plugin: plugin_exclusive_loop helper to service one plugin synchronously.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/plugin.c

@@ -1053,3 +1053,21 @@ void plugin_request_send(struct plugin *plugin,
 	 * pointer here */
 	req->stream = NULL;
 }
+
+void *plugin_exclusive_loop(struct plugin *plugin)
+{
+	void *ret;
+
+	io_conn_out_exclusive(plugin->stdin_conn, true);
+	io_conn_exclusive(plugin->stdout_conn, true);
+
+	/* We don't service timers here, either! */
+	ret = io_loop(NULL, NULL);
+
+	io_conn_out_exclusive(plugin->stdin_conn, false);
+	if (io_conn_exclusive(plugin->stdout_conn, false))
+		fatal("Still io_exclusive after removing plugin %s?",
+		      plugin->cmd);
+
+	return ret;
+}

lightningd/plugin.h

@@ -79,6 +79,14 @@ void json_add_opt_plugins(struct json_stream *response,
 			  const struct plugins *plugins);
 
 
+/**
+ * Used by db hooks which can't have any other I/O while talking to plugin.
+ *
+ * Returns output of io_loop() (ie. whatever gets passed to io_break()
+ * to end exclusive loop).
+ */
+void *plugin_exclusive_loop(struct plugin *plugin);
+
 /**
  * Add a directory to the plugin path to automatically load plugins.
  */