[BRLTTY] Brltty support on OpenBSD

[Crystal Kolipe]

On Sun, Jun 25, 2023 at 04:27:00PM -0400, Dave Mielke wrote:
> [quoted lines by Crystal Kolipe on 2023/06/25 at 13:02 -0300]
> 
> >The current release of brltty does not compile on OpenBSD due to some missing includes:
> 
> Thanks for figuring those out. I could add them, or perhaps you might crate a PRs for this and further OpenBSD work.

Please feel free to add these changes manually - as I mentioned at the end of my previous mail, I don't expect to be doing a lot of further work on this myself but wanted to pass the information on as it provides a starting point for non-developers to test the current brltty on OpenBSD.

> >and noticed that on OpenBSD brltty has always used a patched version of screen to provide access to the display, 
> 
> We're trying to eliminate that. It's replacement is brltty's (new) Terminal Emulator screen driver.

Ah, OK, removing the dependency on screen seems like a good idea.

> >it would probably be better to have a separate screen driver for the OpenBSD console, and in that case it wouldn't make much sense for my kernel patch to necessarily emulate the data format of the linux vcsa device at all

> Yes! Please do it that way, i.e. with a modern, OpenBSD-specific screen driver.

It's certainly possible to patch OpenBSD to implement a screen readout device that would potentially allow brltty to access the console independently of any particular login session, just like it does on Linux systems.

The code I've written was intended as a proof of concept, but I'll create a version that does a more direct read out of character data instead of trying to emulate the vcsa format.  I haven't published any of this at the moment as it's part of a broader write up that isn't quite finished yet, but it'll land in a week or so.