Ϊʹ豸֧첽֪ͨƣ漰3
1. ֧F_SETOWNfilp->f_ownerΪӦID
   ںɣ豸봦
2. ֧F_SETFLĴÿFASYNC־ıʱеfasync()ִС
   Ӧʵfasync()
   
3. 豸Դɻʱkill_fasync()Ӧź


Ӧó
fcntl(fd, F_SETOWN, getpid());  // ںˣ˭

Oflags = fcntl(fd, F_GETFL);   
fcntl(fd, F_SETFL, Oflags | FASYNC);  // ıfasyncǣջõfaync > fasync_helperʼ/ͷfasync_struct
