netdev - Re: [PATCHv3 net-next 2/3] sunvnet: allow admin to set sunvnet MTU

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Message-Id: <20140913.162101.515634682549373073.davem@davemloft.net>
Date:	Sat, 13 Sep 2014 16:21:01 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	david.stevens@...cle.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCHv3 net-next 2/3] sunvnet: allow admin to set sunvnet MTU

From: David L Stevens <david.stevens@...cle.com>
Date: Sat, 13 Sep 2014 12:00:55 -0400

> This patch allows an admin to set the MTU on a sunvnet device to arbitrary
> values between the minimum (68) and maximum (65535) IPv4 packet sizes.
> 
> Signed-off-by: David L Stevens <david.stevens@...cle.com>

I personally find this scheme where we pretend that the device can
have an arbitrary MTU, when in fact the effective MTU is a product of
the sub-ports, quite ugly.

In fact, that ugly ICMP stuff in the next patch is absolutely required
to avoid bogus behavior possible after this patch.  You have to
combine #2 and #3 otherwise you are adding an intermediate regression.

Logic wise, at the very least you should limit the MTU setting to the
largest MTU of all of the individual ports.
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