Re: [PATCH cgroup/for-3.11 1/3] cgroup: mark "tasks" cgroup file as insane

["Daniel P. Berrange" <berrange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Fri, Jun 07, 2013 at 07:10:40AM +0200, Lennart Poettering wrote:
> On Thu, 06.06.13 14:14, Tejun Heo (tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org) wrote:
> 
> > > You say the old interface will be around for the forseeable future, but
> > > if systemd starts applying a different setup to comply with your new
> > > scheme, then libvirt does get given any option to continue to use the
> > > old scheme. So even if you leave old interfaces around, we're going to
> > > be forced to change. That's not really a back-compatibility story that
> > > works for applications.
> > 
> > Even after unified hierarchy, it will be possible to tell systemd to
> > not to do that and the system should be able to continue using
> > multiple hierarchies as before.  Nothing really should change in that
> > respect.  It may not be the prettiest but is still a workable
> > compatibility.
> 
> Uhm. So I don't think we will support two ways to set this up for long
> in systemd (if at all). And even if we did, the distributions would pick
> one or the other as default, and if you are unlucky, then you couldn't
> run libvirt on it without reconfiguration and rebooting to get the other
> cgroup setup logic...

Yep, that's exactly what concerns me. If systemd introduced the option
for a new style setup, then it would almost certainly be adopted by
default by Fedora (otherwise there's no point adding it). At which
point libvirt is doomed. We can't require people to reconfigure systemd
and reboot to use virt.

Daniel
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