A distributed implementation of {@link org.apache.hadoop.fs.FileSystem}. This is loosely modelled after Google's GFS.

The most important difference is that unlike GFS, Hadoop DFS files have strictly one writer at any one time. Bytes are always appended to the end of the writer's stream. There is no notion of "record appends" or "mutations" that are then checked or reordered. Writers simply emit a byte stream. That byte stream is guaranteed to be stored in the order written.

]]> This method must return as quickly as possible, since it's called in a critical section of the NameNode's operation. @param succeeded Whether authorization succeeded. @param userName Name of the user executing the request. @param addr Remote address of the request. @param cmd The requested command. @param src Path of affected source file. @param dst Path of affected destination file (if any). @param stat File information for operations that change the file's metadata (permissions, owner, times, etc).]]> Use the visitor pattern to visit namespace tree.

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