linux-kernel - Re: Converting struct timer_list callback argument to struct timer

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Date:   Sun, 3 Sep 2017 13:18:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Converting struct timer_list callback argument to struct
 timer_list *

On Sun, Sep 3, 2017 at 12:37 AM, Christoph Hellwig <hch@...radead.org> wrote:
> On Fri, Sep 01, 2017 at 09:24:22AM -0700, Kees Cook wrote:
>> #define list_entry(ptr, type, member) container_of(ptr, type, member)
>> #define rb_entry(ptr, type, member) container_of(ptr, type, member)
>>
>> The use of a "timer_entry()" at the start of callbacks repeats the
>> struct name, which I find irritating (and it usually results in split
>> lines). For example:
>>
>> #define timer_entry(ptr, type, member) container_of(ptr, type, member)
>>
>> -static void snd_card_asihpi_timer_function(unsigned long data)
>> +static void snd_card_asihpi_timer_function(struct timer_list *t)
>>  {
>> -       struct snd_card_asihpi_pcm *dpcm = (struct snd_card_asihpi_pcm *)data;
>> +       struct snd_card_asihpi_pcm *dpcm =
>> +                                timer_entry(t, struct
>> snd_card_asihpi_pcm, timer);
>>
>> I prefer to tie this directly to the variable, so how about renaming
>> TIMER_CONTAINER to timer_of():
>
> The TIMER_CONTAINER semantics are more useful indeed, and I which
> we'd have a general purpose variant of that.  But I was complaining
> about the name anyway.  timer_of sounds ok, but timer_entry still sounds
> a bit more descriptive.  As for the split lines:  you'll generally
> get a lot of these, even TIMER_CONTAINER has a quite a few.  I generally
> prefer to move everything right of the = to the next line as that
> becomes a lot more redable.

It feels weird to have different semantics from container_of() too, so
I'll probably just switch everything around to be like all the others,
in that they are just direct wrappers around container_of()... I'll
settle on something and switch everything over.

I'm down to about 200 more callsites. :) Found a missed pattern that
coccinelle could handle which caught about 1/3rd of my earlier
300ish...

-Kees

-- 
Kees Cook
Pixel Security