sms: Introduce a SMS queue that will be responsible for delivery

The SMSqueue will be responsible of sending to the user. It will
do so in a loop and will also try not to overload the BTS. This
means the throughput of SMS will be limited.
diff --git a/openbsc/src/sms_queue.c b/openbsc/src/sms_queue.c
new file mode 100644
index 0000000..f61cf63
--- /dev/null
+++ b/openbsc/src/sms_queue.c
@@ -0,0 +1,97 @@
+/* SMS queue to continously attempt to deliver SMS */
+/*
+ * (C) 2010 by Holger Hans Peter Freyther <zecke@selfish.org>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+/**
+ * The difficulty of such a queue is to send a lot of SMS without
+ * overloading the paging subsystem and the database and other users
+ * of the MSC. To make the best use we would need to know the number
+ * of pending paging requests, then throttle the number of SMS we
+ * want to send and such.
+ * We will start with a very simple SMS Queue and then try to speed
+ * things up by collecting data from other parts of the system.
+ */
+
+#include <openbsc/sms_queue.h>
+#include <openbsc/chan_alloc.h>
+#include <openbsc/db.h>
+#include <openbsc/debug.h>
+#include <openbsc/gsm_data.h>
+#include <openbsc/gsm_04_11.h>
+#include <openbsc/signal.h>
+
+#include <osmocore/talloc.h>
+
+
+struct gsm_sms_queue {
+	struct gsm_network *network;
+	int max_pending;
+	int pending;
+};
+
+
+int sms_queue_start(struct gsm_network *network, int max_pending)
+{
+	struct gsm_sms_queue *sms = talloc_zero(network, struct gsm_sms_queue);
+	if (!sms) {
+		LOGP(DMSC, LOGL_ERROR, "Failed to create the SMS queue.\n");
+		return -1;
+	}
+
+	network->sms_queue = sms;
+	sms->network = network;
+	sms->max_pending = max_pending;
+
+	return 0;
+}
+
+static int sub_ready_for_sm(struct gsm_subscriber *subscr)
+{
+	struct gsm_subscriber_connection *conn;
+	struct gsm_sms *sms;
+
+	/* A subscriber has attached. Check if there are
+	 * any pending SMS for him to be delivered */
+	conn = connection_for_subscr(subscr);
+	if (!conn)
+		return -1;
+	sms = db_sms_get_unsent_for_subscr(subscr);
+	if (!sms)
+		return -1;
+	gsm411_send_sms(conn, sms);
+	return 0;
+}
+
+static int sms_subscr_cb(unsigned int subsys, unsigned int signal,
+			 void *handler_data, void *signal_data)
+{
+	struct gsm_subscriber *subscr = signal_data;
+
+	if (signal != S_SUBSCR_ATTACHED)
+		return 0;
+
+	/* this is readyForSM */
+	return sub_ready_for_sm(subscr);
+}
+
+static __attribute__((constructor)) void on_dso_load_sms(void)
+{
+	register_signal_handler(SS_SUBSCR, sms_subscr_cb, NULL);
+}