bsnmpd: Return the correct uptime.

Do not assume that the kernel boot time is invariant. It is not. FreeBSD
uses the formula:
	wall_time = boot_time + uptime
where uptime is monotinically increasing and boot_time is adjusted to
get the proper time of day.  FreeBSD offers a way to retrieve the uptime
directly, so use that instead of trying to compute it by subtracting
boot_time from wall_time.

Sponsored by:		Netflix
Reviewed by:		cy@
Differential Revision:	https://reviews.freebsd.org/D30114

1 files changed, 7 insertions, 30 deletions

diff --git a/usr.sbin/bsnmpd/modules/snmp_hostres/hostres_scalars.c b/usr.sbin/bsnmpd/modules/snmp_hostres/hostres_scalars.c
index 6634ae271a45..872b8a5da329 100644
--- a/usr.sbin/bsnmpd/modules/snmp_hostres/hostres_scalars.c
+++ b/usr.sbin/bsnmpd/modules/snmp_hostres/hostres_scalars.c
@@ -47,9 +47,6 @@
 #include "hostres_oid.h"
 #include "hostres_tree.h"
 
-/* boot timestamp in centi-seconds */
-static uint64_t kernel_boot;
-
 /* physical memory size in Kb */
 static uint64_t phys_mem_size;
 
@@ -76,39 +73,19 @@ fini_scalars(void)
 static int
 OS_getSystemUptime(uint32_t *ut)
 {
-	struct timeval right_now;
-	uint64_t now;
-
-	if (kernel_boot == 0) {
-		/* first time, do the sysctl */
-		struct timeval kernel_boot_timestamp;
-		int mib[2] = { CTL_KERN, KERN_BOOTTIME };
-		size_t len = sizeof(kernel_boot_timestamp);
-
-		if (sysctl(mib, nitems(mib), &kernel_boot_timestamp,
-		    &len, NULL, 0) == -1) {
-			syslog(LOG_ERR, "sysctl KERN_BOOTTIME failed: %m");
-			return (SNMP_ERR_GENERR);
-		}
+	uint64_t uptime;
+	struct timespec ts;
 
-		HRDBG("boot timestamp from kernel: {%lld, %ld}",
-		    (long long)kernel_boot_timestamp.tv_sec,
-		    (long)kernel_boot_timestamp.tv_usec);
-
-		kernel_boot = ((uint64_t)kernel_boot_timestamp.tv_sec * 100) +
-		    (kernel_boot_timestamp.tv_usec / 10000);
-	}
-
-	if (gettimeofday(&right_now, NULL) < 0) {
-		syslog(LOG_ERR, "gettimeofday failed: %m");
+	if (clock_gettime(CLOCK_UPTIME, &ts)) {
+		syslog(LOG_ERR, "clock_gettime failed: %m");
 		return (SNMP_ERR_GENERR);
 	}
-	now = ((uint64_t)right_now.tv_sec * 100) + (right_now.tv_usec / 10000);
 
-	if (now - kernel_boot > UINT32_MAX)
+	uptime = ts.tv_sec * 100 + ts.tv_nsec / 1000000;
+	if (uptime > UINT32_MAX)
 		*ut = UINT32_MAX;
 	else
-		*ut = now - kernel_boot;
+		*ut = (uint32_t)uptime;
 
 	return (SNMP_ERR_NOERROR);
 }