netdev - Re: [PATCH net 1/2] net: ipv4: update fnhe

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Message-Id: <20181008.105809.771177177568692611.davem@davemloft.net>
Date:   Mon, 08 Oct 2018 10:58:09 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     netdev@...r.kernel.org, sbrivio@...hat.com
Subject: Re: [PATCH net 1/2] net: ipv4: update fnhe_pmtu when first hop's
 MTU changes

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Mon,  8 Oct 2018 14:36:38 +0200

> Since commit 5aad1de5ea2c ("ipv4: use separate genid for next hop
> exceptions"), exceptions get deprecated separately from cached
> routes. In particular, administrative changes don't clear PMTU anymore.
> 
> As Stefano described in commit e9fa1495d738 ("ipv6: Reflect MTU changes
> on PMTU of exceptions for MTU-less routes"), the PMTU discovered before
> the local MTU change can become stale:
>  - if the local MTU is now lower than the PMTU, that PMTU is now
>    incorrect
>  - if the local MTU was the lowest value in the path, and is increased,
>    we might discover a higher PMTU
> 
> Similarly to what commit e9fa1495d738 did for IPv6, update PMTU in those
> cases.
> 
> If the exception was locked, discovered the PMTU was smaller than the
> minimal accepted PMTU. In that case, if the new local MTU is smaller
> than the current PMTU, let PMTU discovery figure out if locking of the
> exception is still needed.
> 
> To do this, we need to know the old link MTU in the NETDEV_CHANGEMTU
> notifier. By the time the notifier is called, dev->mtu has been
> changed. This patch adds the old MTU as additional information in the
> notifier structure, and a new call_netdevice_notifiers_u32() function.
> 
> Fixes: 5aad1de5ea2c ("ipv4: use separate genid for next hop exceptions")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
> Reviewed-by: Stefano Brivio <sbrivio@...hat.com>

Please, when you respin this to address David Ahern's feedback, provide
a proper "0/N" header posting.

Thank you.