From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 2 Aug 2002 09:45:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 2 Aug 2002 09:44:57 -0400 Received: from host194.steeleye.com ([216.33.1.194]:61705 "EHLO pogo.mtv1.steeleye.com") by vger.kernel.org with ESMTP id ; Fri, 2 Aug 2002 09:44:47 -0400 Message-Id: <200208021348.g72Dm7q03058@localhost.localdomain> X-Mailer: exmh version 2.4 06/23/2000 with nmh-1.0.4 To: suparna@in.ibm.com cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, axboe@kernel.org, B.Zolnierkiewicz@elka.pw.edu.pl, akpm@zip.com.au Subject: Re: [PATCH] Bio Traversal Changes In-Reply-To: Message from Suparna Bhattacharya of "Fri, 02 Aug 2002 18:05:13 +0530." <20020802180513.A1802@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 02 Aug 2002 08:48:06 -0500 From: James Bottomley X-AntiVirus: scanned for viruses by AMaViS 0.2.1 (http://amavis.org/) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org The SCSI changes (small that they are) look reasonable. This does look like it exposes an existing problem in the tag/barrier approach, though. The bio can be split by making multiple requests over segements of the bio, correct? If this is a BIO_RW_BARRIER, then each of these requests will be a REQ_BARRIER. However, in the SCSI paradigm where we translate REQ_BARRIER to ordered tag, each of the requests will get a new ordered tag as it comes back around through end_that_request_first, potentially allowing other tags to be inserted in between these, which would be incorrect, since other bios would be inserted in between the segments of this one, thus violating the barrier. Is the above correct? If it is, I may have finally found a use for linked scsi tasks (gives you the ability to have one tag cover multiple commands). James