linux-ext4 - Re: [Gluster-devel] regressions due to 64-bit ext4 directory cookies

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Message-ID: <20130214061002.GM26694@dastard>
Date:	Thu, 14 Feb 2013 17:10:02 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Anand Avati <anand.avati@...il.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>,
	sandeen@...hat.com, linux-nfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, gluster-devel@...gnu.org
Subject: Re: [Gluster-devel] regressions due to 64-bit ext4 directory cookies

On Wed, Feb 13, 2013 at 05:20:52PM -0500, Theodore Ts'o wrote:
> Telldir() and seekdir() are basically implementation horrors for any
> file system that is using anything other than a simple array of
> directory entries ala the V7 Unix file system or the BSD FFS.  For any
> file system which is using a more advanced data structure, like
> b-trees hash trees, etc, there **can't** possibly be a "offset" into a
> readdir stream. 

I'll just point you to this:

http://marc.info/?l=linux-ext4&m=136081996316453&w=2

so you can see that XFS implements what you say can't possibly be
done. ;)

FWIW, that post only talked about the data segment. I didn't mention
that XFS has 2 other segments in the directory file (both beyond
EOF) for the directory data indexes. One contains the name-hash btree
index used for name based lookups and the other contains a freespace
index for tracking free space in the data segment.

IOWs persistent, deterministic, low cost telldir/seekdir behaviour
was a problem solved in the 1990s. :)

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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