Merge branch 'ipv6-Improve-user-experience-with-multipath-routes'

David Ahern says:

====================
net: ipv6: Improve user experience with multipath routes

This series closes a couple of gaps between IPv4 and IPv6 with respect
to multipath routes:

1. IPv4 allows all nexthops of multipath routes to be deleted using just
   the prefix and length; IPv6 only deletes the first nexthop for the
   route if only the prefix and length are given.

2. IPv4 returns multipath routes encoded in the RTA_MULTIPATH attribute.
   IPv6 returns a series of routes with the same prefix and length - one
   for each nexthop. This happens for both dumps and notifications.

IPv6 does accept RTA_MULTIPATH encoded routes, but installs them as a
series of routes.

Patch 1 addresses the first item by allowing IPv6 multipath routes to be
deleted using just the prefix and length. Patch 2 addresses the second
allowing IPv6 multipath routes to be returned encoded in the RTA_MULTIPATH.

Patches 3 and 4 upate the RTM_{NEW,DEL}ROUTE notifications to generate
1 notification with RTA_MULTIPATH where applicable.

Patch 5 prints IPv6 addresses in compressed format when showing route
replace errors. This was noticed testing REPLACE failures.

The end result for multipath routes:
1. Dump
   - RTA_MULTIPATH used for multipath routes

    $ ip -6 ro ls vrf red
    2001:db8:1::/120 dev eth1 proto kernel metric 256  pref medium
    2001:db8:2::/120 dev eth2 proto kernel metric 256  pref medium
    2001:db8:200::/120 metric 1024
	    nexthop via 2001:db8:1::2  dev eth1 weight 1
	    nexthop via 2001:db8:2::2  dev eth2 weight 1
    ...

2. Route Add
   - one notification with RTA_MULTIPATH attribute

    $ ip -6 ro add vrf red 2001:db8:200::/120 nexthop via 2001:db8:1::2 nexthop via 2001:db8:2::2

    $ ip mon route
    2001:db8:200::/120 table red metric 1024
	nexthop via 2001:db8:1::2  dev eth1 weight 1
	nexthop via 2001:db8:2::2  dev eth2 weight 1

2. Route Replace
   - one notification with RTA_MULTIPATH attribute

    $ ip -6 ro replace vrf red 2001:db8:200::/120 nexthop via 2001:db8:1::16 nexthop via 2001:db8:2::16

    $ ip mon route
    Replaced 2001:db8:200::/120 table red metric 1024
	    nexthop via 2001:db8:1::16  dev eth1 weight 1
	    nexthop via 2001:db8:2::16  dev eth2 weight 1

   - on a failure after the insertion of the first nexthop (which means
     the original route has been replaced in the FIB), a notification is
     sent with the successful nexthops and then the nexthops are deleted
     with one notification per hop. This is consistent with how it works
     today except the successful additions are coalesced into 1
     notification.

3. Route Delete
   - delete of entire multipath route using prefix/length only 1
     notification is generated:
    $ ip -6 ro del vrf red 2001:db8:200::/120

    $ ip mon route
    Deleted 2001:db8:200::/120 table red metric 1024
	    nexthop via 2001:db8:1::16  dev eth1 weight 1
	    nexthop via 2001:db8:2::16  dev eth2 weight 1

   - if a delete request contains nexthops one notification is
     generated per nexthop deleted. This is unavoidable since IPv6
     alllows a single nexthop to be deleted within a multipath route

4. Route Appends
   - IPv6 allows nexthops to be appended to an existing route. In this
     case one notification is sent for the new route with the append
     flag set.

