Re: [RFC PATCH 1/4] sysctl: add SYSCTL_ENTRY/SYSCTL_RANGE_ENTRY helpers for ctl_table init

[Wen Yang]

On 1/22/26 17:56, Joel Granados wrote:
> On Wed, Jan 14, 2026 at 01:40:30AM +0800, wen.yang@xxxxxxxxx wrote:
> > From: Wen Yang <wen.yang@xxxxxxxxx>
> >
> > Introduce SYSCTL_ENTRY() and SYSCTL_RANGE_ENTRY() (built on __SYSCTL_ENTRY())
> > to consolidate common struct ctl_table initializers in one place.
> > This is a preparatory refactor in support of future tree-wide sysctl
> > cleanups by making the how to build a ctl_table entry logic uniform.
> >
> > Also add SYSCTL_NULL for explicitly passing a NULL .data pointer through
> > the new macros, and convert a few in-tree users (kernel/sysctl.c) to
> > validate the new helpers.
> >
> > No functional change intended.
> >
> > Selftest were also made:
> >
> > [19:31:40] Starting KUnit Kernel (1/1)...
> > [19:31:40] ============================================================
> > Running tests with:
> > $ .kunit/linux kunit.filter_glob=sysctl_test kunit.enable=1 mem=1G console=tty kunit_shutdown=halt
> > [19:31:40] ================ sysctl_test (10 subtests) =================
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_null_tbl_data
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_table_maxlen_unset
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_table_len_is_zero
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_table_read_but_position_set
> > [19:31:40] [PASSED] sysctl_test_dointvec_read_happy_single_positive
> > [19:31:40] [PASSED] sysctl_test_dointvec_read_happy_single_negative
> > [19:31:40] [PASSED] sysctl_test_dointvec_write_happy_single_positive
> > [19:31:40] [PASSED] sysctl_test_dointvec_write_happy_single_negative
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_write_single_less_int_min
> > [19:31:40] [PASSED] sysctl_test_api_dointvec_write_single_greater_int_max
> > [19:31:40] =================== [PASSED] sysctl_test ===================
> > [19:31:40] ============================================================
> > [19:31:40] Testing complete. Ran 10 tests: passed: 10
> > [19:31:40] Elapsed time: 26.755s total, 0.002s configuring, 26.632s building, 0.102s running
> >
> > Suggested-by: Joel Granados <joel.granados@xxxxxxxxxx>
> > Link: https://lore.kernel.org/all/7mevcgca7xsd5gckrap22byjinhrgqnelu4y7hzo2r5t2cq7w4@nyaa42khwqez/#t
> > Signed-off-by: Wen Yang <wen.yang@xxxxxxxxx>
> > ---
> >   include/linux/sysctl.h |  18 ++++++
> >   kernel/sysctl-test.c   | 131 ++++++++++-------------------------------
> >   kernel/sysctl.c        |  43 ++------------
> >   3 files changed, 56 insertions(+), 136 deletions(-)
> >
> > diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> > index 2886fbceb5d6..683422bc3e7f 100644
> > --- a/include/linux/sysctl.h
> > +++ b/include/linux/sysctl.h
> > @@ -53,6 +53,7 @@ struct ctl_dir;
> >   #define SYSCTL_MAXOLDUID		((void *)&sysctl_vals[10])
> >   #define SYSCTL_NEG_ONE			((void *)&sysctl_vals[11])
> >   
> > +#define SYSCTL_NULL			((void *)NULL)
> >   extern const int sysctl_vals[];
> >   
> >   #define SYSCTL_LONG_ZERO	((void *)&sysctl_long_vals[0])
> > @@ -175,6 +176,23 @@ struct ctl_table {
> >   	void *extra2;
> >   } __randomize_layout;
> >   
> > +#define __SYSCTL_ENTRY(NAME, DATA, TYPE, MODE, HANDLER, SMIN, SMAX)\
> > +	{							\
> > +		.procname	= NAME,				\
> > +		.data		= DATA,				\
> I would like to see at least one lvalue check for the macro parameters.
> Something like this
>
> .data = (*(typeof(DATA)*)&(DATA))
>
> In such a way that the compiler fails if an expression is passed.
> We can handle these cases (if they exist) in some other way
>
> > +		.maxlen		= sizeof(TYPE),			\
> > +		.mode		= MODE,				\
> > +		.proc_handler	= HANDLER,			\
> > +		.extra1		= SMIN,				\
> > +		.extra2		= SMAX,				\
> > +	}
> > +
> > +#define SYSCTL_ENTRY(NAME, DATA, TYPE, MODE)			\
> > +	__SYSCTL_ENTRY(NAME, DATA, TYPE, MODE, proc_do##TYPE##vec, NULL, NULL)
> > +
> > +#define SYSCTL_RANGE_ENTRY(NAME, DATA, TYPE, MODE, SMIN, SMAX)	\
> I'm leaning more towards SYSCTL_ENTRY_RANGE or SYSCTL_ENTRY_R.
>
> I am also keeping notes here if you are interested
> https://sysctl-dev-rtd.readthedocs.io/en/latest/notes/ctltable_entry_macro.html#table-entry-macro

Great, thank you for your detailed comments.
These suggestions are indeed the best, implementable, robust, and highly 
readable.
I will soon make these changes according to them soon, probably within a 
day or two.


--
Best wishes,
Wen

> > +	__SYSCTL_ENTRY(NAME, DATA, TYPE, MODE, proc_do##TYPE##vec_minmax, SMIN, SMAX)
> > +
> >   struct ctl_node {
> >   	struct rb_node node;
> >   	struct ctl_table_header *header;
> > diff --git a/kernel/sysctl-test.c b/kernel/sysctl-test.c
> > index 92f94ea28957..7fb0e7f1e62f 100644
> > --- a/kernel/sysctl-test.c
> > +++ b/kernel/sysctl-test.c
> > @@ -15,20 +15,14 @@
> ....
> > -	{
> > -		.procname	= "ignore-unaligned-usertrap",
> > -		.data		= &no_unaligned_warning,
> > -		.maxlen		= sizeof (int),
> > -		.mode		= 0644,
> > -		.proc_handler	= proc_dointvec,
> > -	},
> > +	SYSCTL_ENTRY("ignore-unaligned-usertrap", &no_unaligned_warning, int, 0644),
> >   #endif
> >   };
> >   
> > --
> > 2.25.1