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

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Message-ID: <20101103150658.GA5627@quack.suse.cz>
Date:	Wed, 3 Nov 2010 16:06:58 +0100
From:	Jan Kara <jack@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, hch@...radead.org, linux-kernel@...r.kernel.org,
	petero2@...ia.com, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, jack@...e.cz, akpm@...ux-foundation.org,
	adilger.kernel@...ger.ca, tytso@....edu, mfasheh@...e.com,
	joel.becker@...cle.com, aelder@....com, dm-devel@...hat.com,
	drbd-dev@...ts.linbit.com, neilb@...e.de, leochen@...adcom.com,
	sbranden@...adcom.com, chris.mason@...cle.com, swhiteho@...hat.com,
	shaggy@...ux.vnet.ibm.com, joern@...fs.org,
	konishi.ryusuke@....ntt.co.jp, reiserfs-devel@...r.kernel.org,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH 4/5] block: make blkdev_get/put() handle exclusive
 access

On Mon 01-11-10 17:15:28, Tejun Heo wrote:
> Over time, block layer has accumulated a set of APIs dealing with bdev
> open, close, claim and release.
> 
> * blkdev_get/put() are the primary open and close functions.
> 
> * bd_claim/release() deal with exclusive open.
> 
> * open/close_bdev_exclusive() are combination of open and claim and
>   the other way around, respectively.
> 
> * bd_link/unlink_disk_holder() to create and remove holder/slave
>   symlinks.
> 
> * open_by_devnum() wraps bdget() + blkdev_get().
> 
> The interface is a bit confusing and the decoupling of open and claim
> makes it impossible to properly guarantee exclusive access as
> in-kernel open + claim sequence can disturb the existing exclusive
> open even before the block layer knows the current open if for another
> exclusive access.  Reorganize the interface such that,
...
  The patch looks OK to me as far as ext3, ext4, and reiserfs are
concerned. One thing I wondered about when I looked at it - does someone
use the 'mode' argument of the blkdev_put() function (well, apart from the
exclusive flag)? Because I've looked at a few random disk ->release()
functions and none of them used it...

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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