Could add a utility method:

```scala
private def registerFileSystemStat[T](name: String, scheme: String, f: FileSystem.Statistics => T, defaultValue: T) = {
  metricRegistry.register(MetricRegistry.name("filesystem", scheme, name), new Guage[T] {
    override def getValue: T = fileStats(scheme).map(f).getOrElse(defaultValue)
  })
}

registerFileSystemStat("hdfs", "bytesRead", _.getBytesRead(), 0L)
registerFileSystemStat("hdfs", "bytesWritten", _.getBytesWrriten(), 0L)
...
```

(Sorry, just reading pull requests and got distracted. Typing off the top of my head, but it should work.)