From mboxrd@z Thu Jan 1 00:00:00 1970 From: FUJITA Tomonori Subject: Re: [PATCH] block: fix residual byte count handling Date: Mon, 3 Mar 2008 21:17:28 +0900 Message-ID: <20080303211727P.tomof@acm.org> References: <47CB79E9.8000505@gmail.com> <20080303172623O.fujita.tomonori@lab.ntt.co.jp> <47CBC309.7090106@gmail.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mo10.iij4u.or.jp ([210.138.174.78]:36699 "EHLO mo10.iij4u.or.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752017AbYCCMYZ (ORCPT ); Mon, 3 Mar 2008 07:24:25 -0500 In-Reply-To: <47CBC309.7090106@gmail.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: htejun@gmail.com Cc: fujita.tomonori@lab.ntt.co.jp, tomof@acm.org, jens.axboe@oracle.com, James.Bottomley@HansenPartnership.com, efault@gmx.de, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org, jgarzik@pobox.comfujita.tomonori@lab.ntt.co.jp On Mon, 03 Mar 2008 18:21:13 +0900 Tejun Heo wrote: > FUJITA Tomonori wrote: > >>> I can't see what changing the meaning of rq->data_len (and > >>> investigating all the block drivers) gives us. > >> No matter which way you go, you change the meaning of rq->data_len and > >> you MUST inspect rq->data_len usage whichever way you go. > > > > The patch doens't change that rq->data_len means the true data > > length. But yeah, it breaks rq->data_len == sum(sg). So it might break > > some drivers. > > Yeah, that's what I was saying. You end up breaking one of the two > assumptions. As sglist is getting modified for any driver if it has DMA > alignment set, whether rq->data_len is adjusted together or not, sglist > and data_len usages have to be audited. My patch (well, James' original approach) doesn't affect drivers that don't use drain buffer. rq->data_len still means the true data length and rq->data_len is equal to sum(sg) for them. So right now we need to audit only libata. But your patch changes the meaning of rq->data_len. It affects all the drivers. So it breaks non libata stuff, like the SMP handler. We need to audit all the drivers.