linux-kernel - Re: [PATCH v6 1/2] lib/string.c: add __sysfs_match_string_with

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Message-ID: <CAHp75Ve06gYFE+U_XNZfTFceMEzmADR6wd0OYr+tVMQ6hW3MLQ@mail.gmail.com>
Date:   Tue, 22 Dec 2020 15:42:52 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v6 1/2] lib/string.c: add __sysfs_match_string_with_gaps() helper

On Tue, Dec 22, 2020 at 3:09 PM Alexandru Ardelean
<alexandru.ardelean@...log.com> wrote:
>
> The original docstring of the __sysfs_match_string() and match_string()
> helper, implied that -1 could be used to search through NULL terminated
> arrays, and positive 'n' could be used to go through arrays that may have
> NULL elements in the middle of the array.
>
> This isn't true. Regardless of the value of 'n', the first NULL element in
> the array will stop the search, even if the element may be after a NULL
> element.
>
> To allow for a behavior where we can use the __sysfs_match_string() to
> search over arrays with NULL elements in the middle, the
> __sysfs_match_string_with_gaps() helper is added.
> If n > 0, the search will continue until the element is found or n is
> reached.
> If n < 0, the search will continue until the element is found or a NULL
> character is found.

I'm wondering if we can leave __sysfs_match_string() alone (w/o adding
unnecessary branch).

int __sysfs_match_string_with_gaps(const char * const *array, size_t
n, const char *str)
{
       const char *item;
       int index;

       for (index = 0; index < n; index++) {
               item = array[index];
               if (!item)
                       continue;
               if (sysfs_streq(item, str))
                       return index;
       }
       return -EINVAL;
}

Note, the check n>0 seems redundant for this particular function.

> +static int __sysfs_match_string_common(const char * const *array, ssize_t n,
> +                                      const char *str, bool gaps)
> +{
> +       const char *item;
> +       int index;
> +
> +       for (index = 0; index < n; index++) {
> +               item = array[index];
> +               if (!item) {
> +                       if (gaps && n > 0)
> +                               continue;
> +                       break;
> +               }
> +               if (sysfs_streq(item, str))
> +                       return index;
> +       }
> +
> +       return -EINVAL;
> +}
> +
>  /**
>   * __sysfs_match_string - matches given string in an array
>   * @array: array of strings
> @@ -770,21 +790,32 @@ EXPORT_SYMBOL(match_string);
>   */
>  int __sysfs_match_string(const char * const *array, size_t n, const char *str)
>  {
> -       const char *item;
> -       int index;
> -
> -       for (index = 0; index < n; index++) {
> -               item = array[index];
> -               if (!item)
> -                       break;
> -               if (sysfs_streq(item, str))
> -                       return index;
> -       }
> -
> -       return -EINVAL;
> +       return __sysfs_match_string_common(array, n, str, false);
>  }

-- 
With Best Regards,
Andy Shevchenko