WdfRequestRetrieveOutputMemory function (wdfrequest.h)
[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
NTSTATUS WdfRequestRetrieveOutputMemory(
[in] WDFREQUEST Request,
[out] WDFMEMORY *Memory
);
Parameters
[in] Request
A handle to a framework request object.
[out] Memory
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 |
---|---|
|
An input parameter is invalid. |
|
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. |
|
The request has already been completed. |
|
The output buffer's length is zero. |
|
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
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 | <=DISPATCH_LEVEL |
DDI compliance rules | DriverCreate(kmdf), InvalidReqAccess(kmdf), InvalidReqAccessLocal(kmdf), KmdfIrql(kmdf), KmdfIrql2(kmdf), KmdfIrqlExplicit(kmdf), MemAfterReqCompletedIntIoctl(kmdf), MemAfterReqCompletedIntIoctlA(kmdf), MemAfterReqCompletedIoctl(kmdf), MemAfterReqCompletedIoctlA(kmdf), MemAfterReqCompletedRead(kmdf), MemAfterReqCompletedReadA(kmdf), MemAfterReqCompletedWrite(kmdf), OutputBufferAPI(kmdf) |