linux-kernel - Re: [PATCH v8 1/3] devres: provide devm

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Message-ID: <CAMRc=Me=D1cOsaRqK-BwHT7f-_=3=eciduA=G95FfE2e_XUWfg@mail.gmail.com>
Date:   Fri, 21 Aug 2020 10:59:19 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Michal Simek <michal.simek@...inx.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH v8 1/3] devres: provide devm_krealloc()

On Fri, Aug 21, 2020 at 10:35 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Aug 20, 2020 at 08:51:08PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> >
> > 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@...libre.com>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>
> ...
>
> > +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