HDFS-11407. Document the missing usages of OfflineImageViewer processors. Contributed by Yiqun Lin.

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsImageViewer.md

@@ -133,6 +133,69 @@ Applying the Offline Image Viewer with XML processor would result in the followi
          </inode>
        ...remaining output omitted...
 
+### ReverseXML Processor
+
+ReverseXML processor is the opposite of the XML processor. Users can specify input XML file and output fsimage file via -i and -o command-line.
+
+       bash$ bin/hdfs oiv -p ReverseXML -i fsimage.xml -o fsimage
+
+This will reconstruct an fsimage from an XML file.
+
+### FileDistribution Processor
+
+FileDistribution processor can analyze file sizes in the namespace image. Users can specify maxSize (128GB by default) and step (2MB by default) in bytes via -maxSize and -step command-line.
+
+       bash$ bin/hdfs oiv -p FileDistribution -maxSize maxSize -step size -i fsimage -o output
+
+The processor will calculate how many files in the system fall into each segment. The output file is formatted as a tab separated two column table showed as the following output:
+
+       Size	NumFiles
+       4	1
+       12	1
+       16	1
+       20	1
+       totalFiles = 4
+       totalDirectories = 2
+       totalBlocks = 4
+       totalSpace = 48
+       maxFileSize = 21
+
+To make the output result look more readable, users can specify -format option in addition.
+
+       bash$ bin/hdfs oiv -p FileDistribution -maxSize maxSize -step size -format -i fsimage -o output
+
+This would result in the following output:
+
+       Size Range	NumFiles
+       (0 B, 4 B]	1
+       (8 B, 12 B]	1
+       (12 B, 16 B]	1
+       (16 B, 21 B]	1
+       totalFiles = 4
+       totalDirectories = 2
+       totalBlocks = 4
+       totalSpace = 48
+       maxFileSize = 21
+
+### Delimited Processor
+
+Delimited processor generates a text representation of the fsimage, with each element separated by a delimiter string (\t by default). Users can specify a new delimiter string by -delimiter option.
+
+       bash$ bin/hdfs oiv -p Delimited -delimiter delimiterString -i fsimage -o output
+
+In addition, users can specify a temporary dir to cache intermediate result by the following command:
+
+       bash$ bin/hdfs oiv -p Delimited -delimiter delimiterString -t temporaryDir -i fsimage -o output
+
+If not set, Delimited processor will construct the namespace in memory before outputting text. The output result of this processor should be like the following output:
+
+       Path	Replication	ModificationTime	AccessTime	PreferredBlockSize	BlocksCount	FileSize	NSQUOTA	DSQUOTA	Permission	UserName	GroupName
+       /	0	2017-02-13 10:39	1970-01-01 08:00	0	0	0	9223372036854775807	-1	drwxr-xr-x	root	supergroup
+       /dir0	0	2017-02-13 10:39	1970-01-01 08:00	0	0	0	-1	-1	drwxr-xr-x	root	supergroup
+       /dir0/file0	1	2017-02-13 10:39	2017-02-13 10:39	134217728	1	1	0	0	-rw-r--r--	root	supergroup
+       /dir0/file1	1	2017-02-13 10:39	2017-02-13 10:39	134217728	1	1	0	0	-rw-r--r--	root	supergroup
+       /dir0/file2	1	2017-02-13 10:39	2017-02-13 10:39	134217728	1	1	0	0	-rw-r--r--	root	supergroup
+
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