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, 13 insertions, 3 deletions

diff --git a/share/man/man9/microtime.9 b/share/man/man9/microtime.9
index fc69d8ae607..f8904c6f6a0 100644
--- a/share/man/man9/microtime.9
+++ b/share/man/man9/microtime.9
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: microtime.9,v 1.20 2020/05/20 17:21:07 cheloha Exp $
+.\"	$OpenBSD: microtime.9,v 1.21 2020/06/22 21:16:07 cheloha Exp $
 .\"     $NetBSD: microtime.9,v 1.2 1999/03/16 00:40:47 garbled Exp $
 .\"
 .\" Copyright (c) 1998 The NetBSD Foundation, Inc.
@@ -28,7 +28,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: May 20 2020 $
+.Dd $Mdocdate: June 22 2020 $
 .Dt MICROTIME 9
 .Os
 .Sh NAME
@@ -46,7 +46,9 @@
 .Nm bintime ,
 .Nm binuptime ,
 .Nm binruntime ,
-.Nm binboottime
+.Nm binboottime ,
+.Nm gettime ,
+.Nm getuptime
 .Nd system clocks
 .Sh SYNOPSIS
 .In sys/time.h
@@ -110,6 +112,14 @@
 .Fo binboottime
 .Fa "struct bintime *tv"
 .Fc
+.Ft time_t
+.Fo gettime
+.Fa "void"
+.Fc
+.Ft time_t
+.Fo getuptime
+.Fa "void"
+.Fc
 .Sh DESCRIPTION
 This family of functions return different system clocks in various formats.
 The "uptime" functions return the monotonically increasing time since boot.