linux-ext4 - Re: [PATCH 14/19] ext3: remove unnecessary dentry_unhash on rmdir/rename

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Message-ID: <Pine.LNX.4.64.1105241603330.9500@cobra.newdream.net>
Date:	Tue, 24 May 2011 16:57:53 -0700 (PDT)
From:	Sage Weil <sage@...dream.net>
To:	Jan Kara <jack@...e.cz>
cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org, hch@....de,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 14/19] ext3: remove unnecessary dentry_unhash on
 rmdir/rename_dir

On Tue, 24 May 2011, Jan Kara wrote:
> On Tue 24-05-11 13:06:17, Sage Weil wrote:
> > ext3 has no problems with lingering references to unlinked directory
> > inodes.
>   OK, so if I understand right, dentry_unhash() has been there only so that
> filesystem can detect whether (something under) removed directory is in
> use? So filesystems which can happily handle unlinked but open directories
> don't need it, right? If that's the case, you can add:
>   Acked-by: Jan Kara <jack@...e.cz>
> to this patch and also the ext2 version.

Right.  Basically, a simple fs can return EBUSY if the dentry is hashed 
(implying there are still references) and not worry about a racing process 
traversing into the directory while rmdir is running.  A sane fs can 
handle references and doesn't care if a racing process traverses into the 
dir before the ->rmdir method completes.

Thanks!
sage
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