linux-kernel - Re: [PATCH v5 02/12] mm: constify pagemap related test functions for improved const-correctness

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Message-ID: <8e3f20bf-eda7-496c-9fb2-60f5f940af22@lucifer.local>
Date: Mon, 1 Sep 2025 16:14:58 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Max Kellermann <max.kellermann@...os.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, axelrasmussen@...gle.com,
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Subject: Re: [PATCH v5 02/12] mm: constify pagemap related test functions for
 improved const-correctness

On Mon, Sep 01, 2025 at 04:50:50PM +0200, Max Kellermann wrote:
> On Mon, Sep 1, 2025 at 4:25 PM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> > 1. (most useful) Const pointer (const <type> *<param>) means that the dereffed
> >    value is const, so *<param> = <val> or <param>-><field> = <val> are prohibited.
>
> Only this was what my initial patch was about.

Right agreed then.

>
> > 2. (less useful) We can't modify the actual pointer value either, so
> >    e.g. <param> = <new param> is prohibited.
>
> This wasn't my idea, it was Andrew Morton's idea, supported by Yuanchu Xie:
>  https://lore.kernel.org/lkml/CAJj2-QHVC0QW_4X95LLAnM=1g6apH==-OXZu65SVeBj0tSUcBg@mail.gmail.com/

Andrew said:

"Not that I'm suggesting that someone go in and make this change."

And Yuanchu said:

"Longer function readability would benefit from that, but it's IMO infeasible to
do so everywhere."

(he also mentions it'd be good if gcc could wran on it).

So this isn't quite true actually.

Let's please just drop this, sorry.

The noise for multiple const params is too much, we can do it on a case-by-case
basis going forward for larger functions.

> You know that because you participated in the discussion. In that

A point of advice given how this series has gone so far - please don't say
things like this :)

I have an extremely heavy review load, and often work 12 hour days. I don't
necessarily see everything though I try to.

I had missed this.

Just add a little civility and empathy it really helps, thanks.

> thread, nobody objected, so I took the time and adjusted all of my
> patches.
> There is some value, but of course it's very small.

Yeah sorry that you had extra work as a result.

But let's please drop this.

>
> Note that I added the value-level "const" only to the implementation,
> never to prototypes, because it would have no effect there.

Right.

Thanks, Lorenzo