WdfUsbTargetDeviceFormatRequestForControlTransfer method

[Applies to KMDF and UMDF]

The WdfUsbTargetDeviceFormatRequestForControlTransfer method builds a USB control transfer request, but it does not send the request.

Syntax

NTSTATUS WdfUsbTargetDeviceFormatRequestForControlTransfer(
  [in]            WDFUSBDEVICE UsbDevice,
  [in]            WDFREQUEST Request,
  [in]            PWDF_USB_CONTROL_SETUP_PACKET SetupPacket,
  [in, optional]  WDFMEMORY TransferMemory,
  [in, optional]  PWDFMEMORY_OFFSET TransferOffset
);

Parameters

UsbDevice [in]

A handle to a USB device object that was obtained from a previous call to WdfUsbTargetDeviceCreateWithParameters.

Request [in]

A handle to a framework request object. For more information, see the following Remarks section.

SetupPacket [in]

A pointer to a caller-allocated WDF_USB_CONTROL_SETUP_PACKET structure that describes the control transfer.

TransferMemory [in, optional]

A handle to a framework memory object that describes either an input or an output buffer, depending on the device-specific command. This pointer is optional and can be NULL. For more information, see the following Remarks section.

TransferOffset [in, optional]

A pointer to a caller-allocated WDFMEMORY_OFFSET structure that supplies optional byte offset and length values. The framework uses these values to determine the beginning address and length, within the buffer that TransferMemory specifies. If this pointer is NULL, the framework uses the entire buffer.

Return value

WdfUsbTargetDeviceFormatRequestForControlTransfer returns STATUS_SUCCESS if the operation succeeds. Otherwise, this method can return one of the following values:

This method also might return other NTSTATUS values.

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

Remarks

Use WdfUsbTargetDeviceFormatRequestForControlTransfer, followed by WdfRequestSend, to send a USB control transfer request either synchronously or asynchronously. Alternatively, use the WdfUsbTargetDeviceSendControlTransferSynchronously method to send a request synchronously.

You can forward an I/O request that your driver received in an I/O queue, or you can create and send a new request. In either case, the framework requires a request object and, depending on the type of control transfer, possibly some buffer space.

To forward an I/O request that your driver received in an I/O queue:

1. Specify the received request's handle for the WdfUsbTargetDeviceFormatRequestForControlTransfer method's Request parameter.

2. Use the received request's input or output buffer for the TransferMemory parameter.

   The driver must call WdfRequestRetrieveInputMemory or WdfRequestRetrieveOutputMemory to obtain a handle to a framework memory object that represents the request's input or output buffer, and use that handle as the value for TransferMemory.

To create a new I/O request and a new buffer:

1. Create a new request object and supply its handle for the WdfUsbTargetDeviceFormatRequestForControlTransfer method's Request parameter.

   Call WdfRequestCreate to preallocate one or more request objects. You can reuse these request objects by calling WdfRequestReuse. Your driver's EvtDriverDeviceAdd callback function can preallocate request objects for a device.

2. Provide buffer space, and supply the buffer's handle for the WdfUsbTargetDeviceFormatRequestForControlTransfer method's TransferMemory parameter.

   Your driver must specify this buffer space as a WDFMEMORY handle to framework-managed memory. Your driver can do either of the following:

   • Call WdfMemoryCreate or WdfMemoryCreatePreallocated to create a new memory buffer, if you want the driver to pass a new buffer to the I/O target.
   • Call WdfRequestRetrieveInputMemory or WdfRequestRetrieveOutputMemory to obtain a handle to the memory object that represents a received I/O request's buffer, if you want the driver to pass that buffer's contents to the I/O target.

   Note that if your driver calls WdfRequestRetrieveInputMemory or WdfRequestRetrieveOutputMemory and passes the memory handle to WdfUsbTargetDeviceFormatRequestForControlTransfer, the driver must not complete the received I/O request until after the driver deletes, reuses, or reformats the new, driver-created request object. (WdfUsbTargetDeviceFormatRequestForControlTransfer increments the memory object's reference count. Deleting, reusing, or reformatting a request object decrements the memory object's reference count.)

After calling WdfUsbTargetDeviceFormatRequestForControlTransfer to format an I/O request, the driver must call WdfRequestSend to send the request (either synchronously or asynchronously) to an I/O target.

Multiple calls to WdfUsbTargetDeviceFormatRequestForControlTransfer that use the same request do not cause additional resource allocations. Therefore, to reduce the chance that WdfRequestCreate will return STATUS_INSUFFICIENT_RESOURCES, your driver's EvtDriverDeviceAdd callback function can call WdfRequestCreate to preallocate one or more request objects for a device. The driver can subsequently reuse (call WdfRequestReuse), reformat (call WdfUsbTargetDeviceFormatRequestForControlTransfer), and resend (call WdfRequestSend) each request object without risking a STATUS_INSUFFICIENT_RESOURCES return value from a later call to WdfRequestCreate. All subsequent calls to WdfUsbTargetDeviceFormatRequestForControlTransfer for the reused request object will return STATUS_SUCCESS, if parameter values do not change. (If the driver does not call the same request-formatting method each time, additional resources might be allocated.)

The framework sets the USBD_SHORT_TRANSFER_OK flag in its internal URB. Setting this flag allows the last packet of a data transfer to be less than the maximum packet size.

For information about obtaining status information after an I/O request completes, see Obtaining Completion Information.

For more information about the WdfUsbTargetDeviceFormatRequestForControlTransfer method and USB I/O targets, see USB I/O Targets.

Examples

The following code example creates a request object and a memory object, and then it initializes a WDF_USB_CONTROL_SETUP_PACKET structure for a "get status" control transfer. Next, the example calls WdfUsbTargetDeviceFormatRequestForControlTransfer to format the request. Then, the example sets a CompletionRoutine callback function and sends the request to an I/O target.

WDF_USB_CONTROL_SETUP_PACKET packet;
NTSTATUS status;
WDF_OBJECT_ATTRIBUTES attributes;
WDFMEMORY memHandle;

WDF_OBJECT_ATTRIBUTES_INIT(&attributes);

status = WdfRequestCreate(
                          &attributes,
                          WdfUsbTargetDeviceGetIoTarget(
                              UsbTargetDevice,
                              &request
                              )
                          );
if (!NT_SUCCESS(status)){
    return status;
}

WDF_OBJECT_ATTRIBUTES_INIT(&attributes);
attributes.ParentObject = request;
status = WdfMemoryCreate(
                         &attributes,
                         NonPagedPool,
                         0,
                         sizeof(USHORT),
                         &memHandle,
                         NULL
                         );
if (!NT_SUCCESS(status)){
    return status;
}

WDF_USB_CONTROL_SETUP_PACKET_INIT_GET_STATUS(
                                             &packet,
                                             BmRequestToDevice,
                                             0
                                             );
status = WdfUsbTargetDeviceFormatRequestForControlTransfer(
                         UsbTargetDevice,
                         request,
                         &packet,
                         memHandle,
                         NULL
                         );
if (!NT_SUCCESS(status)){
    return status;
}
WdfRequestSetCompletionRoutine(
                               request,
                               MyCompletionRoutine,
                               NULL
                               );
if (WdfRequestSend(
                   request,
                   WdfUsbTargetDeviceGetIoTarget(UsbTargetDevice),
                   NULL
                   ) == FALSE) {
    status = WdfRequestGetStatus(request);
}

Requirements

See also

WDF_USB_CONTROL_SETUP_PACKET

WDF_USB_CONTROL_SETUP_PACKET_INIT_GET_STATUS

WdfUsbTargetDeviceSendControlTransferSynchronously

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