tipc: receive group membership events via member socket

Like with any other service, group members' availability can be
subscribed for by connecting to be topology server. However, because
the events arrive via a different socket than the member socket, there
is a real risk that membership events my arrive out of synch with the
actual JOIN/LEAVE action. I.e., it is possible to receive the first
messages from a new member before the corresponding JOIN event arrives,
just as it is possible to receive the last messages from a leaving
member after the LEAVE event has already been received.

Since each member socket is internally also subscribing for membership
events, we now fix this problem by passing those events on to the user
via the member socket. We leverage the already present member synch-
ronization protocol to guarantee correct message/event order. An event
is delivered to the user as an empty message where the two source
addresses identify the new/lost member. Furthermore, we set the MSG_OOB
bit in the message flags to mark it as an event. If the event is an
indication about a member loss we also set the MSG_EOR bit, so it can
be distinguished from a member addition event.

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, 20 insertions, 2 deletions

diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index e438716d2372..1b527b154e46 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -65,7 +65,8 @@ struct plist;
 #define TIPC_MCAST_MSG          1
 #define TIPC_NAMED_MSG          2
 #define TIPC_DIRECT_MSG         3
-#define TIPC_GRP_BCAST_MSG      4
+#define TIPC_GRP_MEMBER_EVT     4
+#define TIPC_GRP_BCAST_MSG      5
 
 /*
  * Internal message users
@@ -258,7 +259,14 @@ static inline void msg_set_type(struct tipc_msg *m, u32 n)
 
 static inline int msg_in_group(struct tipc_msg *m)
 {
-	return (msg_type(m) == TIPC_GRP_BCAST_MSG);
+	int mtyp = msg_type(m);
+
+	return (mtyp == TIPC_GRP_BCAST_MSG) || (mtyp == TIPC_GRP_MEMBER_EVT);
+}
+
+static inline bool msg_is_grp_evt(struct tipc_msg *m)
+{
+	return msg_type(m) == TIPC_GRP_MEMBER_EVT;
 }
 
 static inline u32 msg_named(struct tipc_msg *m)
@@ -824,6 +832,16 @@ static inline void msg_set_grp_bc_syncpt(struct tipc_msg *m, u16 n)
 
 /* Word 10
  */
+static inline u16 msg_grp_evt(struct tipc_msg *m)
+{
+	return msg_bits(m, 10, 0, 0x3);
+}
+
+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_seqno(struct tipc_msg *m)
 {
 	return msg_bits(m, 10, 16, 0xffff);