libvirt users - May 2018 - Hello ,How Can I do USB emulation

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.