public String preModifyColumnFamilyStoreFileTracker(final TableName tableName,
    final byte[] family, final String dstSFT) throws IOException {
    if (coprocEnvironments.isEmpty()) {
      return dstSFT;
    }
    return execOperationWithResult(
      new ObserverOperationWithResult<MasterObserver, String>(masterObserverGetter, dstSFT) {
        @Override
        protected String call(MasterObserver observer) throws IOException {
          return observer.preModifyColumnFamilyStoreFileTracker(this, tableName, family,
            getResult());
        }
      });
  }
@return An instance of MasterServices, an object NOT for general user-space Coprocessor
        consumption.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterCoprocessorHost.java