tipc: clean up handling of message priorities

Messages transferred by TIPC are assigned an "importance priority", -an
integer value indicating how to treat the message when there is link or
destination socket congestion.

There is no separate header field for this value. Instead, the message
user values have been chosen in ascending order according to perceived
importance, so that the message user field can be used for this.

This is not a good solution. First, we have many more users than the
needed priority levels, so we end up with treating more priority
levels than necessary. Second, the user field cannot always
accurately reflect the priority of the message. E.g., a message
fragment packet should really have the priority of the enveloped
user data message, and not the priority of the MSG_FRAGMENTER user.
Until now, we have been working around this problem in different ways,
but it is now time to implement a consistent way of handling such
priorities, although still within the constraint that we cannot
allocate any more bits in the regular data message header for this.

In this commit, we define a new priority level, TIPC_SYSTEM_IMPORTANCE,
that will be the only one used apart from the four (lower) user data
levels. All non-data messages map down to this priority. Furthermore,
we take some free bits from the MSG_FRAGMENTER header and allocate
them to store the priority of the enveloped message. We then adjust
the functions msg_importance()/msg_set_importance() so that they
read/set the correct header fields depending on user type.

This small protocol change is fully compatible, because the code at
the receiving end of a link currently reads the importance level
only from user data messages, where there is no change.

Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 31 deletions

diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index e5fc5fdb2ea7..bd3969a80dd4 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -54,6 +54,8 @@ struct plist;
  * - TIPC_HIGH_IMPORTANCE
  * - TIPC_CRITICAL_IMPORTANCE
  */
+#define TIPC_SYSTEM_IMPORTANCE  4
+
 
 /*
  * Payload message types
@@ -64,6 +66,19 @@ struct plist;
 #define TIPC_DIRECT_MSG         3
 
 /*
+ * Internal message users
+ */
+#define  BCAST_PROTOCOL       5
+#define  MSG_BUNDLER          6
+#define  LINK_PROTOCOL        7
+#define  CONN_MANAGER         8
+#define  CHANGEOVER_PROTOCOL  10
+#define  NAME_DISTRIBUTOR     11
+#define  MSG_FRAGMENTER       12
+#define  LINK_CONFIG          13
+#define  SOCK_WAKEUP          14       /* pseudo user */
+
+/*
  * Message header sizes
  */
 #define SHORT_H_SIZE              24    /* In-cluster basic payload message */
@@ -170,16 +185,6 @@ static inline void msg_set_user(struct tipc_msg *m, u32 n)
         msg_set_bits(m, 0, 25, 0xf, n);
 }
 
-static inline u32 msg_importance(struct tipc_msg *m)
-{
-        return msg_bits(m, 0, 25, 0xf);
-}
-
-static inline void msg_set_importance(struct tipc_msg *m, u32 i)
-{
-        msg_set_user(m, i);
-}
-
 static inline u32 msg_hdr_sz(struct tipc_msg *m)
 {
         return msg_bits(m, 0, 21, 0xf) << 2;
@@ -336,6 +341,25 @@ static inline void msg_set_seqno(struct tipc_msg *m, u32 n)
 /*
  * Words 3-10
  */
+static inline u32 msg_importance(struct tipc_msg *m)
+{
+        if (unlikely(msg_user(m) == MSG_FRAGMENTER))
+                return msg_bits(m, 5, 13, 0x7);
+        if (likely(msg_isdata(m) && !msg_errcode(m)))
+                return msg_user(m);
+        return TIPC_SYSTEM_IMPORTANCE;
+}
+
+static inline void msg_set_importance(struct tipc_msg *m, u32 i)
+{
+        if (unlikely(msg_user(m) == MSG_FRAGMENTER))
+                msg_set_bits(m, 5, 13, 0x7, i);
+        else if (likely(i < TIPC_SYSTEM_IMPORTANCE))
+                msg_set_user(m, i);
+        else
+                pr_warn("Trying to set illegal importance in message\n");
+}
+
 static inline u32 msg_prevnode(struct tipc_msg *m)
 {
         return msg_word(m, 3);
@@ -458,20 +482,6 @@ static inline struct tipc_msg *msg_get_wrapped(struct tipc_msg *m)
  */
 
 /*
- * Internal message users
- */
-#define  BCAST_PROTOCOL       5
-#define  MSG_BUNDLER          6
-#define  LINK_PROTOCOL        7
-#define  CONN_MANAGER         8
-#define  ROUTE_DISTRIBUTOR    9         /* obsoleted */
-#define  CHANGEOVER_PROTOCOL  10
-#define  NAME_DISTRIBUTOR     11
-#define  MSG_FRAGMENTER       12
-#define  LINK_CONFIG          13
-#define  SOCK_WAKEUP          14       /* pseudo user */
-
-/*
  *  Connection management protocol message types
  */
 #define CONN_PROBE        0
@@ -743,13 +753,6 @@ static inline void msg_set_link_tolerance(struct tipc_msg *m, u32 n)
         msg_set_bits(m, 9, 0, 0xffff, n);
 }
 
-static inline u32 tipc_msg_tot_importance(struct tipc_msg *m)
-{
-        if ((msg_user(m) == MSG_FRAGMENTER) && (msg_type(m) == FIRST_FRAGMENT))
-                return msg_importance(msg_get_wrapped(m));
-        return msg_importance(m);
-}
-
 static inline u32 msg_tot_origport(struct tipc_msg *m)
 {
         if ((msg_user(m) == MSG_FRAGMENTER) && (msg_type(m) == FIRST_FRAGMENT))