Add the CLOCK_BOOTTIME clockid for use with clock_gettime(2)

and put it to use in userspace in lieu of the kern.boottime
sysctl.

Its absolute value is the time that has elapsed since the
system booted, i.e., the system uptime.

Use in top(1), w(1), and snmpd(8) eliminates a race with
settimeofday(2), adjtime(2), etc. inherent to deriving the
system uptime via the kern.boottime sysctl.

Product of a great deal of discussion/revision with jca@, tb@,
and guenther@.

ok tb@ jca@ guenther@ dlg@ mlarkin@ tom@

2 files changed, 9 insertions, 23 deletions

diff --git a/usr.bin/top/display.c b/usr.bin/top/display.c
index 30b20b06489..2b2e678b63f 100644
--- a/usr.bin/top/display.c
+++ b/usr.bin/top/display.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: display.c,v 1.52 2017/03/15 04:24:14 deraadt Exp $	 */
+/* $OpenBSD: display.c,v 1.53 2017/12/18 05:51:53 cheloha Exp $	 */
 
 /*
  *  Top users/processes display for Unix
@@ -57,7 +57,6 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <sys/sysctl.h>
 
 #include "screen.h"		/* interface to screen package */
 #include "layout.h"		/* defines for screen position layout */
@@ -209,22 +208,15 @@ display_init(struct statics * statics)
 static void
 format_uptime(char *buf, size_t buflen)
 {
-	time_t now, uptime;
+	time_t uptime;
 	int days, hrs, mins;
-	int mib[2];
-	size_t size;
-	struct timeval boottime;
+	struct timespec boottime;
 
-	now = time(NULL);
 	/*
 	 * Print how long system has been up.
-	 * (Found by getting "boottime" from the kernel)
 	 */
-	mib[0] = CTL_KERN;
-	mib[1] = KERN_BOOTTIME;
-	size = sizeof(boottime);
-	if (sysctl(mib, 2, &boottime, &size, NULL, 0) != -1) {
-		uptime = now - boottime.tv_sec;
+	if (clock_gettime(CLOCK_BOOTTIME, &boottime) != -1) {
+		uptime = boottime.tv_sec;
 		uptime += 30;
 		days = uptime / (3600 * 24);
 		uptime %= (3600 * 24);
diff --git a/usr.bin/w/w.c b/usr.bin/w/w.c
index e85784a49b6..5642197f418 100644
--- a/usr.bin/w/w.c
+++ b/usr.bin/w/w.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: w.c,v 1.64 2017/12/14 18:03:03 jasper Exp $	*/
+/*	$OpenBSD: w.c,v 1.65 2017/12/18 05:51:53 cheloha Exp $	*/
 
 /*-
  * Copyright (c) 1980, 1991, 1993, 1994
@@ -66,7 +66,6 @@
 
 #include "extern.h"
 
-struct timeval	boottime;
 struct utmp	utmp;
 struct winsize	ws;
 kvm_t	       *kd;
@@ -426,10 +425,9 @@ static void
 pr_header(time_t *nowp, int nusers)
 {
 	double avenrun[3];
+	struct timespec boottime;
 	time_t uptime;
 	int days, hrs, i, mins;
-	int mib[2];
-	size_t size;
 	char buf[256];
 
 	/*
@@ -441,13 +439,9 @@ pr_header(time_t *nowp, int nusers)
 
 	/*
 	 * Print how long system has been up.
-	 * (Found by getting "boottime" from the kernel)
 	 */
-	mib[0] = CTL_KERN;
-	mib[1] = KERN_BOOTTIME;
-	size = sizeof(boottime);
-	if (sysctl(mib, 2, &boottime, &size, NULL, 0) != -1) {
-		uptime = now - boottime.tv_sec;
+	if (clock_gettime(CLOCK_BOOTTIME, &boottime) != -1) {
+		uptime = boottime.tv_sec;
 		if (uptime > 59) {
 			uptime += 30;
 			days = uptime / SECSPERDAY;