linux-kernel - Re: [PATCH] printk: Add loglevel for "do not print to consoles".

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Date:   Thu, 7 May 2020 09:50:21 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Joe Perches <joe@...ches.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, Dmitry Safonov <dima@...sta.com>,
        Michal Hocko <mhocko@...e.com>,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".

On 2020/05/07 0:26, Joe Perches wrote:
> On Wed, 2020-05-06 at 18:45 +0900, Tetsuo Handa wrote:
>> On 2020/04/28 20:33, Tetsuo Handa wrote:
>>> On 2020/04/27 15:21, Sergey Senozhatsky wrote:
>>>>> KERN_NO_CONSOLES is for type of messages where "saved for later analysis" is
>>>>> important but "printed for immediate notification" is not important.
>>>>> In other words, KERN_NO_CONSOLES is NOT for dying messages where "printed for
>>>>> immediate notification" is important.
>>>>
>>>> per-console loglevel is a user configurable parameter.
>>>> KERN_NO_CONSOLES is a hard-coded policy.
>>>
>>> But given that whether to use KERN_NO_CONSOLES is configurable via e.g. sysctl,
>>> KERN_NO_CONSOLES will become a user configurable parameter. What's still wrong?
>>>
>>
>> Any problems remaining?
> 
> printk_get_level / printk_skip_level and the various
> uses of %pV using printk_get_level
> 

Excuse me, but what do you mean?

I wish printk() accepts "loglevel" argument detached from "fmt" argument (e.g.

  int printkl(int loglevel, const char *fmt_without_loglevel, ...);
  int vprintkl(int loglevel, const char *fmt_without_loglevel, va_list args);

) so that users of KERN_NO_CONSOLES need not to do like

  if (sysctl_no_console_for_XX)
    printk(KERN_INFO KERN_NO_CONSOLES pr_fmt(fmt) "%s\n", "hello");
  else
    printk(KERN_INFO pr_fmt(fmt) "%s\n", "hello");

or

  printk("%s" pr_fmt(fmt) "%s\n", sysctl_no_console_for_XX ? KERN_INFO KERN_NO_CONSOLES : KERN_INFO, "hello");

in order to conditionally embed KERN_NO_CONSOLES into

  pr_info("%s\n", "hello");

. But this patch is about whether KERN_NO_CONSOLES is acceptable. How to
pass KERN_NO_CONSOLES (if KERN_NO_CONSOLES is acceptable) is a future patch.