batman-adv: add bonding again

With the new interface alternating, the first hop may send packets
in a round robin fashion to it's neighbors because it has multiple
valid routes built by the multi interface optimization. This patch
enables the feature if bonding is selected. Note that unlike the
bonding implemented before, this version is much simpler and may
even enable multi path routing to a certain degree.

Signed-off-by: Simon Wunderlich <simon@open-mesh.com>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

1 files changed, 114 insertions, 3 deletions

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 55e9aebcbc80..153065a8785c 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -427,16 +427,127 @@ 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 = NULL;
+        struct batadv_neigh_node *router, *cand_router = NULL;
+        struct batadv_neigh_node *last_cand_router = NULL;
+        struct batadv_orig_ifinfo *cand, *first_candidate = NULL;
+        struct batadv_orig_ifinfo *next_candidate = NULL;
+        struct batadv_orig_ifinfo *last_candidate;
+        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();
+        last_candidate = orig_node->last_bonding_candidate;
+        if (last_candidate)
+                last_cand_router = rcu_dereference(last_candidate->router);
+
+        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 (last_cand_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 (!last_candidate || last_candidate_found) {
+                        next_candidate = cand;
+                        next_candidate_router = cand_router;
+                        break;
+                }
+
+                if (last_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;
 }