linux-ext4 - Re: punch-hole should go beyond i

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Message-ID: <20120112025547.GC2806@dastard>
Date:	Thu, 12 Jan 2012 13:55:47 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Allison Henderson <achender@...ux.vnet.ibm.com>,
	linux-ext4@...r.kernel.org
Subject: Re: punch-hole should go beyond i_size

On Wed, Jan 11, 2012 at 05:02:12PM -0800, Hugh Dickins wrote:
> Hi Allison,
> 
> In thinking about fallocate() on tmpfs, I cross-check with ext4
> and find this bug in its implementation of FALLOC_FL_PUNCH_HOLE:
> 
> rm -f temp
> fallocate    -l 4096 temp
> du temp				# shows 4, right
> fallocate -p -l 4096 temp
> du temp				# shows 0, right
> rm -f temp
> fallocate -n -l 4096 temp
> du temp				# shows 4, right
> fallocate -p -l 4096 temp
> du temp				# shows 4, wrong
> rm temp
> 
> ext4_ext_punch_hole() contains /* No need to punch hole beyond i_size */
> early return, and trimming to i_size below, but forgets that the other
> variety of fallocate(), with FALLOC_FL_KEEP_SIZE set, may have allocated
> blocks beyond i_size.  They can be removed with ftruncate(), but it is
> unexpected for fallocate() not to undo its own work, and xfs does so.

I'm pretty sure that's a bug as XFS allows punching holes in extents
beyond EOF.

Cheers,

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