WdfRequestRetrieveOutputMemory method

[Applies to KMDF and UMDF]

The WdfRequestRetrieveOutputMemory method retrieves a handle to a framework memory object that represents an I/O request's output buffer.

Syntax

C++


NTSTATUS WdfRequestRetrieveOutputMemory(
  [in]   WDFREQUEST Request,
  [out]  WDFMEMORY *Memory
);

Parameters

Request [in]: A handle to a framework request object.
Memory [out]: A pointer to a location that receives a handle to a framework memory object.

Return value

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

Return code	Description
STATUS_INVALID_PARAMETER	An input parameter is invalid.
STATUS_INVALID_DEVICE_REQUEST	The request type is not valid or the request is using neither buffered nor direct I/O. For more information about supported methods for accessing data buffers, see the following Remarks section.
STATUS_INTERNAL_ERROR	The request has already been completed.
STATUS_BUFFER_TOO_SMALL	The output buffer's length is zero.
STATUS_INSUFFICIENT_RESOURCES	There is insufficient memory.

This method might also return other NTSTATUS values.

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

Remarks

A request's output buffer receives information, such as data from a disk, that the driver provides to the originator of the request. Your driver can call WdfRequestRetrieveOutputMemory to obtain the output buffer for a read request or a device I/O control request, but not for a write request (because write requests do not provide output data).

The WdfRequestRetrieveOutputMemory method retrieves the output buffer for I/O requests that use the buffered I/O method or the direct I/O method for accessing data buffers. If the request's I/O control code is IRP_MJ_INTERNAL_DEVICE_CONTROL, or if the request came from another kernel-mode driver, WdfRequestRetrieveOutputMemory also supports I/O requests that use neither buffered nor direct I/O.

If WdfRequestRetrieveOutputMemory returns STATUS_SUCCESS, the driver receives a handle to a framework memory object that represents the output buffer. To access the buffer, the driver must call WdfMemoryGetBuffer.

The driver can access the retrieved framework memory object until it completes the I/O request that the Request parameter represents.

Instead of calling WdfRequestRetrieveOutputMemory, the driver can call WdfRequestRetrieveOutputBuffer, which retrieves the buffer's address and length.

For more information about WdfRequestRetrieveOutputMemory, see Accessing Data Buffers in Framework-Based Drivers.

Examples

The following code example shows how an EvtIoRead callback function can obtain a handle to the framework memory object that represents a read request's output buffer. The example then formats and sends the read request to a USB I/O target.


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

    //
    // The driver previously stored a pipe handle in 
    // the device object's context space.
    //
    pDeviceContext = GetDeviceContext(WdfIoQueueGetDevice(Queue));
    pipe = pDeviceContext->BulkReadPipe;

    //
    // Get output memory.
    //
    status = WdfRequestRetrieveOutputMemory(
                                            Request,
                                            &reqMemory
                                            );
    if(!NT_SUCCESS(status)){
        goto Exit;
    }
    //
    // Format the request.
    //
    status = WdfUsbTargetPipeFormatRequestForRead(
                                           pipe,
                                           Request,
                                           reqMemory,
                                           NULL
                                           ); 
    if (!NT_SUCCESS(status)) {
        goto Exit;
    }
    WdfRequestSetCompletionRoutine(
                                   Request,
                                   EvtRequestReadCompletionRoutine,
                                   pipe
                                   );
    //
    // Send the request.
    //
    if (WdfRequestSend(
                       Request,
                       WdfUsbTargetPipeGetIoTarget(pipe),
                       WDF_NO_SEND_OPTIONS
                       ) == FALSE) {
        status = WdfRequestGetStatus(Request);
        goto Exit;
    }
Exit:
    //
    // Complete the request now if an error occurred.
    //
    if (!NT_SUCCESS(status)) {
        WdfRequestCompleteWithInformation(
                                          Request,
                                          status,
                                          0
                                          );
    }
    return;
}

Requirements

Minimum KMDF version	1.0
Minimum UMDF version	2.0
Header	Wdfrequest.h (include Wdf.h)
Library	Wdf01000.sys (KMDF); WUDFx02000.dll (UMDF)
IRQL	<=DISPATCH_LEVEL
DDI compliance rules	DriverCreate, InvalidReqAccess, InvalidReqAccessLocal, KmdfIrql, KmdfIrql2, MemAfterReqCompletedIntIoctl, MemAfterReqCompletedIntIoctlA, MemAfterReqCompletedIoctl, MemAfterReqCompletedIoctlA, MemAfterReqCompletedRead, MemAfterReqCompletedReadA, MemAfterReqCompletedWrite, OutputBufferAPI