linux-kernel - Re: [Devel] Re: [PATCH] allow a task to join a pid namespace

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Message-ID: <4FCE0101.6010908@free.fr>
Date:	Tue, 05 Jun 2012 14:52:17 +0200
From:	Daniel Lezcano <daniel.lezcano@...e.fr>
To:	Glauber Costa <glommer@...allels.com>
CC:	Serge Hallyn <serge.hallyn@...onical.com>, kir@...allels.com,
	Michael@...nvz.org, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org, Kerrisk <mtk.manpages@...il.com>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	devel@...nvz.org, "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [Devel] Re: [PATCH] allow a task to join a pid namespace

On 06/05/2012 12:00 PM, Glauber Costa wrote:
> On 06/05/2012 01:37 PM, Glauber Costa wrote:
>> On 06/05/2012 01:36 PM, Daniel Lezcano wrote:
>>> On 06/04/2012 03:33 PM, Glauber Costa wrote:
>>>> Currently, it is possible for a process to join existing
>>>> net, uts and ipc namespaces. This patch allows a process to join an
>>>> existing pid namespace as well.
>>>>
>>>> For that to remain sane, some restrictions are made in the calling
>>>> process:
>>>>
>>>> * It needs to be in the parent namespace of the namespace it wants to
>>>> jump to
>>>> * It needs to sit in its own session and group as a leader.
>>>>
>>>> The rationale for that, is that people want to trigger actions in a
>>>> Container
>>>> from the outside. For instance, mainstream linux recently gained the
>>>> ability
>>>> to safely reboot a container. It would be desirable, however, that
>>>> this
>>>> action is triggered from an admin in the outside world, very much
>>>> like a
>>>> power switch in a physical box.
>>>>
>>>> This would also allow us to connect a console to the container,
>>>> provide a
>>>> repair mode for setups without networking (or with a broken one), etc.
>>>
>>> Hi Glauber,
>>>
>>> I am in favor of this patch but I think the pidns support won't be
>>> complete and some corner-cases are not handled.
>>>
>>> May be you can look at Eric's patchset [1] where, IMO, everything is
>>> taken into account. Some of the patches may be already upstream.
>>>
>>> Thanks
>>> -- Daniel
>>
>> I don't remember seeing such patchset in the mailing lists, but that
>> might be my fault, due to traffic...
>>
>> I'll take a look. If it does what I need, I can just drop this.
>>
>
> Ok. In a quick look, it does not seem to go all the way. This is just
> by reading, but your reboot patch, for instance, is unlikely to work
> with that, since if it doesn't alter pid->level, things like task
> ns_of_pid won't work.
>
> Running the test scripts I wrote for my testing of that patch also
> doesn't seem to produce the expected result:
>
> after doing setns, the pid won't show up in that namespace.

Yes, AFAIR, pid won't show up, you have to do fork-exec.


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