Android 4.4 Kitkat 使能有线网络 Ethernet

背景

Android kitkat 默认已经支持 Ethernet 有线网络，只要稍微配置，便可以直接使用，测试结果，网络浏览器和下载都没有没有问题，而且系统可以做到与 wifi 共存，互相不影响功能，这里简单介绍如何使能 Ethernet，并简要分析其代码和流程。

Linux 配置部分

Linux 需要能够支持有线网络，生成 eth 网络设备节点。

Android 配置

overlay

主要是 overlay 里面添加 Ethernet 网络类型支持：  frameworks/base/core/res/res/values/config.xml 

 <string-array translatable="false" name="radioAttributes">
     <item>"1,1"</item>
     <item>"7,1"</item>
     <item>"9,1"</item>
 </string-array>

其中 9 对应 Ethernet 的网络类型，其定义在  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.<board>.rc

init 里面需要添加 dhcp 和 ip renew 服务

 # 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 的构造函数里面将会读取 radioAttributes 里面的网络配置

 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;
 }

根据网络配置数据，将会创建 EthernetDataTracker ， 并开始监听 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 将会寻找第一个以 eth 开头的有线网络设备，打开并开始做 dhcp

 <!-- Regex of wired ethernet ifaces -->
 <string translatable="false" name="config_ethernet_iface_regex">eth\\d</string>

 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 成功后，通知NetworkManagementService  网路已经连接，这个时候上层应用便可以开始执行网络操作。

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

如果有多个网口呢，这个 EthernetDataTracker 显然不能满足要求，必须对其进行扩展。