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

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Date:   Wed, 24 Aug 2022 20:50:04 +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 4:37 PM Yury Norov <yury.norov@...il.com> wrote:
> On Wed, Aug 24, 2022 at 12:22:33PM +0300, Andy Shevchenko wrote:
> > On Wed, Aug 24, 2022 at 5:17 AM Yury Norov <yury.norov@...il.com> wrote:

...

> > > 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?
>
> Because there is a codebase that relies on existing types, mostly in
> filesystem code. And those fs fixes would require 5 or 6 patches.
>
> This would triple the length of this series, and is completely
> unrelated. That's why I think that:
>         > > This should be fixed for all in a separate series.

So comment update then, if a new version is required?

...

> > > +#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!"
>
> This is a local header which is not intended to be included anywhere
> except lib/find_bit{,_be}.c. I don't expect someone else would want to
> include it, even in lib. So what you suggest is a bit overthinking to
> me. But if you insist, I can do that.

Basically by the above you assured me that #error is the right
approach, please do it that way and we will definitely catch the
incorrect users (even by `git grep -lw __ffs_word_op` if they slip
into the kernel somehow).

-- 
With Best Regards,
Andy Shevchenko