linux-kernel - Re: CGroup Namespaces (v4)

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Message-ID: <CAFLxGvzVmbZHrpaTmXUAK03hsnVPwEs3SJGNFNXfthh3NL8EDg@mail.gmail.com>
Date:	Mon, 16 Nov 2015 21:41:15 +0100
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	LXC development mailing-list 
	<lxc-devel@...ts.linuxcontainers.org>, Tejun Heo <tj@...nel.org>,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: CGroup Namespaces (v4)

Serge,

On Mon, Nov 16, 2015 at 8:51 PM,  <serge@...lyn.com> wrote:
> To summarize the semantics:
>
> 1. CLONE_NEWCGROUP re-uses 0x02000000, which was previously CLONE_STOPPED
>
> 2. unsharing a cgroup namespace makes all your current cgroups your new
> cgroup root.
>
> 3. /proc/pid/cgroup always shows cgroup paths relative to the reader's
> cgroup namespce root.  A task outside of  your cgroup looks like
>
>         8:memory:/../../..
>
> 4. when a task mounts a cgroupfs, the cgroup which shows up as root depends
> on the mounting task's  cgroup namespace.
>
> 5. setns to a cgroup namespace switches your cgroup namespace but not
> your cgroups.
>
> With this, using github.com/hallyn/lxc #2015-11-09/cgns (and
> github.com/hallyn/lxcfs #2015-11-10/cgns) we can start a container in a full
> proper cgroup namespace, avoiding either cgmanager or lxcfs cgroup bind mounts.
>
> This is completely backward compatible and will be completely invisible
> to any existing cgroup users (except for those running inside a cgroup
> namespace and looking at /proc/pid/cgroup of tasks outside their
> namespace.)
>    cgroupns-root.

IIRC one downside of this series was that only the new "sane" cgroup
layout was supported
and hence it was useless for everything which expected the default layout.
Hence, still no systemd for us. :)

Is this now different?

-- 
Thanks,
//richard
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