Groups > linux.kernel > #1451919

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

From	ebiederm@xmission.com (Eric W. Biederman)
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces
Date	2016-07-28 15:20 +0200
Message-ID	<rZTod-6L3-15@gated-at.bofh.it> (permalink)
References	(7 earlier) <rZ5B8-7Yz-25@gated-at.bofh.it> <rZfqN-5ya-5@gated-at.bofh.it> <rZg3v-616-19@gated-at.bofh.it> <rZR33-53d-3@gated-at.bofh.it> <rZR33-53d-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> writes:

> On 07/26/2016 10:39 PM, Andrew Vagin wrote:
>> On Tue, Jul 26, 2016 at 09:17:31PM +0200, Michael Kerrisk (man-pages) wrote:

>> If we want to compare two file descriptors of the current process,
>> it is one of cases for which kcmp can be used. We can call kcmp to
>> compare two namespaces which are opened in other processes.
>
> Is there really a use case there? I assume we're talking about the
> scenario where a process in one namespace opens a /proc/PID/ns/*
> file descriptor and passes that FD to another process via a UNIX
> domain socket. Is that correct?
>
> So, supposing that we want to build a map of the relationships
> between namespaces using the proposed kcmp() API, and there are
> say N namespaces? Does this mena we make (N * (N-1) / 2) calls
> to kcmp()?

Potentially.  The numbers are small enough O(N^2) isn't fatal.

Where kcmp shines is that it allows migration to happen.  Inode numbers
to change (which they very much will today), and still have things work.

We can keep it O(Nlog(N)) by taking advantage of not just the equality
but the ordering relationship.  Although Ugh.  One disadvantage of
kcmp currently is that the way the ordering relationship is defined
the order is not preserved over migration :(

Eric

Thread

Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-26 10:10 +0200
  Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "W. Trevor King" <wking@tremily.us> - 2016-07-26 20:40 +0200
  Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-26 21:20 +0200
    Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-28 12:50 +0200
      Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-28 15:20 +0200
        Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-28 21:10 +0200
          Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces ebiederm@xmission.com (Eric W. Biederman) - 2016-07-29 20:20 +0200
            Re: [PATCH 0/5 RFC] Add an interface to discover relationships  between namespaces "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> - 2016-07-31 23:40 +0200

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