IoGetRelatedDeviceObject学习

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;
}

这个也是网上很普及的东西了。传入开启设备或者文件产生的文件对象获得文件对象对应的设备所在的设备堆栈的最顶层设备。

根据 FileObject->Vpb != NULL && FileObject->Vpb->DeviceObject != NULL (!(FileObject->Flags & FO_DIRECT_DEVICE_OPEN 来判断设备对象的获取方式。 FILE_DEVICE_DISK等磁盘设备类型，如果卷设备挂载完成，则fileobject->vpb是存在的，那么获取到fileobject->vpb->deviceobject,。如果卷设备挂载进行中，那么fileobject->vpb可能不存在，返回fileobject->devieobject->vpb->deviceobject。

对于非磁盘设备等设备类型上述两种条件是无法满足的函数获取文件对象结构中的设备对象。

然后通过不断轮询设备的AttachedDevice 直到为NULL 获取设备堆栈中最顶层设备（IoGetAttachedDevice）

获取文件对象的fileObjectExtension 验证这个设备 fileObjectExtension->TopDeviceObjectHint != NULL && IopVerifyDeviceObjectOnStack()

然后返回获得的设备对象