Message-ID: <4B282189.70202@gmail.com>
Date:	Wed, 16 Dec 2009 00:53:45 +0100
From:	Emese Revfy <re.emese@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Paul Mundt <lethal@...ux-sh.org>, Matthew Wilcox <matthew@....cx>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 0/1] Constify struct address_space_operations for 2.6.32-git-053fe57ac
 v2

Arjan van de Ven wrote:
> On Mon, 14 Dec 2009 23:20:58 +0100
> Emese Revfy <re.emese@...il.com> wrote:
> 
>> Paul Mundt wrote:
>>> I don't see anything relating to sparse in that mail. You've
>>> effectively lumped sparse and constification together in the same
>>> camp, but it's unclear why this makes constification a better
>>> option other than that it's simply the option you opted for. All of
>>> your arguments "against" sparse in that context are equally
>>> applicable to constification, so I'll reiterate that you haven't
>>> sufficiently addressed the sparse angle.
>>>
>>> At present you seem to be the only one convinced that
>>> constification is the way to go, despite it being highly intrusive
>>> and ignoring the potential for more favourable and less intrusive
>>> options. You've also failed to adequately address the issues and
>>> suggestsions pointed out by others, and until this happens there is
>>> little point in posting any follow-up patches.
>>>
>>>>> Until such a consensus is reached one way or the other, please
>>>>> refrain from sending hundreds of patches -- one or two are
>>>>> sufficient for showing what you want to do until folks are on
>>>>> board with it, as is the typical nature of mechanical changes.
>>>> I think there is consensus to constify ops variables as much as
>>>> possible (e.g., Alexey's similar patches).
>>>>
>>>> The discussions in these threads were about constifying the ops
>>>> structure fields themselves and I already explained why they are
>>>> useful, see the above link and this one:
>>>> http://lkml.org/lkml/2009/12/8/492
>>> And in here as well in the reply to that mail the same criticism
>>> exists as does the suggestion to look at doing it cleanly in
>>> sparse, which brings us back to what was already mentioned earlier.
>> Let me summarise the discussion so far:
>>
>> As per Al Viro, Arjan and other developers the goal is to force
>> static allocations and prevent runtime modification of ops structures
>> (where it is possible, there are always exceptions like
>> ata_port_operations).
>>
>> The current strategy of constifying variables achieves the second
>> goal only, it still requires human review to catch violations of the
>> first goal.
> 
> this is not correct.
> 
> When the ops variable is const... the compiler will also warn if you
> change it. Make some core APIs use const in their parameter that gets
> a pointer to the ops structure, so that the compiler can optimize.
> That is all goodness.
> 
> But if someone somewhere makes one that is not const.. that's what
> checkpatch.pl is for .. make it warn!
> But don't crap all over structures... I agree with Pavel/Al/etc.. 
> that's bad code without gains.
 
I still think it is a good idea for several reasons (see my last
response to Pavel, http://lkml.org/lkml/2009/12/15/559), but I will
remove the field constifications from the next patch series.

As for splitting up the patches, do you all agree that it should
be one series per structure type at a time (as suggested by Pavel),
with each patch mailed to the respective maintainers? If so, 
how can I reliably determine the maintainers of a given file
without spamming too many people?
--
Emese

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