From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261793AbTKGWOt (ORCPT ); Fri, 7 Nov 2003 17:14:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261786AbTKGWN6 (ORCPT ); Fri, 7 Nov 2003 17:13:58 -0500 Received: from web25205.mail.ukl.yahoo.com ([217.12.10.65]:64375 "HELO web25205.mail.ukl.yahoo.com") by vger.kernel.org with SMTP id S264469AbTKGQke (ORCPT ); Fri, 7 Nov 2003 11:40:34 -0500 Message-ID: <20031107164033.19095.qmail@web25205.mail.ukl.yahoo.com> Date: Fri, 7 Nov 2003 17:40:33 +0100 (CET) From: =?iso-8859-1?q?francois=20donzet?= Subject: checksum offloading To: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, please answer to my mail (not subscribed) i've posted this on netdev, and get no reply. I try there : It is about tcp checksum offloading : in my understanding of the process, if the device supports checksum offloading : - an incoming packet is handled by the driver networking code associated to the ethernet card (for example) 1) the checksum is hardware computed. But in the case of e100 for example, skb->csum is filled with a sum covering the entire packet 2) then the packet passes through ip layer, checksum is verified (not using skb->csum) 3) the packet comes to tcp layer, skb->csum is extracted and used to compute (folding with the pseudo header checksum) the final checksum 4) if the packet is incorrect, drop it. You see the problem is between 1) and 2). In my understanding, skb->csum is used by tcp, but as skb->csum as been filled with a sum on the entire packet content as seen by netif_rx() (that is what is indicated in skbuff.h by yourself), there is a problem because tcp only needs the sum on tcpheader+data no ? no the entire sum computed by the hardware. Before reading the code, i thought that the TCP checksum was computed by hardware. (not a sum on ipheader+tcpheader+data). Thanks please answer to my mail (not subscribed ___________________________________________________________ Do You Yahoo!? -- Une adresse @yahoo.fr gratuite et en français ! Yahoo! Mail : http://fr.mail.yahoo.com