linux-kernel - Re: Device to write to all (serial) consoles

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Message-ID: <20190802160243.GA15484@kroah.com>
Date:   Fri, 2 Aug 2019 18:02:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     linux-serial@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Donald Buczek <buczek@...gen.mpg.de>
Subject: Re: Device to write to all (serial) consoles

On Fri, Aug 02, 2019 at 03:23:08PM +0200, Paul Menzel wrote:
> Dear Linux folks,
> 
> 
> On a lot of devices, like servers, you have more than one serial console,
> and you do not always know, how they are numbered. Therefore, we start a
> console on ttyS0 and ttyS1.
> 
> In user space, we also would like to write to both consoles to not worry
> about the numbering. Writing to `/dev/console` only write to the active
> console.

So the same data to multiple console devices with just one userspace
call?  Why?

>     $ more /proc/consoles # I think
>     tty0                 -WU (EC p  )    4:1
>     ttyS0                -W- (E  p a)    4:65
>     ttyS1                -W- (E  p a)    4:65
> 
> Does a device exist, or can a device be configured so you can write to
> all (serial) consoles from user space?

With one syscall, not that I know of, sorry.

greg k-h