linux-kernel - Re: [PATCH v2 5/8] printk: move printk sysctl to printk/sysctl.c

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Message-ID: <YaDYWhq8V8BHZbwm@alley>
Date:   Fri, 26 Nov 2021 13:51:38 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     akpm@...ux-foundation.org, keescook@...omium.org,
        yzaikin@...gle.com, nixiaoming@...wei.com, ebiederm@...ssion.com,
        steve@....org, gregkh@...uxfoundation.org, rafael@...nel.org,
        tytso@....edu, viro@...iv.linux.org.uk, senozhatsky@...omium.org,
        rostedt@...dmis.org, john.ogness@...utronix.de,
        dgilbert@...erlog.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, mcgrof@...badil.infradead.org,
        linux-scsi@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/8] printk: move printk sysctl to printk/sysctl.c

On Wed 2021-11-24 15:14:32, Luis Chamberlain wrote:
> From: Xiaoming Ni <nixiaoming@...wei.com>
> 
> The kernel/sysctl.c is a kitchen sink where everyone leaves
> their dirty dishes, this makes it very difficult to maintain.
> 
> To help with this maintenance let's start by moving sysctls to
> places where they actually belong. The proc sysctl maintainers
> do not want to know what sysctl knobs you wish to add for your own
> piece of code, we just care about the core logic.
> 
> So move printk sysctl from kernel/sysctl.c to kernel/printk/sysctl.c.
> Use register_sysctl() to register the sysctl interface.
> 
> diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile
> index d118739874c0..f5b388e810b9 100644
> --- a/kernel/printk/Makefile
> +++ b/kernel/printk/Makefile
> @@ -2,5 +2,8 @@
>  obj-y	= printk.o
>  obj-$(CONFIG_PRINTK)	+= printk_safe.o
>  obj-$(CONFIG_A11Y_BRAILLE_CONSOLE)	+= braille.o
> -obj-$(CONFIG_PRINTK)	+= printk_ringbuffer.o
>  obj-$(CONFIG_PRINTK_INDEX)	+= index.o
> +
> +obj-$(CONFIG_PRINTK)                 += printk_support.o
> +printk_support-y	             := printk_ringbuffer.o
> +printk_support-$(CONFIG_SYSCTL)	     += sysctl.o

I have never seen this trick. It looks like a dirty hack ;-)
Anyway, I do not see it described in the documentation. I wonder
if it works only by chance.

IMHO, a cleaner solution would be to add the following
into init/Kconfig:

config BUILD_PRINTK_SYSCTL
	bool
	default (PRINTK && SYSCTL)

and then use:

obj-$(CONFIG_BUILD_PRINTK_SYSCTL)    += sysctl.o


> diff --git a/kernel/printk/sysctl.c b/kernel/printk/sysctl.c
> new file mode 100644
> index 000000000000..653ae04aab7f
> --- /dev/null
> +++ b/kernel/printk/sysctl.c
> @@ -0,0 +1,85 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * sysctl.c: General linux system control interface
> + */
> +
> +#include <linux/sysctl.h>
> +#include <linux/printk.h>
> +#include <linux/capability.h>
> +#include <linux/ratelimit.h>
> +#include "internal.h"
> +
> +static const int ten_thousand = 10000;

The patch should also remove the variable in kernel/sysctl.c.

Otherwise, it looks like a really nice clean up.

Best Regards,
Petr