Messages in this thread | ![/](/images/icornerl.gif) | | Date | Fri, 21 Jul 2023 20:12:48 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH v2 1/8] iio: core: Add opaque_struct_size() helper and use it |
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Hello Andy,
On Fri, Jul 21, 2023 at 08:25:12PM +0300, Andy Shevchenko wrote: > 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.
I don't think sizeof evaluates its parameter? It should only defer its type and then calculate the respective size.
> > Perhaps this variant is better: > > > > #define opaque_struct_data(p, a) ALIGN((p) + 1, (a)))
Still I like this better.
> > 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).
Depending on the value of a, the bytes "wasted" here might not be saved anyhow because the memory allocator will round up the allocation size to a multiple of some chunk size anyhow.
> #define opaque_struct_size(p, a, s) size_add(ALIGN(sizeof(*(p)), (a)), (s)) > > (with the respective documentation update).
That would be my favourite.
Possible users of this helper include:
__spi_alloc_controller() in drivers/spi/spi.c alloc_netdev_mqs in net/core/dev.c
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [unhandled content-type:application/pgp-signature] | ![\](/images/icornerr.gif) |