Re: [Propose] Isolate core_pattern in mnt namespace.

[Dongsheng Yang <yangds.fnst@cn.fujitsu.com>]

On 12/20/2015 05:47 PM, 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.

Do you mean the core dump helper? But I think I don't want to touch it
in my development. I think I can use non-pipe way to get what I want,
Let me try to explain what I want here.

(1). introduce a --core-path option in docker run command to specify the
path in host to store core file in one container.
E.g: docker run --core-path=/core/test --name=test IMAGE

(2). When the container starting, docker attach a volume to it, similar
with "-v /core/test:/var/lib/docker/coredump". That means, the path of
/var/lib/docker/coredump in container is a link to /core/test in host.

(3). Set the /proc/sys/kernel/core_pattern in container as
"/var/lib/docker/coredump". But that should not affect the core_pattern
in host or other containers.

Then I think I can collect the core files from each container and save
them in the paths where I want.

Thanx
Yang
>
> Eric
>
>
>