linux-kernel - Re: [RFC PATCH] printk: console: Allow each console to have its own loglevel

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Date:   Thu, 19 May 2022 17:25:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Chris Down <chris@...isdown.name>
Cc:     linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        kernel-team@...com
Subject: Re: [RFC PATCH] printk: console: Allow each console to have its own
 loglevel

On Thu, May 19, 2022 at 04:08:04PM +0100, Chris Down wrote:
> Greg Kroah-Hartman writes:
> > >  struct console {
> > >  	char	name[16];
> > >  	void	(*write)(struct console *, const char *, unsigned);
> > > @@ -179,9 +173,11 @@ struct console {
> > >  	void	*data;
> > >  	struct	 console *next;
> > >  	int	level;
> > > -	struct	device classdev;
> > > +	struct	device *classdev;
> > 
> > Ick, no, keep the real structure here.  It can properly handle the
> > reference counting for the object.  Just correctly clean up in the
> > release function, not anywhere else.
> 
> Sorry, I'm getting more and more confused about what you're asking me to do,
> and less and less clear on the rationale.
> 
> Can you please clarify what "correctly cleaning up" would mean for a
> non-pointer `struct device'?
> 
> Is your concern that...
> 
>     register_console(c)
>         device_initialize(c->d)
>         device_add(c->d)
>     unregister_console(c)
>         device_unregister(c->d)      console_classdev_release(c->d)
>     register_console(c)
>         device_initialize(c->d)  <-- classdev was not previously zeroed out
> 				     in console_classdev_release() and bad 				     things may happen

Note, you can not "recycle" a structure in the driver model.  So when
the console is unregistered, it should be freed.  When it is registered,
it should be created.  Perhaps that is the confusion here?

thakns,

greg k-h