    $ ip -6 ro append vrf red 2001:db8:200::/120 nexthop via 2001:db8:2::20 nexthop via 2001:db8:1::20

    $ ip mon route
    Append 2001:db8:200::/120 table red metric 1024
	    nexthop via 2001:db8:1::2  dev eth1 weight 1
	    nexthop via 2001:db8:2::2  dev eth2 weight 1
	    nexthop via 2001:db8:2::20  dev eth2 weight 1
	    nexthop via 2001:db8:1::20  dev eth1 weight 1

  - on failure of an append, a notification is sent with the route
    containing all of the nexthops successfully added, and it is
    followed by delete notifications as the hops are removed
    returning the route to its prior state. This is consistent with
    how it works today except the successful additions are coalesced
    into 1 notification.

Addresses some of the inconsistencies also noted by Roopa at netdev0.1:
https://www.netdev01.org/docs/prabhu-linux_ipv4_ipv6_inconsistencies_talk_slides.pdf

v4
- changed series to do encoding in 1 patch and updating notificatons
  in separate patches to make it easier to review and understand

- 1 notification for delete when using prefix/length; 1 notification for
  append

- handle delete of a single nexthop without RTA_MULTIPATH in delete request

- upated commit messages and cover letter

v3
- removed the need for a user API to opt-in to change. Requiring an
  API just shifts the difference from same API with different
  behavior to different API to achieve equivalent behavior
- route notifications changed to use RTA_MULTIPATH for add and replace
- upated commit messages and cover letter

v2
- fixed locking in patch 1 as noted by DaveM
- changed user API for patch 2 to require an rtmsg with RTM_F_ALL_NEXTHOPS
  set in rtm_flags
- revamped explanation of patch 2 and cover letter
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -37,7 +37,9 @@ struct fib6_config {
 	int		fc_ifindex;
 	u32		fc_flags;
 	u32		fc_protocol;
-	u32		fc_type;	/* only 8 bits are used */
+	u16		fc_type;        /* only 8 bits are used */
+	u16		fc_delete_all_nh : 1,
+			__unused : 15;
 
 	struct in6_addr	fc_dst;
 	struct in6_addr	fc_src;

include/net/netlink.h

@@ -229,6 +229,7 @@ struct nl_info {
 	struct nlmsghdr		*nlh;
 	struct net		*nl_net;
 	u32			portid;
+	bool			skip_notify;
 };
 
 int netlink_rcv_skb(struct sk_buff *skb,

net/ipv6/ip6_fib.c

@@ -318,6 +318,16 @@ static int fib6_dump_node(struct fib6_walker *w)
 			w->leaf = rt;
 			return 1;
 		}
+
+		/* Multipath routes are dumped in one route with the
+		 * RTA_MULTIPATH attribute. Jump 'rt' to point to the
+		 * last sibling of this route (no need to dump the
+		 * sibling routes again)
+		 */
+		if (rt->rt6i_nsiblings)
+			rt = list_last_entry(&rt->rt6i_siblings,
+					     struct rt6_info,
+					     rt6i_siblings);
 	}
 	w->leaf = NULL;
 	return 0;
@@ -871,7 +881,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 		*ins = rt;
 		rt->rt6i_node = fn;
 		atomic_inc(&rt->rt6i_ref);
-		inet6_rt_notify(RTM_NEWROUTE, rt, info, nlflags);
+		if (!info->skip_notify)
+			inet6_rt_notify(RTM_NEWROUTE, rt, info, nlflags);
 		info->nl_net->ipv6.rt6_stats->fib_rt_entries++;
 
 		if (!(fn->fn_flags & RTN_RTINFO)) {
@@ -897,7 +908,8 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 		rt->rt6i_node = fn;
 		rt->dst.rt6_next = iter->dst.rt6_next;
 		atomic_inc(&rt->rt6i_ref);
-		inet6_rt_notify(RTM_NEWROUTE, rt, info, NLM_F_REPLACE);
+		if (!info->skip_notify)
+			inet6_rt_notify(RTM_NEWROUTE, rt, info, NLM_F_REPLACE);
 		if (!(fn->fn_flags & RTN_RTINFO)) {
 			info->nl_net->ipv6.rt6_stats->fib_route_nodes++;
 			fn->fn_flags |= RTN_RTINFO;
@@ -1442,7 +1454,8 @@ static void fib6_del_route(struct fib6_node *fn, struct rt6_info **rtp,
 
 	fib6_purge_rt(rt, fn, net);
 
