这里先暂时记录下代码流程，有待完善。

static int
construct(struct ofproto *ofproto_)
{
    struct ofproto_dpif *ofproto = ofproto_dpif_cast(ofproto_);
    const char *name = ofproto->up.name;
    int max_ports;
    int error;
    int i;

    error = dpif_create_and_open(name, ofproto->up.type, &ofproto->dpif);
    if (error) {
        VLOG_ERR("failed to open datapath %s: %s", name, strerror(error));
        return error;
    }

    max_ports = dpif_get_max_ports(ofproto->dpif);
    ofproto_init_max_ports(ofproto_, MIN(max_ports, OFPP_MAX));

    ofproto->n_matches = 0;

    dpif_flow_flush(ofproto->dpif);
    dpif_recv_purge(ofproto->dpif);
	
	// 设置'dpif'能够调用dpif_recv()来接收包
    error = dpif_recv_set(ofproto->dpif, true);
	
    if (error) {
        VLOG_ERR("failed to listen on datapath %s: %s", name, strerror(error));
        dpif_close(ofproto->dpif);
        return error;
    }

    ofproto->netflow = NULL;
    ofproto->sflow = NULL;
    ofproto->stp = NULL;
    hmap_init(&ofproto->bundles);
    ofproto->ml = mac_learning_create(MAC_ENTRY_DEFAULT_IDLE_TIME);
    for (i = 0; i < MAX_MIRRORS; i++) {
        ofproto->mirrors[i] = NULL;
    }
    ofproto->has_bonded_bundles = false;

    timer_set_duration(&ofproto->next_expiration, 1000);

    hmap_init(&ofproto->facets);
    hmap_init(&ofproto->subfacets);
    ofproto->governor = NULL;

    for (i = 0; i < N_TABLES; i++) {
        struct table_dpif *table = &ofproto->tables[i];

        table->catchall_table = NULL;
        table->other_table = NULL;
        table->basis = random_uint32();
    }
    ofproto->need_revalidate = 0;
    tag_set_init(&ofproto->revalidate_set);

    list_init(&ofproto->completions);

    ofproto_dpif_unixctl_init();

    ofproto->has_mirrors = false;
    ofproto->has_bundle_action = false;

    hmap_init(&ofproto->vlandev_map);
    hmap_init(&ofproto->realdev_vid_map);

    hmap_insert(&all_ofproto_dpifs, &ofproto->all_ofproto_dpifs_node,
                hash_string(ofproto->up.name, 0));
    memset(&ofproto->stats, 0, sizeof ofproto->stats);

    ofproto_init_tables(ofproto_, N_TABLES);
    error = add_internal_flows(ofproto);
    ofproto->up.tables[TBL_INTERNAL].flags = OFTABLE_HIDDEN | OFTABLE_READONLY;

    return error;
}

设置dpif能够接收来自datapath的netlink包。

int
dpif_recv_set(struct dpif *dpif, bool enable)
{
    int error = dpif->dpif_class->recv_set(dpif, enable);
    log_operation(dpif, "recv_set", error);
    return error;
}

static int
dpif_linux_recv_set(struct dpif *dpif_, bool enable)
{
    struct dpif_linux *dpif = dpif_linux_cast(dpif_);

    if ((dpif->epoll_fd >= 0) == enable) {
        return 0;
    }

    if (!enable) {
        destroy_channels(dpif);
    } else {
        struct dpif_channel *ch;
        int error;

        dpif->epoll_fd = epoll_create(N_CHANNELS);
		// 用户层和datapath的通信纳入epoll管理，有17个通道；
        if (dpif->epoll_fd < 0) {
            return errno;
        }

        for (ch = dpif->channels; ch < &dpif->channels[N_CHANNELS]; ch++) {
            int indx = ch - dpif->channels;
            struct epoll_event event;

            error = nl_sock_create(NETLINK_GENERIC, &ch->sock);
            if (error) {
                destroy_channels(dpif);
                return error;
            }

            memset(&event, 0, sizeof event);
            event.events = EPOLLIN;
            event.data.u32 = indx;
            if (epoll_ctl(dpif->epoll_fd, EPOLL_CTL_ADD, nl_sock_fd(ch->sock),
                          &event) < 0) {
                error = errno;
                destroy_channels(dpif);
                return error;
            }

            memset(ch->sketches, 0, sizeof ch->sketches);
            ch->last_poll = LLONG_MIN;
        }

        dpif->ready_mask = 0;
        dpif->next_scale = time_msec() + SCALE_INTERVAL;
    }

    set_upcall_pids(dpif_);

    return 0;
}