kill_fasync及fasync_helper
kill_fasync及fasync_helperkill_fasync及fasync_helper用于异步通知中kill_fasync(&dev->async_queue, SIGIO, POLL_IN); //向app发可读信号,dev->async_queue可用来区分向谁发那个进程调用这个fasync_helper就向谁发int fasync_helpe