Re: Device to write to all (serial) consoles
From: Greg Kroah-Hartman
Date: Sat Aug 03 2019 - 02:46:46 EST
On Fri, Aug 02, 2019 at 09:59:06PM +0200, Paul Menzel wrote:
> Dear Greg,
> On 02.08.19 18:02, Greg Kroah-Hartman wrote:
> > On Fri, Aug 02, 2019 at 03:23:08PM +0200, Paul Menzel wrote:
> > > 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?
> Because the cable is always connected to the port on the back side, and
> sometimes the port in the front has ID 0, and the one in the back 1, and
> other times vice versa. We do not want to track that, and it would be
> convenient to just write to both ports.
> > > $ 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.
> Can such a device be created with udev or so?
No, a single device node can not reference multiple device nodes at the
same time, sorry. That's just not how they work at all.