linux-kernel - Re: [PATCH] lib/string: update match_string() doc-strings with correct behavior

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Message-ID: <27677d8f08e1d9c1327b9771a9b93c99661ed2d0.camel@analog.com>
Date:   Thu, 13 Feb 2020 07:09:49 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>
CC:     "keescook@...omium.org" <keescook@...omium.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "tobin@...nel.org" <tobin@...nel.org>
Subject: Re: [PATCH] lib/string: update match_string() doc-strings with
 correct behavior

On Wed, 2020-02-12 at 18:46 +0200, Andy Shevchenko wrote:
> [External]
> 
> On Wed, Feb 12, 2020 at 04:47:23PM +0200, Alexandru Ardelean wrote:
> > There were a few attempts at changing behavior of the match_string()
> > helpers (i.e. 'match_string()' & 'sysfs_match_string()'), to change &
> > extend the behavior according to the doc-string.
> > 
> > But the simplest approach is to just fix the doc-strings. The current
> > behavior is fine as-is, and some bugs were introduced trying to fix it.
> > 
> > As for extending the behavior, new helpers can always be introduced if
> > needed.
> > 
> > The match_string() helpers behave more like 'strncmp()' in the sense that
> > they go up to n elements or until the first NULL element in the array of
> > strings.
> > 
> > This change updates the doc-strings with this info.
> > 
> > Some references to the previous attempts (in no particular order):
> >   
> > https://lore.kernel.org/lkml/20190508111913.7276-1-alexandru.ardelean@analog.com/
> >   
> > https://lore.kernel.org/lkml/20190625130104.29904-1-alexandru.ardelean@analog.com/
> >   
> > https://lore.kernel.org/lkml/20190422083257.21805-1-alexandru.ardelean@analog.com/
> 
> ...
> 
> >  /**
> >   * match_string - matches given string in an array
> >   * @array:	array of strings
> > - * @n:		number of strings in the array or -1 for NULL terminated
> > arrays
> > + * @n:		number of strings in the array to compare
> 
> But this change won't be helpful, it actually hides the part of behaviour that
> is being used.
> 
> >   * @string:	string to match with
> >   *
> > + * This routine will look for a string in an array of strings up to the
> > + * n-th element in the array or until the first NULL element.
> > + *
> 
> Perhaps this needs to be rephrased. Because now it has completely hidden the
> -1 case.

Hmm, it does make sense to specify the -1 behavior purely for historical
purposes.
Otheriwse, I don't feel it's that important to mention it, since you could
technically specify UINT_MAX [or similar] and get the same behavior.

> 
> >   * Return:
> >   * index of a @string in the @array if matches, or %-EINVAL otherwise.
> >   */
> 
> Ditto for the second part.
>