usbredir is a protocol for redirection USB traffic from a single USB device, to a different (virtual) machine then the one to which the USB device is attached. See usb-redirection-protocol.txt for the description / definition of this protocol. With the official 0.3 release the protocol is now frozen (only extensions advertised through capabilities can be added from now on). WWW: http://cgit.freedesktop.org/spice/usbredir