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

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Date:   Tue, 7 Dec 2021 07:30:59 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Joe Perches <joe@...ches.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Xiaoming Ni <nixiaoming@...wei.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>, cocci@...ia.fr,
        linux-kernel@...r.kernel.org, mcgrof@...nel.org,
        viro@...iv.linux.org.uk, ebiederm@...ssion.com,
        keescook@...omium.org, jlayton@...nel.org, bfields@...ldses.org,
        yzaikin@...gle.com, wangle6@...wei.com
Subject: Re: [PATCH] sysctl: Add a group of macro functions to initcall the
 sysctl table of each feature



On Mon, 6 Dec 2021, Joe Perches wrote:

> On Mon, 2021-12-06 at 17:38 -0800, Andrew Morton wrote:
> > On Tue, 7 Dec 2021 09:13:20 +0800 Xiaoming Ni <nixiaoming@...wei.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.

Is there a typical example of the open coded version?

julia