linux-kernel - Re: [PATCH v2] s390/sclp_vt220: Fix console name to match device

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Message-ID: <20210428133836.GD21939@linux.ibm.com>
Date:   Wed, 28 Apr 2021 15:38:36 +0200
From:   Hendrik Brueckner <brueckner@...ux.ibm.com>
To:     Valentin Vidic <vvidic@...entin-vidic.from.hr>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, Philipp Kern <pkern@...ian.org>,
        Benjamin Zimmermann <dave@....volkswagen.com>,
        debian-s390@...ts.debian.org,
        Peter Oberparleiter <oberpar@...ux.ibm.com>
Subject: Re: [PATCH v2] s390/sclp_vt220: Fix console name to match device

Hi Valentin,

I just had the chance to look into this console topic yesterday.

On Tue, Apr 27, 2021 at 09:40:10PM +0200, Valentin Vidic wrote:
> Console name reported in /proc/consoles:
> 
>   ttyS1                -W- (EC p  )    4:65

It is been a while ago when working on consoles. However, consoles are
typically devices without having a device node associated. There is special
handling for /dev/console wrt. to the preferred console in the tty layer.

A console device might be associated with a tty device but this is not a
requirement. For example, consider the net console that streams console
messages thru UDP and is not associated with a tty.

Because console and tty are different devices, names can also be different
which is, unfortunately, the case on s390.

Therefore my suggestion here is not derive the tty device from the name
of the console, but rather looking at the associated tty being reported
as major minor number in /proc/console.

> 
> does not match the char device name:
> 
>   crw--w----    1 root     root        4,  65 May 17 12:18 /dev/ttysclp0

In the example above, 4:65 excactly ends up in /dev/ttysclp0.

I am also in contact with Christian and thanks to him to try this out
internally.  At least, there are options to bring this forward and let's
figure out what the best solution will be.

Thanks and kind regards,
  Hendrik

-- 
Hendrik Brueckner
brueckner@...ux.ibm.com           | IBM Deutschland Research & Development GmbH
                                  | Schoenaicher Str. 220, 71032 Boeblingen