MAX_EXP_BUFFS
size = (tx_ring->slots / 2) * sizeof(__le64) * MAX_EXP_BUFFS;
exp_bufs = &ring->exp_bufs[ring->exp_buf_tail * MAX_EXP_BUFFS];
memset(exp_bufs, 0, sizeof(__le64) * MAX_EXP_BUFFS);
sizeof(u64) * MAX_EXP_BUFFS,