linux-kernel - Re: [PATCH v2 1/8] iio: core: Add opaque_struct

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Date:   Fri, 21 Jul 2023 20:25:12 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Nuno Sa <nuno.sa@...log.com>
Subject: Re: [PATCH v2 1/8] iio: core: Add opaque_struct_size() helper and
 use it

On Fri, Jul 21, 2023 at 08:22:35PM +0300, Andy Shevchenko wrote:
> On Fri, Jul 21, 2023 at 08:00:15PM +0300, Andy Shevchenko wrote:
> > Introduce opaque_struct_size() helper, which may be moved
> > to overflow.h in the future, and use it in the IIO core.

...

> > +#define opaque_struct_size(p, a, s)	({		\
> > +	size_t _psize = sizeof(*(p));			\
> > +	size_t _asize = ALIGN(_psize, (a));		\
> > +	size_t _ssize = s;				\
> > +	_ssize ? size_add(_asize, _ssize) : _psize;	\
> > +})
> > +
> > +#define opaque_struct_data(p, a)			\
> > +	((void *)(p) + ALIGN(sizeof(*(p)), (a)))
> 
> Hmm... This can potentially evaluate p twice.
> 
> Perhaps this variant is better:
> 
> #define opaque_struct_data(p, a)	ALIGN((p) + 1, (a)))
> 
> Besides, I don't think we should worry about @s evaluation in the main macro
> which may be simplified to
> 
> #define opaque_struct_size(p, a, s)					\
> 	((s) ? size_add(ALIGN(sizeof(*(p)), (a)), (s)) : sizeof(*(p)))
> 
> Thoughts?

Also we may leave the struct always be aligned which makes the above even
simpler (but might waste bytes if @s = 0).

#define opaque_struct_size(p, a, s)	size_add(ALIGN(sizeof(*(p)), (a)), (s))

(with the respective documentation update).

-- 
With Best Regards,
Andy Shevchenko