code: private synchronized String ufsFingerprint(long fileId) throws IOException {
      FileInfo fileInfo = mBlockWorker.getFileInfo(fileId);
      String dstPath = fileInfo.getUfsPath();
      try (CloseableResource<UnderFileSystem> ufsResource =
          mUfsManager.get(fileInfo.getMountId()).acquireUfsResource()) {
        UnderFileSystem ufs = ufsResource.get();
        return ufs.isFile(dstPath) ? ufs.getFingerprint(dstPath) : null;
      }
    }
docs: Returns the ufs fingerprint of the given file, or null if the file doesn't exist.
  
  @param fileId the file id
  @return the ufs fingerprint of the file if it exists, null otherwise