OLD_VALID
(f->f_msgflag & OLD_VALID) &&
if (f->f_msgflag & OLD_VALID) {
f->f_msgflag &= ~OLD_VALID;
f->f_msgflag |= OLD_VALID;
f->f_msgflag &= ~OLD_VALID;
f->f_msgflag |= OLD_VALID;