If you get on the calls, you’ll find zero hostility across the operating systems devs. The focus is on OpenZFS, with the Linux branch gradually becoming baseline for the FreeBSD work as well. Illumos ( where OpenZFS originated after Illumos was formed post the OpenSolaris shutdown) hasn’t moved to this baseline yet due to the significant OS level differences and instead code is pulled between the “branches” as needed. The collaboration happens via email and regular calls.