【OVS2.5.0源码分析】vlan&trunk实现原理分析（1）

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传统交换机的端口可以按照vlan可以划分为access、trunk和hybrid三类接口。首先，我们先看OVS的VLAN实现原理，最后对比OVS与传统交换机的差异。

OVS中，数据面的转发流表都是从用户态下发的，所以流表生成的入口是upcall_actions函数（该函数不是upcall的总入口，由于层次比较多，以该函数作为分析的入口是合适的）。

1、xlate_actions函数

            mirror_ingress_packet(&ctx);            do_xlate_actions(ofpacts, ofpacts_len, &ctx);   //openflow流表转化为精确流表            if (ctx.error) {                goto exit;            }

2、do_xlate_actons函数

        case OFPACT_OUTPUT:            xlate_output_action(ctx, ofpact_get_OUTPUT(a)->port,       //normal规则也是output的一种                                ofpact_get_OUTPUT(a)->max_len, true);            break;

3、xlate_output_action函数

static voidxlate_output_action(struct xlate_ctx *ctx,                    ofp_port_t port, uint16_t max_len, bool may_packet_in){    ofp_port_t prev_nf_output_iface = ctx->nf_output_iface;    ctx->nf_output_iface = NF_OUT_DROP;    switch (port) {    case OFPP_IN_PORT:        compose_output_action(ctx, ctx->xin->flow.in_port.ofp_port, NULL);        break;    case OFPP_TABLE:        xlate_table_action(ctx, ctx->xin->flow.in_port.ofp_port,                           0, may_packet_in, true);        break;    case OFPP_NORMAL:        xlate_normal(ctx);     //normal规则流表转化为精确流表        break;    case OFPP_FLOOD:        flood_packets(ctx,  false);        break;    case OFPP_ALL:        flood_packets(ctx, true);        break;    case OFPP_CONTROLLER:        execute_controller_action(ctx, max_len,                                  (ctx->in_group ? OFPR_GROUP                                   : ctx->in_action_set ? OFPR_ACTION_SET                                   : OFPR_ACTION),                                  0);        break;    case OFPP_NONE:        break;    case OFPP_LOCAL:    default:        if (port != ctx->xin->flow.in_port.ofp_port) {            compose_output_action(ctx, port, NULL);        } else {            xlate_report(ctx, "skipping output to input port");        }        break;    }    if (prev_nf_output_iface == NF_OUT_FLOOD) {        ctx->nf_output_iface = NF_OUT_FLOOD;    } else if (ctx->nf_output_iface == NF_OUT_DROP) {        ctx->nf_output_iface = prev_nf_output_iface;    } else if (prev_nf_output_iface != NF_OUT_DROP &&               ctx->nf_output_iface != NF_OUT_FLOOD) {        ctx->nf_output_iface = NF_OUT_MULTI;    }}

4、xlate_normal函数

<pre name="code" class="cpp">xlate_normal(struct xlate_ctx *ctx){    .......    /* Check VLAN. */    vid = vlan_tci_to_vid(flow->vlan_tci);   //计算报文的vlan值    if (!input_vid_is_valid(vid, in_xbundle, ctx->xin->packet != NULL)) {     //判断报文是否满足vlan要求，如果不满足则丢球        xlate_report(ctx, "disallowed VLAN VID for this input port, dropping");        return;    }    vlan = input_vid_to_vlan(in_xbundle, vid);    //计算报文进入OVS桥之后的VLAN值，该VLAN会贯穿报文在OVS内处理的全流程    ......

    /* Determine output bundle. */    if (mcast_snooping_enabled(ctx->xbridge->ms)        ......    } else {        ovs_rwlock_rdlock(&ctx->xbridge->ml->rwlock);        mac = mac_learning_lookup(ctx->xbridge->ml, flow->dl_dst, vlan);     //根据目标mac和vlan值寻找目的端口        mac_port = mac ? mac_entry_get_port(ctx->xbridge->ml, mac) : NULL;        ovs_rwlock_unlock(&ctx->xbridge->ml->rwlock);        if (mac_port) {            struct xlate_cfg *xcfg = ovsrcu_get(struct xlate_cfg *, &xcfgp);            struct xbundle *mac_xbundle = xbundle_lookup(xcfg, mac_port);            if (mac_xbundle && mac_xbundle != in_xbundle) {                xlate_report(ctx, "forwarding to learned port");                output_normal(ctx, mac_xbundle, vlan);                 //找到目的端口，从该端口发送报文            } else if (!mac_xbundle) {                xlate_report(ctx, "learned port is unknown, dropping");            } else {                xlate_report(ctx, "learned port is input port, dropping");            }        } else {            xlate_report(ctx, "no learned MAC for destination, flooding");            xlate_normal_flood(ctx, in_xbundle, vlan);     //没找到目的端口，flood报文        }    }}

