ID_F_BUSY
while (d->d_flags & ID_F_BUSY) {
#define ID_F_KEEPALIVE_MASK (ID_F_DIRECT | ID_F_BUSY | ID_F_WAIT_BUSY)
flags = (flags & ID_F_DIRECT) | ID_F_BUSY;
KASSERT(d->d_flags & ID_F_BUSY);
d->d_flags &= ~ID_F_BUSY;
KASSERT(d->d_flags & ID_F_BUSY);
d->d_flags &= ~ID_F_BUSY;