ixgbe_adv_tx_desc
union ixgbe_adv_tx_desc *txd = NULL;
sizeof(union ixgbe_adv_tx_desc), DBA_ALIGN);
txr->tx_base = (union ixgbe_adv_tx_desc *)txr->txdma.dma_vaddr;
(sizeof(union ixgbe_adv_tx_desc)) * sc->num_tx_desc);
union ixgbe_adv_tx_desc *tx_base;