netdev - Re: [PATCH v2 2/2] ipv6 addrconf: don't cleanup route prefix for IFA_F

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Date:	Wed, 8 Jan 2014 00:09:36 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Thomas Haller <thaller@...hat.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
	stephen@...workplumber.org, dcbw@...hat.com
Subject: Re: [PATCH v2 2/2] ipv6 addrconf: don't cleanup route prefix for IFA_F_NOPREFIXROUTE

On Tue, Jan 07, 2014 at 11:54:22PM +0100, Thomas Haller wrote:
> Hi,
> 
> 
> I think, the modify case is not that hairy and the patch does IMO the
> sensible thing:
> 
> case 1) "change NOPREFIXROUTE -> !NOPREFIXROUTE":
>     update or add prefix route (as before);;
> case 2) "change !NOPREFIXROUTE -> !NOPREFIXROUTE":
>     update or add prefix route (as before);;
> case 3) "change NOPREFIXROUTE -> NOPREFIXROUTE":
>     ;;
> case 4) "change !NOPREFIXROUTE -> NOPREFIXROUTE":
>     cleanup prefix route;;
> 
> where "cleanup" means the same as done in ipv6_del_addr(), as determined
> by check_cleanup_prefix_routes().
> 
> 
> Allowing modify with case 2) and 3) is important. But for case 4) (and
> possibly 1)), we could also fail with error. I tend to the scheme above
> though because it makes it easier for userspace and is likely what it
> wants.
> 
> 
> 
> The problem of deleting a route created by somebody else is already
> present without this patch in ipv6_del_addr. This is indeed a bit shaky,
> but I guess it's good enough in practice. Do I understand correctly,
> that you think about to use the information from ifp->rt to ensure, that
> what we really cleanup the correct route? If that's what you intend, can
> you elaborate a bit on how to do that?

The ifp->rt thing, I thought of, does not work. It only holds the RTF_LOCAL
route (over loopback) which has nothing to do with the prefix route. We don't
have a link from ifp to the prefix route.

Currently I am fine with the semantics you described above but won't
have time to review them today. I'll do that tomorrow.

Thanks,

  Hannes

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