usb-hub can not be detached when detach usb device from VM

[Michael liu]

I give a host usb device to guest in the way of using "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,but could not be seen in xml file of libvirt. So when executing the migration of VM or resuming VM after suspended,it report error like "Unknown savevm section or instance '0000:00:01.2/2/usb-hub' 0"

[Michael liu (ztehypervisor)]

I found that when I attached an usb device to the VM, the VM would add an usb-hub automatically if there was no usb-hub.
After adding an usb-hub,the VM assigned a port to the actual usb device. When detaching the usb device,the qemu only detach the port,without detaching the usb-hub.So when doing action like migrating or suspending/resumming,the VM will fail.

[Michael liu (ztehypervisor)]

Try detach the usb-hub device by the virsh detach-device usb-hub.xml?

[LiChunlin (lichl)]

The usb-hub device should be deleted when the usb device was detached. When do you fix this bug?

[Gerd Hoffmann (kraxel-redhat)]

Use a newer libvirt version which manages usb addressing and assigns usb devices to usb ports. This is required to make sure the physical device tree is the same after vmsave/vmload or live migration.