[BIRD 2.0.x] Netlink: ignore dead routes

[Vincent Bernat]

 ❦ 14 janvier 2021 08:23 +01, Vincent Bernat:

>> Although it would make sense to handle dead routes as withdraws instead
>> of just ingore them (for async notification), it does not matter for sync
>> scan, and as i noticed during testing, Linux kernel does not send async
>> notifications (when the flag changes to dead) anyways, so it does not
>> really matter.
>
> It would makes sense to fix Linux for that. I'll try to send a patch and
> ping here again if it gets accepted.

It is more complex that I would have expected. First, in-kernel, the
next-hop only has RTNH_F_LINKDOWN, not RTNH_F_DEAD. This later flag is
added when sending the flags over netlink only.

Second, there is no async notification when a route goes down either.
There is a notification on the interface. How BIRD handles this case? Is
a route scan triggered when an interface goes down? I'll test more
later, it's a bit late for me.
-- 
He that breaks a thing to find out what it is has left the path of wisdom.
		-- J.R.R. Tolkien