Change in osmo-bsc[master]: handover: fix detection for ambiguous HO neighbor ident

[neels]

neels has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bsc/+/19901 )


Change subject: handover: fix detection for ambiguous HO neighbor ident
......................................................................

handover: fix detection for ambiguous HO neighbor ident

Adding rate counter checks to TC_ho_neighbor_config_1 (1.c) uncovers that the
test passes for the wrong reason. The ambiguous cell identification should be
the cause for the handover error, but the log shows that instead a handover is
attempted to BTS 3 which is not connected.

find_handover_target_cell() first tries to find a precise match of values, and
in a second pass applies wildcards like BSIC_ANY and
NEIGHBOR_IDENT_KEY_ANY_BTS. That second pass lacks detection of ambiguous
matches.

Use the same code for both passes, by encapsulating in a loop of two, which
first runs with exact_match == true and then false.

Proper detection of the ambiguous target cell identification in
TC_ho_neighbor_config_1() is shown by the resulting 'handover:error' count,
see I10bc0b67ca8dcf41dbb02332ed18017e819c2b32 (osmo-ttcn3-hacks).

Related: OS#4736
Related: I10bc0b67ca8dcf41dbb02332ed18017e819c2b32 (osmo-ttcn3-hacks)
Change-Id: Ib0087b6566ae4d82f8c3ef272c1256bcd1d08bf1
---
M src/osmo-bsc/handover_logic.c
1 file changed, 21 insertions(+), 19 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/01/19901/1

diff --git a/src/osmo-bsc/handover_logic.c b/src/osmo-bsc/handover_logic.c
index 071228e..ade330d 100644
--- a/src/osmo-bsc/handover_logic.c
+++ b/src/osmo-bsc/handover_logic.c
@@ -183,32 +183,34 @@
 		/* No explicit neighbor entries exist for this BTS. Hence apply the legacy default behavior that all
 		 * local cells are neighbors. */
 		struct gsm_bts *bts;
-		struct gsm_bts *wildcard_match = NULL;
+		int i;
 
 		LOG_HO(conn, LOGL_DEBUG, "No explicit neighbors, regarding all local cells as neighbors\n");
 
-		llist_for_each_entry(bts, &net->bts_list, list) {
-			struct neighbor_ident_key bts_key = *bts_ident_key(bts);
-			if (neighbor_ident_key_match(&bts_key, search_for, true)) {
-				if (local_target_cell) {
-					if (log_errors)
-						LOG_HO(conn, LOGL_ERROR,
-						       "NEIGHBOR CONFIGURATION ERROR: Multiple local cells match %s"
-						       " (BTS %d and BTS %d)."
-						       " Aborting Handover because of ambiguous network topology.\n",
-						       neighbor_ident_key_name(search_for),
-						       local_target_cell->nr, bts->nr);
-					return -EINVAL;
+		/* For i == 0, look for an exact 1:1 match of all ident_key fields.
+		 * For i == 1, interpret wildcard values, when no exact match exists. */
+		for (i = 0; i < 2; i++) {
+			bool exact_match = !i;
+			llist_for_each_entry(bts, &net->bts_list, list) {
+				struct neighbor_ident_key bts_key = *bts_ident_key(bts);
+				if (neighbor_ident_key_match(&bts_key, search_for, exact_match)) {
+					if (local_target_cell) {
+						if (log_errors)
+							LOG_HO(conn, LOGL_ERROR,
+							       "NEIGHBOR CONFIGURATION ERROR: Multiple local cells match %s"
+							       " (BTS %d and BTS %d)."
+							       " Aborting Handover because of ambiguous network topology.\n",
+							       neighbor_ident_key_name(search_for),
+							       local_target_cell->nr, bts->nr);
+						return -EINVAL;
+					}
+					local_target_cell = bts;
 				}
-				local_target_cell = bts;
 			}
-			if (neighbor_ident_key_match(&bts_key, search_for, false))
-				wildcard_match = bts;
+			if (local_target_cell)
+				break;
 		}
 
-		if (!local_target_cell)
-			local_target_cell = wildcard_match;
-
 		if (!local_target_cell) {
 			if (log_errors)
 				LOG_HO(conn, LOGL_ERROR, "Cannot Handover, no cell matches %s\n",

-- 
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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: Ib0087b6566ae4d82f8c3ef272c1256bcd1d08bf1
Gerrit-Change-Number: 19901
Gerrit-PatchSet: 1
Gerrit-Owner: neels <nhofmeyr at sysmocom.de>
Gerrit-MessageType: newchange
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