I'm using Spice and want to share a USB device on workstation with a VM running on another physical host.  The filters are all set up for the VM in its domain XML.  The Spice "Select USB devices for redirection" dialog shows the device I want to redirect.  However, all the USB devices are greyed out and Alert text says, "Some USB devices are blocked by host policy".  My understanding, from the doc, is that the following XML needs to be configured on the "host physical machine's domain XML" which I am interpreting as the workstation, although it could be the hypervisor host, to unblock the USB device:

<redirfilter>
  <usbdev class='0x08' vendor='0x0951' product='0x1625' version='2.0' allow='yes'/>
  <usbdev allow='no'/>
</redirfilter>
Either way, I cannot figure out what the name or location of the file where this XML would go, let alone find a complete schema or example of what the file would look like.  Has anyone else done this?  Please... <gasp> Help!