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

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Message-ID: <CAKPOu+_aj3wA14VaZo8_k+ukw0OafsSz_Bxa120SQbYi4SqR7g@mail.gmail.com>
Date: Mon, 1 Sep 2025 16:50:50 +0200
From: Max Kellermann <max.kellermann@...os.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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Subject: Re: [PATCH v5 02/12] mm: constify pagemap related test functions for
 improved const-correctness

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.

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

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