记录两个函数

直接贴WRK的源码吧，包括注释

NTSTATUS
IoGetDeviceObjectPointer(
    IN PUNICODE_STRING ObjectName,
    IN ACCESS_MASK DesiredAccess,
    OUT PFILE_OBJECT *FileObject,
    OUT PDEVICE_OBJECT *DeviceObject
    )


/*++


Routine Description:


    This routine returns a pointer to the device object specified by the
    object name.  It also returns a pointer to the referenced file object
    that has been opened to the device that ensures that the device cannot
    go away.


    To close access to the device, the caller should dereference the file
    object pointer.


Arguments:


    ObjectName - Name of the device object for which a pointer is to be
        returned.


    DesiredAccess - Access desired to the target device object.


    FileObject - Supplies the address of a variable to receive a pointer
        to the file object for the device.


    DeviceObject - Supplies the address of a variable to receive a pointer
        to the device object for the specified device.


Return Value:


    The function value is a referenced pointer to the specified device
    object, if the device exists.  Otherwise, NULL is returned.


--*/


{
    PFILE_OBJECT fileObject;
    OBJECT_ATTRIBUTES objectAttributes;
    HANDLE fileHandle;
    IO_STATUS_BLOCK ioStatus;
    NTSTATUS status;


    PAGED_CODE();


    //
    // Initialize the object attributes to open the device.
    //


    InitializeObjectAttributes( &objectAttributes,
                                ObjectName,
                                OBJ_KERNEL_HANDLE,
                                (HANDLE) NULL,
                                (PSECURITY_DESCRIPTOR) NULL );


    status = ZwOpenFile( &fileHandle,
                         DesiredAccess,
                         &objectAttributes,
                         &ioStatus,
                         0,
                         FILE_NON_DIRECTORY_FILE );


    if (NT_SUCCESS( status )) {


        //
        // The open operation was successful.  Dereference the file handle
        // and obtain a pointer to the device object for the handle.
        //


        status = ObReferenceObjectByHandle( fileHandle,
                                            0,
                                            IoFileObjectType,
                                            KernelMode,
                                            (PVOID *) &fileObject,
                                            NULL );
        if (NT_SUCCESS( status )) {


            *FileObject = fileObject;


            //
            // Get a pointer to the device object for this file.
            //
            *DeviceObject = IoGetRelatedDeviceObject( fileObject );
        }


        (VOID) ZwClose( fileHandle );
    }


    return status;
}

PDEVICE_OBJECT
IoGetRelatedDeviceObject(
    IN PFILE_OBJECT FileObject
    )


/*++


Routine Description:


    This routine returns a pointer to the actual device object than an I/O
    Request Packet (IRP) should be given to based on the specified file
    object.


    N.B. - Callers of this function must ensure no device object is
    attaching or detaching from this stack for the duration of this call.
    This is because the database lock is *not* held!


Arguments:


    FileObject - Pointer to the file object representing the open file.


Return Value:


    The return value is a pointer to the device object for the driver to
    whom the request is to be given.


--*/


{
    PDEVICE_OBJECT deviceObject;


    //
    // If the file object was taken out against the mounted file system, it
    // will have a Vpb. Traverse it to get to the DeviceObject. Note that in
    // this case we should never follow FileObject->DeviceObject, as that
    // mapping may be invalid after a forced dismount.
    //


    if (FileObject->Vpb != NULL && FileObject->Vpb->DeviceObject != NULL) {


        ASSERT(!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN));
        deviceObject = FileObject->Vpb->DeviceObject;




        //
        // If a driver opened a disk device using direct device open and
        // later on it uses IoGetRelatedTargetDeviceObject to find the
        // device object it wants to send an IRP then it should not get the
        // filesystem device object. This is so that if the device object is in the
        // process of being mounted then vpb is not stable.
        //


    } else if (!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN) &&
               FileObject->DeviceObject->Vpb != NULL &&
               FileObject->DeviceObject->Vpb->DeviceObject != NULL) {


            deviceObject = FileObject->DeviceObject->Vpb->DeviceObject;


    //
    // This is a direct open against the device stack (and there is no mounted
    // file system to strain the IRPs through).
    //


    } else {


        deviceObject = FileObject->DeviceObject;
    }


    ASSERT( deviceObject != NULL );


    //
    // Check to see whether or not the device has any associated devices.
    // If so, return the highest level device; otherwise, return a pointer
    // to the device object itself.
    //


    if (deviceObject->AttachedDevice != NULL) {
        if (FileObject->Flags & FO_FILE_OBJECT_HAS_EXTENSION) {


            PIOP_FILE_OBJECT_EXTENSION  fileObjectExtension =
                (PIOP_FILE_OBJECT_EXTENSION)(FileObject + 1);


            ASSERT(!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN));


            if (fileObjectExtension->TopDeviceObjectHint != NULL &&
                IopVerifyDeviceObjectOnStack(deviceObject, fileObjectExtension->TopDeviceObjectHint)) {
                return fileObjectExtension->TopDeviceObjectHint;
            }
        }
        deviceObject = IoGetAttachedDevice( deviceObject );
    }


    return deviceObject;
}