vold挂载管理

看了很长时间Vold存储模块的相关知识，也深入的研究一段时间的Android源码，打算把自己看过的经验之贴、参考资料和自己的一些见解，以帖子的形式发出来，供有兴趣的同仁们参考，有不对的地方请指正，我们相互交流。

1.1 vold的原理与机制分析

1.1.1 Vold 架构

从上图中可知：

·  Vold中的NetlinkManager模块接收来自Linux内核的uevent消息。例如SD卡的插拔等动作都会引起Kernel向NM发送uevent消息。

·  NetlinkManager将这些消息转发给VolumeManager模块。VolumeManager会对应做一些操作，然后把相关信息通过CommandListener发送给MountService，MountService根据收到的消息会发送相关的处理命令给VolumeManager做进一步的处理。例如待SD卡插入后，VolumeManager会将来自NetlinkManager的“Disk Insert”消息发送给MountService，而后MountService则发送“Mount”指令给Vold，指示它挂载这个SD卡。

·  CommandListener模块内部封装了一个Socket用于跨进程通信。它在Vold进程中属于监听端（即是服务端），而它的连接端（即客户端）则是MountService。它一方面接收来自MountService的控制命令（例如卸载存储卡、格式化存储卡等），另一方面VolumeManager和NetlinkManager模块又会通过它，将一些信息发送给MountService。

1.1.2初识Vold

下面来初步的认识Vold，代码在system\vold\main.cpp

int main() {
    mkdir("/dev/block/vold", 0755);  //创建一个目录/dev/block/vold

  //创建一个VolumeManager对象，该对象为单例模式
    if (!(vm = VolumeManager::Instance())) {
        SLOGE("Unable to create VolumeManager");
        exit(1);
    };

  //创建一个NetlinkManager对象，该对象为单例模式
    if (!(nm = NetlinkManager::Instance())) {
        SLOGE("Unable to create NetlinkManager");
        exit(1);
    };

  //创建一个CommandListener对象
    cl = new CommandListener();
    vm->setBroadcaster((SocketListener *) cl);
    nm->setBroadcaster((SocketListener *) cl);

//启动VolumeManager
    if (vm->start()) {
        SLOGE("Unable to start VolumeManager (%s)", strerror(errno));
        exit(1);
    }

//根据fstab配置文件初始化VolumeManager
    if (process_config(vm)) {
        SLOGE("Error reading configuration (%s)... continuing anyways", strerror(errno));
    }

//启动NetlinkManager对象
    if (nm->start()) {
        SLOGE("Unable to start NetlinkManager (%s)", strerror(errno));
        exit(1);
    }
//通过往/sys/block目录下对应的uevent文件写“add\n”来触发内核发送Uevent消息
    coldboot("/sys/block");

//启动CommandListener
    if (cl->startListener()) {
        SLOGE("Unable to start CommandListener (%s)", strerror(errno));
        exit(1);
    }
}

1.2 NetlinkManager模块的分析

1.2.1 NetlinkManager架构流程图

上图中的虚线为启动是的调用流程。

 (1) class NetlinkManager(在其start函数中创建了NetlinkHandler对象，并把创建的socket作为参数)

 (2)class NetlinkHandler: public NetlinkListener(实现了onEvent)

 (3) class NetlinkListener : public SocketListener (实现了onDataAvailable)

 (4) class SocketListener(实现了runListener，在一个线程中通过select查看哪些socket有数据，通过onDataAvailable来读取数据)

1.2.2 start的分析

NetlinkManager模块将使用Netlink套接字实现用户进程与内核进程通信的一种特殊的进程间通信(IPC) ,一起看下面代码

int NetlinkManager::start() {
    struct sockaddr_nl nladdr;
    int sz = 64 * 1024;
    int on = 1;
    memset(&nladdr, 0, sizeof(nladdr));
    nladdr.nl_family = AF_NETLINK;
    nladdr.nl_pid = getpid();
    nladdr.nl_groups = 0xffffffff;
    // 创建一个socket用于内核空间和用户空间的异步通信，监控系统的hotplug事件
    if ((mSock = socket(PF_NETLINK,
                        SOCK_DGRAM,NETLINK_KOBJECT_UEVENT)) < 0) {
        SLOGE("Unable to create uevent socket: %s", strerror(errno));
        return -1;
    }
    if (setsockopt(mSock, SOL_SOCKET, SO_RCVBUFFORCE, &sz, sizeof(sz)) < 0) {
        SLOGE("Unable to set uevent socket SO_RECBUFFORCE option: %s", strerror(errno));
        return -1;
    }
    if (setsockopt(mSock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on)) < 0) {
        SLOGE("Unable to set uevent socket SO_PASSCRED option: %s", strerror(errno));
        return -1;
    }

