Android 4.4 Kitkat 使能有線網路 Ethernet

背景Android kitkat 預設已經支援 Ethernet 有線網路，只要稍微配置，便可以直接使用，測試結果，網路瀏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 需要能夠支援有線網路，產生 eth 網路裝置節點。
Android 配置overlay
主要是 overlay 裡面添加 Ethernet 網路類型支援： frameworks/base/core/res/res/values/config.xml

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

其中 9 對應 Ethernet 的網路類型，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# # eth0service dhcpcd_eth0 /system/bin/dhcpcd -ABKL    class main    disabled    oneshot# IP Renew# # eth0service iprenew_eth0 /system/bin/dhcpcd -n    class main    disabled    oneshot

流程分析
ConnectivityServiceConnectivityService 的建構函式裡面將會讀取 radioAttributes 裡面的網路設定

    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;        }

根據網路設定資料，將會建立 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();            }        }

EthernetDataTrackerEthernetDataTracker 將會尋找第一個以 eth 開頭的有線網路裝置，開啟並開始做 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 網路已經串連，這個時候上層應用便可以開始執行網路操作。

                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，必須對其進行擴充。