Turn the wallclock module into a subsystem.

(This may be slightly gratuitous.)

src/app/main/main.c

@@ -1394,7 +1394,6 @@ tor_run_main(const tor_main_configuration_t *tor_cfg)
 
   init_protocol_warning_severity_level();
 
-  update_approx_time(time(NULL));
   tor_compress_init();
   monotime_init();
 

src/app/main/subsystem_list.c

@@ -9,9 +9,10 @@
 #include "lib/cc/torint.h"
 
 #include "lib/err/torerr_sys.h"
+#include "lib/log/log_sys.h"
 #include "lib/process/winprocess_sys.h"
 #include "lib/thread/thread_sys.h"
-#include "lib/log/log_sys.h"
+#include "lib/wallclock/wallclock_sys.h"
 
 #include <stddef.h>
 
@@ -21,6 +22,7 @@
 const subsys_fns_t *tor_subsystems[] = {
   &sys_winprocess,
   &sys_torerr,
+  &sys_wallclock,
   &sys_threads,
   &sys_logging,
 };

src/lib/wallclock/.may_include

@@ -3,4 +3,5 @@ lib/cc/*.h
 lib/err/*.h
 lib/wallclock/*.h
 lib/string/*.h
+lib/subsys/*.h
 lib/testsupport/*.h

src/lib/wallclock/approx_time.c

@@ -9,7 +9,9 @@
  **/
 
 #include "orconfig.h"
+#include "lib/subsys/subsys.h"
 #include "lib/wallclock/approx_time.h"
+#include "lib/wallclock/wallclock_sys.h"
 
 /* =====
  * Cached time
@@ -41,3 +43,17 @@ update_approx_time(time_t now)
   cached_approx_time = now;
 }
 #endif /* !defined(TIME_IS_FAST) */
+
+static int
+init_wallclock_subsys(void)
+{
+  update_approx_time(time(NULL));
+  return 0;
+}
+
+const subsys_fns_t sys_wallclock = {
+  .name = "wallclock",
+  .supported = true,
+  .level = -99,
+  .initialize = init_wallclock_subsys,
+};

src/lib/wallclock/include.am

@@ -19,4 +19,5 @@ noinst_HEADERS +=					\
 	src/lib/wallclock/approx_time.h			\
 	src/lib/wallclock/timeval.h			\
 	src/lib/wallclock/time_to_tm.h			\
-	src/lib/wallclock/tor_gettimeofday.h
+	src/lib/wallclock/tor_gettimeofday.h		\
+	src/lib/wallclock/wallclock_sys.h

src/lib/wallclock/wallclock_sys.h

@@ -0,0 +1,14 @@
+/* Copyright (c) 2018, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file wallclock_sys.h
+ * \brief Declare subsystem object for the wallclock module.
+ **/
+
+#ifndef TOR_WALLCLOCK_SYS_H
+#define TOR_WALLCLOCK_SYS_H
+
+extern const struct subsys_fns_t sys_wallclock;
+
+#endif /* !defined(TOR_WALLCLOCK_SYS_H) */