linux-kernel - Re: [PATCH v6 1/8] bitops: Introduce the for_each_set

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Date:   Fri, 11 Jan 2019 10:00:46 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     William Breathitt Gray <vilhelm.gray@...il.com>,
        linus.walleij@...aro.org
Cc:     akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        andriy.shevchenko@...ux.intel.com,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 1/8] bitops: Introduce the for_each_set_clump8 macro

On 19/12/2018 07.00, William Breathitt Gray wrote:
> +/**
> + * bitmap_set_value8 - set an 8-bit value within a memory region
> + * @bitmap: address to the bitmap memory region
> + * @value: the 8-bit value
> + * @start: bit offset of the 8-bit value
> + */
> +void bitmap_set_value8(unsigned long *const bitmap,
> +		       const unsigned long *const value,
> +		       const unsigned int start)
> +{
> +	const size_t index = BIT_WORD(start);
> +	const unsigned int offset = start % BITS_PER_LONG;
> +	const unsigned long mask = GENMASK(7, offset);
> +
> +	bitmap[index] &= ~mask;
> +	bitmap[index] |= (*value << offset) & mask;
> +}

errh, why pass the value by reference? That seems rather odd. Also, if
anybody passes a value that doesn't fit in 8 bits, they get what they
deserve; IOW I don't see a reason for the masking in the last line, but
if its convenient for the users, keep it. In any case, please change the
type of value.

Rasmus