linux-kernel - Re: [PATCH] ext34: ensure do_split leaves enough free space in both blocks

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Date:	Mon, 17 Sep 2007 14:57:38 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Eric Sandeen <sandeen@...deen.net>,
	Eric Sandeen <sandeen@...hat.com>,
	ext4 development <linux-ext4@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hooanon05@...oo.co.jp, Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH] ext34: ensure do_split leaves enough free space in both blocks

On Sep 17, 2007  13:30 -0700, Andrew Morton wrote:
> On Mon, 17 Sep 2007 12:21:40 -0500
> > Eric Sandeen wrote:
> > > The do_split() function for htree dir blocks is intended to split a
> > > leaf block to make room for a new entry.  It sorts the entries in the
> > > original block by hash value, then moves the last half of the entries to 
> > > the new block - without accounting for how much space this actually moves.  
> > > (IOW, it moves half of the entry *count* not half of the entry *space*).
> > > If by chance we have both large & small entries, and we move only the 
> > > smallest entries, and we have a large new entry to insert, we may not have 
> > > created enough space for it.
> > 
> > (btw, the upshot of this is that in add_dirent_to_buf(),
> > memcpy(de->name, name, namelen) will overshoot the buffer and actually
> > corrupt memory.)
> 
> So this looks like 2.6.22 and 2.6.23 material, but the timing is getting
> pretty squeezy.  Could people please give this change an extra-close
> review, let me know?

I already discussed it at length with Eric and inspected the patch, so we
could add:
Signed-off-by: Andreas Dilger <adilger@...sterfs.com>

Haven't actually tested the code myself.

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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