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

[wen.yang@linux.dev]

From: Wen Yang <wen.yang@linux.dev>

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.

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.

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@intel.com/

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