tipc: merge link->exec_mode and link->state into one FSM

Until now, we have been handling link failover and synchronization
by using an additional link state variable, "exec_mode". This variable
is not independent of the link FSM state, something causing a risk of
inconsistencies, apart from the fact that it clutters the code.

The conditions are now in place to define a new link FSM that covers
all existing use cases, including failover and synchronization, and
eliminate the "exec_mode" field altogether. The FSM must also support
non-atomic resetting of links, which will be introduced later.

The new link FSM is shown below, with 7 states and 8 events.
Only events leading to state change are shown as edges.

+------------------------------------+
|RESET_EVT                           |
|                                    |
|                             +--------------+
|           +-----------------|   SYNCHING   |-----------------+
|           |FAILURE_EVT      +--------------+   PEER_RESET_EVT|
|           |                  A            |                  |
|           |                  |            |                  |
|           |                  |            |                  |
|           |                  |SYNCH_      |SYNCH_            |
|           |                  |BEGIN_EVT   |END_EVT           |
|           |                  |            |                  |
|           V                  |            V                  V
|    +-------------+          +--------------+          +------------+
|    |  RESETTING  |<---------|  ESTABLISHED |--------->| PEER_RESET |
|    +-------------+ FAILURE_ +--------------+ PEER_    +------------+
|           |        EVT        |    A         RESET_EVT       |
|           |                   |    |                         |
|           |                   |    |                         |
|           |    +--------------+    |                         |
|  RESET_EVT|    |RESET_EVT          |ESTABLISH_EVT            |
|           |    |                   |                         |
|           |    |                   |                         |
|           V    V                   |                         |
|    +-------------+          +--------------+        RESET_EVT|
+--->|    RESET    |--------->| ESTABLISHING |<----------------+
     +-------------+ PEER_    +--------------+
      |           A  RESET_EVT       |
      |           |                  |
      |           |                  |
      |FAILOVER_  |FAILOVER_         |FAILOVER_
      |BEGIN_EVT  |END_EVT           |BEGIN_EVT
      |           |                  |
      V           |                  |
     +-------------+                 |
     | FAILINGOVER |<----------------+
     +-------------+

These changes are fully backwards compatible.
Tested-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.h

@@ -49,13 +49,17 @@
  */
 #define INVALID_LINK_SEQ 0x10000
 
-
-/* Link endpoint receive states
+/* Link FSM events:
  */
 enum {
-	TIPC_LINK_OPEN,
-	TIPC_LINK_BLOCKED,
-	TIPC_LINK_TUNNEL
+	LINK_ESTABLISH_EVT       = 0xec1ab1e,
+	LINK_PEER_RESET_EVT      = 0x9eed0e,
+	LINK_FAILURE_EVT         = 0xfa110e,
+	LINK_RESET_EVT           = 0x10ca1d0e,
+	LINK_FAILOVER_BEGIN_EVT  = 0xfa110bee,
+	LINK_FAILOVER_END_EVT    = 0xfa110ede,
+	LINK_SYNCH_BEGIN_EVT     = 0xc1ccbee,
+	LINK_SYNCH_END_EVT       = 0xc1ccede
 };
 
 /* Events returned from link at packet reception or at timeout
@@ -120,7 +124,6 @@ struct tipc_stats {
  * @pmsg: convenience pointer to "proto_msg" field
  * @priority: current link priority
  * @net_plane: current link network plane ('A' through 'H')
- * @exec_mode: transmit/receive mode for link endpoint instance
  * @backlog_limit: backlog queue congestion thresholds (indexed by importance)
  * @exp_msg_count: # of tunnelled messages expected during link changeover
  * @reset_rcv_checkpt: seq # of last acknowledged message at time of link reset
@@ -155,7 +158,7 @@ struct tipc_link {
 	u32 tolerance;
 	unsigned long keepalive_intv;
 	u32 abort_limit;
-	int state;
+	u32 state;
 	u32 silent_intv_cnt;
 	struct {
 		unchar hdr[INT_H_SIZE];
@@ -166,7 +169,6 @@ struct tipc_link {
 	char net_plane;
 
 	/* Failover/synch */
-	u8 exec_mode;
 	u16 drop_point;
 	struct sk_buff *failover_reasm_skb;
 
@@ -214,8 +216,13 @@ void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
 			   int mtyp, struct sk_buff_head *xmitq);
 void tipc_link_build_bcast_sync_msg(struct tipc_link *l,
 				    struct sk_buff_head *xmitq);
+int tipc_link_fsm_evt(struct tipc_link *l, int evt);
 void tipc_link_reset_fragments(struct tipc_link *l_ptr);
-int tipc_link_is_up(struct tipc_link *l_ptr);
+bool tipc_link_is_up(struct tipc_link *l);
+bool tipc_link_is_reset(struct tipc_link *l);
+bool tipc_link_is_synching(struct tipc_link *l);
+bool tipc_link_is_failingover(struct tipc_link *l);
+bool tipc_link_is_blocked(struct tipc_link *l);
 int tipc_link_is_active(struct tipc_link *l_ptr);
 void tipc_link_purge_queues(struct tipc_link *l_ptr);
 void tipc_link_purge_backlog(struct tipc_link *l);

net/tipc/node.c

@@ -334,7 +334,6 @@ static void tipc_node_link_up(struct tipc_node *n, int bearer_id,
 	if (!ol) {
 		*slot0 = bearer_id;
 		*slot1 = bearer_id;
-		nl->exec_mode = TIPC_LINK_OPEN;
 		tipc_link_build_bcast_sync_msg(nl, xmitq);
 		node_established_contact(n);
 		return;
@@ -368,7 +367,7 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id)
 	struct sk_buff_head xmitq;
 
 	l = n->links[bearer_id].link;
-	if (!l || !tipc_link_is_up(l))
+	if (!l || tipc_link_is_reset(l))
 		return;
 
