linux-kernel - Re: [PATCH v2] printk: Set console_set_on_cmdline=1 when __add_preferred_console() is called with user

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Date:   Tue, 15 Feb 2022 18:58:14 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andre Kalb <andre.kalb@....de>, john.ogness@...utronix.de,
        linux-kernel@...r.kernel.org, rostedt@...dmis.org
Subject: Re: [PATCH v2] printk: Set console_set_on_cmdline=1 when
 __add_preferred_console() is called with user_specified == true

On Tue 2022-02-15 12:15:58, Sergey Senozhatsky wrote:
> On (22/02/14 14:21), Andre Kalb wrote:
> > +static void set_user_specified(struct console_cmdline *c, bool user_specified)
> > +{
> > +	if (!user_specified)
> > +		return;
> > +
> > +	c->user_specified = true;
> > +	console_set_on_cmdline = 1;
> > +}
> 
> In original code we always set c->user_specified. Is it guaranteed that
> ->user_specified is properly initialized to 0? Maybe can do something like:

It is guaranteed. console_cmdline is a static array initialized with
zeroes. The 2nd set_user_specified() call is done for a not-yet-used
slot in the array, so it must be zero.

> static void set_user_specified(struct console_cmdline *c, bool user_specified)
> {
> 	c->user_specified = user_specified;

This will change the behavior for the 1st set_user_specified() call.
It happens when the same console is added more times by device tree,
SPCR, and/or command line. c->user_specified must stay "true" when
at least one __add_preferred_console() call added it from the command line.

> 	if (!user_specified)
> 		return;
> 
> 	console_set_on_cmdline = 1;
> }

I agree that it is not obvious. It would make sense to add a comment
into the code. I am going to propose something in a reply to the
original post.

Best Regards,
Petr