linux-kernel - Re: [PATCH v8 1/4] ttynull: Always initialize console index to -1

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Message-ID: <4810112.n0HT0TaD9V@nerdopolis2>
Date: Thu, 13 Mar 2025 08:09:36 -0400
From: Adam Simonelli <adamsimonelli@...il.com>
To: Petr Mladek <pmladek@...e.com>
Cc: linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jiri Slaby <jirislaby@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Andy Shevchenko <andy.shevchenko@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>,
 John Ogness <john.ogness@...utronix.de>,
 Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v8 1/4] ttynull: Always initialize console index to -1

On Wednesday, March 12, 2025 10:38:59 AM EDT Petr Mladek wrote:
> On Mon 2025-03-10 23:31:30, adamsimonelli@...il.com wrote:
> > From: Adam Simonelli <adamsimonelli@...il.com>
> > 
> > This allows ttynull to be considered in console selection.
> 
> This is not true. It should be possible to register ttynull even
> when .index == 0.
> 
> The .index is important only for drivers which support more devices,
> e.g. the serial port or virtual terminal.
> 
> > 
> > Suggested-by: Petr Mladek <pmladek@...e.com>
> > Signed-off-by: Adam Simonelli <adamsimonelli@...il.com>
> > ---
> >  drivers/tty/ttynull.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/tty/ttynull.c b/drivers/tty/ttynull.c
> > index 6b2f7208b564..d8b51edde628 100644
> > --- a/drivers/tty/ttynull.c
> > +++ b/drivers/tty/ttynull.c
> > @@ -57,6 +57,7 @@ static struct tty_driver *ttynull_device(struct console *c, int *index)
> >  static struct console ttynull_console = {
> >  	.name = "ttynull",
> >  	.device = ttynull_device,
> > +	.index = -1,
> 
> There is only one "/dev/ttynull". And its index is initialized to "0".
> At least it seems to be the last parameter in:
> 
> static int __init ttynull_init(void)
> {
> [...]
> 	tty_port_link_device(&ttynull_port, driver, 0);
> [...]
> }
> 
> So, I believe this it should be perfectly fine to keep the default "0"
> here. Note that it is special for ttynull because it is only one...
> 
> IMHO, this patch adds more harm than good :-)
> 
> Best Regards,
> Petr
> 
Understood, thanks for the explanation about that.