linux-kernel - Re: [PATCH 1/2] init/console: Use ttynull as a fallback when there is no console

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Message-ID: <X6yTyvIfRUH7TOOx@jagdpanzerIV.localdomain>
Date:   Thu, 12 Nov 2020 10:45:46 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        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,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 1/2] init/console: Use ttynull as a fallback when there
 is no console

On (20/11/12 09:17), Sergey Senozhatsky wrote:
> On (20/11/11 14:54), Petr Mladek wrote:
> [..]
> > diff --git a/init/main.c b/init/main.c
> > index 130376ec10ba..24413c055a85 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -1470,8 +1470,14 @@ void __init console_on_rootfs(void)
> >  	struct file *file = filp_open("/dev/console", O_RDWR, 0);
> >  
> >  	if (IS_ERR(file)) {
> > -		pr_err("Warning: unable to open an initial console.\n");
> > -		return;
> > +		pr_err("Warning: unable to open an initial console. Fallback to ttynull.\n");
> > +		register_ttynull_console();
> > +
> 
> A nit, this probably can be done in console_device() function.
> 
> For several reasons:
> 
> - we will get covered all the future cases when something other than
>   console_on_rootfs() will filp_open("/dev/console")

And the existing ones (including user-space). For instance,
kernel/bpf/preload/iterators/iterators.c probably fails (?)
on systems with console=

	debug_fd = open("/dev/console", O_WRONLY | O_NOCTTY | O_CLOEXEC);
	if (debug_fd < 0)
		return 1;

	-ss