linux-kernel - Re: CGroup Namespaces (v4)

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Message-ID: <564A41AF.4040208@nod.at>
Date:	Mon, 16 Nov 2015 21:50:55 +0100
From:	Richard Weinberger <richard@....at>
To:	"Serge E. Hallyn" <serge@...lyn.com>,
	Richard Weinberger <richard.weinberger@...il.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)

Am 16.11.2015 um 21:46 schrieb Serge E. Hallyn:
> 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.
> 

Should read "now"? :-)
If so, *awesome*!

Thanks,
//richard
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