From mboxrd@z Thu Jan 1 00:00:00 1970 From: Evgeniy Polyakov Subject: Re: Data corruption issue with splice() on 2.6.27.10 Date: Wed, 7 Jan 2009 15:57:56 +0300 Message-ID: <20090107125756.GA32336@ioremap.net> References: <20090106094138.GE25644@1wt.eu> <20090106100112.GB9513@ff.dom.local> <20090106155715.GA28783@1wt.eu> <20090107093915.GA6899@ff.dom.local> <20090107122205.GA6051@1wt.eu> <20090107123153.GA9597@ff.dom.local> <20090107123504.GN32491@kernel.dk> <20090107124034.GB31255@ioremap.net> <20090107125201.GB6307@1wt.eu> <20090107125356.GB26235@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Willy Tarreau , Jens Axboe , Jarek Poplawski , Changli Gao , linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: Herbert Xu Return-path: Received: from genesysrack.ru ([195.178.208.66]:33774 "EHLO tservice.net.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756491AbZAGM55 (ORCPT ); Wed, 7 Jan 2009 07:57:57 -0500 Content-Disposition: inline In-Reply-To: <20090107125356.GB26235@gondor.apana.org.au> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Jan 07, 2009 at 11:53:56PM +1100, Herbert Xu (herbert@gondor.apana.org.au) wrote: > On Wed, Jan 07, 2009 at 01:52:01PM +0100, Willy Tarreau wrote: > > > > Evgeniy, I'd like to understand something related to our apparent lack of > > knowledge of when the data is effectively transmitted. If we're focusing > > on the send part, I can't understand why I never reproduce the corruption > > when the data source is a file or loopback, but I only see it when the source > > is an ethernet interface. How is it possible that a problem affecting only > > It doesn't happen with a file because in that case you don't > start with an skb so there is no skb->head. It probably doesn't > happen with loopback because loopback does GSO so again skb->head > does not exist (so to speak). Yup, basically splice's transmit pipe buffer contains page references, where the first one is actually not a real page but skb, while in the case of sendfile() and/or splice() from the file first page is a real page of the appropriate file. -- Evgeniy Polyakov