Bulk Operation

HDFS-5182 The DataNode should use its shared memory segment to mark short-circuit replicas that have been unlinked as stale

HDFS-5182 Fix a case where zero-copy or no-checksum reads were not allowed even when the block was cached

HDFS-5182 Allow dfs.datanode.shared.file.descriptor.path to contain multiple entries and fall back when needed

HDFS-5182 add dfs.client.mmap.enabled

HDFS-5182 fix DFSClient issue without libhadoop.so and some other ShortCircuitShm cleanups

HDFS-5182 Forcibly timeout misbehaving DFSClients that try to do no-checksum reads that extend too long

HDFS-5182 add DomainSocket#shutdown method

HDFS-5182 The DFSClient and DataNode should use shared memory segments to communicate short-circuit information

HDFS-5182 Minor cleanups to ShortCircuitReplica, FsDatasetCache, and DomainSocketWatcher

HDFS-5182 Make BlockReaderFactory#BlockReaderPeer a static class

HDFS-5182 Unify mmap cache and short-circuit file descriptor cache

HDFS-5182 add ShortCircuitSharedMemorySegment