linux-kernel - Re: [PATCH v2 0/7] lib: string: add functions to case-convert strings

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Message-ID: <CAGt4E5vqiUOVmgqY8OvRPNpoS54hZMOHid6ND4CRyb5p9y5ndw@mail.gmail.com>
Date:	Tue, 5 Jul 2016 15:36:22 -0700
From:	Markus Mayer <markus.mayer@...adcom.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Kees Cook <keescook@...omium.org>,
	dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
	linux-acpi@...r.kernel.org, speakup@...ux-speakup.org,
	devel@...verdev.osuosl.org, linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org, linux-pm@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/7] lib: string: add functions to case-convert strings

On 5 July 2016 at 15:14, Joe Perches <joe@...ches.com> wrote:
> On Tue, 2016-07-05 at 13:47 -0700, Markus Mayer wrote:
>> This series introduces a family of generic string case conversion
>> functions. This kind of functionality is needed in several places in
>> the kernel. Right now, everybody seems to be implementing their own
>> copy of this functionality.
>>
>> Based on the discussion of the previous version of this series[1] and
>> the use cases found in the kernel, it does look like having several
>> flavours of case conversion functions is beneficial. The use cases fall
>> into three categories:
>>     - copying a string and converting the case while specifying a
>>       maximum length to mimic strncpy()
>>     - copying a string and converting the case without specifying a
>>       length to mimic strcpy()
>>     - converting the case of a string in-place (i.e. modifying the
>>       string that was passed in)
>>
>> Consequently, I am proposing these new functions:
>>     char *strncpytoupper(char *dst, const char *src, size_t len);
>>     char *strncpytolower(char *dst, const char *src, size_t len);
>>     char *strcpytoupper(char *dst, const char *src);
>>     char *strcpytolower(char *dst, const char *src);
>>     char *strtoupper(char *s);
>>     char *strtolower(char *s);
>
> I think there isn't much value in anything other
> than strto<upper|lower>.
>
> Using str[n]cpy followed by strto<upper|lower> is
> pretty obvious and rarely used anyway.

First time around, folks were proposing the "copy" variants when I
submitted just strtolower() by itself[1]. They just asked for source
and destination parameters to strtolower(), but looking at the use
cases that wouldn't have worked so well. Hence it evolved into these 6
functions.

Here's a breakdown of how the functions are being used (patches 2-7),
see also [2]:

Patch 2: strncpytolower()
Patch 3: strtolower()
Patch 4: strncpytolower() and strtolower()
Patch 5: strtolower()
Patch 6: strcpytoupper()
Patch 7: strcpytoupper()

So it does look like the copy + change case variant is more frequently
used than just strto<upper|lower>.

Regards,
-Markus

[1] https://lkml.org/lkml/2016/7/1/652
[2] https://lkml.org/lkml/2016/7/5/542