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Date: Fri, 26 Feb 2016 21:45:14 +0000
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
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On Fri, Feb 26, 2016 at 10:36:50PM +0100, Stanislav Brabec wrote:

> It should definitely report error whenever trying -oloop on top of
> anything else than a file. Or at least a warning.
> 
> Well, even losetup should report a warning.

Keep in mind that with crypto in the game it just might be useful to have
loop-over-loop - it might be _not_ a no-op (hell, you might have two
layers of encryption - not the smartest thing to do, but if that's what
got dumped on your lap, you deal with what you've got).  So such warnings
shouldn't be hard errors.