broadband-modem: check if skeleton exists when creating device id

The logic that creates the device identifier uses some fields that are
exposed in DBus (e.g. model, manufacturer...).

We should not attempt to load any of that info if the DBus skeleton
for the Modem interface is no longer available, as e.g. the device may
have gone away already.

Fixes https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/374

src/mm-broadband-modem-mbim.c

@@ -857,15 +857,19 @@ modem_load_device_identifier (MMIfaceModem *self,
                               GAsyncReadyCallback callback,
                               gpointer user_data)
 {
-    gchar *device_identifier;
-    GTask *task;
+    gchar  *device_identifier;
+    GTask  *task;
+    GError *error = NULL;
+
+    task = g_task_new (self, NULL, callback, user_data);
 
     /* Just use dummy ATI/ATI1 replies, all the other internal info should be
      * enough for uniqueness */
-    device_identifier = mm_broadband_modem_create_device_identifier (MM_BROADBAND_MODEM (self), "", "");
-
-    task = g_task_new (self, NULL, callback, user_data);
-    g_task_return_pointer (task, device_identifier, g_free);
+    device_identifier = mm_broadband_modem_create_device_identifier (MM_BROADBAND_MODEM (self), "", "", &error);
+    if (!device_identifier)
+        g_task_return_error (task, error);
+    else
+        g_task_return_pointer (task, device_identifier, g_free);
     g_object_unref (task);
 }
 

src/mm-broadband-modem-qmi.c

@@ -679,17 +679,21 @@ modem_load_device_identifier (MMIfaceModem *self,
                               GAsyncReadyCallback callback,
                               gpointer user_data)
 {
-    gchar *device_identifier;
-    GTask *task;
+    gchar  *device_identifier;
+    GTask  *task;
+    GError *error = NULL;
+
+    task = g_task_new (self, NULL, callback, user_data);
 
     mm_obj_dbg (self, "loading device identifier...");
 
     /* Just use dummy ATI/ATI1 replies, all the other internal info should be
      * enough for uniqueness */
-    device_identifier = mm_broadband_modem_create_device_identifier (MM_BROADBAND_MODEM (self), "", "");
-
-    task = g_task_new (self, NULL, callback, user_data);
-    g_task_return_pointer (task, device_identifier, g_free);
+    device_identifier = mm_broadband_modem_create_device_identifier (MM_BROADBAND_MODEM (self), "", "", &error);
+    if (!device_identifier)
+        g_task_return_error (task, error);
+    else
+        g_task_return_pointer (task, device_identifier, g_free);
     g_object_unref (task);
 }
 

src/mm-broadband-modem.c

@@ -1146,9 +1146,9 @@ modem_load_device_identifier_finish (MMIfaceModem *self,
                                      GAsyncResult *res,
                                      GError **error)
 {
-    GError *inner_error = NULL;
-    gpointer ctx = NULL;
-    gchar *device_identifier;
+    GError   *inner_error = NULL;
+    gpointer  ctx = NULL;
+    gchar    *device_identifier;
 
     mm_base_modem_at_sequence_finish (MM_BASE_MODEM (self), res, &ctx, &inner_error);
     if (inner_error) {
@@ -1157,10 +1157,16 @@ modem_load_device_identifier_finish (MMIfaceModem *self,
     }
 
     g_assert (ctx != NULL);
-    device_identifier = (mm_broadband_modem_create_device_identifier (
-                             MM_BROADBAND_MODEM (self),
-                             ((DeviceIdentifierContext *)ctx)->ati,
-                             ((DeviceIdentifierContext *)ctx)->ati1));
+    device_identifier = mm_broadband_modem_create_device_identifier (
+                            MM_BROADBAND_MODEM (self),
+                            ((DeviceIdentifierContext *)ctx)->ati,
+                            ((DeviceIdentifierContext *)ctx)->ati1,
+                            &inner_error);
+    if (!device_identifier) {
+        g_propagate_error (error, inner_error);
+        return NULL;
+    }
+
     mm_obj_dbg (self, "loaded device identifier: %s", device_identifier);
     return device_identifier;
 }
@@ -12521,10 +12527,18 @@ mm_broadband_modem_get_current_charset (MMBroadbandModem *self)
 /*****************************************************************************/
 
 gchar *
-mm_broadband_modem_create_device_identifier (MMBroadbandModem *self,
-                                             const gchar *ati,
-                                             const gchar *ati1)
+mm_broadband_modem_create_device_identifier (MMBroadbandModem  *self,
+                                             const gchar       *ati,
+                                             const gchar       *ati1,
+                                             GError           **error)
 {
+    /* do nothing if device has gone already */
+    if (!self->priv->modem_dbus_skeleton) {
+        g_set_error (error, MM_CORE_ERROR, MM_CORE_ERROR_FAILED,
+                     "Modem interface skeleton unavailable");
+        return NULL;
+    }
+
     return (mm_create_device_identifier (
                 mm_base_modem_get_vendor_id (MM_BASE_MODEM (self)),
                 mm_base_modem_get_product_id (MM_BASE_MODEM (self)),

src/mm-broadband-modem.h

@@ -104,9 +104,10 @@ MMModemCharset mm_broadband_modem_get_current_charset (MMBroadbandModem *self);
 
 /* Create a unique device identifier string using the ATI and ATI1 replies and some
  * additional internal info */
-gchar *mm_broadband_modem_create_device_identifier (MMBroadbandModem *self,
-                                                    const gchar *ati,
-                                                    const gchar *ati1);
+gchar *mm_broadband_modem_create_device_identifier (MMBroadbandModem  *self,
+                                                    const gchar       *ati,
+                                                    const gchar       *ati1,
+                                                    GError           **error);
 
 /* Locking/unlocking SMS storages */
 void     mm_broadband_modem_lock_sms_storages        (MMBroadbandModem *self,