WdfRequestRetrieveOutputBuffer - NtDoc
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// wdfrequest.h
NTSTATUS WdfRequestRetrieveOutputBuffer(
[in] WDFREQUEST Request,
[in] size_t MinimumRequiredSize,
[out] PVOID *Buffer,
[out, optional] size_t *Length
);
View the official Windows Driver Kit DDI referenceNo description available.
[Applies to KMDF and UMDF]
The WdfRequestRetrieveOutputBuffer method retrieves an I/O request's output buffer.
Request [in]A handle to a framework request object.
MinimumRequiredSize [in]The minimum buffer size, in bytes, that the driver needs to process the I/O request.
Buffer [out]A pointer to a location that receives the buffer's address.
Length [out, optional]A pointer to a location that receives the buffer's size, in bytes. This parameter is optional and can be NULL.
WdfRequestRetrieveOutputBuffer 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_BUFFER_TOO_SMALL | The output buffer's length is zero, or the MinimumRequiredSize parameter specifies a buffer size that is larger than the buffer's actual size. |
| 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_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.
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.
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;
}
WdfRequestRetrieveOutputMemory