linux-kernel - Re: [PATCH] batman-adv: Revert "use core MTU range checking in misc drivers"

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Message-ID: <20161023010826.GD32569@redhat.com>
Date:   Sat, 22 Oct 2016 21:08:26 -0400
From:   Jarod Wilson <jarod@...hat.com>
To:     Sven Eckelmann <sven@...fation.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        b.a.t.m.a.n@...ts.open-mesh.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] batman-adv: Revert "use core MTU range checking in misc
 drivers"

On Sat, Oct 22, 2016 at 09:46:24AM +0200, Sven Eckelmann wrote:
> The maximum MTU is defined via the slave devices of an batman-adv
> interface. Thus it is not possible to calculate the max_mtu during the
> creation of the batman-adv device when no slave devices are attached. Doing
> so would for example break non-fragmentation setups which then
> (incorrectly) allow an MTU of 1500 even when underlying device cannot
> transport 1500 bytes + batman-adv headers.
> 
> Checking the dynamically calculated max_mtu via the minimum of the slave
> devices MTU during .ndo_change_mtu is also used by the bridge interface.
> 
> Cc: Jarod Wilson <jarod@...hat.com>
> Fixes: b3e3893e1253 ("net: use core MTU range checking in misc drivers")
> Signed-off-by: Sven Eckelmann <sven@...fation.org>
> ---
> Original patch + my comment: https://patchwork.ozlabs.org/patch/684722/
> 
> I just got informed about this patch when it was already applied in net-next.
> So I can only ask for an revet of the batman-adv parts

Apologies, I tried to cc everyone I could find in MAINTAINERS, but your
name wasn't one of the three listed for batman devices. You're going to
need more than just this revert though, since batman-adv calls
ether_setup, which will set min_mtu = 68, max_mtu = 1500, unless
batadv_hardif_min_mtu() always returns something 1500 or less. Actually,
looking at that, you could omit the mtu < 68 bit from
batadv_interface_change_mtu() too, since that'll already get done in the
core, but I have no clue what you need for max_mtu.

-- 
Jarod Wilson
jarod@...hat.com