message: rafs: initialize localfs backend's metrics when blob file is specified in config
  When using localfs as backend, and blob file is specified directly in
  config, 'metrics' wasn't initialized and default to None. This causes
  unwrap() failure, as Localfs::metrics() assumes 'metrics' field is
  always Some() not None.
diff: @@ -88,12 +88,14 @@ pub fn new(config: serde_json::value::Value, id: Option<&str>) -> Result<LocalFs
  return Err(einval!("blob file or dir is required"));
  }
  + let metrics = id.map(|i| BackendMetrics::new(i, "localfs"));
  if !config.blob_file.is_empty() {
  return Ok(LocalFs {
  blob_file: config.blob_file,
  readahead: config.readahead,
  readahead_sec: config.readahead_sec,
  file_table: RwLock::new(HashMap::new()),
  + metrics,
  ..Default::default()
  });
  }
  @@ -103,7 +105,7 @@ pub fn new(config: serde_json::value::Value, id: Option<&str>) -> Result<LocalFs
  readahead: config.readahead,
  readahead_sec: config.readahead_sec,
  file_table: RwLock::new(HashMap::new()),
  - metrics: id.map(|i| BackendMetrics::new(i, "localfs")),
  + metrics,
  ..Default::default()
  })
  }
  