linux-ext4 - Re: [PATCH, RFC V3] ext3: add ioctl to force 32-bit hashes from indexed dirs

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Message-ID: <20130401181718.GB22443@thunk.org>
Date:	Mon, 1 Apr 2013 14:17:18 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>,
	Anand Avati <avati@...hat.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH, RFC V3] ext3: add ioctl to force 32-bit hashes from
 indexed dirs

On Mon, Apr 01, 2013 at 10:33:41AM -0500, Eric Sandeen wrote:
> +		/* Have we already started readdir on this dx dir? */
> +		if (filp->private_data) {
> +			err = -EINVAL;
> +			goto hash32bits_out;
> +		}

I'm not sure how much we care, but if filp->private_data is non-NULL
and filp->f_pos == 0, then the application must have called
rewinddir(), and at that point it would be fair game for us to free
the rb_tree (see the code in ext4_dx_readdir() just after the comment
"Some one has messed with f_pos; reset the world".)

This would allow a bit more flexibility than just requiring that the
ioctl be issued just after the opendir(), and allow it just after a
call to rewinddir().

This this would invalidate any previously issued telldir() cookies,
but according to SuSv3, telldir() cookies are not guaranteed to be
consistent after a rewinddir() or a closedir(), so it would be
standards compliant to do this.

						- Ted
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