collector/diskstats: Ignore udev when directory unreadable

Log a single error message when the udev data directory (`/run/udev/data` by
default) is unreadable, and then don't try to get device properties out of it.

Also lower the log level from error to debug when we can't parse the udev files
properly, since these messages would be sent every time the node exporter gets
scraped.

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>

collector/diskstats_linux.go

@@ -77,14 +77,15 @@ func (d *typedFactorDesc) mustNewConstMetric(value float64, labels ...string) pr
 }
 
 type diskstatsCollector struct {
-	deviceFilter         deviceFilter
-	fs                   blockdevice.FS
-	infoDesc             typedFactorDesc
-	descs                []typedFactorDesc
-	filesystemInfoDesc   typedFactorDesc
-	deviceMapperInfoDesc typedFactorDesc
-	ataDescs             map[string]typedFactorDesc
-	logger               log.Logger
+	deviceFilter            deviceFilter
+	fs                      blockdevice.FS
+	infoDesc                typedFactorDesc
+	descs                   []typedFactorDesc
+	filesystemInfoDesc      typedFactorDesc
+	deviceMapperInfoDesc    typedFactorDesc
+	ataDescs                map[string]typedFactorDesc
+	logger                  log.Logger
+	getUdevDeviceProperties func(uint32, uint32) (udevInfo, error)
 }
 
 func init() {
@@ -105,7 +106,7 @@ func NewDiskstatsCollector(logger log.Logger) (Collector, error) {
 		return nil, fmt.Errorf("failed to parse device filter flags: %w", err)
 	}
 
-	return &diskstatsCollector{
+	collector := diskstatsCollector{
 		deviceFilter: deviceFilter,
 		fs:           fs,
 		infoDesc: typedFactorDesc{
@@ -256,7 +257,16 @@ func NewDiskstatsCollector(logger log.Logger) (Collector, error) {
 			},
 		},
 		logger: logger,
-	}, nil
+	}
+
+	// Only enable getting device properties from udev if the directory is readable.
+	if stat, err := os.Stat(*udevDataPath); err != nil || !stat.IsDir() {
+		level.Error(logger).Log("msg", "Failed to open directory, disabling udev device properties", "path", *udevDataPath)
+	} else {
+		collector.getUdevDeviceProperties = getUdevDeviceProperties
+	}
+
+	return &collector, nil
 }
 
 func (c *diskstatsCollector) Update(ch chan<- prometheus.Metric) error {
@@ -273,7 +283,7 @@ func (c *diskstatsCollector) Update(ch chan<- prometheus.Metric) error {
 
 		info, err := getUdevDeviceProperties(stats.MajorNumber, stats.MinorNumber)
 		if err != nil {
-			level.Error(c.logger).Log("msg", "Failed to parse udev info", "err", err)
+			level.Debug(c.logger).Log("msg", "Failed to parse udev info", "err", err)
 		}
 
 		ch <- c.infoDesc.mustNewConstMetric(1.0, dev,