[libvirt] disable usb?

[Gerd Hoffmann]

  Hi,

Is there some way to disable usb altogether?  libvirt used to just pass
in '-usb'.  With the arrival of usb2 support that changed into '-device
uhci,...'.  Problem is that this breaks with several machine types such
as isapc.  '-usb' is silently ignored in case the machine type can't
handle usb.  '-device uhci,...' leads to an error message though and the
guest doesn't start.

/me tried "<controller type='usb' model='none'/>" which didn't work.
Just removing the controller from the xml doesn't work too, it gets
automagically readded.

Suggestions?

thanks,
  Gerd