anchor.diff:  copy_file_contents_sfm(FromHandle, ToHandle) ->
       {ok, OpenFromHandle} = storage_file_manager:open(FromHandle, read),
       {ok, OpenToHandle} = storage_file_manager:open(ToHandle, write),
  -    ChunkSize = application:get_env(?APP_NAME, ?CHUNK_SIZE_ENV_KEY),
  +    {ok, ChunkSize} = application:get_env(?APP_NAME, ?CHUNK_SIZE_ENV_KEY),
       copy_file_contents_sfm(OpenFromHandle, OpenToHandle, 0, ChunkSize).
   
   -spec copy_file_contents_sfm(HandleFrom :: storage_file_manager:handle(),
  
positive.code: copy_file_contents(SessId, From, To) ->
      {ok, FromHandle} = logical_file_manager:open(SessId, From, read),
      {ok, ToHandle} = logical_file_manager:open(SessId, To, write),
      ChunkSize = application:get_env(?APP_NAME, ?CHUNK_SIZE_ENV_KEY),
      copy_file_contents(SessId, FromHandle, ToHandle, 0, ChunkSize).
  
  -spec copy_file_contents(session:id(), FromHandle :: logical_file_manager:handle(),
  
negative.code: -spec list_all_children(Entry :: fslogic_worker:file()) ->
      {ok, [#child_link{}]}.
  list_all_children(Entry) ->
      {ok, ChunkSize} = application:get_env(?APP_NAME, ls_chunk_size),
      list_all_children(Entry, 0, ChunkSize, []).
  
  -spec list_all_children(Entry :: fslogic_worker:file(),
      Offset :: non_neg_integer(), Count :: non_neg_integer(),
  