means that the file could change from not-cached to cached and we
need to redo the direct I/O checks. We should also redo the direct I/O
checks when the file size changes regardless if O_APPEND is set or not.

SGI-PV: 963483
SGI-Modid: xfs-linux-melb:xfs-kern:28440a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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