[1190] Provide logging descriptions

src/bin/msgq/msgq.py.in

@@ -287,8 +287,8 @@ class MsgQ:
         try:
             routing, data = self.read_packet(fd, sock)
         except MsgQReceiveError as err:
-            self.kill_socket(fd, sock)
             logger.error(MSGQ_RECV_ERR, fd, err)
+            self.kill_socket(fd, sock)
             return
 
         try:
@@ -491,7 +491,7 @@ class MsgQ:
                 if err.args[0] == errno.EINTR:
                     events = []
                 else:
-                    logger.error(MSGQ_POLL_ERR, err)
+                    logger.fatal(MSGQ_POLL_ERR, err)
                     break
             for (fd, event) in events:
                 if fd == self.listen_socket.fileno():
@@ -502,7 +502,7 @@ class MsgQ:
                     elif event & select.POLLIN:
                         self.process_socket(fd)
                     else:
-                        logger.error(MSGQ_POLL_UNKNOWN_EVENT, event)
+                        logger.error(MSGQ_POLL_UNKNOWN_EVENT, fd, event)
 
     def run_kqueue(self):
         while self.running:

src/bin/msgq/msgq_messages.mes

@@ -20,48 +20,69 @@
 # messages are in the correct order.
 
 % MSGQ_HDR_DECODE_ERR Error decoding header received from socket %1: %2
-Error
+The socket with mentioned file descriptor sent a packet. However, it was not
+possible to decode the routing header of the packet. The packet is ignored.
+This may be caused by a programmer error (one of the components sending invalid
+data) or possibly by incompatible version of msgq and the component (but that's
+unlikely, as the protocol is not changed often).
 
 % MSGQ_LISTENER_FAILED Failed to initialize listener on socket file '%1': %2
-Fatal
+The message queue daemon tried to listen on a file socket (the path is in the
+message), but it failed. The error from the operating system is logged.
 
 % MSGQ_LISTENER_SETUP Starting to listen on socket file '%1'
-Debug
+Debug message. The listener is trying to open a listening socket.
 
 % MSGQ_LISTENER_STARTED Successfully started to listen
-Debug
+Debug message. The message queue successfully opened a listening socket and
+waits for incoming connections.
 
 % MSGQ_POLL_ERR Error while polling for events: %1
-Error
+A low-level error happened when waiting for events, the error is logged. The
+reason for this varies, but it usually means the system is short on some
+resources.
 
-% MSGQ_POLL_UNKNOWN_EVENT Got an unknown event from the poller: %1
-Error
+% MSGQ_POLL_UNKNOWN_EVENT Got an unknown event from the poller for fd %1: %2
+An unknown event got out from the poll() system call. This should generally not
+happen and it is either a programmer error or OS bug. The event is ignored. The
+number noted as the event is the raw encoded value, which might be useful to
+the authors when figuring the problem out.
 
 % MSGQ_READ_UNKNOWN_FD Got read on strange socket %1
-Error, ignoring
+The OS reported a file descriptor is ready to read. But the daemon doesn't know
+the mentioned file descriptor, which is either a programmer error or OS bug.
+The read event is ignored.
 
 % MSGQ_RECV_ERR Error reading from socket %1: %2
-Error
+There was a low-level error when reading from a socket. The error is logged and
+the corresponding socket is dropped.
 
 % MSGQ_RECV_HDR Received header: %1
-Debug
+Debug message. This message includes the whole routing header of a packet.
 
 % MSGQ_RECV_INVALID_CMD Received invalid command: %1
-Error
+An unknown command listed in the log has been received. It is ignored. This
+indicates either a programmer error (eg. a typo in the command name) or
+incompatible version of a module and message queue daemon.
 
 % MSGQ_SEND_ERR Error while sending to socket %1: %2
-Error
+There was a low-level error when sending data to a socket. The error is logged
+and the corresponding socket is dropped.
 
 % MSGQ_SOCK_CLOSE Closing socket fd %1
-Debug
+Debug message. Closing the mentioned socket.
 
 % MSGQ_START Msgq version %1 starting
-Debug
+Debug message. The message queue is starting up.
 
 % MSGQ_START_FAIL Error during startup: %1
+There was an error during early startup of the daemon. More concrete error is
+in the log. The daemon terminates as a result.
 
 % MSGQ_SUBS_APPEND_TARGET Appending to existing target for subscription to group '%1' for instance '%2'
-Debug
+Debug message. Creating a new subscription by appending it to already existing
+data structure.
 
 % MSGQ_SUBS_NEW_TARGET Creating new target for subscription to group '%1' for instance '%2'
-Debug
+Debug message. Creating a new subscription. Also creating a new data structure
+to hold it.