Verify that punching holes at ends of files does not alter st_size
if we pass FALLOC_FL_KEEP_SIZE to fallocate().
[eguan: add comment about xfs_io's fpunch KEEP_SIZE flag]
Signed-off-by: Calvin Owens <calvinowens@fb.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>