device hotplug & file handles

Hi, For usb device pass-through (aka -device usb-host) it would be very useful to pass file handles from libvirt to qemu. The workflow would change from ... (1) libvirt enables access to /dev/usb/$bus/$dev (2) libvirt passes $bus + $dev (using hostbus + hostaddr properties) to qemu. (3) qemu opens /dev/usb/$bus/$dev ... to ... (1) libvirt opens /dev/usb/$bus/$dev (2) libvirt passes filehandle to qemu. Question is how can we pass the file descriptor best? My idea would be to simply add an fd property to usb-host: * Coldplug would be "-device usb-host,fd=<nr>" (cmd line). * Hotplug would be "device_add usb-host,fd=<getfd-name>" (monitor). Will that work from libvirt point of view? Or does anyone have an better idea? thanks, Gerd PS: background: https://bugzilla.redhat.com/show_bug.cgi?id=1595525