From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 6 Jan 2001 15:03:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 6 Jan 2001 15:03:38 -0500 Received: from islay.mach.uni-karlsruhe.de ([129.13.162.92]:21265 "EHLO mailout.plan9.de") by vger.kernel.org with ESMTP id ; Sat, 6 Jan 2001 15:03:28 -0500 Date: Sat, 6 Jan 2001 20:57:26 +0100 From: Marc Lehmann To: David Woodhouse Cc: "Stephen C. Tweedie" , Stefan Traby , Daniel Phillips , Rik van Riel , linux-kernel@vger.kernel.org Subject: Re: Journaling: Surviving or allowing unclean shutdown? Message-ID: <20010106205726.A9664@cerebro.laendle> Mail-Followup-To: David Woodhouse , "Stephen C. Tweedie" , Stefan Traby , Daniel Phillips , Rik van Riel , linux-kernel@vger.kernel.org In-Reply-To: <20010104224946.C1290@redhat.com> <3A5352ED.A263672D@innominate.de> <20010104192104.C2034@redhat.com> <20010104220821.B775@stefan.sime.com> <20010104224946.C1290@redhat.com> <1628.978695936@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1628.978695936@redhat.com>; from dwmw2@infradead.org on Fri, Jan 05, 2001 at 11:58:56AM +0000 X-Operating-System: Linux version 2.2.18 (root@cerebro) (gcc version pgcc-2.95.2.1 20001224 (release)) X-Copyright: copyright 2000 Marc Alexander Lehmann - all rights reserved Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 05, 2001 at 11:58:56AM +0000, David Woodhouse wrote: > You mount it read-only, recover as much as possible from it, and bin it. > > You _don't_ want the fs code to ignore your explicit instructions not to > write to the medium, and to destroy whatever data were left. The problem is: where did you give the explicit instruction? Just that you define "read-only" as "the medium should not be written" does not mean everybody else thinks the same. actually, I regard "ro" mainly as a "hey kernel, I won't handle writes now, so please don't try it", like for cd-roms or other non-writeale media, and please filesystem stay in a clean state. That ro means "the medium is never written" is an assumption that does not hold for most disks anyway and is, in the case of journlaing filesystems, often impossible to implement. You simply can't salvage data without a log reply. Sure, you can do virtual log replays, but for example the reiserfs log is currently 32mb. Pinning down that much memory for a virtual log reply is not possible on low-memory machines. So the first thing would be to precisely define the meaning of the "ro" flag. Before this has happened it is ansolutely senseless to argue about what it means, as it doesn't mean anything at the moment, except (man mount): ro Mount the file system read-only. Which it does even with journaling filesystems... -- -----==- | ----==-- _ | ---==---(_)__ __ ____ __ Marc Lehmann +-- --==---/ / _ \/ // /\ \/ / pcg@opengroup.org |e| -=====/_/_//_/\_,_/ /_/\_\ XX11-RIPE --+ The choice of a GNU generation | | - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/