netdev - Re: UDP path MTU discovery

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Message-ID: <20100330061627.GM20695@one.firstfloor.org>
Date:	Tue, 30 Mar 2010 08:16:27 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"Templin, Fred L" <Fred.L.Templin@...ing.com>,
	Rick Jones <rick.jones2@...com>,
	"Edgar E. Iglesias" <edgar.iglesias@...il.com>,
	Glen Turner <gdt@....id.au>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: UDP path MTU discovery

> > Right now there is no right socket option to set the path mtu. We
> > have a IP_MTU option, but it only works for getting the MTU.
> > That's because the PMTU is in the routing cache entry and shared
> > by multiple sockets. Presumably one could add a special case
> > with an MTU in the socket overriding the one in the destination entry.
> 
> We have IP_MTU_DISCOVER option with four existing values

I think you would just need a sk->pmtu and a option to set/unset it
Or perhaps just a flag that clamps to 1280? 

Then the existing mtu discover options would be sufficient.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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