tipc: smooth change between replicast and broadcast

Currently, a multicast stream may start out using replicast, because
there are few destinations, and then it should ideally switch to
L2/broadcast IGMP/multicast when the number of destinations grows beyond
a certain limit. The opposite should happen when the number decreases
below the limit.

To eliminate the risk of message reordering caused by method change,
a sending socket must stick to a previously selected method until it
enters an idle period of 5 seconds. Means there is a 5 seconds pause
in the traffic from the sender socket.

If the sender never makes such a pause, the method will never change,
and transmission may become very inefficient as the cluster grows.

With this commit, we allow such a switch between replicast and
broadcast without any need for a traffic pause.

Solution is to send a dummy message with only the header, also with
the SYN bit set, via broadcast or replicast. For the data message,
the SYN bit is set and sending via replicast or broadcast (inverse
method with dummy).

Then, at receiving side any messages follow first SYN bit message
(data or dummy message), they will be held in deferred queue until
another pair (dummy or data message) arrived in other link.

v2: reverse christmas tree declaration

Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Hoang Le <hoang.h.le@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/tipc/bcast.h b/net/tipc/bcast.h
index 37c55e7347a5..484bde289d3a 100644
--- a/net/tipc/bcast.h
+++ b/net/tipc/bcast.h
@@ -67,11 +67,13 @@ void tipc_nlist_del(struct tipc_nlist *nl, u32 node);
 /* Cookie to be used between socket and broadcast layer
  * @rcast: replicast (instead of broadcast) was used at previous xmit
  * @mandatory: broadcast/replicast indication was set by user
+ * @deferredq: defer queue to make message in order
  * @expires: re-evaluate non-mandatory transmit method if we are past this
  */
 struct tipc_mc_method {
 	bool rcast;
 	bool mandatory;
+	struct sk_buff_head deferredq;
 	unsigned long expires;
 };
 
@@ -99,6 +101,9 @@ int tipc_bclink_reset_stats(struct net *net);
 u32 tipc_bcast_get_broadcast_mode(struct net *net);
 u32 tipc_bcast_get_broadcast_ratio(struct net *net);
 
+void tipc_mcast_filter_msg(struct sk_buff_head *defq,
+			   struct sk_buff_head *inputq);
+
 static inline void tipc_bcast_lock(struct net *net)
 {
 	spin_lock_bh(&tipc_net(net)->bclock);