Fix possibly missing metrics in nfs collector

We should not rely on the availablity of certain nfs metrics at just the
collector start time. Allow new metrics to come in at any point.

collectors/nfsMetric.go

@@ -44,38 +44,6 @@ type nfsCollector struct {
 	data map[string]NfsCollectorData
 }
 
-func (m *nfsCollector) initStats() error {
-	cmd := exec.Command(m.config.Nfsstats, `-l`, `--all`)
-
-	// Wait for cmd end
-	if err := cmd.Wait(); err != nil {
-		return fmt.Errorf("%s initStats(): %w", m.name, err)
-	}
-
-	buffer, err := cmd.Output()
-	if err == nil {
-		for line := range strings.Lines(string(buffer)) {
-			lf := strings.Fields(line)
-			if len(lf) != 5 {
-				continue
-			}
-			if lf[1] == m.version {
-				name := strings.Trim(lf[3], ":")
-				if _, exist := m.data[name]; !exist {
-					value, err := strconv.ParseInt(lf[4], 0, 64)
-					if err == nil {
-						x := m.data[name]
-						x.current = value
-						x.last = value
-						m.data[name] = x
-					}
-				}
-			}
-		}
-	}
-	return err
-}
-
 func (m *nfsCollector) updateStats() error {
 	cmd := exec.Command(m.config.Nfsstats, `-l`, `--all`)
 
@@ -85,27 +53,42 @@ func (m *nfsCollector) updateStats() error {
 	}
 
 	buffer, err := cmd.Output()
-	if err == nil {
-		for line := range strings.Lines(string(buffer)) {
-			lf := strings.Fields(line)
-			if len(lf) != 5 {
-				continue
-			}
-			if lf[1] == m.version {
-				name := strings.Trim(lf[3], ":")
-				if _, exist := m.data[name]; exist {
-					value, err := strconv.ParseInt(lf[4], 0, 64)
-					if err == nil {
-						x := m.data[name]
-						x.last = x.current
-						x.current = value
-						m.data[name] = x
-					}
-				}
-			}
+	if err != nil {
+		return err
+	}
+
+	for name, data := range m.data {
+		m.data[name] = NfsCollectorData{
+			last:    data.current,
+			current: -1,
 		}
 	}
-	return err
+
+	for line := range strings.Lines(string(buffer)) {
+		lf := strings.Fields(line)
+		if len(lf) != 5 {
+			continue
+		}
+		if lf[1] != m.version {
+			continue
+		}
+		name := strings.Trim(lf[3], ":")
+		value, err := strconv.ParseInt(lf[4], 0, 64)
+		if err != nil {
+			return err
+		}
+
+		collectorData, exist := m.data[name]
+		collectorData.current = value
+
+		if !exist {
+			collectorData.last = -1
+		}
+
+		m.data[name] = collectorData
+	}
+
+	return nil
 }
 
 func (m *nfsCollector) MainInit(config json.RawMessage) error {
@@ -130,7 +113,7 @@ func (m *nfsCollector) MainInit(config json.RawMessage) error {
 		return fmt.Errorf("%s Init(): Failed to find nfsstat binary '%s': %w", m.name, m.config.Nfsstats, err)
 	}
 	m.data = make(map[string]NfsCollectorData)
-	if err := m.initStats(); err != nil {
+	if err := m.updateStats(); err != nil {
 		return fmt.Errorf("%s Init(): %w", m.name, err)
 	}
 	m.init = true
@@ -165,8 +148,12 @@ func (m *nfsCollector) Read(interval time.Duration, output chan lp.CCMessage) {
 		if slices.Contains(m.config.ExcludeMetrics, name) {
 			continue
 		}
-		value := data.current - data.last
-		y, err := lp.NewMessage(fmt.Sprintf("%s_%s", prefix, name), m.tags, m.meta, map[string]any{"value": value}, timestamp)
+
+		valueMap := make(map[string]any)
+		if data.current >= 0 && data.last >= 0 {
+			valueMap["value"] = data.current - data.last
+		}
+		y, err := lp.NewMessage(fmt.Sprintf("%s_%s", prefix, name), m.tags, m.meta, valueMap, timestamp)
 		if err == nil {
 			y.AddMeta("version", m.version)
 			output <- y