[IPV6]: ROUTE: Add support for Router Preference (RFC4191).

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/icmpv6.h

@@ -40,14 +40,16 @@ struct icmp6hdr {
                 struct icmpv6_nd_ra {
 			__u8		hop_limit;
 #if defined(__LITTLE_ENDIAN_BITFIELD)
-			__u8		reserved:6,
+			__u8		reserved:4,
+					router_pref:2,
 					other:1,
 					managed:1;
 
 #elif defined(__BIG_ENDIAN_BITFIELD)
 			__u8		managed:1,
 					other:1,
-					reserved:6;
+					router_pref:2,
+					reserved:4;
 #else
 #error	"Please fix <asm/byteorder.h>"
 #endif
@@ -70,8 +72,13 @@ struct icmp6hdr {
 #define icmp6_addrconf_managed	icmp6_dataun.u_nd_ra.managed
 #define icmp6_addrconf_other	icmp6_dataun.u_nd_ra.other
 #define icmp6_rt_lifetime	icmp6_dataun.u_nd_ra.rt_lifetime
+#define icmp6_router_pref	icmp6_dataun.u_nd_ra.router_pref
 };
 
+#define ICMPV6_ROUTER_PREF_LOW		0x3
+#define ICMPV6_ROUTER_PREF_MEDIUM	0x0
+#define ICMPV6_ROUTER_PREF_HIGH		0x1
+#define ICMPV6_ROUTER_PREF_INVALID	0x2
 
 #define ICMPV6_DEST_UNREACH		1
 #define ICMPV6_PKT_TOOBIG		2

include/linux/ipv6_route.h

@@ -27,8 +27,16 @@
 #define RTF_FLOW	0x02000000	/* flow significant route	*/
 #define RTF_POLICY	0x04000000	/* policy route			*/
 
+#define RTF_PREF(pref)	((pref) << 27)
+#define RTF_PREF_MASK	0x18000000
+
 #define RTF_LOCAL	0x80000000
 
+#ifdef __KERNEL__
+#define IPV6_EXTRACT_PREF(flag)	(((flag) & RTF_PREF_MASK) >> 27)
+#define IPV6_DECODE_PREF(pref)	((pref) ^ 2)	/* 1:low,2:med,3:high */
+#endif
+
 struct in6_rtmsg {
 	struct in6_addr		rtmsg_dst;
 	struct in6_addr		rtmsg_src;

include/net/ip6_route.h

@@ -87,7 +87,8 @@ extern struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev,
 extern struct rt6_info *	rt6_get_dflt_router(struct in6_addr *addr,
 						    struct net_device *dev);
 extern struct rt6_info *	rt6_add_dflt_router(struct in6_addr *gwaddr,
-						    struct net_device *dev);
+						    struct net_device *dev,
+						    unsigned int pref);
 
 extern void			rt6_purge_dflt_routers(void);
 

net/ipv6/Kconfig

@@ -38,6 +38,17 @@ config IPV6_PRIVACY
 
 	  See <file:Documentation/networking/ip-sysctl.txt> for details.
 
+config IPV6_ROUTER_PREF
+	bool "IPv6: Router Preference (RFC 4191) support"
+	depends on IPV6
+	---help---
+	  Router Preference is an optional extension to the Router
+	  Advertisement message to improve the ability of hosts
+	  to pick more appropriate router, especially when the hosts
+	  is placed in a multi-homed network.
+
+	  If unsure, say N.
+
 config INET6_AH
 	tristate "IPv6: AH transformation"
 	depends on IPV6

net/ipv6/ndisc.c

@@ -1023,6 +1023,7 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 	int lifetime;
 	struct ndisc_options ndopts;
 	int optlen;
+	unsigned int pref = 0;
 
 	__u8 * opt = (__u8 *)(ra_msg + 1);
 
@@ -1086,6 +1087,13 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 
 	lifetime = ntohs(ra_msg->icmph.icmp6_rt_lifetime);
 
+#ifdef CONFIG_IPV6_ROUTER_PREF
+	pref = ra_msg->icmph.icmp6_router_pref;
+	/* 10b is handled as if it were 00b (medium) */
+	if (pref == ICMPV6_ROUTER_PREF_INVALID)
+		pref = ICMPV6_ROUTER_PREF_MEDIUM;
+#endif
+
 	rt = rt6_get_dflt_router(&skb->nh.ipv6h->saddr, skb->dev);
 
 	if (rt)
@@ -1101,7 +1109,7 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 		ND_PRINTK3(KERN_DEBUG
 			   "ICMPv6 RA: adding default router.\n");
 
-		rt = rt6_add_dflt_router(&skb->nh.ipv6h->saddr, skb->dev);
+		rt = rt6_add_dflt_router(&skb->nh.ipv6h->saddr, skb->dev, pref);
 		if (rt == NULL) {
 			ND_PRINTK0(KERN_ERR
 				   "ICMPv6 RA: %s() failed to add default route.\n",
@@ -1120,6 +1128,8 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 			return;
 		}
 		neigh->flags |= NTF_ROUTER;
+	} else if (rt) {
+		rt->rt6i_flags |= (rt->rt6i_flags & ~RTF_PREF_MASK) | RTF_PREF(pref);
 	}
 
 	if (rt)

net/ipv6/route.c

@@ -251,8 +251,11 @@ static int rt6_score_route(struct rt6_info *rt, int oif,
 	int m = rt6_check_dev(rt, oif);
 	if (!m && (strict & RT6_SELECT_F_IFACE))
 		return -1;
+#ifdef CONFIG_IPV6_ROUTER_PREF
+	m |= IPV6_DECODE_PREF(IPV6_EXTRACT_PREF(rt->rt6i_flags)) << 2;
+#endif
 	if (rt6_check_neigh(rt))
-		m |= 4;
+		m |= 16;
 	else if (strict & RT6_SELECT_F_REACHABLE)
 		return -1;
 	return m;
@@ -1256,7 +1259,8 @@ struct rt6_info *rt6_get_dflt_router(struct in6_addr *addr, struct net_device *d
 }
 
 struct rt6_info *rt6_add_dflt_router(struct in6_addr *gwaddr,
-				     struct net_device *dev)
+				     struct net_device *dev,
+				     unsigned int pref)
 {
 	struct in6_rtmsg rtmsg;
 
@@ -1264,7 +1268,8 @@ struct rt6_info *rt6_add_dflt_router(struct in6_addr *gwaddr,
 	rtmsg.rtmsg_type = RTMSG_NEWROUTE;
 	ipv6_addr_copy(&rtmsg.rtmsg_gateway, gwaddr);
 	rtmsg.rtmsg_metric = 1024;
-	rtmsg.rtmsg_flags = RTF_GATEWAY | RTF_ADDRCONF | RTF_DEFAULT | RTF_UP | RTF_EXPIRES;
+	rtmsg.rtmsg_flags = RTF_GATEWAY | RTF_ADDRCONF | RTF_DEFAULT | RTF_UP | RTF_EXPIRES |
+			    RTF_PREF(pref);
 
 	rtmsg.rtmsg_ifindex = dev->ifindex;