// On success a sorted meta cache stream will be returned.
// Metadata has data stripped, if any.
func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writer) (err error) {
	legacyFS := !(s.fsType == xfs || s.fsType == ext4)

	s.RLock()
	legacy := s.formatLegacy
	s.RUnlock()

	// Verify if volume is valid and it exists.
	volumeDir, err := s.getVolDir(opts.Bucket)
	if err != nil {
		return err
	}

//
//msgp:tuple DiskInfo
type DiskInfo struct {
	Total      uint64
	Free       uint64
	Used       uint64
	UsedInodes uint64
	FreeInodes uint64
	Major      uint32
	Minor      uint32
	NRRequests uint64
	FSType     string
	RootDisk   bool
	Healing    bool
	Scanning   bool
	Endpoint   string
	MountPath  string
	ID         string
	Rotational bool
	Metrics    DiskMetrics

  // to determine if Kubernetes should modify ownership and permissions of the volume.
  // With the default policy the defined fsGroup will only be applied
  // if a fstype is defined and the volume's access mode contains ReadWriteOnce.
  //
  // +optional
  optional string fsGroupPolicy = 5;

  // tokenRequests indicates the CSI driver needs pods' service account

  // to determine if Kubernetes should modify ownership and permissions of the volume.
  // With the default policy the defined fsGroup will only be applied
  // if a fstype is defined and the volume's access mode contains ReadWriteOnce.
  //
  // +optional
  optional string fsGroupPolicy = 5;

  // tokenRequests indicates the CSI driver needs pods' service account