Implement new converter generation macros that remove repeated logic and
prep the proc handler converter infrastructure for exposure to the
greater kernel. Macros will be exposed in a later series so they can be
used in jiffies.c and pipe.c (like in this branch [1]).
What is done?
=============
Three integer macros (SYSCTL_{KERN_TO_USER,USER_TO_KERN}_INT_CONV and
SYSCTL_INT_CONV_CUSTOM) are created.
* SYSCTL_INT_CONV_CUSTOM: creates a bi-directional (handles both user
to kernel and kernel to user writes) converter that optionally
implements a range checker for when kernel memory is written.
* SYSCTL_KERN_TO_USER_INT_CONV: is a uni-directional converter that
writes to a user buffer avoiding tears with READ_ONCE and setting
the negp variable appropriately; it generates functions that do not
fail.
* SYSCTL_USER_TO_KERN_INT_CONV: is a uni-directional converter that
writes to a kernel buffer, checks for integer overflow and avoids
tears by using with WRITE_ONCE; returns -EINVAL when an overflow is
detected.
Two unsigned integer macros (SYSCTL_USER_TO_KERN_UINT_CONV and
SYSCTL_UINT_CONV_CUSTOM) are created.
* SYSCTL_UINT_CONV_CUSTOM: Same as SYSCTL_INT_CONV_CUSTOM except that
there are no special cases for negative values.
* SYSCTL_USER_TO_KERN_UINT_CONV: Same as SYSCTL_USER_TO_KERN_INT_CONV
except that there is no need to indicate when the value is negative.
The check for overflow is done against UINT_MAX instead of INT_MAX.
For now these macros produce static functions that are used from within
kernel/sysctl.c. The idea is to move them to include/kernel/sysctl.h in
another series so they can be used to create custom converters.
Why it is done?
===============
Motivation is to move non-sysctl logic out of kernel/sysctl.c which had
become a dumping ground for ctl_tables until this trend was changed by
the commits leading to (and including) 73184c8e4ff4 ("sysctl: rename
kern_table -> sysctl_subsys_table"). This series does not move the
jiffie logic out, but it sets things up so it can eventually be evicted
from kernel/sysctl.c.
Testing
=======
* I ran this through the sysctl selftests and sysctl kunit tests on an
x86_64 arch
* This also goes through the sysctl-testing 0-day CI infra.
Versions
========
Changes in v2:
- Corrected cover letter wording
- Added macros for unsigned int converters. Three new commits:
- sysctl: Create macro for user-to-kernel uint converter
- sysctl: Add optional range checking to SYSCTL_UINT_CONV_CUSTOM
- sysctl: Create unsigned int converter using new macro
Added to prepare for when the macros will be used from outside of
sysctl.c (to be added in another series)
- Link to v1: https://lore.kernel.org/r/20251013-jag-sysctl_conv-v1-0-4dc35ceae733@kernel.org
Any comments are greatly appreciated
[1] https://git.kernel.org/pub/scm/linux/kernel/git/joel.granados/linux.git/log/?h=jag/sysctl_jiffies
---
Joel Granados (11):
sysctl: Replace void pointer with const pointer to ctl_table
sysctl: Remove superfluous tbl_data param from "dovec" functions
sysctl: Remove superfluous __do_proc_* indirection
sysctl: Indicate the direction of operation with macro names
sysctl: Discriminate between kernel and user converter params
sysctl: Create converter functions with two new macros
sysctl: Create integer converters with one macro
sysctl: Add optional range checking to SYSCTL_INT_CONV_CUSTOM
sysctl: Create unsigned int converter using new macro
sysctl: Add optional range checking to SYSCTL_UINT_CONV_CUSTOM
sysctl: Create macro for user-to-kernel uint converter
fs/pipe.c | 6 +-
include/linux/sysctl.h | 5 +-
kernel/sysctl.c | 694 +++++++++++++++++++++----------------------------
3 files changed, 298 insertions(+), 407 deletions(-)
---
base-commit: e5f0a698b34ed76002dc5cff3804a61c80233a7a
change-id: 20251012-jag-sysctl_conv-570844f5fdaf
Best regards,
--
Joel Granados <joel.granados@kernel.org>