From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:54120 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755426AbeCSNEs (ORCPT ); Mon, 19 Mar 2018 09:04:48 -0400 Date: Mon, 19 Mar 2018 14:02:23 +0100 From: David Sterba To: Hugo Mills , "Misono, Tomohiro" , linux-btrfs Subject: Re: [PATCH] btrfs-progs: mkfs: add uuid and otime to ROOT_ITEM of FS_TREE Message-ID: <20180319130222.GE6955@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <7ca269db-a724-5938-f4d8-b85e893fd558@jp.fujitsu.com> <20180319082010.GC17966@carfax.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180319082010.GC17966@carfax.org.uk> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, Mar 19, 2018 at 08:20:10AM +0000, Hugo Mills wrote: > On Mon, Mar 19, 2018 at 05:16:42PM +0900, Misono, Tomohiro wrote: > > Currently, the top-level subvolume lacks the UUID. As a result, both > > non-snapshot subvolume and snapshot of top-level subvolume do not have > > Parent UUID and cannot be distinguisued. Therefore "fi show" of > > top-level lists all the subvolumes which lacks the UUID in > > "Snapshot(s)" filed. Also, it lacks the otime information. > > > > Fix this by adding the UUID and otime at the mkfs time. As a > > consequence, snapshots of top-level subvolume now have a Parent UUID and > > UUID tree will create an entry for top-level subvolume at mount time. > > This should not cause the problem for current kernel, but user program > > which relies on the empty Parent UUID may be affected by this change. > > Is there any way of adding a UUID to the top level subvol on an > existing filesystem? It would be helpful not to have to rebuild every > filesystem in the world to fix this. We can do that by a special purpose tool. The easiest way is to set the uuid on an unmouted filesystem, but as this is a one-time action I hope this is acceptable. Added to todo, thanks for the suggestion.