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

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Message-ID: <CA+U=Dsp-eZXgmp-+EJ8Nv3BE6ttRwyYTtS1a0oaz3ooiDP7eHQ@mail.gmail.com>
Date:   Wed, 23 Dec 2020 09:31:08 +0200
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Alexandru Ardelean <alexandru.ardelean@...log.com>,
        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 3:43 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> 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).

Works for me.
Will re-spin.

>
> 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