linux-kernel - Re: console output duplicated when registering additional consoles

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Date:   Tue, 19 Nov 2019 10:46:22 -0800
From:   Jonathan Richardson <jonathan.richardson@...adcom.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>, gregkh@...uxfoundation.org,
        jslaby@...e.com, sergey.senozhatsky@...il.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Scott Branden <scott.branden@...adcom.com>,
        Ray Jui <ray.jui@...adcom.com>,
        Srinath Mannam <srinath.mannam@...adcom.com>
Subject: Re: console output duplicated when registering additional consoles

> > 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.

OK I missed that case.

>
> 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.

I meant mine would be the only driver that didn't set CON_PRINTBUFFER.
Thanks for clarifying why it would be set. I guess what I didn't
understand is why are all the consoles updated (potentially) when a
new console is registered. As I mentioned before I can not set
CON_PRINTBUFFER to avoid the issue but it's probably not what I want.
I would possibly lose some of the log I guess if there was something
in the buffer during registration of the new console. So I tried the
patch but the issue remains as I originally described.

Thanks,
Jon