linux-kernel - Re: union: was: Re: [PATCH printk v1 05/18] printk: Add non-BKL console basic infrastructure

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Date:   Tue, 28 Mar 2023 10:20:26 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: union: was: Re: [PATCH printk v1 05/18] printk: Add non-BKL
 console basic infrastructure

On Mon 2023-03-27 18:34:22, John Ogness wrote:
> On 2023-03-21, Petr Mladek <pmladek@...e.com> wrote:
> > It is not completely clear that that this struct is stored
> > as atomic_long_t atomic_state[2] in struct console.
> >
> > What about adding?
> >
> > 		atomic_long_t atomic;
> 
> The struct is used to simplify interpretting and creating values to be
> stored in the atomic state variable. I do not think it makes sense that
> the atomic variable type itself is part of it.

It was just an idea. Feel free to keep it as is (not to add the atomic
into the union).

> > Anyway, we should at least add a comment into struct console
> > about that atomic_state[2] is used to store and access
> > struct cons_state an atomic way. Also add a compilation
> > check that the size is the same.
> 
> A compilation check would be nice. Is that possible?

I think the following might do the trick:

static_assert(sizeof(struct cons_state) == sizeof(atomic_long_t));


> I am renaming the struct to nbcon_state. Also the variable will be
> called nbcon_state. With the description updated, I think it makes it
> clearer that "struct nbcon_state" is used to interpret/create values of
> console->nbcon_state.

Sounds good.

Best Regards,
Petr