linux-kernel - Re: [PATCH][V4] lib: fix __sysfs_match

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Date:   Tue, 25 Jun 2019 16:28:12 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        alexander.shishkin@...ux.intel.com, akpm@...ux-foundation.org,
        ndesaulniers@...gle.com
Subject: Re: [PATCH][V4] lib: fix __sysfs_match_string() helper when n != -1

On Tue, Jun 25, 2019 at 04:01:04PM +0300, Alexandru Ardelean wrote:
> The documentation the `__sysfs_match_string()` helper mentions that `n`
> (the size of the given array) should be:
>  * @n: number of strings in the array or -1 for NULL terminated arrays
> 
> The behavior of the function is different, in the sense that it exits on
> the first NULL element in the array.
> 
> This patch changes the behavior, to exit the loop when a NULL element is
> found, and the size of the array is provided as -1.
> 
> All current users of __sysfs_match_string() & sysfs_match_string() provide
> contiguous arrays of strings, so this behavior change doesn't influence
> anything (at this point in time).
> 
> This behavior change allows for an array of strings to have NULL elements
> within the array, which will be ignored. This is particularly useful when
> creating mapping of strings and integers (as bitfields or other HW
> description).

Since it does nothing for current users and comes without an example,
it's hard to justify the need.

The code itself looks good to me.

> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
> 
> Changelog v3 -> v4:
> * split this patch away from series; there are some unsolved discussions
>   that will probably need resolving per sub-system
> 
>  lib/string.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/string.c b/lib/string.c
> index 3ab861c1a857..5bea3f98478a 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -674,8 +674,11 @@ int __sysfs_match_string(const char * const *array, size_t n, const char *str)
>  
>  	for (index = 0; index < n; index++) {
>  		item = array[index];
> -		if (!item)
> +		if (!item) {
> +			if (n != (size_t)-1)
> +				continue;
>  			break;
> +		}
>  		if (sysfs_streq(item, str))
>  			return index;
>  	}
> -- 
> 2.20.1
> 

-- 
With Best Regards,
Andy Shevchenko