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Message-ID: <ZMgTCzslTd2REumj@smile.fi.intel.com>
Date: Mon, 31 Jul 2023 23:01:15 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
Lars-Peter Clausen <lars@...afoo.de>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Kees Cook <keescook@...omium.org>, Nuno Sa <nuno.sa@...log.com>
Subject: Re: [PATCH v3 2/4] iio: core: Add opaque_struct_size() helper and
use it
On Sat, Jul 29, 2023 at 12:46:18PM +0100, Jonathan Cameron wrote:
> On Mon, 24 Jul 2023 14:02:02 +0300
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
...
> > + * Note, when @s is 0, the alignment @a is added to the sizeof(*(@p))
> > + * and the result, depending on the @a, may be way off the initial size.
>
> How often is this true? A quick and dirty grep suggests at least 2 so perhaps
> worth retaining the old behaviour.
You mean that the sizeof(_some_grepped_struct_) is much less than an alignment
in those uses?
> Can we take that into account? Maybe something like
>
> #define opaque_struct_size(p, a, s) ((s) ? size_add(ALIGN(sizeof(*(p)), (a)), (s)): sizeof(*p))
(s) will be evaluated twice, not good. So, not in this form.
> Or do it at the call site below.
Looks much better to me.
...
> if (sizeof_priv)
> alloc_size = opaque_struct_size(iio_dev_opaque, IIO_DMA_MINALIGN, sizeof_priv);
> else
> alloc_size = sizeof(struct iio_dev_opaque);
Right.
...
> > - indio_dev->priv = (char *)iio_dev_opaque +
> > - ALIGN(sizeof(struct iio_dev_opaque), IIO_DMA_MINALIGN);
> > + indio_dev->priv = opaque_struct_data(iio_dev_opaque, IIO_DMA_MINALIGN);
>
> Would have been safer if original code set this to NULL if
> sizeof_priv == 0
Yeah, original code and proposed change has no difference in this sense.
> A driver doing that should never have used iio_priv() but nicer if it was
> NULL rather than off the end of the allocation.
Agree.
But looking at the above, I would rather see that in a form of
if (...)
priv = opaque_struct_data(...);
else
priv = NULL;
--
With Best Regards,
Andy Shevchenko
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