Split native collector into it's component parts and make them enablable.

Last login is disabled by default as it's broken on ubuntu 12.04
Interrupts is disabled by default as it's very granular and we'll have total interrupts from /proc/stat

Allow ignoring devices from diskstats, ignore ram and loop devices by default.

Use glog for logging.

collector/meminfo.go

@@ -0,0 +1,101 @@
+// +build !nomeminfo
+
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/golang/glog"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	procMemInfo = "/proc/meminfo"
+)
+
+var (
+	memInfoMetrics = map[string]prometheus.Gauge{}
+)
+
+type meminfoCollector struct {
+	registry prometheus.Registry
+	config   Config
+}
+
+func init() {
+	Factories["meminfo"] = NewMeminfoCollector
+}
+
+// Takes a config struct and prometheus registry and returns a new Collector exposing
+// memory stats.
+func NewMeminfoCollector(config Config, registry prometheus.Registry) (Collector, error) {
+	c := meminfoCollector{
+		config:   config,
+		registry: registry,
+	}
+	return &c, nil
+}
+
+func (c *meminfoCollector) Update() (updates int, err error) {
+	memInfo, err := getMemInfo()
+	if err != nil {
+		return updates, fmt.Errorf("Couldn't get meminfo: %s", err)
+	}
+	glog.V(1).Infof("Set node_mem: %#v", memInfo)
+	for k, v := range memInfo {
+		if _, ok := memInfoMetrics[k]; !ok {
+			memInfoMetrics[k] = prometheus.NewGauge()
+			c.registry.Register(
+				"node_memory_"+k,
+				k+" from /proc/meminfo",
+				prometheus.NilLabels,
+				memInfoMetrics[k],
+			)
+		}
+		updates++
+		memInfoMetrics[k].Set(nil, v)
+	}
+	return updates, err
+}
+
+func getMemInfo() (map[string]float64, error) {
+	file, err := os.Open(procMemInfo)
+	if err != nil {
+		return nil, err
+	}
+	return parseMemInfo(file)
+}
+
+func parseMemInfo(r io.ReadCloser) (map[string]float64, error) {
+	defer r.Close()
+	memInfo := map[string]float64{}
+	scanner := bufio.NewScanner(r)
+	re := regexp.MustCompile("\\((.*)\\)")
+	for scanner.Scan() {
+		line := scanner.Text()
+		parts := strings.Fields(string(line))
+		fv, err := strconv.ParseFloat(parts[1], 64)
+		if err != nil {
+			return nil, fmt.Errorf("Invalid value in meminfo: %s", err)
+		}
+		switch len(parts) {
+		case 2: // no unit
+		case 3: // has unit, we presume kB
+			fv *= 1024
+		default:
+			return nil, fmt.Errorf("Invalid line in %s: %s", procMemInfo, line)
+		}
+		key := parts[0][:len(parts[0])-1] // remove trailing : from key
+		// Active(anon) -> Active_anon
+		key = re.ReplaceAllString(key, "_${1}")
+		memInfo[key] = fv
+	}
+	return memInfo, nil
+
+}