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/netdev.go

@@ -0,0 +1,125 @@
+// +build !nonetDev
+
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	procNetDev = "/proc/net/dev"
+)
+
+var (
+	netStatsMetrics = map[string]prometheus.Gauge{}
+)
+
+type netDevCollector struct {
+	registry prometheus.Registry
+	config   Config
+}
+
+func init() {
+	Factories["netdev"] = NewNetDevCollector
+}
+
+// Takes a config struct and prometheus registry and returns a new Collector exposing
+// network device stats.
+func NewNetDevCollector(config Config, registry prometheus.Registry) (Collector, error) {
+	c := netDevCollector{
+		config:   config,
+		registry: registry,
+	}
+	return &c, nil
+}
+
+func (c *netDevCollector) Update() (updates int, err error) {
+	netStats, err := getNetStats()
+	if err != nil {
+		return updates, fmt.Errorf("Couldn't get netstats: %s", err)
+	}
+	for direction, devStats := range netStats {
+		for dev, stats := range devStats {
+			for t, value := range stats {
+				key := direction + "_" + t
+				if _, ok := netStatsMetrics[key]; !ok {
+					netStatsMetrics[key] = prometheus.NewGauge()
+					c.registry.Register(
+						"node_network_"+key,
+						t+" "+direction+" from /proc/net/dev",
+						prometheus.NilLabels,
+						netStatsMetrics[key],
+					)
+				}
+				updates++
+				v, err := strconv.ParseFloat(value, 64)
+				if err != nil {
+					return updates, fmt.Errorf("Invalid value %s in netstats: %s", value, err)
+				}
+				netStatsMetrics[key].Set(map[string]string{"device": dev}, v)
+			}
+		}
+	}
+	return updates, err
+}
+
+func getNetStats() (map[string]map[string]map[string]string, error) {
+	file, err := os.Open(procNetDev)
+	if err != nil {
+		return nil, err
+	}
+	return parseNetStats(file)
+}
+
+func parseNetStats(r io.ReadCloser) (map[string]map[string]map[string]string, error) {
+	defer r.Close()
+	netStats := map[string]map[string]map[string]string{}
+	netStats["transmit"] = map[string]map[string]string{}
+	netStats["receive"] = map[string]map[string]string{}
+
+	scanner := bufio.NewScanner(r)
+	scanner.Scan() // skip first header
+	scanner.Scan()
+	parts := strings.Split(string(scanner.Text()), "|")
+	if len(parts) != 3 { // interface + receive + transmit
+		return nil, fmt.Errorf("Invalid header line in %s: %s",
+			procNetDev, scanner.Text())
+	}
+	header := strings.Fields(parts[1])
+	for scanner.Scan() {
+		parts := strings.Fields(string(scanner.Text()))
+		if len(parts) != 2*len(header)+1 {
+			return nil, fmt.Errorf("Invalid line in %s: %s",
+				procNetDev, scanner.Text())
+		}
+
+		dev := parts[0][:len(parts[0])-1]
+		receive, err := parseNetDevLine(parts[1:len(header)+1], header)
+		if err != nil {
+			return nil, err
+		}
+
+		transmit, err := parseNetDevLine(parts[len(header)+1:], header)
+		if err != nil {
+			return nil, err
+		}
+		netStats["transmit"][dev] = transmit
+		netStats["receive"][dev] = receive
+	}
+	return netStats, nil
+}
+
+func parseNetDevLine(parts []string, header []string) (map[string]string, error) {
+	devStats := map[string]string{}
+	for i, v := range parts {
+		devStats[header[i]] = v
+	}
+	return devStats, nil
+}