':param pool: The filesystem\'s pool name, e.g. ``b"hpool"``.
:param dataset: The filesystem\'s dataset name, e.g. ``b"myfs"``, or
``None`` for the top-level filesystem.
:param twisted.python.filepath.FilePath mountpoint: Where the
filesystem is mounted.
:param VolumeSize size: The capacity information for this filesystem.'

def __init__(self, pool, dataset, mountpoint=None, size=None, reactor=None):

    self.pool = pool
    self.dataset = dataset
    self._mountpoint = mountpoint
    self.size = size
    if (reactor is None):
        from twisted.internet import reactor
    self._reactor = reactor
