From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [PATCH] scsi_debug: disable clustering Date: Sun, 17 Feb 2008 09:02:14 -0600 Message-ID: <1203260534.3082.15.camel@localhost.localdomain> References: <20080217141045.GB21012@parisc-linux.org> <1203257892.3082.11.camel@localhost.localdomain> <20080217142848.GD21012@parisc-linux.org> <20080217235244N.tomof@acm.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080217235244N.tomof@acm.org> Sender: linux-ide-owner@vger.kernel.org To: FUJITA Tomonori Cc: matthew@wil.cx, dougg@torque.net, linux-scsi@vger.kernel.org, fujita.tomonori@lab.ntt.co.jp, linux-ide List-Id: linux-scsi@vger.kernel.org On Sun, 2008-02-17 at 23:52 +0900, FUJITA Tomonori wrote: > On Sun, 17 Feb 2008 07:28:48 -0700 > Matthew Wilcox wrote: > > > On Sun, Feb 17, 2008 at 08:18:11AM -0600, James Bottomley wrote: > > > No, he means that kmap_atomic can only map a page of data. This makes > > > single page only sg list entries and input assumption into this loop. > > > with ENABLE_CLUSTERING, that's potentially not true. Of course, this > > > accidentally works most of the time because of the way kmap functions. > > > > Ah, right. I'm on the verge of releasing a ram-based scsi driver I've > > been working on ... this loop should work fine with clustering as it > > takes account of the sg potentially having multiple pages: > > > > scsi_for_each_sg(cmnd, sg, scsi_sg_count(cmnd), i) { > > struct page *sgpage = sg_page(sg); > > unsigned int to_off = sg->offset; > > unsigned int sg_copy = sg->length; > > if (sg_copy > len) > > sg_copy = len; > > len -= sg_copy; > > stex driver has a similar function to copies data between a buffer and > a scatter list. I think that scsi_kmap_atomic_sg is a bit primitive > (and not very popular). I'll send a patch to add a helper function to > scsi_lib.c that copies data between a buffer and a scatter list. It > would be useful for several drivers. Actually, if you're going to sweep up them all, libata also does this. However, mapping and copying data isn't a SCSI specific function, it's one any virtual block driver should do, so I think block might be the correct location for such a function. James