tipc: enable broadcast retrans via unicast

In some environment, broadcast traffic is suppressed at high rate (i.e.
a kind of bandwidth limit setting). When it is applied, TIPC broadcast
can still run successfully. However, when it comes to a high load, some
packets will be dropped first and TIPC tries to retransmit them but the
packet retransmission is intentionally broadcast too, so making things
worse and not helpful at all.

This commit enables the broadcast retransmission via unicast which only
retransmits packets to the specific peer that has really reported a gap
i.e. not broadcasting to all nodes in the cluster, so will prevent from
being suppressed, and also reduce some overheads on the other peers due
to duplicates, finally improve the overall TIPC broadcast performance.

Note: the functionality can be turned on/off via the sysctl file:

echo 1 > /proc/sys/net/tipc/bc_retruni
echo 0 > /proc/sys/net/tipc/bc_retruni

Default is '0', i.e. the broadcast retransmission still works as usual.

Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/bcast.h b/net/tipc/bcast.h
index 9e847d9..97d3cf9 100644
--- a/net/tipc/bcast.h
+++ b/net/tipc/bcast.h
@@ -45,6 +45,7 @@ struct tipc_nl_msg;
 struct tipc_nlist;
 struct tipc_nitem;
 extern const char tipc_bclink_name[];
+extern unsigned long sysctl_tipc_bc_retruni;
 
 #define TIPC_METHOD_EXPIRE msecs_to_jiffies(5000)
 
@@ -93,7 +94,8 @@ int tipc_bcast_rcv(struct net *net, struct tipc_link *l, struct sk_buff *skb);
 void tipc_bcast_ack_rcv(struct net *net, struct tipc_link *l,
 			struct tipc_msg *hdr);
 int tipc_bcast_sync_rcv(struct net *net, struct tipc_link *l,
-			struct tipc_msg *hdr);
+			struct tipc_msg *hdr,
+			struct sk_buff_head *retrq);
 int tipc_nl_add_bc_link(struct net *net, struct tipc_nl_msg *msg);
 int tipc_nl_bc_link_set(struct net *net, struct nlattr *attrs[]);
 int tipc_bclink_reset_stats(struct net *net);