-	inet6_rt_notify(RTM_DELROUTE, rt, info, 0);
+	if (!info->skip_notify)
+		inet6_rt_notify(RTM_DELROUTE, rt, info, 0);
 	rt6_release(rt);
 }
 

net/ipv6/route.c

@@ -98,6 +98,12 @@ static void		rt6_do_redirect(struct dst_entry *dst, struct sock *sk,
 					struct sk_buff *skb);
 static void		rt6_dst_from_metrics_check(struct rt6_info *rt);
 static int rt6_score_route(struct rt6_info *rt, int oif, int strict);
+static size_t rt6_nlmsg_size(struct rt6_info *rt);
+static int rt6_fill_node(struct net *net,
+			 struct sk_buff *skb, struct rt6_info *rt,
+			 struct in6_addr *dst, struct in6_addr *src,
+			 int iif, int type, u32 portid, u32 seq,
+			 unsigned int flags);
 
 #ifdef CONFIG_IPV6_ROUTE_INFO
 static struct rt6_info *rt6_add_route_info(struct net *net,
@@ -2143,6 +2149,54 @@ int ip6_del_rt(struct rt6_info *rt)
 	return __ip6_del_rt(rt, &info);
 }
 
+static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
+{
+	struct nl_info *info = &cfg->fc_nlinfo;
+	struct sk_buff *skb = NULL;
+	struct fib6_table *table;
+	int err;
+
+	table = rt->rt6i_table;
+	write_lock_bh(&table->tb6_lock);
+
+	if (rt->rt6i_nsiblings && cfg->fc_delete_all_nh) {
+		struct rt6_info *sibling, *next_sibling;
+
+		/* prefer to send a single notification with all hops */
+		skb = nlmsg_new(rt6_nlmsg_size(rt), gfp_any());
+		if (skb) {
+			u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
+
+			if (rt6_fill_node(info->nl_net, skb, rt,
+					  NULL, NULL, 0, RTM_DELROUTE,
+					  info->portid, seq, 0) < 0) {
+				kfree_skb(skb);
+				skb = NULL;
+			} else
+				info->skip_notify = 1;
+		}
+
+		list_for_each_entry_safe(sibling, next_sibling,
+					 &rt->rt6i_siblings,
+					 rt6i_siblings) {
+			err = fib6_del(sibling, info);
+			if (err)
+				goto out;
+		}
+	}
+
+	err = fib6_del(rt, info);
+out:
+	write_unlock_bh(&table->tb6_lock);
+	ip6_rt_put(rt);
+
+	if (skb) {
+		rtnl_notify(skb, info->nl_net, info->portid, RTNLGRP_IPV6_ROUTE,
+			    info->nlh, gfp_any());
+	}
+	return err;
+}
+
 static int ip6_route_del(struct fib6_config *cfg)
 {
 	struct fib6_table *table;
@@ -2179,7 +2233,11 @@ static int ip6_route_del(struct fib6_config *cfg)
 			dst_hold(&rt->dst);
 			read_unlock_bh(&table->tb6_lock);
 
-			return __ip6_del_rt(rt, &cfg->fc_nlinfo);
+			/* if gateway was specified only delete the one hop */
+			if (cfg->fc_flags & RTF_GATEWAY)
+				return __ip6_del_rt(rt, &cfg->fc_nlinfo);
+
+			return __ip6_del_rt_siblings(rt, cfg);
 		}
 	}
 	read_unlock_bh(&table->tb6_lock);
@@ -2952,7 +3010,7 @@ static void ip6_print_replace_route_err(struct list_head *rt6_nh_list)
 	struct rt6_nh *nh;
 
