linux-kernel - Re: [PATCH] tty: Add NULL TTY driver

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Message-ID: <20190405090043.vnsftwpdm56cx2hr@axis.com>
Date:   Fri, 5 Apr 2019 11:00:43 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
Cc:     Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Add NULL TTY driver

On Fri, Apr 05, 2019 at 10:39:43AM +0200, Enrico Weigelt, metux IT consult wrote:
> On 03.04.19 16:11, Vincent Whitchurch wrote:
> 
> > Especially on embedded systems, it would be convenient to have a simple
> > way to disable the console (both for kernel and userspace) on a system
> > which normally uses it, to free up the UART for other things.
> 
> Just symlinking to /dev/null does not work ?

No, /dev/null does not support the TTY ioctls.

> OTOH, if you're introducing a dummy console, wouldn't a ringbuffer that,
> can be read out later, a better option ?

There is already a ttyprintk driver in mainline to send these messages
to the printk ring buffer if one is actually intrested in what is
written to the console.  There's no option to enable it via console= in
mainline but I have a patch for that too.