[ipv6] Allow for multiple routers

Select the IPv6 source address and corresponding router (if any) using
a very simplified version of the algorithm from RFC6724:

- Ignore any source address that has a smaller scope than the
  destination address.  For example, do not use a link-local source
  address when sending to a global destination address.

- If we have a source address which is on the same link as the
  destination address, then use that source address.

- If we are left with multiple possible source addresses, then choose
  the address with the smallest scope.  For example, if we are sending
  to a site-local destination address and we have both a global source
  address and a site-local source address, then use the site-local
  source address.

- If we are still left with multiple possible source addresses, then
  choose the address with the longest matching prefix.

For the purposes of this algorithm, we treat RFC4193 Unique Local
Addresses as having organisation-local scope.  Since we use only
link-local scope for our multicast transmissions, this approximation
should remain valid in all practical situations.

Originally-implemented-by: Thomas Bächler <thomas@archlinux.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/in.h

@@ -69,8 +69,12 @@ struct in6_addr {
 	( ( *( ( const uint16_t * ) (addr) ) & htons ( 0xffc0 ) ) ==	\
 	  htons ( 0xfe80 ) )
 
-#define IN6_IS_ADDR_NONGLOBAL( addr )					\
-	( IN6_IS_ADDR_LINKLOCAL (addr) || IN6_IS_ADDR_MULTICAST (addr) )
+#define IN6_IS_ADDR_SITELOCAL( addr )					\
+	( ( *( ( const uint16_t * ) (addr) ) & htons ( 0xffc0 ) ) ==	\
+	  htons ( 0xfec0 ) )
+
+#define IN6_IS_ADDR_ULA( addr )						\
+	( ( *( ( const uint8_t * ) (addr) ) & 0xfe ) == 0xfc )
 
 /**
  * IPv4 socket address

src/include/ipxe/ipv6.h

@@ -158,6 +158,24 @@ struct ipv6_pseudo_header {
 	uint8_t next_header;
 } __attribute__ (( packed ));
 
+/** IPv6 address scopes */
+enum ipv6_address_scope {
+	/** Interface-local address scope */
+	IPV6_SCOPE_INTERFACE_LOCAL = 0x1,
+	/** Link-local address scope */
+	IPV6_SCOPE_LINK_LOCAL = 0x2,
+	/** Admin-local address scope */
+	INV6_SCOPE_ADMIN_LOCAL = 0x4,
+	/** Site-local address scope */
+	IPV6_SCOPE_SITE_LOCAL = 0x5,
+	/** Organisation-local address scope */
+	IPV6_SCOPE_ORGANISATION_LOCAL = 0x8,
+	/** Global address scope */
+	IPV6_SCOPE_GLOBAL = 0xe,
+	/** Maximum scope */
+	IPV6_SCOPE_MAX = 0xf,
+};
+
 /** An IPv6 address/routing table entry */
 struct ipv6_miniroute {
 	/** List of miniroutes */
@@ -174,6 +192,8 @@ struct ipv6_miniroute {
 	struct in6_addr prefix_mask;
 	/** Router address */
 	struct in6_addr router;
+	/** Scope */
+	unsigned int scope;
 	/** Flags */
 	unsigned int flags;
 };
@@ -244,6 +264,18 @@ static inline void ipv6_all_routers ( struct in6_addr *addr ) {
 	addr->s6_addr[15] = 2;
 }
 
+/**
+ * Get multicast address scope
+ *
+ * @v addr		Multicast address
+ * @ret scope		Address scope
+ */
+static inline unsigned int
+ipv6_multicast_scope ( const struct in6_addr *addr ) {
+
+	return ( addr->s6_addr[1] & 0x0f );
+}
+
 /** IPv6 settings sibling order */
 enum ipv6_settings_order {
 	/** No address */
@@ -264,6 +296,13 @@ extern struct list_head ipv6_miniroutes;
 extern struct net_protocol ipv6_protocol __net_protocol;
 
 extern int ipv6_has_addr ( struct net_device *netdev, struct in6_addr *addr );
+extern int ipv6_add_miniroute ( struct net_device *netdev,
+				struct in6_addr *address,
+				unsigned int prefix_len,
+				struct in6_addr *router );
+extern void ipv6_del_miniroute ( struct ipv6_miniroute *miniroute );
+extern struct ipv6_miniroute * ipv6_route ( unsigned int scope_id,
+					    struct in6_addr **dest );
 extern int parse_ipv6_setting ( const struct setting_type *type,
 				const char *value, void *buf, size_t len );
 extern int format_ipv6_setting ( const struct setting_type *type,