[BRLTTY] Linux console hacking (was: Re: Footsteps towards better accessibility in Linux)

[Nicolas Pitre]

On Thu, 22 May 2025, Aura Kelloniemi wrote:

> Linux console does not have alternate screen support. Probably all modern
> terminal emulators have a notion of an alternate screen buffer. Applications
> can switch between these screen buffers with an escape sequence. This is used
> to preserve original contents of a terminal while an interactive application
> is running. Applications which utilize this include less, emacs, nano, mutt,
> lynx, and almost any TUI application.
> 
> Supporting this requires recognizing the escape sequences and allocating space
> for the alternate screen buffer, which effectively doubles the amount of
> memory allocated for screen contents.
> 
> Do you Nicolas think this could be accepted, and would you like to do this?

This is now available in kernels v6.18.20 or later, v6.19.10 or later, 
and the upcoming v7.0.

Disclaimer: Someone else contributed this support to v6.18.0 but it was 
completely broken for /dev/vcsu users like BRLTTY. This prompted me to 
finally look at it and contribute a fix, hence those kernel versions 
above.


Nicolas