WdfIoTargetWdmGetTargetFileHandle function (wdfiotarget.h)

Artikel
04/18/2022

[Applies to KMDF and UMDF]

The WdfIoTargetWdmGetTargetFileHandle method returns a handle to the file that is associated with a specified remote I/O target.

Syntax

HANDLE WdfIoTargetWdmGetTargetFileHandle(
  [in] WDFIOTARGET IoTarget
);

Parameters

[in] IoTarget

A handle to a remote I/O target object. This handle was obtained from a previous call to WdfIoTargetCreate.

Return value

If the driver specified an object name when it called WdfIoTargetOpen, WdfIoTargetWdmGetTargetFileHandle returns the file handle that is associated with the specified I/O target. Otherwise WdfIoTargetWdmGetTargetFileHandle returns NULL.

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

Remarks

For KMDF, the returned file handle is a kernel-mode handle that is valid in an arbitrary thread context. For information about how a driver can use this file handle, see Using a File Handle.

The file handle that the WdfIoTargetWdmGetTargetFileHandle method returns is valid until the driver calls WdfIoTargetClose or WdfIoTargetCloseForQueryRemove, or until the remote I/O target object is deleted. If the driver provides an EvtCleanupCallback function for the remote I/O target object, and if the object is deleted before the remote I/O target is closed, the pointer is valid until the EvtCleanupCallback function returns.

If the driver attempts to access the WDM device object after it has been removed, the driver can cause the system to crash. The toastmon sample demonstrates how the driver can provide an EvtIoTargetQueryRemove callback function so that it is notified if the I/O target is removed.

For UMDF, WdfIoTargetWdmGetTargetFileHandle returns a Win32 HANDLE valid only in the current process. A legacy UMDF driver (version 1.x) calls IWDFDevice::RetrieveDeviceName to get the name of the underlying kernel-mode device and then opens a handle to it with CreateFile. The driver can then send I/O directly to the lower device(s) using DeviceIoControl. Starting in UMDF 2.15, UMDF v2 drivers can open the local I/O target by file (WDF_IO_TARGET_OPEN_PARAMS_INIT_OPEN_BY_FILE) and retrieve the file handle using WdfIoTargetWdmGetTargetFileHandle. The framework opens and closes the file handle when the remote target is closed or deleted. The file handle remains valid within the contract of WdfIoTargetWdmGetTargetFileHandle described above.

Warning

If a UMDF v2 driver calls WdfIoTargetWdmGetTargetFileHandle to obtain the Win32 handle from a remote target opened using WDF_IO_TARGET_OPEN_PARAMS_INIT_OPEN_BY_FILE, do not submit overlapped/asynchronous I/O with APIs like DeviceIoControl. Doing so can crash the process hosting the driver. If the driver must submit overlapped I/O, it must also set the low-order bit of the hEvent member of the OVERLAPPED structure. This is because the framework internally binds the handle to an I/O completion port. A valid event handle whose low-order bit is set keeps I/O completion from being queued to the completion port.

For more information about WdfIoTargetWdmGetTargetFileHandle, see Obtaining Information About a General I/O Target.

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

Examples

The following code example obtains a handle to the file that is associated with a specified remote I/O target.

HANDLE h;

h = WdfIoTargetWdmGetTargetFileHandle(IoTarget);

A legacy UMDF driver (version 1.x) calls IWDFDevice::RetrieveDeviceName to get the name of the underlying kernel-mode device and then open a handle to it with CreateFile. The driver then sends I/O directly to the device using DeviceIoControl.

Starting in UMDF 2.15, the driver opens the local I/O target by file and retrieves its handle. The framework opens and closes the file handle. The file handle remains valid within the contract of WdfIoTargetWdmGetTargetFileHandle.

NTSTATUS status;

WDF_IO_TARGET_OPEN_PARAMS params;

WDFIOTARGET ioTarget = NULL;

HANDLE handle = NULL;

status = WdfIoTargetCreate(Device, &attr, &ioTarget);

if (!NT_SUCCESS(status)) {

    // error handling

}

WDF_IO_TARGET_OPEN_PARAMS_INIT_OPEN_BY_FILE(&params, NULL);

status = WdfIoTargetOpen(ioTarget, &params);

if (!NT_SUCCESS(status)) {

    // error handling

}

handle = WdfIoTargetWdmGetTargetFileHandle(ioTarget);

if (handle == NULL) {

    // error handling

}

if (ioTarget != NULL) {
    WdfIoTargetClose(ioTarget);
}
// You can now call DeviceIoControl(handle, ...) etc.
// NOTE: See Warning above on submitting overlapped or asynchronous I/O

Requirements

Requirement	Value
Target Platform	Universal
Minimum KMDF version	1.0
Minimum UMDF version	2.15
Header	wdfiotarget.h (include Wdf.h)
Library	Wdf01000.sys (see Framework Library Versioning.)
IRQL	<=DISPATCH_LEVEL
DDI compliance rules	DriverCreate(kmdf), KmdfIrql(kmdf), KmdfIrql2(kmdf), KmdfIrqlExplicit(kmdf)

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