From mboxrd@z Thu Jan  1 00:00:00 1970
From: Johannes Berg <johannes@sipsolutions.net>
Subject: Re: [RFC 1/4] netlink: make extended ACK setting NULL-friendly
Date: Tue, 25 Apr 2017 10:13:34 +0200
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On Tue, 2017-04-25 at 01:06 -0700, Jakub Kicinski wrote:

> +#define NL_SET_ERR_MSG(extack, msg) do {		\
> +	struct netlink_ext_ack *_extack = (extack);	\
> +	static const char _msg[] = (msg);		\
> +							\
> +	if (_extack)					\
> +		_extack->_msg = _msg;			\
> +	else						\
> +		pr_info("%s\n", _msg);			\
>  } while (0)

That's a good point, I used it only for genetlink so far where it was
guaranteed non-NULL.

I'm not really sure about the printing though - I'd rather not people
start relying on that and then we convert to have non-NULL and the
message disappears as a result ...

johannes