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, 21 insertions, 0 deletions

diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index d6f98215267e..52c6a2e01995 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -547,6 +547,7 @@ static inline void msg_set_nameupper(struct tipc_msg *m, u32 n)
 #define GRP_JOIN_MSG         0
 #define GRP_LEAVE_MSG        1
 #define GRP_ADV_MSG          2
+#define GRP_ACK_MSG          3
 
 /*
  * Word 1
@@ -839,6 +840,16 @@ static inline void msg_set_grp_bc_syncpt(struct tipc_msg *m, u16 n)
 	msg_set_bits(m, 9, 16, 0xffff, n);
 }
 
+static inline u16 msg_grp_bc_acked(struct tipc_msg *m)
+{
+	return msg_bits(m, 9, 16, 0xffff);
+}
+
+static inline void msg_set_grp_bc_acked(struct tipc_msg *m, u16 n)
+{
+	msg_set_bits(m, 9, 16, 0xffff, n);
+}
+
 /* Word 10
  */
 static inline u16 msg_grp_evt(struct tipc_msg *m)
@@ -851,6 +862,16 @@ static inline void msg_set_grp_evt(struct tipc_msg *m, int n)
 	msg_set_bits(m, 10, 0, 0x3, n);
 }
 
+static inline u16 msg_grp_bc_ack_req(struct tipc_msg *m)
+{
+	return msg_bits(m, 10, 0, 0x1);
+}
+
+static inline void msg_set_grp_bc_ack_req(struct tipc_msg *m, bool n)
+{
+	msg_set_bits(m, 10, 0, 0x1, n);
+}
+
 static inline u16 msg_grp_bc_seqno(struct tipc_msg *m)
 {
 	return msg_bits(m, 10, 16, 0xffff);