gpu-kms: Check for DRM resources when constructing

drmModeGetResources() can fail if the DRM driver doesn't implement
modesetting. We shouldn't crash in this case, but instead error out.

This moves the call into the constructor of the MetaGpuKms, as it is
easier to fail constructing directly rather than deal with it later on.

Fixes #223.

src/backends/native/meta-gpu-kms.c

@@ -68,6 +68,8 @@ struct _MetaGpuKms
   int max_buffer_height;
 
   gboolean page_flips_not_supported;
+
+  MetaKmsResources resources;
 };
 
 G_DEFINE_TYPE (MetaGpuKms, meta_gpu_kms, META_TYPE_GPU)
@@ -726,20 +728,29 @@ init_outputs (MetaGpuKms       *gpu_kms,
   setup_output_clones (gpu);
 }
 
-static void
+static gboolean
 meta_kms_resources_init (MetaKmsResources *resources,
-                         int               fd)
+                         int               fd,
+                         GError          **error)
 {
   drmModeRes *drm_resources;
   unsigned int i;
 
   drm_resources = drmModeGetResources (fd);
+
+  if (drm_resources == NULL) {
+    g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED, "No resources");
+    return FALSE;
+  }
+
   resources->resources = drm_resources;
 
   resources->n_encoders = (unsigned int) drm_resources->count_encoders;
   resources->encoders = g_new (drmModeEncoder *, resources->n_encoders);
   for (i = 0; i < resources->n_encoders; i++)
     resources->encoders[i] = drmModeGetEncoder (fd, drm_resources->encoders[i]);
+
+  return TRUE;
 }
 
 static void
@@ -761,9 +772,7 @@ meta_gpu_kms_read_current (MetaGpu  *gpu,
   MetaGpuKms *gpu_kms = META_GPU_KMS (gpu);
   MetaMonitorManager *monitor_manager =
     meta_gpu_get_monitor_manager (gpu);
-  MetaKmsResources resources;
-
-  meta_kms_resources_init (&resources, gpu_kms->fd);
+  MetaKmsResources resources = gpu_kms->resources;
 
   gpu_kms->max_buffer_width = resources.resources->max_width;
   gpu_kms->max_buffer_height = resources.resources->max_height;
@@ -812,6 +821,11 @@ meta_gpu_kms_new (MetaMonitorManagerKms  *monitor_manager_kms,
   gpu_kms->fd = kms_fd;
   gpu_kms->file_path = g_strdup (kms_file_path);
 
+  if (!meta_kms_resources_init (&gpu_kms->resources, gpu_kms->fd, error)) {
+    g_clear_object (&gpu_kms);
+    return NULL;
+  }
+
   drmSetClientCap (gpu_kms->fd, DRM_CLIENT_CAP_UNIVERSAL_PLANES, 1);
 
   source = g_source_new (&kms_event_funcs, sizeof (MetaKmsSource));
@@ -841,7 +855,7 @@ meta_gpu_kms_finalize (GObject *object)
     meta_launcher_close_restricted (launcher, gpu_kms->fd);
   g_clear_pointer (&gpu_kms->file_path, g_free);
 
-  g_source_destroy (gpu_kms->source);
+  g_clear_pointer (&gpu_kms->source, g_source_destroy);
 
   free_resources (gpu_kms);