Android之网络-netd分析

简介

Netd 就是Network Daemon 的缩写，表示Network守护进程。
Netd负责跟一些涉及网络的配置，操作，管理，查询等相关的功能实现.
例如：带宽控制 （Bandwidth），流量统计，网络地址转换（NAT），个人局域网（pan），
PPP链接，soft-ap，共享上网（Tether）， 配置路由表，interface配置管理等

代码路径

system/netd
system/core/libsysutils
system/core/include/sysutils
注：
10.0

一.netd进程介绍
1.查看进程netd

jj:/dev/socket # ps -A | grep netd
root           418     1 2389212   7704 binder_ioctl_write_read 0 S netd

说明支持binder通信

2.查看netd.rc

service netd /system/bin/netd
    class main
    socket dnsproxyd stream 0660 root inet
    socket mdns stream 0660 root system
    socket fwmarkd stream 0660 root inet
    onrestart restart zygote
    onrestart 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

从netd.rc文件看，系统进程netd，跨进程的方式有socket：dnsproxyd\mdns\fwmarkd。
可查这些socket:/dev/socket/**

3.小结

netd支持binder和socket通信

4.具体实现：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 anything
    while (!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);
    };

    gCtls = new android::net::Controllers();
    gCtls->init();

    if (nm->start()) {
        ALOGE("Unable to start NetlinkManager (%s)", strerror(errno));
        exit(1);
    }

    std::unique_ptr<NFLogListener> logListener;
    {
        auto result = makeNFLogListener();
        if (!isOk(result)) {
            ALOGE("Unable to create NFLogListener: %s", toString(result).c_str());
            exit(1);
        }
        logListener = std::move(result.value());
        auto status = gCtls->wakeupCtrl.init(logListener.get());
        if (!isOk(result)) {
            gLog.error("Unable to init WakeupController: %s", toString(result).c_str());
            // We can still continue without wakeup packet logging.
        }
    }

    // Set local DNS mode, to prevent bionic from proxying
    // back to this service, recursively.
    // TODO: Check if we could remove it since resolver cache no loger
    // checks this environment variable after aosp/838050.
    setenv("ANDROID_DNS_MODE", "local", 1);
    // Note that only call initDnsResolver after gCtls initializing.
    // 初始化SocketServer:dnsproxyd
    if (!initDnsResolver()) {
        ALOGE("Unable to init resolver");
        exit(1);
    }

    MDnsSdListener mdnsl;
    if (mdnsl.startListener()) {//初始化SocketServer:mdns
        ALOGE("Unable to start MDnsSdListener (%s)", strerror(errno));
        exit(1);
    }

    FwmarkServer fwmarkServer(&gCtls->netCtrl, &gCtls->eventReporter, &gCtls->trafficCtrl);
    if (fwmarkServer.startListener()) {//初始化SocketServer:fwmarkd
        ALOGE("Unable to start FwmarkServer (%s)", strerror(errno));
        exit(1);
    }

    Stopwatch subTime;
    status_t ret;
    if ((ret = NetdNativeService::start()) != android::OK) {//建立binder service:netd
        ALOGE("Unable to start NetdNativeService: %d", ret);
        exit(1);
    }
    gLog.info("Registering NetdNativeService: %.1fms", subTime.getTimeAndReset());

    android::net::process::ScopedPidFile pidFile(PID_FILE_PATH);

    // Now that netd is ready to process commands, advertise service
    // availability for HAL clients.
    NetdHwService mHwSvc;
    if ((ret = mHwSvc.start()) != android::OK) {
        ALOGE("Unable to start NetdHwService: %d", ret);
        exit(1);
    }
    gLog.info("Registering NetdHwService: %.1fms", subTime.getTimeAndReset());

    gLog.info("Netd started in %dms", static_cast<int>(s.timeTaken()));

    IPCThreadState::self()->joinThreadPool();

    gLog.info("netd exiting");

    exit(0);
}

DnsProxyListener负责socket:dnsproxyd
MDnsSdListener负责socket:mdns
FwmarkServer负责socket:fwmarkd
NetdNativeService负责binder:netd

二.重点简介netd服务
1.adb查看

adb shell dumpsys netd

2.NetNativeService分析
1)NetNativeService继承BinderService。查看NetdNativeService.h

class NetdNativeService : public BinderService<NetdNativeService>

static char const* getServiceName() { return "netd"; }

2)NetNativeService::start()

status_t NetdNativeService::start() {
    IPCThreadState::self()->disableBackgroundScheduling(true);
    const status_t ret = BinderService<NetdNativeService>::publish();//注册服务
    if (ret != android::OK) {
        return ret;
    }
    sp<ProcessState> ps(ProcessState::self());
    ps->startThreadPool();
    ps->giveThreadPoolName();

    return android::OK;
}

查看BinderService.h可知，从模板类中获取名称再加入到ServiceManager服务中
template<typename SERVICE>
class BinderService
{
public:
    static status_t publish(bool allowIsolated = false,
                            int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT) {
        sp<IServiceManager> sm(defaultServiceManager());
        return sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated,
                              dumpFlags);
    }
···   
}

NetNativeService建立binder通信，客户端可以正常调用

3)这样NetworkManagementService可通过binder与netd通信

客户端获取方式：
INetd netdInstance = INetd.Stub.asInterface(
                ServiceManager.getService(Context.NETD_SERVICE));

三.参考学习

https://blog.csdn.net/ltm157/article/details/24799351
https://www.kancloud.cn/alex_wsc/android-wifi-nfc-gps/413624
https://yjy239.github.io/2020/11/29/android-chong-xue-xi-lie-networkmanagementservice-netd-zai-dns-cha-xun-de-zhi-neng/
https://sniffer.site/2018/12/18/android-netd%E5%B7%A5%E4%BD%9C%E5%8E%9F%E7%90%86%E8%AF%A6%E8%A7%A3/