Re: [gdm-list] Multi-seat and multi-display support design

[Jukka Honkela <jukka honkela org>]

Hi,

wanted to point out a few issues, which have been partially already 
brought up earlier in this thread:

Currently the only realistic way (afaik) to configure a multiseat system 
is to use xorg.conf; one major reason for this is the fact that hal is 
used to configure the input devices; the current -keyboard etc command 
line options are useless without manually configured xorg.conf because 
without manual mapping, there won't be any names to point at with those 
options. -> as mentioned earlier, this needs to change. But even then, 
mapping the devices to a specific seat is a bit problematic; one can/could 
have a static file that mentions that /dev/input/by-id/XYZ-event belongs 
to seat A and ABC-event belongs to seat B. Unfortunately this doesn't help 
at all what should be done with a new device, let's say a wacom tablet, 
that was plugged into the system. Who will get it? If everything has to be 
edited via somekind of configuration editor (or manually, editing the 
files), it's not really a hugely userfriendly system on the longer term.

The only semi reasonable solution to that so far has been using the usb 
bus id to map all devices belonging to a certain usb hub to belong to a 
certain seat. In princible, the problem is not only related to 
HID-devices, mass storage is another issue, how and what policies actually 
to follow with those. In some environments (home?) it is more probable 
that it doesn't matter if everybody sees the plugged in mass storage 
device but in others (school?) it might be a bad idea.

Audio devices are another problem here and adding pulseaudio into to the 
mix makes the problem further complicated, even though it can also help 
solving it.

Overall; on a multi-seat system, what happens when a new USB device is 
plugged in? possible scenarios/solutions/proposals:
1) it's ignored, unless
  a) the device is known and has already been assigned to somebody before
     in the past
  b) a user with specific rights assigns it to somebody
2) a global query is sent, the first one to click "Mine!" gets the device
3) user has to do somekind of extra trick before inserting the new device,
   indicating that she/he is the one who will be the owner of the new
   device. This option is not without its share of problems...
4) a mapping between usb ports/hubs to seats is manually made

Ideally there should be a way to handle all that one way or another, and 
why not even supporting hot-pluggable local seats; it's technically a not 
so likely case, but could be possible, especially with laptops with a 
docking station etc...

--
Jukka Honkela