From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753450AbZKOSUk (ORCPT ); Sun, 15 Nov 2009 13:20:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753404AbZKOSUj (ORCPT ); Sun, 15 Nov 2009 13:20:39 -0500 Received: from mgw2.diku.dk ([130.225.96.92]:41378 "EHLO mgw2.diku.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753402AbZKOSUj (ORCPT ); Sun, 15 Nov 2009 13:20:39 -0500 Date: Sun, 15 Nov 2009 19:20:40 +0100 (CET) From: Julia Lawall To: Joe Perches Cc: Ingo Molnar , "Eric W. Biederman" , Am??rico Wang , LKML , Andrew Morton Subject: Re: [PATCH] sysctl.c: Change a .proc_handler = proc_dointvec to &proc_dointvec, In-Reply-To: <1258306299.21668.30.camel@Joe-Laptop.home> Message-ID: 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> <1258306299.21668.30.camel@Joe-Laptop.home> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 15 Nov 2009, Joe Perches wrote: > 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 Searching for things that are declared as functions (either a definition or a prototype), and then referenced as &f gives over 2000 results in almost 600 files. Here are a couple of typical examples: arch/arm/mach-omap1/clock.c: static const struct clkops clkops_dspck = { .enable = &omap1_clk_enable_dsp_domain, .disable = &omap1_clk_disable_dsp_domain, }; arch/arm/mach-omap1/serial.c: ret = request_irq(gpio_to_irq(gpio_nr), &omap_serial_wake_interrupt, IRQF_TRIGGER_RISING, "serial wakeup", NULL); Should both cases lose the initial &? julia