ipv6: Add support for non-equal-cost multipath

The use of hash-threshold instead of modulo-N makes it trivial to add
support for non-equal-cost multipath.

Instead of dividing the multipath hash function's output space equally
between the nexthops, each nexthop is assigned a region size which is
proportional to its weight.

Signed-off-by: Ido Schimmel <[email protected]>
Acked-by: David Ahern <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: idosch

include/net/ip6_fib.h

@@ -171,6 +171,7 @@ struct rt6_info {
 	u32				rt6i_metric;
 	u32				rt6i_pmtu;
 	/* more non-fragment space at head required */
+	int				rt6i_nh_weight;
 	unsigned short			rt6i_nfheader_len;
 	u8				rt6i_protocol;
 	u8				exception_bucket_flushed:1,

net/ipv6/route.c

@@ -2594,6 +2594,7 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
 #endif
 
 	rt->rt6i_metric = cfg->fc_metric;
+	rt->rt6i_nh_weight = 1;
 
 	/* We cannot add true routes via loopback here,
 	   they would result in kernel looping; promote them to reject routes
@@ -3507,11 +3508,11 @@ static int rt6_multipath_total_weight(const struct rt6_info *rt)
 	int total = 0;
 
 	if (!rt6_is_dead(rt))
-		total++;
+		total += rt->rt6i_nh_weight;
 
 	list_for_each_entry(iter, &rt->rt6i_siblings, rt6i_siblings) {
 		if (!rt6_is_dead(iter))
-			total++;
+			total += iter->rt6i_nh_weight;
 	}
 
 	return total;
@@ -3522,7 +3523,7 @@ static void rt6_upper_bound_set(struct rt6_info *rt, int *weight, int total)
 	int upper_bound = -1;
 
 	if (!rt6_is_dead(rt)) {
-		(*weight)++;
+		*weight += rt->rt6i_nh_weight;
 		upper_bound = DIV_ROUND_CLOSEST_ULL((u64) (*weight) << 31,
 						    total) - 1;
 	}
@@ -4024,6 +4025,8 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 			goto cleanup;
 		}
 
+		rt->rt6i_nh_weight = rtnh->rtnh_hops + 1;
+
 		err = ip6_route_info_append(&rt6_nh_list, rt, &r_cfg);
 		if (err) {
 			dst_release_immediate(&rt->dst);
@@ -4246,7 +4249,7 @@ static int rt6_add_nexthop(struct sk_buff *skb, struct rt6_info *rt)
 	if (!rtnh)
 		goto nla_put_failure;
 
-	rtnh->rtnh_hops = 0;
+	rtnh->rtnh_hops = rt->rt6i_nh_weight - 1;
 	rtnh->rtnh_ifindex = rt->dst.dev ? rt->dst.dev->ifindex : 0;
 
 	if (rt6_nexthop_info(skb, rt, &flags, true) < 0)