Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 19 Nov 2019 09:34:57 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To:     Jonathan Richardson <jonathan.richardson@broadcom.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Petr Mladek <pmladek@suse.com>, gregkh@linuxfoundation.org,
        jslaby@suse.com, sergey.senozhatsky@gmail.com,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        Scott Branden <scott.branden@broadcom.com>,
        Ray Jui <ray.jui@broadcom.com>,
        Srinath Mannam <srinath.mannam@broadcom.com>
Subject: Re: console output duplicated when registering additional consoles
Message-ID: <20191119003457.GA208047@google.com>
References: <CAHrpVsUHgJA3wjh4fDg43y5OFCCvQb-HSRpyGyhFEKXcWw8WnQ@mail.gmail.com>
 <CAHrpVsW6jRUYK_mu+dLaBvucAAtUPQ0zcH6_NxsUsTrPewiY_w@mail.gmail.com>
 <20191114095737.wl5nvxu3w6p5thfc@pathway.suse.cz>
 <20191115043356.GA220831@google.com>
 <CAHrpVsWu54rKg3bGhY6WVj5d-myYxGSEkxGhOJKTyyc1EH4qOA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHrpVsWu54rKg3bGhY6WVj5d-myYxGSEkxGhOJKTyyc1EH4qOA@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On (19/11/18 13:38), Jonathan Richardson wrote:
> > +static bool known_console_driver(struct console *newcon)
> > +{
> > +       struct console *con;
> > +
> > +       for_each_console(con) {
> > +               if (!(con->flags & CON_ENABLED))
> > +                       continue;
> > +               if (con->device && con->device == newcon->device)
> > +                       return true;
> > +       }
> > +       return false;
> > +}
> > +
> >  /*
> >   * The console driver calls this routine during kernel initialization
> >   * to register the console printing procedure with printk() and to
> > @@ -2828,6 +2841,9 @@ void register_console(struct console *newcon)
> >         if (newcon->flags & CON_EXTENDED)
> >                 nr_ext_console_drivers++;
> >
> > +       if (known_console_driver(newcon))
> > +               newcon->flags &= ~CON_PRINTBUFFER;
> > +
> >         if (newcon->flags & CON_PRINTBUFFER) {
> >                 /*
> >                  * console_unlock(); will print out the buffered messages
>
> Thanks. It also needs to be cleared when the second console driver is
> registered (of the same type, boot or normal)

The second 'normal' console can be, for instance, netcon - it's sort
of OK to have CON_PRINTBUFFER tty and CON_PRINTBUFFER netcon consoles.

Maybe

> not just when a normal con replaces a bootconsole. A simple way of
> avoiding the problem I'm seeing is to not even set the CON_PRINTBUFFER
> flag on my consoles.

This is up to the console driver to decide.

> It skips the replay and the output on all consoles looks fine. The flag
> is only used by register_console(), although I don't think that is the
> intended usage? There are no console drivers that do this.

Not sure I'm following. There are consoles that want all logbuf messages
once those consoles are available.

$ git grep "\.flags" drivers/tty/ | grep -c CON_PRINTBUFFER
72

	-ss