From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steffen Klassert Subject: Re: [PATCH 2/5] ipv4: Kill ip_rt_frag_needed(). Date: Wed, 13 Jun 2012 12:07:09 +0200 Message-ID: <20120613100709.GO27795@secunet.com> References: <20120612114440.GM27795@secunet.com> <20120612.133333.527780673034196147.davem@davemloft.net> <20120613080152.GN27795@secunet.com> <20120613.024225.1623724542402950589.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: David Miller Return-path: Received: from a.mx.secunet.com ([195.81.216.161]:34948 "EHLO a.mx.secunet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125Ab2FMKHc (ORCPT ); Wed, 13 Jun 2012 06:07:32 -0400 Content-Disposition: inline In-Reply-To: <20120613.024225.1623724542402950589.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Jun 13, 2012 at 02:42:25AM -0700, David Miller wrote: > From: Steffen Klassert > Date: Wed, 13 Jun 2012 10:01:52 +0200 > > > I think an application that sets IP_PMTUDISC_WANT explicitly will > > rely on the fact that the kernel does pmtu discovery. Changing > > the socket setting to IP_PMTUDISC_DONT the first time we get into > > trouble makes IP_PMTUDISC_WANT pointless for udp and raw sockets. > > How so? > > We are mimicking exactly what would happen if we had just created > a new routing cache entry when the application openned the socket. > > There is no behavioral difference whatsoever. > > We absolutely do perform PMTU discovery, the first large packet > will trigger it. And then, as if we had lowered the PMTU in > the routing cache entry, we will stop setting DF in the packets. Maybe I missunderstood what you meant. I thought that you don't want to update the pmtu cache informations at all on udp and raw. If we update the pmtu cache informations with first large packet, I agree absolutely.