Re: Getty on USB serial port

[Michael van Elst <mlelstv%serpens.de@localhost>]

On Fri, Sep 15, 2017 at 11:16:31AM -0400, William D. Jones wrote:

> > Intercepting the console with a program is another method. This still
> > causes early messages to be sent to the serial port, but that is seen by
> > ppp as line noise and filtered out.
> Yes, basically this is my concern. I don't know how well ppp will cope with
> random bursts of text. Just out of curiosity, I assume I need to write this
> program myself; how might I go about doing that? I know I need to `dup2` to
> redirect, but the problem is getting the correct fd to redirect so processes
> writing text to the console "see" my altered fd.

You redirect console to some terminal with the TIOCCONS ioctl. I.e.
something like

fd = open("/dev/ttyU0", O_RDONLY);
ioctl(fd, TIOCCONS);
close(fd);

Redirects console output to /dev/ttyU0.

xconsole uses a pseudo-tty instead, so that it can read the output
and render it into a window.

Again, that's the "higher level" console. When the kernel enters DDB
or shuts down, the lowlevel console will be used again.


Greetings,
-- 
                                Michael van Elst
Internet: mlelstv%serpens.de@localhost
                                "A potential Snark may lurk in every tree."