func btrfsSubVolumesDelete(subvol string) error {
	// Delete subsubvols.
	subsubvols, err := btrfsSubVolumesGet(subvol)
	if err != nil {
		return err
	}
	sort.Sort(sort.Reverse(sort.StringSlice(subsubvols)))

	for _, subsubvol := range subsubvols {
		err := btrfsSubVolumeDelete(path.Join(subvol, subsubvol))
		if err != nil {
			return err
		}
	}

	// Delete the subvol itself
	err = btrfsSubVolumeDelete(subvol)
	if err != nil {
		return err
	}

	return nil
}
func btrfsSubVolumesDelete(subvol string) error {
	// Delete subsubvols.
	subsubvols, err := btrfsSubVolumesGet(subvol)
	if err != nil {
		return err
	}
	sort.Sort(sort.Reverse(sort.StringSlice(subsubvols)))

	for _, subsubvol := range subsubvols {
		err := btrfsSubVolumeDelete(path.Join(subvol, subsubvol))
		if err != nil {
			return err
		}
	}

	// Delete the subvol itself
	err = btrfsSubVolumeDelete(subvol)
	if err != nil {
		return err
	}

	return nil
}
// btrfsPoolVolumesDelete is the recursive variant on btrfsPoolVolumeDelete,
// it first deletes subvolumes of the subvolume and then the
// subvolume itself.