int VolumeManager::start() {return 0;
}

VolumeManager启动过程什么都没有做。

void NetlinkHandler::onEvent(NetlinkEvent *evt) {……//将消息传递给VolumeManager处理if (!strcmp(subsys, "block")) {vm->handleBlockEvent(evt);}
}

    void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {//有状态变化设备路径const char *devpath = evt->findParam("DEVPATH");//遍历VolumeManager中所管理Volume对象（各存储设备代码抽象）for (it = mVolumes->begin(); it != mVolumes->end(); ++it) {if (!(*it)->handleBlockEvent(evt)) {hit = true;break;}}

VolumeManager将消息交给各个DirectVolume对象处理：

int DirectVolume::handleBlockEvent(NetlinkEvent *evt) {//从NetlinkEvent消息中取出有状态变化设备路径const char *dp = evt->findParam("DEVPATH");PathCollection::iterator  it;//遍历所有的存储设备for (it = mPaths->begin(); it != mPaths->end(); ++it) {//根据存储设备路径进行匹配if (!strncmp(dp, *it, strlen(*it))) {/* 从NetlinkEvent消息中取出设备变化的动作 */int action = evt->getAction();/* 从NetlinkEvent消息中取出设备类型 */const char *devtype = evt->findParam("DEVTYPE");SLOGE("DirectVolume::handleBlockEvent() evt's DEVPATH= %s DEVTYPE= %s action= %d",dp, devtype, action);    //设备插入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);SLOGE("DirectVolume::handleBlockEvent() NlActionAdd - /dev/block/vold/%d:%d\n", major, minor);if (createDeviceNode(nodepath, major, minor)) {SLOGE("Error making device node '%s' (%s)", nodepath,strerror(errno));}//新增磁盘if (!strcmp(devtype, "disk")) {handleDiskAdded(dp, evt);//新增分区} else {handlePartitionAdded(dp, evt);}//设备移除} else if (action == NetlinkEvent::NlActionRemove) {SLOGE("Volume  partition %d:%d removed",  atoi(evt->findParam("MAJOR")), atoi(evt->findParam("MINOR")));//删除磁盘if (!strcmp(devtype, "disk")) {handleDiskRemoved(dp, evt);//删除分区} else {handlePartitionRemoved(dp, evt);}//设备改变} else if (action == NetlinkEvent::NlActionChange) {//磁盘变化if (!strcmp(devtype, "disk")) {handleDiskChanged(dp, evt);//分区变化} else {handlePartitionChanged(dp, evt);}} else {SLOGW("Ignoring non add/remove/change event");}return 0;}}errno = ENODEV;return -1;
}

每一个Volume可能对应多个Path；即一个挂载点对应多个物理设备，因此VolumeManager中的每一个Volume对象都需要处理SD状态变换消息，当新增一个disk时：

void DirectVolume::handleDiskAdded(const char *devpath, NetlinkEvent *evt) {//主次设备号mDiskMajor = atoi(evt->findParam("MAJOR"));mDiskMinor = atoi(evt->findParam("MINOR"));//设备分区情况const char *tmp = evt->findParam("NPARTS");mDiskNumParts = atoi(tmp);if (mDiskNumParts == 0) {//没有分区，Volume状态为IdlesetState(Volume::State_Idle);} else {//有分区未加载，设置Volume状态PendingsetState(Volume::State_Pending);}//格式化通知msg："Volume sdcard /mnt/sdcard disk inserted (179:0)"char msg[255];snprintf(msg, sizeof(msg), "Volume %s %s disk inserted (%d:%d)",getLabel(), getMountpoint(), mDiskMajor, mDiskMinor);//调用VolumeManager中的Broadcaster——>CommandListener 发送此msgmVm->getBroadcaster()->sendBroadcast(ResponseCode::VolumeDiskInserted,msg, false);
}

将新增一个disk以消息的方式通过CommandListener向MountService发送，由于CommandListener继承于FrameworkListener，而FrameworkListener又继承于SocketListener，CommandListener和FrameworkListener都没用重写父类的sendBroadcast方法，因此消息是通过 SocketListener的sendBroadcast函数向上层发送的，VolumeManager通知上层的消息流程图：

void SocketListener::sendBroadcast(int code, const char *msg, bool addErrno)
{pthread_mutex_lock(&mClientsLock);//遍历所有的消息接收时创建的Client SocketClient// SocketClient将消息通过socket（“vold”）通信for (i = mClients->begin(); i != mClients->end(); ++i) {(*i)->sendMsg(code, msg, addErrno, false);}pthread_mutex_unlock(&mClientsLock);
}

