netdev - Re: [PATCH net-next 1/3 v3] net: track link-status of ipv4 nexthops

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Message-ID: <20150611112313.GA588@gospo.home.greyhouse.net>
Date:	Thu, 11 Jun 2015 07:23:14 -0400
From:	Andy Gospodarek <gospo@...ulusnetworks.com>
To:	Scott Feldman <sfeldma@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>, ddutt@...ulusnetworks.com,
	Alexander Duyck <alexander.duyck@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [PATCH net-next 1/3 v3] net: track link-status of ipv4 nexthops

On Wed, Jun 10, 2015 at 11:07:28PM -0700, Scott Feldman wrote:
> On Wed, Jun 10, 2015 at 7:37 PM, Andy Gospodarek
> <gospo@...ulusnetworks.com> wrote:
> > Add a fib flag called RTNH_F_LINKDOWN to any ipv4 nexthops that are
> > reachable via an interface where carrier is off.  No action is taken,
> > but additional flags are passed to userspace to indicate carrier status.
> 
> Andy, it seems now RTNH_F_LINKDOWN and RTNH_F_DEAD are very similar
> and I'm wondering if this could be done without introducing a new flag
> and just use RTNH_F_DEAD.  The link change event would set RTNH_F_DEAD
> on nh on dev link down, and clear on link up.  The sysctl knob would
> be something like "nexthop_dead_on_linkdown", default off.  So
> basically expanding the ways RTNH_F_DEAD can be set.  That would
> simplify the patch set quite a bit and require no changes to iproute2.
> 

You are absolutely correct that what you describe would be less churn to
userspace.  From a functionality standpoint that is close to what was
originally proposed, but Alex specifically did not like the behavioral
change to what having RTNH_F_DEAD set (at least that was what I
understood).

That was what made me make the move to add this additional flag that was
exported to userspace, so it was possible to differentiate the old dead
routes/nexthop functionality from those that were not going to be dead
due to link being down.  

At this point I think I prefer the additional data provided by the new
flag exported to userspace.
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