The derivative portions of the ZFS driver are dual-licensed GPLv2/CDDL.

The CDDL-only parts of the driver are portable between OSes, removing the "derivative code" argument (similar argumentation goes back to introduction of AFS driver for Linux, IIRC).

Remember, GPLv2 does not talk about linking. Derivativeness is decided by source code, among other things whether or not the non-GPL code can't exist/operate without GPL code.

I appreciate the detailed explanations. I understand some of the basics, and this has given me some more routes to read up on and learn.