virtual: 0.954
device: 0.952
VMM: 0.926
KVM: 0.926
vnc: 0.891
peripherals: 0.889
performance: 0.884
hypervisor: 0.865
graphic: 0.843
semantic: 0.803
kernel: 0.793
network: 0.782
PID: 0.769
ppc: 0.757
architecture: 0.746
permissions: 0.746
socket: 0.730
x86: 0.670
i386: 0.668
risc-v: 0.664
arm: 0.655
user-level: 0.635
mistranslation: 0.613
register: 0.592
debug: 0.564
files: 0.562
TCG: 0.543
boot: 0.466
assembly: 0.290

usb-hub can not be detached when detach usbdevice  VM

I give a host usb device to guest in the way of passthrough,use "virsh attach-device" cmd. In guest os,use "lsusb" cmd I can see two devices have been added,one is usb device and the other is usb-hub（0409:55aa NEC Corp. Hub）.
when I use "virsh detach-device" detach the usb device,in guest os the usb-hub was still exists.
It can create a bad impression when operating the VM,for example,suspend and resume the VM,qemu would report that:

2016-05-24T12:03:54.434369Z qemu-kvm: Unknown savevm section or instance '0000:00:01.2/2/usb-hub' 0

2016-05-24T12:03:54.434742Z qemu-kvm: load of migration failed: Invalid argument  

From qemu's code,it can be sure that the usb-hub is generated by qemu,and the process of detaching usb-hub has already been executed,but failed.With adding print information,error as follows:
libusbx: error [do_close] Device handle closed while transfer was still being processed, but the device is still connected as far as we know
libusbx: warning [do_close] A cancellation for an in-flight transfer hasn't completed but closing the device handle