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Date:   Sat, 22 Oct 2016 21:08:26 -0400
From:   Jarod Wilson <>
To:     Sven Eckelmann <>
Subject: Re: [PATCH] batman-adv: Revert "use core MTU range checking in misc

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 <>
> Fixes: b3e3893e1253 ("net: use core MTU range checking in misc drivers")
> Signed-off-by: Sven Eckelmann <>
> ---
> Original patch + my comment:
> 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

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