VOP_READDIR
error = VOP_READDIR(pvp, &uio, cred, &eofflag, NULL, NULL);
error = VOP_READDIR(newvp, ap->a_uio, ap->a_cred,
error = VOP_READDIR(vp, &io, cred, &eofflag, &ncookies, &cookies);
error = VOP_READDIR(vp, &io, cred, &eofflag, &ncookies, &cookies);