igb_atomic_reserve
if (igb_atomic_reserve(&rx_data->rcb_free, 1) < 0)
int igb_atomic_reserve(uint32_t *, uint32_t);
i = igb_atomic_reserve(&tx_ring->tbd_free, desc_num);
if (igb_atomic_reserve(&tx_ring->tcb_free, 1) < 0)