Re: [RFC][PATCH 0/9] Make containers kernel objects

From	James Bottomley <James.Bottomley@HansenPartnership.com>
Newsgroups	linux.kernel
Subject	Re: [RFC][PATCH 0/9] Make containers kernel objects
Date	2017-05-23 17:50 +0200
Message-ID	<tKkel-58v-11@gated-at.bofh.it> (permalink)
References	(2 earlier) <tJYnv-80c-3@gated-at.bofh.it> <tJYQy-8az-29@gated-at.bofh.it> <tKjrY-4z9-23@gated-at.bofh.it> <tKjLl-4VL-33@gated-at.bofh.it> <tKjV0-51B-25@gated-at.bofh.it>
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On Tue, 2017-05-23 at 10:17 -0500, Eric W. Biederman wrote:
> David Howells <dhowells@redhat.com> writes:
> > Eric W. Biederman <ebiederm@xmission.com> wrote:
> > > It does solve this in userspace rather simply.
> > 
> > Ummm...  How?  The kernel DNS resolver is not namespace aware.
> 
> But it works fine if called in the proper context and we have a 
> defacto standard for where to put all of the files (the tricky part) 
> if you are dealing with multiple network namespaces simultaneously.

I think you're missing each other's points slightly.

What David is pointing out is that the kernel has a DNS cache
(net/dns_resolver/) it can do name to IP translations, but isn't
namespaced.  Once it has one entry all containers would see it if they
cause a lookup to go through the kernel cache, so going through the
cache you can't have a name resolving to different IP addresses on a
per container basis.

I think Eric's point is that if you need the same DNS names resolving
to different IP addresses on a per container basis, you can do this in
userspace today but you have to disable the in-kernel DNS cache.

James

Thread

[RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-22 18:30 +0200
  [PATCH 8/9] Honour CONTAINER_NEW_EMPTY_FS_NS David Howells <dhowells@redhat.com> - 2017-05-22 18:30 +0200
  [PATCH 3/9] Provide /proc/containers David Howells <dhowells@redhat.com> - 2017-05-22 18:30 +0200
  Re: [RFC][PATCH 0/9] Make containers kernel objects James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-05-22 19:00 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects Aleksa Sarai <asarai@suse.de> - 2017-05-22 19:20 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 17:00 +0200
        Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-23 17:10 +0200
          Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 17:20 +0200
            Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-23 17:30 +0200
              Re: [RFC][PATCH 0/9] Make containers kernel objects James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-05-23 17:50 +0200
                Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 18:40 +0200
                Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-24 10:40 +0200
                Re: [RFC][PATCH 0/9] Make containers kernel objects Ian Kent <raven@themaw.net> - 2017-05-24 11:20 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects Jessica Frazelle <me@jessfraz.com> - 2017-05-22 19:30 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects Jeff Layton <jlayton@redhat.com> - 2017-05-22 20:40 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-05-22 21:30 +0200
        Re: [RFC][PATCH 0/9] Make containers kernel objects Jeff Layton <jlayton@redhat.com> - 2017-05-23 00:20 +0200
        Re: [RFC][PATCH 0/9] Make containers kernel objects Ian Kent <raven@themaw.net> - 2017-05-23 12:40 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects Ian Kent <raven@themaw.net> - 2017-05-23 11:40 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 16:00 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects James Bottomley <James.Bottomley@HansenPartnership.com> - 2017-05-23 17:10 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-23 17:40 +0200
  Re: [RFC][PATCH 0/9] Make containers kernel objects Jessica Frazelle <me@jessfraz.com> - 2017-05-22 19:20 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 17:20 +0200
  Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-22 21:20 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects Jeff Layton <jlayton@redhat.com> - 2017-05-23 00:30 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-23 15:10 +0200
        Re: [RFC][PATCH 0/9] Make containers kernel objects Jeff Layton <jlayton@redhat.com> - 2017-05-23 16:30 +0200
        Re: [RFC][PATCH 0/9] Make containers kernel objects Djalal Harouni <tixxdz@gmail.com> - 2017-05-23 16:40 +0200
          Re: [RFC][PATCH 0/9] Make containers kernel objects Colin Walters <walters@verbum.org> - 2017-05-23 17:00 +0200
            Re: [RFC][PATCH 0/9] Make containers kernel objects Colin Walters <walters@verbum.org> - 2017-05-23 17:40 +0200
            Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 17:40 +0200
            Re: [RFC][PATCH 0/9] Make containers kernel objects Jeff Layton <jlayton@redhat.com> - 2017-05-23 17:40 +0200
      Re: [RFC][PATCH 0/9] Make containers kernel objects Djalal Harouni <tixxdz@gmail.com> - 2017-05-23 16:30 +0200
    Re: [RFC][PATCH 0/9] Make containers kernel objects David Howells <dhowells@redhat.com> - 2017-05-23 18:20 +0200
  Re: [RFC][PATCH 0/9] Make containers kernel objects Ian Kent <raven@themaw.net> - 2017-05-23 12:20 +0200
  Re: [RFC][PATCH 0/9] Make containers kernel objects ebiederm@xmission.com (Eric W. Biederman) - 2017-05-23 17:40 +0200

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