WdfRequestSend function (wdfrequest.h)

Article
06/20/2023

[Applies to KMDF and UMDF]

The WdfRequestSend method sends a specified I/O request to a specified I/O target.

Syntax

BOOLEAN WdfRequestSend(
  [in] WDFREQUEST                Request,
  [in] WDFIOTARGET               Target,
       PWDF_REQUEST_SEND_OPTIONS Options
);

Parameters

[in] Request

A handle to a framework request object.

[in] Target

A handle to a framework I/O target object. For more information about how to obtain this handle, see the following Remarks section.

Options

A pointer to a WDF_REQUEST_SEND_OPTIONS structure that contains caller-supplied request options. This parameter is optional and can be NULL if you do not want to enable any request options.

Return value

WdfRequestSend returns TRUE if the request was sent to the target. Otherwise, this method returns FALSE, and calling WdfRequestGetStatus returns a status that fails an NT_SUCCESS() test.

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

Remarks

The request object that the driver specifies for the Request parameter can be one that it received or one that it created by calling the WdfRequestCreate method.

To obtain a handle to an I/O target object, the driver can do one of the following:

If the driver is using general I/O targets, it calls WdfDeviceGetIoTarget. For more information, see Initializing a General I/O Target.
If the driver is using a specialized I/O target, it calls one or more methods that the specialized target object defines. For example, a driver for a USB device can call WdfUsbTargetDeviceGetIoTarget or WdfUsbTargetPipeGetIoTarget.

By default, WdfRequestSend delivers the request to the target asynchronously, which means it returns immediately without waiting for the request to be completed. Optionally, the request can be delivered synchronously, which means WdfRequestSend does not return until a driver completes the request. To send the request synchronously, the driver must set the WDF_REQUEST_SEND_OPTION_SYNCHRONOUS flag in the WDF_REQUEST_SEND_OPTIONS structure.

If WdfRequestSend fails, or if your driver sets the WDF_REQUEST_SEND_OPTION_SYNCHRONOUS flag, the driver can call WdfRequestGetStatus immediately after calling WdfRequestSend.

If WdfRequestSend succeeds and your driver does not set the WDF_REQUEST_SEND_OPTION_SYNCHRONOUS flag, the driver typically calls WdfRequestGetStatus from within a CompletionRoutine callback function.

If the driver sends the request synchronously, we recommend that the driver set a time-out value in the WDF_REQUEST_SEND_OPTIONS structure and the time-out flag in the Flags member of this structure.

If the driver supplies a time-out value, it should call WdfRequestAllocateTimer before calling WdfRequestSend. This ensures that WdfRequestSend will not fail if there are insufficient system resources to allocate a timer.

If the driver sets the WDF_REQUEST_SEND_OPTION_SYNCHRONOUS flag, it must call WdfRequestSend at IRQL = PASSIVE_LEVEL. If this flag is not set, the driver must call this method at IRQL <= DISPATCH_LEVEL. WdfRequestSend sends the request at the caller's IRQL.

A driver cannot call WdfRequestSend to send an I/O request to a USB pipe, if the driver has configured a continuous reader for the pipe.

When sending a request to a UMDF driver, a kernel-mode driver must follow the IRQL restrictions outlined in Supporting Kernel-Mode Clients in UMDF Drivers.

For more information about WdfRequestSend, see Forwarding I/O Requests.

Examples

The following code example is a shortened version of an EvtIoWrite callback function from the kmdf_fx2 sample driver. The function validates the request's buffer length, obtains a handle to the buffer, formats the request for a USB target, and sends the request.

VOID 
OsrFxEvtIoWrite(
    IN WDFQUEUE  Queue,
    IN WDFREQUEST  Request,
    IN size_t  Length
    )
{
    WDFUSBPIPE  pipe;
    NTSTATUS  status;
    WDFMEMORY  reqMemory;
    PDEVICE_CONTEXT  pDeviceContext;

    UNREFERENCED_PARAMETER(Queue);
    //
    // Check if the transfer size is valid.
    //
    if (Length > MAX_TRANSFER_BUFFER_SIZE) {
        status = STATUS_INVALID_PARAMETER;
        goto Exit;
    }
    //
    // Get driver-defined context space from
    // the device object. The driver stored the
    // pipe handle there.
    //
    pDeviceContext = GetDeviceContext(WdfIoQueueGetDevice(Queue));
    pipe = pDeviceContext->BulkWritePipe;
 
    //
    // Get a handle to a memory object that represents
    // the input buffer.
    //
    status = WdfRequestRetrieveInputMemory(Request, &reqMemory);
    if (!NT_SUCCESS(status)){
        goto Exit;
    }
    //
    // Format the request so it can be sent to a USB target.
    //
    status = WdfUsbTargetPipeFormatRequestForWrite(
                            pipe,
                            Request,
                            reqMemory,
                            NULL // Offsets
                            ); 
    if (!NT_SUCCESS(status)) {
        goto Exit;
    }
    //
    // Set a CompletionRoutine callback function.
    //
    WdfRequestSetCompletionRoutine(
                            Request,
                            EvtRequestReadCompletionRoutine,
                            pipe
                            );
    //
    // Send the request. If an error occurs, complete the request.
    //
    if (WdfRequestSend(
                       Request,
                       WdfUsbTargetPipeGetIoTarget(pipe),
                       WDF_NO_SEND_OPTIONS
                       ) == FALSE) {
        status = WdfRequestGetStatus(Request);
        goto Exit;
    }
Exit:
    if (!NT_SUCCESS(status)) {
        WdfRequestCompleteWithInformation(
                                          Request,
                                          status,
                                          0
                                          );
    }
    return;
}

Requirements

Requirement	Value
Target Platform	Universal
Minimum KMDF version	1.0
Minimum UMDF version	2.0
Header	wdfrequest.h (include Wdf.h)
Library	Wdf01000.sys (KMDF); WUDFx02000.dll (UMDF)
IRQL	See Remarks section.
DDI compliance rules	DeferredRequestCompleted(kmdf), DriverCreate(kmdf), InvalidReqAccess(kmdf), InvalidReqAccessLocal(kmdf), KmdfIrql(kmdf), ReqCompletionRoutine(kmdf), ReqMarkCancelableSend(kmdf), ReqSendFail(kmdf), ReqSendWhileSpinlock(kmdf), RequestCompleted(kmdf), RequestCompletedLocal(kmdf), RequestFormattedValid(kmdf), RequestGetStatusValid(kmdf), RequestSendAndForgetNoFormatting(kmdf), RequestSendAndForgetNoFormatting2(kmdf), SyncReqSend2(kmdf), WdfRequestSendSyncAtDispatch(kmdf), WdfRequestSendSyncAtDispatch2(kmdf)

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