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From: Stanislav Brabec <sbrabec@suse.cz>
To: Al Viro <viro@ZenIV.linux.org.uk>,
	"Austin S. Hemmelgarn" <ahferroin7@gmail.com>
Cc: linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
	David Sterba <dsterba@suse.cz>,
	Valdis.Kletnieks@vt.edu
Subject: Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes
Date: Tue, 12 Apr 2016 20:38:26 +0200	[thread overview]
Message-ID: <570D40A2.7030209@suse.cz> (raw)
In-Reply-To: <20160226203010.GD17997@ZenIV.linux.org.uk>

On Feb 26, 2016 at 21:30 Al Viro wrote:
> Sigh...  sys_mount() (mount_bdev(), actually) has no way to tell if two
> loop devices refer to the same underlying object.  As far as it's
> concerned, you are asking to mount a completely unrelated block device.
> Which just happens to see the data (living in separate pagecache, even)
> modified behind its back (with some delay) after it gets written to another
> device.  Filesystem drivers generally don't like when something is screwing
> the underlying data, to put it mildly...
>

I wrote a loop device reuse patch for mount -oloop.

[PATCH 0/3] btrfs-safe implementation of -oloop
http://marc.info/?l=util-linux-ng&m=146048532307963&w=2

[PATCH 1/3] libmount: Re-organize is_mounted_same_loopfile()
http://marc.info/?l=util-linux-ng&m=146048535907971&w=2

[PATCH 2/3] libmount: reuse existing loop device
http://marc.info/?l=util-linux-ng&m=146048537807980&w=2

[PATCH 3/3] mount: Handle EROFS before calling mount() syscall
http://marc.info/?l=util-linux-ng&m=146048542007990&w=2

However it works for me, there are still some controversial issues
described in [PATCH 0/3].

These patches will hide corruption of kernel loop control structures
mentioned earlier in this thread and in most cases prevent data
corruption.

-- 
Best Regards / S pozdravem,

Stanislav Brabec
software developer
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  parent reply	other threads:[~2016-04-12 18:38 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-25 19:22 loop subsystem corrupted after mounting multiple btrfs sub-volumes Stanislav Brabec
2016-02-26 12:33 ` Austin S. Hemmelgarn
2016-02-26 15:50   ` Stanislav Brabec
2016-02-26 16:39     ` Austin S. Hemmelgarn
2016-02-26 17:07       ` Stanislav Brabec
2016-02-26 18:22         ` Austin S. Hemmelgarn
2016-02-26 19:31           ` Stanislav Brabec
2016-02-26 17:53       ` Al Viro
2016-02-26 19:12         ` Stanislav Brabec
2016-02-26 20:05           ` Austin S. Hemmelgarn
2016-02-26 20:30             ` Al Viro
2016-02-26 20:36               ` Austin S. Hemmelgarn
2016-02-26 21:00               ` Stanislav Brabec
2016-02-26 22:00                 ` Valdis.Kletnieks
2016-02-29 14:56                   ` Stanislav Brabec
2016-03-01 13:44                     ` Ming Lei
2016-04-12 18:38               ` Stanislav Brabec [this message]
2016-02-26 20:37             ` Stanislav Brabec
2016-02-26 21:03               ` Al Viro
2016-02-26 21:36                 ` Stanislav Brabec
2016-02-26 21:45                   ` Al Viro
2016-02-29 13:11                     ` Austin S. Hemmelgarn

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