linux-kernel - Re: [PATCH v10 1/2] lib/bitmap: add bitmap

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Date:   Thu, 26 Oct 2023 17:24:32 +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 v10 1/2] lib/bitmap: add bitmap_{read,write}()

On Thu, Oct 26, 2023 at 03:59:11PM +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.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

One nit below, though.

...

> +/**
> + * bitmap_write - write n-bit value within a memory region
> + * @map: address to the bitmap memory region
> + * @value: value to write, clamped to nbits
> + * @start: bit offset of the n-bit value
> + * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG.
> + *
> + * bitmap_write() behaves as-if implemented as @nbits calls of __assign_bit(),
> + * i.e. bits beyond @nbits are ignored:
> + *
> + *   for (bit = 0; bit < nbits; bit++)
> + *           __assign_bit(start + bit, bitmap, val & BIT(bit));
> + *
> + * For @nbits > BITS_PER_LONG no writes are performed.

nbits == 0 hasn't been mentioned.

(no, the main nit below)

> + */
> +static inline void bitmap_write(unsigned long *map,
> +				unsigned long value,
> +				unsigned long start, unsigned long nbits)

While noticing strange indentation (you have space for the parameter on
the previous line, I realized that this is a counter-intuitive interface.
Can you actually make value the last parameter?

-- 
With Best Regards,
Andy Shevchenko