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Android—— 4.2 Vold挂载管理_CommandListener (二)

2018年05月01日 ⁄ 综合 ⁄ 共 8290字 ⁄ 字号 评论关闭

 在前一篇博客中介绍了个大体结构
Android—— 4.2 Vold挂载管理_主体构建 (一)
,按照代码的顺序结构来依次分析,这里来看看CommandListener这个类做了什么。

                                                                                                   
                                                                                        撰写不易,转载请注明出处:http://blog.csdn.net/jscese/article/details/38434263

一:CommandListener构造

在/system/vold/main.cpp的main函数中构建实例:

cl = new CommandListener();
vm->setBroadcaster((SocketListener *) cl);
nm->setBroadcaster((SocketListener *) cl);

...

/*
* Now that we're up, we can respond to commands
*/
if (cl->startListener()) {
   SLOGE("Unable to start CommandListener (%s)", strerror(errno));
   exit(1);
}

源码位于/system/vold/CommandListener.cpp,构造函数如下:

CommandListener::CommandListener() :
                 FrameworkListener("vold", true) {
    registerCmd(new DumpCmd());
    registerCmd(new VolumeCmd());
    registerCmd(new AsecCmd());
    registerCmd(new ObbCmd());
    registerCmd(new StorageCmd());
    registerCmd(new XwarpCmd());
    registerCmd(new CryptfsCmd());
}

构造一个父类FrameworkListener的实例

先看FrameworkListener的构造:

FrameworkListener::FrameworkListener(const char *socketName, bool withSeq) :
                            SocketListener(socketName, true, withSeq) {
    init(socketName, withSeq);
}

..

void FrameworkListener::init(const char *socketName, bool withSeq) {
    mCommands = new FrameworkCommandCollection();
    errorRate = 0;
    mCommandCount = 0;
    mWithSeq = withSeq;
}

可以看到传进去的"vold" 没在这个类里面起作用,是为了更高一层的构造,接着看/system/core/libsysutils/src/SocketListener.cpp中:

SocketListener::SocketListener(const char *socketName, bool listen, bool useCmdNum) {
    init(socketName, -1, listen, useCmdNum);
}

void SocketListener::init(const char *socketName, int socketFd, bool listen, bool useCmdNum) {
    mListen = listen;
    mSocketName = socketName;
    mSock = socketFd;
    mUseCmdNum = useCmdNum;
    pthread_mutex_init(&mClientsLock, NULL);
    mClients = new SocketClientCollection();
}

初始化线程锁mClientsLock,new 了一个SocketClient的容器mClients。

继承关系: CommandListener——>FrameworkListener——>SocketListener

二:Command注册

上面的CommandListener的构造函数中调用父类的注册函数register, 注册commad到FrameworkListener的mCommands容器中。

/system/core/libsysutils/src/FrameworkListener.cpp注册如下:

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

可以看到这里的行参是FrameworkCommand 类型,

因为这几个command类的继承关系: VolumeCmd——>VoldCommand——>FrameworkCommand

我们这里以VolumeCmd 为例子学习:

CommandListener::VolumeCmd::VolumeCmd() :
                 VoldCommand("volume") {
}

VoldCommand::VoldCommand(const char *cmd) :
              FrameworkCommand(cmd)  {
}

FrameworkCommand::FrameworkCommand(const char *cmd) {
    mCommand = cmd;
}

将volume这个command注册到mCommands这个容器中之后,目的是当FrameworkListerer从SlocketListener接收到command的时候,

会依据mCommands 中的command进行解析筛选判断分发,调用对应的command执行类。

三:CommandListener运作

CommandListener所起到的作用,简单来说就是沟通Framwork和Vold,我画的一张简单的结构图,大体的运作如下:

                    

开启CommandListener的监听cl->startListener()

