Add openbsd meminfo (#724)

* Implements meminfo collector for OpenBSD

This is a rework of #151.

* Fix CGO import

* Add some useful metrics

* Rename total -> size for normalization

collector/meminfo.go

@@ -11,7 +11,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// +build darwin dragonfly freebsd linux
+// +build darwin dragonfly freebsd linux openbsd
 // +build !nomeminfo
 
 package collector

collector/meminfo_openbsd.go

@@ -0,0 +1,65 @@
+// Copyright 2015 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build openbsd
+// +build !nomeminfo
+
+package collector
+
+import (
+	"fmt"
+)
+
+/*
+#include <sys/param.h>
+#include <sys/types.h>
+#include <sys/sysctl.h>
+
+int
+sysctl_uvmexp(struct uvmexp *uvmexp)
+{
+        static int uvmexp_mib[] = {CTL_VM, VM_UVMEXP};
+        size_t sz = sizeof(struct uvmexp);
+
+        if(sysctl(uvmexp_mib, 2, uvmexp, &sz, NULL, 0) < 0)
+                return -1;
+
+        return 0;
+}
+
+*/
+import "C"
+
+func (c *meminfoCollector) getMemInfo() (map[string]float64, error) {
+	var uvmexp C.struct_uvmexp
+
+	if _, err := C.sysctl_uvmexp(&uvmexp); err != nil {
+		return nil, fmt.Errorf("sysctl CTL_VM VM_UVMEXP failed: %v", err)
+	}
+
+	ps := uvmexp.pagesize
+
+	// see uvm(9)
+	return map[string]float64{
+		"active_bytes":                  float64(ps * uvmexp.active),
+		"cache_bytes":                   float64(ps * uvmexp.vnodepages),
+		"free_bytes":                    float64(ps * uvmexp.free),
+		"inactive_bytes":                float64(ps * uvmexp.inactive),
+		"size_bytes":                    float64(ps * uvmexp.npages),
+		"swap_size_bytes":               float64(ps * uvmexp.swpages),
+		"swap_used_bytes":               float64(ps * uvmexp.swpgonly),
+		"swapped_in_pages_bytes_total":  float64(ps * uvmexp.pgswapin),
+		"swapped_out_pages_bytes_total": float64(ps * uvmexp.pgswapout),
+		"wired_bytes":                   float64(ps * uvmexp.wired),
+	}, nil
+}