varlink: add generic impl. of io.systemd.varlink.Ping()

src/shared/varlink-io.systemd.service.c

@@ -16,3 +16,14 @@ VARLINK_DEFINE_INTERFACE(
                 &vl_method_Ping,
                 &vl_method_Reload,
                 &vl_method_SetLogLevel);
+
+int varlink_method_ping(Varlink *link, JsonVariant *parameters, VarlinkMethodFlags flags, void *userdata) {
+        assert(link);
+
+        if (json_variant_elements(parameters) > 0)
+                return varlink_error_invalid_parameter(link, parameters);
+
+        log_debug("Received io.systemd.service.Ping");
+
+        return varlink_reply(link, NULL);
+}

src/shared/varlink-io.systemd.service.h

@@ -1,6 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 #pragma once
 
+#include "varlink.h"
 #include "varlink-idl.h"
 
 extern const VarlinkInterface vl_interface_io_systemd_service;
+
+int varlink_method_ping(Varlink *link, JsonVariant *parameters, VarlinkMethodFlags flags, void *userdata);