Hi Ethan, I'm happy to see your enthusiasm for my driver but, if you want to help, I think you should simply send the changes you have in mind to the out-of-tree repo. That way you'll start learning the codebase while I can review your work and run xfstests for you. Filesystems are very dangerous things; I've probably done a lot of damage myself back in the day trying to help out with the hfs drivers. As for upstreaming, the driver still has a few rough edges, but I don't think that's the real reason I never tried to submit. I'm just no longer confident that filesystem compatibility is a reasonable goal, and I don't expect much interest from reviewers. There are too many risks, and too many hardware restrictions these days; regular users have much easier (even if slower) ways to move their files around. Other uses exist of course (like Aditya can explain), but they are a bit esoteric. Of course if upstream people disagree, and they do want the apfs support, I will be glad to prepare a patch series. Ernesto