Bluetooth: host: Improve error reporting on gatt subscribe

* Return EALREADY when the subscription already exists but it is a different entry. This indicates to the application to not wait on subscribe callback. This is needed because the callback is called from the ccc_write which does not happen when another subscription exists Signed-off-by: Yago Fontoura do Rosario <[email protected]>
zephyrproject-rtos · Nov 27, 2024 · f22ac17 · f22ac17
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diff --git a/doc/releases/migration-guide-4.0.rst b/doc/releases/migration-guide-4.0.rst
@@ -404,6 +404,9 @@ Bluetooth Audio
 Bluetooth Host
 ==============
 
+* ``bt_gatt_subscribe`` returns ``-EALREADY`` when another subscription exists. This indicates to
+  the application that it should not wait for the subscribe callback
+
 Automatic advertiser resumption is deprecated
 ---------------------------------------------
 

diff --git a/subsys/bluetooth/host/gatt.c b/subsys/bluetooth/host/gatt.c
@@ -5541,7 +5541,11 @@ int bt_gatt_subscribe(struct bt_conn *conn,
 	 */
 	sys_slist_prepend(&sub->list, &params->node);
 
-	return 0;
+	/*
+	 * Report already if subscription exist so that application does not wait
+	 * for the subscribe callback
+	 */
+	return has_subscription ? -EALREADY : 0;
 }
 
 int bt_gatt_resubscribe(uint8_t id, const bt_addr_le_t *peer,