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

[James Bottomley <James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>]

On Tue, 2017-05-23 at 10:17 -0500, Eric W. Biederman wrote:
> David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> writes:
> > Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> 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


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