1 /**
2  * Licensed to the Apache Software Foundation (ASF) under one
3  * or more contributor license agreements.  See the NOTICE file
4  * distributed with this work for additional information
5  * regarding copyright ownership.  The ASF licenses this file
6  * to you under the Apache License, Version 2.0 (the
7  * "License"); you may not use this file except in compliance
8  * with the License.  You may obtain a copy of the License at
9  *
10  *     http://www.apache.org/licenses/LICENSE-2.0
11  *
12  * Unless required by applicable law or agreed to in writing, software
13  * distributed under the License is distributed on an "AS IS" BASIS,
14  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15  * See the License for the specific language governing permissions and
16  * limitations under the License.
17  */
18 package org.apache.hadoop.hdfs.protocol;
19 
20 import java.io.DataInputStream;
21 import java.io.DataOutputStream;
22 import java.io.IOException;
23 
24 import org.apache.hadoop.classification.InterfaceAudience;
25 
26 import com.google.common.base.Joiner;
27 import com.google.common.base.Preconditions;
28 import com.google.common.collect.ImmutableSet;
29 import com.google.common.collect.Sets;
30 
31 /**
32  * LayoutFlags represent features which the FSImage and edit logs can either
33  * support or not, independently of layout version.
34  *
35  * Note: all flags starting with 'test' are reserved for unit test purposes.
36  */
37 @InterfaceAudience.Private
38 public class LayoutFlags {
39   /**
40    * Load a LayoutFlags object from a stream.
41    *
42    * @param in            The stream to read from.
43    * @throws IOException
44    */
read(DataInputStream in)45   public static LayoutFlags read(DataInputStream in)
46       throws IOException {
47     int length = in.readInt();
48     if (length < 0) {
49       throw new IOException("The length of the feature flag section " +
50           "was negative at " + length + " bytes.");
51     } else if (length > 0) {
52       throw new IOException("Found feature flags which we can't handle. " +
53           "Please upgrade your software.");
54     }
55     return new LayoutFlags();
56   }
57 
LayoutFlags()58   private LayoutFlags() {
59   }
60 
write(DataOutputStream out)61   public static void write(DataOutputStream out) throws IOException {
62     out.writeInt(0);
63   }
64 }
65