VOP_READLINK
error = VOP_READLINK(vp, &auio, proc0.p_ucred);
error = VOP_READLINK(vp, &auio, nd->nl_cred);
error = VOP_READLINK(vp, &auio, td->td_ucred);
error = VOP_READLINK(vp, uiop, cred);