to guarantee forward progress for a specified I/O queue.

Parameters

Queue [in]

A handle to a framework queue object.

ForwardProgressPolicy [in]

A pointer to a driver-allocated WDF_IO_QUEUE_FORWARD_PROGRESS_POLICY structure.

Return value

WdfIoQueueAssignForwardProgressPolicy returns STATUS_SUCCESS if the operation succeeds. Otherwise, this method might return one of these values:

This method also might return other NTSTATUS values. In addition, if your driver's EvtIoAllocateResourcesForReservedRequest callback function returns an error status value, WdfIoQueueAssignForwardProgressPolicy returns that value.

A bug check occurs if the driver supplies an invalid object handle.

Remarks

TheWdfIoQueueAssignForwardProgressPolicy method creates request objects that the framework reserves for low-memory situations and registers callback functions that the framework calls to handle low-memory situations.

In KMDF version 1.9, the I/O queue that the Queue parameter represents must be a device's default I/O queue, or a queue for which your driver has called WdfDeviceConfigureRequestDispatching. The driver can call WdfIoQueueAssignForwardProgressPolicy any time after it has called WdfDeviceConfigureRequestDispatching.

In KMDF versions 1.11 and later, the I/O queue that the Queue parameter represents can be any queue that receives a request directly from the framework. For example, the driver might specify a queue to which it will dynamically forward IRPs.

Before WdfIoQueueAssignForwardProgressPolicy returns, the framework does the following:

• Creates and stores the number of request objects that the driver has specified for the TotalForwardProgressRequests member of the WDF_IO_QUEUE_FORWARD_PROGRESS_POLICY structure.
• If the driver previously called WdfDeviceInitSetRequestAttributes, each allocation includes context space that WdfDeviceInitSetRequestAttributes specified.
• Calls the driver's EvtIoAllocateResourcesForReservedRequest callback function for each request object that the framework creates.

After the driver has called WdfIoQueueAssignForwardProgressPolicy to create reserved request objects, the framework uses those reserved objects whenever its attempt to create a new request object fails. (Typically, such failures are caused by low memory situations.)

The framework deletes its reserved request objects only when it deletes the framework queue object that they belong to. If your driver calls WdfDeviceInitSetRequestAttributes and specifies an EvtCleanupCallback or EvtDestroyCallback callback function for its request objects, the framework calls these callback functions for its reserved request objects when it deletes the objects.

For more information about the WdfIoQueueAssignForwardProgressPolicy method and how to use the framework's guaranteed forward progress capability, see Guaranteeing Forward Progress of I/O Operations.

Examples

This code example configures a previously created I/O queue to receive write requests, and then it enables guaranteed forward progress for the queue.

#define MAX_RESERVED_REQUESTS 10

WDF_IO_QUEUE_FORWARD_PROGRESS_POLICY queueForwardProgressPolicy;
WDFQUEUE writeQueue;
NTSTATUS status = STATUS_SUCCESS;
...
status = WdfDeviceConfigureRequestDispatching(
             device,
             writeQueue,
             WdfRequestTypeWrite
             );
if(!NT_SUCCESS(status)) {
    return status;
}
WDF_IO_QUEUE_FORWARD_PROGRESS_POLICY_DEFAULT_INIT(
    &queueForwardProgressPolicy,
    MAX_RESERVED_REQUESTS
    );
status = WdfIoQueueAssignForwardProgressPolicy(
             writeQueue,
             &queueForwardProgressPolicy
             );
if(!NT_SUCCESS(status)) {
    return status;
}

See also

EvtIoAllocateResourcesForReservedRequest

WDF_IO_QUEUE_FORWARD_PROGRESS_POLICY

WdfDeviceConfigureRequestDispatching