LCS: SCCP next conn id: prepare Lb-interface

When adding the Lb interface, it is necessary to determine an unused conn id
across *all* SCCP users. Prepare adding Lb by moving conn id creation out of
the gscon code and generalizing.

Change-Id: I12fcb18f6e4380f72929cfe7681bac05330a8c9a

1 files changed, 57 insertions, 0 deletions

diff --git a/src/osmo-bsc/bsc_sccp.c b/src/osmo-bsc/bsc_sccp.c
new file mode 100644
index 000000000..9d4289f3d
--- /dev/null
+++ b/src/osmo-bsc/bsc_sccp.c
@@ -0,0 +1,57 @@
+/* Generic SCCP handling across all OsmoBSC users */
+/*
+ * (C) 2020 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <neels@hofmeyr.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <osmocom/bsc/gsm_data.h>
+#include <osmocom/bsc/bsc_msc_data.h>
+
+/* We need an unused SCCP conn_id across all SCCP users. */
+int bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp)
+{
+	static uint32_t next_id = 1;
+	int i;
+
+	/* This looks really suboptimal, but in most cases the static next_id should indicate exactly the next unused
+	 * conn_id, and we only iterate all conns once to make super sure that it is not already in use. */
+
+	for (i = 0; i < 0xFFFFFF; i++) {
+		struct gsm_subscriber_connection *conn;
+		uint32_t conn_id = next_id;
+		bool conn_id_already_used = false;
+		next_id = (next_id + 1) & 0xffffff;
+
+		llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
+			if (conn->sccp.msc && conn->sccp.msc->a.sccp == sccp) {
+				if (conn_id == conn->sccp.conn_id) {
+					conn_id_already_used = true;
+					break;
+				}
+			}
+
+			/* Future for LCS: also check Lb-interface conn IDs here */
+		}
+
+		if (!conn_id_already_used)
+			return conn_id;
+	}
+	return -1;
+}