code: def backend(self):
      return "cpu:gloo,cuda:nccl"
  
file_path: pytorch/test/distributed/checkpoint/test_fsdp_model_state.py
imports: import torch
  import torch.distributed
  import torch.distributed.checkpoint
  from torch.distributed.checkpoint.default_planner import DefaultLoadPlanner, DefaultSavePlanner
  from torch.distributed.fsdp import FullyShardedDataParallel
  from torch.distributed.fsdp.fully_sharded_data_parallel import StateDictType
  from torch.testing._internal.common_distributed import skip_if_lt_x_gpu
  from torch.testing._internal.common_utils import run_tests
  from torch.testing._internal.distributed._tensor.common_dtensor import DTensorTestBase, with_comms
  from torch.testing._internal.distributed.checkpoint_utils import with_temp_dir
label_desc: Use image node_id 1 for calling the FsdpModelStateCheckpoint obj's underlying member method code with example usage: obj.backend() and returns: str