code: func diskSetUp(manager diskManager, b rbdMounter, volPath string, mounter mount.Interface, fsGroup *int64) error {
  	globalPDPath := manager.MakeGlobalPDName(*b.rbd)
  	notMnt, err := mounter.IsLikelyNotMountPoint(globalPDPath)
  	if err != nil && !os.IsNotExist(err) {
  		klog.Errorf("cannot validate mountpoint: %s", globalPDPath)
  		return err
  	}
  	if notMnt {
  		return fmt.Errorf("no device is mounted at %s", globalPDPath)
  	}
  
  	notMnt, err = mounter.IsLikelyNotMountPoint(volPath)
  	if err != nil && !os.IsNotExist(err) {
  		klog.Errorf("cannot validate mountpoint: %s", volPath)
  		return err
  	}
  	if !notMnt {
  		return nil
  	}
  
  	if err := os.MkdirAll(volPath, 0750); err != nil {
  		klog.Errorf("failed to mkdir:%s", volPath)
  		return err
  	}
  	// Perform a bind mount to the full path to allow duplicate mounts of the same disk.
  	options := []string{"bind"}
  	if (&b).GetAttributes().ReadOnly {
  		options = append(options, "ro")
  	}
  	mountOptions := util.JoinMountOptions(b.mountOptions, options)
  	err = mounter.Mount(globalPDPath, volPath, "", mountOptions)
  	if err != nil {
  		klog.Errorf("failed to bind mount:%s", globalPDPath)
  		return err
  	}
  	klog.V(3).Infof("rbd: successfully bind mount %s to %s with options %v", globalPDPath, volPath, mountOptions)
  
  	if !b.ReadOnly {
  		volume.SetVolumeOwnership(&b, fsGroup)
  	}
  
  	return nil
  }
docs: // utility to mount a disk based filesystem