zebra: When registering a nexthop, we do not always need to re-eval

The code prior to this change, was allowing clients to register
for nexthop tracking.  Then zebra would look up the rnh and
send to that particular client any known data.  Additionally
zebra was blindly re-evaluating the rnh for every registration.

This leads to interesting behavior in that all people registered
for that nexthop will get callbacks even if nothing changes.

Modify the code to know if we have evaluated the rnh or not
and if so limit the re-evaluation to when absolutely necessary

This is of particular importance to do because of nht callbacks
for protocols cause those protocols to do not insignificant
work and as more protocols are registering for nht callbacks
we will cause more work than is necessary.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/zebra/zebra_rnh.c b/zebra/zebra_rnh.c
index 156600c105..0b585af6a0 100644
--- a/zebra/zebra_rnh.c
+++ b/zebra/zebra_rnh.c
@@ -103,7 +103,8 @@ char *rnh_str(struct rnh *rnh, char *buf, int size)
 	return buf;
 }
 
-struct rnh *zebra_add_rnh(struct prefix *p, vrf_id_t vrfid, rnh_type_t type)
+struct rnh *zebra_add_rnh(struct prefix *p, vrf_id_t vrfid, rnh_type_t type,
+			  bool *exists)
 {
 	struct route_table *table;
 	struct route_node *rn;
@@ -119,6 +120,7 @@ struct rnh *zebra_add_rnh(struct prefix *p, vrf_id_t vrfid, rnh_type_t type)
 		prefix2str(p, buf, sizeof(buf));
 		zlog_warn("%u: Add RNH %s type %d - table not found", vrfid,
 			  buf, type);
+		exists = false;
 		return NULL;
 	}
 
@@ -136,7 +138,9 @@ struct rnh *zebra_add_rnh(struct prefix *p, vrf_id_t vrfid, rnh_type_t type)
 		route_lock_node(rn);
 		rn->info = rnh;
 		rnh->node = rn;
-	}
+		*exists = false;
+	} else
+		*exists = true;
 
 	route_unlock_node(rn);
 	return (rn->info);
@@ -190,6 +194,14 @@ void zebra_delete_rnh(struct rnh *rnh, rnh_type_t type)
 	route_unlock_node(rn);
 }
 
+/*
+ * This code will send to the registering client
+ * the looked up rnh.
+ * For a rnh that was created, there is no data
+ * so it will send an empty nexthop group
+ * If rnh exists then we know it has been evaluated
+ * and as such it will have a resolved rnh.
+ */
 void zebra_add_rnh_client(struct rnh *rnh, struct zserv *client,
 			  rnh_type_t type, vrf_id_t vrf_id)
 {
@@ -201,8 +213,7 @@ void zebra_add_rnh_client(struct rnh *rnh, struct zserv *client,
 	}
 	if (!listnode_lookup(rnh->client_list, client)) {
 		listnode_add(rnh->client_list, client);
-		send_client(rnh, client, type,
-			    vrf_id); // Pending: check if its needed
+		send_client(rnh, client, type, vrf_id);
 	}
 }
 
@@ -247,9 +258,10 @@ void zebra_register_rnh_pseudowire(vrf_id_t vrf_id, struct zebra_pw *pw)
 {
 	struct prefix nh;
 	struct rnh *rnh;
+	bool exists;
 
 	addr2hostprefix(pw->af, &pw->nexthop, &nh);
-	rnh = zebra_add_rnh(&nh, vrf_id, RNH_NEXTHOP_TYPE);
+	rnh = zebra_add_rnh(&nh, vrf_id, RNH_NEXTHOP_TYPE, &exists);
 	if (rnh && !listnode_lookup(rnh->zebra_pseudowire_list, pw)) {
 		listnode_add(rnh->zebra_pseudowire_list, pw);
 		pw->rnh = rnh;