 	list_for_each_entry(nh, rt6_nh_list, next) {
-		pr_warn("IPV6: multipath route replace failed (check consistency of installed routes): %pI6 nexthop %pI6 ifi %d\n",
+		pr_warn("IPV6: multipath route replace failed (check consistency of installed routes): %pI6c nexthop %pI6c ifi %d\n",
 		        &nh->r_cfg.fc_dst, &nh->r_cfg.fc_gateway,
 		        nh->r_cfg.fc_ifindex);
 	}
@@ -2991,13 +3049,37 @@ static int ip6_route_info_append(struct list_head *rt6_nh_list,
 	return 0;
 }
 
+static void ip6_route_mpath_notify(struct rt6_info *rt,
+				   struct rt6_info *rt_last,
+				   struct nl_info *info,
+				   __u16 nlflags)
+{
+	/* if this is an APPEND route, then rt points to the first route
+	 * inserted and rt_last points to last route inserted. Userspace
+	 * wants a consistent dump of the route which starts at the first
+	 * nexthop. Since sibling routes are always added at the end of
+	 * the list, find the first sibling of the last route appended
+	 */
+	if ((nlflags & NLM_F_APPEND) && rt_last && rt_last->rt6i_nsiblings) {
+		rt = list_first_entry(&rt_last->rt6i_siblings,
+				      struct rt6_info,
+				      rt6i_siblings);
+	}
+
+	if (rt)
+		inet6_rt_notify(RTM_NEWROUTE, rt, info, nlflags);
+}
+
 static int ip6_route_multipath_add(struct fib6_config *cfg)
 {
+	struct rt6_info *rt_notif = NULL, *rt_last = NULL;
+	struct nl_info *info = &cfg->fc_nlinfo;
 	struct fib6_config r_cfg;
 	struct rtnexthop *rtnh;
 	struct rt6_info *rt;
 	struct rt6_nh *err_nh;
 	struct rt6_nh *nh, *nh_safe;
+	__u16 nlflags;
 	int remaining;
 	int attrlen;
 	int err = 1;
@@ -3006,6 +3088,10 @@ static int ip6_route_multipath_add(struct fib6_config *cfg)
 		       (cfg->fc_nlinfo.nlh->nlmsg_flags & NLM_F_REPLACE));
 	LIST_HEAD(rt6_nh_list);
 
+	nlflags = replace ? NLM_F_REPLACE : NLM_F_CREATE;
+	if (info->nlh && info->nlh->nlmsg_flags & NLM_F_APPEND)
+		nlflags |= NLM_F_APPEND;
+
 	remaining = cfg->fc_mp_len;
 	rtnh = (struct rtnexthop *)cfg->fc_mp;
 
@@ -3048,9 +3134,20 @@ static int ip6_route_multipath_add(struct fib6_config *cfg)
 		rtnh = rtnh_next(rtnh, &remaining);
 	}
 
+	/* for add and replace send one notification with all nexthops.
+	 * Skip the notification in fib6_add_rt2node and send one with
+	 * the full route when done
+	 */
+	info->skip_notify = 1;
+
 	err_nh = NULL;
 	list_for_each_entry(nh, &rt6_nh_list, next) {
-		err = __ip6_ins_rt(nh->rt6_info, &cfg->fc_nlinfo, &nh->mxc);
+		rt_last = nh->rt6_info;
+		err = __ip6_ins_rt(nh->rt6_info, info, &nh->mxc);
+		/* save reference to first route for notification */
+		if (!rt_notif && !err)
+			rt_notif = nh->rt6_info;
+
 		/* nh->rt6_info is used or freed at this point, reset to NULL*/
 		nh->rt6_info = NULL;
 		if (err) {
@@ -3072,9 +3169,18 @@ static int ip6_route_multipath_add(struct fib6_config *cfg)
 		nhn++;
 	}
 
