Create system state entry in dataman - ATTN Anton

Create persistent system state id for data manager to store system state
that will persist across resets.

src/modules/dataman/dataman.h

@@ -53,6 +53,7 @@ extern "C" {
 		DM_KEY_WAYPOINTS_OFFBOARD_0,	/* Mission way point coordinates sent over mavlink */
 		DM_KEY_WAYPOINTS_OFFBOARD_1,	/* (alernate between 0 and 1) */
 		DM_KEY_WAYPOINTS_ONBOARD,	/* Mission way point coordinates generated onboard */
+		DM_KEY_SYSTEM_STATE,		/* Persistent system state storage */
 		DM_KEY_NUM_KEYS			/* Total number of item types defined */
 	} dm_item_t;
 
@@ -62,7 +63,8 @@ extern "C" {
 		DM_KEY_FENCE_POINTS_MAX = GEOFENCE_MAX_VERTICES,
 		DM_KEY_WAYPOINTS_OFFBOARD_0_MAX = NUM_MISSIONS_SUPPORTED,
 		DM_KEY_WAYPOINTS_OFFBOARD_1_MAX = NUM_MISSIONS_SUPPORTED,
-		DM_KEY_WAYPOINTS_ONBOARD_MAX = NUM_MISSIONS_SUPPORTED
+		DM_KEY_WAYPOINTS_ONBOARD_MAX = NUM_MISSIONS_SUPPORTED,
+		DM_KEY_SYSTEM_STATE_MAX = 1
 	};
 
 	/** Data persistence levels */
@@ -101,6 +103,18 @@ extern "C" {
 		size_t buflen			/* Length in bytes of data to retrieve */
 	);
 
+	/** Lock all items of this type */
+	__EXPORT void
+	dm_lock(
+		dm_item_t item			/* The item type to clear */
+		);
+
+	/** Unlock all items of this type */
+	__EXPORT void
+	dm_unlock(
+		dm_item_t item			/* The item type to clear */
+		);
+
 	/** Erase all items of this type */
 	__EXPORT int
 	dm_clear(
@@ -113,6 +127,16 @@ extern "C" {
 		dm_reset_reason restart_type	/* The last reset type */
 	);
 
+	/* NOTE: The following structure defines the persistent system state data stored in the single
+	   entry DM_KEY_SYSTEM_STATE_KEY item type. It contains global system state information that
+	   needs to survive restarts. This definition is application specific so it doesn't really belong
+	   in this header, but till I find it a better home here it is */
+
+	typedef struct {
+		char current_offboard_waypoint_id;	/* the index of the active offboard waypoint data */
+							/* (DM_KEY_WAYPOINTS_OFFBOARD_n) or -1 for none */
+	} persistent_system_state_t;
+
 #ifdef __cplusplus
 }
 #endif