Quoting russell@coker.com.au (russell@coker.com.au):
Well in the real world ZFS on Ubuntu is working well. I prefer Debian but Ubuntu has better support for ZFS due to different legal advice.
Different and quite clearly wrong, in my view. (No, I'm not an attorney, but I have been a major participant in OSI's licence evaluations for some decades, and made a particular study of such things.) In my view, Canonical are willful copyright violators and are staking a great deal on a guess that kernel stakeholders are not going to haul them into court, where they would very likely lose in a major way, be ordered to pay a great deal in monetary damages, and be enjoined against further violation. If such an action were brought under USA copyright law, and Canonical were to lose, the basic level of statutory damages would be between US $750 and US $30,000, depending on the facts of the case and the court's mood (and the seriousness of the infringing act, and the infringer's financial net worth), but if willfulness is proved, then plaintiff would also be awarded up to US $150,000 in additional statutory damages. That's aside from, in addition to, any compensatory aka 'actual' damages plus profits made by the infringer.