linux-kernel - [RFC 0/2] printk: Official way to mute consoles

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Date:   Thu, 22 Oct 2020 13:42:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shreyas Joshi <shreyas.joshi@...mp.com>,
        shreyasjoshi15@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>
Subject: [RFC 0/2] printk: Official way to mute consoles

The long discussion about handling empty console= came up with several
problems. This patchset tries to solve the two original problems
with empty console="" parameter:

  + Prevent the potential crash by registering console for /dev/console.
  + Prevent the performance regression by muting the consoles.

IMHO, the patchset makes sense on its own. It fixes a regression. It seems
that people want this functionality [1][2][3].

Note that there are still some problems that might be solved later:

  + Invalid console=bla name might still prevent registering any console.

  + The kernel should not crash even when /dev/console does not point
    to any real console. 

  + Should we add some fallback for stdin, stdout, and stderr when /dev/console
    can't be opened? For example, /dev/null?
    
  + How user space handle missing none-console associated with /dev/console?

[1] https://www.programmersought.com/article/19374022450/
[2] https://developer.toradex.com/knowledge-base/how-to-disable-enable-debug-messages-in-linux
[3] https://unix.stackexchange.com/questions/117926/try-to-disable-console-output-console-null-doesnt-work


Petr Mladek (2):
  printk: Add kernel parameter: mute_console
  printk: Restore and document obsolete ways to disable console output

 .../admin-guide/kernel-parameters.txt         | 11 +++++++
 kernel/printk/printk.c                        | 30 +++++++++++++++++--
 2 files changed, 39 insertions(+), 2 deletions(-)

-- 
2.26.2