From 3db15a3f80f193826e144b1944727a65c13340fe Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Sat, 25 Jul 2015 18:23:10 +0200
Subject: kern: add boot-time clock, use it for time stamps

The kernel keeps track of task and thread creation times by saving a
time stamp.  Previously, the real-time clock was used for this.  When
the real-time clock is changed, however, the reference frame for the
time stamps is lost.  This surfaced in Hurd systems reporting
spuriously long uptimes.

Fix this by creating a boot-time clock and use it as reference frame
for the time stamps.

* kern/mach_clock.c (clock_boottime_offset): Create clock by keeping
track of the offset from the real-time.
(clock_boottime_update): New function.
(record_time_stamp): Use the boot-time clock for time stamps.
(read_time_stamp): New function to convert it back to real-time.
(host_set_time): Call `clock_boottime_update'.
* kern/mach_clock.h (record_time_stamp): Amend comment.
(read_time_stamp): New declaration.
* kern/task.c (task_info): Use `read_time_stamp'.
* kern/thread.c (thread_info): Likewise.
---
 kern/mach_clock.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

(limited to 'kern/mach_clock.h')

diff --git a/kern/mach_clock.h b/kern/mach_clock.h
index 89fd335..1af0cda 100644
--- a/kern/mach_clock.h
+++ b/kern/mach_clock.h
@@ -86,9 +86,18 @@ extern boolean_t reset_timeout(timer_elt_t telt);
 
 extern void init_timeout (void);
 
-/* Read the current time into STAMP.  */
+/*
+ * Record a timestamp in STAMP.  Records values in the boot-time clock
+ * frame.
+ */
 extern void record_time_stamp (time_value_t *stamp);
 
+/*
+ * Read a timestamp in STAMP into RESULT.  Returns values in the
+ * real-time clock frame.
+ */
+extern void read_time_stamp (time_value_t *stamp, time_value_t *result);
+
 extern kern_return_t host_get_time(
    host_t host,
    time_value_t *current_time);
-- 
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