Re: [PATCH v8 1/3] devres: provide devm_krealloc()

[Bartosz Golaszewski]

On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> >
> > Implement the managed variant of krealloc(). This function works with
> > all memory allocated by devm_kmalloc() (or devres functions using it
> > implicitly like devm_kmemdup(), devm_kstrdup() etc.).
> >
> > Managed realloc'ed chunks can be manually released with devm_kfree().
> >
> > Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
>
> ...
>
> > +static struct devres *to_devres(void *data)
> > +{
> > +     return data - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
> > +
> > +static size_t devres_data_size(size_t total_size)
> > +{
> > +     return total_size - ALIGN(sizeof(struct devres), ARCH_KMALLOC_MINALIGN);
> > +}
>
> I'm fine with above, but here is a side note, perhaps
>
>         offsetof(struct devres, data)
>
> will be more practical (no duplication of alignment and hence slightly better
> maintenance)? (Note, I didn't check if it provides the correct result)
>

Hi Andy,

The data pointer in struct devres is defined as:

    u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];

And this value (assigned the value of ARCH_DMA_MINALIGN) varies from
one arch to another. I wasn't really sure if offsetof() would work for
every case so I went with something very explicit.

> Another side note: do we have existing users of these helpers?
>

Which ones? Because I assume you're not referring to the ones I'm
adding in this patch. :)

Bart