I'm working on in-kernel ext3/4fs journalling support for NetBSD. The code is hot garbage but I love it because of the learning journey it's taken me on: about working in a kernel, about filesystems, etc. I'm gonna clean it up massively once I've figured out how to make the support complete, and even then I expect to be raked over the coals by the NetBSD devs for my code quality. On top of that there's the fact that real ones use ZFS or btrfs these days, and ext4 is a toy; like FAT, by comparison, so this may not even be that useful. But it's fun and lets me say hey Ma, I'm a kernel hacker now!
Ext4 is most certainly still in use and not a toy. Its trusted. It takes a lot for folks to adopt a new file system.
I worked on a research topic in grad school and learned about holes in files, and how data isn’t removed until the last fd is closed. I use that systems knowledge in my job weekly.
A tip. Kernel development can be lonely, share what you are working on and find others.
