From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753370AbZKORbh (ORCPT ); Sun, 15 Nov 2009 12:31:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752827AbZKORbg (ORCPT ); Sun, 15 Nov 2009 12:31:36 -0500 Received: from mail.perches.com ([173.55.12.10]:1071 "EHLO mail.perches.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752803AbZKORbf (ORCPT ); Sun, 15 Nov 2009 12:31:35 -0500 Subject: Re: [PATCH] sysctl.c: Change a .proc_handler = proc_dointvec to &proc_dointvec, From: Joe Perches To: Ingo Molnar , julia Lawall Cc: "Eric W. Biederman" , Am??rico Wang , LKML , Andrew Morton In-Reply-To: <20091115103307.GB24931@elte.hu> References: <1258249925.16857.198.camel@Joe-Laptop.home> <20091115065958.GA2459@hack> <20091115081126.GD15432@elte.hu> <1258273714.21668.13.camel@Joe-Laptop.home> <20091115083951.GA27393@elte.hu> <20091115103307.GB24931@elte.hu> Content-Type: text/plain; charset="UTF-8" Date: Sun, 15 Nov 2009 09:31:39 -0800 Message-ID: <1258306299.21668.30.camel@Joe-Laptop.home> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2009-11-15 at 11:33 +0100, Ingo Molnar wrote: > * Eric W. Biederman wrote: > > Ingo Molnar writes: > > > * Joe Perches wrote: > > >> On Sun, 2009-11-15 at 09:11 +0100, Ingo Molnar wrote: > > >> > * Am??rico Wang wrote: > > >> > > On Sat, Nov 14, 2009 at 05:52:05PM -0800, Joe Perches wrote: > > >> > > >Seems to be a typo. > > >> > > Acked-by: WANG Cong > > >> > (Cc:-ed Eric who is running the sysctl tree these days) > > >> > Almost everywhere in the kernel we use the shorter version, so all of > > >> > sysctl.c should eventually change to that variant. > > >> It's closer to 50/50, but it's 1 vs 133 in that file. > > >> $ grep -Pr --include=*.[ch] '\.proc_handler\s*=\s*&\s*\w+' * | wc -l > > >> 339 > > >> $ grep -Pr --include=*.[ch] '\.proc_handler\s*=\s*[^&]\s*\w+' * | wc -l > > >> 432 > > > I did not mean this specific initialization method of proc_handler, i > > > meant pointers to functions in general. > > There was an argument put forward by Alexy (I think) a while ago. > > That argued for the form without the address of operator. > > The reason being that without it you can do: > > #define proc_dointvec NULL > > in a header when sysctl support it compiled out. Using address of > > you wind up with stub functions in sysctl.c to handle the case when > > sysctl is compiled out. > > It isn't a strong case but since not using & is also shorter and as > > Ingo pointed out more common I think no & wins. > I can think of another reason as well: the & operator can be dangerous > if code is changed from functions to function pointers. > > The short form: > > val = do_my_func; > > will work just fine if 'my_func' is changed to a function pointer, as it > will evaluate to the value of the function pointer - i.e. the address of > the function. > > The longer form: > > val = &do_my_func; > > might break in a subtle way, because it will now become the address of > the function pointer - not the function address. > > Combined the shortness, the NULL init, the function pointer invariance, > plus existing in-kernel practice all suggest that the short form should > be used. > > ( i didnt want to turn this small issue into a long argument - it's just > that the code was going in the wrong direction. ) That sounds like something coccinelle would do well, so I've cc'd Julia Lawall. http://lkml.org/lkml/2009/11/15/55