tipc: optimize link synching mechanism

This commit along with the next one are to resolve the issues with the
link changeover mechanism. See that commit for details.

Basically, for the link synching, from now on, we will send only one
single ("dummy") SYNCH message to peer. The SYNCH message does not
contain any data, just a header conveying the synch point to the peer.

A new node capability flag ("TIPC_TUNNEL_ENHANCED") is introduced for
backward compatible!
Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Suggested-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/link.c

@@ -1665,6 +1665,7 @@ void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
 	struct sk_buff_head *queue = &l->transmq;
 	struct sk_buff_head tmpxq, tnlq;
 	u16 pktlen, pktcnt, seqno = l->snd_nxt;
+	u16 syncpt;
 
 	if (!tnl)
 		return;
@@ -1684,6 +1685,31 @@ void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
 	tipc_link_xmit(l, &tnlq, &tmpxq);
 	__skb_queue_purge(&tmpxq);
 
+	/* Link Synching:
+	 * From now on, send only one single ("dummy") SYNCH message
+	 * to peer. The SYNCH message does not contain any data, just
+	 * a header conveying the synch point to the peer.
+	 */
+	if (mtyp == SYNCH_MSG && (tnl->peer_caps & TIPC_TUNNEL_ENHANCED)) {
+		tnlskb = tipc_msg_create(TUNNEL_PROTOCOL, SYNCH_MSG,
+					 INT_H_SIZE, 0, l->addr,
+					 tipc_own_addr(l->net),
+					 0, 0, 0);
+		if (!tnlskb) {
+			pr_warn("%sunable to create dummy SYNCH_MSG\n",
+				link_co_err);
+			return;
+		}
+
+		hdr = buf_msg(tnlskb);
+		syncpt = l->snd_nxt + skb_queue_len(&l->backlogq) - 1;
+		msg_set_syncpt(hdr, syncpt);
+		msg_set_bearer_id(hdr, l->peer_bearer_id);
+		__skb_queue_tail(&tnlq, tnlskb);
+		tipc_link_xmit(tnl, &tnlq, xmitq);
+		return;
+	}
+
 	/* Initialize reusable tunnel packet header */
 	tipc_msg_init(tipc_own_addr(l->net), &tnlhdr, TUNNEL_PROTOCOL,
 		      mtyp, INT_H_SIZE, l->addr);

net/tipc/msg.h

@@ -877,6 +877,16 @@ static inline void msg_set_msgcnt(struct tipc_msg *m, u16 n)
 	msg_set_bits(m, 9, 16, 0xffff, n);
 }
 
+static inline u16 msg_syncpt(struct tipc_msg *m)
+{
+	return msg_bits(m, 9, 16, 0xffff);
+}
+
+static inline void msg_set_syncpt(struct tipc_msg *m, u16 n)
+{
+	msg_set_bits(m, 9, 16, 0xffff, n);
+}
+
 static inline u32 msg_conn_ack(struct tipc_msg *m)
 {
 	return msg_bits(m, 9, 16, 0xffff);

net/tipc/node.c

@@ -1649,7 +1649,6 @@ static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
 	int usr = msg_user(hdr);
 	int mtyp = msg_type(hdr);
 	u16 oseqno = msg_seqno(hdr);
-	u16 iseqno = msg_seqno(msg_inner_hdr(hdr));
 	u16 exp_pkts = msg_msgcnt(hdr);
 	u16 rcv_nxt, syncpt, dlv_nxt, inputq_len;
 	int state = n->state;
@@ -1748,7 +1747,10 @@ static bool tipc_node_check_state(struct tipc_node *n, struct sk_buff *skb,
 
 	/* Initiate synch mode if applicable */
 	if ((usr == TUNNEL_PROTOCOL) && (mtyp == SYNCH_MSG) && (oseqno == 1)) {
-		syncpt = iseqno + exp_pkts - 1;
+		if (n->capabilities & TIPC_TUNNEL_ENHANCED)
+			syncpt = msg_syncpt(hdr);
+		else
+			syncpt = msg_seqno(msg_inner_hdr(hdr)) + exp_pkts - 1;
 		if (!tipc_link_is_up(l))
 			__tipc_node_link_up(n, bearer_id, xmitq);
 		if (n->state == SELF_UP_PEER_UP) {

net/tipc/node.h

@@ -53,7 +53,8 @@ enum {
 	TIPC_NODE_ID128       = (1 << 5),
 	TIPC_LINK_PROTO_SEQNO = (1 << 6),
 	TIPC_MCAST_RBCTL      = (1 << 7),
-	TIPC_GAP_ACK_BLOCK    = (1 << 8)
+	TIPC_GAP_ACK_BLOCK    = (1 << 8),
+	TIPC_TUNNEL_ENHANCED  = (1 << 9)
 };
 
 #define TIPC_NODE_CAPABILITIES (TIPC_SYN_BIT           |  \
@@ -64,7 +65,8 @@ enum {
 				TIPC_NODE_ID128        |   \
 				TIPC_LINK_PROTO_SEQNO  |   \
 				TIPC_MCAST_RBCTL       |   \
-				TIPC_GAP_ACK_BLOCK)
+				TIPC_GAP_ACK_BLOCK     |   \
+				TIPC_TUNNEL_ENHANCED)
 #define INVALID_BEARER_ID -1
 
 void tipc_node_stop(struct net *net);