Messages in this thread | | | Date | Sun, 15 Nov 2009 11:33:07 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] sysctl.c: Change a .proc_handler = proc_dointvec to &proc_dointvec, |
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* 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. )
Ingo
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