multiseat (was: Re: Input Devices (was: Re: [Xgl/Xegl] Input Devices))

David Balažic davidtest at
Sun Aug 21 09:09:08 PDT 2005

Daniel Stone wrote:
> On Thu, Jul 28, 2005 at 01:45:49AM -0400, Jon Smirl wrote:
>> On 7/28/05, Daniel Stone <daniel at> wrote:
>> > On Wed, Jul 27, 2005 at 04:22:42PM -0400, Jon Smirl wrote:
>> > > Different users on each card is easy.
>> > 
>> > No, it really isn't.
>> Why?
> 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.

First : Great that multiseat is considered !
Second : I set up a two-seat system a few months ago.

Assigning the input devices was the least problem.

Problem from my point of view :
  - video drivers not working well in multi-card setup
  - X server driving the secondary seat messes with first VGA card, VT
system on first seat, and other things it shouldn't mess with
(why is VT handling so "hardwired" into X code ? It should be a platform
specific _option_, eg. you can easily turn it off)

IMHO, the high level problems, like "Which USB floppy is mine" are not
in scope of X.
This problem already exists with multiple logins (over VTs or network)
and are treated by distros since a while (more or less successfuly).

Here is what I would expect for multiseat in next version of X :
  - improved video driver behavior in multi-card setups (are the problems
for multiseat different than for "classic" multimonitor/multihead setup ?)
  - dropping legacy kbd driver for "evdev" (or whatever its called; the
thing that allows selection of keyboards by some ID)
  - same for mouse (if needed at all)
  - option for X not to touch VT system (so the first seat would have
classic VTs, while the other would just run X)

This way no kernel changes are needed.

One more thought about "after user unplugs USB keyboard and plugs it
into "wrong" port, it does not work anymore" (because that port is not
associated with his seat).
Imagine you have two plain single-seat PCs. If the user unplugs the USB
keyboard from PC 1 and plugs it into PC 2, the first PC wont work
anymore. Just like in the multiseat case. Does that mean that "two PCs
are a hard problem" ? No. It was a simple user error. Claiming that this
issue makes multiseat "hard" is stupid, IMO.

David Balažic

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