Interesting. They need that for lowest-possible latency? And it should be fairly safe?

Assuming they're USB devices they shouldn't be a reason to do this... Apple moved third-party drivers for USB devices and audio HAL extensions to user space, so there's some minor overhead choosing DriverKit over IOKit. Everything I've dug up says it's low single digit percentages. I wouldn't be developing USB drivers against IOKit anymore personally and I'd be looking to move over pretty aggressively before Apple drops the hammer.

How about file system drivers? If there is such a thing any more... fuse and friends...

There is a port of FUSE for macOS, and Apple also has a first party API for this called FSKit…

https://developer.apple.com/documentation/fskit

I know there was a port of FUSE. But iirc it requires old style extensions. Has it changed?

Per the MacFUSE documentation…

> macFUSE 5.0 supports multiple APIs for mounting file systems.

> By default, macFUSE uses the VFS API to mount file systems. When specifying the mount-time option -o backend=fskit, macFUSE will use FSKit to mount the file system.

https://github.com/macfuse/macfuse/wiki/FUSE-Backends

UAD drivers have always been very creative... lol