Re: cannot disable output processing in pseudo-terminal (between openpty(3) parent and child)

[RVP <rvp%SDF.ORG@localhost>]

On Sun, 30 Jul 2023, pouya+lists.netbsd%nohup.io@localhost wrote:

> One of my use cases requires the child process to emit a binary
> stream to be read by the parent.  The parent is notified first via
> a specific escape sequence.  This almost works, except I can't
> figure out how to disable output processing on this stream, and in
> particular the parent receives extra CR characters for every LF
> (NL) the child sends.

You'll have to turn off the NL -> CRNL output processing the kernel
does on your behalf (after all, this is still a "terminal" we're
talking about and not a simple pipe). Don't set the ONLCR bit in
the output-modes of the child pty.

Note that the shell you're running on the child-side also matters.
If that does any fancy line-editing using libedit or readline, say,
then that could change the ONLCR bit every time the shell has to
read input.

> P.S. This other one's not as important but I'm also confused by
> why disabling ECHO on the parent stdin also disables it for the
> pseudo-terminal.

It shouldn't--unless you've unset that bit on the master then copied
those settings over onto the child pty FD.

-RVP