[Applies to KMDF and UMDF]
The WdfIoTargetSendReadSynchronously method builds a read request and sends it synchronously to an I/O target.
NTSTATUS WdfIoTargetSendReadSynchronously( WDFIOTARGET IoTarget, WDFREQUEST Request, PWDF_MEMORY_DESCRIPTOR OutputBuffer, PLONGLONG DeviceOffset, PWDF_REQUEST_SEND_OPTIONS RequestOptions, PULONG_PTR BytesRead );
A handle to a framework request object. This parameter is optional and can be NULL. For more information about this parameter, see the following Remarks section.
A pointer to a caller-allocated WDF_MEMORY_DESCRIPTOR structure that describes the buffer that will receive data from the device.This parameter is optional and can be NULL. For more information about this parameter, see the following Remarks section.
A pointer to a location that specifies a starting offset for the transfer. The I/O target (that is, the next-lower driver) defines how to use this value. For example, the drivers in a disk's driver stack might specify an offset from the beginning of the disk. The I/O target obtains this information in the Parameters.Read.DeviceOffset member of the request's WDF_REQUEST_PARAMETERS structure. This pointer is optional. Most drivers set this pointer to NULL.
A pointer to a caller-allocated WDF_REQUEST_SEND_OPTIONS structure that specifies options for the read request. This pointer is optional and can be NULL.
A pointer to a location that receives the number of bytes read, if the operation succeeds. This pointer is optional and can be NULL.
If the operation succeeds, WdfIoTargetSendReadSynchronously returns after the I/O request completes, and the return value is the request's completion status value. Otherwise, this method might return one of the following values:
||An invalid parameter was detected.|
||The size of the WDF_REQUEST_SEND_OPTIONS structure that the RequestOptions parameter pointed to was incorrect.|
||The I/O request was already queued to an I/O target.|
||The framework could not allocate system resources (typically memory).|
||The driver supplied a time-out value and the request did not complete within the allotted time.|
||The I/O request packet (IRP) that the Request parameter represents does not provide enough IO_STACK_LOCATION structures to allow the driver to forward the request.|
This method also might return other NTSTATUS values.
A bug check occurs if the driver supplies an invalid object handle.
Use the WdfIoTargetSendReadSynchronously method to send read requests synchronously. To send read requests asynchronously, use the WdfIoTargetFormatRequestForRead method, followed by the WdfRequestSend method.
WdfIoTargetSendReadSynchronously does not return until the request has completed, unless the driver supplies a time-out value in the RequestOptions parameter's WDF_REQUEST_SEND_OPTIONS structure, or unless an error is detected.
You can forward an I/O request that your driver received in an I/O queue, or you can create and send a new request. In either case, the framework requires a request object and some buffer space.
To forward an I/O request that your driver received in an I/O queue:
- Specify the received request's handle for the Request parameter.
Use the received request's output buffer for the WdfIoTargetSendReadSynchronously method's OutputBuffer parameter.
The driver must call WdfRequestRetrieveOutputMemory to obtain a handle to a framework memory object that represents the request's output buffer. Then the driver must place that handle in the WDF_MEMORY_DESCRIPTOR structure that the driver supplies for the OutputBuffer parameter.
Drivers often divide received I/O requests into smaller requests that they send to an I/O target, so your driver might create new requests.
To create a new I/O request:
Supply a NULL request handle for the WdfIoTargetSendReadSynchronously method's Request parameter, or create a new request object and supply its handle:
- If you supply a NULL request handle, the framework uses an internal request object. This technique is simple to use, but the driver cannot cancel the request.
- If you call WdfRequestCreate to create one or more request objects, you can reuse these request objects by calling WdfRequestReuse. This technique enables your driver's EvtDriverDeviceAdd callback function to preallocate request objects for a device. Additionally, another driver thread can call WdfRequestCancelSentRequest to cancel the request, if necessary.
Your driver can specify a non-NULL RequestOptions parameter, whether the driver provides a non-NULL or a NULL Request parameter. You can, for example, use the RequestOptions parameter to specify a time-out value.
Provide buffer space for the WdfIoTargetSendReadSynchronously method's OutputBuffer parameter.
Your driver can specify this buffer space as a locally allocated buffer, as a WDFMEMORY handle, or as a memory descriptor list (MDL). You can use whichever method is most convenient.
If necessary, the framework converts the buffer description to one that is correct for the I/O target's method for accessing data buffers.
The following techniques to specify buffer space are available:
Supply a local buffer.
Because WdfIoTargetSendReadSynchronously handles I/O requests synchronously, the driver can create request buffers that are local to the calling routine, as the following code example shows.
WDF_MEMORY_DESCRIPTOR MemoryDescriptor; MY_BUFFER_TYPE MyBuffer; WDF_MEMORY_DESCRIPTOR_INIT_BUFFER(&MemoryDescriptor, (PVOID) &MyBuffer, sizeof(MyBuffer));
Supply a WDFMEMORY handle.
WDF_MEMORY_DESCRIPTOR MemoryDescriptor; WDFMEMORY MemoryHandle = NULL; status = WdfMemoryCreate(NULL, NonPagedPool, POOL_TAG, MY_BUFFER_SIZE, &MemoryHandle, NULL); WDF_MEMORY_DESCRIPTOR_INIT_HANDLE(&MemoryDescriptor, MemoryHandle, NULL);
Alternatively, the driver can call WdfRequestRetrieveOutputMemory to obtain a handle to a framework memory object that represents a received I/O request's output buffer, if you want the driver to pass that buffer's contents to the I/O target. The driver must not complete the received I/O request until the new request that WdfIoTargetSendReadSynchronously sends to the I/O target has been deleted, reused, or reformatted. (WdfIoTargetSendReadSynchronously increments the memory object's reference count. Deleting, reusing, or reformatting a request object decrements the memory object's reference count.)
Supply an MDL.
Drivers can obtain the MDL that is associated with a received I/O request by calling WdfRequestRetrieveOutputWdmMdl.
- Supply a local buffer.
For information about obtaining status information after an I/O request completes, see Obtaining Completion Information.
For more information about WdfIoTargetSendReadSynchronously, see Sending I/O Requests to General I/O Targets.
For more information about I/O targets, see Using I/O Targets.
The following code example creates a framework memory object, initializes a WDF_MEMORY_DESCRIPTOR structure, and passes the structure to WdfIoTargetSendReadSynchronously. This example specifies NULL for the request object handle, so the framework will create a new request object for the I/O target.
WDF_MEMORY_DESCRIPTOR MemoryDescriptor; WDFMEMORY MemoryHandle = NULL; ULONG_PTR bytesRead = NULL; status = WdfMemoryCreate( NULL, NonPagedPool, POOL_TAG, MY_BUFFER_SIZE, &MemoryHandle, NULL ); WDF_MEMORY_DESCRIPTOR_INIT_HANDLE( &MemoryDescriptor, MemoryHandle, NULL ); status = WdfIoTargetSendReadSynchronously( ioTarget, NULL, &MemoryDescriptor, NULL, NULL, &bytesRead );
|Minimum KMDF version||1.0|
|Minimum UMDF version||2.0|
|Header||wdfiotarget.h (include Wdf.h)|
|Library||Wdf01000.sys (KMDF); WUDFx02000.dll (UMDF)|
|DDI compliance rules||DeferredRequestCompleted, DriverCreate, InternalIoctlReqs, IoctlReqs, KmdfIrql, KmdfIrql2, RequestCompleted, RequestCompletedLocal, SyncReqSend, WriteReqs|