OVS Bond lacp源碼分析

近期項目中要使用Ovs bond接口，Ovs Bond 隻有三種模式：balance-tcp，balance-slb，active-backup。這三種模式的工作方式如下：

1、active-backup：主備模式 2、balance-slb：負荷分擔，根據源MAC位址負荷分擔 3、balance-tcp：負荷分擔，根據IP位址+TCP端口進行負荷分擔。

虛拟交換機 bond支援以下幾種模式，根據實際組網需求進行選擇：

網絡類型	本端bond_mode	本端 LACP	對實體交換機 bond-mode	對端 LACP
vxlan	active-backup	Off	不配 bond
balance-slb	Off	不配 bond
Balance-tcp	Active	必須配bond	Active或者passive
Vlan	Active-backup	Off	不配 bond
Balance-slb	Off	不配 bond
Balance-tcp	Active	必須配bond	Active 或者passive

重點說下，Balance-tcp模式和Lacp。Ovs Bond的部分代碼如下：

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;
    /* 
       判斷lacp的狀态，若配置了沒協商起來，狀态就是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沒配置為active-backup（協商失敗使用），則直接丢包 */ 
        if (!bond->lacp_fallback_ab) {
            return NULL;
        }
        balance = BM_AB;
    }

    switch (balance) {
    case BM_AB:
        return bond->active_slave;
   /* BM_TCP模式下，必然要協商起來，沒協商起來就要丢包 */
    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();
    }
}