linux-kernel - Re: [for-next][PATCH 23/24] string.h: Add strncmp

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Message-ID: <098d7abf-5b62-6a01-a370-97d96bece299@rasmusvillemoes.dk>
Date:   Sun, 23 Dec 2018 23:01:52 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Joe Perches <joe@...ches.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andreas Schwab <schwab@...ux-m68k.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper
 macro

On 21/12/2018 23.20, Joe Perches wrote:
> On Fri, 2018-12-21 at 16:08 -0500, Steven Rostedt wrote:
>> On Fri, 21 Dec 2018 21:58:32 +0100
>> Andreas Schwab <schwab@...ux-m68k.org> wrote:
>>
>>
>>>> Well, perhaps I can just remove the ending ones. I get paranoid with
>>>> macro variables, and tend to over do it so that there's no question.  
>>>
>>> Why not make it an inline function?
>>
>> Matters if that removes the strlen(const) optimization. I could try it
>> and see what happens.
> 
> Using
> 
> static inline bool str_has_prefix(const char *str, const char prefix[])
> {
> 	return !strncmp(str, prefix, strlen(prefix));
> }
> 

We already have exactly that function, it's called strstarts().

commit 66f92cf9d415e96a5bdd6c64de8dd8418595d2fc
Author: Rusty Russell <rusty@...tcorp.com.au>
Date:   Tue Mar 31 13:05:36 2009 -0600

    strstarts: helper function for !strncmp(str, prefix, strlen(prefix))

Please don't add a copy under another name.

As for converting existing users, go for it. FWIW, I ran a cocci script
a few years ago to find suspicious strncmp() cases, and there were some
(e87c3f, ca957b6), but fewer than I expected. There are some
confused/confusing ones that apparently deliberately do strncmp(a, b,
sizeof(b)) instead of the equivalent to strcmp(a, b) (e.g. 'strncmp(str,
"hwc", 4) == 0')

Rasmus