[mce-sensorfw] Do not retry loading of unavailable sensors. JB#41369

Now that it is possible for sensorfwd to refuse loading a sensor plugin
(due to the device not having such sensor), this can trigger MCE into
perpetual retry-in-N-seconds D-Bus IPC loop.

Differentiate between "sensor was not loaded" replies and "there were
issues while requesting sensor load" error replies - so that former
is taken to mean that the sensor is not available, and the latter as
something that might be helped with retrying a bit later.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

mce-sensorfw.c

@@ -702,6 +702,9 @@ typedef enum
     /** Something went wrong */
     PLUGIN_ERROR,
 
+    /** Plugin not available */
+    PLUGIN_NA,
+
     PLUGIN_NUMSTATES
 } sfw_plugin_state_t;
 
@@ -2654,6 +2657,7 @@ sfw_plugin_state_name(sfw_plugin_state_t state)
         [PLUGIN_LOADING]  = "LOADING",
         [PLUGIN_LOADED]   = "LOADED",
         [PLUGIN_ERROR]    = "ERROR",
+        [PLUGIN_NA]       = "NA",
     };
 
     return (state < PLUGIN_NUMSTATES) ? lut[state] : 0;
@@ -2823,6 +2827,7 @@ sfw_plugin_trans(sfw_plugin_t *self, sfw_plugin_state_t state)
     case PLUGIN_IDLE:
     case PLUGIN_ERROR:
     case PLUGIN_INITIAL:
+    case PLUGIN_NA:
         sfw_plugin_do_session_reset(self);
 
         if( self->plg_state == PLUGIN_ERROR )
@@ -2931,6 +2936,7 @@ sfw_plugin_load_cb(DBusPendingCall *pc, void *aptr)
     DBusMessage  *rsp  = 0;
     DBusError     err  = DBUS_ERROR_INIT;
     dbus_bool_t   ack  = FALSE;
+    bool          nak  = true;
 
     if( !pc || !self || pc != self->plg_load_pc )
         goto EXIT;
@@ -2958,13 +2964,17 @@ sfw_plugin_load_cb(DBusPendingCall *pc, void *aptr)
         goto EXIT;
     }
 
+    nak = false;
+
 EXIT:
 
     if( self->plg_state == PLUGIN_LOADING) {
-        if( ack )
+        if( nak )
+            sfw_plugin_trans(self, PLUGIN_ERROR);
+        else if( ack )
             sfw_plugin_trans(self, PLUGIN_LOADED);
         else
-            sfw_plugin_trans(self, PLUGIN_ERROR);
+            sfw_plugin_trans(self, PLUGIN_NA);
     }
 
     if( rsp ) dbus_message_unref(rsp);

mce-sensorfw.dot

@@ -116,15 +116,16 @@ digraph mce_sensorfw
     PLUGIN_LOADING;
     PLUGIN_LOADED;
     PLUGIN_ERROR;
+    PLUGIN_NA;
     PLUGIN_ANY [label="*"];
 
-    PLUGIN_ANY  -> PLUGIN_IDLE    [label="reset()"];
-    PLUGIN_IDLE -> PLUGIN_LOADING [label="load()"];
+    PLUGIN_ANY  -> PLUGIN_IDLE       [label="reset()"];
+    PLUGIN_IDLE -> PLUGIN_LOADING    [label="load()"];
+    PLUGIN_LOADING -> PLUGIN_NA      [label="not-available"];
+    PLUGIN_LOADING -> PLUGIN_LOADED  [label="loaded"];
+    PLUGIN_ANY     -> PLUGIN_ERROR   [label="failure"];
 
-    PLUGIN_LOADING -> PLUGIN_LOADED;
-    PLUGIN_ANY     -> PLUGIN_ERROR [label="failure"];
-
-    PLUGIN_LOADED  -> SESSION_IDLE [style=dotted, lhead=clusterSESSION];
+    PLUGIN_LOADED  -> SESSION_IDLE   [style=dotted, lhead=clusterSESSION];
 
     PLUGIN_ERROR   -> PLUGIN_LOADING [label="retry"];
   }