HDFS-14922. Prevent snapshot modification time got change on startup. Contributed by hemanthboyina.

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

@@ -34,6 +34,7 @@ import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
 import org.apache.hadoop.hdfs.server.namenode.snapshot.SnapshotManager;
 import org.apache.hadoop.hdfs.util.ReadOnlyList;
 import org.apache.hadoop.util.ChunkedArrayList;
+import org.apache.hadoop.util.Time;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -104,16 +105,18 @@ class FSDirSnapshotOp {
 
     String snapshotPath;
     verifySnapshotName(fsd, snapshotName, snapshotRoot);
+    // time of snapshot creation
+    final long now = Time.now();
     fsd.writeLock();
     try {
       snapshotPath = snapshotManager.createSnapshot(
           fsd.getFSNamesystem().getLeaseManager(),
-          iip, snapshotRoot, snapshotName);
+          iip, snapshotRoot, snapshotName, now);
     } finally {
       fsd.writeUnlock();
     }
     fsd.getEditLog().logCreateSnapshot(snapshotRoot, snapshotName,
-        logRetryCache);
+        logRetryCache, now);
 
     return snapshotPath;
   }

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

@@ -1116,10 +1116,19 @@ public class FSEditLog implements LogsPurgeable {
       .setNewHolder(newHolder);
     logEdit(op);
   }
-  
+
-  void logCreateSnapshot(String snapRoot, String snapName, boolean toLogRpcIds) {
+  /**
+   * Log that a snapshot is created.
+   * @param snapRoot Root of the snapshot.
+   * @param snapName Name of the snapshot.
+   * @param toLogRpcIds If it is logging RPC ids.
+   * @param mtime The snapshot creation time set by Time.now().
+   */
+  void logCreateSnapshot(String snapRoot, String snapName, boolean toLogRpcIds,
+      long mtime) {
     CreateSnapshotOp op = CreateSnapshotOp.getInstance(cache.get())
-        .setSnapshotRoot(snapRoot).setSnapshotName(snapName);
+        .setSnapshotRoot(snapRoot).setSnapshotName(snapName)
+        .setSnapshotMTime(mtime);
     logRpcIds(op, toLogRpcIds);
     logEdit(op);
   }

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

@@ -801,7 +801,8 @@ public class FSEditLogLoader {
       INodesInPath iip = fsDir.getINodesInPath(snapshotRoot, DirOp.WRITE);
       String path = fsNamesys.getSnapshotManager().createSnapshot(
           fsDir.getFSNamesystem().getLeaseManager(),
-          iip, snapshotRoot, createSnapshotOp.snapshotName);
+          iip, snapshotRoot, createSnapshotOp.snapshotName,
+          createSnapshotOp.mtime);
       if (toAddRetryCache) {
         fsNamesys.addCacheEntryWithPayload(createSnapshotOp.rpcClientId,
             createSnapshotOp.rpcCallId, path);

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

@@ -3437,6 +3437,8 @@ public abstract class FSEditLogOp {
   static class CreateSnapshotOp extends FSEditLogOp {
     String snapshotRoot;
     String snapshotName;
+    /** Modification time of the edit set by Time.now(). */
+    long mtime;
     
     public CreateSnapshotOp() {
       super(OP_CREATE_SNAPSHOT);
@@ -3450,22 +3452,32 @@ public abstract class FSEditLogOp {
     void resetSubFields() {
       snapshotRoot = null;
       snapshotName = null;
+      mtime = 0L;
     }
 
+    /* set the name of the snapshot. */
     CreateSnapshotOp setSnapshotName(String snapName) {
       this.snapshotName = snapName;
       return this;
     }
 
+    /* set the directory path where the snapshot is taken. */
     public CreateSnapshotOp setSnapshotRoot(String snapRoot) {
       snapshotRoot = snapRoot;
       return this;
     }
-    
+
+    /* The snapshot creation time set by Time.now(). */
+    CreateSnapshotOp setSnapshotMTime(long mTime) {
+      this.mtime = mTime;
+      return this;
+    }
+
     @Override
     void readFields(DataInputStream in, int logVersion) throws IOException {
       snapshotRoot = FSImageSerialization.readString(in);
       snapshotName = FSImageSerialization.readString(in);
+      mtime = FSImageSerialization.readLong(in);
       
