HDFS-13688. [SBN read] Introduce msync API call. Contributed by Chen Liang.

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -3153,4 +3153,18 @@ public class DFSClient implements java.io.Closeable, RemotePeerFactory,
     checkOpen();
     return new OpenFilesIterator(namenode, tracer, openFilesTypes, path);
   }
+
+  /**
+   * A blocking call to wait for Observer NameNode state ID to reach to the
+   * current client state ID. Current client state ID is given by the client
+   * alignment context.
+   * An assumption is that client alignment context has the state ID set at this
+   * point. This is become ObserverReadProxyProvider sets up the initial state
+   * ID when it is being created.
+   *
+   * @throws IOException
+   */
+  public void msync() throws IOException {
+    namenode.msync();
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocol/ClientProtocol.java

@@ -1788,4 +1788,15 @@ public interface ClientProtocol {
   @ReadOnly
   BatchedEntries<OpenFileEntry> listOpenFiles(long prevId,
       EnumSet<OpenFilesType> openFilesTypes, String path) throws IOException;
+
+  /**
+   * Called by client to wait until the server has reached the state id of the
+   * client. The client and server state id are given by client side and server
+   * side alignment context respectively. This can be a blocking call.
+   *
+   * @throws IOException
+   */
+  @Idempotent
+  @ReadOnly
+  void msync() throws IOException;
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolTranslatorPB.java

@@ -158,6 +158,8 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MetaSa
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MkdirsRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ModifyCacheDirectiveRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ModifyCachePoolRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MsyncRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MsyncResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.OpenFilesBatchResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RecoverLeaseRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RefreshNodesRequestProto;
@@ -1944,4 +1946,13 @@ public class ClientNamenodeProtocolTranslatorPB implements
     }
   }
 
+  @Override
+  public void msync() throws IOException {
+    MsyncRequestProto.Builder req = MsyncRequestProto.newBuilder();
+    try {
+      rpcProxy.msync(null, req.build());
+    } catch (ServiceException e) {
+      throw ProtobufHelper.getRemoteException(e);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/main/proto/ClientNamenodeProtocol.proto

@@ -831,6 +831,12 @@ message ListOpenFilesResponseProto {
   repeated OpenFilesTypeProto types = 3;
 }
 
+message MsyncRequestProto {
+}
+
+message MsyncResponseProto {
+}
+
 service ClientNamenodeProtocol {
   rpc getBlockLocations(GetBlockLocationsRequestProto)
       returns(GetBlockLocationsResponseProto);
@@ -1017,4 +1023,6 @@ service ClientNamenodeProtocol {
       returns(GetQuotaUsageResponseProto);
   rpc listOpenFiles(ListOpenFilesRequestProto)
       returns(ListOpenFilesResponseProto);
+  rpc msync(MsyncRequestProto)
+      returns(MsyncResponseProto);
 }

hadoop-hdfs-project/hadoop-hdfs-client/src/test/java/org/apache/hadoop/hdfs/protocol/TestReadOnly.java

@@ -71,7 +71,8 @@ public class TestReadOnly {
           "getDataEncryptionKey",
           "getCurrentEditLogTxid",
           "getEditsFromTxid",
-          "getQuotaUsage"
+          "getQuotaUsage",
+          "msync"
       )
   );
 

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterClientProtocol.java

@@ -1535,6 +1535,11 @@ public class RouterClientProtocol implements ClientProtocol {
     return null;
   }
 
+  @Override
+  public void msync() throws IOException {
+    rpcServer.checkOperation(NameNode.OperationCategory.READ, false);
+  }
+
   /**
    * Determines combinations of eligible src/dst locations for a rename. A
    * rename cannot change the namespace. Renames are only allowed if there is an

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcServer.java

@@ -1191,6 +1191,11 @@ public class RouterRpcServer extends AbstractService
     return clientProto.listOpenFiles(prevId, openFilesTypes, path);
   }
 
+  @Override // ClientProtocol
+  public void msync() throws IOException {
+    clientProto.msync();
+  }
+
   @Override // NamenodeProtocol
   public BlocksWithLocations getBlocks(DatanodeInfo datanode, long size,
       long minBlockSize) throws IOException {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/protocolPB/ClientNamenodeProtocolServerSideTranslatorPB.java

@@ -175,6 +175,8 @@ import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.Modify
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ModifyCacheDirectiveResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ModifyCachePoolRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.ModifyCachePoolResponseProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MsyncRequestProto;
+import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.MsyncResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RecoverLeaseRequestProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RecoverLeaseResponseProto;
 import org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos.RefreshNodesRequestProto;
@@ -1886,4 +1888,15 @@ public class ClientNamenodeProtocolServerSideTranslatorPB implements
       throw new ServiceException(e);
     }
   }
+
+  @Override
+  public MsyncResponseProto msync(RpcController controller,
+      MsyncRequestProto req) throws ServiceException {
+    try {
+      server.msync();
+      return MsyncResponseProto.newBuilder().build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNodeRpcServer.java

@@ -1366,6 +1366,11 @@ public class NameNodeRpcServer implements NamenodeProtocols {
     return namesystem.listOpenFiles(prevId, openFilesTypes, path);
   }
 
+  @Override // ClientProtocol
+  public void msync() throws IOException {
+    // TODO : need to be filled up if needed. May be a no-op here.
+  }
+
   @Override // ClientProtocol
   public CorruptFileBlocks listCorruptFileBlocks(String path, String cookie)
       throws IOException {