[ipv6] Match user expectations for IPv6 settings priorities

A reasonable user expectation is that ${net0/ip6} should show the
"highest-priority" of the IPv6 addresses, even when multiple IPv6
addresses are active.  The expected order of priority is likely to be
manually-assigned addresses first, then stateful DHCPv6 addresses,
then SLAAC addresses, and lastly link-local addresses.

Using ${priority} to enforce an ordering is undesirable since that
would affect the priority assigned to each of the net<N> blocks as a
whole, so use the sibling ordering capability instead.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/ipv6.h

 	addr->s6_addr[15] = 2;
 }
 
+/** IPv6 settings sibling order */
+enum ipv6_settings_order {
+	/** No address */
+	IPV6_ORDER_PREFIX_ONLY = -4,
+	/** Link-local address */
+	IPV6_ORDER_LINK_LOCAL = -3,
+	/** Address assigned via SLAAC */
+	IPV6_ORDER_SLAAC = -2,
+	/** Address assigned via DHCPv6 */
+	IPV6_ORDER_DHCPV6 = -1,
+};
+
 /** IPv6 link-local address settings block name */
 #define IPV6_SETTINGS_NAME "link"
 

src/net/ipv6.c

 	ref_init ( &ipv6set->refcnt, NULL );
 	settings_init ( &ipv6set->settings, &ipv6_settings_operations,
 			&ipv6set->refcnt, &ipv6_scope );
+	ipv6set->settings.order = IPV6_ORDER_LINK_LOCAL;
 
 	/* Register settings */
 	if ( ( rc = register_settings ( &ipv6set->settings, parent,

src/net/ndp.c

 	size_t option_len;
 	unsigned int prefixes;
 	unsigned int instance;
+	int order;
 	int rc;
 
 	/* Count number of prefix options.  We can assume that the
 	 * options are well-formed, otherwise they would have been
 	 * rejected prior to being stored.
 	 */
+	order = IPV6_ORDER_PREFIX_ONLY;
 	for ( prefixes = 0, offset = 0 ; offset < len ; offset += option_len ) {
+
+		/* Skip non-prefix options */
 		option = ( ( ( void * ) options ) + offset );
 		option_len = ( option->header.blocks * NDP_OPTION_BLKSZ );
-		if ( option->header.type == NDP_OPT_PREFIX )
-			prefixes++;
+		if ( option->header.type != NDP_OPT_PREFIX )
+			continue;
+
+		/* Count number of prefixes */
+		prefixes++;
+
+		/* Increase overall order if we have SLAAC addresses */
+		if ( option->prefix.flags & NDP_PREFIX_AUTONOMOUS )
+			order = IPV6_ORDER_SLAAC;
 	}
 
 	/* Allocate and initialise structure */
 	ref_init ( &ndpset->refcnt, NULL );
 	settings_init ( &ndpset->settings, &ndp_settings_operations,
 			&ndpset->refcnt, &ndp_settings_scope );
+	ndpset->settings.order = order;
 	memcpy ( &ndpset->router, router, sizeof ( ndpset->router ) );
 	ndpset->lifetime = lifetime;
 	ndpset->len = len;
 		settings_init ( &prefset->settings,
 				&ndp_prefix_settings_operations,
 				&ndpset->refcnt, &ndp_settings_scope );
+		prefset->settings.order =
+			( ( option->prefix.flags & NDP_PREFIX_AUTONOMOUS ) ?
+			  IPV6_ORDER_SLAAC : IPV6_ORDER_PREFIX_ONLY );
 		prefset->prefix = &option->prefix;
 		snprintf ( prefset->name, sizeof ( prefset->name ), "%d",
 			   instance++ );

src/net/udp/dhcpv6.c

 	ref_init ( &dhcpv6set->refcnt, NULL );
 	settings_init ( &dhcpv6set->settings, &dhcpv6_settings_operations,
 			&dhcpv6set->refcnt, &dhcpv6_scope );
+	dhcpv6set->settings.order = IPV6_ORDER_DHCPV6;
 	data = ( ( ( void * ) dhcpv6set ) + sizeof ( *dhcpv6set ) );
 	len = options->len;
 	memcpy ( data, options->data, len );