Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces

From: Serge E. Hallyn
Date: Wed Feb 11 2015 - 11:18:59 EST

Quoting Tejun Heo (tj@xxxxxxxxxx):
> On Wed, Feb 11, 2015 at 05:00:23PM +0100, Serge E. Hallyn wrote:
> > We absolutely would love to use cgroup namespaces to run older
> > userspace in containers. I don't know that it's actually possible
> > to do both that and use unified hierarchy at the same time though,
> > which is unfortunate. So an Ubuntu 12.04 container will never, afaics,
> > be able to run inside an ubuntu 16.04 host that is using unified
> > hierarchy, without using backported newer versions of lxc (etc) in
> > the container.
> So, the constraint there are the controllers. A controller can't be
> attached to two hierarchies at the same time for obvious reasons, so
> regardless of NS, you can't use the same controller on a unified
> hierarchy *and* a traditional hierarchy. NS doesn't adds or
> substracts from the situation. If you decide to attach a controller
> to a traditional hierarchy, that's where it's gonna be available. If
> you attach it to the unified hierarchy, the same story.

Right, exactly.

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