systemd, logind, upstart, wayland, weston chat at Munich BSP

[Àlex Fiestas]

On Saturday 23 November 2013 15:27:44 Jonathan Riddell wrote:
> We chatted a bit about this topics at Munich BSP
> 
> without Mir or Plasma 2 to worry about in this cycle there's no immediate
> issues but we need to keep an eye on them
> 
> cgroups (control groups) is a feature of Linux to limit, account and
> isolate resource usage (CPU, memory, disk I/O, etc.) of process groups.
> this is used in logind to get the system compositor without privilages
> which is needed by kwin.  so kwin will probably need an init system with
> cgroup support.  fortunately I see plans are under way for this in upstart
> https://lists.ubuntu.com/archives/upstart-devel/2013-November/002942.html

CGroups by default only group processes and their children and no policy is 
applied.

For example, this will allow us to spawn N nepomuk index processes and keep 
track of them since all of them will be in the same cgroup.

Then, you can enable "subsystems" that make use of these cgroups in a 
particular way, for example given a certain amount of resources, or giving 
them special access to a certain device.

More about cgroups here:
https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

> the current version of logind in ubuntu is not enough for wayland because
> it needs to get special access to hardware for compositing (which it does
> through cgroups) so we will need an updated version of logind at some
> point.  but that's hard because logind is now inseperable from systemd.
Systemd and logind are developed as a whole, so application developers will 
use systemd interfaces while working with logind.

One example is in PowerDevil, we check the version of systemd to know what 
features are available (and work) on logind, things like 
suspend/hibernate/inhibition... That call to check the version is not even 
implemented in systemd-shim (the systemd emulation Ubuntu uses), and we had to 
add a workaround for Kubuntu days before the release.

So even if Ubuntu developers "strip' a new logind version for 14.04, that 
doesn't mean that all applications depending on logind1 will work well.

> afiestas has started working on looking at using systemd for KDE Plasma
> startup, this should have a magic export to make a simple script to start
> up if you don't use systemd but it won't be as fast.
This only relates to the startup, systemd will affect other things.

> So no easy answers yet, lots happening in the future we should keep an eye
> on.

There are things to do right now, we should:
-Get knowledge of how upstart works, so we can add support in KDE for it.
-Track all programs using systemd, make sure that them work with the fake 
Ubuntu implementation and the "stripped" logind1 (PowerDevil, user-manager, 
DM, logout/switch user/...)
-Before beta of 4.12, 4.13, 5.0... Make sure everything works, track what new 
dependencies have been added to systemd etc.

Basically, as long as Ubuntu uses forks and weird versions of systemd, Kubuntu 
should focus on making sure all the software works.

Maybe we can start with a list of programs using 
systemd/logind/dated/hostnamed.... and add them to the list of things to test.

Cheers !