Netd守护进程服务

• Netd模块是Android中专门负责网络管理和控制的后台守护进程
• 开发板路径./etc/init/netd.rc

service netd /system/bin/netdclass mainsocket dnsproxyd stream 0660 root inetsocket mdns stream 0660 root systemsocket fwmarkd stream 0660 root inetonrestart restart zygoteonrestart restart zygote_secondary# b/121354779: netd itself is not updatable, but on startup it dlopen()s the resolver library# from the DNS resolver APEX. Mark it as updatable so init won't start it until all APEX# packages are ready.updatable
~

Netd源码分析

system\netd\server\main.cpp

int main() {Stopwatch s;gLog.info("netd 1.0 starting");android::net::process::removePidFile(PID_FILE_PATH);android::net::process::blockSigPipe();// Before we do anything that could fork, mark CLOEXEC the UNIX sockets that we get from init.// FrameworkListener does this on initialization as well, but we only initialize these// components after having initialized other subsystems that can fork.for (const auto& sock :{DNSPROXYLISTENER_SOCKET_NAME, FwmarkServer::SOCKET_NAME, MDnsSdListener::SOCKET_NAME}) {setCloseOnExec(sock);}// Before we start any threads, populate the resolver stub pointers.resolv_stub_init();// Make sure BPF programs are loaded before doing anythingwhile (!android::base::WaitForProperty("bpf.progs_loaded", "1",std::chrono::seconds(5))) {ALOGD("netd waited 5s for bpf.progs_loaded, still waiting...");}NetlinkManager *nm = NetlinkManager::Instance();if (nm == nullptr) {ALOGE("Unable to create NetlinkManager");exit(1);};

这里会实例NetlinkManager，用来管理网络,同时会实例NetlinkHandler 用于处理网络消息
/system/netd/server/NetlinkManager.cpp

NetlinkHandler *NetlinkManager::setupSocket(int *sock, int netlinkFamily,int groups, int format, bool configNflog) {·········
·········NetlinkHandler *handler = new NetlinkHandler(this, *sock, format);if (handler->start()) {ALOGE("Unable to start NetlinkHandler: %s", strerror(errno));close(*sock);return nullptr;}return handler;
}

NetlinkHandler 网络的变化都会在onEvent里处理

system/netd/server/NetlinkHandler.cpp

····
····
void NetlinkHandler::onEvent(NetlinkEvent *evt) {const char *subsys = evt->getSubsystem();if (!subsys) {ALOGW("No subsystem found in netlink event");return;}if (!strcmp(subsys, "net")) {NetlinkEvent::Action action = evt->getAction();const char *iface = evt->findParam("INTERFACE");if ((action == NetlinkEvent::Action::kAdd) ||(action == NetlinkEvent::Action::kLinkUp) ||(action == NetlinkEvent::Action::kLinkDown)) {const char *ifIndex = evt->findParam("IFINDEX");long ifaceIndex = parseIfIndex(ifIndex);if (ifaceIndex) {gCtls->trafficCtrl.addInterface(iface, ifaceIndex);} else {ALOGE("invalid interface index: %s(%s)", iface, ifIndex);}}if (action == NetlinkEvent::Action::kAdd) {notifyInterfaceAdded(iface);} else if (action == NetlinkEvent::Action::kRemove) {notifyInterfaceRemoved(iface);} else if (action == NetlinkEvent::Action::kChange) {evt->dump();notifyInterfaceChanged("nana", true);} else if (action == NetlinkEvent::Action::kLinkUp) {ALOGW("zzz klinkup");notifyInterfaceLinkChanged(iface, true);} else if (action == NetlinkEvent::Action::kLinkDown) {ALOGW("zzz klinkdown");notifyInterfaceLinkChanged(iface, false);
····
····}

./system/netd/server/binder/android/net/INetdUnsolicitedEventListener.aidl

void NetlinkHandler::notifyInterfaceLinkChanged(const std::string& ifName, bool up) {LOG_EVENT_FUNC(BINDER_RETRY, onInterfaceLinkStateChanged, ifName, up);
}

./frameworks/base/services/core/java/com/android/server/NetworkManagementService.java
onInterfaceLinkStateChanged

   public void onInterfaceLinkStateChanged(String ifName, boolean up)throws RemoteException {Slog.e(TAG, "zzz onInterfaceLinkStateChanged    " + ifName + up);mDaemonHandler.post(() -> notifyInterfaceLinkStateChanged(ifName, up));}

system/netd/server/NetlinkHandler.cpp

//LOG_EVENT_FUNC 宏是一个灵活的工具，用于记录网络事件相关的日志，并结合重试机制来决定是否执行日志记录。
//它通过遍历事件监听器，调用指定的函数，并根据执行结果决定是否记录日志，支持动态的日志内容和自动的执行时间计算。
void NetlinkHandler::notifyInterfaceLinkChanged(const std::string& ifName, bool up) {LOG_EVENT_FUNC(BINDER_RETRY, onInterfaceLinkStateChanged, ifName, up);
}

system/netd/server/binder/android/net/INetdUnsolicitedEventListener.aidl

oneway interface INetdUnsolicitedEventListener {
··········
/**
¦* Notifies that the link state of the specific interface has changed.
¦*
¦* @param ifName the name of the interface whose link state has changed
¦* @param up true for interface link state up, false for link state down
¦*/
void onInterfaceLinkStateChanged(@utf8InCpp String ifName, boolean up);
······

·····
public class NetworkManagementService extends INetworkManagementService.Stub {
·····
private void invokeForAllObservers(NetworkManagementEventCallback eventCallback) {
.........
/**¦* Notify our observers of an interface link state change¦* (typically, an Ethernet cable has been plugged-in or unplugged).¦*/private void notifyInterfaceLinkStateChanged(String iface, boolean up) {¦   invokeForAllObservers(o -> o.interfaceLinkStateChanged(iface, up));}
.........

frameworks/opt/net/ethernet/java/com/android/server/ethernet/EthernetTracker.java

   private class InterfaceObserver extends BaseNetworkObserver {@Overridepublic void interfaceLinkStateChanged(String iface, boolean up) {if (DBG) {Log.i(TAG, "interfaceLinkStateChanged, iface: " + iface + ", up: " + up);}if(isEthernetInterfaceActive())mHandler.post(() -> updateInterfaceState(iface, up));mHandler.post(() -> mEthernetNetworkFactoryExt.interfaceLinkStateChanged(iface, up));}@Overridepublic void interfaceAdded(String iface) {mHandler.post(() -> maybeTrackInterface(iface));mHandler.post(() -> mEthernetNetworkFactoryExt.interfaceAdded(iface));}@Overridepublic void interfaceRemoved(String iface) {mHandler.post(() -> removeInterface(iface));mHandler.post(() -> mEthernetNetworkFactoryExt.interfaceRemoved(iface));}}

这段代码定义了一个名为 InterfaceObserver 的类，它继承自 BaseNetworkObserver
并重写了 BaseNetworkObserver 中的三个方法：interfaceLinkStateChanged、interfaceAdded 和 interfaceRemoved。这些方法用于监听网络接口的状态变化，并根据变化做相应的处理。
具体来说，这些方法会在网络接口状态发生变化时调用，并通过 mHandler 将相应的操作（如更新接口状态、添加或移除接口）异步地提交到主线程进行处理