Remove some unused code and updated docs for metrics

docs/configure_nydus.md

@@ -128,7 +128,10 @@ The Nydus snapshotter will get the new secret and parse the authorization. If yo
 
 ## Metrics
 
-Nydusd records metrics in its own format. The metrics are exported via a HTTP server on top of unix domain socket. Nydus-snapshotter fetches the metrics and convert them in to Prometheus format which is exported via a network address. Nydus-snapshotter by default does not fetch metrics from nydusd. You can enable the nydusd metrics download by assigning an network address to `metrics.address` in nydus-snapshotter's toml [configuration file](../misc/snapshotter/config.toml).
+Nydusd records metrics in its own format. The metrics are exported via a HTTP server on top of unix domain socket. Nydus-snapshotter fetches the metrics and convert them in to Prometheus format which is exported via a network address. Nydus-snapshotter by default does not fetch metrics from nydusd. You can enable the nydusd metrics download by assigning a network address to `metrics.address` in nydus-snapshotter's toml [configuration file](../misc/snapshotter/config.toml).
+
+Once this entry is enabled, not only nydusd metrics, but also some information about the nydus-snapshotter 
+runtime and snapshot related events are exported in Prometheus format as well.
 
 ## Diagnose
 

pkg/metrics/serve.go

@@ -28,20 +28,12 @@ const defaultHungIOInterval = 10 * time.Second
 type ServerOpt func(*Server) error
 
 type Server struct {
-	rootDir           string
 	managers          []*manager.Manager
 	snCollectors      []*collector.SnapshotterMetricsCollector
 	fsCollector       *collector.FsMetricsVecCollector
 	inflightCollector *collector.InflightMetricsVecCollector
 }
 
-func WithRootDir(rootDir string) ServerOpt {
-	return func(s *Server) error {
-		s.rootDir = rootDir
-		return nil
-	}
-}
-
 func WithProcessManager(pm *manager.Manager) ServerOpt {
 	return func(s *Server) error {
 		s.managers = append(s.managers, pm)

snapshot/snapshot.go

@@ -117,7 +117,6 @@ func NewSnapshotter(ctx context.Context, cfg *config.SnapshotterConfig) (snapsho
 
 	metricServer, err := metrics.NewServer(
 		ctx,
-		metrics.WithRootDir(cfg.Root),
 		metrics.WithProcessManager(manager),
 	)
 	if err != nil {