Multiseat X sessions and Xorg configs

[Dave Airlie]

On Wed, Jul 17, 2013 at 1:49 AM, Glen Gray <slaine at slaine.org> wrote:
> Hey guys,
>
> I originally posted this to the systemd-devel list but Lennart pointed me to conversations already happening in here so I've moved this over.
>
> I'm currently working with a Plugable DisplayLink usb hub/adaptor for adding multi-seat support to an embedded PC.
>
> I've been running into difficulties with the changes to GDM and systemd with regards to multiseat support and having a configured environment/session for each seat.
>
> As way of backstory, for GDM, I've patched it to do the following...
> 1) In daemon/gdm-display.c where it currently checks if the seat != seat0. Rather than doing "goto out;" immediately, it queries the username. If the username is utilising the script method then let the automated login proceed. The script method will parse the login name as a script path if it ends with | character.
>
> 2) In daemon/gdm-simple-slave.c, rather than using a global level GDM_RAN_ONCE_FILE_MARKER, create one per seat. This allows the wants_autologin() to return True on a another seat rather than drop through to simply start_greeter().
>
> 3) In daemon/gdm-slave.c, Export the GDM_SEAT_ID for the initial gdm slave display. This allows you to check the current seat in the script for item 1) above.
>
> That solved my gdm automated login process on the different seats. I've emailed the patch to the gdm list.
>
> However, I also ran into a problem with Xorg configurations. As has been discussed the multi-seat-x tool currently wraps the call to the X server and appends some appropriate parameters. I've seen mention of tailoring the Match options for input classes to include a MatchSeat option. However, the Device section is another area that needs consideration.
>
> In my setup, the host system runs on an embedded PC and has an xorg.conf.d Device entry for the Intel driver to enable certain options. However, this is global and caused problems with the displays on the other seats. e.g. with the second seat starting Xorg it was looking for the Intel device as described in the xorg.conf.d file, rather than using the appropriate Frame-buffer device. I've patched the systemd/login/multi-seat-x.c to also pass over a -configdir parameter to the Xorg it launches. I'm not entirely confident that's the correct path I should be using.
> ..-configdir /etc/X11/xorg.conf.d/multi-session-x/seat-usb-pci-0000_00_1d_7-usb-0_3_1_4
>

Maybe add Option "AutoAddGPU" "FALSE" to your xorg.conf.

Dave.