Re: [PATCH v2 0/6] sysctl: add typed field descriptors

[Joel Granados <joel.granados@kernel.org>]

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On Mon, Sep 21, 2026 at 12:54:47PM +0200, Alexey Gladkov wrote:
> Hi,
> 
> Some sysctl users allocate a private copy of an otherwise static ctl_table
> for every namespace or device, then rewrite data and limit pointers before
> registration.  Besides the per-instance allocation, these fixups are often
> addressed by table index, so changing the table can silently associate an
> entry with the wrong data or limits.
> 
> This series adds struct sysctl_field as an alternative descriptor for such
> tables.  A field records the value type and an offset into an object
> selected at registration time.  The type-specific offset helpers are small
> wrappers around offsetof() and only add a compile-time check of the
> referenced member type.  The sysctl core derives the handler, size, data
> and limits, and builds a temporary ctl_table when invoking existing
> handler, permission and BPF interfaces.
> 
> A struct sysctl_context identifies the object shared by the whole
> registration and is copied into the table header.  Subsystems which need
> more than a namespace can embed it as the first member of a larger context
> and select the object to which field offsets apply.
> 
> Existing ctl_table users are unchanged, and subsystems can migrate one
> table at a time.  Converted tables remain static and read-only instead of
> being copied and patched for every instance.
> 
> Compared with the previous RFC [1], this drops the per-field accessor
> functions and the macros which generated them.  The first two patches
> prepare the sysctl core without changing its external behaviour.  The third
> patch adds the new descriptor, followed by conversions of the IPC, mqueue
> and ucount tables as small users of the interface.
> 
> This is only the first part of the conversion.  Network sysctls and the
> other subsystem-specific users will be submitted as separate follow-up
> series so they can be reviewed by their respective maintainers without
> making this initial series excessively large.
> 
> [1] https://lore.kernel.org/all/cover.1787770053.git.legion@kernel.org/
> 
> Alexey Gladkov (6):
>   proc: sysctl: address table entries by index
>   sysctl: add unsigned int limit constants
>   sysctl: add typed field descriptors
>   sysctl: ipc: use typed fields for IPC namespace sysctls
>   sysctl: mq: use typed fields for IPC namespace sysctls
>   sysctl: use typed fields for ucount limits
> 
>  fs/proc/inode.c        |   2 +-
>  fs/proc/internal.h     |   2 +-
>  fs/proc/proc_sysctl.c  | 601 ++++++++++++++++++++++++++++++-----------
>  include/linux/sysctl.h | 150 +++++++++-
>  ipc/ipc_sysctl.c       | 188 ++++++-------
>  ipc/mq_sysctl.c        | 104 +++----
>  kernel/sysctl.c        |   3 +
>  kernel/ucount.c        |  64 ++---
>  8 files changed, 750 insertions(+), 364 deletions(-)

I was thinking more along the lines of [1]. I understand that you have
had 2 or 3 versions of this series and it would be great to get your
feedback to see if I missed anything obvious

Best

[1] https://lore.kernel.org/all/20260924-lklm-sysctl-headerctx-template-v1-0-b25e51c66ba7@kernel.org/


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