Re: [PATCH] sysctl: Add a group of macro functions to initcall the sysctl table of each feature

[Joe Perches <joe@perches.com>]

On Mon, 2021-12-06 at 17:38 -0800, Andrew Morton wrote:
> On Tue, 7 Dec 2021 09:13:20 +0800 Xiaoming Ni <nixiaoming@huawei.com> wrote:
> 
> > To avoid duplicated code, add a set of macro functions to initialize the
> > sysctl table for each feature.
> > 
> > The system initialization process is as follows:
> > 
> > 	start_kernel () {
> > 		...
> > 		/* init proc and sysctl base,
> > 		 * proc_root_init()-->proc_sys_init()-->sysctl_init_bases()
> > 		 */
> > 		proc_root_init(); /* init proc and sysctl base */
> > 		...
> > 		arch_call_rest_init();
> > 	}
> > 
> > 	arch_call_rest_init()-->rest_init()-->kernel_init()
> > 	kernel_init() {
> > 		...
> > 		kernel_init_freeable(); /* do all initcalls */
> > 		...
> > 		do_sysctl_args(); /* Process the sysctl parameter: sysctl.*= */
> > 	}
> > 
> > 	kernel_init_freeable()--->do_basic_setup()-->do_initcalls()
> > 	do_initcalls() {
> > 		for (level = 0; level < ARRAY_SIZE(initcall_levels) - 1; level++) {
> > 			do_initcall_level
> > 	}
> > 
> > The sysctl interface of each subfeature should be registered after
> > sysctl_init_bases() and before do_sysctl_args(). It seems that the sysctl
> > interface does not depend on initcall_levels. To prevent the sysctl
> > interface from being initialized before the feature itself. The
> > lowest-level late_initcall() is used as the common sysctl interface
> > registration level.
> 
> I'm not normally a fan of wrapping commonly-used code sequences into
> magical macros, but this one does seem to make sense.
> 
> I wonder if it is possible to cook up a checkpatch rule to tell people
> to henceforth use the magic macros rather than to open-code things in
> the old way.  Sounds hard.

Almost impossible for checkpatch.
Likely easier in coccinelle.