Re: [RFC PATCH v4 0/2] sysctl: refactor ctl_table initialization

[Joel Granados]

Hey Wen

Comments inline

On Wed, Mar 18, 2026 at 01:36:13AM +0800, wen.yang@xxxxxxxxx wrote:
> From: Wen Yang <wen.yang@xxxxxxxxx>
> 
> The main motivation for this series is to avoid treewide patch series.
> Historically, changes to how struct ctl_table entries are initialized
> (e.g. removing the child field, const-qualifying ctl_table) required
> touching hundreds of files across all subsystems. Such series require
> the attention of many maintainers, sometimes need to be pulled into
> mainline in a special way, and create lots of unnecessary churn.
LGTM: Clear motivation.

> 
> By introducing a family of CTLTBL_ENTRY_XXX() helper macros in
> <linux/sysctl.h>, any future structural changes to struct ctl_table can
> be handled in one place — the macro definition — without requiring a
> treewide sweep of all callers. Individual subsystem maintainers can also
> migrate their sysctl tables to use the macros at their own pace.
I think this paragraph is redundant; I would remove it. And just add
"This will all go away with the CTLTBL_ENTRY_XXX helper macros" as the
last sentence in the first paragraph.

Migration strategy
==================
You touched on this when you mentioned that the maintainers can migrate
to the new macro at their pace. In my experience this will never happen
if you give the responsibility to the subsys maintainers (They are busy
with other matters). I think the more successful strategy is to lead the
conversion from sysctl.

> 
> Based on discussion and suggestions from:
> [1] https://sysctl-dev-rtd.readthedocs.io/en/latest/notes/ctltable_entry_macro.html#table-entry-macro
> [2] https://lore.kernel.org/all/psot4oeauxi3yyj2w4ajm3tfgtcsvao4rhv5sgd5s6ymmjgojk@p3vrj3qluban/
> 
> This series:
>  1. Introduces the CTLTBL_ENTRY_XXX() macros in include/linux/sysctl.h,
>     allowing callers to initialize struct ctl_table entries indirectly
>     via the macro instead of assigning each field directly. The macros
>     use _Generic() for automatic type detection and proc_handler
>     selection, provide smart defaults (auto address-of, auto maxlen via
>     sizeof), and include compile-time validation of name, mode, and
>     handler.
>  2. Converts kernel/sysctl-test.c to use the new macros as a
>     demonstration, replacing direct struct ctl_table field assignments
>     with CTLTBL_ENTRY_XXX() calls. Four new tests are added to cover the
>     previously untested variants (CTLTBL_ENTRY_V, VN, VNM, VNMH), bringing
>     the total to 16 passing tests.
> 
> ---
> Changes in v4:
>   - Fix Wpointer-type-mismatch warnings detected by lkp:
>     https://lore.kernel.org/oe-kbuild-all/202603050724.SZxrEyyu-lkp@xxxxxxxxx/
> 
> Changes in v3:
>   - replace the unique macro with "capital letter approach" 
>   - reduce the name further  
>   https://lore.kernel.org/all/rn4rsazh7kxf5byq65vw2phyqgzvwm3scczu3l5h2r4aqit2r6@znlpb24z2zuo/
> 
> Changes in v2:
>   - add lvalue check, handler type check, etc.
>   https://lore.kernel.org/all/xptwb3uwbzposd4xf7khj52ifv4tchcjdgllhv7aabi6d7wgef@2msurl564v53/
> 
> Wen Yang (2):
>   sysctl: introduce CTLTBL_ENTRY_XXX() helper macros
>   sysctl: convert kernel/sysctl-test.c to use CTLTBL_ENTRY_XXX()
> 
>  include/linux/sysctl.h | 294 +++++++++++++++++++++++++++++++++++++++++
>  kernel/sysctl-test.c   | 240 +++++++++++++++++++--------------
>  kernel/sysctl.c        |   2 +
>  3 files changed, 437 insertions(+), 99 deletions(-)
> 
> -- 
> 2.25.1
> 

Best

-- 

Joel Granados

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