I have a usb.img file, and i want to create a usbdisk(USB emulation) for vpc in a kvm server.
I found something like this:

qemu-system-x86_64 -device piix3-usb-uhci \
    -drive id=my_usb_disk,file=usbdisk.img,if=none \
    -device usb-storage,drive=my_usb_disk

but i want  to do it in a xml files for libvirt.

i did not find any example for it. 

how can i do it


thank u very much.