protocol: add wl_display_upgrade global

This global allows the IPC library to upgrade the version of the
wl_display global. To ensure maximum flexibility, there are strict
requirements on the connection state at the time of the upgrade. In
particular, after the compositor has destroyed the wl_display_upgrade
object, the wl_display is the only object in the connection.

Since there are many consumers of wl_display and wl_registry, and the
version of these objects is fixed after the upgrade, care must be taken
not to break any of these consumers. Since no consumer checks the
version of these objects and there is no way to get a wl_registry with a
lower version, incrementing the minor version cannot change the
semantics of existing messages and no new events can be added to
wl_registry. As an exception, new events can be added to wl_display
since those events are handled internally by the IPC library which is
also in charge of upgrading the version.

An additional change that could be made in version 2 of wl_display is
adding a wl_display.delete_server_id request, implementing symmetric
delete_id. A global that wants to make full use of destructor events
could then specify that the global must only be exposed on a wl_registry
whose version (and therefore the version of the wl_display) is at least
2.

Signed-off-by: Julian Orth <ju.orth@gmail.com>

src/wayland-client-core.h

@@ -245,6 +245,9 @@ wl_display_connect_to_fd(int fd);
 void
 wl_display_disconnect(struct wl_display *display);
 
+void
+wl_display_upgrade(struct wl_display *display);
+
 int
 wl_display_get_fd(struct wl_display *display);
 

src/wayland-client.c

@@ -1405,6 +1405,84 @@ wl_display_disconnect(struct wl_display *display)
 	free(display);
 }
 
+struct upgrade_listener {
+	struct wl_fixes *wl_fixes;
+	struct wl_display_upgrade *wl_display_upgrade;
+	uint32_t version;
+};
+
+static void upgrade_max_version(void *data,
+				struct wl_display_upgrade *wl_display_upgrade,
+				uint32_t version)
+{
+	struct upgrade_listener *listener = data;
+	listener->version = version;
+}
+
+static struct wl_display_upgrade_listener upgrade_upgrade_listener = {
+	.max_version = upgrade_max_version,
+};
+
+static void upgrade_global(void *data, struct wl_registry *wl_registry,
+			   uint32_t name, const char *interface,
+			   uint32_t version)
+{
+	struct upgrade_listener *listener = data;
+	if (!listener->wl_fixes && strcmp(interface, wl_fixes_interface.name) == 0)
+		listener->wl_fixes = wl_registry_bind(wl_registry, name, &wl_fixes_interface, 1);
+	else if (!listener->wl_display_upgrade && strcmp(interface, wl_display_upgrade_interface.name) == 0) {
+		listener->wl_display_upgrade = wl_registry_bind(wl_registry, name, &wl_display_upgrade_interface, 1);
+		wl_display_upgrade_add_listener(listener->wl_display_upgrade, &upgrade_upgrade_listener, data);
+	}
+}
+
+static void upgrade_global_remove(void *data, struct wl_registry *wl_registry,
+				  uint32_t name)
+{
+	// nothing
+}
+
+static struct wl_registry_listener upgrade_registry_listener = {
+	.global = upgrade_global,
+	.global_remove = upgrade_global_remove,
+};
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+/** Upgrade the wl_display version.
+ *
+ * \param display The display context object
+ *
+ * Tries to upgrade the version of the wl_display. After this function returns,
+ * wl_display_get_version can be used to retrieve the new version of the
+ * wl_display.
+ *
+ * This function should be called immediately after creating the display. It
+ * must not be called any later than that or multiple times, otherwise a
+ * protocol error might occur.
+ *
+ * \memberof wl_display
+ */
+WL_EXPORT void
+wl_display_upgrade(struct wl_display *display)
+{
+	struct wl_registry *registry = wl_display_get_registry(display);
+	struct upgrade_listener listener = { };
+	wl_registry_add_listener(registry, &upgrade_registry_listener, &listener);
+	wl_display_roundtrip(display);
+	if (listener.wl_display_upgrade)
+		wl_display_roundtrip(display);
+	if (listener.wl_fixes) {
+		wl_fixes_destroy_registry(listener.wl_fixes, registry);
+		wl_fixes_destroy(listener.wl_fixes);
+	}
+	if (listener.wl_display_upgrade) {
+		uint32_t version = min(listener.version, (uint32_t)wl_display_interface.version);
+		wl_display_upgrade_upgrade(listener.wl_display_upgrade, version);
+		display->proxy.version = version;
+	}
+}
+
 /** Get a display context's file descriptor
  *
  * \param display The display context object

src/wayland-server-core.h

@@ -697,6 +697,9 @@ wl_shm_buffer_create(struct wl_client *client,
 		     uint32_t id, int32_t width, int32_t height,
 		     int32_t stride, uint32_t format);
 
