subscr_conn: introduce usage tokens for ref error tracking

When hunting a conn use count bug, it was very hard to figure out who's (not)
using the conn. To ease tracking down this bug and future bugs, explicitly name
what a conn is being reserved for, and track in a bit mask.

Show in the DREF logs what uses and un-uses a conn. See the test expectation
updates, which nicely show how that clarifies the state of the conn in the
logs.

On errors, log them, but don't fail hard: if one conn use/un-use fails, we
don't want to crash the entire MSC before we have to.

Change-Id: I259aa0eec41efebb4c8221275219433eafaa549b

2 files changed, 22 insertions, 4 deletions

diff --git a/include/osmocom/msc/gsm_data.h b/include/osmocom/msc/gsm_data.h
index e0fbcec9f..696cef1c3 100644
--- a/include/osmocom/msc/gsm_data.h
+++ b/include/osmocom/msc/gsm_data.h
@@ -139,6 +139,7 @@ struct gsm_subscriber_connection {
 	/* usage count. If this drops to zero, we start the release
 	 * towards A/Iu */
 	uint32_t use_count;
+	uint32_t use_tokens;
 
 	/* The MS has opened the conn with a CM Service Request, and we shall
 	 * keep it open for an actual request (or until timeout). */
diff --git a/include/osmocom/msc/osmo_msc.h b/include/osmocom/msc/osmo_msc.h
index 5f4713ee8..bf455c309 100644
--- a/include/osmocom/msc/osmo_msc.h
+++ b/include/osmocom/msc/osmo_msc.h
@@ -84,14 +84,31 @@ void msc_subscr_conn_communicating(struct gsm_subscriber_connection *conn);
 void msc_subscr_conn_close(struct gsm_subscriber_connection *conn,
 			   uint32_t cause);
 
-#define msc_subscr_conn_get(conn) \
-	_msc_subscr_conn_get(conn, __BASE_FILE__, __LINE__)
-#define msc_subscr_conn_put(conn) \
-	_msc_subscr_conn_put(conn, __BASE_FILE__, __LINE__)
+enum msc_subscr_conn_use {
+	MSC_CONN_USE_UNTRACKED = -1,
+	MSC_CONN_USE_COMPL_L3,
+	MSC_CONN_USE_DTAP,
+	MSC_CONN_USE_FSM,
+	MSC_CONN_USE_TRANS_CC,
+	MSC_CONN_USE_TRANS_SMS,
+	MSC_CONN_USE_TRANS_USSD,
+	MSC_CONN_USE_SILENT_CALL,
+};
+
+extern const struct value_string msc_subscr_conn_use_names[];
+static inline const char *msc_subscr_conn_use_name(enum msc_subscr_conn_use val)
+{ return get_value_string(msc_subscr_conn_use_names, val); }
+
+#define msc_subscr_conn_get(conn, balance_token) \
+	_msc_subscr_conn_get(conn, balance_token, __BASE_FILE__, __LINE__)
+#define msc_subscr_conn_put(conn, balance_token) \
+	_msc_subscr_conn_put(conn, balance_token, __BASE_FILE__, __LINE__)
 struct gsm_subscriber_connection *
 _msc_subscr_conn_get(struct gsm_subscriber_connection *conn,
+		     enum msc_subscr_conn_use balance_token,
 		     const char *file, int line);
 void _msc_subscr_conn_put(struct gsm_subscriber_connection *conn,
+			  enum msc_subscr_conn_use balance_token,
 			  const char *file, int line);
 
 void msc_stop_paging(struct vlr_subscr *vsub);