From: Al Viro <viro@ZenIV.linux.org.uk>
To: Stanislav Brabec <sbrabec@suse.cz>
Cc: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>,
linux-kernel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
Btrfs BTRFS <linux-btrfs@vger.kernel.org>,
David Sterba <dsterba@suse.cz>
Subject: Re: loop subsystem corrupted after mounting multiple btrfs sub-volumes
Date: Fri, 26 Feb 2016 21:03:02 +0000 [thread overview]
Message-ID: <20160226210302.GE17997@ZenIV.linux.org.uk> (raw)
In-Reply-To: <56D0B782.20606@suse.cz>
On Fri, Feb 26, 2016 at 09:37:22PM +0100, Stanislav Brabec wrote:
> Do I understand, that you are saying:
>
> Yes, mounting multiple loop devices associated with one file is a
> legitimate use, but mount(8) should never do it, because it has other
> ugly side effects?
It's on the same level as "hey, let's have an nbd daemon run in qemu
guest, exporting a host file over nbd, import it to host as /dev/nbd69,
set a loopback device over the underlying file as /dev/loop42 and
ask e.g. xfs to recognize that it's dealing with the same underlying array
of bytes in both cases - wouldn't it be neat if it could do that?"
There's no magic. Really. Unexpected sharing of backing store between
apparently unrelated devices can cause trouble. And I'm not sure how
to deal with -o loop in a sane way, TBH - automagical losetup is bloody
hard to get right. Keep in mind that loop-over-loop is also possible...
next prev parent reply other threads:[~2016-02-26 21:03 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <56CF5490.7040102@suse.cz>
2016-02-26 12:33 ` loop subsystem corrupted after mounting multiple btrfs sub-volumes 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
2016-02-26 20:37 ` Stanislav Brabec
2016-02-26 21:03 ` Al Viro [this message]
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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