Re: [RFC PATCH v5 0/2] sysctl: add CTLTBL_ENTRY_XXX() macros for ctl_table initialization

[Joel Granados]

Hey Kees

I have been trying to avoid having to do a treewide change everytime
that the sysctl ctl_table struct are changed, it creates unnecessary
churn and requires a "review" when there is really no need for it.

This series tries to move the definitions of the struct elements into a
macro within sysctl. I was wondering if you see any red flags that
should be address before this moves forward.

Best

On Thu, Mar 26, 2026 at 02:39:14AM +0800, wen.yang@xxxxxxxxx wrote:
> From: Wen Yang <wen.yang@xxxxxxxxx>
> 
> 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.  With
> CTLTBL_ENTRY_XXX(), future structural changes to struct ctl_table need
> only update the macro definitions.
> 
> Conversion of existing call sites will proceed incrementally from
> kernel/sysctl.c outward, rather than as a treewide sweep.
> 
> This series:
>  1. Introduces the CTLTBL_ENTRY_XXX() macros in include/linux/sysctl.h,
>     using _Generic() for automatic proc_handler selection, auto
>     address-of, auto maxlen via sizeof(), and compile-time validation.
>     Supported types: int, unsigned int, long, unsigned long, bool, u8.
>  2. Converts kernel/sysctl-test.c as a demonstration, adding a
>     parameterized KUnit test covering all macro variants (V, VM, VMR,
>     VN, VNM, VNMH) across int, u8, bool, and char[] types.
> 
> Based on discussion and suggestions from:
> [1] https://sysctl-dev-rtd.readthedocs.io/en/latest/notes/ctltable_entry_macro.html
> [2] https://lore.kernel.org/all/psot4oeauxi3yyj2w4ajm3tfgtcsvao4rhv5sgd5s6ymmjgojk@p3vrj3qluban/
> 
> ---
> Changes in v5:
>   - Extend __CTL_AUTO_HANDLER to support bool and u8
>   - Replace individual test functions with a single parameterized KUnit
>     test (KUNIT_CASE_PARAM) covering all variants and types
>   - Use struct ctl_table as the expected-value container in the param
>     struct, eliminating custom expected_* fields
> 
> 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 | 307 +++++++++++++++++++++++++++++++++++++++++
>  kernel/sysctl-test.c   | 237 ++++++++++++++++++-------------
>  kernel/sysctl.c        |   2 +
>  3 files changed, 447 insertions(+), 99 deletions(-)
> 
> -- 
> 2.25.1
> 

-- 

Joel Granados

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