Re: [Qemu-devel] multihead & multiseat in qemu

[Gerd Hoffmann]

  Hi,

> > I'd like to have some way to assign tags such as seat=foo or head=1 to
> > devices.  Preferably in some way which can easily picked up with udev
> > rules, so it is easily usable by system-logind and Xorg server.
> 
> The only current example of seat autoconfiguration is for the usb hubs
> from displaylink I think, which have video/audio/ethernet/usb behind a
> hub that udev detects as being part of a seat, I'd need to look up the
> specifics,

udev can match upstream devices, so it's easy to tag all devices below
the usb hub as belonging to the seat.

> > We have virtio devices (virtio-gpu for example).  For these it is easy,
> > we can put something into the virtio protocol, and the guest driver can
> > create a sysfs file where udev/systemd can pick it up.
> >
> > We have pci devices (cirrus for example).  One idea for them would be to
> > create a vendor-specific pci capabiliy for tags.  Probably needs some
> > small utility to read them, or kernel driver support to export them via
> > sysfs.
> >
> > We have usb devices (kbd/mouse/tablet).  We could put something into the
> > string table, or have some vendor-specific descriptor.  Same problem
> > here, not easy accessible, needs a tool or kernel support.
> >
> > Comments?  Better ideas?  Other suggestions?
> 
> It does seems like tagging the devices somehow would be better than providing
> a seat device, like we could in theory have a pci and usb controller
> per seat, and
> have devices move around between them, this would be like what we for
> the real hw,
> however per-device tags does look like it might be nicer in the long run.

I've been thinking about this too.  Use a pci-bridge, then group the
devices belonging to the seat below the pci-bridge for easy udev
matching.  That doesn't help for the multihead case though.  And we have
to tag the devices for qemu's internal usage (host-side input routing)
anyway.  Thats why I think the tagging will work better.

cheers,
  Gerd