code: void setQuota(String path, long nsQuota, long dsQuota) throws IOException {
      writeLock();
      try {
        if (isInSafeMode()) {
          throw new SafeModeException("Cannot setQuota " + path, safeMode);
        }
        INode[] inodes = this.dir.getExistingPathINodes(path);
        if (isPermissionEnabled
            && isPermissionCheckingEnabled(inodes)) {
          checkSuperuserPrivilege();
        }
  
        dir.setQuota(path, nsQuota, dsQuota);
      } finally {
        writeUnlock();
      }
      getEditLog().logSync(false);
    }
docs: Set the namespace quota and diskspace quota for a directory.
  See {@link ClientProtocol#setQuota(String, long, long)} for the
  contract.