iface: RFC3376 §8.6/§8.7 startup query burst

When becoming IGMP querier (on interface startup or after the prior
querier times out), immediately send the first General Query, then
schedule (Robustness Variable − 1) additional queries at the Startup
Query Interval (Query Interval / 4, default ≈ 31 s).

This lets hosts learn about the querier quickly at startup rather than
waiting up to one full Query Interval for the second query.

The startup timer is cancelled when the interface leaves service or
when a better querier is discovered; the query callback self-cancels
if the querier flag is no longer set when it fires.

Fixes #5

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

src/iface.c

@@ -25,6 +25,9 @@ static void stop_iface         (struct ifi *ifi);
 static void send_query         (struct ifi *v, uint32_t dst, int code, uint32_t group);
 static void query_groups       (int timeout, void *arg);
 
+static void startup_query_cb   (int timeout, void *arg);
+static void startup_query_timer(struct ifi *ifi);
+
 static void router_timeout_cb  (int timeout, void *arg);
 
 static void delete_group_cb    (int timeout, void *arg);
@@ -87,6 +90,7 @@ void iface_zero(struct ifi *ifi)
     ifi->ifi_querier	= NULL;
     ifi->ifi_query_interval = igmp_query_interval;
     ifi->ifi_timerid	= 0;
+    ifi->ifi_startup_timerid = 0;
     ifi->ifi_igmpv1_warn = 0;
 }
 
@@ -173,6 +177,7 @@ void iface_check_election(struct ifi *ifi)
     dbg("Assuming %squerier duties on interface %s",
           is_igmp_proxy(ifi) ? "proxy " : "", ifi->ifi_name);
     send_query(ifi, allhosts_group, igmp_response_interval, 0);
+    startup_query_timer(ifi);	/* RFC3376 §8.6, §8.7 startup query burst */
 }
 
 /*
@@ -361,8 +366,12 @@ static void stop_iface(struct ifi *ifi)
     struct listaddr *a, *tmp;
 
     /*
-     * Stop query timer
+     * Stop query timers (periodic and startup burst)
      */
+    if (ifi->ifi_startup_timerid > 0) {
+	pev_timer_del(ifi->ifi_startup_timerid);
+	ifi->ifi_startup_timerid = 0;
+    }
     if (ifi->ifi_timerid > 0)
         pev_timer_del(ifi->ifi_timerid);
     ifi->ifi_timerid = 0;
@@ -899,6 +908,61 @@ void accept_membership_report(int ifindex, int vid, uint32_t src, uint32_t dst,
     }
 }
 
+/*
+ * RFC3376 §8.6/§8.7: Send remaining startup queries at Startup Query Interval.
+ * Called once per fire; re-arms itself until the count reaches zero.
+ */
+static void startup_query_cb(int timeout, void *arg)
+{
+    cbk_t *cbk = (cbk_t *)arg;
+    struct ifi *ifi;
+
+    ifi = config_find_iface(cbk->ifindex, cbk->vid);
+    if (!ifi || !(ifi->ifi_flags & IFIF_IGMP_QUERIER))
+	goto end;
+
+    send_query(ifi, allhosts_group, igmp_response_interval, 0);
+    if (--cbk->num > 0) {
+	pev_timer_set(ifi->ifi_startup_timerid, cbk->delay * 1000000);
+	return;
+    }
+
+end:
+    if (ifi)
+	ifi->ifi_startup_timerid = pev_timer_del(ifi->ifi_startup_timerid);
+}
+
+/*
+ * Schedule the startup query burst: igmp_robustness - 1 additional queries
+ * (the first was already sent) at Startup Query Interval (Query Interval / 4).
+ */
+static void startup_query_timer(struct ifi *ifi)
+{
+    uint32_t qi = ifi->ifi_query_interval ? ifi->ifi_query_interval : igmp_query_interval;
+    uint32_t sqi = qi / 4 > 0 ? qi / 4 : 1;
+    cbk_t *cbk;
+
+    if (igmp_robustness <= 1)
+	return;
+
+    cbk = calloc(1, sizeof(cbk_t));
+    if (!cbk) {
+	err("failed allocating startup query timer");
+	exit(EX_OSERR);
+    }
+
+    cbk->ifindex = ifi->ifi_index;
+    cbk->vid     = ifi->ifi_vlan;
+    cbk->num     = igmp_robustness - 1;
+    cbk->delay   = sqi;
+
+    if (ifi->ifi_startup_timerid > 0)
+	pev_timer_del(ifi->ifi_startup_timerid);
+
+    ifi->ifi_startup_timerid = pev_timer_add(sqi * 1000000, 0, startup_query_cb, cbk);
+    pev_timer_set_cb_del(ifi->ifi_startup_timerid, free);
+}
+
 /*
  * When an active querier times out we assume the role here.
  */
@@ -913,6 +977,7 @@ static void router_timeout_cb(int timeout, void *arg)
 
     ifi->ifi_flags |= IFIF_IGMP_QUERIER;
     send_query(ifi, allhosts_group, igmp_response_interval, 0);
+    startup_query_timer(ifi);	/* RFC3376 §8.6, §8.7 startup query burst */
 }
 
 /*

src/iface.h

@@ -18,10 +18,11 @@ struct ifi {
     int		     ifi_vlan;	         /* Raw VLAN ID for send and accept   */
     char	     ifi_name[IFNAMSIZ]; /* interface name                    */
     int		     ifi_index;          /* Primarily for Linux systems       */
-    uint32_t	     ifi_inaddr;      /* Current address of this interface */
+    uint32_t	     ifi_inaddr;         /* Current address of this interface */
     uint32_t	     ifi_query_interval; /* IGMP query interval               */
     struct listaddr *ifi_querier;        /* IGMP querier (one or none)        */
     int		     ifi_timerid;	 /* IGMP query timer           	      */
+    int		     ifi_startup_timerid;/* startup query burst timer         */
     int		     ifi_igmpv1_warn;    /* To rate-limit IGMPv1 warnings     */
     uint8_t	     ifi_hwaddr[6];	 /* MAC address of this interface     */
 };