+static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
+{
+ /* Black hole detection */
+ if (sysctl_tcp_mtu_probing) {
+ if (!icsk->icsk_mtup.enabled) {
+ icsk->icsk_mtup.enabled = 1;
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ } else {
+ struct tcp_sock *tp = tcp_sk(sk);
+ int mss;
+
+ mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
+ mss = min(sysctl_tcp_base_mss, mss);
+ mss = max(mss, 68 - tp->tcp_header_len);
+ icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ }
+ }
+}
+