Re: [PATCH net-next] netlink: provide an ability to set default extack message

[Vladimir Oltean <olteanv@gmail.com>]

On Fri, Jan 27, 2023 at 07:22:26AM +0200, Leon Romanovsky wrote:
> It means changing ALL error unwind places where extack was forwarded
> before to subfunctions.
> 
> Places like this:
>  ret = func(..., extack)
>  if (ret) {
>    NL_SET_ERR_MSG_MOD...
>    return ret;
>  }
> 
> will need to be changed to something like this:
>  ret = func(..., extack)
>  if (ret) {
>    NL_SET_ERR_MSG_WEAK...
>    return ret;
>  }

Yeah, but my point is that you inspect the code that you plan to convert,
rather than converting it in bulk and inspecting later...

> Can we please discuss current code and not over-engineered case which
> doesn't exist in the reality?
> 
> Even for your case, I would like to see NL_SET_ERR_MSG_FORCE() to
> explicitly say that message will be overwritten.

__nla_validate_parse()

	if (unlikely(rem > 0)) {
		pr_warn_ratelimited("netlink: %d bytes leftover after parsing attributes in process `%s'.\n",
				    rem, current->comm);
		NL_SET_ERR_MSG(extack, "bytes leftover after parsing attributes");
		if (validate & NL_VALIDATE_TRAILING)
			return -EINVAL;
	}

	return 0;

called by nla_validate_deprecated() with validate == NL_VALIDATE_LIBERAL

followed by other extack setting in tunnel_key_copy_opts(), which will
not overwrite the initial warning message.