HO: add queue to cache DTAP messages during handover/assignment

Add ho_dtap_cache to gsm_subscriber_connection, a stock msgb queue to be used
with msgb_enqueue() and msgb_dequeue().

Keep a counter of queue length, to enforce a sane maximum counter for cached
messages. So far a hardcoded maximum of 23 messages will be cached.

Have balanced ho_dtap_cache_add() and ho_dtap_cache_flush() functions.

The original patch was by jolly, but I have basically completely replaced it
with the simpler msgb queue pattern.

Change-Id: I6e4d93628befb3d97e5cee0343cd9f8ba0b8620c

1 files changed, 73 insertions, 0 deletions

diff --git a/src/libbsc/bsc_api.c b/src/libbsc/bsc_api.c
index dad1d54c1..9c60af9c0 100644
--- a/src/libbsc/bsc_api.c
+++ b/src/libbsc/bsc_api.c
@@ -39,6 +39,8 @@
 
 #define GSM0808_T10_VALUE    6, 0
 
+#define HO_DTAP_CACHE_MSGB_CB_LINK_ID 0
+#define HO_DTAP_CACHE_MSGB_CB_ALLOW_SACCH 1
 
 static void rll_ind_cb(struct gsm_lchan *, uint8_t, void *, enum bsc_rllr_ind);
 static void send_sapi_reject(struct gsm_subscriber_connection *conn, int link_id);
@@ -274,10 +276,54 @@ struct gsm_subscriber_connection *bsc_subscr_con_allocate(struct gsm_lchan *lcha
 	conn->lchan = lchan;
 	conn->bts = lchan->ts->trx->bts;
 	lchan->conn = conn;
+	INIT_LLIST_HEAD(&conn->ho_dtap_cache);
 	llist_add_tail(&conn->entry, &net->subscr_conns);
 	return conn;
 }
 
+static void ho_dtap_cache_add(struct gsm_subscriber_connection *conn, struct msgb *msg,
+			      int link_id, bool allow_sacch)
+{
+	if (conn->ho_dtap_cache_len >= 23) {
+		LOGP(DHO, LOGL_ERROR, "%s: Cannot cache more DTAP messages,"
+		     " already reached sane maximum of %u cached messages\n",
+		     bsc_subscr_name(conn->bsub), conn->ho_dtap_cache_len);
+		msgb_free(msg);
+		return;
+	}
+	conn->ho_dtap_cache_len ++;
+	LOGP(DHO, LOGL_DEBUG, "%s: Caching DTAP message during ho/ass (%u)\n",
+	     bsc_subscr_name(conn->bsub), conn->ho_dtap_cache_len);
+	msg->cb[HO_DTAP_CACHE_MSGB_CB_LINK_ID] = (unsigned long)link_id;
+	msg->cb[HO_DTAP_CACHE_MSGB_CB_ALLOW_SACCH] = allow_sacch ? 1 : 0;
+	msgb_enqueue(&conn->ho_dtap_cache, msg);
+}
+
+static void ho_dtap_cache_flush(struct gsm_subscriber_connection *conn, int send)
+{
+	struct msgb *msg;
+	unsigned int flushed_count = 0;
+
+	if (conn->secondary_lchan || conn->ho_lchan) {
+		LOGP(DHO, LOGL_ERROR, "%s: Cannot send cached DTAP messages, handover/assignment is still ongoing\n",
+		     bsc_subscr_name(conn->bsub));
+		send = 0;
+	}
+
+	while ((msg = msgb_dequeue(&conn->ho_dtap_cache))) {
+		conn->ho_dtap_cache_len --;
+		flushed_count ++;
+		if (send) {
+			int link_id = (int)msg->cb[HO_DTAP_CACHE_MSGB_CB_LINK_ID];
+			bool allow_sacch = !!msg->cb[HO_DTAP_CACHE_MSGB_CB_ALLOW_SACCH];
+			LOGP(DHO, LOGL_DEBUG, "%s: Sending cached DTAP message after handover/assignment (%u/%u)\n",
+			     bsc_subscr_name(conn->bsub), flushed_count, conn->ho_dtap_cache_len);
+			gsm0808_submit_dtap(conn, msg, link_id, allow_sacch);
+		} else
+			msgb_free(msg);
+	}
+}
+
 void bsc_subscr_con_free(struct gsm_subscriber_connection *conn)
 {
 	if (!conn)
@@ -301,6 +347,9 @@ void bsc_subscr_con_free(struct gsm_subscriber_connection *conn)
 		conn->secondary_lchan->conn = NULL;
 	}
 
