Ever wondered how the #OpenZFS readonly filesystem property interacts with the ro and rw mount options, and if using mount(8) vs zfs-mount(8) changes anything, and if your choice of platform changes anything?
I certainly hadn't, until I got a bug report that I'd subtly changed a couple of cases in 2.4.2 for Linux. I unbroke it, but not before spending a bunch of time trying to figure out what "unbroke" means. Emphasis on "trying".
Here's the fix, with my endless 🤔 in the collapsed "bonus" section. Good speluncking opportunity available if you'd like to figure it out!