multiseat with several videocards

[Oleg Samarin]

Hello!

I am building a multi-seat system with several sets of monitor, keyboard
and mouse. Several users can work with this system independently.

Recent versions of systemd allows it with registering one of device as a
master of seat. It causes gdm launches several instances of Xorg with
-seat <number-of-seat> option.

If you have several pci videocards, you need to specify which card,
screen and layout to use on each seat. It might be done by -config or
-layout command line option. Unfortunnaly, gdm does not allow to
customise Xorg command line.

It would be more comfortable to have single configuration file with
several devices or layout and associate each element of it with a
particular seat. I propose to introduce the new element "MatchSeat" for
this issue. Here is an example of my /etc/X11/xorg.conf.d/90-seats.conf
file:

-------------------------------------------------------------------------
Section "Device"
    Identifier     "Nvidia250"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTS 250"
    BusID          "PCI:1:0:0"
    Option         "ProbeAllGpus" "FALSE"
    MatchSeat      "seat0"
EndSection

Section "Device"
    Identifier     "Nvidia430dvi"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GT 430"
    BusID          "PCI:2:0:0"
    Screen          0
    Option         "ProbeAllGpus" "FALSE"
    MatchSeat	   "seat1"
EndSection
-------------------------------------------------------------------------

I cann not use /etc/X11/xorg.conf file because systemd submit another
config file.

I have prepared a patch that adds support of MatchSeat keyword in
"Device", "Screen" and "Layout" sections. There is no necessary to use
MatchSeat with "InputDevice" section because systemd allows to attach
usb devices to a particular seat and Xorg already uses it