HDFS-8417. Erasure Coding: Pread failed to read data starting from not-first stripe. Contributed by Walter Su.

hadoop-hdfs-project/hadoop-hdfs/CHANGES-HDFS-EC-7285.txt

@@ -217,3 +217,6 @@
     assigning new tasks. (umamahesh)
 
     HDFS-8367. BlockInfoStriped uses EC schema. (Kai Sasaki via Kai Zheng)
+
+    HDFS-8417. Erasure Coding: Pread failed to read data starting from not-first stripe.
+    (Walter Su via jing9)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/util/StripedBlockUtil.java

@@ -379,7 +379,8 @@ public static AlignedStripe[] divideByteRangeIntoStripes (
     int firstCellIdxInBG = (int) (start / cellSize);
     int lastCellIdxInBG = (int) (end / cellSize);
     int firstCellSize = Math.min(cellSize - (int) (start % cellSize), len);
-    long firstCellOffsetInBlk = start % cellSize;
+    long firstCellOffsetInBlk = firstCellIdxInBG / dataBlkNum * cellSize +
+        start % cellSize;
     int lastCellSize = lastCellIdxInBG == firstCellIdxInBG ?
         firstCellSize : (int) (end % cellSize) + 1;
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSStripedInputStream.java

@@ -38,6 +38,7 @@
 import org.apache.hadoop.io.erasurecode.ECSchema;
 import org.apache.hadoop.io.erasurecode.rawcoder.RSRawDecoder;
 import org.junit.After;
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -115,10 +116,13 @@ public void testPread() throws Exception {
     DFSTestUtil.createStripedFile(cluster, filePath, null, numBlocks,
         NUM_STRIPE_PER_BLOCK, false);
     LocatedBlocks lbs = fs.getClient().namenode.getBlockLocations(
-        filePath.toString(), 0, BLOCK_GROUP_SIZE);
+        filePath.toString(), 0, BLOCK_GROUP_SIZE * numBlocks);
+    int fileLen = BLOCK_GROUP_SIZE * numBlocks;
 
-    assert lbs.get(0) instanceof LocatedStripedBlock;
+    byte[] expected = new byte[fileLen];
-    LocatedStripedBlock bg = (LocatedStripedBlock)(lbs.get(0));
+    assertEquals(numBlocks, lbs.getLocatedBlocks().size());
+    for (int bgIdx = 0; bgIdx < numBlocks; bgIdx++) {
+      LocatedStripedBlock bg = (LocatedStripedBlock) (lbs.get(bgIdx));
       for (int i = 0; i < DATA_BLK_NUM; i++) {
         Block blk = new Block(bg.getBlock().getBlockId() + i,
             NUM_STRIPE_PER_BLOCK * CELLSIZE,
@@ -127,28 +131,40 @@ public void testPread() throws Exception {
         cluster.injectBlocks(i, Arrays.asList(blk),
             bg.getBlock().getBlockPoolId());
       }
-    DFSStripedInputStream in =
-        new DFSStripedInputStream(fs.getClient(),
-            filePath.toString(), false, schema);
-    int readSize = BLOCK_GROUP_SIZE;
-    byte[] readBuffer = new byte[readSize];
-    int ret = in.read(0, readBuffer, 0, readSize);
 
-    byte[] expected = new byte[readSize];
       /** A variation of {@link DFSTestUtil#fillExpectedBuf} for striped blocks */
       for (int i = 0; i < NUM_STRIPE_PER_BLOCK; i++) {
         for (int j = 0; j < DATA_BLK_NUM; j++) {
           for (int k = 0; k < CELLSIZE; k++) {
             int posInBlk = i * CELLSIZE + k;
             int posInFile = i * CELLSIZE * DATA_BLK_NUM + j * CELLSIZE + k;
-          expected[posInFile] = SimulatedFSDataset.simulatedByte(
+            expected[bgIdx*BLOCK_GROUP_SIZE + posInFile] =
+                SimulatedFSDataset.simulatedByte(
                     new Block(bg.getBlock().getBlockId() + j), posInBlk);
           }
         }
       }
+    }
+    DFSStripedInputStream in = new DFSStripedInputStream(fs.getClient(),
+            filePath.toString(), false, schema);
 
-    assertEquals(readSize, ret);
+    int[] startOffsets = {0, 1, CELLSIZE - 102, CELLSIZE, CELLSIZE + 102,
-    assertArrayEquals(expected, readBuffer);
+        CELLSIZE*DATA_BLK_NUM, CELLSIZE*DATA_BLK_NUM + 102,
+        BLOCK_GROUP_SIZE - 102, BLOCK_GROUP_SIZE, BLOCK_GROUP_SIZE + 102,
+        fileLen - 1};
+    for (int startOffset : startOffsets) {
+      startOffset = Math.max(0, Math.min(startOffset, fileLen - 1));
+      int remaining = fileLen - startOffset;
+      byte[] buf = new byte[fileLen];
+      int ret = in.read(startOffset, buf, 0, fileLen);
+      assertEquals(remaining, ret);
+      for (int i = 0; i < remaining; i++) {
+        Assert.assertEquals("Byte at " + (startOffset + i) + " should be the " +
+                "same",
+            expected[startOffset + i], buf[i]);
+      }
+    }
+    in.close();
   }
 
   @Test

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/SimulatedFSDataset.java

@@ -100,7 +100,7 @@ public static void setFactory(Configuration conf) {
 
   public static byte simulatedByte(Block b, long offsetInBlk) {
     byte firstByte = (byte) (b.getBlockId() & BYTE_MASK);
-    return (byte) ((firstByte + offsetInBlk) & BYTE_MASK);
+    return (byte) ((firstByte + offsetInBlk % 29) & BYTE_MASK);
   }
   
   public static final String CONFIG_PROPERTY_CAPACITY =