timecounting: add gettime(9), getuptime(9)

time_second and time_uptime are used widely in the tree.  This is a
problem on 32-bit platforms because time_t is 64-bit, so there is a
potential split-read whenever they are used at or below IPL_CLOCK.

Here are two replacement interfaces: gettime(9) and getuptime(9).
The "get" prefix signifies that they do not read the hardware
timecounter, i.e. they are fast and low-res.  The lack of a unit
(e.g. micro, nano) signifies that they yield a plain time_t.

As an optimization on LP64 platforms we can just return time_second or
time_uptime, as a single read is atomic.  On 32-bit platforms we need
to do the lockless read loop and get the values from the timecounter.

In a subsequent diff these will be substituted for time_second and
time_uptime almost everywhere in the kernel.

With input from visa@ and dlg@.

ok kettenis@

1 files changed, 4 insertions, 1 deletions

diff --git a/sys/sys/time.h b/sys/sys/time.h
index e758a64ce07..8d462ce71b7 100644
--- a/sys/sys/time.h
+++ b/sys/sys/time.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: time.h,v 1.51 2020/05/20 17:21:08 cheloha Exp $	*/
+/*	$OpenBSD: time.h,v 1.52 2020/06/22 21:16:07 cheloha Exp $	*/
 /*	$NetBSD: time.h,v 1.18 1996/04/23 10:29:33 mycroft Exp $	*/
 
 /*
@@ -298,6 +298,9 @@ void	nanoboottime(struct timespec *);
 void	binruntime(struct bintime *);
 void	nanoruntime(struct timespec *);
 
+time_t	gettime(void);
+time_t	getuptime(void);
+
 struct proc;
 int	clock_gettime(struct proc *, clockid_t, struct timespec *);