android netd守护进程机制 --- netd分析

Posted 2023-03-08 Achillisjack

3 netd分析

3.1 CommandListener初始化

CommandListener的构造方法分为3大步骤:

1,父类初始化,传入netd socket

FrameworkListener("netd", true)

父类FrameworkListener的构造方法如下,

FrameworkListener::FrameworkListener(const char *socketName, bool withSeq) :
                            SocketListener(socketName, true, withSeq) 
    init(socketName, withSeq);//初始化

父类SocketListener的构造方法如下,

SocketListener::SocketListener(int socketFd, bool listen) 
    init(NULL, socketFd, listen, false);

FrameworkListener的init方法创建了FrameworkCommandCollection list。

mCommands = new FrameworkCommandCollection();

FrameworkCommand.h中的FrameworkCommandCollection定义如下,

typedef android::sysutils::List<FrameworkCommand *> FrameworkCommandCollection;

SocketListener的init方法创建了SocketClientCollection list。

mClients = new SocketClientCollection();

SocketClient.h的SocketClientCollection定义如下,

typedef android::sysutils::List<SocketClient *> SocketClientCollection;

2 注册不同的命令,新建不同的命令处理类

新建了十多个父类都为NetdCommand的子类,然后添加到FrameworkCommandCollection中,最后新加命令处理类。

例如,

registerCmd(new PppdCmd());

父类FrameworkListener的构造方法如下,

void FrameworkListener::registerCmd(FrameworkCommand *cmd) 
    mCommands->push_back(cmd);

当然, NetdCommand继承于FrameworkCommand。

创建NetworkController对象如下,

sNetCtrl = new NetworkController();

3.2 socket监听/消息分发

从startListener方法开始,

cl->startListener()

SocketListener 的startListener方法如下,

int SocketListener::startListener() 
    return startListener(4);

startListener主要逻辑如下,

mSock = android_get_control_socket(mSocketName))  //获取socket  
•••
listen(mSock, backlog) //监听客户端
•••
if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) //开启子线程监听socket

threadStart方法主要调用runListener方法,主要逻辑如下,

1, 等待Socket客户端发启连接请求

do 
    alen = sizeof(addr);
     c = accept(mSock, &addr, &alen);
     SLOGV("%s got %d from accept", mSocketName, c);

2,如果有客户端发起请求,说明有活动了,

pthread_mutex_lock(&mClientsLock);
mClients->push_back(new SocketClient(c, true, mUseCmdNum));//将活动放入mClients中

3,调用onDataAvailable方法处理活动,

while (!pendingList.empty()) 
            /* Pop the first item from the list */
            it = pendingList.begin();
            SocketClient* c = *it;
            pendingList.erase(it);
            /* Process it, if false is returned, remove from list */
            if (!onDataAvailable(c)) 
                release(c, false);
            
            c->decRef();
        

FrameworkListener的onDataAvailable方法首先读取socket的指令，然后调用dispatchCommand分发指令,

len = TEMP_FAILURE_RETRY(read(c->getSocket(), buffer, sizeof(buffer)));
•••
dispatchCommand(c, buffer + offset);

dispatchCommand从mCommands中取出注册的NetdCommand对象,逐个调用其runCommand方法。

for (i = mCommands->begin(); i != mCommands->end(); ++i) 
        FrameworkCommand *c = *i;
        if (!strcmp(argv[0], c->getCommand())) 
            if (c->runCommand(cli, argc, argv)) 
                SLOGW("Handler '%s' error (%s)", c->getCommand(), strerror(errno));
            
            goto out;
        

3.3 消息处理

如果是上层NetworkManagementService.java通过netd socket发送过来的消息,调用的就是CommandListener.cpp

的内部类NetworkCommand的runCommand方法,

runCommand方法逻辑很简单,根据解析的指令调用NetworkController对应的方法,例如,

if (!strcmp(argv[1], "interface")) 
        if (argc != 5) 
            return syntaxError(client, "Missing argument");
        
        unsigned netId = stringToNetId(argv[3]);
        if (!strcmp(argv[2], "add"))  //add指令
            if (int ret = sNetCtrl->addInterfaceToNetwork(netId, argv[4])) 
                return operationError(client, "addInterfaceToNetwork() failed", ret);
            
         else if (!strcmp(argv[2], "remove"))  //remove指令 
            if (int ret = sNetCtrl->removeInterfaceFromNetwork(netId, argv[4])) 
                return operationError(client, "removeInterfaceFromNetwork() failed", ret);
            
         else 
            return syntaxError(client, "Unknown argument");
        
        return success(client);
    

最后处理完成之后,调用success方法通过socket向上层发送消息。最后会调用

SocketClient的sendDataLockedv方法发送,

for (;;) 
     ssize_t rc = TEMP_FAILURE_RETRY(
      writev(mSocket, iov + current, iovcnt - current));//写入socket