[PATCH v3 0/5] sysctl: add typed field descriptors

[Alexey Gladkov <legion@kernel.org>]

Hi,

Some sysctl users copy an otherwise static ctl_table for each namespace or
device, then replace data and limit pointers before registration. Besides
the per-instance allocation, these fixups often depend on table indices:
reordering an entry without updating the fixup can silently bind it to the
wrong data or limits.

This series lets such users describe a table once with static, read-only
sysctl_field entries. Each field names a data type and an offset into an
object selected by a sysctl_context at registration time. The offset
helpers check the member type at build time. Limits and custom handlers
remain optional properties of a field; the field type does not encode a
choice of handler or whether limits are present. A subsystem that needs
more than a namespace can embed sysctl_context in its own registration
context.

The sysctl core keeps the context with the table header and materializes
a ctl_table entry when an existing handler, permission check or BPF hook
needs one. Legacy ctl_table registrations retain their own path, and
subsystems can convert tables independently. The IPC, mqueue and ucount
conversions here remove table copies without changing their backing data.

Changes since v2:

- Drop sysctl_uint_vals, as requested by Joel. Existing limit constants
  suffice for these conversions.
- Drop the *_MINMAX field types. A field's type now describes its data,
  while optional min/max pointers supply bounds to the selected handler.
- Keep __register_sysctl_table() and __register_sysctl_fields() as separate
  registration paths, sharing only allocation and tree insertion helpers.
- Address the sashiko findings: avoid calling mode_fn under sysctl_lock,
  validate the effective maxlen against the context object, and reject
  NO_DATA fields paired with standard handlers that require data.

This is the first part of the conversion. Network sysctls and other
subsystem-specific users will follow in separate series for review by
their maintainers.


Alexey Gladkov (5):
  proc: sysctl: address table entries by index
  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  | 681 +++++++++++++++++++++++++++++------------
 include/linux/sysctl.h | 138 ++++++++-
 ipc/ipc_sysctl.c       | 189 +++++-------
 ipc/mq_sysctl.c        | 104 +++----
 kernel/ucount.c        |  64 ++--
 7 files changed, 772 insertions(+), 408 deletions(-)


base-commit: 587858367581b9c55c3690f4e63382ad622719d4
-- 
2.55.0