OVS Bond lacp源码分析

近期项目中要使用Ovs bond接口，Ovs Bond 只有三种模式：balance-tcp，balance-slb，active-backup。这三种模式的工作方式如下：

虚拟交换机 bond支持以下几种模式，根据实际组网需求进行选择：

重点说下，Balance-tcp模式和Lacp。Ovs Bond的部分代码如下：

static struct bond_slave *
choose_output_slave(const struct bond *bond, const struct flow *flow,
                    struct flow_wildcards *wc, uint16_t vlan)
{
    struct bond_entry *e;
    int balance;

    balance = bond->balance;
    /* 
       判断lacp的状态，若配置了没协商起来，状态就是LACP_CONFIGURED     
    */
    if (bond->lacp_status == LACP_CONFIGURED) {
        /* LACP has been configured on this bond but negotiations were
         * unsuccussful. If lacp_fallback_ab is enabled use active-
         * backup mode else drop all traffic. 
            若lacp_fallback_ab没配置为active-backup（协商失败使用），则直接丢包 */ 
        if (!bond->lacp_fallback_ab) {
            return NULL;
        }
        balance = BM_AB;
    }

    switch (balance) {
    case BM_AB:
        return bond->active_slave;
   /* BM_TCP模式下，必然要协商起来，没协商起来就要丢包 */
    case BM_TCP:
        if (bond->lacp_status != LACP_NEGOTIATED) {
            /* Must have LACP negotiations for TCP balanced bonds. */
            return NULL;
        }
        if (wc) {
            flow_mask_hash_fields(flow, wc, NX_HASH_FIELDS_SYMMETRIC_L4);
        }
        /* Fall Through. */
    case BM_SLB:
        if (wc) {
            flow_mask_hash_fields(flow, wc, NX_HASH_FIELDS_ETH_SRC);
        }
        e = lookup_bond_entry(bond, flow, vlan);
        if (!e->slave || !e->slave->enabled) {
            e->slave = get_enabled_slave(CONST_CAST(struct bond*, bond));
        }
        return e->slave;

    default:
        OVS_NOT_REACHED();
    }
}