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Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes

From Stanislav Brabec <sbrabec@suse.cz>
Newsgroups linux.kernel
Subject Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes
Date 2016-02-26 20:40 +0100
Message-ID <r6wp4-83i-1@gated-at.bofh.it> (permalink)
References (1 earlier) <r6pQD-3e7-39@gated-at.bofh.it> <r6sYa-5ut-1@gated-at.bofh.it> <r6tAR-640-7@gated-at.bofh.it> <r6u3T-6vT-3@gated-at.bofh.it> <r6vjk-7ja-15@gated-at.bofh.it>
Organization SUSE Linux, s. r. o.

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On Feb 26, 2016 at 19:22 Austin S. Hemmelgarn wrote:
> The first commit is just test cases, and the others are specific issues
> that only affected BTRFS which have nothing to do with this thread at
> all other than involving mount(8) and BTRFS.

Yes, it is a bit off topic. It just demonstrates, how complex mount(8) 
for btrfs is.

The test case is all-fail in util-linux 2.27.1.

> mount(8) behavior has the potential to cause either data
> corruption or similar behavior in the future (I would expect that XFS
> with metadata checksumming enabled would cause a similar interaction,
> although they probably would handle it better).

Especially "mount -a" has a hard time to recognize what was already 
mounted and what still needs to be mounted.

The only information mount(8) has is the one from mountinfo. 
Interpreting of the mountinfo contents to reconstruct possible mount 
options used is a task far from being trivial.

Some of them are even impossible to discriminate:

Suppose you have:
mount -osubvol=/ /dev/sda2 /mnt/1
mount -osubvol=/sbv /dev/sda2 /mnt/2

Case 1:
mount -obind /mnt/1/sbv/bnd /mnt/3

Case 2:
mount -obind /mnt/2/bnd /mnt/3

Case 1 and case 2 have exactly the same mountinfo, but different 
reference counts for /mnt/1 and /mnt/2.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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Thread

loop subsystem corrupted after mounting multiple btrfs sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-25 20:30 +0100
  Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-26 13:40 +0100
    Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 17:00 +0100
      Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-26 17:40 +0100
        Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 18:10 +0100
          Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-26 19:30 +0100
            Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 20:40 +0100
        Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Al Viro <viro@ZenIV.linux.org.uk> - 2016-02-26 19:00 +0100
          Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 20:20 +0100
            Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-26 21:10 +0100
              Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-26 21:40 +0100
              Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Al Viro <viro@ZenIV.linux.org.uk> - 2016-02-26 21:40 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 22:10 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes Valdis.Kletnieks@vt.edu - 2016-02-26 23:20 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-29 16:00 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes Ming Lei <tom.leiming@gmail.com> - 2016-03-01 14:50 +0100
              Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 21:40 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Al Viro <viro@ZenIV.linux.org.uk> - 2016-02-26 22:10 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Stanislav Brabec <sbrabec@suse.cz> - 2016-02-26 22:40 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes Al Viro <viro@ZenIV.linux.org.uk> - 2016-02-26 22:50 +0100
                Re: loop subsystem corrupted after mounting multiple btrfs  sub-volumes "Austin S. Hemmelgarn" <ahferroin7@gmail.com> - 2016-02-29 14:20 +0100

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