ipv6: Plumb support for nexthop object in a fib6_info

Add struct nexthop and nh_list list_head to fib6_info. nh_list is the
fib6_info side of the nexthop <-> fib_info relationship. Since a fib6_info
referencing a nexthop object can not have 'sibling' entries (the old way
of doing multipath routes), the nh_list is a union with fib6_siblings.

Add f6i_list list_head to 'struct nexthop' to track fib6_info entries
using a nexthop instance. Update __remove_nexthop_fib to walk f6_list
and delete fib entries using the nexthop.

Add a few nexthop helpers for use when a nexthop is added to fib6_info:
- nexthop_fib6_nh - return first fib6_nh in a nexthop object
- fib6_info_nh_dev moved to nexthop.h and updated to use nexthop_fib6_nh
  if the fib6_info references a nexthop object
- nexthop_path_fib6_result - similar to ipv4, select a path within a
  multipath nexthop object. If the nexthop is a blackhole, set
  fib6_result type to RTN_BLACKHOLE, and set the REJECT flag

Update the fib6_info references to check for nh and take a different path
as needed:
- rt6_qualify_for_ecmp - if a fib entry uses a nexthop object it can NOT
  be coalesced with other fib entries into a multipath route
- rt6_duplicate_nexthop - use nexthop_cmp if either fib6_info references
  a nexthop
- addrconf (host routes), RA's and info entries (anything configured via
  ndisc) does not use nexthop objects
- fib6_info_destroy_rcu - put reference to nexthop object
- fib6_purge_rt - drop fib6_info from f6i_list
- fib6_select_path - update to use the new nexthop_path_fib6_result when
  fib entry uses a nexthop object
- rt6_device_match - update to catch use of nexthop object as a blackhole
  and set fib6_type and flags.
- ip6_route_info_create - don't add space for fib6_nh if fib entry is
  going to reference a nexthop object, take a reference to nexthop object,
  disallow use of source routing
- rt6_nlmsg_size - add space for RTA_NH_ID
- add rt6_fill_node_nexthop to add nexthop data on a dump

As with ipv4, most of the changes push existing code into the else branch
of whether the fib entry uses a nexthop object.

Update the nexthop code to walk f6i_list on a nexthop deleted to remove
fib entries referencing it.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_fib.h

@@ -146,7 +146,10 @@ struct fib6_info {
 	 * destination, but not the same gateway. nsiblings is just a cache
 	 * to speed up lookup.
 	 */
-	struct list_head		fib6_siblings;
+	union {
+		struct list_head	fib6_siblings;
+		struct list_head	nh_list;
+	};
 	unsigned int			fib6_nsiblings;
 
 	refcount_t			fib6_ref;
@@ -170,6 +173,7 @@ struct fib6_info {
 					unused:3;
 
 	struct rcu_head			rcu;
+	struct nexthop			*nh;
 	struct fib6_nh			fib6_nh[0];
 };
 
@@ -441,11 +445,6 @@ void rt6_get_prefsrc(const struct rt6_info *rt, struct in6_addr *addr)
 	rcu_read_unlock();
 }
 
-static inline struct net_device *fib6_info_nh_dev(const struct fib6_info *f6i)
-{
-	return f6i->fib6_nh->fib_nh_dev;
-}
-
 int fib6_nh_init(struct net *net, struct fib6_nh *fib6_nh,
 		 struct fib6_config *cfg, gfp_t gfp_flags,
 		 struct netlink_ext_ack *extack);

include/net/ip6_route.h

@@ -27,6 +27,7 @@ struct route_info {
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/route.h>
+#include <net/nexthop.h>
 
 #define RT6_LOOKUP_F_IFACE		0x00000001
 #define RT6_LOOKUP_F_REACHABLE		0x00000002
@@ -66,10 +67,13 @@ static inline bool rt6_need_strict(const struct in6_addr *daddr)
 		(IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL | IPV6_ADDR_LOOPBACK);
 }
 
+/* fib entries using a nexthop object can not be coalesced into
+ * a multipath route
+ */
 static inline bool rt6_qualify_for_ecmp(const struct fib6_info *f6i)
 {
 	/* the RTF_ADDRCONF flag filters out RA's */
-	return !(f6i->fib6_flags & RTF_ADDRCONF) &&
+	return !(f6i->fib6_flags & RTF_ADDRCONF) && !f6i->nh &&
 		f6i->fib6_nh->fib_nh_gw_family;
 }
 
@@ -275,8 +279,13 @@ static inline struct in6_addr *rt6_nexthop(struct rt6_info *rt,
 
 static inline bool rt6_duplicate_nexthop(struct fib6_info *a, struct fib6_info *b)
 {
-	struct fib6_nh *nha = a->fib6_nh, *nhb = b->fib6_nh;
+	struct fib6_nh *nha, *nhb;
 
+	if (a->nh || b->nh)
+		return nexthop_cmp(a->nh, b->nh);
+
+	nha = a->fib6_nh;
+	nhb = b->fib6_nh;
 	return nha->fib_nh_dev == nhb->fib_nh_dev &&
 	       ipv6_addr_equal(&nha->fib_nh_gw6, &nhb->fib_nh_gw6) &&
 	       !lwtunnel_cmp_encap(nha->fib_nh_lws, nhb->fib_nh_lws);

include/net/nexthop.h

@@ -10,6 +10,7 @@
 #define __LINUX_NEXTHOP_H
 
 #include <linux/netdevice.h>
+#include <linux/route.h>
 #include <linux/types.h>
 #include <net/ip_fib.h>
 #include <net/ip6_fib.h>
@@ -78,6 +79,7 @@ struct nh_group {
 struct nexthop {
 	struct rb_node		rb_node;    /* entry on netns rbtree */
 	struct list_head	fi_list;    /* v4 entries using nh */
+	struct list_head	f6i_list;   /* v6 entries using nh */
 	struct list_head	grp_list;   /* nh group entries using this nh */
 	struct net		*net;
 
@@ -255,4 +257,52 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel)
 
 	return &fi->fib_nh[nhsel];
 }
+
+/*
+ * IPv6 variants
+ */
+int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg,
+		       struct netlink_ext_ack *extack);
+
+static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
+{
+	struct nh_info *nhi;
+
+	if (nexthop_is_multipath(nh)) {
+		nh = nexthop_mpath_select(nh, 0);
+		if (!nh)
+			return NULL;
+	}
+
+	nhi = rcu_dereference_rtnl(nh->nh_info);
+	if (nhi->family == AF_INET6)
+		return &nhi->fib6_nh;
+
+	return NULL;
+}
+
+static inline struct net_device *fib6_info_nh_dev(struct fib6_info *f6i)
+{
+	struct fib6_nh *fib6_nh;
+
+	fib6_nh = f6i->nh ? nexthop_fib6_nh(f6i->nh) : f6i->fib6_nh;
+	return fib6_nh->fib_nh_dev;
+}
+
+static inline void nexthop_path_fib6_result(struct fib6_result *res, int hash)
+{
+	struct nexthop *nh = res->f6i->nh;
+	struct nh_info *nhi;
+
+	nh = nexthop_select_path(nh, hash);
+
+	nhi = rcu_dereference_rtnl(nh->nh_info);
+	if (nhi->reject_nh) {
+		res->fib6_type = RTN_BLACKHOLE;
+		res->fib6_flags |= RTF_REJECT;
+		res->nh = nexthop_fib6_nh(nh);
+	} else {
+		res->nh = &nhi->fib6_nh;
+	}
+}
 #endif