linux-kernel - Re: [PATCH] loop: Update mtime when writing using aops

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Message-ID: <20100408193838.GY10103@kernel.dk>
Date:	Thu, 8 Apr 2010 21:38:38 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
Cc:	Nikanth Karthikesan <knikanth@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] loop: Update mtime when writing using aops

On Thu, Apr 08 2010, Tvrtko Ursulin wrote:
> On Thursday 08 April 2010 13:45:39 Jens Axboe wrote:
> > On Thu, Apr 08 2010, Nikanth Karthikesan wrote:
> > > Update mtime when writing to backing filesystem using the address space
> > > operations write_begin and write_end.
> >
> > You forgot to include a 'why' :-)
> >
> > Not that I disagree with the patch, just curious what made you make the
> > change.
> 
> You mean how the bug was found? I originally reported this problem against
> openSUSE 11.2 kernel, where when you have a dm-crypt loop filesystem the
> container file modification time does not get updated with use. Consequence
> of that is that backup runs would miss the fact container has changed.
> 
> Maybe one could argue it is a security feature in this scenario :), but as the
> problem turns out to be unrelated to the crypto case, rather contained in the
> loop driver itself, it looks like that would not hold.

:-)

I suppose you could update the mtime on tear down, since then it would
also be safe to actually backup. But same difference in the end I
suppose, I'll add the patch.

-- 
Jens Axboe

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