Subject: Re: [Propose] Isolate core_pattern in mnt namespace.
To: "Eric W. Biederman" <ebiederm@xmission.com>,
        Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
References: <56729B3D.1040502@cn.fujitsu.com>
 <56760F05.3020308@cn.fujitsu.com> <20151220023712.GT20997@ZenIV.linux.org.uk>
 <567616D6.6060202@cn.fujitsu.com> <87fuyx1mfn.fsf@x220.int.ebiederm.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>, containers@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>, cgroups@vger.kernel.org
From: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Message-ID: <567740BA.9070307@jp.fujitsu.com>
Date: Mon, 21 Dec 2015 08:58:50 +0900
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On 2015/12/20 18:47, Eric W. Biederman wrote:
> Dongsheng Yang <yangds.fnst@cn.fujitsu.com> writes:
> 
>> On 12/20/2015 10:37 AM, Al Viro wrote:
>>> On Sun, Dec 20, 2015 at 10:14:29AM +0800, Dongsheng Yang wrote:
>>>> On 12/17/2015 07:23 PM, Dongsheng Yang wrote:
>>>>> Hi guys,
>>>>>       We are working on making core dump behaviour isolated in
>>>>> container. But the problem is, the /proc/sys/kernel/core_pattern
>>>>> is a kernel wide setting, not belongs to a container.
>>>>>
>>>>>       So we want to add core_pattern into mnt namespace. What
>>>>> do you think about it?
>>>>
>>>> Hi Eric,
>>>> 	I found your patch about "net: Implement the per network namespace
>>>> sysctl infrastructure", I want to do the similar thing
>>>> in mnt namespace. Is that suggested way?
>>>
>>> Why mnt namespace and not something else?
>>
>> Hi Al,
>>
>> Well, because core_pattern indicates the path to store core file.
>> In different mnt namespace, we would like to change the path with
>> different value.
>>
>> In addition, Let's considering other namespaces:
>> UTS ns: contains informations of kernel and arch, not proper for core_pattern.
>> IPC ns: communication informations, not proper for core_pattern
>> PID ns: core_pattern is not related with pid
>> net ns: obviousely no.
>> user ns: not proper too.
>>
>> Then I believe it's better to do this in mnt namespace. of course,
>> core_pattern is just one example. After this infrastructure finished,
>> we can implement more sysctls as per-mnt if necessary, I think.
>>
>> Al, what do you think about this idea?
> 
> The hard part is not the sysctl.  The hard part is starting the usermode
> helper, in an environment that it can deal with.  The mount namespace
> really provides you with no help there.
> 
Let me ask. I think user-mode-helper shouldn be found in container's namespace.
Or Do you mean running user-mode-helper out of a container ?

I think if a user need to send cores to outside of a container, a file descriptor
or a network end point should be able to be passed to sysctl. 

Thanks,
-Kame


> Eric
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