EVT_WDF_IO_QUEUE_IO_WRITE callback function (wdfio.h)

Article
10/21/2021

[Applies to KMDF and UMDF]

A driver's EvtIoWrite event callback function processes a specified write request.

Syntax

EVT_WDF_IO_QUEUE_IO_WRITE EvtWdfIoQueueIoWrite;

void EvtWdfIoQueueIoWrite(
  [in] WDFQUEUE Queue,
  [in] WDFREQUEST Request,
  [in] size_t Length
)
{...}

Parameters

[in] Queue

A handle to the framework queue object that is associated with the I/O request.

[in] Request

A handle to a framework request object.

[in] Length

The number of bytes to be written.

Return value

None

Remarks

A driver registers an EvtIoWrite callback function when it calls WdfIoQueueCreate. For more information about calling WdfIoQueueCreate, see Creating I/O Queues.

If a driver has registered an EvtIoWrite callback function for a device's I/O queue, the callback function receives every write request from the queue. For more information, see Request Handlers.

The EvtIoWrite callback function must process each received I/O request in some manner. For more information, see Processing I/O Requests.

Write requests require an input buffer, which contains data that the driver receives. For information about how the driver can access a write request's buffer, see Accessing Data Buffers in Framework-Based Drivers.

This callback function can be called at IRQL <= DISPATCH_LEVEL, unless the ExecutionLevel member of the device or driver's WDF_OBJECT_ATTRIBUTES structure is set to WdfExecutionLevelPassive.

If the IRQL is PASSIVE_LEVEL, the framework calls the callback function within a critical region.

For more information about IRQL levels for request handlers, see Using Automatic Synchronization.

A driver's EvtIoWrite callback function should not call the following queue object methods:

WdfIoQueueDrainSynchronously

WdfIoQueuePurgeSynchronously

WdfIoQueueStopSynchronously

Requirements

Requirement	Value
Target Platform	Universal
Minimum KMDF version	1.0
Minimum UMDF version	2.0
Header	wdfio.h (include Wdf.h)
IRQL	<= DISPATCH_LEVEL (see Remarks section)