linux-kernel - Re: [RFC 0/2] readdir() as an inode operation

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Message-ID: <20071031034305.GD23984@cynthia.pants.nu>
Date:	Tue, 30 Oct 2007 20:43:05 -0700
From:	Brad Boyer <flar@...andria.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Jan Blunck <jblunck@...e.de>, Christoph Hellwig <hch@....de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Linux-Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [RFC 0/2] readdir() as an inode operation

On Tue, Oct 30, 2007 at 04:26:04PM +0100, Jan Kara wrote:
> > This is a first try to move readdir() to become an inode operation. This is
> > necessary for a VFS implementation of "something like union-mounts" where a
> > readdir() needs to read the directory contents of multiple directories.
> > Besides that the new interface is no longer giving the struct file to the
> > filesystem implementations anymore.
> > 
> > Comments, please?
>   Hmm, are you sure there are no users which keep some per-struct-file
> information for directories? File offset is one such obvious thing which
> you've handled but actually filesystem with more complicated structure
> of directory may remember some hints about where we really are, keep
> some readahead information or so...

The hfsplus code keeps some extra data in the ->private_data of directories,
although I've lost track of the exact benefit from not looking at the code
in some years. As I recall it was a performance enhancement due to the
fact that the data for all directories is effectively in a single file.
I believe it was easier to keep the current position as a structure
rather than just an offset and be careful about the tracking. The hfs
code is almost identical to the hfsplus code in this area.

	Brad Boyer
	flar@...andria.com

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