Add node_filesystem_device_errors_total metric

This metric is the total number of errors occurred when getting stats
for the given device.

collector/filesystem_common.go

@@ -48,6 +48,7 @@ type filesystemCollector struct {
 	ignoredFSTypesPattern     *regexp.Regexp
 	sizeDesc, freeDesc, availDesc,
 	filesDesc, filesFreeDesc, roDesc *prometheus.Desc
+	devErrors *prometheus.CounterVec
 }
 
 type filesystemStats struct {
@@ -102,6 +103,11 @@ func NewFilesystemCollector() (Collector, error) {
 		filesystemLabelNames, nil,
 	)
 
+	devErrors := prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: prometheus.BuildFQName(Namespace, subsystem, "device_errors_total"),
+		Help: "Total number of errors occurred when getting stats for device",
+	}, filesystemLabelNames)
+
 	return &filesystemCollector{
 		ignoredMountPointsPattern: mountPointPattern,
 		ignoredFSTypesPattern:     filesystemsTypesPattern,
@@ -111,6 +117,7 @@ func NewFilesystemCollector() (Collector, error) {
 		filesDesc:                 filesDesc,
 		filesFreeDesc:             filesFreeDesc,
 		roDesc:                    roDesc,
+		devErrors:                 devErrors,
 	}, nil
 }
 
@@ -145,5 +152,6 @@ func (c *filesystemCollector) Update(ch chan<- prometheus.Metric) (err error) {
 			s.ro, s.labelValues...,
 		)
 	}
+	c.devErrors.Collect(ch)
 	return nil
 }

collector/filesystem_linux.go

@@ -52,9 +52,11 @@ func (c *filesystemCollector) GetStats() (stats []filesystemStats, err error) {
 			log.Debugf("Ignoring fs type: %s", mpd.fsType)
 			continue
 		}
+		labelValues := []string{mpd.device, mpd.mountPoint, mpd.fsType}
 		buf := new(syscall.Statfs_t)
 		err := syscall.Statfs(mpd.mountPoint, buf)
 		if err != nil {
+			c.devErrors.WithLabelValues(labelValues...).Inc()
 			log.Debugf("Statfs on %s returned %s",
 				mpd.mountPoint, err)
 			continue
@@ -65,7 +67,6 @@ func (c *filesystemCollector) GetStats() (stats []filesystemStats, err error) {
 			ro = 1
 		}
 
-		labelValues := []string{mpd.device, mpd.mountPoint, mpd.fsType}
 		stats = append(stats, filesystemStats{
 			labelValues: labelValues,
 			size:        float64(buf.Blocks) * float64(buf.Bsize),