[RFC][PATCH 1/6] x86_64: Enable arch-generic vsyscall support.

[john stultz <johnstul@us.ibm.com>]

Provides generic infrastructure for vsyscall-gtod.

Signed-off-by: John Stultz <johnstul@us.ibm.com>

 include/linux/clocksource.h |    2 ++
 kernel/timer.c              |    7 +++++++
 2 files changed, 9 insertions(+)

linux-2.6.18-rc4_timeofday-vsyscall-support_C5.patch
============================================
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index d852024..f554273 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -46,6 +46,7 @@ typedef u64 cycle_t;
  * @shift:		cycle to nanosecond divisor (power of two)
  * @update_callback:	called when safe to alter clocksource values
  * @is_continuous:	defines if clocksource is free-running.
+ * @vread:		vsyscall based read
  * @cycle_interval:	Used internally by timekeeping core, please ignore.
  * @xtime_interval:	Used internally by timekeeping core, please ignore.
  */
@@ -59,6 +60,7 @@ struct clocksource {
 	u32 shift;
 	int (*update_callback)(void);
 	int is_continuous;
+	cycle_t (*vread)(void);
 
 	/* timekeeping specific data, ignore */
 	cycle_t cycle_last, cycle_interval;
diff --git a/kernel/timer.c b/kernel/timer.c
index b650f04..08b4a02 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1023,6 +1023,12 @@ static int __init timekeeping_init_devic
 
 device_initcall(timekeeping_init_device);
 
+#ifdef CONFIG_GENERIC_TIME_VSYSCALL
+extern void update_vsyscall(struct timespec* ts, struct clocksource* c);
+#else
+#define update_vsyscall(now, c)
+#endif
+
 /*
  * If the error is already larger, we look ahead even further
  * to compensate for late or lost adjustments.
@@ -1165,6 +1171,7 @@ static void update_wall_time(void)
 		clock->xtime_nsec = 0;
 		clocksource_calculate_interval(clock, tick_nsec);
 	}
+	update_vsyscall(&xtime, clock);
 }
 
 /*