HDFS-11794. Add ec sub command -listCodec to show currently supported ec codecs. Contributed by SammiChen.

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/erasurecode/CodecRegistry.java

@@ -179,4 +179,13 @@ public final class CodecRegistry {
   public Map<String, String> getCodec2CoderCompactMap() {
     return coderNameCompactMap;
   }
+
+  /**
+   * Get all codec names and their corresponding coder list.
+   * @return a map of all codec names, and their corresponding code list
+   * separated by ','.
+   */
+  public HashMap<String, String> getCodec2CoderCompactMap() {
+    return coderNameCompactMap;
+  }
 }

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

@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.EnumSet;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
@@ -1761,6 +1762,25 @@ public class ClientNamenodeProtocolServerSideTranslatorPB implements
     }
   }
 
+  @Override
+  public GetErasureCodingCodecsResponseProto getErasureCodingCodecs(
+      RpcController controller, GetErasureCodingCodecsRequestProto request)
+      throws ServiceException {
+    try {
+      HashMap<String, String> codecs = server.getErasureCodingCodecs();
+      GetErasureCodingCodecsResponseProto.Builder resBuilder =
+          GetErasureCodingCodecsResponseProto.newBuilder();
+      for (Map.Entry<String, String> codec : codecs.entrySet()) {
+        resBuilder.addCodec(
+            PBHelperClient.convertErasureCodingCodec(
+                codec.getKey(), codec.getValue()));
+      }
+      return resBuilder.build();
+    } catch (IOException e) {
+      throw new ServiceException(e);
+    }
+  }
+
   @Override
   public AddErasureCodingPoliciesResponseProto addErasureCodingPolicies(
       RpcController controller, AddErasureCodingPoliciesRequestProto request)

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

@@ -7655,6 +7655,20 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     }
   }
 
+  /**
+   * Get available erasure coding codecs and corresponding coders.
+   */
+  HashMap<String, String> getErasureCodingCodecs() throws IOException {
+    checkOperation(OperationCategory.READ);
+    readLock();
+    try {
+      checkOperation(OperationCategory.READ);
+      return FSDirErasureCodingOp.getErasureCodingCodecs(this);
+    } finally {
+      readUnlock("getErasureCodingCodecs");
+    }
+  }
+
   void setXAttr(String src, XAttr xAttr, EnumSet<XAttrSetFlag> flag,
                 boolean logRetryCache)
       throws IOException {