There is no 'modern' ZFS-like fs in Linux nowadays.
I obviously have nothing like inside knowledge, but I assume the reason there have not been lawsuits over this, is that whoever could bring one (would it be only Oracle?) expects there are even-odds that they would lose? Thus the risk of setting an adverse precedent isn't worth the damages they might be awarded from suing Canonical?
My understanding is that Canonical is shipping ZFS with Ubuntu. Or do I misunderstand? Has Canonical not actually done the big, bad thing of distributing the Linux kernel with ZFS? Did they find some clever just-so workaround so as to technically not be violation of the Linux kernel's license terms?
Otherwise, if Canonical has actually done the big, bad thing, who has standing to bring suit? Would the Linux Foundation sue Canonical, or would Oracle?
I ask this in all humility, and I suspect there is a chance that my questions are nonsense and I don't know enough to know why.
Additionally, GPLv2 does not prevent shipping ZFS combined with GPL code, because CDDL code is not derivative work of GPLv2 code. So it's legal to ship.
It could be problematic to upstream, because kernel development would demand streamlining to the point that the code would be derivative.
Additionally, two or three kernel contributors decided that the long standing consensus on derivative work is not correct and sued Canonical. So far nothing happened out of that, Los Alamos National Laboratory also laughed it off.
The CDDL code is not a derivative work of GPLv2 code, but the combined work as a whole is a derivative work of GPLv2 code (assuming by "combined" we are talking about shipping an executable made by compiling and linking GPLv2 and CDDL code together). Shipping that work does require permission from both the GPLv2 code copyright owners and the CDDL code copyright owners unless the code from on or the other can be justified under fair use or if it was a part of the GPLv2 or CDDL code that is not subject to copyright.
What Canonical does is ship ZFS as a kernel module. That contains minimal GPLv2 code from the kernel that should be justifiable as fair use (which seems like a decent bet after the Oracle vs Google case).
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.