netdev - Re: [PATCH net v2 2/3] geneve: Relax MTU constraints

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Message-Id: <20160218.150715.2026246274939635940.davem@davemloft.net>
Date:	Thu, 18 Feb 2016 15:07:15 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	david@...ve.works
Cc:	tom@...bertland.com, jesse@...nel.org, netdev@...r.kernel.org,
	dev@...nvswitch.org, hannes@...essinduktion.org, tgraf@...g.ch,
	roopa@...ulusnetworks.com
Subject: Re: [PATCH net v2 2/3] geneve: Relax MTU constraints

From: David Wragg <david@...ve.works>
Date: Thu, 18 Feb 2016 16:54:14 +0000

> Tom Herbert <tom@...bertland.com> writes:
>> Please implement like in ip_tunnel_change_mtu (or better yet call it),
>> that is the precedent for tunnels.
> 
> I've made geneve_change_mtu follow ip_tunnel_change_mtu in v2.
> 
> If it were to call it instead, are you suggesting just passing in
> t_hlen?  Or restructuring geneve.c to re-use the whole ip_tunnel
> infrastructure?
> 
> Also, I'm not sure where the 0xFFF8 comes from in
> __ip_tunnel_change_mtu.  Any ideas why 0xFFF8 rather than 0xffff?  It
> goes all the way back to the inital import of the kernel into git.

Some 8 byte multiple requirement, perhaps to do with fragmentation.