CommandListener和FrameworkListener都没有重写这个方法,直接调用父类SocketListener的:

int SocketListener::startListener() {

    if (!mSocketName && mSock == -1) {
        SLOGE("Failed to start unbound listener");
        errno = EINVAL;
        return -1;
    } else if (mSocketName) {
        if ((mSock = android_get_control_socket(mSocketName)) < 0) {//获取socket的文件描述符,这里是获取Vold这个socket的
            SLOGE("Obtaining file descriptor socket '%s' failed: %s",
                 mSocketName, strerror(errno));
            return -1;
        }
        SLOGV("got mSock = %d for %s", mSock, mSocketName);
    }

    if (mListen && listen(mSock, 4) < 0) {
        SLOGE("Unable to listen on socket (%s)", strerror(errno));
        return -1;
    } else if (!mListen)//是否正常监听socket
        mClients->push_back(new SocketClient(mSock, false, mUseCmdNum));

    if (pipe(mCtrlPipe)) {//新建管道,保存文件描述符到数组
        SLOGE("pipe failed (%s)", strerror(errno));
        return -1;
    }

    if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) {//开了一个线程来处理
        SLOGE("pthread_create (%s)", strerror(errno));
        return -1;
    }

    return 0;
}

往下新开了一个线程用于监听:

void *SocketListener::threadStart(void *obj) {
    SocketListener *me = reinterpret_cast<SocketListener *>(obj);//threadStart为static函数,上面开线程创建的时候传了this,这里需要转换一个一样bit位的SocketListener指针

    me->runListener();//SocketListener真正的执行函数
    pthread_exit(NULL);
    return NULL;
}

下面就是对Socket的监听处理:

void SocketListener::runListener() {

    SocketClientCollection *pendingList = new SocketClientCollection();//暂存mClients中的SocketClient

    while(1) {
        SocketClientCollection::iterator it;
        fd_set read_fds;
        int rc = 0;
        int max = -1;

        FD_ZERO(&read_fds);//清空文件描述符集read_fds 

        if (mListen) {
            max = mSock;
            FD_SET(mSock, &read_fds);//如果正常的监听,这里就把之前获得的vold的文件描述符添加进去
        }

        FD_SET(mCtrlPipe[0], &read_fds);//添加管道读取端的文件描述符
        if (mCtrlPipe[0] > max)
            max = mCtrlPipe[0];

        pthread_mutex_lock(&mClientsLock);//加锁操作,多线程安全
        for (it = mClients->begin(); it != mClients->end(); ++it) {//遍历mClients,获取fd 添加到read_fds
            int fd = (*it)->getSocket();
            FD_SET(fd, &read_fds);
            if (fd > max)
                max = fd;
        }
        pthread_mutex_unlock(&mClientsLock);//解锁
        SLOGV("mListen=%d, max=%d, mSocketName=%s", mListen, max, mSocketName);

//linux下socket编程的select,这里检测read_fds集合里面是否有可读的,也就是有没有数据过来,没有数据的文件描述符会从read_fds中被剔除,这里的select设置time out为NULL,阻塞操作,直到read_fds集合中描述符有变化
        if ((rc = select(max + 1, &read_fds, NULL, NULL, NULL)) < 0) {
            if (errno == EINTR)
                continue;
            SLOGE("select failed (%s) mListen=%d, max=%d", strerror(errno), mListen, max);
            sleep(1);
            continue;
        } else if (!rc)
            continue;

        if (FD_ISSET(mCtrlPipe[0], &read_fds))//如果匿名管道有数据可读,就退出
            break;
        if (mListen && FD_ISSET(mSock, &read_fds)) {//如果是正常监听的 mListen 为true,然后mSock这个描述符有可读数据,就创建链接,新建异步处理的SocketClient加入到mClients容器,这里的mSock 是vold这个套接字的描述符
            struct sockaddr addr;
            socklen_t alen;
            int c;

            do {
                alen = sizeof(addr);
                c = accept(mSock, &addr, &alen);
                SLOGV("%s got %d from accept", mSocketName, c);
            } while (c < 0 && errno == EINTR);
            if (c < 0) {
                SLOGE("accept failed (%s)", strerror(errno));
                sleep(1);
                continue;
            }
            pthread_mutex_lock(&mClientsLock);
            mClients->push_back(new SocketClient(c, true, mUseCmdNum));
            pthread_mutex_unlock(&mClientsLock);
        }

