Hi On Thu, Feb 19, 2015 at 3:45 PM, Grzegorz Dwornicki <gd1100@xxxxxxxxx> wrote: > Hello > > Proces have a established tcp socket. It calls sys_revcmsg on that > socket. That function goes all the way to tcp_recvmsg function. > > Function tcp_recvmsg.c (defined in net/ipv4/tcp.c) blocks it self on > function sk_wait_data if socket recv queue is empty. I wanted to know > how socked is checked in time. Soo i Looked up this sk_wait_data > function (http://lxr.free-electrons.com/source/net/core/sock.c#L1933): > > 1933 int sk_wait_data(struct sock *sk, long *timeo) > 1934 { > 1935 int rc; > 1936 DEFINE_WAIT(wait); > 1937 > 1938 prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE); > 1939 set_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags); > 1940 rc = sk_wait_event(sk, timeo, > !skb_queue_empty(&sk->sk_receive_queue)); > 1941 clear_bit(SOCK_ASYNC_WAITDATA, &sk->sk_socket->flags); > 1942 finish_wait(sk_sleep(sk), &wait); > 1943 return rc; > 1944 } > > This function blocks it self on the sk_wait_event macro. Here is it > definition (http://lxr.free-electrons.com/source/include/net/sock.h#L893): > > 893 #define sk_wait_event(__sk, __timeo, __condition) \ > 894 ({ int __rc; \ > 895 release_sock(__sk); \ > 896 __rc = __condition; \ > 897 if (!__rc) { \ > 898 *(__timeo) = schedule_timeout(*(__timeo)); \ > 899 } \ > 900 lock_sock(__sk); \ > 901 __rc = __condition; \ > 902 __rc; \ > 903 }) > > This macro is blocked in the schedule_timeout all the time. I know > this because I added printk functions with some marks easly to target > the line blocking the socket. It hangs on this schedule_timeout and it > magicaly released when some data apear in the revc queue. > > How does the kernel know when to "unblock" the process? Function name: > sk_wait_data and macro name: sk_wait_event tells me that there should > be some queue checning from time to time... > > Can someone explain this to me? Perhaps you should see sk_data_ready callback's default implementation for this. > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies@xxxxxxxxxxxxxxxxx > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- ---P.K.S _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
