From f1560d379d314e0702e878a0ea5fcf2e99884c7c Mon Sep 17 00:00:00 2001
From: Harsh J <harsh@apache.org>
Date: Sun, 13 May 2012 03:33:19 +0000
Subject: [PATCH] HDFS-2312. FSNamesystem javadoc incorrectly says its for DNs.
 (harsh)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1337761 13f79535-47bb-0310-9956-ffa450edef68
---
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt   |  2 ++
 .../hdfs/server/namenode/FSNamesystem.java    | 27 ++++++++++++++-----
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index a1fa36f495..6e0a46daff 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -141,6 +141,8 @@ Trunk (unreleased changes)
     HDFS-3243. TestParallelRead timing out on jenkins. (Henry Robinson via todd)
 
     HDFS-3265. PowerPc Build error. (Kumar Ravi via mattf)
+
+    HDFS-2312. FSNamesystem javadoc incorrectly says its for DNs. (harsh)
     
 Release 2.0.0 - UNRELEASED 
 
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
index f1072f9bfe..d1876ea78a 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java
@@ -197,18 +197,33 @@
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 
-/***************************************************
- * FSNamesystem does the actual bookkeeping work for the
- * DataNode.
+/**
+ * FSNamesystem is a container of both transient
+ * and persisted name-space state, and does all the book-keeping
+ * work on a NameNode.
  *
- * It tracks several important tables.
+ * Its roles are briefly described below:
  *
- * 1)  valid fsname --> blocklist  (kept on disk, logged)
+ * 1) Is the container for BlockManager, DatanodeManager,
+ *    DelegationTokens, LeaseManager, etc. services.
+ * 2) RPC calls that modify or inspect the name-space
+ *    should get delegated here.
+ * 3) Anything that touches only blocks (eg. block reports),
+ *    it delegates to BlockManager.
+ * 4) Anything that touches only file information (eg. permissions, mkdirs),
+ *    it delegates to FSDirectory.
+ * 5) Anything that crosses two of the above components should be
+ *    coordinated here.
+ * 6) Logs mutations to FSEditLog.
+ *
+ * This class and its contents keep:
+ *
+ * 1)  Valid fsname --> blocklist  (kept on disk, logged)
  * 2)  Set of all valid blocks (inverted #1)
  * 3)  block --> machinelist (kept in memory, rebuilt dynamically from reports)
  * 4)  machine --> blocklist (inverted #2)
  * 5)  LRU cache of updated-heartbeat machines
- ***************************************************/
+ */
 @InterfaceAudience.Private
 @Metrics(context="dfs")
 public class FSNamesystem implements Namesystem, FSClusterStats,