Patches are expected but the kernel interfaces shouldn't change right? Like if I write a kernel module no patch should break my compatibility and make my module not build anymore (I think)? I don't care if it changes underneath as long as it doesn't change where I interface.
Userspace doesn't break, but if you don't want your module to break, upstream it (which is an important lesson about hardware selection: if it's not upstream and not being upstreamed, then you're going to get stuck on an old kernel at some point).
ZFS has broken on new releases (I don't recall if they were stable, I think they were), and that is one reason I won't use as the main filesystem on linux.
Upstream stable kernel certainly does not care about compatibility with your particular thirdparty module. You'll just have to add another KERNEL_VERSION #if. Maybe if you're nvidia, or something, things are different.