+	/* success ... tell user about new route */
+	ip6_route_mpath_notify(rt_notif, rt_last, info, nlflags);
 	goto cleanup;
 
 add_errout:
+	/* send notification for routes that were added so that
+	 * the delete notifications sent by ip6_route_del are
+	 * coherent
+	 */
+	if (rt_notif)
+		ip6_route_mpath_notify(rt_notif, rt_last, info, nlflags);
+
 	/* Delete routes that were already added */
 	list_for_each_entry(nh, &rt6_nh_list, next) {
 		if (err_nh == nh)
@@ -3142,8 +3248,10 @@ static int inet6_rtm_delroute(struct sk_buff *skb, struct nlmsghdr *nlh)
 
 	if (cfg.fc_mp)
 		return ip6_route_multipath_del(&cfg);
-	else
+	else {
+		cfg.fc_delete_all_nh = 1;
 		return ip6_route_del(&cfg);
+	}
 }
 
 static int inet6_rtm_newroute(struct sk_buff *skb, struct nlmsghdr *nlh)
@@ -3161,8 +3269,20 @@ static int inet6_rtm_newroute(struct sk_buff *skb, struct nlmsghdr *nlh)
 		return ip6_route_add(&cfg);
 }
 
-static inline size_t rt6_nlmsg_size(struct rt6_info *rt)
+static size_t rt6_nlmsg_size(struct rt6_info *rt)
 {
+	int nexthop_len = 0;
+
+	if (rt->rt6i_nsiblings) {
+		nexthop_len = nla_total_size(0)	 /* RTA_MULTIPATH */
+			    + NLA_ALIGN(sizeof(struct rtnexthop))
+			    + nla_total_size(16) /* RTA_GATEWAY */
+			    + nla_total_size(4)  /* RTA_OIF */
+			    + lwtunnel_get_encap_size(rt->dst.lwtstate);
+
+		nexthop_len *= rt->rt6i_nsiblings;
+	}
+
 	return NLMSG_ALIGN(sizeof(struct rtmsg))
 	       + nla_total_size(16) /* RTA_SRC */
 	       + nla_total_size(16) /* RTA_DST */
@@ -3176,7 +3296,62 @@ static inline size_t rt6_nlmsg_size(struct rt6_info *rt)
 	       + nla_total_size(sizeof(struct rta_cacheinfo))
 	       + nla_total_size(TCP_CA_NAME_MAX) /* RTAX_CC_ALGO */
 	       + nla_total_size(1) /* RTA_PREF */
-	       + lwtunnel_get_encap_size(rt->dst.lwtstate);
+	       + lwtunnel_get_encap_size(rt->dst.lwtstate)
+	       + nexthop_len;
+}
+
+static int rt6_nexthop_info(struct sk_buff *skb, struct rt6_info *rt,
+			    unsigned int *flags)
+{
+	if (!netif_running(rt->dst.dev) || !netif_carrier_ok(rt->dst.dev)) {
+		*flags |= RTNH_F_LINKDOWN;
+		if (rt->rt6i_idev->cnf.ignore_routes_with_linkdown)
+			*flags |= RTNH_F_DEAD;
+	}
+
+	if (rt->rt6i_flags & RTF_GATEWAY) {
+		if (nla_put_in6_addr(skb, RTA_GATEWAY, &rt->rt6i_gateway) < 0)
+			goto nla_put_failure;
+	}
+
+	if (rt->dst.dev &&
+	    nla_put_u32(skb, RTA_OIF, rt->dst.dev->ifindex))
+		goto nla_put_failure;
+
+	if (rt->dst.lwtstate &&
+	    lwtunnel_fill_encap(skb, rt->dst.lwtstate) < 0)
+		goto nla_put_failure;
+
+	return 0;
+
+nla_put_failure:
+	return -EMSGSIZE;
+}
+
+static int rt6_add_nexthop(struct sk_buff *skb, struct rt6_info *rt)
+{
+	struct rtnexthop *rtnh;
+	unsigned int flags = 0;
+
+	rtnh = nla_reserve_nohdr(skb, sizeof(*rtnh));
+	if (!rtnh)
+		goto nla_put_failure;
+
+	rtnh->rtnh_hops = 0;
+	rtnh->rtnh_ifindex = rt->dst.dev ? rt->dst.dev->ifindex : 0;
+
+	if (rt6_nexthop_info(skb, rt, &flags) < 0)
+		goto nla_put_failure;
+
+	rtnh->rtnh_flags = flags;
+
+	/* length of rtnetlink header + attributes */
+	rtnh->rtnh_len = nlmsg_get_pos(skb) - (void *)rtnh;
+
+	return 0;
+
+nla_put_failure:
+	return -EMSGSIZE;
 }
 
