From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH] block: fix residual byte count handling Date: Mon, 03 Mar 2008 22:55:56 +0900 Message-ID: <47CC036C.2060902@gmail.com> References: <47CBC309.7090106@gmail.com> <20080303211727P.tomof@acm.org> <47CBFF6F.4060301@gmail.com> <20080303225024J.tomof@acm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080303225024J.tomof@acm.org> Sender: linux-scsi-owner@vger.kernel.org To: FUJITA Tomonori Cc: fujita.tomonori@lab.ntt.co.jp, 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.com List-Id: linux-ide@vger.kernel.org FUJITA Tomonori 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. >> Your patch does change sglist for any driver which sets DMA alignment. > > I overlook it. Where does it changes sglist? At the end of blk_rq_map_user() together with data_len / extra_len mangling or were you talking about James' original patch? -- tejun