static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
{
	const struct net *net = sock_net(sk);
	int mss;

	/* Black hole detection */
	if (!net->ipv4.sysctl_tcp_mtu_probing)
		return;

	if (!icsk->icsk_mtup.enabled) {
		icsk->icsk_mtup.enabled = 1;
		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
	} else {
		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
		mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
		mss = max(mss, 68 - tcp_sk(sk)->tcp_header_len);
		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
	}
	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
}
Unknown