On 01/11/2012 07:55 PM, Dave Chinner wrote:
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.
Oh I see, I'll take a look at it, I think it will be ok to just take out
the early return. Thx!
Allison
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