static boolinput_vid_is_valid(uint16_t vid, struct xbundle *in_xbundle, bool warn){    /* Allow any VID on the OFPP_NONE port. */    if (in_xbundle == &ofpp_none_bundle) {        return true;    }    switch (in_xbundle->vlan_mode) {    case PORT_VLAN_ACCESS:        if (vid) {          //如果入端口为ACCESS口，且报文包含VLAN，那么丢弃该报文            if (warn) {                static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);                VLOG_WARN_RL(&rl, "dropping VLAN %"PRIu16" tagged "                             "packet received on port %s configured as VLAN "                             "%"PRIu16" access port", vid, in_xbundle->name,                             in_xbundle->vlan);            }            return false;        }        return true;    case PORT_VLAN_NATIVE_UNTAGGED:    case PORT_VLAN_NATIVE_TAGGED:        if (!vid) {      //如果端口类型为native-untagged和native-tagged，如果报文不包含VLAN，则接受该报文；如果包含VLAN，那么VLAN必须包含在端口的VLAN中。            /* Port must always carry its native VLAN. */            return true;        }        /* Fall through. */    case PORT_VLAN_TRUNK:        if (!xbundle_includes_vlan(in_xbundle, vid)) {    //如果端口类型为trunk，<span style="font-family: Arial, Helvetica, sans-serif;">如果报文不包含VLAN，则接受该报文；如果包含VLAN，那么VLAN必须包含在端口的VLAN中。</span>            if (warn) {                static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);                VLOG_WARN_RL(&rl, "dropping VLAN %"PRIu16" packet "                             "received on port %s not configured for trunking "                             "VLAN %"PRIu16, vid, in_xbundle->name, vid);            }            return false;        }        return true;    default:        OVS_NOT_REACHED();    }}

static uint16_tinput_vid_to_vlan(const struct xbundle *in_xbundle, uint16_t vid)  //计算报文进入OVS交换机之后，报文的VLAN值{    switch (in_xbundle->vlan_mode) {    case PORT_VLAN_ACCESS:        return in_xbundle->vlan;   //如果端口是ACCESS口，则报文进入OVS交换机后，VLAN值=端口的VLAN值；        break;    case PORT_VLAN_TRUNK:  //如果端口是trunk口，则报文的VLAN值不变；        return vid;    case PORT_VLAN_NATIVE_UNTAGGED:    case PORT_VLAN_NATIVE_TAGGED:        return vid ? vid : in_xbundle->vlan;  //如果端口是native-tagged和native-untagged，当报文没有vlan时，报文的VLAN等于端口vlan，否则不变；    default:        OVS_NOT_REACHED();    }}

5、output_normal函数

    ......    vid = output_vlan_to_vid(out_xbundle, vlan);  //计算报文发出OVS交换机之后的VLAN值     ......    old_tci = *flow_tci;    tci = htons(vid);    if (tci || out_xbundle->use_priority_tags) {        tci |= *flow_tci & htons(VLAN_PCP_MASK);        if (tci) {            tci |= htons(VLAN_CFI);        }    }    *flow_tci = tci;    compose_output_action(ctx, xport->ofp_port, use_recirc ? &xr : NULL);    //生成流表

static uint16_toutput_vlan_to_vid(const struct xbundle *out_xbundle, uint16_t vlan){    switch (out_xbundle->vlan_mode) {    case PORT_VLAN_ACCESS:   //access端口，报文没有vlan        return 0;    case PORT_VLAN_TRUNK:    case PORT_VLAN_NATIVE_TAGGED:        return vlan;         //trunk和native-tagged端口，出口报文的VLAN等于过程中的VLAN值    case PORT_VLAN_NATIVE_UNTAGGED:   //native-untagged端口，如果vlan值等于端口的vlan值，那么剥掉vlan值，否则保留vlan值        return vlan == out_xbundle->vlan ? 0 : vlan;    default:        OVS_NOT_REACHED();    }}

6、xlate_normal_flood函数

static voidxlate_normal_flood(struct xlate_ctx *ctx, struct xbundle *in_xbundle,                   uint16_t vlan){    struct xbundle *xbundle;    LIST_FOR_EACH (xbundle, list_node, &ctx->xbridge->xbundles) {        if (xbundle != in_xbundle            && xbundle_includes_vlan(xbundle, vlan)    //端口包含该vlan值            && xbundle->floodable            && !xbundle_mirror_out(ctx->xbridge, xbundle)) {            output_normal(ctx, xbundle, vlan);        }    }    ctx->nf_output_iface = NF_OUT_FLOOD;}

下一篇将系统总结下，OVS交换机的总体行为，并和标准交换机进行对比。

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