paxHdrs[paxGNUSparseMap] = strings.Join(sparseMap, ",")
	}
	return paxHdrs, nil
}

// readHeader reads the next block header and assumes that the underlying reader
// is already aligned to a block boundary. It returns the raw block of the
// header in case further processing is required.
//
// The err will be set to io.EOF only when one of the following occurs:
//   - Exactly 0 bytes are read and EOF is hit.

			if !into.Compacted {
				var foundAny bool
				parent := thisHash
				for parent != hashPath(f.updateCache.Info.Name) {
					e := f.updateCache.find(parent.Key())
					if e == nil || e.Compacted {
						foundAny = true
						break
					}
					next := f.updateCache.searchParent(parent)
					if next == nil {
						foundAny = true
						break
					}
					parent = *next
				}