batman-adv: Simple (re)broadcast avoidance

With this patch, (re)broadcasting on a specific interfaces is avoided:

* No neighbor: There is no need to broadcast on an interface if there
  is no node behind it.

* Single neighbor is source: If there is just one neighbor on an
  interface and if this neighbor is the one we actually got this
  broadcast packet from, then we do not need to echo it back.

* Single neighbor is originator: If there is just one neighbor on
  an interface and if this neighbor is the originator of this
  broadcast packet, then we do not need to echo it back.

Goodies for BATMAN V:

("Upgrade your BATMAN IV network to V now to get these for free!")

Thanks to the split of OGMv1 into two packet types, OGMv2 and ELP
that is, we can now apply the same optimizations stated above to OGMv2
packets, too.

Furthermore, with BATMAN V, rebroadcasts can be reduced in certain
multi interface cases, too, where BATMAN IV cannot. This is thanks to
the removal of the "secondary interface originator" concept in BATMAN V.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

1 files changed, 52 insertions, 0 deletions

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index 08ce36147c4c..a7a462e6fee5 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -228,6 +228,58 @@ bool batadv_is_wifi_netdev(struct net_device *net_device)
 	return false;
 }
 
+/**
+ * batadv_hardif_no_broadcast - check whether (re)broadcast is necessary
+ * @if_outgoing: the outgoing interface checked and considered for (re)broadcast
+ * @orig_addr: the originator of this packet
+ * @orig_neigh: originator address of the forwarder we just got the packet from
+ *  (NULL if we originated)
+ *
+ * Checks whether a packet needs to be (re)broadcasted on the given interface.
+ *
+ * Return:
+ *	BATADV_HARDIF_BCAST_NORECIPIENT: No neighbor on interface
+ *	BATADV_HARDIF_BCAST_DUPFWD: Just one neighbor, but it is the forwarder
+ *	BATADV_HARDIF_BCAST_DUPORIG: Just one neighbor, but it is the originator
+ *	BATADV_HARDIF_BCAST_OK: Several neighbors, must broadcast
+ */
+int batadv_hardif_no_broadcast(struct batadv_hard_iface *if_outgoing,
+			       u8 *orig_addr, u8 *orig_neigh)
+{
+	struct batadv_hardif_neigh_node *hardif_neigh;
+	struct hlist_node *first;
+	int ret = BATADV_HARDIF_BCAST_OK;
+
+	rcu_read_lock();
+
+	/* 0 neighbors -> no (re)broadcast */
+	first = rcu_dereference(hlist_first_rcu(&if_outgoing->neigh_list));
+	if (!first) {
+		ret = BATADV_HARDIF_BCAST_NORECIPIENT;
+		goto out;
+	}
+
+	/* >1 neighbors -> (re)brodcast */
+	if (rcu_dereference(hlist_next_rcu(first)))
+		goto out;
+
+	hardif_neigh = hlist_entry(first, struct batadv_hardif_neigh_node,
+				   list);
+
+	/* 1 neighbor, is the originator -> no rebroadcast */
+	if (orig_addr && batadv_compare_eth(hardif_neigh->orig, orig_addr)) {
+		ret = BATADV_HARDIF_BCAST_DUPORIG;
+	/* 1 neighbor, is the one we received from -> no rebroadcast */
+	} else if (orig_neigh &&
+		   batadv_compare_eth(hardif_neigh->orig, orig_neigh)) {
+		ret = BATADV_HARDIF_BCAST_DUPFWD;
+	}
+
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
 static struct batadv_hard_iface *
 batadv_hardif_get_active(const struct net_device *soft_iface)
 {