 	__skb_queue_head_init(&xmitq);
@@ -414,6 +413,7 @@ static void tipc_node_link_down(struct tipc_node *n, int bearer_id)
 	n->sync_point = tnl->rcv_nxt + (U16_MAX / 2 - 1);
 	tipc_link_tnl_prepare(l, tnl, FAILOVER_MSG, &xmitq);
 	tipc_link_reset(l);
+	tipc_link_fsm_evt(l, LINK_FAILOVER_BEGIN_EVT);
 	tipc_bearer_xmit(n->net, tnl->bearer_id, &xmitq, maddr);
 }
 
@@ -749,7 +749,7 @@ static void node_lost_contact(struct tipc_node *n_ptr)
 		struct tipc_link *l_ptr = n_ptr->links[i].link;
 		if (!l_ptr)
 			continue;
-		l_ptr->exec_mode = TIPC_LINK_OPEN;
+		tipc_link_fsm_evt(l_ptr, LINK_FAILOVER_END_EVT);
 		kfree_skb(l_ptr->failover_reasm_skb);
 		l_ptr->failover_reasm_skb = NULL;
 		tipc_link_reset_fragments(l_ptr);
@@ -989,7 +989,7 @@ int tipc_node_xmit_skb(struct net *net, struct sk_buff *skb, u32 dnode,
  * Returns true if state is ok, otherwise consumes buffer and returns false
  */
 static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
-				  int bearer_id)
+				  int bearer_id, struct sk_buff_head *xmitq)
 {
 	struct tipc_msg *hdr = buf_msg(skb);
 	int usr = msg_user(hdr);
@@ -1042,42 +1042,47 @@ static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
 	/* Initiate or update failover mode if applicable */
 	if ((usr == TUNNEL_PROTOCOL) && (mtyp == FAILOVER_MSG)) {
 		syncpt = oseqno + exp_pkts - 1;
-		if (pl && tipc_link_is_up(pl)) {
+		if (pl && tipc_link_is_up(pl))
 			tipc_node_link_down(n, pl->bearer_id);
-			pl->exec_mode = TIPC_LINK_BLOCKED;
-		}
+
 		/* If pkts arrive out of order, use lowest calculated syncpt */
 		if (less(syncpt, n->sync_point))
 			n->sync_point = syncpt;
 	}
 
 	/* Open parallel link when tunnel link reaches synch point */
-	if ((n->state == NODE_FAILINGOVER) && (more(rcv_nxt, n->sync_point))) {
+	if ((n->state == NODE_FAILINGOVER) && !tipc_link_is_failingover(l)) {
+		if (!more(rcv_nxt, n->sync_point))
+			return true;
 		tipc_node_fsm_evt(n, NODE_FAILOVER_END_EVT);
 		if (pl)
-			pl->exec_mode = TIPC_LINK_OPEN;
+			tipc_link_fsm_evt(pl, LINK_FAILOVER_END_EVT);
 		return true;
 	}
 
 	/* Initiate or update synch mode if applicable */
 	if ((usr == TUNNEL_PROTOCOL) && (mtyp == SYNCH_MSG)) {
 		syncpt = iseqno + exp_pkts - 1;
+		if (!tipc_link_is_up(l)) {
+			tipc_link_fsm_evt(l, LINK_ESTABLISH_EVT);
+			tipc_node_link_up(n, bearer_id, xmitq);
+		}
 		if (n->state == SELF_UP_PEER_UP) {
 			n->sync_point = syncpt;
+			tipc_link_fsm_evt(l, LINK_SYNCH_BEGIN_EVT);
 			tipc_node_fsm_evt(n, NODE_SYNCH_BEGIN_EVT);
 		}
-		l->exec_mode = TIPC_LINK_TUNNEL;
 		if (less(syncpt, n->sync_point))
 			n->sync_point = syncpt;
 	}
 
 	/* Open tunnel link when parallel link reaches synch point */
-	if ((n->state == NODE_SYNCHING) && (l->exec_mode == TIPC_LINK_TUNNEL)) {
+	if ((n->state == NODE_SYNCHING) && tipc_link_is_synching(l)) {
 		if (pl)
 			dlv_nxt = mod(pl->rcv_nxt - skb_queue_len(pl->inputq));
 		if (!pl || more(dlv_nxt, n->sync_point)) {
+			tipc_link_fsm_evt(l, LINK_SYNCH_END_EVT);
 			tipc_node_fsm_evt(n, NODE_SYNCH_END_EVT);
-			l->exec_mode = TIPC_LINK_OPEN;
 			return true;
 		}
 		if ((usr == TUNNEL_PROTOCOL) && (mtyp == SYNCH_MSG))
@@ -1143,7 +1148,7 @@ void tipc_rcv(struct net *net, struct sk_buff *skb, struct tipc_bearer *b)
 		tipc_bclink_acknowledge(n, msg_bcast_ack(hdr));
 
 	/* Check and if necessary update node state */
-	if (likely(tipc_node_check_state(n, skb, bearer_id))) {
+	if (likely(tipc_node_check_state(n, skb, bearer_id, &xmitq))) {
 		rc = tipc_link_rcv(le->link, skb, &xmitq);
 		skb = NULL;
 	}