[TCP]: MTU probing

Implementation of packetization layer path mtu discovery for TCP, based on
the internet-draft currently found at
<http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt>.

Signed-off-by: John Heffner <jheffner@psc.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 49 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e9a54ae7d690..0ac388e3d01d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1891,6 +1891,34 @@ static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
         }
 }
 
+static void tcp_mtup_probe_failed(struct sock *sk)
+{
+        struct inet_connection_sock *icsk = inet_csk(sk);
+
+        icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
+        icsk->icsk_mtup.probe_size = 0;
+}
+
+static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct inet_connection_sock *icsk = inet_csk(sk);
+
+        /* FIXME: breaks with very large cwnd */
+        tp->prior_ssthresh = tcp_current_ssthresh(sk);
+        tp->snd_cwnd = tp->snd_cwnd *
+                       tcp_mss_to_mtu(sk, tp->mss_cache) /
+                       icsk->icsk_mtup.probe_size;
+        tp->snd_cwnd_cnt = 0;
+        tp->snd_cwnd_stamp = tcp_time_stamp;
+        tp->rcv_ssthresh = tcp_current_ssthresh(sk);
+
+        icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
+        icsk->icsk_mtup.probe_size = 0;
+        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+}
+
+
 /* Process an event, which can update packets-in-flight not trivially.
  * Main goal of this function is to calculate new estimate for left_out,
  * taking into account both packets sitting in receiver's buffer and
@@ -2023,6 +2051,17 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
                         return;
                 }
 
+                /* MTU probe failure: don't reduce cwnd */
+                if (icsk->icsk_ca_state < TCP_CA_CWR &&
+                    icsk->icsk_mtup.probe_size &&
+                    tp->snd_una == icsk->icsk_mtup.probe_seq_start) {
+                        tcp_mtup_probe_failed(sk);
+                        /* Restores the reduction we did in tcp_mtup_probe() */
+                        tp->snd_cwnd++;
+                        tcp_simple_retransmit(sk);
+                        return;
+                }
+
                 /* Otherwise enter Recovery state */
 
                 if (IsReno(tp))
@@ -2243,6 +2282,13 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
                         tp->retrans_stamp = 0;
                 }
 
+                /* MTU probing checks */
+                if (icsk->icsk_mtup.probe_size) {
+                        if (!after(icsk->icsk_mtup.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
+                                tcp_mtup_probe_success(sk, skb);
+                        }
+                }
+
                 if (sacked) {
                         if (sacked & TCPCB_RETRANS) {
                                 if(sacked & TCPCB_SACKED_RETRANS)
@@ -4101,6 +4147,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
                 if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
                         tp->rx_opt.sack_ok |= 2;
 
+                tcp_mtup_init(sk);
                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
                 tcp_initialize_rcv_mss(sk);
 
@@ -4211,6 +4258,7 @@ discard:
                 if (tp->ecn_flags&TCP_ECN_OK)
                         sock_set_flag(sk, SOCK_NO_LARGESEND);
 
+                tcp_mtup_init(sk);
                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
                 tcp_initialize_rcv_mss(sk);
 
@@ -4399,6 +4447,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                                  */
                                 tp->lsndtime = tcp_time_stamp;
 
+                                tcp_mtup_init(sk);
                                 tcp_initialize_rcv_mss(sk);
                                 tcp_init_buffer_space(sk);
                                 tcp_fast_path_on(tp);