@justine
Looks quite simple port without patch.
But reading the description, it seems to be a wrapper for specific syscall with the same name as the port.
So it would depend if the syscall exists on #OpenBSD and compatible with the one on #FreeBSD.
If #OpenBSD matched above prerequisite, and #OpenBSD ports infrastructure is enough alike with #FreeBSD #ports (IIRC, #NetBSD, the direct origin of #OpenBSD, once introduced #FreeBSD #ports framework far before when it was still quite simple and switched to their own #pkgsrc later), the conversion would be trivial.

On #FreeBSD, porters (including myself) first create a port under specific category directory such as graphics, test, hook on category Makefile, generate diff and file a PR on Bugzilla and/or open review on Phabricator.

For any #ports that are not intended to be included in official #ports, no need to hook to category Makefile and no need to file PRs / opening reviews. Ports framework allows it. Hooking on category Makefile is needed to be picked for official #pkg building. Maybe #OpenBSD #ports, too, as without the allowance, how porters attempt to make new ports?

By searching Internet, found this.
https://www.openbsd.org/faq/ports/guide.html

And FreeBSD has a (large) document "Porter's Handbook".
https://docs.freebsd.org/en/books/porters-handbook/

An example how I've added new FreeBSD port.
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293719
https://reviews.freebsd.org/D55798

And its relevant commit.
https://cgit.freebsd.org/ports/commit/?id=b23b14c3bfc0d930f7757226b06a88008e95909c

Maybe #OpenBSD would have its own workflow, though.