From: Theodore Ts'o Subject: Re: Ext4 external journal UUID mismatch? Date: Mon, 16 Jul 2012 11:40:46 -0400 Message-ID: <20120716154046.GB27656@thunk.org> References: <20120715234058.GA2562@tuon.disenchant.local> <20120716025610.GB2562@tuon.disenchant.local> <11FEA6E4-EF75-4CD9-B2B6-78E42410027B@gmail.com> <20120716100010.GC2562@tuon.disenchant.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , "linux-ext4@vger.kernel.org" To: Kevin Shanahan Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:39315 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752047Ab2GPPkt (ORCPT ); Mon, 16 Jul 2012 11:40:49 -0400 Content-Disposition: inline In-Reply-To: <20120716100010.GC2562@tuon.disenchant.local> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Jul 16, 2012 at 07:30:10PM +0930, Kevin Shanahan wrote: > > The lookup of the journal by UUID (instead of relying on the "device > > hint" in the superblock) _should_ be handled by mount, but I don't > > recall if we ever got a mount.ext4 to handle this or not. It would > > also be possible for the "fast e2fsck" check to verify the journal > > UUID before mounting the filesystem, but again I'm not sure if this > > is done yet, and I can't check right now. > > Ok, thanks. For now I can ask LVM to make the major/minor number > persistent. > > Assuming it's not already done, do you think adding the UUID lookup > would be a reasonable project for a newbie or is it likely to be a bit > complicated? We have a mount option. You can specify it via a mount option, i.e., -o journal_dev=0xFC02 It would be nice if the mount program (in util-linux) did a uuid lookup using the blkid library if there was a mount option string of the form "journal_dev=lookup". I would certainly support getting a feature like that into mount command, but it would be up to the maintainer of the util-linux package to approve the specific patch. Since it would require linking in the ext2fs library, or putting in enough knowledge of the ext3/4 superblock to fetch the external journal uuid, I could imagine the util-linux maintainer insisting that this be done in a helper program (i.e., /sbin/mount.ext3 and /sbin/mount.ext4). So it could potentially get a little complicated, just to warn you ahead of time. Regards, - Ted