    if (bind(mSock, (struct sockaddr *) &nladdr, sizeof(nladdr)) < 0) {
        SLOGE("Unable to bind uevent socket: %s", strerror(errno));
        return -1;
    }
    // 利用新创建的socket实例化一个NetlinkHandler类对象，NetlinkHandler继承了类NetlinkListener，
    // NetlinkListener又继承了类SocketListener
    mHandler = new NetlinkHandler(mSock);
    if (mHandler->start()) {  //启动NetlinkHandler
        SLOGE("Unable to start NetlinkHandler: %s", strerror(errno));
        return -1;
    }
    return 0;
}

NetlinkHandler构造

NetlinkHandler::NetlinkHandler(int listenerSocket) :
                NetlinkListener(listenerSocket) {
}

继承父类

NetlinkListener::NetlinkListener(int socket) :
                            SocketListener(socket, false) {
    mFormat = NETLINK_FORMAT_ASCII;
}

这里又是构造了一个SockListener的实例，传入了上面创建的socket标识。

接着调用的start()函数，也是最终实现在SockListener的startListener()。

int NetlinkHandler::start() {
    return this->startListener();
}

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) {
            SLOGE("Obtaining file descriptor socket '%s' failed: %s",
                 mSocketName, strerror(errno));
            return -1;
        }
    }

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

    if (pipe(mCtrlPipe)) {
        SLOGE("pipe failed (%s)", strerror(errno));
        return -1;
    }

    if (pthread_create(&mThread, NULL, SocketListener::threadStart, this)) {
        SLOGE("pthread_create (%s)", strerror(errno));
        return -1;
    }

    return 0;
}

void *SocketListener::threadStart(void *obj) {
    SocketListener *me = reinterpret_cast(obj);

    me->runListener();
    pthread_exit(NULL);
    return NULL;
}

void SocketListener::runListener() {

    SocketClientCollection *pendingList = new SocketClientCollection();

    while(1) { // 死循环，一直监听
        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); //添加文件描述符到文件描述符集read_fds
        }

        FD_SET(mCtrlPipe[0], &read_fds); //添加管道的读取端文件描述符到read_fds
        if (mCtrlPipe[0] > max)
            max = mCtrlPipe[0];

        pthread_mutex_lock(&mClientsLock); //对容器mClients的操作需要加锁
        for (it = mClients->begin(); it != mClients->end(); ++it) {
            int fd = (*it)->getSocket();
            FD_SET(fd, &read_fds); ////遍历容器mClients的所有成员，调用内联函数getSocket()获取文件描述符，并添加到文件描述符集read_fds
            if (fd > max)
                max = fd;
        }
        pthread_mutex_unlock(&mClientsLock);
        // 等待文件描述符中某一文件描述符或者说socket有数据到来
        if ((rc = select(max + 1, &read_fds, NULL, NULL, NULL)) < 0) {
            if (errno == EINTR)
                continue;
            SLOGE("select failed (%s)", strerror(errno));
            sleep(1);
            continue;
        } else if (!rc)
            continue;

        if (FD_ISSET(mCtrlPipe[0], &read_fds))
            break;
        if (mListen && FD_ISSET(mSock, &read_fds)) { //监听套接字处理
            struct sockaddr addr;
            socklen_t alen;
            int c;

            do {
                alen = sizeof(addr);
                c = accept(mSock, &addr, &alen); //接收链接请求，建立连接，如果成功c即为建立链接后的数据交换套接字,将其添加到mClient容器
            } 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));
            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) {
            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()) { //非监听套接字处理
            /* 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 */
            // ****** onDataAvailable在NetlinkListener中实现*********
             if (!onDataAvailable(c) && mListen) {
                /* Remove the client from our array */
                pthread_mutex_lock(&mClientsLock);
                for (it = mClients->begin(); it != mClients->end(); ++it) {
                    if (*it == c) {
                        mClients->erase(it);
                        break;
                    }
                }
                pthread_mutex_unlock(&mClientsLock);
                /* Remove our reference to the client */
                c->decRef();
            }
        }
    }
    delete pendingList;
}

