prevent ARFCN+BSIC collisions in config

If multiple BTS are configured with identical ARFCN+BSIC, handover cannot
possibly work. Add warn_on_arfcn_bsic_collisions() and when collisions are
detected:

- exit right away on program startup.
- warn on vty bts node-exit (go_parent_cb()), i.e. when ARFCN+BSIC collide
  implicitly from default values.
- warn on vty bts/base_station_id_code cmd coming from telnet vty,
  i.e. when the user actively configures colliding BSIC.
- warn on vty trx/arfcn cmd coming from telnet vty,
  i.e. when the user actively configures colliding ARFCN.

When warning, warn on all of:
- DHO log,
- stderr,
- vty_out() in case a vty instance is passed (i.e. from interactive vty).
It's better to log this once too often than let the user miss it.

Rationale: when I started to implement ttcn3 tests for inter-bsc HO, I saw that
the new code based on ARFCN+BSIC would cause a handover request intended to go
from BTS 0 to BTS 1 to instead go from BTS 0 to back to BTS 0 -- because of
identical ARFCN+BSIC in the config of ttcn3-bsc-tests. Such a config badly
confuses handover: measurement reports interpreted to come from the wrong cell,
all handovers attempted to go to the first BTS (sometimes correctly, sometimes
wrongly), in short, non-obvious failure across the handover board. The network
would appear to work well, but occasionally a handover would kill a call
without apparent reason. It seems worthwhile to prevent such misconfiguration
as early as possible, and even allow previous ARFCN+BSIC misconfiguration that
used to work to instead break now (only upon reading config during program
startup, to not cause program exit just because a user introduces a temporary
collision in an interactive vty session).

Change-Id: Ia7c38188ccbad5d8b7398e3e5220015e62c08c8b

3 files changed, 36 insertions, 0 deletions

diff --git a/include/osmocom/bsc/vty.h b/include/osmocom/bsc/vty.h
index e63275546..bfea69d2a 100644
--- a/include/osmocom/bsc/vty.h
+++ b/include/osmocom/bsc/vty.h
@@ -35,4 +35,6 @@ int bsc_vty_init_extra(void);
 
 struct gsm_network *gsmnet_from_vty(struct vty *vty);
 
+int warn_on_arfcn_bsic_collisions(struct gsm_network *net, struct vty *vty);
+
 #endif
diff --git a/src/osmo-bsc/bsc_vty.c b/src/osmo-bsc/bsc_vty.c
index 27e1bc697..5298644e6 100644
--- a/src/osmo-bsc/bsc_vty.c
+++ b/src/osmo-bsc/bsc_vty.c
@@ -2119,6 +2119,30 @@ DEFUN_HIDDEN(cfg_bts_tsc,
 	return CMD_SUCCESS;
 }
 
+int warn_on_arfcn_bsic_collisions(struct gsm_network *net, struct vty *vty)
+{
+	struct gsm_bts *bts, *bts2;
+	int errors = 0;
+
+	llist_for_each_entry(bts, &net->bts_list, list) {
+		struct neighbor_ident_key *nik = bts_ident_key(bts);
+
+		bts2 = bts_by_neighbor_ident(net, nik);
+		if (bts != bts2) {
+			LOGP(DHO, LOGL_ERROR, "CONFIG ERROR: Multiple BTS match %s: %d and %d\n",
+			     neighbor_ident_key_name(nik), bts->nr, bts2->nr);
+			fprintf(stderr, "CONFIG ERROR: Multiple BTS match %s: %d and %d\n",
+				neighbor_ident_key_name(nik), bts->nr, bts2->nr);
+			if (vty)
+				vty_out(vty, "%% CONFIG ERROR: Multiple BTS match %s: %d and %d%s",
+					neighbor_ident_key_name(nik), bts->nr, bts2->nr,
+					VTY_NEWLINE);
+			errors ++;
+		}
+	}
+	return errors;
+}
+
 DEFUN(cfg_bts_bsic,
       cfg_bts_bsic_cmd,
       "base_station_id_code <0-63>",
@@ -2135,6 +2159,9 @@ DEFUN(cfg_bts_bsic,
 	}
 	bts->bsic = bsic;
 
+	if (vty->type != VTY_FILE)
+		warn_on_arfcn_bsic_collisions(bts->network, vty);
+
 	return CMD_SUCCESS;
 }
 
@@ -3884,6 +3911,9 @@ DEFUN(cfg_trx_arfcn,
 	/* FIXME: use OML layer to update the ARFCN */
 	/* FIXME: use RSL layer to update SYSTEM INFORMATION */
 
+	if (vty->type != VTY_FILE)
+		warn_on_arfcn_bsic_collisions(trx->bts->network, vty);
+
 	return CMD_SUCCESS;
 }
 
diff --git a/src/osmo-bsc/osmo_bsc_main.c b/src/osmo-bsc/osmo_bsc_main.c
index 69db32e55..c46d2fa9e 100644
--- a/src/osmo-bsc/osmo_bsc_main.c
+++ b/src/osmo-bsc/osmo_bsc_main.c
@@ -539,6 +539,8 @@ static int bsc_vty_go_parent(struct vty *vty)
 			vty->index = bts->network;
 			vty->index_sub = NULL;
 		}
+		if (vty->type != VTY_FILE)
+			warn_on_arfcn_bsic_collisions(bsc_gsmnet, vty);
 		break;
 	case TRX_NODE:
 		vty->node = BTS_NODE;
@@ -826,6 +828,8 @@ int main(int argc, char **argv)
 		fprintf(stderr, "Bootstrapping the network failed. exiting.\n");
 		exit(1);
 	}
+	if (warn_on_arfcn_bsic_collisions(bsc_gsmnet, NULL))
+		exit(1);
 
 	/* start control interface after reading config for
 	 * ctrl_vty_get_bind_addr() */