I'm a newbie in WDM. I wanna send IOCTL to my virtual audio driver, but I failed to open my driver in user-mode application. In audio driver side, I registers an interface, AddDevice ( IN PDRIVER_OBJECT DriverObject, IN PDEVICE_OBJECT PhysicalDeviceObject ) { ... ntStatus = PcAddAdapterDevice ( DriverObject, PhysicalDeviceObject, PCPFNSTARTDEVICE(StartDevice), MAX_MINIPORTS, 0 ); ... ntStatus = IoRegisterDeviceInterface(PhysicalDeviceObject, &GUID_DEVINTERFACE_BT_AUDIO, NULL, &ifname); ... ntStatus = IoSetDeviceInterfaceState(&ifname, TRUE); } //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// In application side, HDEVINFO info = SetupDiGetClassDevs(&GUID_DEVINTERFACE_BT_AUDIO, NULL, NULL, DIGCF_PRESENT | DIGCF_INTERFACEDEVICE); ... if (SetupDiEnumDeviceInterfaces(info, NULL, &GUID_DEVINTERFACE_BT_AUDIO, 0, &ifdata)) { ... SetupDiGetDeviceInterfaceDetail(info, &ifdata, NULL, 0, &needed, NULL); PSP_INTERFACE_DEVICE_DETAIL_DATA detail = (PSP_INTERFACE_DEVICE_DETAIL_DATA) malloc(needed); SP_DEVINFO_DATA did = {sizeof(SP_DEVINFO_DATA)}; detail->cbSize = sizeof(SP_INTERFACE_DEVICE_DETAIL_DATA); if (!SetupDiGetDeviceInterfaceDetail(info, &ifdata, detail, needed, NULL, &did)) { ... } ... strcpy(fileName, detail->DevicePath); ... } SetupDiDestroyDeviceInfoList(info); //////////////////////////////////////////////////// HANDLE hdevice = CreateFile(fileName, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL); The CreateFile() always return 2 (ERROR_FILE_NOT_FOUND). What's the problem with my code? Any suggestions/hints will be much appreciated! Holly