linux-kernel - Re: [PATCH 4/5] block: make blkdev_get/put() handle exclusive access

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Message-ID: <20101104150400.GA32504@redhat.com>
Date:	Thu, 4 Nov 2010 11:04:00 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, jack@...e.cz, leochen@...adcom.com,
	heiko.carstens@...ibm.com, adilger.kernel@...ger.ca,
	konishi.ryusuke@....ntt.co.jp, shaggy@...ux.vnet.ibm.com,
	drbd-dev@...ts.linbit.com, joel.becker@...cle.com,
	hch@...radead.org, aelder@....com, mfasheh@...e.com,
	joern@...fs.org, reiserfs-devel@...r.kernel.org,
	viro@...iv.linux.org.uk, swhiteho@...hat.com,
	chris.mason@...cle.com, axboe@...nel.dk, tytso@....edu,
	sbranden@...adcom.com, petero2@...ia.com,
	linux-kernel@...r.kernel.org, schwidefsky@...ibm.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 4/5] block: make blkdev_get/put() handle exclusive access

On Wed, Nov 03 2010 at 12:10pm -0400,
Christoph Hellwig <hch@...radead.org> wrote:

> On Mon, Nov 01, 2010 at 05:15:28PM +0100, Tejun Heo wrote:
> > * blkdev_get() is extended to include exclusive access management.
> >   @holder argument is added and, if is @FMODE_EXCL specified, it will
> >   gain exclusive access atomically w.r.t. other exclusive accesses.
> > 
> > * blkdev_put() is similarly extended.  It now takes @mode argument and
> >   if @FMODE_EXCL is set, it releases an exclusive access.  Also, when
> >   the last exclusive claim is released, the holder/slave symlinks are
> >   removed automatically.
> 
> Could we get rid of FMODE_EXCL and just make a non-NULL holder field
> mean to open it exlusively (and pass a holder to the blkdev_put to
> release it)?

I agree that the need for a FMODE_EXCL flag is awkward.  Christoph's
proposed change should clean things up nicely.

Other than that, for the DM bits:

Acked-by: Mike Snitzer <snitzer@...hat.com>
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