-int clocksource_register(struct clocksource*);
-void clocksource_reselect(void);
-struct clocksource* clocksource_get_next(void);
+extern int clocksource_register(struct clocksource*);
+extern struct clocksource* clocksource_get_next(void);
+extern void clocksource_change_rating(struct clocksource *cs, int rating);
+
+#ifdef CONFIG_GENERIC_TIME_VSYSCALL
+extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
+#else
+static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
+{
+}
+#endif