
multiseat howto (with some multihead coverage)
==============================================

host side
---------

First you must compile qemu with a user interface supporting
multihead/multiseat and input event routing.  Right now this
list includes sdl2 and gtk (both 2+3):

  ./configure --enable-sdl --with-sdlabi=2.0

or

  ./configure --enable-gtk


Next put together the qemu command line:

qemu	-enable-kvm -usb $memory $disk $whatever \
	-display [ sdl | gtk ] \
	-vga std \
	-device usb-tablet

That is it for the first head, which will use the standard vga, the
standard ps/2 keyboard (implicitly there) and the usb-tablet.  Now the
additional switches for the second head:

	-device pci-bridge,addr=12.0,chassis_nr=2,id=head.2 \
	-device secondary-vga,bus=head.2,addr=02.0,id=video.2 \
	-device nec-usb-xhci,bus=head.2,addr=0f.0,id=usb.2 \
	-device usb-kbd,bus=usb.2.0,port=1,display=video.2 \
	-device usb-tablet,bus=usb.2.0,port=2,display=video.2

This places a pci bridge in slot 12, connects a display adapter and
xhci (usb) controller to the bridge.  Then it adds a usb keyboard and
usb mouse, both connected to the xhci and linked to the display.

The "display=video2" sets up the input routing.  Any input coming from
the window which belongs to the video.2 display adapter will be routed
to these input devices.

The sdl2 ui will start up with two windows, one for each display
device.  The gtk ui will start with a single window and each display
in a separate tab.  You can either simply switch tabs to switch heads,
or use the "View / Detach tab" menu item to move one of the displays
to its own window so you can see both display devices side-by-side.

Note on spice: Spice handles multihead just fine.  But it can't do
multiseat.  For tablet events the event source is sent to the spice
agent.  But qemu can't figure it, so it can't do input routing.
Fixing this needs a new or extended input interface between
libspice-server and qemu.  For keyboard events it is even worse:  The
event source isn't included in the spice protocol, so the wire
protocol must be extended to support this.


guest side
----------

You need a pretty recent linux guest.  systemd with loginctl.  kernel
3.14+ with CONFIG_DRM_BOCHS enabled.  Fedora 20 will do.  Must be
fully updated for the new kernel though, i.e. the live iso doesn't cut
it.

Now we'll have to configure the guest.  Boot and login.  "lspci -vt"
should list the pci bridge with the display adapter and usb controller:

    [root@fedora ~]# lspci -vt
    -[0000:00]-+-00.0  Intel Corporation 440FX - 82441FX PMC [Natoma]
               [ ... ]
               \-12.0-[01]--+-02.0  Device 1234:1111
                            \-0f.0  NEC Corporation USB 3.0 Host Controller

Good.  Now lets tell the system that the pci bridge and all devices
below it belong to a separate seat by dropping a file into
/etc/udev/rules.d:

    [root@fedora ~]# cat /etc/udev/rules.d/70-qemu-autoseat.rules
    SUBSYSTEMS=="pci", DEVPATH=="*/0000:00:12.0", TAG+="seat", ENV{ID_AUTOSEAT}="1"

Reboot.  System should come up with two seats.  With loginctl you can
check the configuration:

    [root@fedora ~]# loginctl list-seats
    SEAT
    seat0
    seat-pci-pci-0000_00_12_0

    2 seats listed.

You can use "loginctl seat-status seat-pci-pci-0000_00_12_0" to list
the devices attached to the seat.

Background info is here:
  http://www.freedesktop.org/wiki/Software/systemd/multiseat/

Enjoy!

--
Gerd Hoffmann <kraxel@redhat.com>