neighbor config: allow re-using ARFCN+BSIC pairs

Fix neighbor config to match OsmoBSC manual: implement the plan for neighbor
configuration that was so far only described in the manual without actually
being in operation.

This first allows re-using ARFCN+BSIC pairs in and across BSS.

So far the handover_start() code always looked for handover target cells across
*all* local cells, even if they were not listed as neighbors to a source cell.
Imply all cells as neighbors only as long as there are no explicit neighbors
configured. As soon as the first 'neighbor' line appears in a 'bts' config,
only the listed neighbors are regarded as handover target cells. (The
'neighbor-list' commands are not related to this, only the relatively new
'neighbor (bts|lac|cgi|...)' commands affect actual handover procedures.)

TTCN3 tests TC_ho_neighbor_config_1 thru _7 play through the various aspects of
neighbor configuration: both the legacy implicit all-cells-are-neighbors as
well as allowing only explicit neighbors by config.

Related: OS#4056
Related: osmo-ttcn3-hacks Ia4ba0e75abd3d45a3422b2525e5f938cdc5a04cc
Change-Id: I29bca59ab232eddc74e0d4698efb9c9992443983

3 files changed, 18 insertions, 14 deletions

diff --git a/include/osmocom/bsc/handover.h b/include/osmocom/bsc/handover.h
index 322913da4..b00ee60f8 100644
--- a/include/osmocom/bsc/handover.h
+++ b/include/osmocom/bsc/handover.h
@@ -10,6 +10,15 @@
 #include <osmocom/bsc/neighbor_ident.h>
 #include <osmocom/bsc/gsm_data.h>
 
+#define LOG_HO(conn, level, fmt, args...) do { \
+	if (conn->ho.fi) \
+		LOGPFSML(conn->ho.fi, level, "%s: " fmt, \
+			 handover_status(conn), ## args); \
+	else \
+		LOGP(DHODEC, level, "%s: " fmt, \
+		     handover_status(conn), ## args); \
+	} while(0)
+
 struct gsm_network;
 struct gsm_lchan;
 struct gsm_bts;
@@ -25,6 +34,8 @@ enum handover_result {
 	HO_RESULT_ERROR,
 };
 
+const char *handover_status(struct gsm_subscriber_connection *conn);
+
 extern const struct value_string handover_result_names[];
 inline static const char *handover_result_name(enum handover_result val)
 { return get_value_string(handover_result_names, val); }
@@ -70,8 +81,11 @@ enum handover_result bsc_tx_bssmap_ho_complete(struct gsm_subscriber_connection
 					       struct gsm_lchan *lchan);
 void bsc_tx_bssmap_ho_failure(struct gsm_subscriber_connection *conn);
 
-struct gsm_bts *bts_by_neighbor_ident(const struct gsm_network *net,
-				      const struct neighbor_ident_key *search_for);
+int find_handover_target_cell(struct gsm_bts **local_target_cell_p,
+			      const struct gsm0808_cell_id_list2 **remote_target_cell_p,
+			      struct gsm_subscriber_connection *conn, const struct neighbor_ident_key *search_for,
+			      bool log_errors);
+
 struct neighbor_ident_key *bts_ident_key(const struct gsm_bts *bts);
 
 void handover_parse_inter_bsc_mt(struct gsm_subscriber_connection *conn,
diff --git a/include/osmocom/bsc/handover_fsm.h b/include/osmocom/bsc/handover_fsm.h
index 7c2145e84..1628d8fd9 100644
--- a/include/osmocom/bsc/handover_fsm.h
+++ b/include/osmocom/bsc/handover_fsm.h
@@ -4,18 +4,6 @@
 #include <osmocom/bsc/debug.h>
 #include <osmocom/bsc/handover.h>
 
-const char *handover_status(struct gsm_subscriber_connection *conn);
-
-/* This macro automatically includes a final \n, if omitted. */
-#define LOG_HO(conn, level, fmt, args...) do { \
-	if (conn->ho.fi) \
-		LOGPFSML(conn->ho.fi, level, "%s: " fmt, \
-			 handover_status(conn), ## args); \
-	else \
-		LOGP(DHODEC, level, "%s: " fmt, \
-		     handover_status(conn), ## args); \
-	} while(0)
-
 /* Terminology:
  * Intra-Cell: stays within one BTS, this should actually be an Assignment.
  * Intra-BSC: stays within one BSC, but moves between BTSes.
diff --git a/include/osmocom/bsc/neighbor_ident.h b/include/osmocom/bsc/neighbor_ident.h
index 17bffbc14..aa3827635 100644
--- a/include/osmocom/bsc/neighbor_ident.h
+++ b/include/osmocom/bsc/neighbor_ident.h
@@ -47,6 +47,8 @@ void neighbor_ident_iter(const struct neighbor_ident_list *nil,
 void neighbor_ident_vty_init(struct gsm_network *net, struct neighbor_ident_list *nil);
 void neighbor_ident_vty_write(struct vty *vty, const char *indent, struct gsm_bts *bts);
 
+bool neighbor_ident_bts_entry_exists(uint8_t from_bts);
+
 #define NEIGHBOR_IDENT_VTY_KEY_PARAMS "arfcn <0-1023> bsic (<0-63>|any)"
 #define NEIGHBOR_IDENT_VTY_KEY_DOC \
 	"ARFCN of neighbor cell\n" "ARFCN value\n" \