compositor: add plugin-registry

Implement a simple register and lookup for function tables. This is
intended for plugins to expose APIs to other plugins.

It has been very hard to arrange a plugin to be able to call into
another plugin without modifying Weston core to explicitly support each
case. This patch fixes that.

The tests all pass.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Giulio Camuffo <giuliocamuffo@gmail.com>

Makefile.am

@@ -90,6 +90,8 @@ libweston_la_SOURCES =					\
 	libweston/noop-renderer.c			\
 	libweston/pixman-renderer.c			\
 	libweston/pixman-renderer.h			\
+	libweston/plugin-registry.c				\
+	libweston/plugin-registry.h				\
 	libweston/timeline.c				\
 	libweston/timeline.h				\
 	libweston/timeline-object.h			\
@@ -235,6 +237,7 @@ libwestoninclude_HEADERS =			\
 	libweston/compositor-rdp.h		\
 	libweston/compositor-wayland.h		\
 	libweston/compositor-x11.h		\
+	libweston/plugin-registry.h		\
 	libweston/timeline-object.h		\
 	shared/matrix.h				\
 	shared/config-parser.h			\
@@ -1092,6 +1095,7 @@ shared_tests =					\
 	zuctest
 
 module_tests =					\
+	plugin-registry-test.la			\
 	surface-test.la				\
 	surface-global-test.la
 
@@ -1143,6 +1147,10 @@ noinst_PROGRAMS +=			\
 test_module_ldflags = \
 	-module -avoid-version -rpath $(libdir) $(COMPOSITOR_LIBS)
 
+plugin_registry_test_la_SOURCES = tests/plugin-registry-test.c
+plugin_registry_test_la_LDFLAGS = $(test_module_ldflags)
+plugin_registry_test_la_CFLAGS = $(AM_CFLAGS) $(COMPOSITOR_CFLAGS)
+
 surface_global_test_la_SOURCES = tests/surface-global-test.c
 surface_global_test_la_LDFLAGS = $(test_module_ldflags)
 surface_global_test_la_CFLAGS = $(AM_CFLAGS) $(COMPOSITOR_CFLAGS)

libweston/compositor.c

@@ -61,6 +61,7 @@
 #include "shared/timespec-util.h"
 #include "git-version.h"
 #include "version.h"
+#include "plugin-registry.h"
 
 #define DEFAULT_REPAINT_WINDOW 7 /* milliseconds */
 
@@ -4702,6 +4703,8 @@ weston_compositor_create(struct wl_display *display, void *user_data)
 	wl_list_init(&ec->axis_binding_list);
 	wl_list_init(&ec->debug_binding_list);
 
+	wl_list_init(&ec->plugin_api_list);
+
 	weston_plane_init(&ec->primary_plane, ec, 0, 0);
 	weston_compositor_stack_plane(ec, &ec->primary_plane, NULL);
 
@@ -4947,6 +4950,9 @@ weston_compositor_destroy(struct weston_compositor *compositor)
 
 	if (compositor->backend)
 		compositor->backend->destroy(compositor);
+
+	weston_plugin_api_destroy_list(compositor);
+
 	free(compositor);
 }
 

libweston/compositor.h

@@ -783,6 +783,8 @@ struct weston_compositor {
 
 	struct weston_launcher *launcher;
 
+	struct wl_list plugin_api_list; /* struct weston_plugin_api::link */
+
 	uint32_t output_id_pool;
 
 	struct xkb_rule_names xkb_names;

