Start even if a libblockdev plugin fails to load

Unless somebody tries to do something that actually requires the
plugin, it's not really needed. And if they do, they will get an
error like any other.

The next step is to be able to react dynamically on the
availability of the required tools/libraries/etc. But we need a
better support for that in libblockdev in the first place.

src/udisksdaemon.c

@@ -260,15 +260,30 @@ udisks_daemon_constructed (GObject *object)
      plugins are loaded themselves. */
   BDPluginSpec *plugins[] = {&part_plugin, &swap_plugin, &loop_plugin, &mdraid_plugin,
                              &fs_plugin, &crypto_plugin, NULL};
+  BDPluginSpec **plugin_p = NULL;
   error = NULL;
 
-  ret = bd_ensure_init (plugins, NULL, &error);
+  ret = bd_try_init (plugins, NULL, NULL, &error);
   if (!ret)
+  {
+    if (error)
     {
       udisks_error ("Error initializing libblockdev library: %s (%s, %d)",
                     error->message, g_quark_to_string (error->domain), error->code);
-      g_error_free (error);
+      g_clear_error (&error);
+    }
+    else
+    {
+      /* a missing plugin is okay, calling functions from it will fail, but
+         until that happens, life will just be great */
+      for (plugin_p=plugins; *plugin_p; plugin_p++)
+        if (!bd_is_plugin_available ((*plugin_p)->name))
+          /* TODO: log plugin names when the function below is available */
+          /* udisks_warning ("Failed to load the '%s' libblockdev plugin", */
+          /*                 bd_get_plugin_name ((*plugin_p)->name)); */
+          udisks_warning ("Failed to load a libblockdev plugin");
     }
+  }
 
   daemon->authority = polkit_authority_get_sync (NULL, &error);
   if (daemon->authority == NULL)