ZFS, unionfs - Operation not supported

[Oliver Pinter]

Hi all!

It is the problematic FS:
zpower on /mnt/zpower (zfs, local)
/usr/src on /mnt/zpower/jail/default/ports (nullfs, local)

and the failed command:
mount_unionfs -o below /mnt/zpower/jail/default/ports/
/mnt/zpower/jail/www/usr/ports/

(truss mount_unionfs -o below /mnt/zpower/jail/default/ports/
/mnt/zpower/jail/www/usr/ports/ ) > & /tmp/unionfs.log

Have I any chance, to unionmount ZFS with UFS or ZFS not supported
this operations?