Comment 10 for bug 1635339

An untested hack that might fail cleaner might be:

  error_report("Broken driver ..... migration failed");
  qemu_file_set_error(migrate_get_current()->to_dst_file, -EINVAL);

(untested, probably needs checking it works with savevm).

I must go around and add a return value to pre_save().

We probably also need to make sure some migration testing gets added to the driver dev