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Re: [PATCH, RFC] directory offset overflows in 2.6.28

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, John Stanley <jpsinthemix@xxxxxxxxxxx>
Subject: Re: [PATCH, RFC] directory offset overflows in 2.6.28
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 30 Dec 2008 10:57:26 -0500
In-reply-to: <20081230001117.GA5220@disturbed>
References: <20081229220745.GA12966@xxxxxxxxxxxxx> <20081230001117.GA5220@disturbed>
User-agent: Mutt/1.5.18 (2008-05-17)
On Tue, Dec 30, 2008 at 11:11:17AM +1100, Dave Chinner wrote:
> On Mon, Dec 29, 2008 at 05:07:45PM -0500, Christoph Hellwig wrote:
> > The patch below is a dumb version of just putting back the masking,
> > to make sure we have the same behavior as in 2.6.27 and earlier.
> > I think we should at least hide it in a macro that is well-commented,
> > but I suspect we also need to make sure that we never ever get bigger
> > offsets in directories in some way.
> I think we need that macro sooner rather than later ;)

> In this case, you can do the masking at the time cook is
> assigned. I haven't checked, but I suspect the rest will be the
> same. That will make the patch less invasive and with a macro
> somewhat cleaner...

That way we could replace two assignment by one one time each
in xfs_dir2_leaf.c and xfs_dir2_block.c.

I started working on the macro, but it seems even more hacky.

When looking at the big picture we have two problems:

 - the end of directory marker which always seems to be always too
   large for 32bit values for 32 bit indices
 - directories that actually are too large to be represented using
   32 bit signed offsets.  I guess we just can't support those
   for apps using the 32bit readdir interface and the EOVERFLOW
   is valid for those.  The current approach as in < 2.6.28 and
   with this patch breaks that second case in subtile ways.

So, I'd just push the first hacky opencoded patch into 2.6.29 and
-stable now to revert to the old behaviour with all it's faults, and
in the meantime I'll look into a proper way finding a better end of
directory indicator.  That should also help Russell's BSD concerns.

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