From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH] vxlan: Fix error that was resulting in VXLAN MTU size being 10 bytes too large Date: Mon, 19 Nov 2012 08:03:51 -0800 Message-ID: <20121119080351.477525b3@nehalam.linuxnetplumber.net> References: <20121109233354.17208.36271.stgit@gitlad.jf.intel.com> <20121113.143719.1473223615602040380.davem@davemloft.net> <20121113133353.227ec987@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: David Miller , alexander.h.duyck@intel.com, netdev@vger.kernel.org To: Joseph Glanville Return-path: Received: from mail.vyatta.com ([76.74.103.46]:60384 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753010Ab2KSQE5 (ORCPT ); Mon, 19 Nov 2012 11:04:57 -0500 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 19 Nov 2012 22:33:50 +1100 Joseph Glanville wrote: > On 14 November 2012 08:33, Stephen Hemminger wrote: > > On Tue, 13 Nov 2012 14:37:19 -0500 (EST) > > David Miller wrote: > > > >> From: Alexander Duyck > >> Date: Fri, 09 Nov 2012 15:35:24 -0800 > >> > >> > This change fixes an issue I found where VXLAN frames were fragmented when > >> > they were up to the VXLAN MTU size. I root caused the issue to the fact that > >> > the headroom was 4 + 20 + 8 + 8. This math doesn't appear to be correct > >> > because we are not inserting a VLAN header, but instead a 2nd Ethernet header. > >> > As such the math for the overhead should be 20 + 8 + 8 + 14 to account for the > >> > extra headers that are inserted for VXLAN. > >> > > >> > Signed-off-by: Alexander Duyck > >> > >> Applied, thanks for the detailed commit message. > > > > Probably need smarter code there to look at header length requirement > > of underlying device as well, maybe someone will be perverse and runn > > vxlan over a tunnel or IPoIB. > > Forgive my ignorance but why would running VXLAN on IPoIB require > special header handling? (and would it work or behave strangely?) > > I was planning on giving this a go when 3.7 is released but I might do > that sooner if problems are anticipated. > > > -- > > To unsubscribe from this list: send the line "unsubscribe netdev" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Joseph. > Some lower layers require bigger (or smaller headers). As it was, vxlan was only allocating skb with a fixed amount of headroom. This would lead to lower layers having to copy the skb. My suggestion has already been addressed by a later patch.