Rename io_req_defer() into io_drain_req() and refactor it uncoupling it
from io_queue_sqe() error handling and preparing for coming
optimisations. Also, prioritise non IOSQE_ASYNC path.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4f17dd56e7fbe52d1866f8acd8efe3284d2bebcb.1623709150.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>