From: Eric Sandeen Subject: Re: xt4 - True Readonly mount [WAS - Re: [Bug 14354] Bad corruption with 2.6.32-rc1 and upwards] Date: Fri, 30 Oct 2009 10:14:56 -0500 Message-ID: <4AEB02F0.5040309@redhat.com> References: <87f94c370910300720s5ea3d780o45fcf32303820a3c@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Ted Augustine , Alexey Fisher , linux-ext4@vger.kernel.org To: Greg Freemyer Return-path: Received: from mx1.redhat.com ([209.132.183.28]:41332 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932290AbZJ3PPC (ORCPT ); Fri, 30 Oct 2009 11:15:02 -0400 In-Reply-To: <87f94c370910300720s5ea3d780o45fcf32303820a3c@mail.gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Greg Freemyer wrote: > On Fri, Oct 30, 2009 at 4:22 AM, wrote: >> http://bugzilla.kernel.org/show_bug.cgi?id=14354 >> >> --- Comment #152 from Alexey Fisher 2009-10-30 08:22:10 --- >> Ted, >> Thank you for explanation :) >> Notice: i learning computer forensic, and was trained to mount all evidence >> systems with "-o ro" to not contaminate it. It seems like ext4 break this >> tradition, so many forensics will surprised why md5sum do not match. > > Ted, (Alexey there is a response to further down). > > I have not followed this thread ultra-closely but Alexey's comment got > my attention. > > Ignoring computer forensics, with LVM snapshots, hardware raid array > snapshots, etc. even in the presence of a dirty log, we need to be > able to mount a drive in true read-only fashion fro many backup > operations to function correctly. > > XFS added an extra mount flag for that 5 or so years ago. > I hope ext4 either has or will add a true read-only mount option. > Maybe Eric Sandeen remembers the actual drivers for adding that > feature to XFS. > After a little brief digging I'm not sure when the xfs mount option went in or why... But for both xfs: mount -o ro,norecovery and ext[34]: mount -o ro,noload I don't think either one should touch the disk. Also, both should skip journal replay if you set the block device readonly prior to mount (hdparm -r can do this). -Eric