linux-kernel - Re: CGroup Namespaces (v4)

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Message-ID: <20151116204606.GA30681@mail.hallyn.com>
Date:	Mon, 16 Nov 2015 14:46:06 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	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)

On Mon, Nov 16, 2015 at 09:41:15PM +0100, Richard Weinberger wrote:
> 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?

Yes, all hierachies are no supported.
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