WdfRequestRetrieveOutputBuffer function (wdfrequest.h)
[Applies to KMDF and UMDF]
The WdfRequestRetrieveOutputBuffer method retrieves an I/O request's output buffer.
Syntax
NTSTATUS WdfRequestRetrieveOutputBuffer(
[in] WDFREQUEST Request,
[in] size_t MinimumRequiredSize,
[out] PVOID *Buffer,
[out, optional] size_t *Length
);
Parameters
[in] Request
A handle to a framework request object.
[in] MinimumRequiredSize
The minimum buffer size, in bytes, that the driver needs to process the I/O request.
[out] Buffer
A pointer to a location that receives the buffer's address.
[out, optional] Length
A pointer to a location that receives the buffer's size, in bytes. This parameter is optional and can be NULL.
Return value
WdfRequestRetrieveOutputBuffer 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 output buffer's length is zero, or the MinimumRequiredSize parameter specifies a buffer size that is larger than the buffer's actual size. |
|
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. |
|
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 WdfRequestRetrieveOutputBuffer 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 WdfRequestRetrieveOutputBuffer 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, WdfRequestRetrieveOutputBuffer also supports I/O requests that use neither buffered nor direct I/O.
If WdfRequestRetrieveOutputBuffer returns STATUS_SUCCESS, the driver receives the address and, optionally, the size of the output buffer.
The driver can access the retrieved buffer until it completes the I/O request that the Request parameter represents.
Instead of calling WdfRequestRetrieveOutputBuffer, the driver can call WdfRequestRetrieveOutputMemory, which creates a framework memory object that represents the buffer.
For more information about WdfRequestRetrieveOutputBuffer, see Accessing Data Buffers in Framework-Based Drivers.
Examples
The following code example is part of an EvtIoDeviceControl callback function. This example obtains a USB device's configuration descriptor and places the descriptor in the I/O request's output buffer.
VOID
MyEvtIoDeviceControl(
IN WDFQUEUE Queue,
IN WDFREQUEST Request,
IN size_t OutputBufferLength,
IN size_t InputBufferLength,
IN ULONG IoControlCode
)
{
WDFDEVICE device;
PDEVICE_CONTEXT pDevContext;
size_t bytesReturned = 0;
NTSTATUS status;
device = WdfIoQueueGetDevice(Queue);
//
// GetDeviceContext is a driver-defined function
// to retrieve device object context space.
//
pDevContext = GetDeviceContext(device);
switch(IoControlCode) {
case IOCTL_OSRUSBFX2_GET_CONFIG_DESCRIPTOR: {
PUSB_CONFIGURATION_DESCRIPTOR configurationDescriptor = NULL;
USHORT requiredSize;
//
// First, get the size of the USB configuration descriptor.
//
status = WdfUsbTargetDeviceRetrieveConfigDescriptor(
pDevContext->UsbDevice,
NULL,
&requiredSize
);
if (status == STATUS_BUFFER_TOO_SMALL) {
break;
}
//
// Get the buffer. Make sure the buffer is big
// enough to hold the configuration descriptor.
//
status = WdfRequestRetrieveOutputBuffer(
Request,
(size_t)requiredSize,
&configurationDescriptor,
NULL
);
if(!NT_SUCCESS(status)){
break;
}
//
// Now get the config descriptor.
//
status = WdfUsbTargetDeviceRetrieveConfigDescriptor(
pDevContext->UsbDevice,
configurationDescriptor,
&requiredSize
);
if (!NT_SUCCESS(status)) {
break;
}
bytesReturned = requiredSize;
}
break;
...
(Other case statements removed.)
...
default:
status = STATUS_INVALID_DEVICE_REQUEST;
break;
}
//
// Complete the request.
//
WdfRequestCompleteWithInformation(
Request,
status,
bytesReturned
);
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 | BufAfterReqCompletedIntIoctl(kmdf), BufAfterReqCompletedIntIoctlA(kmdf), BufAfterReqCompletedIoctl(kmdf), BufAfterReqCompletedIoctlA(kmdf), BufAfterReqCompletedRead(kmdf), BufAfterReqCompletedReadA(kmdf), BufAfterReqCompletedWrite(kmdf), DriverCreate(kmdf), InvalidReqAccess(kmdf), InvalidReqAccessLocal(kmdf), KmdfIrql(kmdf), KmdfIrql2(kmdf), KmdfIrqlExplicit(kmdf), OutputBufferAPI(kmdf) |