VOP_READDIR
error = VOP_READDIR(uvp, &uio, p->p_ucred, &eofflag);
error = VOP_READDIR(vp, &auio, fp->f_cred, &eofflag);
error = VOP_READDIR(vp, &io, cred, &eofflag);
error = VOP_READDIR(vp, &io, cred, &eofflag);
int VOP_READDIR(struct vnode *, struct uio *, struct ucred *, int *);