net/smc: add BPF injection on smc negotiation

This patch try add BPF injection on smc negotiation, so that
the application can decided whether to use smc or not through
eBPF progs.

In particular, some applications may need global dynamic information
to make decision. Therefore, we also inject a information collect
point into smc_release.

Note that, in order to make negotiation can be decided by application,
sockets must have SMC_LIMIT_HS set.

Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>

net/smc/af_smc.c

@@ -166,6 +166,9 @@ static bool smc_hs_congested(const struct sock *sk)
 	if (workqueue_congested(WORK_CPU_UNBOUND, smc_hs_wq))
 		return true;
 
+	if (!smc_sock_should_select_smc(smc))
+		return true;
+
 	return false;
 }
 
@@ -320,6 +323,9 @@ static int smc_release(struct socket *sock)
 	sock_hold(sk); /* sock_put below */
 	smc = smc_sk(sk);
 
+	/* trigger info gathering if needed.*/
+	smc_sock_perform_collecting_info(sk, SMC_SOCK_CLOSED_TIMING);
+
 	old_state = sk->sk_state;
 
 	/* cleanup for a dangling non-blocking connect */
@@ -1627,7 +1633,14 @@ static int smc_connect(struct socket *sock, struct sockaddr *addr,
 	}
 
 	smc_copy_sock_settings_to_clc(smc);
-	tcp_sk(smc->clcsock->sk)->syn_smc = 1;
+	/* accept out connection as SMC connection */
+	if (smc_sock_should_select_smc(smc) == SK_PASS) {
+		tcp_sk(smc->clcsock->sk)->syn_smc = 1;
+	} else {
+		tcp_sk(smc->clcsock->sk)->syn_smc = 0;
+		smc_switch_to_fallback(smc, /* just a chooice */ 0);
+	}
+
 	if (smc->connect_nonblock) {
 		rc = -EALREADY;
 		goto out;