Execute using legacy wire protocol ops.

def execute_legacy(self, sock_info, generator, write_concern):
        """Execute using legacy wire protocol ops.
        """
        coll = self.collection
        full_result = {
            "writeErrors": [],
            "writeConcernErrors": [],
            "nInserted": 0,
            "nUpserted": 0,
            "nMatched": 0,
            "nRemoved": 0,
            "upserted": [],
        }
        op_id = _randint()
        stop = False
        for run in generator:
            for idx, operation in enumerate(run.ops):
                try:
                    # To do per-operation reporting we have to do ops one
                    # at a time. That means the performance of bulk insert
                    # will be slower here than calling Collection.insert()
                    if run.op_type == _INSERT:
                        coll._insert(sock_info,
                                     operation,
                                     self.ordered,
                                     write_concern=write_concern,
                                     op_id=op_id)
                        result = {}
                    elif run.op_type == _UPDATE:
                        doc = operation['u']
                        check_keys = True
                        if doc and next(iter(doc)).startswith('$'):
                            check_keys = False
                        result = coll._update(sock_info,
                                              operation['q'],
                                              doc,
                                              operation['upsert'],
                                              check_keys,
                                              operation['multi'],
                                              write_concern=write_concern,
                                              op_id=op_id,
                                              ordered=self.ordered)
                    else:
                        result = coll._delete(sock_info,
                                              operation['q'],
                                              not operation['limit'],
                                              write_concern,
                                              op_id,
                                              self.ordered)
                    _merge_legacy(run, full_result, result, idx)
                except DocumentTooLarge as exc:
                    # MongoDB 2.6 uses error code 2 for "too large".
                    error = _make_error(
                        run.index(idx), _BAD_VALUE, str(exc), operation)
                    full_result['writeErrors'].append(error)
                    if self.ordered:
                        stop = True
                        break
                except OperationFailure as exc:
                    if not exc.details:
                        # Some error not related to the write operation
                        # (e.g. kerberos failure). Re-raise immediately.
                        raise
                    _merge_legacy(run, full_result, exc.details, idx)
                    # We're supposed to continue if errors are
                    # at the write concern level (e.g. wtimeout)
                    if self.ordered and full_result["writeErrors"]:
                        stop = True
                        break
            if stop:
                break

        if full_result["writeErrors"] or full_result['writeConcernErrors']:
            if full_result['writeErrors']:
                full_result['writeErrors'].sort(
                    key=lambda error: error['index'])
            raise BulkWriteError(full_result)
        return full_result