code: def unpack_params(
      params, attr_name, buffer, transfer_dtype, zero_fill, stream=None
  ):
      """Pack parameters into a single CuPy array for efficient communication."""
      if len(params) == 0:
          return
      xp = chainer.backend.get_array_module(
          getattr(params[0], attr_name)
      )
      offset = 0
      for param in params:
          v = getattr(param, attr_name)
          if attr_name == "grad" and v is None and zero_fill:
              v = param.xp.empty_like(param.data)
              setattr(param, attr_name, v)
          size = v.size * np.dtype(transfer_dtype).itemsize
          grad_dtype = v.dtype
          if grad_dtype != transfer_dtype:
              v = xp.array(v, copy=False, dtype=transfer_dtype)
          buffer.to_device(v, size, offset, stream)
          offset += size
          if grad_dtype != transfer_dtype:
              # avoid using setattr as ChainerX array cannot be directly updated
              getattr(param, attr_name)[...] = v.astype(grad_dtype)
  
imports: import ctypes
  import mpi4py.MPI
  import numpy
  from chainermn.communicators import _communication_utility
  import chainer.backends
  import chainerx
label_desc: Use image node_id 6 for calling a global function with example usage: unpack_params(params, attr_name, buffer, transfer_dtype, zero_fill, stream) without return types