DO NOT USE THIS INSTANCE FOR LIVE DATA!!!!
This was added by HDFS-8703. This usually don't come out unless user makes 0-byte read calls, which does happen.
if (ret == 0) { DFSClient.LOG.warn("zero"); }
This was removed by HDFS-8905 in trunk and 3.x, but remained in 2.x.
HDFS-8703 Merge refactor of DFSInputStream from ErasureCoding branch