SocketListener::runListener是线程真正执行的函数：mListen成员用来判定是否监听套接字，Netlink套接字属于udp套接字，非监听套接字，该函数的主要功能体现在，如果该套接字有数据到来，就调用函数onDataAvailable读取数据

bool NetlinkListener::onDataAvailable(SocketClient *cli)
{
    int socket = cli->getSocket();
    ssize_t count;
    uid_t uid = -1;

    count = TEMP_FAILURE_RETRY(uevent_kernel_multicast_uid_recv(
                                       socket, mBuffer, sizeof(mBuffer), &uid)); //从socket中读取event信息
    if (count < 0) {
        if (uid > 0)
            LOG_EVENT_INT(65537, uid);
        SLOGE("recvmsg failed (%s)", strerror(errno));
        return false;
    }

    NetlinkEvent *evt = new NetlinkEvent();
    if (!evt->decode(mBuffer, count, mFormat)) {   //调用NetlinkEvent解析event
        SLOGE("Error decoding NetlinkEvent");
    } else {
        onEvent(evt);  //传递event给子类NetlinkHandler处理
    }

    delete evt;
    return true;
}

到NetlinkHandler.cpp中：

void NetlinkHandler::onEvent(NetlinkEvent *evt) {
    VolumeManager *vm = VolumeManager::Instance();
    const char *subsys = evt->getSubsystem();

    if (!subsys) {
        SLOGW("No subsystem found in netlink event");
        return;
    }
    if (!strcmp(subsys, "block")) {   //EVENT为block类型
        int action = evt->getAction();

        vm->updatePullOutState(evt);
        vm->setHotPlug(true);
        vm->handleBlockEvent(evt);  //把event交给VolumeManager处理
        vm->setHotPlug(false);

    }

1.2.3 NM模块的总结

NM模块的功能就是从Kernel接收Uevent消息，然后转换成一个NetlinkEvent对象，最后会调用VM的处理函数来处理这个NetlinkEvent对象。

1.3 VolumeManager模块的分析

1.3.1 Vold使用VM模块的流程

  调用Instance创建一个VM对象。

  调用setBroadcaster设置CL对象

  调用start启动VM。

  调用process_config配置VM。

1.3.2 VM的创建

VolumeManager *VolumeManager::Instance() {
    if (!sInstance)
        sInstance = new VolumeManager();
    return sInstance;
}

VolumeManager::VolumeManager() {
    mDebug = false;
    mVolumes = new VolumeCollection();  //一个容器，保存Volume的集合
    mActiveContainers = new AsecIdCollection();
    mBroadcaster = NULL;   //指向socketlisten，用于发送挂载事件
    mUmsSharingCount = 0;
    mSavedDirtyRatio = -1;
    mUmsDirtyRatio = dirtyRatio();
    mVolManagerDisabled = 0;
    mIsHotPlug= false;
    mUseBackupContainers =false;
    mIsFirstBoot = false;
    mIpoState = State_Ipo_Start;
}

1.3.3 VM的启动

int VolumeManager::start() {
    return 0;   //VM的启动什么也没有做
}

1.3.4 process_config分析

这个函数用于解析指定的配置文件，根据内容构造DirectVolume以及父类然后保存进VolumeManager的容器中，供VolumeManager用于挂载事件的管理

static int process_config(VolumeManager *vm)
{
    char fstab_filename[PROPERTY_VALUE_MAX + sizeof(FSTAB_PREFIX)];
    fstab = fs_mgr_read_fstab(fstab_filename);   //读取fstab文件
    if (!fstab) {
        SLOGE("failed to open %s\n", fstab_filename);
        return -1;
    }
    /* Loop through entries looking for ones that vold manages */
    for (i = 0; i < fstab->num_entries; i++) {
        if (fs_mgr_is_voldmanaged(&fstab->recs[i])) {
            DirectVolume *dv = NULL;
            flags = 0;

