EVT_WDF_IO_QUEUE_IO_READ callback function (wdfio.h)
[Applies to KMDF and UMDF]
A driver's EvtIoRead event callback function processes a specified read request.
Syntax
EVT_WDF_IO_QUEUE_IO_READ EvtWdfIoQueueIoRead;
void EvtWdfIoQueueIoRead(
[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 read.
Return value
None
Remarks
A driver registers an EvtIoRead callback function when it calls WdfIoQueueCreate. For more information about calling WdfIoQueueCreate, see Creating I/O Queues.
If a driver has registered an EvtIoRead callback function for a device's I/O queue, the callback function receives every read request from the queue. For more information, see Request Handlers.
The EvtIoRead callback function must process each received I/O request in some manner. For more information, see Processing I/O Requests.
Read requests require an output buffer, which receives data that the driver provides. For information about how the driver can access a read 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 EvtIoRead callback function should not call the following queue object methods:
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) |