Re: [PATCH net-next 3/6] genetlink: add helper for checking required attrs and use it in devlink

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 24 Aug 2022 21:44:22 +0200 Johannes Berg wrote:
> On Tue, 2022-08-23 at 21:50 -0700, Jakub Kicinski wrote:
> > 
> > +/* Report that a root attribute is missing */
> > +#define GENL_REQ_ATTR_CHECK(info, attr) ({				\
> > +	struct genl_info *__info = (info);				\
> > +	u32 __attr = (attr);						\
> > +	int __retval;							\
> > +									\
> > +	__retval = !__info->attrs[__attr];				\
> > +	if (__retval)							\
> > +		NL_SET_ERR_ATTR_MISS(__info->extack,			\
> > +				     __info->userhdr ? : __info->genlhdr, \
> > +				     __attr);				\
> > +	__retval;							\
> > +})  
> 
> Not sure this needs to be a macro btw, could be an inline returning a
> bool? You're not really expanding anything here, nor doing something
> with strings (unlike GENL_SET_ERR_MSG for example.)

Initially I typed up both flavors with and without the message 
but I dropped the _MSG() one since I didn't find a strong enough 
reason to use it.

If we do get the _MSG() version at some point (perhaps to preserve 
an existing message during conversion?) having different case
would seem off.

I have no opinion which way is better, LMK if you prefer lower case
(ignoring existing non-MSG helpers being upper case) and I'll sed thru
the patches, no problem at all.