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DateSun, 15 Nov 2009 19:20:40 +0100 (CET)
FromJulia Lawall <>
SubjectRe: [PATCH] sysctl.c: Change a .proc_handler = proc_dointvec to &proc_dointvec,
On Sun, 15 Nov 2009, Joe Perches wrote:

> On Sun, 2009-11-15 at 11:33 +0100, Ingo Molnar wrote:
> > * Eric W. Biederman <ebiederm@xmission.com> wrote:
> > > Ingo Molnar <mingo@elte.hu> writes:
> > > > * Joe Perches <joe@perches.com> wrote:
> > > >> On Sun, 2009-11-15 at 09:11 +0100, Ingo Molnar wrote:
> > > >> > * Am??rico Wang <xiyou.wangcong@gmail.com> wrote:
> > > >> > > On Sat, Nov 14, 2009 at 05:52:05PM -0800, Joe Perches wrote:
> > > >> > > >Seems to be a typo.
> > > >> > > Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
> > > >> > (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


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