linux-kernel - Re: [PATCH] kernel: make module.c itself more explicitly non-modular

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Message-ID: <87bndtid1f.fsf@rustcorp.com.au>
Date:	Thu, 27 Aug 2015 13:43:48 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel: make module.c itself more explicitly non-modular

Paul Gortmaker <paul.gortmaker@...driver.com> writes:
> On 2015-08-26 12:06 AM, Rusty Russell wrote:
>> Paul Gortmaker <paul.gortmaker@...driver.com> writes:
>>> The Kconfig currently controlling compilation of this code is:
>>>
>>> menuconfig MODULES
>>>    bool "Enable loadable module support"
>>>
>>> ...meaning that it currently is not being built as a module by anyone.
>>> No surprise here, since modular support being a module would be an
>>> interesting chicken before the egg problem.
>>>
>>> Lets remove the use of module_init in this code so that when reading
>>> the file, there is less doubt that it is builtin-only.
>>>
>>> Since module_init translates to device_initcall in the non-modular
>>> case, the init ordering remains unchanged with this commit.  However
>>> one could argue that fs_initcall makes more sense for proc stuff,
>>> and we can change the initcall order later and watch for fallout
>>> if so desired.
>> 
>> This patch is just weird; is this part of something larger you are
>> trying to do?
>
> Yes, it is part of a larger cleanup; for subsystems with more than
> one patch I created a 0/N explanatory note; such as:
>
> https://lkml.kernel.org/r/1440459295-21814-1-git-send-email-paul.gortmaker@windriver.com
> https://lkml.kernel.org/r/1437530538-5078-1-git-send-email-paul.gortmaker@windriver.com
>
> and others. Apologies for the lack of context on this single patch.
>  
>> I would argue that module_init() should be the default; it implies
>> no dependencies on the initialization, and it's a common pattern.
>
> To summarize briefly, module_init forces everything into one
> initcall priority bin

That's a feature.  Everything should be in one bin unless there's reason
to specify; once you've specified, it's almost impossible to change
because our system is now so complicated.

module_init() says "I don't care".

> , it encourages people to write module_exit
> functions that are never used

Then write a checker.  It's not that hard for kbuild to show stuff that
can never be a module, I'm sure.

>, and it can make the code appear
> inconsistent with the Kconfig and/or Makefile settings.  So I'd
> hope you'd agree that there is value in not using module_init
> in code that can never be modular.

On the other hand, people cut & paste like crazy, so it makes sense to
have them all use module_init() and not build non-modular code, because
most code is a module.

Since this is total bikeshed, you can apply this yourself:

        Acked-by: Rusty Russell <rusty@...tcorp.com.au> (disagree, but hey...)

Cheers,
Rusty.
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