HDFS-14148. HDFS OIV ReverseXML SnapshotSection parser throws exception when there are more than one snapshottable directory (#1274) Contributed by Siyao Meng.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/OfflineImageReconstructor.java

@@ -1353,9 +1353,11 @@ class OfflineImageReconstructor {
         if (sd == null) {
           break;
         }
-        Long dir = sd.removeChildLong(SNAPSHOT_SECTION_DIR);
-        sd.verifyNoRemainingKeys("<dir>");
-        bld.addSnapshottableDir(dir);
+        Long dir;
+        while ((dir = sd.removeChildLong(SNAPSHOT_SECTION_DIR)) != null) {
+          // Add all snapshottable directories, one by one
+          bld.addSnapshottableDir(dir);
+        }
       }
       header.verifyNoRemainingKeys("SnapshotSection");
       bld.build().writeDelimitedTo(out);

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/tools/offlineImageViewer/TestOfflineImageViewer.java

@@ -288,6 +288,16 @@ public class TestOfflineImageViewer {
       hdfs.truncate(file1, 1);
       writtenFiles.put(file1.toString(), hdfs.getFileStatus(file1));
 
+      // HDFS-14148: Create a second snapshot-enabled directory. This can cause
+      // TestOfflineImageViewer#testReverseXmlRoundTrip to fail before the patch
+      final Path snapshotDir2 = new Path("/snapshotDir2");
+      hdfs.mkdirs(snapshotDir2);
+      // Simply enable snapshot on it, no need to create one
+      hdfs.allowSnapshot(snapshotDir2);
+      dirCount++;
+      writtenFiles.put(snapshotDir2.toString(),
+          hdfs.getFileStatus(snapshotDir2));
+
       // Set XAttrs so the fsimage contains XAttr ops
       final Path xattr = new Path("/xattr");
       hdfs.mkdirs(xattr);