Update cpu collector for OpenBSD 6.4 (#1094)

Starting with (not yet released) OpenBSD 6.4, sysctl KERN_CPTIME2 will
return ENODEV for offline CPUs.

SMT siblings are reported as offline when hw.smt is disabled, which is
the default since one of the later Spectre variants. So this might
affect a few systems.

For more details see:
https://cvsweb.openbsd.org/src/sys/kern/kern_sysctl.c#rev1.348

Signed-off-by: Ralf Horstmann <ralf+github@ackstorm.de>

2 files changed, 5 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e02195f..7c99743 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ Darwin meminfo metrics have been renamed to match Prometheus conventions. #1060
 * [BUGFIX] Handle vanishing PIDs #1043
 * [BUGFIX] Correctly cast Darwin memory info #1060
 * [BUGFIX] Filter systemd units in Go for compatibility with older versions #1083
+* [BUGFIX] Update cpu collector for OpenBSD 6.4
 
 ## 0.16.0 / 2018-05-15
 
diff --git a/collector/cpu_openbsd.go b/collector/cpu_openbsd.go
index e9b102f..996e50e 100644
--- a/collector/cpu_openbsd.go
+++ b/collector/cpu_openbsd.go
@@ -59,10 +59,12 @@ func (c *cpuCollector) Update(ch chan<- prometheus.Metric) (err error) {
         var cp_time [][C.CPUSTATES]C.int64_t
         for i := 0; i < int(ncpus); i++ {
                 cp_timeb, err := unix.SysctlRaw("kern.cp_time2", i)
-                if err != nil {
+                if err != nil && err != unix.ENODEV {
                         return err
                 }
-                cp_time = append(cp_time, *(*[C.CPUSTATES]C.int64_t)(unsafe.Pointer(&cp_timeb[0])))
+                if err != unix.ENODEV {
+                        cp_time = append(cp_time, *(*[C.CPUSTATES]C.int64_t)(unsafe.Pointer(&cp_timeb[0])))
+                }
         }
 
         for cpu, time := range cp_time {