linux-kernel - Re: [PATCH 3/8] lib: bitmap: fold nbits into region struct

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Date:   Tue, 26 Jan 2021 23:16:25 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     linux-kernel@...r.kernel.org, lizefan@...wei.com, mingo@...nel.org,
        tglx@...utronix.de, josh@...htriplett.org, yury.norov@...il.com,
        peterz@...radead.org, paulmck@...nel.org, fweisbec@...il.com,
        linux@...musvillemoes.dk
Subject: Re: [PATCH 3/8] lib: bitmap: fold nbits into region struct

On Tue, Jan 26, 2021 at 12:11:36PM -0500, Paul Gortmaker wrote:
> This will reduce parameter passing and enable using nbits as part
> of future dynamic region parameter parsing.

One nit below, nevertheless
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

> Cc: Yury Norov <yury.norov@...il.com>
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Suggested-by: Yury Norov <yury.norov@...il.com>
> Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> ---
>  lib/bitmap.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 75006c4036e9..162e2850c622 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -487,24 +487,24 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf);
>  
>  /*
>   * Region 9-38:4/10 describes the following bitmap structure:
> - * 0	   9  12    18			38
> - * .........****......****......****......
> - *	    ^  ^     ^			 ^
> - *      start  off   group_len	       end
> + * 0	   9  12    18			38	     N
> + * .........****......****......****..................
> + *	    ^  ^     ^			 ^	     ^
> + *      start  off   group_len	       end	 nbits
>   */
>  struct region {
>  	unsigned int start;
>  	unsigned int off;
>  	unsigned int group_len;
>  	unsigned int end;
> +	unsigned int nbits;
>  };
>  
> -static int bitmap_set_region(const struct region *r,
> -				unsigned long *bitmap, int nbits)
> +static int bitmap_set_region(const struct region *r, unsigned long *bitmap)
>  {
>  	unsigned int start;
>  
> -	if (r->end >= nbits)
> +	if (r->end >= r->nbits)
>  		return -ERANGE;
>  
>  	for (start = r->start; start <= r->end; start += r->group_len)
> @@ -640,7 +640,8 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
>  	struct region r;
>  	long ret;
>  
> -	bitmap_zero(maskp, nmaskbits);
> +	r.nbits = nmaskbits;

> +	bitmap_zero(maskp, r.nbits);

This sounds not right from style perspective.
You have completely uninitialized r on stack, then you assign only one value
for immediate use here and...

>  	while (buf) {
>  		buf = bitmap_find_region(buf);
> @@ -655,7 +656,7 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
>  		if (ret)
>  			return ret;
>  
> -		ret = bitmap_set_region(&r, maskp, nmaskbits);
> +		ret = bitmap_set_region(&r, maskp);

...hiding this fact here. Which I would expect that &r may be rewritten here.

I would leave these unchanged and simple assign the value in
bitmap_set_region().

>  		if (ret)
>  			return ret;
>  	}
> -- 
> 2.17.1
> 

-- 
With Best Regards,
Andy Shevchenko