[HDFS-10982] 'errno' set on successful code path in hdfsOpenFileImpl()

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.7.0
• Component/s: libhdfs
• Labels: easyfix
• Assignee: John Zhuge
• Reporter: Sailesh Mukil
• Created: 07/Oct/16 20:33
• Updated: 10/Oct/16 05:01

Description

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)):

    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;

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.