Add a new struct io_rw_state storing all iov related bits: fast iov,
iterator and iterator state. Not much changes here, simply convert
struct io_async_rw to use it.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e8245ffcb568b228a009ec1eb79c993c813679f1.1634144845.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>