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

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Message-ID: <20150211160347.GE21356@htj.duckdns.org>
Date:	Wed, 11 Feb 2015 11:03:47 -0500
From:	Tejun Heo <tj@...nel.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Richard Weinberger <richard@....at>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCHv3 8/8] cgroup: Add documentation for cgroup namespaces

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.

Thanks.

-- 
tejun
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