linux-kernel - Re: [PATCH] printk: Monitor change of console loglevel.

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Message-ID: <6b56ca73a5686513fc4ce9d3e07e402cfeeac544.camel@perches.com>
Date:   Fri, 24 May 2019 17:56:31 -0700
From:   Joe Perches <joe@...ches.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] printk: Monitor change of console loglevel.

On Sat, 2019-05-25 at 09:14 +0900, Tetsuo Handa wrote:
> On 2019/05/25 2:17, Linus Torvalds wrote:
> > A config option or two that help syzbot doesn't sound like a bad idea to me.
> 
> Thanks for suggestion. I think that #ifdef'ing
> 
>   static bool suppress_message_printing(int level)
>   {
>   	return (level >= console_loglevel && !ignore_loglevel);
>   }
> 
> is simpler.
[]
> On 2019/05/25 2:55, Linus Torvalds wrote:
> > On Fri, May 24, 2019 at 10:41 AM Joe Perches <joe@...ches.com> wrote:
> > > That could also help eliminate unnecessary pr_<foo> output
> > > from object code.
> > 
> > Indeed. The small-config people might like it (if they haven't already
> > given up..)
> 
> Do you mean doing e.g.
> 
>   #define pr_debug(fmt, ...) no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
> 
> depending on the minimal console loglevel kernel config option? Then, OK.

Yes.

Perhaps something like the below (or an equivalent generic wrapper)

#define pr_info(fmt, ...) \
do { \
	if (CONFIG_STATIC_CONSOLE_LEVEL >= LOGLEVEL_INFO) \
		printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__); \
	else \
		no_printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__); \
} while (0)

for each pr_<level>, dev_<level> and netdev_<level>