        /* Add all active clients to the pending list first */
        pendingList->clear();
        pthread_mutex_lock(&mClientsLock);
        for (it = mClients->begin(); it != mClients->end(); ++it) {//把上面有请求建立链接的Client加入到pendingList 容器中,后面处理
            int fd = (*it)->getSocket();
            if (FD_ISSET(fd, &read_fds)) {
                pendingList->push_back(*it);
            }
        }
        pthread_mutex_unlock(&mClientsLock);

        /* Process the pending list, since it is owned by the thread,
         * there is no need to lock it */
        while (!pendingList->empty()) {//遍历处理
            /* Pop the first item from the list */
            it = pendingList->begin();
            SocketClient* c = *it;
            pendingList->erase(it);
            /* Process it, if false is returned and our sockets are
             * connection-based, remove and destroy it */
            if (!onDataAvailable(c) && mListen) {//调用到FrameworkListener 中onDataAvailable处理Socket事件
                /* Remove the client from our array */
                SLOGV("going to zap %d for %s", c->getSocket(), mSocketName);
                pthread_mutex_lock(&mClientsLock);
                for (it = mClients->begin(); it != mClients->end(); ++it) {
                    if (*it == c) {
                        mClients->erase(it);//处理完成之后,从容器中移除这次的监听到的SocketClient
                        break;
                    }
                }
                pthread_mutex_unlock(&mClientsLock);
                /* Remove our reference to the client */
                c->decRef();
            }
        }
    }
    delete pendingList;
}

这个函数是SocketListener的核心所在,真正的处理函数是onDataAvailable,这个是纯虚函数,/system/core/include/sysutils/SocketListener.h:

    virtual bool onDataAvailable(SocketClient *c) = 0;

在其子类 FrameworkListener.cpp中实现:

bool FrameworkListener::onDataAvailable(SocketClient *c) {
    char buffer[255];
    int len;

    len = TEMP_FAILURE_RETRY(read(c->getSocket(), buffer, sizeof(buffer)));//读Socket 内容保存到buffer
    if (len < 0) {
        SLOGE("read() failed (%s)", strerror(errno));
        return false;
    } else if (!len)
        return false;

    int offset = 0;
    int i;

    for (i = 0; i < len; i++) {
        if (buffer[i] == '\0') {//一次传入一个字符串
            /* IMPORTANT: dispatchCommand() expects a zero-terminated string */
            dispatchCommand(c, buffer + offset);
            offset = i + 1;
        }
    }
    return true;
}

调用同类命令执行函数dispatchCommand

void FrameworkListener::dispatchCommand(SocketClient *cli, char *data) {
    FrameworkCommandCollection::iterator i;
    int argc = 0;
    char *argv[FrameworkListener::CMD_ARGS_MAX];
    char tmp[255];

...//解析判断command buffer

    for (i = mCommands->begin(); i != mCommands->end(); ++i) {//遍历之前register到FrameworkListener中的FrameworkCommand容器
        FrameworkCommand *c = *i;

        if (!strcmp(argv[0], c->getCommand())) {//其中有注册“Volume”,如果这里是Volume开头的command,那么就调用,Volume构造的时候所构造的父类FrameworkCommand中的runCommand函数
            if (c->runCommand(cli, argc, argv)) {
                SLOGW("Handler '%s' error (%s)", c->getCommand(), strerror(errno));
            }
            goto out;
        }
    }

}

同时/system/core/include/sysutils/FrameworkCommand.h:

    virtual int runCommand(SocketClient *c, int argc, char **argv) = 0;

实现在子类中,还是以Volume这个runcommand为例 /system/vold/CommandListener.cpp中:

int CommandListener::VolumeCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    dumpArgs(argc, argv, -1);

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    VolumeManager *vm = VolumeManager::Instance();//获取已经存在的VolumeManager实例

...

else if (!strcmp(argv[1], "mount")) {//判断command 内容
        if (argc != 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume mount <path>", false);
            return 0;
        }
        rc = vm->mountVolume(argv[2]);//交给VolumeManager来对Volume进行操作
    }

...

}

对CommandListener的分析就到这里,主要是怎么接收到的Socket,执行相对应的command,最后是怎么传递给VolumeManager,与上层MountService的交互后续分析,后续分析VolumeManager的初始化!

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