            /* Set any flags that might be set for this volume */
            if (fs_mgr_is_nonremovable(&fstab->recs[i])) {
                flags |= VOL_NONREMOVABLE;
            }
            if (fs_mgr_is_encryptable(&fstab->recs[i])) {
                flags |= VOL_ENCRYPTABLE;
            }
            /* Only set this flag if there is not an emulated sd card */
            if (fs_mgr_is_noemulatedsd(&fstab->recs[i]) &&
                !strcmp(fstab->recs[i].fs_type, "vfat")) {
                flags |= VOL_PROVIDES_ASEC;
            }
            dv = new DirectVolume(vm, &(fstab->recs[i]), flags);
            if (dv->addPath(fstab->recs[i].blk_device)) {
                SLOGE("Failed to add devpath %s to volume %s",
                      fstab->recs[i].blk_device, fstab->recs[i].label);
                goto out_fail;
            }
            vm->addVolume(dv);  //添加到volumemanager容器
        }
    }
}

fstab配置文件

# Android fstab file.
#
# The filesystem that contains the filesystem checker binary (typically /system) cannot
# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK

/devices/platform/mtk-msdc.0/mmc_host   auto      vfat      defaults        voldmanaged=sdcard0:emmc@fat,noemulatedsd
/devices/platform/mtk-msdc.1/mmc_host   auto      vfat      defaults        voldmanaged=sdcard1:auto

1.3.5 DirectVolume分析

DirectVolume从Volume类派生，可把它看成是一个外部存储卡（例如一张SD卡）在代码中的代表物。它封装了对外部存储卡的操作，例如加载/卸载存储卡、格式化存储卡等

DirectVolume构造

DirectVolume::DirectVolume(VolumeManager *vm,const char *label,
                           const char*mount_point, int partIdx) :
              Volume(vm, label, mount_point) {//初始化基类
   /*
      注意其中的参数：
     label为”sdcard”,mount_point为”/mnt/sdcard”,partIdx为1
*/
   mPartIdx = partIdx;
//PathCollection定义为typedef android::List PathCollection
//其实就是一个字符串list
    mPaths= new PathCollection();
    for(int i = 0; i < MAX_PARTITIONS; i++)
       mPartMinors[i] = -1;
   mPendingPartMap = 0;
   mDiskMajor = -1;  //存储设备的主设备号
   mDiskMinor = -1;  //存储设备的次设备号，一个存储设备将由主次两个设备号标识。
   mDiskNumParts = 0;
   //设置状态为NoMedia
   setState(Volume::State_NoMedia);
}
//再来看addPath函数，它主要目的是添加设备在sysfs中的路径，
int DirectVolume::addPath(const char *path) {
   mPaths->push_back(strdup(path));
    return0;
}

addPath把和某个存储卡接口相关的设备路径与这个DirectVolume绑定到一起，并且这个设备路径和Uevent中的DEVPATH是对应的，这样就可以根据Uevent的DEVPATH找到是哪个存储卡的DirectVolume发生了变动。当然手机上目前只有一个存储卡接口，所以Vold也只有一个DirectVolume。

1.3.6 VM与NM交互

在分析NM模块的数据处理时发现，NM模块接收到Uevent事件后，会调用VM模块进行处理，如果Uevent是block子系统，则调用handleBlockEvent

void VolumeManager::handleBlockEvent(NetlinkEvent*evt) {
    constchar *devpath = evt->findParam("DEVPATH");

/*
前面在process_config中构造的DirectVolume对象保存在了mVolumes中，它的定义如下：
typedef android::ListVolumeCollection，也是一个列表。
  注意它保存的是Volume指针，而我们的DirectVolume是从Volume派生的
*/
   VolumeCollection::iterator it;
    boolhit = false;
for (it = mVolumes->begin(); it !=mVolumes->end(); ++it) {
        //调用每个Volume的handleBlockEvent事件，实际上将调用
        //DirectVolume的handleBlockEvent函数。
        if(!(*it)->handleBlockEvent(evt)) {
           hit = true;
           break;
        }
    }
}

int DirectVolume::handleBlockEvent(NetlinkEvent*evt) {
    constchar *dp = evt->findParam("DEVPATH");

