Add rudimentary mode setting test

Add a test that uses vkms to test that mode setting works, and that
rendering works. It renders 10 frames in a row after mode setting, then
exits.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2151>

src/backends/native/meta-backend-native-types.h

@@ -43,6 +43,7 @@ typedef enum _MetaBackendNativeMode
 {
   META_BACKEND_NATIVE_MODE_DEFAULT = 0,
   META_BACKEND_NATIVE_MODE_HEADLESS,
+  META_BACKEND_NATIVE_MODE_TEST,
 } MetaBackendNativeMode;
 
 #endif /* META_BACKEND_NATIVE_TYPES_H */

src/backends/native/meta-backend-native.c

@@ -127,10 +127,19 @@ meta_backend_native_create_default_seat (MetaBackend  *backend,
                                          GError      **error)
 {
   MetaBackendNative *backend_native = META_BACKEND_NATIVE (backend);
-  const char *seat_id;
+  const char *seat_id = NULL;
   MetaSeatNativeFlag flags;
 
-  seat_id = meta_backend_native_get_seat_id (backend_native);
+  switch (backend_native->mode)
+    {
+    case META_BACKEND_NATIVE_MODE_DEFAULT:
+    case META_BACKEND_NATIVE_MODE_HEADLESS:
+      seat_id = meta_backend_native_get_seat_id (backend_native);
+      break;
+    case META_BACKEND_NATIVE_MODE_TEST:
+      seat_id = META_BACKEND_TEST_INPUT_SEAT;
+      break;
+    }
 
   if (meta_backend_is_headless (backend))
     flags = META_SEAT_NATIVE_FLAG_NO_LIBINPUT;
@@ -379,6 +388,7 @@ meta_backend_native_get_seat_id (MetaBackendNative *backend_native)
   switch (backend_native->mode)
     {
     case META_BACKEND_NATIVE_MODE_DEFAULT:
+    case META_BACKEND_NATIVE_MODE_TEST:
       return meta_launcher_get_seat_id (backend_native->launcher);
     case META_BACKEND_NATIVE_MODE_HEADLESS:
       return "seat0";
@@ -459,6 +469,21 @@ create_gpu_from_udev_device (MetaBackendNative  *native,
   return meta_gpu_kms_new (native, kms_device, error);
 }
 
+static gboolean
+should_ignore_device (MetaBackendNative *backend_native,
+                      GUdevDevice       *device)
+{
+  switch (backend_native->mode)
+    {
+    case META_BACKEND_NATIVE_MODE_DEFAULT:
+    case META_BACKEND_NATIVE_MODE_HEADLESS:
+      return meta_is_udev_device_ignore (device);
+    case META_BACKEND_NATIVE_MODE_TEST:
+      return !meta_is_udev_test_device (device);
+    }
+  g_assert_not_reached ();
+}
+
 static void
 on_udev_device_added (MetaUdev          *udev,
                       GUdevDevice       *device,
@@ -488,9 +513,9 @@ on_udev_device_added (MetaUdev          *udev,
         }
     }
 
-  if (meta_is_udev_device_ignore (device))
+  if (should_ignore_device (native, device))
     {
-      g_message ("Ignoring DRM device '%s' (from udev rule)", device_path);
+      g_message ("Ignoring DRM device '%s'", device_path);
       return;
     }
 
@@ -524,9 +549,9 @@ init_gpus (MetaBackendNative  *native,
       MetaGpuKms *gpu_kms;
       GError *local_error = NULL;
 
-      if (meta_is_udev_device_ignore (device))
+      if (should_ignore_device (native, device))
         {
-          g_message ("Ignoring DRM device '%s' (from udev rule)",
+          g_message ("Ignoring DRM device '%s'",
                      g_udev_device_get_device_file (device));
           continue;
         }

src/backends/native/meta-backend-native.h

@@ -31,6 +31,8 @@
 #include "backends/native/meta-launcher.h"
 #include "backends/native/meta-udev.h"
 
+#define META_BACKEND_TEST_INPUT_SEAT "meta-test-seat0"
+
 #define META_TYPE_BACKEND_NATIVE (meta_backend_native_get_type ())
 META_EXPORT_TEST
 G_DECLARE_FINAL_TYPE (MetaBackendNative, meta_backend_native,

src/backends/native/meta-udev.c

@@ -108,6 +108,13 @@ meta_is_udev_device_ignore (GUdevDevice *device)
   return meta_has_udev_device_tag (device, "mutter-device-ignore");
 }
 
+gboolean
+meta_is_udev_test_device (GUdevDevice *device)
+{
+  return g_strcmp0 (g_udev_device_get_property (device, "ID_PATH"),
+                    "platform-vkms") == 0;
+}
+
 gboolean
 meta_is_udev_device_preferred_primary (GUdevDevice *device)
 {

src/backends/native/meta-udev.h

@@ -36,6 +36,8 @@ gboolean meta_is_udev_device_disable_modifiers (GUdevDevice *device);
 
 gboolean meta_is_udev_device_ignore (GUdevDevice *device);
 
+gboolean meta_is_udev_test_device (GUdevDevice *device);
+
 gboolean meta_is_udev_device_preferred_primary (GUdevDevice *device);
 
 gboolean meta_udev_is_drm_device (MetaUdev    *udev,