WdfRequestRetrieveUnsafeUserOutputBuffer function (wdfrequest.h)

Article
04/18/2022

[Applies to KMDF only]

The WdfRequestRetrieveUnsafeUserOutputBuffer method retrieves an I/O request's output buffer, if the request's technique for accessing data buffers is neither buffered nor direct I/O.

Syntax

NTSTATUS WdfRequestRetrieveUnsafeUserOutputBuffer(
  [in]            WDFREQUEST Request,
  [in]            size_t     MinimumRequiredLength,
  [out]           PVOID      *OutputBuffer,
  [out, optional] size_t     *Length
);

Parameters

[in] Request

A handle to a framework request object.

[in] MinimumRequiredLength

The minimum buffer size, in bytes, that the driver needs to process the I/O request.

[out] OutputBuffer

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

WdfRequestRetrieveUnsafeUserOutputBuffer 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	This value is returned if one of the following occurs: The method was not called from within the driver's EvtIoInCallerContext callback function. The I/O request's I/O control code is IRP_MJ_WRITE or IRP_MJ_INTERNAL_DEVICE_CONTROL. The request specifies buffered I/O or direct I/O.
STATUS_BUFFER_TOO_SMALL	The MinimumRequiredLength parameter specifies a buffer size that is larger than the buffer's actual size.

This method might also return other NTSTATUS values.

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

Remarks

The WdfRequestRetrieveUnsafeUserOutputBuffer method must be called from an EvtIoInCallerContext callback function. After calling WdfRequestRetrieveUnsafeUserOutputBuffer, the driver must call WdfRequestProbeAndLockUserBufferForWrite.

The driver can call WdfRequestRetrieveUnsafeUserOutputBuffer if a request's I/O control code is IRP_MJ_READ or IRP_MJ_DEVICE_CONTROL.

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

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

Examples

For a code example that uses WdfRequestRetrieveUnsafeUserOutputBuffer, see WdfRequestProbeAndLockUserBufferForRead.

Requirements

Requirement	Value
Target Platform	Universal
Minimum KMDF version	1.0
Header	wdfrequest.h (include Wdf.h)
Library	Wdf01000.sys (see Framework Library Versioning.)
IRQL	PASSIVE_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)

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