SCCP N-PCSTATE: trigger MSC status on PC availability

Related: SYS#6319
Related: Ia1aea4e33230d6a685b72ea5ba20dd9c7d265d44 osmo-ttcn3-hacks
Related: Ib4a5330df30a73e744c316898817b2fa3271d75e osmo-ttcn3-hacks
Change-Id: I3a0869598b8395601a16d78dbc46eec400c0ea84

3 files changed, 111 insertions, 1 deletions

diff --git a/include/osmocom/bsc/bssmap_reset.h b/include/osmocom/bsc/bssmap_reset.h
index fcd850b8b..c0de13c4d 100644
--- a/include/osmocom/bsc/bssmap_reset.h
+++ b/include/osmocom/bsc/bssmap_reset.h
@@ -28,4 +28,5 @@ struct bssmap_reset {
 struct bssmap_reset *bssmap_reset_alloc(void *ctx, const char *label, const struct bssmap_reset_cfg *cfg);
 bool bssmap_reset_is_conn_ready(const struct bssmap_reset *bssmap_reset);
 void bssmap_reset_resend_reset(struct bssmap_reset *bssmap_reset);
+void bssmap_reset_set_disconnected(struct bssmap_reset *bssmap_reset);
 void bssmap_reset_term_and_free(struct bssmap_reset *bssmap_reset);
diff --git a/src/osmo-bsc/bssmap_reset.c b/src/osmo-bsc/bssmap_reset.c
index fa6684d2f..ac304a548 100644
--- a/src/osmo-bsc/bssmap_reset.c
+++ b/src/osmo-bsc/bssmap_reset.c
@@ -251,6 +251,12 @@ void bssmap_reset_resend_reset(struct bssmap_reset *bssmap_reset)
 	osmo_fsm_inst_state_chg_ms(bssmap_reset->fi, BSSMAP_RESET_ST_DISC, 1, 0);
 }
 
+void bssmap_reset_set_disconnected(struct bssmap_reset *bssmap_reset)
+{
+	/* Go to disconnected state, with the normal RESET timeout to re-send RESET. */
+	bssmap_reset_fsm_state_chg(bssmap_reset->fi, BSSMAP_RESET_ST_DISC);
+}
+
 static __attribute__((constructor)) void bssmap_reset_fsm_init(void)
 {
 	OSMO_ASSERT(osmo_fsm_register(&bssmap_reset_fsm) == 0);
diff --git a/src/osmo-bsc/osmo_bsc_sigtran.c b/src/osmo-bsc/osmo_bsc_sigtran.c
index 8837330ec..f4c8f811b 100644
--- a/src/osmo-bsc/osmo_bsc_sigtran.c
+++ b/src/osmo-bsc/osmo_bsc_sigtran.c
@@ -36,6 +36,7 @@
 #include <osmocom/bsc/gsm_data.h>
 #include <osmocom/bsc/bts.h>
 #include <osmocom/bsc/paging.h>
+#include <osmocom/bsc/bssmap_reset.h>
 #include <osmocom/mgcp_client/mgcp_common.h>
 
 /* A pointer to a list with all involved MSCs
@@ -92,7 +93,7 @@ void osmo_bsc_sigtran_tx_reset_ack(const struct bsc_msc_data *msc)
 				  &msc->a.msc_addr, msg);
 }
 
-/* Find an MSC by its sigtran point code */
+/* Find an MSC by its remote SCCP address */
 static struct bsc_msc_data *get_msc_by_addr(const struct osmo_sccp_addr *msc_addr)
 {
 	struct osmo_ss7_instance *ss7;
@@ -107,6 +108,21 @@ static struct bsc_msc_data *get_msc_by_addr(const struct osmo_sccp_addr *msc_add
 	return NULL;
 }
 
+/* Find an MSC by its remote sigtran point code on a given cs7 instance. */
+static struct bsc_msc_data *get_msc_by_pc(struct osmo_ss7_instance *cs7, uint32_t pc)
+{
+	struct bsc_msc_data *msc;
+	llist_for_each_entry(msc, msc_list, entry) {
+		if (msc->a.cs7_instance != cs7->cfg.id)
+			continue;
+		if ((msc->a.msc_addr.presence & OSMO_SCCP_ADDR_T_PC) == 0)
+			continue;
+		if (msc->a.msc_addr.pc == pc)
+			return msc;
+	}
+	return NULL;
+}
+
 /* Received data from MSC, use the connection id which MSC it is */
 static int handle_data_from_msc(struct gsm_subscriber_connection *conn, struct msgb *msg)
 {
@@ -188,6 +204,89 @@ refuse:
 	return rc;
 }
 
