Piggyback a timestamp on all outgoing Hello messages

We use a sub-TLV to do so, which we fill out at the very last moment
to get an accurate timing.

This timestamp will be used to compute the RTT to our neighbours.

message.c

@@ -519,6 +519,21 @@ check_bucket(struct interface *ifp)
     }
 }
 
+static int
+fill_rtt_message(struct interface *ifp)
+{
+    if(ifp->buffered_hello >= 0) {
+        unsigned int time;
+        /* Change the type of sub-TLV. */
+        ifp->sendbuf[ifp->buffered_hello + 8] = SUBTLV_TIMESTAMP;
+        gettime(&now);
+        time = time_us(now);
+        DO_HTONL(ifp->sendbuf + ifp->buffered_hello + 10, time);
+        return 1;
+    }
+    return 0;
+}
+
 void
 flushbuf(struct interface *ifp)
 {
@@ -539,6 +554,7 @@ flushbuf(struct interface *ifp)
             sin6.sin6_port = htons(protocol_port);
             sin6.sin6_scope_id = ifp->ifindex;
             DO_HTONS(packet_header + 2, ifp->buffered);
+            fill_rtt_message(ifp);
             rc = babel_send(protocol_socket,
                             packet_header, sizeof(packet_header),
                             ifp->sendbuf, ifp->buffered,
@@ -737,12 +753,17 @@ send_hello_noupdate(struct interface *ifp, unsigned interval)
     debugf("Sending hello %d (%d) to %s.\n",
            ifp->hello_seqno, interval, ifp->name);
 
-    start_message(ifp, MESSAGE_HELLO, 6);
+    start_message(ifp, MESSAGE_HELLO, 12);
     ifp->buffered_hello = ifp->buffered - 2;
     accumulate_short(ifp, 0);
     accumulate_short(ifp, ifp->hello_seqno);
     accumulate_short(ifp, interval > 0xFFFF ? 0xFFFF : interval);
-    end_message(ifp, MESSAGE_HELLO, 6);
+    /* Sub-TLV containing the local time of emission. We use a Pad4
+       sub-TLV, which we'll fill just before sending. */
+    accumulate_byte(ifp, SUBTLV_PADN);
+    accumulate_byte(ifp, 4);
+    accumulate_int(ifp, 0);
+    end_message(ifp, MESSAGE_HELLO, 12);
 }
 
 void

message.h

@@ -44,6 +44,7 @@ THE SOFTWARE.
 #define SUBTLV_PAD1 0
 #define SUBTLV_PADN 1
 #define SUBTLV_DIVERSITY 2 /* Also known as babelz. */
+#define SUBTLV_TIMESTAMP 3 /* Used to compute RTT. */
 
 extern unsigned short myseqno;
 extern struct timeval seqno_time;

util.h

@@ -66,6 +66,14 @@ seqno_plus(unsigned short s, int plus)
     return ((s + plus) & 0xFFFF);
 }
 
+/* Returns a time in microseconds on 32 bits (thus modulo 2^32,
+   i.e. about 4295 seconds). */
+static inline unsigned int
+time_us(const struct timeval t)
+{
+    return (unsigned int) (t.tv_sec * 1000000 + t.tv_usec);
+}
+
 int roughly(int value);
 void timeval_minus(struct timeval *d,
                    const struct timeval *s1, const struct timeval *s2);