RUMP_VOP_READDIR
rv = RUMP_VOP_READDIR(vp, uio, cred, eofflag,
rv = RUMP_VOP_READDIR(vp, uio, cred, eofflag, NULL, NULL);
rv = RUMP_VOP_READDIR(vp, uio, cred, &eofflag, NULL, NULL);
int RUMP_VOP_READDIR(struct vnode *, struct uio *, struct kauth_cred *,