3.CommandListener模块

int SocketListener::startListener() {//mSocketName = “Vold”mSock = android_get_control_socket(mSocketName);//NetlinkHandler mListen为true 监听socketif (mListen && < 0) {return -1;} else if (!mListen){mClients->push_back(new SocketClient(mSock, false, mUseCmdNum));}//创建匿名管道pipe(mCtrlPipe);//创建线程执行函数threadStart 参数thispthread_create(&mThread, NULL, SocketListener::threadStart, this);
}void *SocketListener::threadStart(void *obj) {SocketListener *me = reinterpret_cast<SocketListener *>(obj);me->runListener();
}void SocketListener::runListener() {//SocketClient ListSocketClientCollection *pendingList = new SocketClientCollection();while(1) {fd_set read_fds;//mListen 为trueif (mListen) {max = mSock;FD_SET(mSock, &read_fds);}//加入一组文件描述符集合 选择fd最大的max select有关FD_SET(mCtrlPipe[0], &read_fds);pthread_mutex_lock(&mClientsLock);for (it = mClients->begin(); it != mClients->end(); ++it) {int fd = (*it)->getSocket();FD_SET(fd, &read_fds);if (fd > max)max = fd;}pthread_mutex_unlock(&mClientsLock);//监听文件描述符是否变化rc = select(max + 1, &read_fds, NULL, NULL, NULL);//匿名管道被写，退出线程if (FD_ISSET(mCtrlPipe[0], &read_fds))break;//mListen 为trueif (mListen && FD_ISSET(mSock, &read_fds)) {//mListen 为ture 表示正常监听socketstruct sockaddr addr;do {c = accept(mSock, &addr, &alen);} while (c < 0 && errno == EINTR);//创建一个客户端SocketClient，加入mClients列表中 到异步延迟处理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();//将所有有消息的Client加入到pendingList中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,*/while (!pendingList->empty()) {it = pendingList->begin();SocketClient* c = *it;//处理有数据发送的socket if (!onDataAvailable(c) && mListen) {//mListen为true……}}}
}

启动CommandListener监听过程其实就是创建一个监听的工作线程，用于监听客户端即MountService发过来的命令。

3.消息处理

当接收到MountService发送的消息时，将回调onDataAvailable函数进行处理。CommandListener父类FrameworkCommand重写了消息处理onDataAvailable函数。

bool FrameworkListener::onDataAvailable(SocketClient *c) {char buffer[255];//读取socket消息len = TEMP_FAILURE_RETRY(read(c->getSocket(), buffer, sizeof(buffer)));for (i = 0; i < len; i++) {if (buffer[i] == '\0') {//根据消息内容 派发命令dispatchCommand(c, buffer + offset);offset = i + 1;}}return true;
}void FrameworkListener::dispatchCommand(SocketClient *cli, char *data) {char *argv[FrameworkListener::CMD_ARGS_MAX];//解析消息内容 命令 参数……//执行对应的消息for (i = mCommands->begin(); i != mCommands->end(); ++i) {FrameworkCommand *c = *i;//匹配命令if (!strcmp(argv[0], c->getCommand())) {//执行命令c->runCommand(cli, argc, argv);goto out;}}
out:return;
}

对于VolumeCommand，其runCommand函数为：

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();int rc = 0;//查看存储设备if (!strcmp(argv[1], "list")) {return vm->listVolumes(cli);} else if (!strcmp(argv[1], "debug")) {if (argc != 3 || (argc == 3 && (strcmp(argv[2], "off") && strcmp(argv[2], "on")))) {cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume debug <off/on>", false);return 0;}vm->setDebug(!strcmp(argv[2], "on") ? true : false);//挂载存储设备} else if (!strcmp(argv[1], "mount")) {if (argc != 3) {cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume mount <path>", false);return 0;}rc = vm->mountVolume(argv[2]);//卸载存储设备} else if (!strcmp(argv[1], "unmount")) {if (argc < 3 || argc > 4 ||((argc == 4 && strcmp(argv[3], "force")) &&(argc == 4 && strcmp(argv[3], "force_and_revert")))) {cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume unmount <path> [force|force_and_revert]", false);return 0;}bool force = false;bool revert = false;if (argc >= 4 && !strcmp(argv[3], "force")) {force = true;} else if (argc >= 4 && !strcmp(argv[3], "force_and_revert")) {force = true;revert = true;}rc = vm->unmountVolume(argv[2], force, revert);//格式化存储设备} else if (!strcmp(argv[1], "format")) {if (argc != 3) {cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: volume format <path>", false);return 0;}rc = vm->formatVolume(argv[2]);//共享存储设备} else if (!strcmp(argv[1], "share")) {if (argc != 4) {cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage: volume share <path> <method>", false);return 0;}rc = vm->shareVolume(argv[2], argv[3]);} else if (!strcmp(argv[1], "unshare")) {if (argc != 4) {cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage: volume unshare <path> <method>", false);return 0;}rc = vm->unshareVolume(argv[2], argv[3]);} else if (!strcmp(argv[1], "shared")) {bool enabled = false;if (argc != 4) {cli->sendMsg(ResponseCode::CommandSyntaxError,"Usage: volume shared <path> <method>", false);return 0;}if (vm->shareEnabled(argv[2], argv[3], &enabled)) {cli->sendMsg(ResponseCode::OperationFailed, "Failed to determine share enable state", true);} else {cli->sendMsg(ResponseCode::ShareEnabledResult,(enabled ? "Share enabled" : "Share disabled"), false);}return 0;} else {cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume cmd", false);}if (!rc) {cli->sendMsg(ResponseCode::CommandOkay, "volume operation succeeded", false);} else {int erno = errno;rc = ResponseCode::convertFromErrno();cli->sendMsg(rc, "volume operation failed", true);}return 0;
}

针对不同的命令，调用VolumeManager的不同函数对存储设备进行操作，如挂载磁盘命令，则调用mountVolume函数：

int VolumeManager::mountVolume(const char *label) {//根据卷标查找VolumeVolume *v = lookupVolume(label);if (!v) {errno = ENOENT;return -1;}return v->mountVol();
}

调用Volume的mountVol函数来挂载设备。MountServcie发送命令的流程图：

整个Vold处理过程框架图如下：