jolly submitted this change.

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Indicate error and release BSS connection when SMS transaction fails

When the creation of the transaction structure fails, the MSC will
send a CP-ERROR message.

This patch ensures that the MSC_A use counter is decremented, so
that the BSS connection is released, if it is not used by any other
transaction.

Without this patch, the msc_a_fsm would wait 5 seconds for an initial
transaction before releasing the BSS connection.

Related: OS#6427
Change-Id: I82da9c283205c69b19ceb4ba40ac5aa7f37d159b
---
M src/libmsc/gsm_04_11.c
1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/libmsc/gsm_04_11.c b/src/libmsc/gsm_04_11.c
index b6d5f4a..209ca28 100644
--- a/src/libmsc/gsm_04_11.c
+++ b/src/libmsc/gsm_04_11.c
@@ -231,6 +231,20 @@
 	return gsm411_sendmsg(trans, msg);
 }
 
+int gsm411_send_cp_error(struct msc_a *msc_a, uint8_t pdisc, uint8_t cause)
+{
+	struct msgb *msg = gsm411_msgb_alloc();
+	struct gsm48_hdr *gh;
+
+	msgb_put_u8(msg, cause);
+
+	gh = (struct gsm48_hdr *) msgb_push(msg, sizeof(*gh));
+	gh->proto_discr = pdisc;
+	gh->msg_type = GSM411_MT_CP_ERROR;
+
+	return msc_a_tx_dtap_to_i(msc_a, msg);
+}
+
 /* mm_send: receive MMCCSMS sap message from SMC */
 static int gsm411_mm_send(struct gsm411_smc_inst *inst, int msg_type,
 			struct msgb *msg, int cp_msg_type)
@@ -1339,6 +1353,12 @@
 			"to us anymore. We are ignoring it, maybe a CP-ERROR "
 			"from a MS?\n",
 			transaction_id);
+		/* Decrement use counter that has been incremented by CM Service Request (SMS).
+		 * If there is no other service request, the BSS connection will be released. */
+		if (!osmo_use_count_by(&msc_a->use_count, MSC_A_USE_CM_SERVICE_SMS))
+			LOG_TRANS(trans, LOGL_ERROR, "MO SMS without prior CM Service Request\n");
+		else
+			msc_a_put(msc_a, MSC_A_USE_CM_SERVICE_SMS);
 		return -EINVAL;
 	}
 
@@ -1346,7 +1366,15 @@
 		new_trans = 1;
 		trans = gsm411_trans_init(net, vsub, msc_a, transaction_id, true);
 		if (!trans) {
-			/* FIXME: send some error message */
+			/* Send error message. */
+			gsm411_send_cp_error(msc_a, GSM48_PDISC_SMS | (transaction_id << 4),
+					     GSM411_CP_CAUSE_NET_FAIL);
+			/* Decrement use counter that has been incremented by CM Service Request (SMS).
+			 * If there is no other service request, the BSS connection will be released. */
+			if (!osmo_use_count_by(&msc_a->use_count, MSC_A_USE_CM_SERVICE_SMS))
+				LOG_TRANS(trans, LOGL_ERROR, "MO SMS without prior CM Service Request\n");
+			else
+				msc_a_put(msc_a, MSC_A_USE_CM_SERVICE_SMS);
 			return -ENOMEM;
 		}
 

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