Github user gengliangwang commented on a diff in the pull request:
https://github.com/apache/spark/pull/21123#discussion_r183318946
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/FileDataSourceV2.scala
---
@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.spark.sql.execution.datasources.v2
+
+import org.apache.spark.sql.execution.datasources.FileFormat
+import org.apache.spark.sql.sources.DataSourceRegister
+import org.apache.spark.sql.sources.v2.DataSourceV2
+import org.apache.spark.sql.sources.v2.ReadSupport
+import org.apache.spark.sql.sources.v2.WriteSupport
+
+/**
+ * The base class for file data source v2. Implementations must have a
public, 0-arg constructor.
+ *
+ * Note that this is an empty interface. Data source implementations
should mix-in at least one of
+ * the plug-in interfaces like {@link ReadSupport} and {@link
WriteSupport}. Otherwise it's just
+ * a dummy data source which is un-readable/writable.
+ */
+trait FileDataSourceV2 extends DataSourceV2 with DataSourceRegister {
+ /**
+ * Returns an optional V1 [[FileFormat]] class of the same file data
source.
+ * This is a solution for the following cases:
+ * 1. File datasource V2 might be implemented partially during migration.
+ * E.g. if [[ReadSupport]] is implemented while [[WriteSupport]] is
not,
+ * write path should fall back to V1 implementation.
+ * 2. File datasource V2 implementations cause regression.
+ * 3. Catalog support is required, which is still under development for
data source V2.
+ */
+ def fallBackFileFormat: Option[Class[_]] = None
--- End diff --
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