From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: [PATCH] lro: IP fragment checking Date: Tue, 02 Dec 2008 15:18:48 +0000 Message-ID: <1228231128.3075.9.camel@achroite> References: <4933A74F.3050809@de.ibm.com> <493423D7.5030203@myri.com> <20081201.131810.158631503.davem@davemloft.net> <49345CCA.1030209@myri.com> <1228169379.3073.13.camel@achroite> <49347B0B.8030705@myri.com> <1228177130.3073.23.camel@achroite> <49354970.10804@myri.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: David Miller , ossthema@de.ibm.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, tklein@de.ibm.com, raisch@de.ibm.com, jb.billaud@gmail.com, hering2@de.ibm.com To: Andrew Gallatin Return-path: Received: from smarthost01.mail.zen.net.uk ([212.23.3.140]:57405 "EHLO smarthost01.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754512AbYLBPS7 (ORCPT ); Tue, 2 Dec 2008 10:18:59 -0500 In-Reply-To: <49354970.10804@myri.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2008-12-02 at 09:42 -0500, Andrew Gallatin wrote: > Ben Hutchings wrote: > > On Mon, 2008-12-01 at 19:02 -0500, Andrew Gallatin wrote: > >> Ben Hutchings wrote: [...] > >>> If your hardware/firmware wrongly claims to be able to verify the > >>> TCP/UDP checksum for an IP fragment, it seems to me you should deal with > >>> that in your driver or fix the firmware. > >> We do partial checksums. > > > > So you should check for IP fragmentation in your get_frag_header() along > > with all the other checks you've got to do. > > Indeed, and that is the patch I intend to submit if the fragment > check in inet_lro is rejected. I still think the check belongs > in the inet lro code though, and I'm worried it is being rejected > for the wrong reasons.. There's a wide variety of capabilities of different hardware: 1. No checksum offload. Probably not worth using LRO. 2. Full-checksum generation. Driver passes packets to inet_lro; get_frag_header() or get_skb_header() parses packets to check that they are TCP/IPv4 and to validate the checksum. inet_lro does further checks. 3. L4 packet parsing and checksum validation. Driver passes TCP/IPv4 packets to inet_lro. inet_lro does further checks. 4. Hardware/firmware LRO. inet_lro not needed. You seem to be proposing that a check that is only needed in case (2) should also be applied in case (3). Maybe it would make more sense to define a generic implementation of get_frag_header() for full-checksum devices, if that's possible? Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.