docs: def fetch(self, vault_client, backends):
          """Updates local resource with context on whether this
          backend is actually mounted and available"""
          if not is_mounted(self.backend, self.path, backends) or \
             self.tune_prefix is None:
              return
  
          backend_details = get_backend(self.backend, self.path, backends)
          self.existing = backend_details['config']
          if backend_details['description']:
              self.existing['description'] = backend_details['description']
  
          if vault_client.version is None:
              return
  
          if not self.managed:
              return
  
          a_prefix = self.tune_prefix
          if self.tune_prefix:
              a_prefix = "%s/" % self.tune_prefix
  
          v_path = "sys/mounts/%s%s/tune" % (a_prefix, self.path)
          t_resp = vault_client.read(v_path)
          if 'data' not in t_resp:
              e_msg = "Unable to retrieve tuning info for %s" % self
              raise aomi_excep.VaultData(e_msg)
  
          e_obj = t_resp['data']
          e_obj['description'] = None
          n_path = normalize_vault_path(self.path)
          if n_path in backends:
              a_mount = backends[n_path]
              if 'description' in a_mount and a_mount['description']:
                  e_obj['description'] = a_mount['description']
  
          self.existing = e_obj