+static void handle_pcstate_ind(struct osmo_ss7_instance *cs7, const struct osmo_scu_pcstate_param *pcst)
+{
+	struct bsc_msc_data *msc;
+	bool connected;
+	bool disconnected;
+
+	LOGP(DMSC, LOGL_DEBUG, "N-PCSTATE ind: affected_pc=%u sp_status=%d remote_sccp_status=%d\n",
+	     pcst->affected_pc, pcst->sp_status, pcst->remote_sccp_status);
+
+	/* If we don't care about that point-code, ignore PCSTATE. */
+	msc = get_msc_by_pc(cs7, pcst->affected_pc);
+	if (!msc)
+		return;
+
+	/* See if this marks the point code to have become available, or to have been lost.
+	 *
+	 * I want to detect two events:
+	 * - connection event (both indicators say PC is reachable).
+	 * - disconnection event (at least one indicator says the PC is not reachable).
+	 *
+	 * There are two separate incoming indicators with various possible values -- the incoming events can be:
+	 *
+	 * - neither connection nor disconnection indicated -- just indicating congestion
+	 *   connected == false, disconnected == false --> do nothing.
+	 * - both incoming values indicate that we are connected
+	 *   --> trigger connected
+	 * - both indicate we are disconnected
+	 *   --> trigger disconnected
+	 * - one value indicates 'connected', the other indicates 'disconnected'
+	 *   --> trigger disconnected
+	 *
+	 * Congestion could imply that we're connected, but it does not indicate that a PC's reachability changed, so no need to
+	 * trigger on that.
+	 */
+	connected = false;
+	disconnected = false;
+
+	switch (pcst->sp_status) {
+	case OSMO_SCCP_SP_S_ACCESSIBLE:
+		connected = true;
+		break;
+	case OSMO_SCCP_SP_S_INACCESSIBLE:
+		disconnected = true;
+		break;
+	default:
+	case OSMO_SCCP_SP_S_CONGESTED:
+		/* Neither connecting nor disconnecting */
+		break;
+	}
+
+	switch (pcst->remote_sccp_status) {
+	case OSMO_SCCP_REM_SCCP_S_AVAILABLE:
+		if (!disconnected)
+			connected = true;
+		break;
+	case OSMO_SCCP_REM_SCCP_S_UNAVAILABLE_UNKNOWN:
+	case OSMO_SCCP_REM_SCCP_S_UNEQUIPPED:
+	case OSMO_SCCP_REM_SCCP_S_INACCESSIBLE:
+		disconnected = true;
+		connected = false;
+		break;
+	default:
+	case OSMO_SCCP_REM_SCCP_S_CONGESTED:
+		/* Neither connecting nor disconnecting */
+		break;
+	}
+
+	if (disconnected && a_reset_conn_ready(msc)) {
+		LOGP(DMSC, LOGL_NOTICE,
+		     "(msc%d) now unreachable: N-PCSTATE ind: pc=%u sp_status=%d remote_sccp_status=%d\n",
+		     msc->nr, pcst->affected_pc, pcst->sp_status, pcst->remote_sccp_status);
+		/* A previously usable MSC has disconnected. Kick the BSSMAP back to DISC state. */
+		bssmap_reset_set_disconnected(msc->a.bssmap_reset);
+	} else if (connected && !a_reset_conn_ready(msc)) {
+		LOGP(DMSC, LOGL_NOTICE,
+		     "(msc%d) now available: N-PCSTATE ind: pc=%u sp_status=%d remote_sccp_status=%d\n",
+		     msc->nr, pcst->affected_pc, pcst->sp_status, pcst->remote_sccp_status);
+		/* A previously unusable MSC has become reachable. Trigger immediate BSSMAP RESET -- we would resend a
+		 * RESET either way, but we might as well do it now to speed up connecting. */
+		bssmap_reset_resend_reset(msc->a.bssmap_reset);
+	}
+}
+
 /* Callback function, called by the SCCP stack when data arrives */
 static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 {
@@ -255,6 +354,10 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		}
 		break;
 
+	case OSMO_PRIM(OSMO_SCU_PRIM_N_PCSTATE, PRIM_OP_INDICATION):
+		handle_pcstate_ind(osmo_sccp_get_ss7(sccp), &scu_prim->u.pcstate);
+		break;
+
 	default:
 		LOGP(DMSC, LOGL_ERROR, "Unhandled SIGTRAN operation %s on primitive %u\n",
 		     get_value_string(osmo_prim_op_names, oph->operation), oph->primitive);