linux-kernel - Re: How to handle concurrent access to /dev/ttyprintk ?

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Date:   Tue, 13 Apr 2021 13:10:50 +0200
From:   Samo Pogačnik <samo_pogacnik@....net>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Jiri Slaby <jirislaby@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: How to handle concurrent access to /dev/ttyprintk ?

Dne 13.04.2021 (tor) ob 11:41 +0200 je Petr Mladek napisal(a):
> On Mon 2021-04-12 14:41:27, Samo Pogačnik wrote:
> > Dne 12.04.2021 (pon) ob 19:39 +0900 je Tetsuo Handa napisal(a):
> > > What is the intended usage of /dev/ttyprintk ?
> > > 
> > 
> > The intended use of 'ttyprintk' is to redirect console to /dev/ttyprintk
> > via the TIOCCONS ioctl. After successfull redirection, all console
> > messages get "merged" with kernel messages and as such automatically
> > processed
> > (stored/transferred) by the syslog service for example.
> 
> The same can be achieved by /dev/kmsg that was created by systemd
> developers.
> 
'kmsg' and 'ttyprintk' are different types of drivers and as such rather
complementary than exclusive. The 'ttyprintk' being a tty driver allows 
for a system wide automatic redirection of anything written to the console.
On the other hand 'kmsg' is probably better suited for a per process
output redirection/injection of its output into kernel messages.

Maybe i am wrong, but 'systemd' could also find 'ttyprintk' usefull?

best regards, Samo