[libvirt] USB 2.0 support in qemu

Hi, Recently USB 2.0 support was merged into upstream qemu, I guess libvirt and virt-manager needs some bits to support this ... The docs/usb2.txt file in the qemu source tree carries some information on how to use it, and also some hints for USB pass-through. The most recent version (not yet merged upstream) can be found here: http://www.kraxel.org/cgit/qemu/tree/docs/usb2.txt?h=usb.15 If there are any questions feel free to ask. cheers, Gerd