linux-kernel - Re: [PATCH v2 2/3] lib/find_bit: create find_first_zero_bit

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Message-ID: <CAHp75VdgXBFH_vxUNYZLc2ahOrC8oBj0x=2GWXZr+CLGX1qyTg@mail.gmail.com>
Date:   Wed, 24 Aug 2022 12:22:33 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Dennis Zhou <dennis@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexey Klimov <aklimov@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Whitcroft <apw@...onical.com>
Subject: Re: [PATCH v2 2/3] lib/find_bit: create find_first_zero_bit_le()

On Wed, Aug 24, 2022 at 5:17 AM Yury Norov <yury.norov@...il.com> wrote:
>
> find_first_zero_bit_le() is an alias to find_next_zero_bit_le(),
> despite that 'next' is known to be slower than the 'first' version.
>
> Now that we have a common FIND_FIRST_BIT() macro helper, it's trivial
> to implement find_first_zero_bit_le() as a real function.
>
> Moving find_*_le() to a separate file helps to fit the FIND_FIRST_BIT()
> to the _le needs by wiring word_op to swab.
>
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
> Like other find_*_le() functions, the new one takes void *addr, instead
> of unsigned long *. This should be fixed for all in a separate series.

>From this comment it is unclear to me why we can't fix them first and
then apply this with the correct type?

...

> +#define word_op swab
> +#include "find_bit.h"

Looking at this, I would rather always require to define __ffs_word_op
(or whatever name) in the user and replace #ifndef in the find_bit.h
with
#error "The __ffs_word_op must be defined before including find_bit.h!"

-- 
With Best Regards,
Andy Shevchenko