linux-kernel - Re: [PATCH v4 0/2] Optionally allow ttynull to be selected as a default console

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Message-ID: <Z7uOsqky4Tw9J6QR@surfacebook.localdomain>
Date: Sun, 23 Feb 2025 23:10:10 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: adamsimonelli@...il.com, Petr Mladek <pmladek@...e.com>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiri Slaby <jirislaby@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v4 0/2] Optionally allow ttynull to be selected as a
 default console

Sun, Feb 23, 2025 at 03:44:54PM -0500, adamsimonelli@...il.com kirjoitti:
> From: Adam Simonelli <adamsimonelli@...il.com>
> 
> When switching to a CONFIG_VT=n world, at least on x86 systems,
> /dev/console becomes /dev/ttyS0. This can cause some undesired effects.
> /dev/console's behavior is now tied to the physical /dev/ttyS0, which when
> disconnected can cause isatty() to fail when /dev/ttyS0 is disconnected,
> and users who upgrade to a theoretical vt-less kernel from their
> distribution who have a device such as a science instrument connected to
> their /dev/ttyS0 port will suddenly see it receive kernel log messages.
> 
> When the new CONFIG_NULL_TTY_CONSOLE option is turned on, this will allow
> the ttynull device to be leveraged as the default console. Distributions
> that had CONFIG_VT turned on before will be able to leverage this option
> to where /dev/console is still backed by a psuedo device, avoiding these
> issues, without needing to enable the entire VT subsystem.

This rings a bell of the following

https://lore.kernel.org/all/20201111135450.11214-1-pmladek@suse.com/
https://lore.kernel.org/all/20210107164400.17904-1-pmladek@suse.com/
https://lore.kernel.org/all/20210108114847.23469-1-pmladek@suse.com/

I don't see any mention in the commit message about these, have you studied the
cases? Will your change anyhow affect the described there?

-- 
With Best Regards,
Andy Shevchenko