+ /* Calculate base mss without TCP options:
+ It is MMS_S - sizeof(tcphdr) of rfc1122
+ */
+ mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
+
+ /* Clamp it (mss_clamp does not include tcp options) */
+ if (mss_now > tp->rx_opt.mss_clamp)
+ mss_now = tp->rx_opt.mss_clamp;
+
+ /* Now subtract optional transport overhead */
+ mss_now -= icsk->icsk_ext_hdr_len;
+
+ /* Then reserve room for full set of TCP options and 8 bytes of data */
+ if (mss_now < 48)
+ mss_now = 48;
+
+ /* Now subtract TCP options size, not including SACKs */
+ mss_now -= tp->tcp_header_len - sizeof(struct tcphdr);
+
+ return mss_now;
+}
+
+/* Inverse of above */
+int tcp_mss_to_mtu(struct sock *sk, int mss)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ int mtu;
+
+ mtu = mss +
+ tp->tcp_header_len +
+ icsk->icsk_ext_hdr_len +
+ icsk->icsk_af_ops->net_header_len;
+
+ return mtu;
+}
+
+void tcp_mtup_init(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ icsk->icsk_mtup.enabled = sysctl_tcp_mtu_probing > 1;
+ icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
+ icsk->icsk_af_ops->net_header_len;
+ icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, sysctl_tcp_base_mss);
+ icsk->icsk_mtup.probe_size = 0;
+}
+
+/* This function synchronize snd mss to current pmtu/exthdr set.
+
+ tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
+ for TCP options, but includes only bare TCP header.
+
+ tp->rx_opt.mss_clamp is mss negotiated at connection setup.
+ It is minimum of user_mss and mss received with SYN.
+ It also does not include TCP options.
+
+ inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
+
+ tp->mss_cache is current effective sending mss, including
+ all tcp options except for SACKs. It is evaluated,
+ taking into account current pmtu, but never exceeds
+ tp->rx_opt.mss_clamp.
+
+ NOTE1. rfc1122 clearly states that advertised MSS
+ DOES NOT include either tcp or ip options.
+
+ NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
+ are READ ONLY outside this function. --ANK (980731)
+ */
+
+unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ int mss_now;
+
+ if (icsk->icsk_mtup.search_high > pmtu)
+ icsk->icsk_mtup.search_high = pmtu;
+
+ mss_now = tcp_mtu_to_mss(sk, pmtu);
+
+ /* Bound mss with half of window */
+ if (tp->max_window && mss_now > (tp->max_window>>1))
+ mss_now = max((tp->max_window>>1), 68U - tp->tcp_header_len);
+
+ /* And store cached results */
+ icsk->icsk_pmtu_cookie = pmtu;
+ if (icsk->icsk_mtup.enabled)
+ mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
+ tp->mss_cache = mss_now;
+
+ return mss_now;
+}
+
+/* Compute the current effective MSS, taking SACKs and IP options,
+ * and even PMTU discovery events into account.
+ *
+ * LARGESEND note: !urg_mode is overkill, only frames up to snd_up
+ * cannot be large. However, taking into account rare use of URG, this
+ * is not a big flaw.
+ */
+unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct dst_entry *dst = __sk_dst_get(sk);
+ u32 mss_now;
+ u16 xmit_size_goal;
+ int doing_tso = 0;
+
+ mss_now = tp->mss_cache;
+
+ if (large_allowed && sk_can_gso(sk) && !tp->urg_mode)
+ doing_tso = 1;
+
+ if (dst) {
+ u32 mtu = dst_mtu(dst);
+ if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
+ mss_now = tcp_sync_mss(sk, mtu);
+ }
+
+ if (tp->rx_opt.eff_sacks)
+ mss_now -= (TCPOLEN_SACK_BASE_ALIGNED +
+ (tp->rx_opt.eff_sacks * TCPOLEN_SACK_PERBLOCK));
+
+#ifdef CONFIG_TCP_MD5SIG
+ if (tp->af_specific->md5_lookup(sk, sk))
+ mss_now -= TCPOLEN_MD5SIG_ALIGNED;
+#endif
+
+ xmit_size_goal = mss_now;
+
+ if (doing_tso) {
+ xmit_size_goal = (65535 -
+ inet_csk(sk)->icsk_af_ops->net_header_len -
+ inet_csk(sk)->icsk_ext_hdr_len -
+ tp->tcp_header_len);
+
+ if (tp->max_window &&
+ (xmit_size_goal > (tp->max_window >> 1)))
+ xmit_size_goal = max((tp->max_window >> 1),
+ 68U - tp->tcp_header_len);
+
+ xmit_size_goal -= (xmit_size_goal % mss_now);
+ }
+ tp->xmit_size_goal = xmit_size_goal;
+
+ return mss_now;
+}
+
+/* Congestion window validation. (RFC2861) */
+
+static void tcp_cwnd_validate(struct sock *sk, struct tcp_sock *tp)
+{
+ __u32 packets_out = tp->packets_out;
+
+ if (packets_out >= tp->snd_cwnd) {
+ /* Network is feed fully. */
+ tp->snd_cwnd_used = 0;
+ tp->snd_cwnd_stamp = tcp_time_stamp;