This adds support for sync O_DIRECT read/write poll support.
Signed-off-by: NJens Axboe <axboe@fb.com>
[hch: split from a larger patch, minor updates]
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NKeith Busch <keith.busch@intel.com>