PCI网卡Driver 中不懂的一点，求助！

以下是取PCI Configuration Space的一段代码：
 IoGetAttachedDeviceReference（）是去取Driver Stack中最顶层的驱动对象。
然后调用IoCallDriver（），但是我理解的是网卡驱动已经是当前PCI Bus驱动堆栈上最顶层的设备了。
再调用IoCallDriver（）不就是调用了自己么？？？
KEVENT event;NTSTATUS status;PIRP irp;IO_STATUS_BLOCK ioStatusBlock;PIO_STACK_LOCATION irpStack;PDEVICE_OBJECT targetObject;DebugPrint(TRACE, DBG_INIT, "GetPciBusInterfaceStandard entered.\n");KeInitializeEvent( &event, NotificationEvent, FALSE );targetObject = IoGetAttachedDeviceReference( DeviceObject );irp = IoBuildSynchronousFsdRequest( IRP_MJ_PNP,                                    targetObject,                                    NULL,                                    0,                                    NULL,                                    &event,                                    &ioStatusBlock );if (irp == NULL) {    status = STATUS_INSUFFICIENT_RESOURCES;    goto End;}irpStack = IoGetNextIrpStackLocation( irp );irpStack->MinorFunction = IRP_MN_QUERY_INTERFACE;irpStack->Parameters.QueryInterface.InterfaceType =                     (LPGUID) &GUID_BUS_INTERFACE_STANDARD ;irpStack->Parameters.QueryInterface.Size = sizeof(BUS_INTERFACE_STANDARD);irpStack->Parameters.QueryInterface.Version = 1;irpStack->Parameters.QueryInterface.Interface =                                     (PINTERFACE)BusInterfaceStandard;irpStack->Parameters.QueryInterface.InterfaceSpecificData = NULL;//    // Initialize the status to error in case the bus driver does not // set it correctly.irp->IoStatus.Status = STATUS_NOT_SUPPORTED ;status = IoCallDriver( targetObject, irp );