+int
+wl_display_init_upgrade(struct wl_display *display, uint32_t max_version);
+
 void
 wl_log_set_handler_server(wl_log_func_t handler);
 

src/wayland-server.c

@@ -86,6 +86,7 @@ struct wl_client {
 	struct wl_priv_signal resource_created_signal;
 	void *data;
 	wl_user_data_destroy_func_t data_dtor;
+	bool has_upgrade;
 };
 
 struct wl_display {
@@ -113,6 +114,7 @@ struct wl_display {
 	struct wl_event_source *term_source;
 
 	size_t max_buffer_size;
+	uint32_t max_upgrade_version;
 };
 
 struct wl_global {
@@ -1077,8 +1079,15 @@ registry_bind(struct wl_client *client,
 		global->bind(client, global->data, version, id);
 }
 
+static void
+registry_release(struct wl_client *client, struct wl_resource *resource)
+{
+	wl_resource_destroy(resource);
+}
+
 static const struct wl_registry_interface registry_interface = {
-	registry_bind
+	.bind = registry_bind,
+	.release = registry_release,
 };
 
 static void
@@ -1114,7 +1123,7 @@ display_get_registry(struct wl_client *client,
 	struct wl_global *global;
 
 	registry_resource =
-		wl_resource_create(client, &wl_registry_interface, 1, id);
+		wl_resource_create(client, &wl_registry_interface, resource->version, id);
 	if (registry_resource == NULL) {
 		wl_client_post_no_memory(client);
 		return;
@@ -2428,6 +2437,59 @@ wl_client_set_max_buffer_size(struct wl_client *client, size_t max_buffer_size)
 	wl_connection_set_max_buffer_size(client->connection, max_buffer_size);
 }
 
+static void
+upgrade_display(struct wl_client *client, struct wl_resource *resource,
+		uint32_t version)
+{
+	wl_resource_destroy(resource);
+	// TODO: Check that there are no other objects.
+	if (version < 1 || version > client->display->max_upgrade_version) {
+		wl_resource_post_error(resource,
+				       WL_DISPLAY_UPGRADE_ERROR_OUT_OF_BOUNDS,
+				       "version is out of bounds");
+		return;
+	}
+	client->display_resource->version = (int)version;
+}
+
+static struct wl_display_upgrade_interface upgrade_interface = {
+	.upgrade = upgrade_display,
+};
+
+static void
+bind_upgrade(struct wl_client *client, void *data, uint32_t version,
+	     uint32_t id)
+{
+	struct wl_resource *resource;
+	resource = wl_resource_create(client, &wl_display_upgrade_interface,
+				      (int)version, id);
+	if (!resource) {
+		wl_client_post_no_memory(client);
+		return;
+	}
+	if (client->has_upgrade) {
+		wl_resource_post_error(resource,
+				       WL_DISPLAY_UPGRADE_ERROR_ALREADY_BOUND,
+				       "wl_display_upgrade has already been bound");
+		return;
+	}
+	client->has_upgrade = true;
+	wl_display_upgrade_send_max_version(resource,
+					    client->display->max_upgrade_version);
+	wl_resource_set_implementation(resource, &upgrade_interface, NULL, NULL);
+}
+
+WL_EXPORT int
+wl_display_init_upgrade(struct wl_display *display, uint32_t max_version)
+{
+	if (max_version > (uint32_t)wl_display_upgrade_interface.version)
+		max_version = wl_display_upgrade_interface.version;
+	display->max_upgrade_version = max_version;
+	if (!wl_global_create(display, &wl_display_upgrade_interface, 1, NULL, bind_upgrade))
+		return -1;
+	return 0;
+}
+
 /** \cond INTERNAL */
 
 /** Initialize a wl_priv_signal object