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

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Date:	Mon, 25 Jul 2016 19:07:36 -0700
From:	Andrew Vagin <avagin@...tuozzo.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Andrey Vagin <avagin@...nvz.org>,
	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@...nvz.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

On Sun, Jul 24, 2016 at 12:10:21AM -0500, Eric W. Biederman wrote:
> 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

Eric, thank you for the detailed comments. I will rework this series and
send it after the merge window.

> 
> > 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