Android Vold - 技术栈

总体框架

plain 复制代码

int main(int argc, char** argv) {
    atrace_set_tracing_enabled(false);
    setenv("ANDROID_LOG_TAGS", "*:d", 1);  // Do not submit with verbose logs enabled
    android::base::InitLogging(argv, &VoldLogger);

    LOG(INFO) << "Vold 3.0 (the awakening) firing up";

    ATRACE_BEGIN("main");

    LOG(DEBUG) << "Detected support for:"
               << (android::vold::IsFilesystemSupported("ext4") ? " ext4" : "")
               << (android::vold::IsFilesystemSupported("f2fs") ? " f2fs" : "")
               << (android::vold::IsFilesystemSupported("vfat") ? " vfat" : "");

    VolumeManager* vm;
    NetlinkManager* nm;

    parse_args(argc, argv);

    sehandle = selinux_android_file_context_handle();
    if (!sehandle) {
        LOG(ERROR) << "Failed to get SELinux file contexts handle";
        exit(1);
    }
    selinux_android_set_sehandle(sehandle);

    mkdir("/dev/block/vold", 0755);

    /* For when cryptfs checks and mounts an encrypted filesystem */
    klog_set_level(6);

    /* Create our singleton managers */
    if (!(vm = VolumeManager::Instance())) {
        LOG(ERROR) << "Unable to create VolumeManager";
        exit(1);
    }

    if (!(nm = NetlinkManager::Instance())) {
        LOG(ERROR) << "Unable to create NetlinkManager";
        exit(1);
    }

    if (android::base::GetBoolProperty("vold.debug", false)) {
        vm->setDebug(true);
    }

    if (vm->start()) {
        PLOG(ERROR) << "Unable to start VolumeManager";
        exit(1);
    }

    VoldConfigs configs = {};
    if (process_config(vm, &configs)) {
        PLOG(ERROR) << "Error reading configuration... continuing anyways";
    }

    android::hardware::configureRpcThreadpool(1, false /* callerWillJoin */);

    ATRACE_BEGIN("VoldNativeService::start");
    if (android::vold::VoldNativeService::start() != android::OK) {
        LOG(ERROR) << "Unable to start VoldNativeService";
        exit(1);
    }
    ATRACE_END();

    LOG(DEBUG) << "VoldNativeService::start() completed OK";

    ATRACE_BEGIN("NetlinkManager::start");
    if (nm->start()) {
        PLOG(ERROR) << "Unable to start NetlinkManager";
        exit(1);
    }
    ATRACE_END();

    // This call should go after listeners are started to avoid
    // a deadlock between vold and init (see b/34278978 for details)
    android::base::SetProperty("vold.has_adoptable", configs.has_adoptable ? "1" : "0");
    android::base::SetProperty("vold.has_quota", configs.has_quota ? "1" : "0");
    android::base::SetProperty("vold.has_reserved", configs.has_reserved ? "1" : "0");
    android::base::SetProperty("vold.has_compress", configs.has_compress ? "1" : "0");

    // Do coldboot here so it won't block booting,
    // also the cold boot is needed in case we have flash drive
    // connected before Vold launched
    coldboot("/sys/block");

    ATRACE_END();

    android::IPCThreadState::self()->joinThreadPool();
    LOG(INFO) << "vold shutting down";

    exit(0);
}

流程分析

存储卡加载流程

总结

从时序图中我们得知挂载相关联的类有VolumeManager、Disk、VolumeBase、StorageManagerService。挂载步骤如下：

1.到VolumeManager中接收到驱动层中的挂载信息后，会创建Disk对象并且调用其Create方法。

2.Disk中的Create方法会先通过binder方式调用onDiskCreated(getId(), mFlags)通知framework层的StorageManagerService，告诉其创建了Disk;r然后调用其成员方法 readMetadata()获取存储卡大小和标签告知framework层的StorageManagerService；再调用其成员方法readPartitions()解析存储卡类型创建Volume对象，通知framework层的StorageManagerService解析完成。

3.VolumeBase是基类，有三种卷，一个是PublicVolume是上面第二步骤解析的存储卡类型为mbr,一种事PrivateVolume解析的是gpt类型，还有一种是内部存储卡EmulatedVolume；中三种都是继承自BaseVolume。我们以PublicVolume为例，创建完volume对象后会调用其create方法，然后通知通知framework层的StorageManagerService volume创建完成。

4.StorageManagerService收到创建volume完成的消息后,会通过binder的方式回调mount的方法，这里首先会回调Binder服务端VoldNativeService中的mount方法，然后再调用VolumeBase中的mount方法。

5.VolumeBase收到mount方法后先发送准备挂载kChecking信息给StorageManagerService、执行挂载方法doMount,挂载成功后发送kMounted消息给StorageManagerService。

参考

https://blog.csdn.net/u014795729/article/details/132355702