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WdfIoTargetFormatRequestForWrite method

[Applies to KMDF and UMDF]

The WdfIoTargetFormatRequestForWrite method builds a write request for an I/O target but does not send the request.

Syntax


NTSTATUS WdfIoTargetFormatRequestForWrite(
  [in]           WDFIOTARGET       IoTarget,
  [in]           WDFREQUEST        Request,
  [in, optional] WDFMEMORY         InputBuffer,
  [in, optional] PWDFMEMORY_OFFSET InputBufferOffset,
  [in, optional] PLONGLONG         DeviceOffset
);

Parameters

IoTarget [in]

A handle to a local or remote I/O target object that was obtained from a previous call to WdfDeviceGetIoTarget or WdfIoTargetCreate, or from a method that a specialized I/O target supplies.

Request [in]

A handle to a framework request object. For more information, see the following Remarks section.

InputBuffer [in, optional]

A handle to a framework memory object. This object represents a buffer that contains data that will be sent to the I/O target. This parameter is optional and can be NULL. For more information about this parameter, see the following Remarks section.

InputBufferOffset [in, optional]

A pointer to a caller-allocated WDFMEMORY_OFFSET structure that supplies optional byte offset and length values. The framework uses these values to determine the beginning address and length, within the input buffer, for the data transfer. If this pointer is NULL, the data transfer begins at the beginning of the input buffer, and the transfer size is the buffer size.

DeviceOffset [in, optional]

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.Write.DeviceOffset member of the request's WDF_REQUEST_PARAMETERS structure. This pointer is optional. Most drivers set this pointer to NULL.

Return value

WdfIoTargetFormatRequestForWrite returns STATUS_SUCCESS if the operation succeeds. Otherwise, this method might return one of the following values:

Return codeDescription
STATUS_INVALID_PARAMETER

An invalid parameter was detected.

STATUS_INVALID_DEVICE_REQUEST

The transfer length was larger than the buffer length, or the I/O request was already queued to an I/O target.

STATUS_INSUFFICIENT_RESOURCES

The framework could not allocate system resources (typically memory).

STATUS_REQUEST_NOT_ACCEPTED

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.

Remarks

Use the WdfIoTargetFormatRequestForWrite method, followed by the WdfRequestSend method, to send write requests either synchronously or asynchronously. Alternatively, use the WdfIoTargetSendWriteSynchronously method to send write requests synchronously.

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:

  1. Specify the received request's handle for the WdfIoTargetFormatRequestForWrite method's Request parameter.

  2. Use the received request's input buffer for the WdfIoTargetFormatRequestForWrite method's InputBuffer parameter.

    The driver must call WdfRequestRetrieveInputMemory to obtain a handle to a framework memory object that represents the request's input buffer and must use that handle as the value for InputBuffer.

For more information about forwarding an I/O request, see Forwarding I/O Requests.

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:

  1. Create a new request object and supply its handle for the WdfIoTargetFormatRequestForWrite method's Request parameter.

    Call WdfRequestCreate to preallocate one or more request objects. You can reuse these request objects by calling WdfRequestReuse. Your driver's EvtDriverDeviceAdd callback function can preallocate request objects for a device.

  2. Provide buffer space, and supply the buffer's handle for the WdfIoTargetFormatRequestForWrite method's InputBuffer parameter.

    Your driver must specify this buffer space as a WDFMEMORY handle to framework-managed memory. Your driver can do either of the following:

    Note that if your driver calls WdfRequestRetrieveInputMemory and passes the memory handle to WdfIoTargetFormatRequestForWrite, the driver must not complete the received I/O request until after the driver deletes, reuses, or reformats the new, driver-created request object. (WdfIoTargetFormatRequestForWrite increments the memory object's reference count. Deleting, reusing, or reformatting a request object decrements the memory object's reference count.)

Some I/O targets accept write requests that have a zero-length buffer. For such I/O targets, your driver can specify NULL for the InputBuffer parameter.

After a driver calls WdfIoTargetFormatRequestForWrite to format an I/O request, it must call WdfRequestSend to send the request (either synchronously or asynchronously) to an I/O target.

Multiple calls to WdfIoTargetFormatRequestForWrite that use the same request do not cause additional resource allocations. Therefore, to reduce the chance that WdfRequestCreate will return STATUS_INSUFFICIENT_RESOURCES, your driver's EvtDriverDeviceAdd callback function can call WdfRequestCreate to preallocate one or more request objects for a device. The driver can subsequently reuse (call WdfRequestReuse), reformat (call WdfIoTargetFormatRequestForWrite), and resend (call WdfRequestSend) each request object without risking a STATUS_INSUFFICIENT_RESOURCES return value from a later call to WdfRequestCreate. All subsequent calls to WdfIoTargetFormatRequestForWrite for the reused request object will return STATUS_SUCCESS, if parameter values do not change. (If the driver does not call the same request-formatting method each time, additional resources might be allocated.)

For information about obtaining status information after an I/O request completes, see Obtaining Completion Information.

For more information about WdfIoTargetFormatRequestForWrite, see Sending I/O Requests to General I/O Targets.

For more information about I/O targets, see Using I/O Targets.

Examples

The following code example creates a framework memory object for a write request's input buffer, formats the write request, registers a CompletionRoutine callback function, and sends the write request to an I/O target.


WDFREQUEST  request;
NTSTATUS  status;
WDFMEMORY  memory;
WDF_OBJECT_ATTRIBUTES  attributes;

WDF_OBJECT_ATTRIBUTES_INIT(&attributes);
status = WdfMemoryCreate(
                         &attributes,
                         NonPagedPool,
                         DRIVER_TAG,
                         WRITE_BUF_SIZE,
                         &memory,
                         NULL
                         );

if (!NT_SUCCESS(status)) {
    return status;
}

status = WdfIoTargetFormatRequestForWrite(
                                          IoTarget,
                                          request,
                                          memory,
                                          NULL,
                                          NULL
                                          );
if (!NT_SUCCESS(status)) {
        return status;
}
WdfRequestSetCompletionRoutine(
                               request,
                               MyReadRequestCompletionRoutine,
                               targetInfo
                               );
if (WdfRequestSend(
                   request,
                   IoTarget,
                   WDF_NO_SEND_OPTIONS
                   ) == FALSE) {
        status = WdfRequestGetStatus(request);
}

Requirements

Target platform

Universal

Minimum KMDF version

1.0

Minimum UMDF version

2.0

Header

Wdfiotarget.h (include Wdf.h)

Library

Wdf01000.sys (KMDF);
WUDFx02000.dll (UMDF)

IRQL

<=DISPATCH_LEVEL

DDI compliance rules

DriverCreate, KmdfIrql, KmdfIrql2, RequestFormattedValid, RequestSendAndForgetNoFormatting, RequestSendAndForgetNoFormatting2

See also

EvtDriverDeviceAdd
WDF_REQUEST_PARAMETERS
WdfDeviceGetIoTarget
WdfIoTargetCreate
WdfIoTargetSendWriteSynchronously
WDFMEMORY_OFFSET
WdfMemoryCreate
WdfMemoryCreatePreallocated
WdfRequestCreate
WdfRequestRetrieveInputMemory
WdfRequestReuse
WdfRequestSend

 

 

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