timekeeping: Introduce read_boot_clock

Add the new function read_boot_clock to get the exact time the system
has been started. For architectures without support for exact boot
time a new weak function is added that returns 0.  Use the exact boot
time to initialize wall_to_monotonic, or xtime if the read_boot_clock
returned 0.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134811.296703241@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index 53a3216f0d1b..f505988398e6 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -102,6 +102,7 @@ extern struct timespec wall_to_monotonic;
 extern seqlock_t xtime_lock;
 
 extern void read_persistent_clock(struct timespec *ts);
+extern void read_boot_clock(struct timespec *ts);
 extern int update_persistent_clock(struct timespec now);
 extern int no_sync_cmos_clock __read_mostly;
 void timekeeping_init(void);