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From: Chris Murphy <lists@colorremedies.com>
To: Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: bind mounts on btrfs cause mountinfo confusion
Date: Mon, 17 Jul 2017 15:47:20 -0600	[thread overview]
Message-ID: <CAJCQCtT=-YoFJgEo=BFqfiPdtMoJCYR3dJPSekf+HQ22GYGztw@mail.gmail.com> (raw)

libOSTree makes use of bind mounts during startup to support multiple
fs trees on any file system for the purpose of atomic updates and
rollback.

Example during boot:

Jul 17 15:18:42 frawhide.localdomain systemd[779]: var.mount:
Executing: /usr/bin/mount
/sysroot/ostree/deploy/fedora-workstation/var /var -o bind

cat /proc/self/mounts

/dev/sda6 /var btrfs
rw,relatime,ssd,space_cache,subvolid=5,subvol=/ostree/deploy/fedora-workstation/var
0 0

findmnt shows basically the same

─/var
/dev/sda6[/ostree/deploy/fedora-workstation/var]
│                                                btrfs
rw,relatime,ssd,space_cache,subvolid=5,subvol=/ostree/deploy/fedora-workstation


There is no such subvolume /ostree/deploy/fedora-workstation/var,
basically it seems like whatever is producing this mount information
(kernel code?) is just assuming a bind mount on Btrfs is a subvolume
without checking if that subvolume really exists, and if it's just an
ordinary directory being bind mounted, which is what's going on here.

I'd say it's confusing. But I don't know if it's a problem otherwise.




-- 
Chris Murphy

             reply	other threads:[~2017-07-17 21:47 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-17 21:47 Chris Murphy [this message]
2017-07-18  7:24 ` bind mounts on btrfs cause mountinfo confusion Duncan
2017-07-18 18:57   ` Andrei Borzenkov

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