[systemd-devel] Ordering after udev applied rules to `/dev/dri/card0`

[Lennart Poettering]

On Do, 02.04.20 11:30, Pekka Paalanen (ppaalanen at gmail.com) wrote:

> > Thinking about this: it might make sense to revisit this
> > eventually... for example maybe instead of having gdm run all the time
> > and just listening to SeatAdded/SeatRemoved and CanGraphical property
> > changes and then spawn off a login UI for that seat, maybe we should
> > just add this behaviour to logind itself that it can spawn
> > compositor@$SEAT.service whenever this happens. That should be easy to
> > do and might be interesting for weston-like setups: i.e. you'd just
> > symlink the compositor at .service template to weston at .service and then
> > weston would get started automatically whenever a graphical seat shows
> > up. does that make sense? i kinda like the idea. it would solve all
> > your problems too, right?)
>
> Hi,
>
> yeah, that sounds attractive, but it has one problem: the idea of a
> usable graphics device might be different between logind and the
> compositor, like you explained.

True, but if implemented this way we could make weston exit if the
seat has nothing it can use. i mean, it's fine to start the compositor
in too many cases. it's more problematic to start it in too
few. i.e. if compositor at seat0.service exits cleanly when it decides it
can't handle the seat then that's totally fine.

> It would work for auto-login cases I guess, but I'm not sure about how
> well it would serve login managers. Wouldn't a login manager like GDM
> be still needed, but instead of listening to SeatAdded/SeatRemoved it
> would have to listen to login-UI actions? I'm really not the right
> person to evaluate that.

Well, gdm is a lot of things. it's both a seat manager and a greeter
implementation. my suggestion would be to move the seat manager to
logind, but leave the greeter in gdm. i.e. gdm would then have the
option to make compositor at .service a symlink to gdm-greeter at .service,
and thus just would need to take care of the greeter, but nothing else
anymore...

Lennart

--
Lennart Poettering, Berlin