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>

2 files changed, 190 insertions, 3 deletions

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 24995a93ef8c..710cafd2e1a9 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -672,6 +672,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
                             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 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
                                         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 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
         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 @@ static void fib6_del_route(struct fib6_node *fn, struct rt6_info **rtp,
         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) {
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 7c7e963260e1..126da562d3eb 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -57,6 +57,7 @@
 #include <net/xfrm.h>
 #include <net/netevent.h>
 #include <net/netlink.h>
+#include <net/nexthop.h>
 
 #include <asm/uaccess.h>
 
@@ -289,6 +290,8 @@ static inline struct rt6_info *ip6_dst_alloc(struct net *net,
                 memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
                 rt6_init_peer(rt, table ? &table->tb6_peers : net->ipv6.peers);
                 rt->rt6i_genid = rt_genid(net);
+                INIT_LIST_HEAD(&rt->rt6i_siblings);
+                rt->rt6i_nsiblings = 0;
         }
         return rt;
 }
@@ -385,6 +388,69 @@ static bool rt6_need_strict(const struct in6_addr *daddr)
                 (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL | IPV6_ADDR_LOOPBACK);
 }
 
+/* Multipath route selection:
+ *   Hash based function using packet header and flowlabel.
+ * Adapted from fib_info_hashfn()
+ */
+static int rt6_info_hash_nhsfn(unsigned int candidate_count,
+                               const struct flowi6 *fl6)
+{
+        unsigned int val = fl6->flowi6_proto;
+
+        val ^= fl6->daddr.s6_addr32[0];
+        val ^= fl6->daddr.s6_addr32[1];
+        val ^= fl6->daddr.s6_addr32[2];
+        val ^= fl6->daddr.s6_addr32[3];
+
+        val ^= fl6->saddr.s6_addr32[0];
+        val ^= fl6->saddr.s6_addr32[1];
+        val ^= fl6->saddr.s6_addr32[2];
+        val ^= fl6->saddr.s6_addr32[3];
+
+        /* Work only if this not encapsulated */
+        switch (fl6->flowi6_proto) {
+        case IPPROTO_UDP:
+        case IPPROTO_TCP:
+        case IPPROTO_SCTP:
+                val ^= fl6->fl6_sport;
+                val ^= fl6->fl6_dport;
+                break;
+
+        case IPPROTO_ICMPV6:
+                val ^= fl6->fl6_icmp_type;
+                val ^= fl6->fl6_icmp_code;
+                break;
+        }
+        /* RFC6438 recommands to use flowlabel */
+        val ^= fl6->flowlabel;
+
+        /* Perhaps, we need to tune, this function? */
+        val = val ^ (val >> 7) ^ (val >> 12);
+        return val % candidate_count;
+}
+
+static struct rt6_info *rt6_multipath_select(struct rt6_info *match,
+                                             struct flowi6 *fl6)
+{
+        struct rt6_info *sibling, *next_sibling;
+        int route_choosen;
+
+        route_choosen = rt6_info_hash_nhsfn(match->rt6i_nsiblings + 1, fl6);
+        /* Don't change the route, if route_choosen == 0
+         * (siblings does not include ourself)
+         */
+        if (route_choosen)
+                list_for_each_entry_safe(sibling, next_sibling,
+                                &match->rt6i_siblings, rt6i_siblings) {
+                        route_choosen--;
+                        if (route_choosen == 0) {
+                                match = sibling;
+                                break;
+                        }
+                }
+        return match;
+}
+
 /*
  *      Route lookup. Any table->tb6_lock is implied.
  */
@@ -702,6 +768,8 @@ static struct rt6_info *ip6_pol_route_lookup(struct net *net,
 restart:
         rt = fn->leaf;
         rt = rt6_device_match(net, rt, &fl6->saddr, fl6->flowi6_oif, flags);
+        if (rt->rt6i_nsiblings && fl6->flowi6_oif == 0)
+                rt = rt6_multipath_select(rt, fl6);
         BACKTRACK(net, &fl6->saddr);
 out:
         dst_use(&rt->dst, jiffies);
@@ -863,7 +931,8 @@ restart_2:
 