libweston/plugin-registry.c

@@ -0,0 +1,156 @@
+/*
+ * Copyright (C) 2016 DENSO CORPORATION
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <assert.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "compositor.h"
+#include "plugin-registry.h"
+
+struct weston_plugin_api {
+	struct wl_list link;     /**< in weston_compositor::plugin_api_list */
+
+	char *api_name;          /**< The search key */
+	const void *vtable;      /**< The function table */
+	size_t vtable_size;      /**< Size of the function table in bytes */
+};
+
+/** Register an implementation of an API
+ *
+ * \param compositor The compositor instance.
+ * \param api_name The API name which other plugins use to find the
+ * implementation.
+ * \param vtable Pointer to the function table of the API.
+ * \param vtable_size Size of the function table in bytes.
+ * \return 0 on success, -1 on error, -2 if api_name already registered
+ *
+ * This call makes the given vtable to be reachable via
+ * weston_plugin_api_get(). Calls through the vtable may start happening
+ * as soon as the caller returns after success. Argument vtable must not be
+ * NULL. Argument api_name must be non-NULL and non-zero length.
+ *
+ * You can increase the function table size without breaking the ABI.
+ * To cater for ABI breaks, it is recommended to have api_name include a
+ * version number.
+ *
+ * A registered API cannot be unregistered. However, calls through a
+ * registered API must not be made from the compositor destroy signal handlers.
+ */
+WL_EXPORT int
+weston_plugin_api_register(struct weston_compositor *compositor,
+			   const char *api_name,
+			   const void *vtable,
+			   size_t vtable_size)
+{
+	struct weston_plugin_api *wpa;
+
+	assert(api_name);
+	assert(strlen(api_name) > 0);
+	assert(vtable);
+
+	if (!api_name || !vtable || strlen(api_name) == 0)
+		return -1;
+
+	wl_list_for_each(wpa, &compositor->plugin_api_list, link)
+		if (strcmp(wpa->api_name, api_name) == 0)
+			return -2;
+
+	wpa = zalloc(sizeof(*wpa));
+	if (!wpa)
+		return -1;
+
+	wpa->api_name = strdup(api_name);
+	wpa->vtable = vtable;
+	wpa->vtable_size = vtable_size;
+
+	if (!wpa->api_name) {
+		free(wpa);
+
+		return -1;
+	}
+
+	wl_list_insert(&compositor->plugin_api_list, &wpa->link);
+	weston_log("Registered plugin API '%s' of size %zd\n",
+		   wpa->api_name, wpa->vtable_size);
+
+	return 0;
+}
+
+/** Internal function to free registered APIs
+ *
+ * \param compositor The compositor instance.
+ */
+void
+weston_plugin_api_destroy_list(struct weston_compositor *compositor)
+{
+	struct weston_plugin_api *wpa, *tmp;
+
+	wl_list_for_each_safe(wpa, tmp, &compositor->plugin_api_list, link) {
+		free(wpa->api_name);
+		wl_list_remove(&wpa->link);
+		free(wpa);
+	}
+}
+
+/** Fetch the implementation of an API
+ *
+ * \param compositor The compositor instance.
+ * \param api_name The name of the API to search for.
+ * \param vtable_size The expected function table size in bytes.
+ * \return Pointer to the function table, or NULL on error.
+ *
+ * Find the function table corresponding to api_name. The vtable_size here
+ * must be less or equal to the vtable_size given in the corresponding
+ * weston_plugin_api_register() call made by the implementing plugin.
+ *
+ * Calls can be made through the function table immediately. However, calls
+ * must not be made from or after the compositor destroy signal handler.
+ */
+WL_EXPORT const void *
+weston_plugin_api_get(struct weston_compositor *compositor,
+		      const char *api_name,
+		      size_t vtable_size)
+{
+	struct weston_plugin_api *wpa;
+
+	assert(api_name);
+	if (!api_name)
+		return NULL;
+
+	wl_list_for_each(wpa, &compositor->plugin_api_list, link) {
+		if (strcmp(wpa->api_name, api_name) != 0)
+			continue;
+
+		if (vtable_size <= wpa->vtable_size)
+			return wpa->vtable;
+
+		return NULL;
+	}
+
+	return NULL;
+}

libweston/plugin-registry.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2016 DENSO CORPORATION
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef WESTON_PLUGIN_REGISTRY_H
+#define WESTON_PLUGIN_REGISTRY_H
+
+#include <stddef.h>
+
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
+struct weston_compositor;
+
+int
+weston_plugin_api_register(struct weston_compositor *compositor,
+			   const char *api_name,
+			   const void *vtable,
+			   size_t vtable_size);
+
+const void *
+weston_plugin_api_get(struct weston_compositor *compositor,
+		      const char *api_name,
+		      size_t vtable_size);
+
+void
+weston_plugin_api_destroy_list(struct weston_compositor *compositor);
+
+#ifdef  __cplusplus
+}
+#endif
+
+#endif /* WESTON_PLUGIN_REGISTRY_H */

tests/plugin-registry-test.c

@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2016 DENSO CORPORATION
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <assert.h>
+
+#include "compositor.h"
+#include "plugin-registry.h"
+
+static void
+dummy_func(void)
+{
+}
+
+static const struct my_api {
+	void (*func1)(void);
+	void (*func2)(void);
+	void (*func3)(void);
+} my_test_api = {
+	dummy_func,
+	dummy_func,
+	dummy_func,
+};
+
+#define MY_API_NAME "test_my_api_v1"
+
+static void
+init_tests(struct weston_compositor *compositor)
+{
+	assert(weston_plugin_api_get(compositor, MY_API_NAME,
+				     sizeof(my_test_api)) == NULL);
+
+	assert(weston_plugin_api_register(compositor, MY_API_NAME, &my_test_api,
+					  sizeof(my_test_api)) == 0);
+
+	assert(weston_plugin_api_register(compositor, MY_API_NAME, &my_test_api,
+					  sizeof(my_test_api)) == -2);
+
+	assert(weston_plugin_api_get(compositor, MY_API_NAME,
+				     sizeof(my_test_api)) == &my_test_api);
+
+	assert(weston_plugin_api_register(compositor, "another", &my_test_api,
+					  sizeof(my_test_api)) == 0);
+}
+
+static void
+runtime_tests(void *data)
+{
+	struct weston_compositor *compositor = data;
+	const struct my_api *api;
+	size_t sz = sizeof(struct my_api);
+
+	assert(weston_plugin_api_get(compositor, MY_API_NAME, sz) ==
+				     &my_test_api);
+
+	assert(weston_plugin_api_get(compositor, MY_API_NAME, sz - 4) ==
+				     &my_test_api);
+
+	assert(weston_plugin_api_get(compositor, MY_API_NAME, sz + 4) == NULL);
+
+	api = weston_plugin_api_get(compositor, MY_API_NAME, sz);
+	assert(api && api->func2 == dummy_func);
+
+	wl_display_terminate(compositor->wl_display);
+}
+
+WL_EXPORT int
+module_init(struct weston_compositor *compositor, int *argc, char *argv[])
+{
+	struct wl_event_loop *loop;
+
+	init_tests(compositor);
+
+	loop = wl_display_get_event_loop(compositor->wl_display);
+	wl_event_loop_add_idle(loop, runtime_tests, compositor);
+
+	return 0;
+}