linux-kernel - Re: [PATCH v7 1/5] lib/bitmap: add bitmap

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Message-ID: <ZSbinxApgdd+aif2@smile.fi.intel.com>
Date:   Wed, 11 Oct 2023 20:59:59 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     catalin.marinas@....com, will@...nel.org, pcc@...gle.com,
        andreyknvl@...il.com, aleksander.lobakin@...el.com,
        linux@...musvillemoes.dk, yury.norov@...il.com,
        alexandru.elisei@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, eugenis@...gle.com,
        syednwaris@...il.com, william.gray@...aro.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v7 1/5] lib/bitmap: add bitmap_{read,write}()

On Wed, Oct 11, 2023 at 07:28:31PM +0200, Alexander Potapenko wrote:
> From: Syed Nayyar Waris <syednwaris@...il.com>
> 
> The two new functions allow reading/writing values of length up to
> BITS_PER_LONG bits at arbitrary position in the bitmap.
> 
> The code was taken from "bitops: Introduce the for_each_set_clump macro"
> by Syed Nayyar Waris with a number of changes and simplifications:
>  - instead of using roundup(), which adds an unnecessary dependency
>    on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
>  - indentation is reduced by not using else-clauses (suggested by
>    checkpatch for bitmap_get_value());
>  - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
>    and bitmap_write();
>  - some redundant computations are omitted.

I realized that the corner case with these functions is when agnostic user
wants to read / write > 32 bits at a time without ifdeffery applied.

At bare minimum this has to be documented explicitly, that callers
may have an issue of the above calls on 32-bit platforms.

-- 
With Best Regards,
Andy Shevchenko