boff := 0 // starting read position in buf
	nbuf := 0 // end valid data in buf

	for {
		if boff >= nbuf {
			boff = 0
			stop := globalOSMetrics.time(osMetricReadDirent)
			nbuf, err = syscall.ReadDirent(fd, buf)
			stop()
			if err != nil {
				if isSysErrNotDir(err) {
					return nil
				}
				err = osErrToFileErr(err)
				if err == errFileNotFound {
					return nil
				}
				return err