 restart:
         rt = rt6_select(fn, oif, strict | reachable);
-
+        if (rt->rt6i_nsiblings && oif == 0)
+                rt = rt6_multipath_select(rt, fl6);
         BACKTRACK(net, &fl6->saddr);
         if (rt == net->ipv6.ip6_null_entry ||
             rt->rt6i_flags & RTF_CACHE)
@@ -2249,6 +2318,7 @@ static const struct nla_policy rtm_ipv6_policy[RTA_MAX+1] = {
         [RTA_IIF]               = { .type = NLA_U32 },
         [RTA_PRIORITY]          = { .type = NLA_U32 },
         [RTA_METRICS]           = { .type = NLA_NESTED },
+        [RTA_MULTIPATH]         = { .len = sizeof(struct rtnexthop) },
 };
 
 static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
@@ -2326,11 +2396,65 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
         if (tb[RTA_TABLE])
                 cfg->fc_table = nla_get_u32(tb[RTA_TABLE]);
 
+        if (tb[RTA_MULTIPATH]) {
+                cfg->fc_mp = nla_data(tb[RTA_MULTIPATH]);
+                cfg->fc_mp_len = nla_len(tb[RTA_MULTIPATH]);
+        }
+
         err = 0;
 errout:
         return err;
 }
 
+static int ip6_route_multipath(struct fib6_config *cfg, int add)
+{
+        struct fib6_config r_cfg;
+        struct rtnexthop *rtnh;
+        int remaining;
+        int attrlen;
+        int err = 0, last_err = 0;
+
+beginning:
+        rtnh = (struct rtnexthop *)cfg->fc_mp;
+        remaining = cfg->fc_mp_len;
+
+        /* Parse a Multipath Entry */
+        while (rtnh_ok(rtnh, remaining)) {
+                memcpy(&r_cfg, cfg, sizeof(*cfg));
+                if (rtnh->rtnh_ifindex)
+                        r_cfg.fc_ifindex = rtnh->rtnh_ifindex;
+
+                attrlen = rtnh_attrlen(rtnh);
+                if (attrlen > 0) {
+                        struct nlattr *nla, *attrs = rtnh_attrs(rtnh);
+
+                        nla = nla_find(attrs, attrlen, RTA_GATEWAY);
+                        if (nla) {
+                                nla_memcpy(&r_cfg.fc_gateway, nla, 16);
+                                r_cfg.fc_flags |= RTF_GATEWAY;
+                        }
+                }
+                err = add ? ip6_route_add(&r_cfg) : ip6_route_del(&r_cfg);
+                if (err) {
+                        last_err = err;
+                        /* If we are trying to remove a route, do not stop the
+                         * loop when ip6_route_del() fails (because next hop is
+                         * already gone), we should try to remove all next hops.
+                         */
+                        if (add) {
+                                /* If add fails, we should try to delete all
+                                 * next hops that have been already added.
+                                 */
+                                add = 0;
+                                goto beginning;
+                        }
+                }
+                rtnh = rtnh_next(rtnh, &remaining);
+        }
+
+        return last_err;
+}
+
 static int inet6_rtm_delroute(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
 {
         struct fib6_config cfg;
@@ -2340,7 +2464,10 @@ static int inet6_rtm_delroute(struct sk_buff *skb, struct nlmsghdr* nlh, void *a
         if (err < 0)
                 return err;
 
-        return ip6_route_del(&cfg);
+        if (cfg.fc_mp)
+                return ip6_route_multipath(&cfg, 0);
+        else
+                return ip6_route_del(&cfg);
 }
 
 static int inet6_rtm_newroute(struct sk_buff *skb, struct nlmsghdr* nlh, void *arg)
@@ -2352,7 +2479,10 @@ static int inet6_rtm_newroute(struct sk_buff *skb, struct nlmsghdr* nlh, void *a
         if (err < 0)
                 return err;
 
-        return ip6_route_add(&cfg);
+        if (cfg.fc_mp)
+                return ip6_route_multipath(&cfg, 1);
+        else
+                return ip6_route_add(&cfg);
 }
 
 static inline size_t rt6_nlmsg_size(void)