ipv6: add support of equal cost multipath (ECMP)
Each nexthop is added like a single route in the routing table. All routes
that have the same metric/weight and destination but not the same gateway
are considering as ECMP routes. They are linked together, through a list called
rt6i_siblings.
ECMP routes can be added in one shot, with RTA_MULTIPATH attribute or one after
the other (in both case, the flag NLM_F_EXCL should not be set).
The patch is based on a previous work from
Luc Saillard <luc.saillard@6wind.com>.
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 24995a9..710cafd 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -672,6 +672,8 @@
iter->rt6i_idev == rt->rt6i_idev &&
ipv6_addr_equal(&iter->rt6i_gateway,
&rt->rt6i_gateway)) {
+ if (rt->rt6i_nsiblings)
+ rt->rt6i_nsiblings = 0;
if (!(iter->rt6i_flags & RTF_EXPIRES))
return -EEXIST;
if (!(rt->rt6i_flags & RTF_EXPIRES))
@@ -680,6 +682,21 @@
rt6_set_expires(iter, rt->dst.expires);
return -EEXIST;
}
+ /* If we have the same destination and the same metric,
+ * but not the same gateway, then the route we try to
+ * add is sibling to this route, increment our counter
+ * of siblings, and later we will add our route to the
+ * list.
+ * Only static routes (which don't have flag
+ * RTF_EXPIRES) are used for ECMPv6.
+ *
+ * To avoid long list, we only had siblings if the
+ * route have a gateway.
+ */
+ if (rt->rt6i_flags & RTF_GATEWAY &&
+ !(rt->rt6i_flags & RTF_EXPIRES) &&
+ !(iter->rt6i_flags & RTF_EXPIRES))
+ rt->rt6i_nsiblings++;
}
if (iter->rt6i_metric > rt->rt6i_metric)
@@ -692,6 +709,35 @@
if (ins == &fn->leaf)
fn->rr_ptr = NULL;
+ /* Link this route to others same route. */
+ if (rt->rt6i_nsiblings) {
+ unsigned int rt6i_nsiblings;
+ struct rt6_info *sibling, *temp_sibling;
+
+ /* Find the first route that have the same metric */
+ sibling = fn->leaf;
+ while (sibling) {
+ if (sibling->rt6i_metric == rt->rt6i_metric) {
+ list_add_tail(&rt->rt6i_siblings,
+ &sibling->rt6i_siblings);
+ break;
+ }
+ sibling = sibling->dst.rt6_next;
+ }
+ /* For each sibling in the list, increment the counter of
+ * siblings. BUG() if counters does not match, list of siblings
+ * is broken!
+ */
+ rt6i_nsiblings = 0;
+ list_for_each_entry_safe(sibling, temp_sibling,
+ &rt->rt6i_siblings, rt6i_siblings) {
+ sibling->rt6i_nsiblings++;
+ BUG_ON(sibling->rt6i_nsiblings != rt->rt6i_nsiblings);
+ rt6i_nsiblings++;
+ }
+ BUG_ON(rt6i_nsiblings != rt->rt6i_nsiblings);
+ }
+
/*
* insert node
*/
@@ -1193,6 +1239,17 @@
if (fn->rr_ptr == rt)
fn->rr_ptr = NULL;
+ /* Remove this entry from other siblings */
+ if (rt->rt6i_nsiblings) {
+ struct rt6_info *sibling, *next_sibling;
+
+ list_for_each_entry_safe(sibling, next_sibling,
+ &rt->rt6i_siblings, rt6i_siblings)
+ sibling->rt6i_nsiblings--;
+ rt->rt6i_nsiblings = 0;
+ list_del_init(&rt->rt6i_siblings);
+ }
+
/* Adjust walkers */
read_lock(&fib6_walker_lock);
FOR_WALKERS(w) {