[v3,6/8] batman-adv: add bonding again

diff --git a/originator.c b/originator.c
index b485f1c..9f0ae77 100644
--- a/originator.c
+++ b/originator.c
@@ -698,6 +698,10 @@  batadv_purge_orig_ifinfo(struct batadv_priv *bat_priv,
 
 		hlist_del_rcu(&orig_ifinfo->list);
 		batadv_orig_ifinfo_free_ref(orig_ifinfo);
+		if (orig_node->last_bonding_candidate == orig_ifinfo) {
+			orig_node->last_bonding_candidate = NULL;
+			batadv_orig_ifinfo_free_ref(orig_ifinfo);
+		}
 	}
 
 	spin_unlock_bh(&orig_node->neigh_list_lock);
diff --git a/routing.c b/routing.c
index 760692d..69620e0 100644
--- a/routing.c
+++ b/routing.c
@@ -424,16 +424,123 @@  static int batadv_check_unicast_packet(struct batadv_priv *bat_priv,
 struct batadv_neigh_node *
 batadv_find_router(struct batadv_priv *bat_priv,
 		   struct batadv_orig_node *orig_node,
-		   const struct batadv_hard_iface *recv_if)
+		   struct batadv_hard_iface *recv_if)
 {
-	struct batadv_neigh_node *router;
+	struct batadv_algo_ops *bao = bat_priv->bat_algo_ops;
+	struct batadv_neigh_node *first_candidate_router = NULL;
+	struct batadv_neigh_node *next_candidate_router;
+	struct batadv_neigh_node *router, *cand_router = NULL;
+	struct batadv_orig_ifinfo *cand, *first_candidate = NULL;
+	struct batadv_orig_ifinfo *next_candidate = NULL;
+	bool last_candidate_found = false;
 
 	if (!orig_node)
 		return NULL;
 
 	router = batadv_orig_router_get(orig_node, recv_if);
 
-	/* TODO: fill this later with new bonding mechanism */
+	/* only consider bonding for recv_if == BATADV_IF_DEFAULT (first hop)
+	 * and if activated.
+	 */
+	if (recv_if == BATADV_IF_DEFAULT || !atomic_read(&bat_priv->bonding) ||
+	    !router)
+		return router;
+
+	/* bonding: loop through the list of possible routers found
+	 * for the various outgoing interfaces and find a candidate after
+	 * the last chosen bonding candidate (next_candidate). If no such
+	 * router is found, use the first candidate found (the previously
+	 * chosen bonding candidate might have been the last one in the list).
+	 * If this can't be found either, return the previously choosen
+	 * router - obviously there are no other candidates.
+	 */
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(cand, &orig_node->ifinfo_list, list) {
+		/* acquire some structures and references ... */
+		if (!atomic_inc_not_zero(&cand->refcount))
+			continue;
+
+		cand_router = rcu_dereference(cand->router);
+		if (!cand_router)
+			goto next;
+
+		if (!atomic_inc_not_zero(&cand_router->refcount)) {
+			cand_router = NULL;
+			goto next;
+		}
+
+		/* alternative candidate should be good enough to be
+		 * considered
+		 */
+		if (!bao->bat_neigh_is_equiv_or_better(cand_router,
+						       cand->if_outgoing,
+						       router, recv_if))
+			goto next;
+
+		/* don't use the same router twice */
+		if (orig_node->last_bonding_candidate &&
+		    (orig_node->last_bonding_candidate->router == cand_router))
+				goto next;
+
+		/* mark the first possible candidate */
+		if (!first_candidate) {
+			atomic_inc(&cand_router->refcount);
+			atomic_inc(&cand->refcount);
+			first_candidate = cand;
+			first_candidate_router = cand_router;
+		}
+
+		/* check if the loop has already passed the previously selected
+		 * candidate ... this function should select the next candidate
+		 * AFTER the previously used bonding candidate.
+		 */
+		if (!orig_node->last_bonding_candidate ||
+		    last_candidate_found) {
+			next_candidate = cand;
+			next_candidate_router = cand_router;
+			break;
+		}
+
+		if (orig_node->last_bonding_candidate == cand)
+			last_candidate_found = true;
+next:
+		/* free references */
+		if (cand_router) {
+			batadv_neigh_node_free_ref(cand_router);
+			cand_router = NULL;
+		}
+		batadv_orig_ifinfo_free_ref(cand);
+	}
+	rcu_read_unlock();
+
+	/* last_bonding_candidate is reset below, remove the old reference. */
+	if (orig_node->last_bonding_candidate)
+		batadv_orig_ifinfo_free_ref(orig_node->last_bonding_candidate);
+
+	/* After finding candidates, handle the three cases:
+	 * 1) there is a next candidate, use that
+	 * 2) there is no next candidate, use the first of the list
+	 * 3) there is no candidate at all, return the default router
+	 */
+	if (next_candidate) {
+		batadv_neigh_node_free_ref(router);
+
+		/* remove references to first candidate, we don't need it. */
+		if (first_candidate) {
+			batadv_neigh_node_free_ref(first_candidate_router);
+			batadv_orig_ifinfo_free_ref(first_candidate);
+		}
+		router = next_candidate_router;
+		orig_node->last_bonding_candidate = next_candidate;
+	} else if (first_candidate) {
+		batadv_neigh_node_free_ref(router);
+
+		/* refcounting has already been done in the loop above. */
+		router = first_candidate_router;
+		orig_node->last_bonding_candidate = first_candidate;
+	} else {
+		orig_node->last_bonding_candidate = NULL;
+	}
 
 	return router;
 }
diff --git a/routing.h b/routing.h
index e1e36db..4143898 100644
--- a/routing.h
+++ b/routing.h
@@ -41,7 +41,7 @@  int batadv_recv_unhandled_unicast_packet(struct sk_buff *skb,
 struct batadv_neigh_node *
 batadv_find_router(struct batadv_priv *bat_priv,
 		   struct batadv_orig_node *orig_node,
-		   const struct batadv_hard_iface *recv_if);
+		   struct batadv_hard_iface *recv_if);
 int batadv_window_protected(struct batadv_priv *bat_priv, int32_t seq_num_diff,
 			    unsigned long *last_reset);
 
diff --git a/types.h b/types.h
index 9a127b6..245a547 100644
--- a/types.h
+++ b/types.h
@@ -195,6 +195,7 @@  struct batadv_orig_bat_iv {
  * @orig: originator ethernet address
  * @primary_addr: hosts primary interface address
  * @ifinfo_list: list for routers per outgoing interface
+ * @last_bonding_candidate: pointer to last ifinfo of last used router
  * @batadv_dat_addr_t:  address of the orig node in the distributed hash
  * @last_seen: time when last packet from this node was received
  * @bcast_seqno_reset: time when the broadcast seqno window was reset
@@ -235,6 +236,7 @@  struct batadv_orig_node {
 	uint8_t orig[ETH_ALEN];
 	uint8_t primary_addr[ETH_ALEN];
 	struct hlist_head ifinfo_list;
+	struct batadv_orig_ifinfo *last_bonding_candidate;
 #ifdef CONFIG_BATMAN_ADV_DAT
 	batadv_dat_addr_t dat_addr;
 #endif