libvirt users - Jul 2017 - node device lifecycle callback can't resive event

Hi all, 
I registe node device lifecycle event callback function after connect qemu. In
the callback function, I printf the event and detail.
When I plug a USB into host, and then pull out, but there is nothing happen. The
callback was not called.
Could you tell me Why? And what dose node device mean?

I want to auto-hotplug usb devices by using libvirt.


Bellow the call of libvirt:
 // node device lifecycle callback function
void nodeDeviceEventLifecycleCallback(virConnectPtr conn, virNodeDevicePtr dev,
int event,
                int detail, void * opaque)
{
    printf("event = %d, detail= %d\n", event, detail);
}


// registe node device lifecycle event
int registeNodeDevEvent()
{
    int ret = virEventRegisterDefaultImpl();
    if (ret) { return -1;}


    ret = virConnectNodeDeviceEventRegisterAny(vmh_conn, NULL,
VIR_NODE_DEVICE_EVENT_ID_LIFECYCLE,
            VIR_NODE_DEVICE_EVENT_CALLBACK(nodeDeviceEventLifecycleCallback),
NULL, NULL);
    if (-1 == ret) { return ret;}
}


Below some information about my hypervisor:
root@ubuntu-05:/datapool/zhuohf# virsh -v
3.4.0
root@ubuntu-05:/datapool/zhuohf# qemu-x86_64 -version
qemu-x86_64 version 2.9.0
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers