tipc: add support for link state subscriptions

When links are established over a bearer plane, we create a node
local publication containing information about the peer node and
bearer plane. This allows TIPC applications to use the standard
TIPC topology server subscription mechanism to get notifications
when a link goes up or down.
Signed-off-by: Erik Hugne <erik.hugne@ericsson.com>
Reviewed-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/tipc.h

@@ -87,6 +87,7 @@ static inline unsigned int tipc_node(__u32 addr)
 
 #define TIPC_CFG_SRV		0	/* configuration service name type */
 #define TIPC_TOP_SRV		1	/* topology service name type */
+#define TIPC_LINK_STATE		2	/* link state name type */
 #define TIPC_RESERVED_TYPES	64	/* lowest user-publishable name type */
 
 /*

net/tipc/node.c

@@ -144,9 +144,11 @@ void tipc_node_stop(void)
 void tipc_node_link_up(struct tipc_node *n_ptr, struct tipc_link *l_ptr)
 {
 	struct tipc_link **active = &n_ptr->active_links[0];
+	u32 addr = n_ptr->addr;
 
 	n_ptr->working_links++;
-
+	tipc_nametbl_publish(TIPC_LINK_STATE, addr, addr, TIPC_NODE_SCOPE,
+			     l_ptr->bearer_id, addr);
 	pr_info("Established link <%s> on network plane %c\n",
 		l_ptr->name, l_ptr->net_plane);
 
@@ -203,8 +205,10 @@ static void node_select_active_links(struct tipc_node *n_ptr)
 void tipc_node_link_down(struct tipc_node *n_ptr, struct tipc_link *l_ptr)
 {
 	struct tipc_link **active;
+	u32 addr = n_ptr->addr;
 
 	n_ptr->working_links--;
+	tipc_nametbl_withdraw(TIPC_LINK_STATE, addr, l_ptr->bearer_id, addr);
 
 	if (!tipc_link_is_active(l_ptr)) {
 		pr_info("Lost standby link <%s> on network plane %c\n",