// partial will be called when there is disagreement between disks.
	// if disk did not return any result, but also haven't errored
	// the entry will be empty and errs will
	partial func(entries metaCacheEntries, errs []error)

	// finished will be called when all streams have finished and
	// more than one disk returned an error.
	// Will not be called if everything operates as expected.
	finished func(errs []error)

type WriteOnCloser struct {
	io.Writer
	hasWritten bool
}

func (w *WriteOnCloser) Write(p []byte) (int, error) {
	w.hasWritten = true
	return w.Writer.Write(p)
}

// Close closes the WriteOnCloser. It behaves like io.Closer.
func (w *WriteOnCloser) Close() error {
	if !w.hasWritten {
		_, err := w.Write(nil)
		if err != nil {
			return err
		}
	}
	if closer, ok := w.Writer.(io.Closer); ok {
		return closer.Close()

// branch level, and contains link to children branches or leaves.
//
// The leaves are "compacted" based on a number of properties.
// A compacted leaf contains the totals of all files beneath it.
//
// A leaf is only scanned once every dataUsageUpdateDirCycles,
// rarer if the bloom filter for the path is clean and no lifecycles are applied.
// Skipped leaves have their totals transferred from the previous cycle.
//