HDFS-4819. Merging changes r1492064 from branch-2.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1492787 13f79535-47bb-0310-9956-ffa450edef68

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -825,6 +825,9 @@ Release 2.1.0-beta - UNRELEASED
     HDFS-4873. callGetBlockLocations returns incorrect number of blocks for 
     snapshotted files. (jing9)
 
+    HDFS-4819. Update Snapshot doc to clarify that nested snapshots are not
+    allowed.  (szetszwo)
+
 Release 2.0.5-alpha - 06/06/2013
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/site/xdoc/HdfsSnapshots.xml

@@ -70,13 +70,13 @@
     the directory can be neither deleted nor renamed
     before all the snapshots are deleted.
   </p>
-<!--
+
   <p>
     Nested snapshottable directories are currently not allowed.
     In other words, a directory cannot be set to snapshottable
-    if one of its ancestors is a snapshottable directory.
+    if one of its ancestors/descendants is a snapshottable directory.
   </p>
--->
+
   </subsection>
 
   <subsection name="Snapshot Paths" id="SnapshotPaths">
@@ -100,7 +100,7 @@
       <source>hdfs dfs -cp /foo/.snapshot/s0/bar /tmp</source></li>
   </ul>
   <p>
-    The name ".snapshot" is now a reserved file name in HDFS
+    <b>Note</b> that the name ".snapshot" is now a reserved file name in HDFS
     so that users cannot create a file/directory with ".snapshot" as the name.
     If ".snapshot" is used in a previous version of HDFS, it must be renamed before upgrade;
     otherwise, upgrade will fail.