 static int rt6_fill_node(struct net *net,
@@ -3230,11 +3405,6 @@ static int rt6_fill_node(struct net *net,
 	else
 		rtm->rtm_type = RTN_UNICAST;
 	rtm->rtm_flags = 0;
-	if (!netif_running(rt->dst.dev) || !netif_carrier_ok(rt->dst.dev)) {
-		rtm->rtm_flags |= RTNH_F_LINKDOWN;
-		if (rt->rt6i_idev->cnf.ignore_routes_with_linkdown)
-			rtm->rtm_flags |= RTNH_F_DEAD;
-	}
 	rtm->rtm_scope = RT_SCOPE_UNIVERSE;
 	rtm->rtm_protocol = rt->rt6i_protocol;
 	if (rt->rt6i_flags & RTF_DYNAMIC)
@@ -3298,17 +3468,35 @@ static int rt6_fill_node(struct net *net,
 	if (rtnetlink_put_metrics(skb, metrics) < 0)
 		goto nla_put_failure;
 
-	if (rt->rt6i_flags & RTF_GATEWAY) {
-		if (nla_put_in6_addr(skb, RTA_GATEWAY, &rt->rt6i_gateway) < 0)
-			goto nla_put_failure;
-	}
-
-	if (rt->dst.dev &&
-	    nla_put_u32(skb, RTA_OIF, rt->dst.dev->ifindex))
-		goto nla_put_failure;
 	if (nla_put_u32(skb, RTA_PRIORITY, rt->rt6i_metric))
 		goto nla_put_failure;
 
+	/* For multipath routes, walk the siblings list and add
+	 * each as a nexthop within RTA_MULTIPATH.
+	 */
+	if (rt->rt6i_nsiblings) {
+		struct rt6_info *sibling, *next_sibling;
+		struct nlattr *mp;
+
+		mp = nla_nest_start(skb, RTA_MULTIPATH);
+		if (!mp)
+			goto nla_put_failure;
+
+		if (rt6_add_nexthop(skb, rt) < 0)
+			goto nla_put_failure;
+
+		list_for_each_entry_safe(sibling, next_sibling,
+					 &rt->rt6i_siblings, rt6i_siblings) {
+			if (rt6_add_nexthop(skb, sibling) < 0)
+				goto nla_put_failure;
+		}
+
+		nla_nest_end(skb, mp);
+	} else {
+		if (rt6_nexthop_info(skb, rt, &rtm->rtm_flags) < 0)
+			goto nla_put_failure;
+	}
+
 	expires = (rt->rt6i_flags & RTF_EXPIRES) ? rt->dst.expires - jiffies : 0;
 
 	if (rtnl_put_cacheinfo(skb, &rt->dst, 0, expires, rt->dst.error) < 0)
@@ -3317,8 +3505,6 @@ static int rt6_fill_node(struct net *net,
 	if (nla_put_u8(skb, RTA_PREF, IPV6_EXTRACT_PREF(rt->rt6i_flags)))
 		goto nla_put_failure;
 
-	if (lwtunnel_fill_encap(skb, rt->dst.lwtstate) < 0)
-		goto nla_put_failure;
 
 	nlmsg_end(skb, nlh);
 	return 0;