netdev - Re: [PATCH] ip_tunnel(ipv4): fix tunnels with "local any remote $remote

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Message-Id: <20140729214931.9ae11fe3ddfd49ca6f499db6@qrator.net>
Date:	Tue, 29 Jul 2014 21:49:31 +0400
From:	Dmitry Popov <ixaphire@...tor.net>
To:	Cong Wang <cwang@...pensource.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Sergey Popov <pinkbyte@...too.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH] ip_tunnel(ipv4): fix tunnels with
 "local any remote $remote_ip"

On Mon, 28 Jul 2014 16:39:23 -0700
Cong Wang <cwang@...pensource.com> wrote:

> On Mon, Jul 28, 2014 at 4:07 PM, Dmitry Popov <ixaphire@...tor.net> wrote:
> > --- a/include/net/ip_tunnels.h
> > +++ b/include/net/ip_tunnels.h
> > @@ -40,6 +40,7 @@ struct ip_tunnel_prl_entry {
> >
> >  struct ip_tunnel_dst {
> >         struct dst_entry __rcu          *dst;
> > +       __be32                           saddr;
> >  };
> 
> 
> It looks odd to save a source address in some struct named dst,
> maybe it's the time to rename it.

Yes, maybe a bit odd, but ip_tunnel_flow/ip_tunnel_route doesn't look much 
better for me, so I decided to keep it with old name. David is ok with this
name too.

> >         if (dst) {
> > -               if (dst->obsolete && dst->ops->check(dst, cookie) == NULL) {
> > +               if (!dst->obsolete || dst->ops->check(dst, cookie)) {
> > +                       *saddr = idst->saddr;
> > +               } else {
> 
> I am wondering if this always works, that is, if saddr could be still valid
> as long as dst is valid?

Right, this is not a very smooth place, but a) it should work with current ipv4
route implementation (it obsoletes all dst_entries on any route/addr change).
Yes, we shouldn't rely on implementation, but b) I don't know how (and why) this
implementation should be changed to break it. I think the assumption that
dst_entry is obsoleted when saddr is changed is pretty natural.
Please correct me if I'm wrong.
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