dcopy_cmd_alloc
ret = dcopy_cmd_alloc(channel, dcopy_flags, &cmd);
int dcopy_cmd_alloc(dcopy_handle_t handle, int flags, dcopy_cmd_t *cmd);
rc = dcopy_cmd_alloc(handle, flags, &cmds[idx]);
e = dcopy_cmd_alloc(channel, flags, &cmd);
e = dcopy_cmd_alloc(channel, flags, &cmd);