linux-kernel - Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

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Date:   Tue, 27 Feb 2018 00:00:42 +0100
From:   Robert Abel <rabel@...ertabel.eu>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
        eldad@...refinery.com, me@...in.cc, corbet@....net,
        pantelis.antoniou@...sulko.com
Subject: Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

Hi @ll,

this is a discussion stemming from drivers/auxdisplay about the usage
and possible deprecation of simple_strto* set of functions found in
lib/vsprintf.
I cc'ed everybody who signed off and also everybody who
signed/authored/added/removed more than 20% of lib/vsprintf.

This has come up, because some auxdisplay functionality was broken by a
well-intentioned patch to switch from simple_strtoul to kstrtoul in
129957069e6af42a6e021d90679c56662c95f7e1
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=129957069e6af42a6e021d90679c56662c95f7e1)
and now there is discussion about whether the simple_strto* functions
are really obsolete.

On 26 Feb 2018 18:26, Miguel Ojeda wrote:
> On Mon, Feb 26, 2018 at 6:09 PM, Andy Shevchenko wrote:
>> On Mon, Feb 26, 2018 at 6:54 PM, Miguel Ojeda wrote:
>>> On Mon, Feb 26, 2018 at 12:44 PM, Andy Shevchenko wrote:
>>>> Perhaps instead of dancing around kstrtox() better to switch to
>>>> simple_strtoul() ?
>>>
>>> It seems deprecated:
>>>
>>> /* Obsolete, do not use.  Use kstrto<foo> instead */
>>> extern unsigned long simple_strtoul(const char *,char **,unsigned int);
>>
>> It has been discussed several times. The comment is simple wrong.
>>
>> Because of the requirement of kstrtox() to have a \0 or \n followed by
>> \0 as "end of field".
>> simple_strto*() is suitable to be run in place.
> 
> I agree that in-place versions of these kind of string functions are
> very useful, don't get me wrong! But unless someone changes the
> "official" comment, we shouldn't add new code relying on them.

So can we get clarity in form of a patch here, or not?
I'm hesitant to move back to simple_kstroul, because to me it seems that
general consensus (at least when the comment was put there) was to
remove it:

> commit 462e471107624fe9bd8b6353ac13e06305c3f3fd
> Author: Eldad Zack <>
> Date:   Mon Dec 17 16:03:05 2012 -0800
> 
>     simple_strto*: annotate function as obsolete
> 
>     Update the documentation for simple_strto* to reflect that it has been
>     obsoleted and advise the usage of kstrto*.
> 
>     Signed-off-by: Eldad Zack <>
>     Cc: J. Bruce Fields <>
>     Cc: Joe Perches <>
>     Cc: Randy Dunlap <>
>     Cc: Alexey Dobriyan <>
>     Cc: Rob Landley <>
>     Signed-off-by: Andrew Morton <>
>     Signed-off-by: Linus Torvalds <>

One big advantage simple_kstro* functions have over their kstrto*
cousins is that strings don't need to be null-terminated. Instead, they
will be parsed as far as they can be and a pointer to the end of the
respective number will be returned.

Regards,

Robert