HDFS-14111. hdfsOpenFile on HDFS causes unnecessary IO from file offset 0. Contributed by Sahil Takiar.

Signed-off-by: Wei-Chiu Chuang <weichiu@apache.org>

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/CryptoInputStream.java

@@ -740,6 +740,7 @@ public boolean hasCapability(String capability) {
     case StreamCapabilities.READAHEAD:
     case StreamCapabilities.DROPBEHIND:
     case StreamCapabilities.UNBUFFER:
+    case StreamCapabilities.READBYTEBUFFER:
       return true;
     default:
       return false;

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/StreamCapabilities.java

@@ -59,6 +59,12 @@ public interface StreamCapabilities {
    */
   String UNBUFFER = "in:unbuffer";
 
+  /**
+   * Stream read(ByteBuffer) capability implemented by
+   * {@link ByteBufferReadable#read(java.nio.ByteBuffer)}.
+   */
+  String READBYTEBUFFER = "in:readbytebuffer";
+
   /**
    * Capabilities that a stream can support and be queried for.
    */

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java

@@ -1779,6 +1779,7 @@ public boolean hasCapability(String capability) {
     case StreamCapabilities.READAHEAD:
     case StreamCapabilities.DROPBEHIND:
     case StreamCapabilities.UNBUFFER:
+    case StreamCapabilities.READBYTEBUFFER:
       return true;
     default:
       return false;

hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/hdfs.c

@@ -1013,7 +1013,7 @@ static hdfsFile hdfsOpenFileImpl(hdfsFS fs, const char *path, int flags,
        return f{is|os};
     */
     int accmode = flags & O_ACCMODE;
-    jstring jStrBufferSize = NULL, jStrReplication = NULL;
+    jstring jStrBufferSize = NULL, jStrReplication = NULL, jCapabilityString = NULL;
     jobject jConfiguration = NULL, jPath = NULL, jFile = NULL;
     jobject jFS = (jobject)fs;
     jthrowable jthr;
@@ -1171,16 +1171,22 @@ static hdfsFile hdfsOpenFileImpl(hdfsFS fs, const char *path, int flags,
     file->flags = 0;
 
     if ((flags & O_WRONLY) == 0) {
-        // Try a test read to see if we can do direct reads
+        // Check the StreamCapabilities of jFile to see if we can do direct reads
-        char buf;
+        jthr = newJavaStr(env, "in:readbytebuffer", &jCapabilityString);
-        if (readDirect(fs, file, &buf, 0) == 0) {
+        if (jthr) {
-            // Success - 0-byte read should return 0
+            ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                                        "hdfsOpenFile(%s): newJavaStr", path);
+            goto done;
+        }
+        jthr = invokeMethod(env, &jVal, INSTANCE, jFile, HADOOP_ISTRM,
+                            "hasCapability", "(Ljava/lang/String;)Z", jCapabilityString);
+        if (jthr) {
+            ret = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
+                                        "hdfsOpenFile(%s): FSDataInputStream#hasCapability", path);
+            goto done;
+        }
+        if (jVal.z) {
             file->flags |= HDFS_FILE_SUPPORTS_DIRECT_READ;
-        } else if (errno != ENOTSUP) {
-            // Unexpected error. Clear it, don't set the direct flag.
-            fprintf(stderr,
-                  "hdfsOpenFile(%s): WARN: Unexpected error %d when testing "
-                  "for direct read compatibility\n", path, errno);
         }
     }
     ret = 0;
@@ -1191,6 +1197,7 @@ done:
     destroyLocalReference(env, jConfiguration); 
     destroyLocalReference(env, jPath); 
     destroyLocalReference(env, jFile);
+    destroyLocalReference(env, jCapabilityString);
     if (ret) {
         if (file) {
             if (file->file) {

hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/tests/hdfs_ext_test.cc

@@ -503,7 +503,10 @@ TEST_F(HdfsExtTest, TestReadStats) {
   hdfsFileFreeReadStatistics(stats);
 
   EXPECT_EQ(0, hdfsCloseFile(fs, file));
-  EXPECT_EQ(0, errno);
+  // Since libhdfs is not guaranteed to set errno to 0 on successful
+  // operations, we disable this check for now, see HDFS-14325 for a
+  // long term solution to this problem
+  // EXPECT_EQ(0, errno);
 }
 
 //Testing working directory