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

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Message-ID: <CABg5FUUns7n1h0JCrvwFPd_1AHg0jGH5FH6xwj1msBqE=wpMjg@mail.gmail.com>
Date:	Thu, 11 Jun 2015 09:53:15 -0700
From:	Dinesh Dutt <ddutt@...ulusnetworks.com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	Andy Gospodarek <gospo@...ulusnetworks.com>,
	Scott Feldman <sfeldma@...il.com>,
	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	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

Yes, this is what I liked about the 2 flag solution too compared to
the original.

Dinesh

On Thu, Jun 11, 2015 at 7:50 AM, Alexander Duyck
<alexander.h.duyck@...hat.com> wrote:
>
>
> On 06/11/2015 04:23 AM, Andy Gospodarek wrote:
>>
>> 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.
>>   this point I think I prefer the additional data provided by the new
>> flag exported to userspace.
>
>
> I preferred the 2 flag solution as the original solution still required 2
> flags, it just only exposed 1 to user-space.  As a result it was much more
> error prone since it was fairly easy to get into a confused state about why
> the link was dead.
>
> With the 2 flag solution it becomes much easier to sort out why the route is
> not functional and it is much easier to isolate for things like the sysctl
> which only disables the use of LINKDOWN and not DEAD.
>
> - Alex
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