[BRLTTY] Brltty support on OpenBSD

[Crystal Kolipe]

Hi,

The current release of brltty does not compile on OpenBSD due to some missing includes:

In Programs/beep_wskbd.c, we need to add <sys/ioctl.h> and <time.h> before wsconsio.h.
In Programs/rgx_internal.h, the path to pcre2.h needs to be /usr/local/include/pcre2.h, (pcre2 is not part of the base system on OpenBSD, but can be installed from a package).

With these changes, it's possible to compile brltty-6.5 on OpenBSD 7.3 using the following configure options:

./configure --disable-speech-support --disable-api --without-pcm-package --disable-icu

It's also necessary to use gmake rather than the native bsd make for the build.

The resulting binaries seem to run OK, but I've only done basic testing using the XW driver for a virtual braille display in X.

However, the system is not fully usable:

Overall, support for running brltty on OpenBSD is not as comprehensive as it is for Linux systems.  This was mentioned last month in a post to one of the OpenBSD mailing lists [1].

A quick aside - I'm not a regular user of brltty on any platform, and only became aware of this issue when I read the above linked mailing list post.  The main reason I started looking in to it is because I've been doing various development on the OpenBSD console code for some time, and noticed that on OpenBSD brltty has always used a patched version of screen to provide access to the display, since the method used on Linux systems, (reading from /dev/vcsa0), is not available on OpenBSD.  Writing a kernel patch to provide a vcsa-like device on OpenBSD seemed fairly trivial, (and in fact it was), so I began to look further at whether getting a modern version of brltty properly running on OpenBSD, (as requested in the above post), would be practical.

The documentation on brltty.com still refers to OpenBSD 3.4, which was released in 2003, and screen-4.0.1.  Obviously things have moved on quite a lot in the last 20 years.  The shm patched version of screen which is maintained in the OpenBSD ports tree has been updated to 4.0.3, but this is still very out of date.  Discussion in 2021 floated the idea of interfacing with tmux instead [2].

For testing purposes, I was able to use the patched version of screen-4.0.3 together with brltty-6.5 compiled as described above on an OpenBSD 7.3 system, using the XW driver.  It displayed what seemed to be the correct output in the brltty X window.

Having got this far, I was hoping to get brltty working with my new vcsa-like kernel device.  Unfortunately, the relevant screen driver code is quite linux-specific and uses various interfaces that are not present on OpenBSD.  If this functionality was ever going to be added to brltty, 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, we might as well send the data out as the raw unicode codepoints from the wscons display buffer.  This would likely keep the code simpler, and potentially give more flexibility when handling non-ASCII characters.

At this point, I can't really do much more to make any further progress that would be useful to the wider community of brltty users.  I'm hoping that there are some brltty developers who are interested in the OpenBSD platform that can make use of the information I've provided above.

[1] https://marc.info/?l=openbsd-misc&m=168453178604532&w=2
[2] https://marc.info/?l=openbsd-misc&m=161670969314602&w=2