fsm: add ignore_invalid_events bit-mask

An invalid fsm event is an event which is not valid in the current fsm state.
Such invalid events will be logged and osmo_fsm_inst_dispatch() return != 0.
To prevent this log message which could be misleading for the user, the code needed
to add this event to the allstate_event_mask or add it independent to each state.
Or as alternative create a proxy function in front of osmo_fsm_inst_dispatch()
which checks the fsm state before dispatching the signal.
By using ignore_invalid_events the logline can be ignored for certain events
while for others the old behaviour is still preserved.

Related: SYS#6145
Change-Id: Id010ade76de83ccf428f2d18e9f85bcce1d1ea2c

include/osmocom/core/fsm.h

@@ -81,6 +81,16 @@ struct osmo_fsm {
 	const struct value_string *event_names;
 	/*! graceful exit function, called at the beginning of termination */
 	void (*pre_term)(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause cause);
+	/*! bit-mask of events which will be ignored if they are not valid in the current fsm state.
+	 *
+	 *  An invalid event is an event which is neither part of the allstat_event_mask nor state->in_event_mask.
+	 *  If an invalid event is dispatched to an fsm, the fsm core will log it (error) and
+	 *  osmo_fsm_inst_dispatch() will return != 0.
+	 *
+	 *  To silence those log lines and change the return code of osmo_fsm_inst_dispatch, add the
+	 *  event to ignore_invalid_events.
+	 */
+	uint32_t ignore_invalid_events;
 };
 
 /*! a single instanceof an osmocom finite state machine */

src/fsm.c

@@ -865,6 +865,9 @@ int _osmo_fsm_inst_dispatch(struct osmo_fsm_inst *fi, uint32_t event, void *data
 	}
 
 	if (!((1 << event) & fs->in_event_mask)) {
+		if ((1 << event) & fsm->ignore_invalid_events)
+			return 0;
+
 		LOGPFSMLSRC(fi, LOGL_ERROR, file, line,
 			    "Event %s not permitted\n",
 			    osmo_fsm_event_name(fsm, event));