PathCollection::iterator  it;
//将Uevent的DEVPATH和addPath添加的路径进行对比，判断属不属于自己管理的范围。
    for(it = mPaths->begin(); it != mPaths->end(); ++it) {
        if(!strncmp(dp, *it, strlen(*it))) {
           int action = evt->getAction();
           const char *devtype = evt->findParam("DEVTYPE");

           if (action == NetlinkEvent::NlActionAdd) {
               int major = atoi(evt->findParam("MAJOR"));
               int minor = atoi(evt->findParam("MINOR"));
               char nodepath[255];

               snprintf(nodepath,
                         sizeof(nodepath),"/dev/block/vold/%d:%d",
                         major, minor);
                 //创建设备节点
               if (createDeviceNode(nodepath, major, minor)) {
                    ......
               }
               if (!strcmp(devtype, "disk")) {
                    handleDiskAdded(dp, evt);//添加一个磁盘
               } else {
                    /*
对于有分区的SD卡，先收到上面的“disk”消息，然后每个分区就会收到
                   一个分区添加消息。
                   */
                    handlePartitionAdded(dp,evt);
               }
           } else if (action == NetlinkEvent::NlActionRemove) {
                ......
           } else if (action == NetlinkEvent::NlActionChange) {
              ......
           }
           ......
           return 0;
        }
    }
    errno= ENODEV;
    return-1;
}

1.4 commandlisten模块分析

1.4.1 commandlisten构造

 /system/vold/main.cpp

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);
}

构造函数/system/vold/CommandListener.cpp

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());
    registerCmd(new FstrimCmd());
    //M{
#ifndef MTK_EMULATOR_SUPPORT
    registerCmd(new USBCmd());
#endif
    registerCmd(new CDROMCmd());
    //}M
#if defined (ENG_BUILD_ENG)
    registerCmd(new SilkRoad());
#endif
}

构造一个父类FrameworkListener

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;
}

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();
}

1.4.2 Command注册

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

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

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

1.4.3 startListener的分析和数据处理

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;
}

开启线程用于监听

void *SocketListener::threadStart(void *obj) {
    SocketListener *me = reinterpret_cast(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;
}

对socket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;
}

SocketListener的核心处理函数是onDataAvailable

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
           "font-family: Arial; font-size: 14px; line-height: 26px; background-color: rgb(240, 247, 254);"> //分发命令，最终会调用对应命令对象的runCommand进行函数处理。
            dispatchCommand(c, buffer + offset);
            offset = i + 1;
        }
    }
    return true;
}

调用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;
        }
    }
}

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 ", false);
            return 0;
        }
        rc = vm->mountVolume(argv[2]);//交给VolumeManager来对Volume进行操作
    }

...

}

1.4.4 commandlisten 数据处理流程图

1.5 mountservice模块的介绍

1.5.1 mountservice构造

public MountService(Context context) {
        mContext = context;

        synchronized (mVolumesLock) {
            readStorageListLocked(); // 解析/frameworks/base/core/res/res/xml/storage_list.xml保存volume到 MountService的list ：mVolumes中
        }

        // XXX: This will go away soon in favor of IMountServiceObserver
        mPms = (PackageManagerService) ServiceManager.getService("package");

        mHandlerThread = new HandlerThread("MountService");
        mHandlerThread.start();
        mHandler = new MountServiceHandler(mHandlerThread.getLooper());//新建消息处理handler

        // Watch for user changes
        final IntentFilter userFilter = new IntentFilter();
        userFilter.addAction(Intent.ACTION_USER_ADDED);
        userFilter.addAction(Intent.ACTION_USER_REMOVED);
        mContext.registerReceiver(mUserReceiver, userFilter, null, mHandler);//注册广播接收

