tipc: guarantee that group broadcast doesn't bypass group unicast

We need a mechanism guaranteeing that group unicasts sent out from a
socket are not bypassed by later sent broadcasts from the same socket.
We do this as follows:

- Each time a unicast is sent, we set a the broadcast method for the
  socket to "replicast" and "mandatory". This forces the first
  subsequent broadcast message to follow the same network and data path
  as the preceding unicast to a destination, hence preventing it from
  overtaking the latter.

- In order to make the 'same data path' statement above true, we let
  group unicasts pass through the multicast link input queue, instead
  of as previously through the unicast link input queue.

- In the first broadcast following a unicast, we set a new header flag,
  requiring all recipients to immediately acknowledge its reception.

- During the period before all the expected acknowledges are received,
  the socket refuses to accept any more broadcast attempts, i.e., by
  blocking or returning EAGAIN. This period should typically not be
  longer than a few microseconds.

- When all acknowledges have been received, the sending socket will
  open up for subsequent broadcasts, this time giving the link layer
  freedom to itself select the best transmission method.

- The forced and/or abrupt transmission method changes described above
  may lead to broadcasts arriving out of order to the recipients. We
  remedy this by introducing code that checks and if necessary
  re-orders such messages at the receiving end.

Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 3 deletions

diff --git a/net/tipc/group.h b/net/tipc/group.h
index e432066a211e..d525e1cd7de5 100644
--- a/net/tipc/group.h
+++ b/net/tipc/group.h
@@ -61,7 +61,7 @@ void tipc_group_proto_rcv(struct tipc_group *grp, bool *wakeup,
 			  struct tipc_msg *hdr,
 			  struct sk_buff_head *inputq,
 			  struct sk_buff_head *xmitq);
-void tipc_group_update_bc_members(struct tipc_group *grp, int len);
+void tipc_group_update_bc_members(struct tipc_group *grp, int len, bool ack);
 bool tipc_group_cong(struct tipc_group *grp, u32 dnode, u32 dport,
 		     int len, struct tipc_member **m);
 bool tipc_group_bc_cong(struct tipc_group *grp, int len);
@@ -69,7 +69,5 @@ void tipc_group_update_rcv_win(struct tipc_group *grp, int blks, u32 node,
 			       u32 port, struct sk_buff_head *xmitq);
 u16 tipc_group_bc_snd_nxt(struct tipc_group *grp);
 void tipc_group_update_member(struct tipc_member *m, int len);
-struct tipc_member *tipc_group_find_sender(struct tipc_group *grp,
-					   u32 node, u32 port);
 int tipc_group_size(struct tipc_group *grp);
 #endif