OSX has searchfs extensions to support spotlight functionality. This is missing from the current release of MacZFS and wasn't released as part of the 10a286 drop since it was purely Apple open-source license

This is something else I may be able to do. Again, I don't think my saying that I just might do something about this item at some future date is going to impede progress that might otherwise occur.

You can get a feel for this in the apple hfs+ code on the developer site. Also you can trace what is calling it iirc. Look for searchfs in dtrace -l

Cross-reference:

VNOP_SEARCHFS · Issue #100 · zfs-osx/zfs https://github.com/zfs-osx/zfs/issues/100