        // Watch for USB changes on primary volume
        final StorageVolume primary = getPrimaryPhysicalVolume();
        if (primary != null && primary.allowMassStorage()) {
            mContext.registerReceiver(
                    mUsbReceiver, new IntentFilter(UsbManager.ACTION_USB_STATE), null, mHandler);
        }

        // Add OBB Action Handler to MountService thread.
        mObbActionHandler = new ObbActionHandler(mHandlerThread.getLooper());

        /*
         * Create the connection to vold with a maximum queue of twice the
         * amount of containers we'd ever expect to have. This keeps an
         * "asec list" from blocking a thread repeatedly.
         */
        mConnector = new NativeDaemonConnector(this, "vold", MAX_CONTAINERS * 2, VOLD_TAG, 25);//创建 vold 的监听接收，用于接收system中Vold的socket消息

        Thread thread = new Thread(mConnector, VOLD_TAG);
        thread.start();//启动线程，NativeDaemonConnector实现了Runnable接口，实现在 run中

        // Add ourself to the Watchdog monitors if enabled.
        if (WATCHDOG_ENABLE) {
            Watchdog.getInstance().addMonitor(this);
        }
    }

1.5.2构造了NativeDaemonConnector用来接收来自下层的socket消息

NativeDaemonConnector(INativeDaemonConnectorCallbacks callbacks, String socket,
        int responseQueueSize, String logTag, int maxLogSize) {
    mCallbacks = callbacks; //回调
    mSocket = socket; // socket名称
    mResponseQueue = new ResponseQueue(responseQueueSize);//构建一个响应队列
    mSequenceNumber = new AtomicInteger(0);
    TAG = logTag != null ? logTag : "NativeDaemonConnector";
  }

开启监测线程的run方法

public void run() {
    HandlerThread thread = new HandlerThread(TAG + ".CallbackHandler"); //TAG 为 VoldConnector，这里新建一个名为VoldConnector.CallbackHandler的消息处理线程，用于下面接收到vold 的socket之后的处理
    thread.start();
    mCallbackHandler = new Handler(thread.getLooper(), this); //创建handler 用于分发消息
     while (true) {
        try {
            listenToSocket();// while 循环 监听socket
        } catch (Exception e) {
            loge("Error in NativeDaemonConnector: " + e);
            SystemClock.sleep(5000);
        }
    }
}

private void listenToSocket() throws IOException {
    LocalSocket socket = null;

    try {
        socket = new LocalSocket();  //创建本地socket
        LocalSocketAddress address = new LocalSocketAddress(mSocket,
                LocalSocketAddress.Namespace.RESERVED);//获得服务端vold socket的地址

        socket.connect(address);//连接

        InputStream inputStream = socket.getInputStream();
        synchronized (mDaemonLock) {
            mOutputStream = socket.getOutputStream();
        }//获取输入输出流

        mCallbacks.onDaemonConnected();//回调，在MountService中执行，初始化一些Volume状态信息

        byte[] buffer = new byte[BUFFER_SIZE];
        int start = 0;

        while (true) {
            int count = inputStream.read(buffer, start, BUFFER_SIZE - start);//读取数据到buffer
            if (count < 0) {//连接断开，跳出当前while ，外部while循环 重新调用该函数连接
                loge("got " + count + " reading with start = " + start);
                break;
            }


            // Add our starting point to the count and reset the start.
            count += start;
            start = 0;

            for (int i = 0; i < count; i++) {
                if (buffer[i] == 0) {
                    final String rawEvent = new String(
                            buffer, start, i - start, Charsets.UTF_8);
                    log("RCV <- {" + rawEvent + "}");

                    try {
                        final NativeDaemonEvent event = NativeDaemonEvent.parseRawEvent(
                                rawEvent);   //解析成event 保存
                        if (event.isClassUnsolicited()) {    //判断event的code范围 code >= 600 && code < 700
                            // TODO: migrate to sending NativeDaemonEvent instances
                            mCallbackHandler.sendMessage(mCallbackHandler.obtainMessage( //发送消息，把event交给handle来分发处理
                                    event.getCode(), event.getRawEvent()));
                        } else {
                            mResponseQueue.add(event.getCmdNumber(), event);//加入到响应队列
                        }
                    } catch (IllegalArgumentException e) {
                        log("Problem parsing message: " + rawEvent + " - " + e);
                    }