       // read RPC ids if necessary
       readRpcIds(in, logVersion);
@@ -3475,6 +3487,7 @@ public abstract class FSEditLogOp {
     public void writeFields(DataOutputStream out) throws IOException {
       FSImageSerialization.writeString(snapshotRoot, out);
       FSImageSerialization.writeString(snapshotName, out);
+      FSImageSerialization.writeLong(mtime, out);
       writeRpcIds(rpcClientId, rpcCallId, out);
     }
 
@@ -3482,6 +3495,7 @@ public abstract class FSEditLogOp {
     protected void toXml(ContentHandler contentHandler) throws SAXException {
       XMLUtils.addSaxString(contentHandler, "SNAPSHOTROOT", snapshotRoot);
       XMLUtils.addSaxString(contentHandler, "SNAPSHOTNAME", snapshotName);
+      XMLUtils.addSaxString(contentHandler, "MTIME", Long.toString(mtime));
       appendRpcIdsToXml(contentHandler, rpcClientId, rpcCallId);
     }
 
@@ -3489,6 +3503,7 @@ public abstract class FSEditLogOp {
     void fromXml(Stanza st) throws InvalidXmlException {
       snapshotRoot = st.getValue("SNAPSHOTROOT");
       snapshotName = st.getValue("SNAPSHOTNAME");
+      this.mtime = Long.parseLong(st.getValue("MTIME"));
       
       readRpcIdsFromXml(st);
     }
@@ -3499,7 +3514,8 @@ public abstract class FSEditLogOp {
       builder.append("CreateSnapshotOp [snapshotRoot=")
           .append(snapshotRoot)
           .append(", snapshotName=")
-          .append(snapshotName);
+          .append(snapshotName)
+          .append(", mtime=").append(mtime);
       appendRpcIdsToString(builder, rpcClientId, rpcCallId);
       builder.append("]");
       return builder.toString();

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

@@ -276,12 +276,17 @@ public class INodeDirectory extends INodeWithAdditionalFields
     getDirectorySnapshottableFeature().setSnapshotQuota(snapshotQuota);
   }
 
+  /**
+   * Add a snapshot.
+   * @param name Name of the snapshot.
+   * @param mtime The snapshot creation time set by Time.now().
+   */
   public Snapshot addSnapshot(int id, String name,
       final LeaseManager leaseManager, final boolean captureOpenFiles,
-      int maxSnapshotLimit)
+      int maxSnapshotLimit, long mtime)
       throws SnapshotException {
     return getDirectorySnapshottableFeature().addSnapshot(this, id, name,
-        leaseManager, captureOpenFiles, maxSnapshotLimit);
+        leaseManager, captureOpenFiles, maxSnapshotLimit, mtime);
   }
 
   public Snapshot removeSnapshot(

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

@@ -166,10 +166,17 @@ public class DirectorySnapshottableFeature extends DirectoryWithSnapshotFeature
     this.snapshotsByNames.add(snapshot);
   }
 
-  /** Add a snapshot. */
+  /**
+   * Add a snapshot.
+   * @param snapshotRoot Root of the snapshot.
+   * @param name Name of the snapshot.
+   * @param mtime The snapshot creation time set by Time.now().
+   * @throws SnapshotException Throw SnapshotException when there is a snapshot
+   *           with the same name already exists or snapshot quota exceeds
+   */
   public Snapshot addSnapshot(INodeDirectory snapshotRoot, int id, String name,
       final LeaseManager leaseManager, final boolean captureOpenFiles,
-      int maxSnapshotLimit)
+      int maxSnapshotLimit, long now)
       throws SnapshotException {
     //check snapshot quota
     final int n = getNumSnapshots();
@@ -195,8 +202,7 @@ public class DirectorySnapshottableFeature extends DirectoryWithSnapshotFeature
     d.setSnapshotRoot(s.getRoot());
     snapshotsByNames.add(-i - 1, s);
 
-    // set modification time
+    // modification time is the snapshot creation time
-    final long now = Time.now();
     snapshotRoot.updateModificationTime(now, Snapshot.CURRENT_STATE_ID);
     s.getRoot().setModificationTime(now, Snapshot.CURRENT_STATE_ID);
 

