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Date: Sun, 12 Dec 2021 17:58:48 +0800
From: Xiaoming Ni <nixiaoming@...wei.com>
To: Luis Chamberlain <mcgrof@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <viro@...iv.linux.org.uk>,
<ebiederm@...ssion.com>, <keescook@...omium.org>,
<jlayton@...nel.org>, <bfields@...ldses.org>, <yzaikin@...gle.com>,
<apw@...onical.com>, <joe@...ches.com>, <dwaipayanray1@...il.com>,
<lukas.bulwahn@...il.com>, <julia.lawall@...ia.fr>,
<akpm@...ux-foundation.org>, <wangle6@...wei.com>
Subject: Re: [PATCH v2] sysctl: Add a group of macro functions to initcall the
sysctl table of each feature
On 2021/12/11 1:20, Luis Chamberlain wrote:
> On Fri, Dec 10, 2021 at 04:58:49PM +0800, Xiaoming Ni 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
>> }
>
> It was nice to have this documented in the commit log, however you
> don't provide a developer documentation for this in your changes.
> Can you justify through documentation why we can use init levels
> with the above information for the sysctl_initcall() macro?
>
>> The sysctl interface of each subfeature should be registered after
>> sysctl_init_bases() and before do_sysctl_args().
>
> Indeed.
>
>> It seems
>
> Seems is poor judgement for a change in the kernel. It is or not.
>
>> 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
>
> Lower to me means early, but since we are talking about time, best
> to clarify and say the latest init level during kernel bootup.
>
>> late_initcall() is used as the common sysctl interface
>> registration level.
>>
>> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
>>
>> ---
>> v2:
>> Add a simple checkpatch check.
>> Add code comment.
>> v1:
>> https://lore.kernel.org/lkml/20211207011320.100102-1-nixiaoming@huawei.com/
>> ---
>> fs/coredump.c | 7 +------
>> fs/dcache.c | 7 +------
>> fs/exec.c | 8 +-------
>> fs/file_table.c | 7 +------
>> fs/inode.c | 7 +------
>> fs/locks.c | 7 +------
>> fs/namei.c | 8 +-------
>> fs/namespace.c | 7 +------
>> include/linux/sysctl.h | 19 +++++++++++++++++++
>> kernel/stackleak.c | 7 +------
>> scripts/checkpatch.pl | 6 ++++++
>> 11 files changed, 34 insertions(+), 56 deletions(-)
>>
>> diff --git a/fs/coredump.c b/fs/coredump.c
>> index 570d98398668..8f6c6322651d 100644
>> --- a/fs/coredump.c
>> +++ b/fs/coredump.c
>> @@ -943,12 +943,7 @@ static struct ctl_table coredump_sysctls[] = {
>> { }
>> };
>>
>> -static int __init init_fs_coredump_sysctls(void)
>> -{
>> - register_sysctl_init("kernel", coredump_sysctls);
>> - return 0;
>> -}
>> -fs_initcall(init_fs_coredump_sysctls);
>> +kernel_sysctl_initcall(coredump_sysctls);
>
> Nice.
>
> Yes, although I went with fs_initcall() your documentation above
> does give us certainty that this is fine as well. No need to kick
> this through earlier.
>
>> #endif /* CONFIG_SYSCTL */
>>
>> /*
>> diff --git a/fs/dcache.c b/fs/dcache.c
>> index 0eef1102f460..c1570243aaee 100644
>> --- a/fs/dcache.c
>> +++ b/fs/dcache.c
>> @@ -195,12 +195,7 @@ static struct ctl_table fs_dcache_sysctls[] = {
>> { }
>> };
>>
>> -static int __init init_fs_dcache_sysctls(void)
>> -{
>> - register_sysctl_init("fs", fs_dcache_sysctls);
>> - return 0;
>> -}
>> -fs_initcall(init_fs_dcache_sysctls);
>> +fs_sysctl_initcall(fs_dcache_sysctls);
>
> Seems fine by me using the same logic as above and I like that
> you are splitting this by bases. Likewise for the others, this
> is looking good.
>
>> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
>> index acf0805cf3a0..ce33e61a8287 100644
>> --- a/include/linux/sysctl.h
>> +++ b/include/linux/sysctl.h
>> @@ -231,6 +231,25 @@ extern int sysctl_init_bases(void);
>> extern void __register_sysctl_init(const char *path, struct ctl_table *table,
>> const char *table_name);
>
> Yes please take the time to write some documentation here which can
> explain to developers *why* we use the init levels specified.
>
>> #define register_sysctl_init(path, table) __register_sysctl_init(path, table, #table)
>> +
/**
* sysctl_initcall() - register and init sysctl leaf node to path
* @path: path name for sysctl base
* @table: This is the sysctl leaf table that needs to be registered to
the path
*
* Leaf node in the sysctl tree:
* a) File, .child = NULL
* b) Directory, which is not shared by multiple features, .child !=
NULL
*
* The sysctl interface for each subfeature should be in the after
* sysctl_init_bases() and before do_sysctl_args().
* sysctl_init_bases() is executed before early_initcall().
* do_sysctl_args() is executed after late_initcall().
* Therefore, it is safe to add leaves to the sysctl tree using
late_initcall().
*/
How about that description?
>> +#define sysctl_initcall(path, table) \
>> + static int __init init_##table(void) \
>> + { \
>> + register_sysctl_init(path, table); \
>> + return 0;\
>> + } \
>> + late_initcall(init_##table)
>> +
>> +/*
>> + * Use xxx_sysctl_initcall() to initialize your sysctl interface unless you want
>> + * to register the sysctl directory and share it with other features.
>> + */
>> +#define kernel_sysctl_initcall(table) sysctl_initcall("kernel", table)
>> +#define fs_sysctl_initcall(table) sysctl_initcall("fs", table)
>> +#define vm_sysctl_initcall(table) sysctl_initcall("vm", table)
>> +#define debug_sysctl_initcall(table) sysctl_initcall("debug", table)
>> +#define dev_sysctl_initcall(table) sysctl_initcall("dev", table)
>> +
>> extern struct ctl_table_header *register_sysctl_mount_point(const char *path);
>>
>> void do_sysctl_args(void);
>
> Luis
> .
>
Thanks
Xiaoming Ni
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