Multiseat Support in HAL

[Oliver Grawert]

hi,
Am Dienstag, den 19.09.2006, 10:26 +0200 schrieb Holger Macht:
> On Tue 19. Sep - 07:19:42, Fabian Steiner wrote:
> > Oliver Grawert wrote:
> > > hi,
> > > Am Montag, den 18.09.2006, 21:46 +0200 schrieb Fabian Steiner:
> > >> Since Xorg 7.0 it is possible to set up a real multiseat box ([1], [2])
> > >> (several independent workplaces on one machine) without having to apply
> > >> additional patches (Ruby [3], etc.).
> > >>
> > >> We are running such setups (OS: Ubuntu Dapper 6.06) at school and so far
> > >> almost everything works quite well. We are really content with that work
> > >> since it saves us a lot of money and time. Unfortunately, there is still
> > >> one feature missing, though. So far it is not possible to assign proper
> > >> permissions to hotpluggable devices such as memory sticks and cameras.
> > > 
> > > 
> > > thats no hal problem at all, please see
> > > https://launchpad.net/distros/ubuntu/+source/gnome-vfs/+bug/50554
> > > we fixed it in edgy (ubuntu 6.10) when we added local device support for
> > > ltsp, the patch is supposed to be sent upstream as well so gnome-vfs2
> > > will behave properly in the future even on other distros and only show
> > > the user devices he/she has access to.
> > 
> > I do think it's a HAL "problem" because this would be the best place to
> > solve such an issue.
> > 
> > Can you explain more detailed how you managed to associate a display
> > (i.e. the user who is in front of it) with a USB hub for example? How do
> > you know which user is the owner of which usb stick?
> > 
> > Moreover, your solution seems to be limited to the linux terminal server
> > project and to gnome. Does this patch also work with a simple multiseat
> > setup and other desktop environments that don't depend on gnome-vfs but
> > use something more generel (HAL, pmount, etc.)?
> 
> Just a note: Such a "locking feature" is also needed in other cases and it
> should be available in a general way IMO. The same problems with multiseat
> arise with the display brightness or the cpufreq methods. Multiple users
> may use the same methods to the same time fighting about a setting they
> want to set.
right, in general i agree, but wrt block devices gnome-vfs had that bug
we solved, indeed it might be better to solve it for hal as well but i
think you agree that its silly behavior of gnome-vfs to put devices on
the users desktop he hasnt access to :)

in ubuntu ltsp (and in ltsp5 even upstream since we merge the projects
now) we use ssh with an attached communication socket on the client
instead of insecure xdmcp. all commands executed through that socket are
run with privileges of the user who owns the ssh tunnel. so if udev
recognizes a new block device, it issues an ltspfs (fuse based) mount
command through that socket in the users session on the server which
then mounts the device from the client. the mount is owned by the
specific user, there is no need for additional DISPLAY association.
the bug we solved just avoids that you end up with 200 devices on the
desktop in case of 200 logged in users who all plug in their usb sticks.

ciao
	oli
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