linux-kernel - Re: [PATCH v3 2/4] lib/find_bit: create find_first_zero_bit

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Message-ID: <xhsmhedwnb15r.mognet@vschneid.remote.csb>
Date:   Wed, 07 Sep 2022 17:27:12 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Yury Norov <yury.norov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Alexey Klimov <klimov.linux@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andy Whitcroft <apw@...onical.com>,
        Catalin Marinas <catalin.marinas@....com>,
        David Laight <David.Laight@...LAB.COM>,
        Dennis Zhou <dennis@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Kees Cook <keescook@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v3 2/4] lib/find_bit: create find_first_zero_bit_le()

On 27/08/22 10:58, Yury Norov wrote:
> find_first_zero_bit_le() is an alias to find_next_zero_bit_le(),
> despite that 'next' is known to be slower than 'first' version.
>
> Now that we have common FIND_FIRST_BIT() macro helper, it's trivial
> to implement find_first_zero_bit_le() as a real function.
>
> Signed-off-by: Yury Norov <yury.norov@...il.com>

Declaration ordering nit below, otherwise:
Reviewed-by: Valentin Schneider <vschneid@...hat.com>

> ---
>  include/linux/find.h | 23 ++++++++++++++++++-----
>  lib/find_bit.c       | 14 ++++++++++++++
>  2 files changed, 32 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/find.h b/include/linux/find.h
> index 424ef67d4a42..a1861d0ba533 100644
> --- a/include/linux/find.h
> +++ b/include/linux/find.h
> @@ -17,6 +17,10 @@ extern unsigned long _find_first_and_bit(const unsigned long *addr1,
>  extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
>  extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);
>  
> +#ifdef __BIG_ENDIAN
> +unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size);
> +#endif
> +
>  #ifndef find_next_bit
>  /**
>   * find_next_bit - find the next set bit in a memory region
> @@ -251,6 +255,20 @@ unsigned long find_next_zero_bit_le(const void *addr, unsigned
>  }
>  #endif
>  
> +#ifndef find_first_zero_bit_le
> +static inline
> +unsigned long find_first_zero_bit_le(const unsigned long *addr, unsigned long size)
> +{
> +	if (small_const_nbits(size)) {
> +		unsigned long val = swab(*addr) | ~GENMASK(size - 1, 0);
> +
> +		return val == ~0UL ? size : ffz(val);
> +	}
> +
> +	return _find_first_zero_bit_le(addr, size);
> +}
> +#endif
> +

Nit: this should be placed after the declaration of find_next_bit_le() to
match the __LITTLE_ENDIAN declaration order above.

>  #ifndef find_next_bit_le
>  static inline
>  unsigned long find_next_bit_le(const void *addr, unsigned
> @@ -270,11 +288,6 @@ unsigned long find_next_bit_le(const void *addr, unsigned
>  }
>  #endif
>  
> -#ifndef find_first_zero_bit_le
> -#define find_first_zero_bit_le(addr, size) \
> -	find_next_zero_bit_le((addr), (size), 0)
> -#endif
> -
>  #else
>  #error "Please fix <asm/byteorder.h>"
>  #endif
> diff --git a/lib/find_bit.c b/lib/find_bit.c
> index 894b656f6836..f4d9b9684811 100644
> --- a/lib/find_bit.c
> +++ b/lib/find_bit.c
> @@ -160,3 +160,17 @@ unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
>  	return offset;
>  }
>  EXPORT_SYMBOL(find_next_clump8);
> +
> +#ifdef __BIG_ENDIAN
> +#ifndef find_first_zero_bit_le
> +/*
> + * Find the first cleared bit in an LE memory region.
> + */
> +unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size)
> +{
> +	return FIND_FIRST_BIT(~addr[idx], swab, size);
> +}
> +EXPORT_SYMBOL(_find_first_zero_bit_le);
> +#endif
> +
> +#endif /* __BIG_ENDIAN */
> -- 
> 2.34.1