From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751649Ab1JMA2p (ORCPT ); Wed, 12 Oct 2011 20:28:45 -0400 Received: from ipmail07.adl2.internode.on.net ([150.101.137.131]:12523 "EHLO ipmail07.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751190Ab1JMA2o (ORCPT ); Wed, 12 Oct 2011 20:28:44 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Av0EAEEvlk55LabZ/2dsb2JhbABDDqgzgQaBUwEBBAE6HCMFCwgDDgouFCUDIROHfrhnDodKBKUSSw Date: Thu, 13 Oct 2011 11:28:39 +1100 From: Dave Chinner To: Theodore Tso Cc: dave@jikos.cz, Hugo Mills , Kay Sievers , Alan Cox , linux-kernel@vger.kernel.org, lennart@poettering.net, harald@redhat.com, david@fubar.dk, greg@kroah.com, Chris Mason , Btrfs mailing list Subject: Re: A Plumber???s Wish List for Linux Message-ID: <20111013002839.GL3159@dastard> References: <1317943022.1095.25.camel@mop> <20111007111231.6e11d18e@lxorguk.ukuu.org.uk> <20111007113820.3b8424a8@lxorguk.ukuu.org.uk> <20111007152137.GE28351@carfax.org.uk> <20111010111813.GF17912@twin.jikos.cz> <4C18E3B8-FA7E-4BC1-BE5D-B517004321A2@mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C18E3B8-FA7E-4BC1-BE5D-B517004321A2@mit.edu> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 10, 2011 at 09:09:37AM -0400, Theodore Tso wrote: > > On Oct 10, 2011, at 7:18 AM, David Sterba wrote: > > > "Resetting the UUID on btrfs isn't a quick-and-easy thing - you > > have to walk the entire tree and change every object. We've got > > a bad-hack in meego that uses btrfs-debug-tree and changes the > > UUID while it runs the entire tree, but it's ugly as hell." > > Changing the UUID is going to be harder for ext4 as well, once we > integrate metadata checksums. And for XFS, we're modifying the on-disk format to encode the UUID into every single piece of metadata in the filesystem. Hence changing it entails a similar problem to btrfs - an entire filesystem metadata RMW cycle. > So while it makes sense to have > on-line ways of updating labels for mounted file systems it > probably makes muchness sense to support it for UUIDs. ^^^^ less Agreed. > I suspect what it means in practice is that it will be useful for > file systems to provide fs image copying tools that also generate > a new UUID while you're at it, for use by IT administrators and > embedded systems manufacturers. Yup. xfs_admin already provides an interface for offline modification of the UUID for XFS filesytems. I.e. clone the filesytem using xfs_copy, then run xfs_admin -U generate to generate a new uuid in the cloned copy before you mount the clone.... Cheers, Dave. -- Dave Chinner david@fromorbit.com