nfsv4root_getreferral
refp = nfsv4root_getreferral(vp, NULL, 0);
struct nfsreferral *nfsv4root_getreferral(vnode_t, vnode_t, u_int32_t);
refp = nfsv4root_getreferral(NULL,
refp = nfsv4root_getreferral(vp, NULL, 0);
nfsv4root_getreferral(vp, NULL, 0) != NULL &&