multiseat

[Jon Smirl]

Check out udev. It addresses your complaints about USB renumbering.

People will also use common sense. I doubt if they will try to share a
hub between two users. More likely you will give them each their own
hub. Hubs are only $10.

On 7/28/05, Adam Jackson <ajax at nwnk.net> wrote:
> On Thursday 28 July 2005 08:46, Jon Smirl wrote:
> > On 7/28/05, Daniel Stone <daniel at fooishbar.org> wrote:
> > > Input is hard.  How do you associate a particular input device to a
> > > particular user?  Now imagine the world of USB, where you have to deal
> > > with hotplug input devices.  Oh, and don't forget real users, who will
> > > want to do audio, and plug in USB thumbdrives.  If you plug in a
> > > thumbdrive with your GPG key on it, you don't want someone else to get
> > > their grubby mitts on it.
> >
> > PAM will have console groups which include screen, keyboard, audio,
> > mouse and USB ports. When you login to Linux you are assigned
> > ownership of the devices in the console group. You own USB ports so
> > things that are plugged into those ports automatically belong to you
> > too.
> 
> Just don't add hubs, or reconfigure the topology between reboots, or change
> kernels.  Oh, and remember that the three leftmost ports on the first card
> are yours but the right port and the second card are Jimmy's (scale that out
> to about four seats and then just start beating yourself on the head with a
> pipe wrench to relieve the pain).
> 
> > > VGA routing is a bitch.  If you don't believe me, stick four utterly
> > > random cards in one machine, start four X servers, and watch it quickly
> > > collapse in a heap.
> >
> > Benh already has a working prototype of VGA arbitration for the
> > kernel. It was discussed at Kernel Summit this year.
> 
> The arbitration idea is lovely but it assumes that the card gives a damn when
> you tell it not to decode the VGA space, and there are many video cards that
> will stick their fingers in their ears and go LA LA LA I CAN'T HEAR YOU when
> you try.  You could assert that those cards are broken, but that's sort of
> the point: hardware is broken and will actively defeat attempts to be used in
> a multiseat setup.
> 
> > > That and trying to deal with four separate heads when the VT system only
> > > has the concept of one.  Anywhere from one to four heads can be present
> > > on a four-user system, and you have to deal with that accordingly, and
> > > DTRT with sharing VTs, and what to do when someone hits the console.
> >
> > This was discussed at Kernel Summit too. The solution is to give the
> > VT system the boot since it is single user.
> 
> ... which just defers the problem to userspace, which now has to cope with the
> kernel renumbering the USB busses across reboots and whatever else breaks
> between now and 2.6.next.
> 
> Multiseat X almost kinda sorta works.  Multiseat VTs is slightly more possible
> if you kick them out to userspace, but still a broken idea, because people
> expect the console to have a well-defined set of input devices all the time
> and the brain-damaged nature of USB makes that impossible to guarantee.
> 
> And yet when I say "just don't use VTs", people give me a look like I have a
> cat growing out of my neck.
> 
> > > It's a surprisingly non-trival problem space, trust me.
> >
> > Work has been going on this area for the last year.
> 
> You do know that about a third of the multiseat support in 7.0 is Daniel's
> code, right?  He knows what he's talking about here.  Oh, speaking of, you
> also know that 7.0 has multiseat support that works (as well as multiseat
> ever works) on stock 2.6 kernels?
> 
> Let's try less preaching to the choir, k?
> 
> - ajax
> 
> 
> 


-- 
Jon Smirl
jonsmirl at gmail.com