lightningd/plugin.c: Add important plugins, which if they terminate, lightningd also terminates.

Changelog-Added: New option `--important-plugin` loads a plugin is so important that if it dies, `lightningd` will exit rather than continue.  You can still `--disable-plugin` it, however, which trumps `--important-plugin` and it will not be started at all.

lightningd/plugin.c

@@ -53,6 +53,7 @@ struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 	p->startup = true;
 	p->json_cmds = tal_arr(p, struct command *, 0);
 	p->blacklist = tal_arr(p, const char *, 0);
+	p->shutdown = false;
 	uintmap_init(&p->pending_requests);
 	memleak_add_helper(p, memleak_help_pending_requests);
 
@@ -62,6 +63,9 @@ struct plugins *plugins_new(const tal_t *ctx, struct log_book *log_book,
 void plugins_free(struct plugins *plugins)
 {
 	struct plugin *p;
+
+	plugins->shutdown = true;
+
 	/* Plugins are usually the unit of allocation, and they are internally
 	 * consistent, so let's free each plugin first. */
 	while (!list_empty(&plugins->plugins)) {
@@ -105,6 +109,7 @@ struct command_result *plugin_register_all_complete(struct lightningd *ld,
 static void destroy_plugin(struct plugin *p)
 {
 	struct plugin_rpccall *call;
+
 	plugin_hook_unregister_all(p);
 	list_del(&p->list);
 
@@ -118,10 +123,23 @@ static void destroy_plugin(struct plugin *p)
 	/* Don't call this if we're still parsing options! */
 	if (p->plugin_state != UNCONFIGURED)
 		check_plugins_resolved(p->plugins);
+
+	/* If we are shutting down, do not continue to checking if
+	 * the dying plugin is important.  */
+	if (p->plugins->shutdown)
+		return;
+
+	/* Now check if the dying plugin is important.  */
+	if (p->important) {
+		log_broken(p->log,
+			   "Plugin marked as important, "
+			   "shutting down lightningd!");
+		lightningd_exit(p->plugins->ld, 1);
+	}
 }
 
 struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
-			       struct command *start_cmd)
+			       struct command *start_cmd, bool important)
 {
 	struct plugin *p, *p_temp;
 
@@ -130,6 +148,9 @@ struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
 		if (streq(path, p_temp->cmd)) {
 			if (taken(path))
 				tal_free(path);
+		 	/* If added as "important", upgrade to "important".  */
+			if (important)
+				p_temp->important = true;
 			return NULL;
 		}
 	}
@@ -153,6 +174,8 @@ struct plugin *plugin_register(struct plugins *plugins, const char* path TAKES,
 	list_add_tail(&plugins->plugins, &p->list);
 	tal_add_destructor(p, destroy_plugin);
 	list_head_init(&p->pending_rpccalls);
+
+	p->important = important;
 	return p;
 }
 
@@ -186,6 +209,8 @@ void plugin_blacklist(struct plugins *plugins, const char *name)
 			log_info(plugins->log, "%s: disabled via disable-plugin",
 				 p->cmd);
 			list_del_from(&plugins->plugins, &p->list);
+			/* disable-plugin overrides important-plugin.  */
+			p->important = false;
 			tal_free(p);
 		}
 	}
@@ -1188,7 +1213,7 @@ char *add_plugin_dir(struct plugins *plugins, const char *dir, bool error_ok)
 			log_info(plugins->log, "%s: disabled via disable-plugin",
 				 fullpath);
 		} else {
-			p = plugin_register(plugins, fullpath, NULL);
+			p = plugin_register(plugins, fullpath, NULL, false);
 			if (!p && !error_ok)
 				return tal_fmt(NULL, "Failed to register %s: %s",
 				               fullpath, strerror(errno));
@@ -1396,24 +1421,35 @@ void plugins_config(struct plugins *plugins)
 	plugins->startup = false;
 }
 
-void json_add_opt_plugins(struct json_stream *response,
-			  const struct plugins *plugins)
+/** json_add_opt_plugins_array
+ *
+ * @brief add a named array of plugins to the given response,
+ * depending on whether it is important or not important.
+ *
+ * @param response - the `json_stream` to write into.
+ * @param name - the field name of the array.
+ * @param plugins - the plugins object to query.
+ * @param important - match the `important` setting of the
+ * plugins to be added.
+ */
+static
+void json_add_opt_plugins_array(struct json_stream *response,
+				const char *name,
+				const struct plugins *plugins,
+				bool important)
 {
 	struct plugin *p;
-	struct plugin_opt *opt;
 	const char *plugin_name;
+	struct plugin_opt *opt;
 	const char *opt_name;
 
-	/* DEPRECATED: duplicated JSON "plugin" entries */
-	if (deprecated_apis) {
-		list_for_each(&plugins->plugins, p, list) {
-			json_add_string(response, "plugin", p->cmd);
-		}
-	}
-
 	/* we output 'plugins' and their options as an array of substructures */
-	json_array_start(response, "plugins");
+	json_array_start(response, name);
 	list_for_each(&plugins->plugins, p, list) {
+		/* Skip if not matching.  */
+		if (p->important != important)
+			continue;
+
 		json_object_start(response, NULL);
 		json_add_string(response, "path", p->cmd);
 
@@ -1444,6 +1480,23 @@ void json_add_opt_plugins(struct json_stream *response,
 	json_array_end(response);
 }
 
+void json_add_opt_plugins(struct json_stream *response,
+			  const struct plugins *plugins)
+{
+	struct plugin *p;
+
+	json_add_opt_plugins_array(response, "plugins", plugins, false);
+	json_add_opt_plugins_array(response, "important-plugins", plugins, true);
+
+	/* DEPRECATED: duplicated JSON "plugin" entries */
+	if (deprecated_apis) {
+		list_for_each(&plugins->plugins, p, list) {
+			json_add_string(response, p->important ? "important-plugin" : "plugin", p->cmd);
+		}
+	}
+
+}
+
 void json_add_opt_disable_plugins(struct json_stream *response,
 				  const struct plugins *plugins)
 {
@@ -1546,7 +1599,6 @@ static void mark_plugin_destroyed(const struct plugin *unused,
 	pd->plugin = NULL;
 }
 
-
 struct plugin_destroyed *plugin_detect_destruction(const struct plugin *plugin)
 {
 	struct plugin_destroyed *pd = tal(NULL, struct plugin_destroyed);