linux-kernel - Re: [PATCH] printk: Export log_buf

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Message-ID: <YvmsNEYPtdOUsaxy@google.com>
Date:   Mon, 15 Aug 2022 11:15:16 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Marc Aurèle La France <tsi@...oix.net>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [PATCH] printk: Export log_buf_len to userland

Cc-ing John and Steven

On (22/08/10 14:25), Marc Aurèle La France wrote:
> 
> Make the kernel log's buffer size available to userland so it can be used with
> `dmesg -s`.

And what doesn't work now?

> This change is not eligible for stable@.
> 
> Please Reply-To-All.
> 
> Thanks and have a great day.
> 
> Marc.

These lines don't belong here. Please see
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.0-rc1

> Signed-off-by: Marc Aurèle La France <tsi@...oix.net>
> 
> diff -aNpRruz -X /etc/diff.excludes linux-5.17.1/include/linux/printk.h devel-5.17.1/include/linux/printk.h
> --- linux-5.17.1/include/linux/printk.h	2022-03-28 02:03:22.000000000 -0600
> +++ devel-5.17.1/include/linux/printk.h	2022-03-28 07:14:10.803008293 -0600
> @@ -318,6 +337,7 @@ extern void __printk_cpu_unlock(void);
>  #endif /* CONFIG_SMP */
> 
>  extern int kptr_restrict;
> +extern u32 log_buf_len;
> 
>  /**
>   * pr_fmt - used by the pr_*() macros to generate the printk format string
> diff -aNpRruz -X /etc/diff.excludes linux-5.17.1/kernel/printk/printk.c devel-5.17.1/kernel/printk/printk.c
> --- linux-5.17.1/kernel/printk/printk.c	2022-03-28 02:03:22.000000000 -0600
> +++ devel-5.17.1/kernel/printk/printk.c	2022-03-28 07:14:10.803008293 -0600
> @@ -404,7 +404,7 @@ static struct latched_seq clear_seq = {
>  #define LOG_BUF_LEN_MAX (u32)(1 << 31)
>  static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
>  static char *log_buf = __log_buf;
> -static u32 log_buf_len = __LOG_BUF_LEN;
> +u32 log_buf_len = __LOG_BUF_LEN;
> 
>  /*
>   * Define the average message size. This only affects the number of
> diff -aNpRruz -X /etc/diff.excludes linux-5.17.1/kernel/printk/sysctl.c devel-5.17.1/kernel/printk/sysctl.c
> --- linux-5.17.1/kernel/printk/sysctl.c	2022-03-28 02:03:22.000000000 -0600
> +++ devel-5.17.1/kernel/printk/sysctl.c	2022-03-28 07:14:10.803008293 -0600
> @@ -22,6 +22,13 @@ static int proc_dointvec_minmax_sysadmin(struct ctl_table *table, int write,
> 
>  static struct ctl_table printk_sysctls[] = {
>  	{
> +		.procname	= "log_buf_len",
> +		.data		= &log_buf_len,
> +		.maxlen		= sizeof(u32),
> +		.mode		= 0444,
> +		.proc_handler	= proc_dointvec,
> +	},
> +	{
>  		.procname	= "printk",
>  		.data		= &console_loglevel,
>  		.maxlen		= 4*sizeof(int),