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Date: Fri, 7 Oct 2016 20:34:20 +0000 (UTC)
From: "Sailesh Mukil (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.13010593.1475872408000.767493.1475872460627@Atlassian.JIRA>
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Subject: [jira] [Created] (HDFS-10982) 'errno' set on successful code path
 in hdfsOpenFileImpl()
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archived-at: Fri, 07 Oct 2016 20:34:24 -0000

Sailesh Mukil created HDFS-10982:
------------------------------------

             Summary: 'errno' set on successful code path in hdfsOpenFileImpl()
                 Key: HDFS-10982
                 URL: https://issues.apache.org/jira/browse/HDFS-10982
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: libhdfs
    Affects Versions: 2.7.0
            Reporter: Sailesh Mukil


In hdfsOpenFileImpl() in libhdfs/hdfs.c, the following code is used to check if the underlying FileSystem class supports direct reads (i.e. read(ByteBuffer)):

{code:java}
    if ((flags & O_WRONLY) == 0) {
        // Try a test read to see if we can do direct reads
        char buf;
        if (readDirect(fs, file, &buf, 0) == 0) {
            // Success - 0-byte read should return 0
            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;
{code}

The S3A connector, specifically S3AInputStream does not support direct reads, and therefore it sets 'errno = ENOTSUP' on a call to readDirect().

This 'errno' should be reset before returning the call because this is not an actual error and we're okay with not having direct reads supported.


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