> system tap, ktap, lttng, ftrace, etc
That's why I'm talking about NIH.
Even with ebfp, they intentionally choose different tracing syntax (just look at it, it's comical). Didn't use ready-to-use CTF. Etc etc etc.
If the CDDL simply didn't matter, after all, they could just add it to the source tree and be done with it. I wonder why they haven't done that...
ZFS is not in the Linux kernel, and Linus has stated that he will never merge CDDL licensed code due to license incompability.
Those Linux distros that distribute ZFS do so as a separate module, not part of the Linux kernel.
DTrace was GPL licensed too late (2018), something even Brendan Gregg stated as he finds eBPF more capable (and he is a leading expert on DTrace).
ZFS is still problematic, specifically because of the GPL-incompatible license. Various distros have found ways around that (or are deliberately ignoring those issues at their own peril), but it's still very much "a real problem", and it took years (if not decades) to get to the point where ZFS on Linux is actually as viable an option as it is today.