[DCCP]: Sample RTT from SYN exchange

Function:

include/linux/dccp.h

@@ -481,10 +481,12 @@ struct dccp_ackvec;
  * @dccps_hc_rx_insert_options -
  * @dccps_hc_tx_insert_options -
  * @dccps_xmit_timer - timer for when CCID is not ready to send
+ * @dccps_syn_rtt - RTT sample from Request/Response exchange (in usecs)
  */
 struct dccp_sock {
 	/* inet_connection_sock has to be the first member of dccp_sock */
 	struct inet_connection_sock	dccps_inet_connection;
+#define dccps_syn_rtt			dccps_inet_connection.icsk_ack.lrcvtime
 	__u64				dccps_swl;
 	__u64				dccps_swh;
 	__u64				dccps_awl;

net/dccp/input.c

@@ -300,6 +300,14 @@ static int dccp_rcv_request_sent_state_process(struct sock *sk,
 		if (dccp_parse_options(sk, skb))
 			goto out_invalid_packet;
 
+		/* Obtain RTT sample from SYN exchange (used by CCID 3) */
+		if (dp->dccps_options_received.dccpor_timestamp_echo) {
+			struct timeval now;
+
+			dccp_timestamp(sk, &now);
+			dp->dccps_syn_rtt = dccp_sample_rtt(sk, &now, NULL);
+		}
+
 		if (dccp_msk(sk)->dccpms_send_ack_vector &&
 		    dccp_ackvec_add(dp->dccps_hc_rx_ackvec, sk,
 				    DCCP_SKB_CB(skb)->dccpd_seq,

net/dccp/options.c

@@ -563,6 +563,14 @@ int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
 	    dccp_insert_options_feat(sk, skb))
 		return -1;
 
+	/*
+	 * Obtain RTT sample from Request/Response exchange.
+	 * This is currently used in CCID 3 initialisation.
+	 */
+	if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_REQUEST &&
+	    dccp_insert_option_timestamp(sk, skb))
+		return -1;
+
 	/* XXX: insert other options when appropriate */
 
 	if (DCCP_SKB_CB(skb)->dccpd_opt_len != 0) {