WdfUsbTargetPipeFormatRequestForRead method

[Applies to KMDF and UMDF]

The WdfUsbTargetPipeFormatRequestForRead method builds a read request for a USB input pipe, but it does not send the request.

Syntax

NTSTATUS WdfUsbTargetPipeFormatRequestForRead(
  [in]            WDFUSBPIPE Pipe,
  [in]            WDFREQUEST Request,
  [in, optional]  WDFMEMORY ReadMemory,
  [in, optional]  PWDFMEMORY_OFFSET ReadOffset
);

Parameters

Pipe [in]

A handle to a framework pipe object that was obtained by calling WdfUsbInterfaceGetConfiguredPipe.

Request [in]

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

ReadMemory [in, optional]

A handle to a framework memory object. This object represents a buffer that will receive data from the pipe. The buffer size must be a multiple of the pipe's maximum packet size unless the driver has called WdfUsbTargetPipeSetNoMaximumPacketSizeCheck. For more information about this buffer, see the following Remarks section.

ReadOffset [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 read buffer, for the data transfer. If this pointer is NULL, the data transfer begins at the beginning of the buffer, and the transfer size is the buffer size.

Return value

WdfUsbTargetPipeFormatRequestForRead 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 WdfUsbTargetPipeFormatRequestForRead, followed by WdfRequestSend, to send read requests either synchronously or asynchronously. Alternatively, use the WdfUsbTargetPipeReadSynchronously method to send read requests synchronously.

The pipe that the Pipe parameter specifies must be an input pipe, and the pipe's type must be WdfUsbPipeTypeBulk or WdfUsbPipeTypeInterrupt.

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 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 WdfUsbTargetPipeFormatRequestForRead method's Request parameter.

2. Use the received request's output buffer for the WdfUsbTargetPipeFormatRequestForRead method's ReadMemory parameter.

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

For more information about forwarding an I/O request, see Forwarding I/O Requests.

Drivers often divide received I/O requests into smaller requests that they send to an I/O target, so your driver might create new requests.

To create a new I/O request:

1. Create a new request object and supply its handle for the WdfUsbTargetPipeFormatRequestForRead 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 WdfUsbTargetPipeFormatRequestForRead method's ReadMemory 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 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 WdfRequestRetrieveOutputMemory and passes the memory handle to WdfUsbTargetPipeFormatRequestForRead, the driver must not complete the received I/O request until after the driver deletes, reuses, or reformats the new, driver-created request object. (WdfUsbTargetPipeFormatRequestForRead increments the memory object's reference count. Deleting, reusing, or reformatting a request object decrements the memory object's reference count.)

After calling WdfUsbTargetPipeFormatRequestForRead 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 WdfUsbTargetPipeFormatRequestForRead 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 WdfUsbTargetPipeFormatRequestForRead), 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 WdfUsbTargetPipeFormatRequestForRead 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 WdfUsbTargetPipeFormatRequestForRead method and USB I/O targets, see USB I/O Targets.

Examples

The following code example is from the kmdf_fx2 sample driver. This example is an EvtIoRead callback function that forwards a read request to a USB pipe. The example calls WdfRequestRetrieveOutputMemory to obtain the request's output buffer, and then it formats the read request so that the request can be sent to a USB pipe. Next, the example registers a CompletionRoutine callback function. Finally, it sends the request to the USB pipe.

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

    //
    // First, validate input parameters.
    //
    if (Length > TEST_BOARD_TRANSFER_BUFFER_SIZE) {
        status = STATUS_INVALID_PARAMETER;
        goto Exit;
    }

    pDeviceContext = GetDeviceContext(WdfIoQueueGetDevice(Queue));
 
    pipe = pDeviceContext->BulkReadPipe;
 
    status = WdfRequestRetrieveOutputMemory(
                                            Request,
                                            &reqMemory
                                            );
    if (!NT_SUCCESS(status)){
        goto Exit;
    }
 
    status = WdfUsbTargetPipeFormatRequestForRead(
                                                  pipe,
                                                  Request,
                                                  reqMemory,
                                                  NULL
                                                  ); 
    if (!NT_SUCCESS(status)) {
        goto Exit;
    }

    WdfRequestSetCompletionRoutine(
                                   Request,
                                   EvtRequestReadCompletionRoutine,
                                   pipe
                                   );
    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

See also

WDFMEMORY_OFFSET

WdfRequestCompleteWithInformation

WdfRequestGetStatus

WdfRequestSend

WdfRequestSetCompletionRoutine

WdfUsbInterfaceGetConfiguredPipe

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