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

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Message-ID: <20190411152845.xomzmhtyejzr4r35@axis.com>
Date:   Thu, 11 Apr 2019 17:28:45 +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 02:32:41PM +0200, Enrico Weigelt, metux IT consult wrote:
> On 05.04.19 11:00, Vincent Whitchurch wrote:
> > 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.
> 
> hmm, wo (which programs) do you need, that really need them ?

I think it was systemd's debug-shell which complained about the 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.
> 
> Great. IMHO, that would be the better way.

Like Krzysztof explained, sometimes you just want to discard these
messages.