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

@@ -312,6 +312,7 @@ public class SnapshotManager implements SnapshotStatsMXBean {
    * @param iip the INodes resolved from the snapshottable directory's path
    * @param snapshotName
    *          The name of the snapshot.
+   * @param mtime is the snapshot creation time set by Time.now().
    * @throws IOException
    *           Throw IOException when 1) the given path does not lead to an
    *           existing snapshottable directory, and/or 2) there exists a
@@ -319,7 +320,8 @@ public class SnapshotManager implements SnapshotStatsMXBean {
    *           snapshot number exceeds quota
    */
   public String createSnapshot(final LeaseManager leaseManager,
-      final INodesInPath iip, String snapshotRoot, String snapshotName)
+      final INodesInPath iip, String snapshotRoot, String snapshotName,
+      long mtime)
       throws IOException {
     INodeDirectory srcRoot = getSnapshottableRoot(iip);
 
@@ -333,7 +335,7 @@ public class SnapshotManager implements SnapshotStatsMXBean {
     }
 
     srcRoot.addSnapshot(snapshotCounter, snapshotName, leaseManager,
-        this.captureOpenFiles, maxSnapshotLimit);
+        this.captureOpenFiles, maxSnapshotLimit, mtime);
       
     //create success, update id
     snapshotCounter++;

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/snapshot/TestSnapshot.java

@@ -456,6 +456,22 @@ public class TestSnapshot {
     assertEquals(0, rootNode.getDirectorySnapshottableFeature().getSnapshotQuota());
   }
 
+  @Test(timeout = 60000)
+  public void testSnapshotMtime() throws Exception {
+    Path dir = new Path("/dir");
+    Path sub = new Path(dir, "sub");
+    Path subFile = new Path(sub, "file");
+    DFSTestUtil.createFile(hdfs, subFile, BLOCKSIZE, REPLICATION, seed);
+
+    hdfs.allowSnapshot(dir);
+    Path snapshotPath = hdfs.createSnapshot(dir, "s1");
+    FileStatus oldSnapshotStatus = hdfs.getFileStatus(snapshotPath);
+    cluster.restartNameNodes();
+    FileStatus newSnapshotStatus = hdfs.getFileStatus(snapshotPath);
+    assertEquals(oldSnapshotStatus.getModificationTime(),
+        newSnapshotStatus.getModificationTime());
+  }
+
   /**
    * Prepare a list of modifications. A modification may be a file creation,
    * file deletion, or a modification operation such as appending to an existing

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/snapshot/TestSnapshotManager.java

@@ -31,6 +31,7 @@ import org.apache.hadoop.hdfs.server.namenode.INodeDirectory;
 import org.apache.hadoop.hdfs.server.namenode.INodesInPath;
 import org.apache.hadoop.hdfs.server.namenode.LeaseManager;
 import org.apache.hadoop.util.StringUtils;
+import org.apache.hadoop.util.Time;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -60,14 +61,15 @@ public class TestSnapshotManager {
     // Create testMaxSnapshotLimit snapshots. These should all succeed.
     //
     for (Integer i = 0; i < testMaxSnapshotLimit; ++i) {
-      sm.createSnapshot(leaseManager, iip, "dummy", i.toString());
+      sm.createSnapshot(leaseManager, iip, "dummy", i.toString(), Time.now());
     }
 
     // Attempt to create one more snapshot. This should fail due to snapshot
     // ID rollover.
     //
     try {
-      sm.createSnapshot(leaseManager, iip, "dummy", "shouldFailSnapshot");
+      sm.createSnapshot(leaseManager, iip, "dummy", "shouldFailSnapshot",
+          Time.now());
       Assert.fail("Expected SnapshotException not thrown");
     } catch (SnapshotException se) {
       Assert.assertTrue(
@@ -82,7 +84,8 @@ public class TestSnapshotManager {
     // to snapshot ID rollover.
     //
     try {
-      sm.createSnapshot(leaseManager, iip, "dummy", "shouldFailSnapshot2");
+      sm.createSnapshot(leaseManager, iip, "dummy", "shouldFailSnapshot2",
+          Time.now());
       Assert.fail("Expected SnapshotException not thrown");
     } catch (SnapshotException se) {
       Assert.assertTrue(