'Return the origin of an LV that is a snapshot, None otherwise.'

def lv_get_origin(self, name):

    cmd = (LVM.LVM_CMD_PREFIX + ['lvdisplay', '--noheading', '-C', '-o', 'Origin', ('%s/%s' % (self.vg_name, name))])
    (out, _err) = self._execute(root_helper=self._root_helper, run_as_root=True, *cmd)
    out = out.strip()
    if out:
        return out
    return None
