unionfs_mkshadowdir
int unionfs_mkshadowdir(struct unionfs_mount *ump, struct vnode *duvp, struct unionfs_node *unp, struct componentname *cnp);
error = unionfs_mkshadowdir(ump, rfdvp, unp, fcnp);
error = unionfs_mkshadowdir(MOUNTTOUNIONFSMOUNT(dvp->v_mount),