From mboxrd@z Thu Jan 1 00:00:00 1970 From: FUJITA Tomonori Subject: Re: [PATCH] scsi_debug: disable clustering Date: Sun, 17 Feb 2008 23:52:23 +0900 Message-ID: <20080217235244N.tomof@acm.org> References: <20080217141045.GB21012@parisc-linux.org> <1203257892.3082.11.camel@localhost.localdomain> <20080217142848.GD21012@parisc-linux.org> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from mo11.iij4u.or.jp ([210.138.174.79]:52958 "EHLO mo11.iij4u.or.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755426AbYBQOwd (ORCPT ); Sun, 17 Feb 2008 09:52:33 -0500 In-Reply-To: <20080217142848.GD21012@parisc-linux.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: matthew@wil.cx Cc: James.Bottomley@HansenPartnership.com, tomof@acm.org, dougg@torque.net, linux-scsi@vger.kernel.org, fujita.tomonori@lab.ntt.co.jpfujita.tomonori@lab.ntt.co.jp 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.