fsm: allow graceful exit on FSM termination

The function _osmo_fsm_inst_term() terminates all child FSMs befor
it calls fi->fsm_cleanup(). This prevents the cleanup callback to
perform last actions on the child FSMs (e.g.
osmo_fsm_inst_unlink_parent()).

- Since moving the cleanup callack to the beginning of the function
  would alter the termination behavior and possibly cause malfunction
  in already existing implementation that use OSMO fsm, a new
  optional callback that is called immediately at the beginning of
  the terminatopn process is added.

Change-Id: I0fdda9fe994753f975a658c0f3fb3615949cc8bb
Closes: OS#2915

1 files changed, 2 insertions, 0 deletions

diff --git a/include/osmocom/core/fsm.h b/include/osmocom/core/fsm.h
index bbfe3123..2c2a9961 100644
--- a/include/osmocom/core/fsm.h
+++ b/include/osmocom/core/fsm.h
@@ -78,6 +78,8 @@ struct osmo_fsm {
 	int log_subsys;
 	/*! human-readable names of events */
 	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);
 };
 
 /*! a single instanceof an osmocom finite state machine */