Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper
 macro
To:     Joe Perches <joe@perches.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andreas Schwab <schwab@linux-m68k.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Tom Zanussi <zanussi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <20181221175618.968519903@goodmis.org>
 <20181221175659.208858193@goodmis.org>
 <CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com>
 <20181221144054.20bdeb33@gandalf.local.home>
 <CAHk-=wgSvRhj6KNRdn9gbK9RJVAswdtKSNjAxdf9O9vn04T5XQ@mail.gmail.com>
 <20181221153526.5e6055ca@gandalf.local.home>
 <077eeb8b09baebe78822819b5f15d671b738a2b2.camel@perches.com>
 <20181221155435.38a9a221@gandalf.local.home> <871s6ad2br.fsf@igel.home>
 <20181221160826.34c544e6@gandalf.local.home>
 <84199633fd49db573c9ba71f1992936422e907d4.camel@perches.com>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <098d7abf-5b62-6a01-a370-97d96bece299@rasmusvillemoes.dk>
Date:   Sun, 23 Dec 2018 23:01:52 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <84199633fd49db573c9ba71f1992936422e907d4.camel@perches.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@linux-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@rustcorp.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