multiseat howto (with some multihead coverage)
==============================================
-host side
----------
+host devices
+------------
First you must compile qemu with a user interface supporting
-multihead/multiseat and input event routing. Right now this list is
-pretty short: sdl2.
+multihead/multiseat and input event routing. Right now this
+list includes sdl2, gtk (both 2+3) and vnc:
- ./configure --enable-sdl --with-sdlabi=2.0
+ ./configure --enable-sdl
+or
-Next put together the qemu command line:
+ ./configure --enable-gtk
-qemu -enable-kvm -usb $memory $disk $whatever \
- -display sdl \
+
+Next put together the qemu command line (sdk/gtk):
+
+qemu -accel 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
+That is it for the first seat, 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:
+additional switches for the second seat:
-device pci-bridge,addr=12.0,chassis_nr=2,id=head.2 \
-device secondary-vga,bus=head.2,addr=02.0,id=video.2 \
the window which belongs to the video.2 display adapter will be routed
to these input devices.
+Starting with qemu 2.4 and linux kernel 4.1 you can also use virtio
+for the input devices, using this ...
+
+ -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 virtio-keyboard-pci,bus=head.2,addr=03.0,display=video.2 \
+ -device virtio-tablet-pci,bus=head.2,addr=03.0,display=video.2
+
+... instead of xhci and usb hid devices.
+
+host ui
+-------
+
+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.
+
+For vnc some additional configuration on the command line is needed.
+We'll create two vnc server instances, and bind the second one to the
+second seat, similar to input devices:
+
+ -display vnc=:1,id=primary \
+ -display vnc=:2,id=secondary,display=video.2
+
+Connecting to vnc display :1 gives you access to the first seat, and
+likewise connecting to vnc display :2 shows the second seat.
+
+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
----------
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. By default
-all devices belong to seat0. You can use "loginctl seat-status seat0"
-to list them all (and to get the sysfs paths for cut+paste). Now
-we'll go assign all pci devices connected the pci bridge in slot 12 to
-a new head:
-
-loginctl attach seat-qemu \
- /sys/devices/pci0000:00/0000:00:12.0/0000:01:02.0/drm/card1
-loginctl attach seat-qemu \
- /sys/devices/pci0000:00/0000:00:12.0/0000:01:02.0/graphics/fb1
-loginctl attach seat-qemu \
- /sys/devices/pci0000:00/0000:00:12.0/0000:01:0f.0/usb2
-
-Use "loginctl seat-status seat-qemu" to check the result. It isn't
-needed to assign the usb devices to the head individually, assigning a
-usb (root) hub will automatically assign all usb devices connected to
-it too.
-
-BTW: loginctl writes udev rules to /etc/udev/rules.d to make these
-device assignments permanent, so you need to do this only once.
-
-Now simply restart gdm (rebooting will do too), and a login screen
-should show up on the second head.
+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/
+
+
+guest side with pci-bridge-seat
+-------------------------------
+
+Qemu version 2.4 and newer has a new pci-bridge-seat device which
+can be used instead of pci-bridge. Just swap the device name in the
+qemu command line above. The only difference between the two devices
+is the pci id. We can match the pci id instead of the device path
+with a nice generic rule now, which simplifies the guest
+configuration:
+
+ [root@fedora ~]# cat /etc/udev/rules.d/70-qemu-pci-bridge-seat.rules
+ SUBSYSTEM=="pci", ATTR{vendor}=="0x1b36", ATTR{device}=="0x000a", \
+ TAG+="seat", ENV{ID_AUTOSEAT}="1"
+
+Patch with this rule has been submitted to upstream udev/systemd, was
+accepted and should be included in the next systemd release (222).
+So, if your guest has this or a newer version, multiseat will work just
+fine without any manual guest configuration.
Enjoy!
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