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 14:25:14 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Julia Lawall <Julia.Lawall@...ia.fr>, <cocci@...ia.fr>
CC:     <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 2021/12/7 9:50, 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.
>

Maybe we can add a rudimentary check to the checkpatch.

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b01c36a15d9d..26e953ae4cc5 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7212,6 +7212,12 @@ sub process {
                              "Deprecated use of '$deprecated_api', 
prefer '$new_api' instead\n" . $herecurr);
                 }

+# check register_sysctl_init
+               if ($prevline =~ /{/ && $rawline =~ 
/\sregister_sysctl_init\(\"(kernel|fs|vm|debug|dev)\",\s+(.*)\)\;/) {
+                       WARN("DEPRECATED_API",
+                            "Deprecated use of 
'register_sysctl_init(\"$1\", $2);', prefer '$1_sysctl_initcall($2);' 
instead\n".$herecurr);
+               }
+
  # check for various structs that are normally const (ops, kgdb, 
device_tree)
  # and avoid what seem like struct definitions 'struct foo {'
                 if (defined($const_structs) &&



Thanks
Xiaoming Ni