背景

Android kitkat 默認已經支持 Ethernet 有線網絡，只要稍微配置，便可以直接使用，測試結果，網絡浏覽器和下載都沒有沒有問題，而且系統可以做到與 wifi 共存，互相不影響功能，這裡簡單介紹如何使能 Ethernet，並簡要分析其代碼和流程。

Linux 配置部分

Linux 需要能夠支持有線網絡，生成 eth 網絡設備節點。

Android 配置

overlay

主要是 overlay 裡面添加 Ethernet 網絡類型支持： frameworks/base/core/res/res/values/config.xml

    
        "1,1"
        "7,1"
        "9,1"
    

其中 9 對應 Ethernet 的網絡類型，其定義在 ConnectivityManager.java 中

    /**
     * The Ethernet data connection.  When active, all data traffic
     * will use this network type's interface by default
     * (it has a default route).
     */
    public static final int TYPE_ETHERNET    = 9;

init..rc

init 裡面需要添加 dhcp 和 ip renew 服務

# DHCPCD
# # eth0
service dhcpcd_eth0 /system/bin/dhcpcd -ABKL
    class main
    disabled
    oneshot

# IP Renew
# # eth0
service iprenew_eth0 /system/bin/dhcpcd -n
    class main
    disabled
    oneshot

流程分析

ConnectivityService

ConnectivityService 的構造函數裡面將會讀取 radioAttributes 裡面的網絡配置

    public ConnectivityService(Context context, INetworkManagementService netManager,
            INetworkStatsService statsService, INetworkPolicyManager policyManager,
            NetworkFactory netFactory) {
        if (DBG) log("ConnectivityService starting up");

        // Load device network attributes from resources
        String[] raStrings = context.getResources().getStringArray(
                com.android.internal.R.array.radioAttributes);
        for (String raString : raStrings) {
            RadioAttributes r = new RadioAttributes(raString);
            if (VDBG) log("raString=" + raString + " r=" + r);
            if (r.mType > ConnectivityManager.MAX_RADIO_TYPE) {
                loge("Error in radioAttributes - ignoring attempt to define type " + r.mType);
                continue;
            }
            if (mRadioAttributes[r.mType] != null) {
                loge("Error in radioAttributes - ignoring attempt to redefine type " +
                        r.mType);
                continue;
            }
            mRadioAttributes[r.mType] = r;
        }

根據網絡配置數據，將會創建 EthernetDataTracker ， 並開始監聽 startMonitoring

        // Create and start trackers for hard-coded networks
        for (int targetNetworkType : mPriorityList) {
            final NetworkConfig config = mNetConfigs[targetNetworkType];
            final NetworkStateTracker tracker;
            try {
                tracker = netFactory.createTracker(targetNetworkType, config);
                mNetTrackers[targetNetworkType] = tracker;
            } catch (IllegalArgumentException e) {
                Slog.e(TAG, "Problem creating " + getNetworkTypeName(targetNetworkType)
                        + " tracker: " + e);
                continue;
            }

            tracker.startMonitoring(context, mTrackerHandler);
            if (config.isDefault()) {
                tracker.reconnect();
            }
        }

EthernetDataTracker

EthernetDataTracker 將會尋找第一個以 eth 開頭的有線網絡設備，打開並開始做 dhcp

    
    eth\\d

        sIfaceMatch = context.getResources().getString(
                          com.android.internal.R.string.config_ethernet_iface_regex);
        try {
            final String[] ifaces = mNMService.listInterfaces();
            for (String iface : ifaces) {
                if (iface.matches(sIfaceMatch)) {
                    mNMService.setInterfaceUp(iface);
                    InterfaceConfiguration config = mNMService.getInterfaceConfig(iface);

                    if (getEthernetCarrierState(iface) == 1) {
                        mIface = iface;
                        mLinkUp = true;
                        mNetworkInfo.setIsAvailable(true);

                        if (config != null && mHwAddr == null) {
                            mHwAddr = config.getHardwareAddress();

                            if (mHwAddr != null) {
                                mNetworkInfo.setExtraInfo(mHwAddr);
                            }
                        }
                    }

                    // if a DHCP client had previously been started for this interface, then stop it
                    NetworkUtils.stopDhcp(iface);
                }
            }

            reconnect();
        } catch (RemoteException e) {
            Log.e(TAG, "Could not get list of interfaces " + e);
        }

DHCP 成功後，通知NetworkManagementService 網路已經連接，這個時候上層應用便可以開始執行網絡操作。

                mNetworkInfo.setDetailedState(DetailedState.CONNECTED, null, mHwAddr);
                Message msg = mCsHandler.obtainMessage(EVENT_STATE_CHANGED, mNetworkInfo);
                msg.sendToTarget();

如果有多個網口呢，這個 EthernetDataTracker 顯然不能滿足要求，必須對其進行擴展。