From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from atl4mhob10.myregisteredsite.com ([209.17.115.48]:58099 "EHLO atl4mhob10.myregisteredsite.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752562Ab3EIOGZ (ORCPT ); Thu, 9 May 2013 10:06:25 -0400 Received: from mailpod1.hostingplatform.com ([10.30.71.116]) by atl4mhob10.myregisteredsite.com (8.14.4/8.14.4) with ESMTP id r49E6O6R026565 for ; Thu, 9 May 2013 10:06:24 -0400 Message-ID: <518BAD64.6080704@chinilu.com> Date: Thu, 09 May 2013 07:06:28 -0700 From: George Mitchell Reply-To: george@chinilu.com MIME-Version: 1.0 To: Karel Zak , util-linux@vger.kernel.org Subject: Re: umount and findmnt commands not working with btrfs labels ... References: <51882EA5.9080805@chinilu.com> <20130507094835.GB7086@x2.net.home> <51891448.5010804@chinilu.com> <20130509094226.GD17527@x2.net.home> In-Reply-To: <20130509094226.GD17527@x2.net.home> Content-Type: text/plain; charset=UTF-8; format=flowed Sender: util-linux-owner@vger.kernel.org List-ID: So what I think I hear you saying on this issue is that though I can easily turn a label into a mount point with my little grep trick, umount is unable to do that so that in my scripts I will always have to use this kluge for things to work correctly? And that of course the same would hold true with findmnt? On 05/09/2013 02:42 AM, Karel Zak wrote: > On Tue, May 07, 2013 at 07:48:40AM -0700, George Mitchell wrote: >> problem. Is there a different debug statement I can use with findmnt? What > LIBMOUNT_DEBUG= for libmount > LIBBLKID_DEBUG= for libblkid > > We usually use /dev/disk/by-label and by-uuid/ to convert LABELs and > UUIDs to device names. These symlinks are maintained by udevd and > created according to result from > > blkid -o udev -p > > the duplicate LABELs are ignored, there is only one LABEL of course. > >> fix or whether I will need to redo this with each reboot? Also you did your >> testing with a simple one partition btrfs volume. My system involves up to > I had two independent partitions, each initialized by mkfs.btrfs. > >> five partitions in a single RAID 1 volume. My boot volume is spread over >> two partitions. I am wondering if that could have something to do with it? >> In any case, here is what I come up with using the same debug prefix with >> findmnt. > Ah, do you mean btrfs raid? For example: > > mkfs.btrfs --data raid1 --label FOO /dev/sdd1 /dev/sdd2 > > then the LABEL and UUID is really duplicate. > > > Anyway, the right way how to umount any filesystem is to specify the > filesystem by mountpoint, for example > > umount /mnt > > this is the way how Linux umount(2) syscall works, because everything > else is unreliable. Don't forget that you can mount the same filesystem > on more places and sometimes filesystem != device (e.g. btrfs), etc. > > The umount-by-device is marked in the umount(8) man page as obsolete. > It seems I have to add a note about RAIDs too. > >> Using findmnt on MAGEIA3BTR-BOOT produces the following. It appears to find >> the mount point and then print the result: >> >> [root@localhost ghmitch]# LIBMOUNT_DEBUG=0xffff findmnt >> LABEL=MAGEIA3BTR-BOOT > [...] >> However, when I do the same operation with MAGEIA3BTR, it DOES seem to find >> the mount point (4814: libmount: CACHE: [0x861c8a0]: add entry [ 1] >> (tag): /dev/sdd1: LABEL). The problem is, that is NOT the mount point. The >> mount point is /dev/sde1. > It seems that we need a note about duplicate LABELs to the man page ;-) > > Note, for Linux RAID (mdadm(8)) we're able to detect that the > filesystem is within a raid member device (e.g. /dev/sda) and the > device is reported as RAID member, the filesystem is ignored. The > filesystem is visible only on the final raid device (e.g /dev/md0). > > It means that the duplicate filesystems (RAID1 members) are invisible. > > > I guess something like this is unnecessary for btrfs, because you can > mount arbitrary btrfs raid member (device) as btrfs kernel code is > able to find the next raid members and compose the final array. > >> Here is my blkid which will give you an overview of the partitions involved. >> NOTE that with btrfs there are often multiple partitions with the same LABEL >> and UUID, but only ONE of those will be the mount point and that mount point >> can change at any time to one of the OTHER partitions sharing the same >> label. If umount OR findmnt happen to get the wrong mountpoint even with >> the right label, things are not going to work out: > So I don't see a bug. All what we need is to more explicitly explain > to users that conversion from to is > not reliable, because the same device could be mounted on more places > or the mountpoint could be connected to more devices. > >> /dev/sda5: LABEL="MAGEIA3BTR-BOOT" UUID="63f13151-dd34-45e1-b40d-7ed7d0d0ec4a" UUID_SUB="978f5c02-5e11-4df4-8f72-4ff6d09e58ff" TYPE="btrfs" >> /dev/sdb5: LABEL="MAGEIA3BTR-BOOT" UUID="63f13151-dd34-45e1-b40d-7ed7d0d0ec4a" UUID_SUB="0587a676-8bad-4d61-a8af-0e262d997ba7" TYPE="btrfs" > Yes, I see. > > Karel > >