+	/* drop pending messages */
+	ho_dtap_cache_flush(conn, 0);
+
 	llist_del(&conn->entry);
 	talloc_free(conn);
 }
@@ -325,6 +374,12 @@ int gsm0808_submit_dtap(struct gsm_subscriber_connection *conn,
 		return -1;
 	}
 
+	/* buffer message during assignment / handover */
+	if (conn->secondary_lchan || conn->ho_lchan) {
+		ho_dtap_cache_add(conn, msg, link_id, !! allow_sacch);
+		return 0;
+	}
+
 	sapi = link_id & 0x7;
 	msg->lchan = conn->lchan;
 	msg->dst = msg->lchan->ts->trx->rsl_link;
@@ -458,6 +513,9 @@ static void handle_ass_compl(struct gsm_subscriber_connection *conn,
 		osmo_signal_dispatch(SS_LCHAN, S_LCHAN_ASSIGNMENT_COMPL, &sig);
 		/* FIXME: release old channel */
 
+		/* send pending messages, if any */
+		ho_dtap_cache_flush(conn, 1);
+
 		return;
 	}
 
@@ -480,6 +538,9 @@ static void handle_ass_compl(struct gsm_subscriber_connection *conn,
 	conn->lchan = conn->secondary_lchan;
 	conn->secondary_lchan = NULL;
 
+	/* send pending messages, if any */
+	ho_dtap_cache_flush(conn, 1);
+
 	if (is_ipaccess_bts(conn_get_bts(conn)) && conn->lchan->tch_mode != GSM48_CMODE_SIGN)
 		rsl_ipacc_crcx(conn->lchan);
 
@@ -508,6 +569,9 @@ static void handle_ass_fail(struct gsm_subscriber_connection *conn,
 		osmo_signal_dispatch(SS_LCHAN, S_LCHAN_ASSIGNMENT_FAIL, &sig);
 		/* FIXME: release allocated new channel */
 
+		/* send pending messages, if any */
+		ho_dtap_cache_flush(conn, 1);
+
 		return;
 	}
 
@@ -523,6 +587,9 @@ static void handle_ass_fail(struct gsm_subscriber_connection *conn,
 		conn->secondary_lchan = NULL;
 	}
 
+	/* send pending messages, if any */
+	ho_dtap_cache_flush(conn, 1);
+
 	gh = msgb_l3(msg);
 	if (msgb_l3len(msg) - sizeof(*gh) != 1) {
 		LOGP(DMSC, LOGL_ERROR, "assignment failure unhandled: %zu\n",
@@ -588,6 +655,9 @@ static void handle_rr_ho_compl(struct msgb *msg)
 	sig.mr = NULL;
 	osmo_signal_dispatch(SS_LCHAN, S_LCHAN_HANDOVER_COMPL, &sig);
 	/* FIXME: release old channel */
+
+	/* send pending messages, if any */
+	ho_dtap_cache_flush(msg->lchan->conn, 1);
 }
 
 /* Chapter 9.1.17 Handover Failure */
@@ -603,6 +673,9 @@ static void handle_rr_ho_fail(struct msgb *msg)
 	sig.mr = NULL;
 	osmo_signal_dispatch(SS_LCHAN, S_LCHAN_HANDOVER_FAIL, &sig);
 	/* FIXME: release allocated new channel */
+
+	/* send pending messages, if any */
+	ho_dtap_cache_flush(msg->lchan->conn, 1);
 }