linux-kernel - Re: [dm-devel] [PATCH][RFC] dm: Do not open log and cow device read-write for read-only mappings

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Message-ID: <20110214143904.GB5825@agk-dp.fab.redhat.com>
Date:	Mon, 14 Feb 2011 14:39:04 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Milan Broz <mbroz@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Tao Ma <tm@....ma>, linux-kernel@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>
Subject: Re: [dm-devel] [PATCH][RFC] dm: Do not open log and cow device
	read-write for read-only mappings

On Mon, Feb 14, 2011 at 03:09:40PM +0100, Tejun Heo wrote:
> But if the underlying device is marked ro, dm shouldn't update it at
> all.  The device should be opened ro and ro policy should be enforced.

Indeed, but dm isn't tracking this today because it didn't need to up-to
now.

I can think of a few scenarios where dm can have the underlying device open
read-write when it only needs read-only.   (E.g. we track and cater for
read-only->read-write transitions but not the opposite and don't propagate
changes through the stack.)

We'll do an audit...
 
Alasdair

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