nbd_unlocked_set_private_data (struct nbd_handle *h, uintptr_t data)
{
  uintptr_t old_data;

  /* atomic_exchange? XXX */
  old_data = h->private_data;
  h->private_data = data;
  return old_data;
}
nbd_unlocked_set_private_data (struct nbd_handle *h, uintptr_t data)
{
  uintptr_t old_data;

   
  old_data = h->private_data;
  h->private_data = data;
  return old_data;
}