                    start = i + 1;
                }
            }

在NativeDaemonConnector中的handle处理为：

public boolean handleMessage(Message msg) {
    String event = (String) msg.obj;
    try {
        if (!mCallbacks.onEvent(msg.what, event, NativeDaemonEvent.unescapeArgs(event))) { //回调到MountService 的onEent函数
            log(String.format("Unhandled event '%s'", event));
        }
    } catch (Exception e) {
        loge("Error handling '" + event + "': " + e);
    }
    return true;
}

MountService中onEvent

public boolean onEvent(int code, String raw, String[] cooked) {
        if (DEBUG_EVENTS) {
            StringBuilder builder = new StringBuilder();
            builder.append("onEvent::");
            builder.append(" raw= " + raw);
            if (cooked != null) {
                builder.append(" cooked = " );
                for (String str : cooked) {
                    builder.append(" " + str);
                }
            }
            Slog.i(TAG, builder.toString());
        }
        if (code == VoldResponseCode.VolumeStateChange) { //根据 Vold的Code 执行
            /*
             * One of the volumes we're managing has changed state.
             * Format: "NNN Volume   state changed
             * from  () to  ()"
             */
            notifyVolumeStateChange(
                    cooked[2], cooked[3], Integer.parseInt(cooked[7]),
                            Integer.parseInt(cooked[10])); //更新状态
        } else if ((code == VoldResponseCode.VolumeDiskInserted) ||
                   (code == VoldResponseCode.VolumeDiskRemoved) ||
                   (code == VoldResponseCode.VolumeBadRemoval))
    ...

                  if (code == VoldResponseCode.VolumeDiskInserted) { //如果接收到的是插入disk的消息，则执行挂载操作
                new Thread() {
                    @Override
                    public void run() {
                        try {
                            int rc;
                            if ((rc = doMountVolume(path)) != StorageResultCode.OperationSucceeded) {
                                Slog.w(TAG, String.format("Insertion mount failed (%d)", rc));
                            }
                        } catch (Exception ex) {
                            Slog.w(TAG, "Failed to mount media on insertion", ex);
                        }
                    }
                }.start();
            }
}

1.5.3 MountService下发command

MountService中对Volume的各种操作都是需要转换成符合Vold中socket command，这样Vold中才能正确的解析识别调用

private int doMountVolume(String path) {
    int rc = StorageResultCode.OperationSucceeded;

    final StorageVolume volume;
    synchronized (mVolumesLock) {
        volume = mVolumesByPath.get(path);
    }

    if (DEBUG_EVENTS) Slog.i(TAG, "doMountVolume: Mouting " + path);
    try {
        mConnector.execute("volume", "mount", path);// 调用到NativeDaemonConnector中的execute
    }

NativeDaemonConnector的execute

public NativeDaemonEvent[] execute(int timeout, String cmd, Object... args)
            throws NativeDaemonConnectorException {
        final ArrayList events = Lists.newArrayList();

        final int sequenceNumber = mSequenceNumber.incrementAndGet();
        final StringBuilder cmdBuilder =
                new StringBuilder(Integer.toString(sequenceNumber)).append(' ');
        final long startTime = SystemClock.elapsedRealtime();

        makeCommand(cmdBuilder, cmd, args); //转换制作成标准的Command

        final String logCmd = cmdBuilder.toString(); /* includes cmdNum, cmd, args */
        log("SND -> {" + logCmd + "}");

        cmdBuilder.append('\0');
        final String sentCmd = cmdBuilder.toString(); /* logCmd + \0 */

        synchronized (mDaemonLock) {
            if (mOutputStream == null) {
                throw new NativeDaemonConnectorException("missing output stream");
            } else {
                try {
                    mOutputStream.write(sentCmd.getBytes(Charsets.UTF_8)); //通过在listenToSocket中获取的输出流，写入转换好的sentCmd
                } catch (IOException e) {
                    throw new NativeDaemonConnectorException("problem sending command", e);
                }
            }
        }
}

1.5.4 Mountservice 数据处理流程图