@Override
    public boolean accept(Path rd) {
      try {
        // only files can be references.
        return !fs.getFileStatus(rd).isDirectory()
          && (StoreFileInfo.isReference(rd) || HFileLink.isHFileLink(rd));
      } catch (IOException ioe) {
        // Maybe the file was moved or the fs was disconnected.
        LOG.warn("Skipping file " + rd + " due to IOException", ioe);
        return false;
      }
    }
Given a particular region dir, return all the familydirs inside it
@param fs        A file system for the Path
@param regionDir Path to a specific region directory
@return List of paths to valid family directories in region dir.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/FSUtils.java