Implement meminfo on BSD without cgo

This removes some error handling, which should be fine. If the calls
fail, we will get the zeroes, which is a safe enough fallback.
Additionally, if the first sysctl (page_size) succeeded it is unlikely
that other ones will fail.

collector/meminfo_bsd.go

@@ -17,30 +17,12 @@
 package collector
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/prometheus/client_golang/prometheus"
+	"golang.org/x/sys/unix"
 )
 
-/*
-#include <stddef.h>
-#include <sys/sysctl.h>
-
-int _sysctl(const char* name) {
-        int val;
-        size_t size = sizeof(val);
-        int res = sysctlbyname(name, &val, &size, NULL, 0);
-        if (res == -1) {
-                return -1;
-        }
-        if (size != sizeof(val)) {
-                return -2;
-        }
-        return val;
-}
-*/
-import "C"
-
 const (
 	memInfoSubsystem = "memory"
 )
@@ -58,34 +40,20 @@ func NewMeminfoCollector() (Collector, error) {
 }
 
 func (c *meminfoCollector) Update(ch chan<- prometheus.Metric) (err error) {
-	var pages map[string]C.int
-	pages = make(map[string]C.int)
-
-	size := C._sysctl(C.CString("vm.stats.vm.v_page_size"))
-	if size == -1 {
-		return errors.New("sysctl(vm.stats.vm.v_page_size) failed")
-	}
-	if size == -2 {
-		return errors.New("sysctl(vm.stats.vm.v_page_size) failed, wrong buffer size")
-	}
-
-	pages["active"] = C._sysctl(C.CString("vm.stats.vm.v_active_count"))
-	pages["inactive"] = C._sysctl(C.CString("vm.stats.vm.v_inactive_count"))
-	pages["wire"] = C._sysctl(C.CString("vm.stats.vm.v_wire_count"))
-	pages["cache"] = C._sysctl(C.CString("vm.stats.vm.v_cache_count"))
-	pages["free"] = C._sysctl(C.CString("vm.stats.vm.v_free_count"))
-	pages["swappgsin"] = C._sysctl(C.CString("vm.stats.vm.v_swappgsin"))
-	pages["swappgsout"] = C._sysctl(C.CString("vm.stats.vm.v_swappgsout"))
-	pages["total"] = C._sysctl(C.CString("vm.stats.vm.v_page_count"))
+	pages := make(map[string]uint32)
 
-	for key := range pages {
-		if pages[key] == -1 {
-			return errors.New("sysctl() failed for " + key)
-		}
-		if pages[key] == -2 {
-			return errors.New("sysctl() failed for " + key + ", wrong buffer size")
-		}
+	size, err := unix.SysctlUint32("vm.stats.vm.v_page_size")
+	if err != nil {
+		return fmt.Errorf("sysctl(vm.stats.vm.v_page_size) failed: %s", err)
 	}
+	pages["active"], _ = unix.SysctlUint32("vm.stats.vm.v_active_count")
+	pages["inactive"], _ = unix.SysctlUint32("vm.stats.vm.v_inactive_count")
+	pages["wire"], _ = unix.SysctlUint32("vm.stats.vm.v_wire_count")
+	pages["cache"], _ = unix.SysctlUint32("vm.stats.vm.v_cache_count")
+	pages["free"], _ = unix.SysctlUint32("vm.stats.vm.v_free_count")
+	pages["swappgsin"], _ = unix.SysctlUint32("vm.stats.vm.v_swappgsin")
+	pages["swappgsout"], _ = unix.SysctlUint32("vm.stats.vm.v_swappgsout")
+	pages["total"], _ = unix.SysctlUint32("vm.stats.vm.v_page_count")
 
 	for k, v := range pages {
 		ch <- prometheus.MustNewConstMetric(