linux-kernel - Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

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Date:	Sun, 24 Jul 2016 00:10:21 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"criu\@openvz.org" <criu@...nvz.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"Michael Kerrisk \(man-pages\)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces

Andrey Vagin <avagin@...nvz.org> writes:

> Hello,
>
> I forgot to add --cc-cover for git send-email, so everyone who is in
> Cc got only a cover letter. All messages were sent in mail lists.
>
> Sorry for inconvenience.

Mostly the code looked sensible.  But I had a couple of issues.
Resend this in September (when the merge window is closed and I am back
from vacation) and I will give this a thorough review and get this
merged.  Or possibly next week if Linus releases another -rc

> On Thu, Jul 14, 2016 at 11:20 AM, Andrey Vagin <avagin@...nvz.org> wrote:
>> Each namespace has an owning user namespace and now there is not way
>> to discover these relationships.
>>
>> Pid and user namepaces are hierarchical. There is no way to discover
>> parent-child relationships too.
>>
>> Why we may want to know relationships between namespaces?
>>
>> One use would be visualization, in order to understand the running system.
>> Another would be to answer the question: what capability does process X have to
>> perform operations on a resource governed by namespace Y?
>>
>> One more use-case (which usually called abnormal) is checkpoint/restart.
>> In CRIU we age going to dump and restore nested namespaces.
>>
>> There [1] was a discussion about which interface to choose to determing
>> relationships between namespaces.
>>
>> Eric suggested to add two ioctl-s [2]:
>>> Grumble, Grumble.  I think this may actually a case for creating ioctls
>>> for these two cases.  Now that random nsfs file descriptors are bind
>>> mountable the original reason for using proc files is not as pressing.
>>>
>>> One ioctl for the user namespace that owns a file descriptor.
>>> One ioctl for the parent namespace of a namespace file descriptor.
>>
>> Here is an implementaions of these ioctl-s.
>>
>> [1] https://lkml.org/lkml/2016/7/6/158
>> [2] https://lkml.org/lkml/2016/7/9/101
>>
>> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
>> Cc: James Bottomley <James.Bottomley@...senPartnership.com>
>> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
>> Cc: "W. Trevor King" <wking@...mily.us>
>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
>> Cc: Serge Hallyn <serge.hallyn@...onical.com>


Eric