Android6.0 MountService和vold详解（三） vold SD卡、otg

既上面两篇博客，继续分析vold、对外置SD卡和OTG的分析：

一、process_config函数

上一篇我们再main函数中分析了VolumeManager的start函数，这次我们接下来分析process_config函数

static int process_config(VolumeManager *vm) {
    std::string path(android::vold::DefaultFstabPath());
    fstab = fs_mgr_read_fstab(path.c_str());
    if (!fstab) {
        PLOG(ERROR) << "Failed to open default fstab " << path;
        return -1;
    }

    /* Loop through entries looking for ones that vold manages */
    bool has_adoptable = false;
    for (int i = 0; i < fstab->num_entries; i++) {
        if (fs_mgr_is_voldmanaged(&fstab->recs[i])) {
            if (fs_mgr_is_nonremovable(&fstab->recs[i])) {
                LOG(WARNING) << "nonremovable no longer supported; ignoring volume";
                continue;
            }

            std::string sysPattern(fstab->recs[i].blk_device);
            std::string nickname(fstab->recs[i].label);
            int flags = 0;

            if (fs_mgr_is_encryptable(&fstab->recs[i])) {
                flags |= android::vold::Disk::Flags::kAdoptable;
                has_adoptable = true;
            }
            if (fs_mgr_is_noemulatedsd(&fstab->recs[i])
                    || property_get_bool("vold.debug.default_primary", false)) {
                flags |= android::vold::Disk::Flags::kDefaultPrimary;
            }
	    PLOG(ERROR) << "process_config:" <<" sysPattern:" << sysPattern <<" nickname:" << nickname<<" end";
            vm->addDiskSource(std::shared_ptr<VolumeManager::DiskSource>(
                    new VolumeManager::DiskSource(sysPattern, nickname, flags)));
        }
    }
    property_set("vold.has_adoptable", has_adoptable ? "1" : "0");
    return 0;
}

process_config函数就是遍历fstab文件，下面就是fstab文件

# Android fstab file.
#<src>                                         <mnt_point>  <type>  <mnt_flags and options>  <fs_mgr_flags>
# 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

/dev/block/platform/comip-mmc.1/by-name/system                    /system          ext4    ro,barrier=1                                                    wait
/dev/block/platform/comip-mmc.1/by-name/cache                     /cache           ext4    noatime,nosuid,nodev,barrier=1,data=ordered                     wait,check
/dev/block/platform/comip-mmc.1/by-name/userdata                  /data            ext4    noatime,nosuid,nodev,barrier=1,data=ordered,noauto_da_alloc     wait,check,encryptable=footer
#/dev/block/platform/comip-mmc.1/by-name/amt                      /amt             ext4    rw                                                              wait
/devices/platform/comip-mmc.0/mmc_host/mmc1/*                       auto             vfat    defaults                                                        voldmanaged=sdcard1:auto,encryptable=false
/devices/a0400000.usb_hcd/usb1/*                                    auto      vfat    defaults        voldmanaged=usbotg:auto,noemulatedsd
/dev/block/mmcblk1p1                                              /sdcard                vfat  defaults  recoveryonly
/dev/block/platform/comip-mmc.1/by-name/kernel                                /kernel          emmc        defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk                   /boot                  emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_recovery          /recovery        emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_amt1              /ramdisk_amt1    emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/ramdisk_amt3              /ramdisk_amt3    emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/kernel_recovery           /kernel_recovery emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/logo                      /logo            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/misc                      /misc            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/fota                      /fota            emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/modemarm                  /modemarm        emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/modemdsp                  /modemdsp        emmc    defaults    defaults
/dev/block/mmcblk0boot0                                           /uboot           emmc    defaults    defaults
/dev/block/platform/comip-mmc.1/by-name/lcboot                          /lcboot          emmc    defaults    defaults
/dev/block/zram0                                                  none          swap    defaults        zramsize=268435456

简单说上面的函数就是遍历fstab文件中有voldmanaged的那项，然后新建一个DiskSource对象，加入volumeManager。

我们再来看看上面加的log的打印

01-01 09:00:25.347   164   164 E vold    :process_config: sysPattern:/devices/platform/comip-mmc.0/mmc_host/mmc1/* nickname:sdcard1 end: Success
01-01 09:00:25.347   164   164 E vold    :process_config: sysPattern:/devices/a0400000.usb_hcd/usb1/* nickname:usbotg end: Success

一个nickname是sdcard1，另一个是usbotg。

二、Disk的创建

下面我们来看下kernel对sdcard的检测到之后，通知vold后，vold如何操作。

kernel收到插入sd或者otg的event后，先到NetlinkHandler的onEvent函数，这个在之前分析android5.1的时候分析过了，不再详述。

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")) {
        vm->handleBlockEvent(evt);
    }
}

然后就到VolumeManager的handleBlockEvent函数，我们先看add的处理

void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
    std::lock_guard<std::mutex> lock(mLock);

    if (mDebug) {
        LOG(VERBOSE) << "----------------";
        LOG(VERBOSE) << "handleBlockEvent with action " << (int) evt->getAction();
        evt->dump();
    }

    std::string eventPath(evt->findParam("DEVPATH"));
    std::string devType(evt->findParam("DEVTYPE"));

    if (devType != "disk") return;

    int major = atoi(evt->findParam("MAJOR"));
    int minor = atoi(evt->findParam("MINOR"));
    dev_t device = makedev(major, minor);

    switch (evt->getAction()) {
    case NetlinkEvent::Action::kAdd: {
        for (auto source : mDiskSources) {//把之前在process_config中加入的disksources的资源遍历，看是否有匹配的
            if (source->matches(eventPath)) {
                // For now, assume that MMC devices are SD, and that
                // everything else is USB
                int flags = source->getFlags();
                if (major == kMajorBlockMmc) {
                    flags |= android::vold::Disk::Flags::kSd;
                } else {
                    flags |= android::vold::Disk::Flags::kUsb;
                }

                auto disk = new android::vold::Disk(eventPath, device,
                        source->getNickname(), flags);
                disk->create();
                mDisks.push_back(std::shared_ptr<android::vold::Disk>(disk));
                break;
            }
        }
        break;
    }

遍历之前在process_config函数中放入VolumeManager的DiskSource，看看是否有匹配的。匹配的新建一个Disk对象，放入VolumeManager的mDisks中。并且调用disk的create函数：

status_t Disk::create() {
    CHECK(!mCreated);
    mCreated = true;
    notifyEvent(ResponseCode::DiskCreated, StringPrintf("%d", mFlags));
    readMetadata();
    readPartitions();
    return OK;
}

在create函数中，先给MountService发送了DiskCreated的消息，我们看看MountService是如何处理的？

在MountService中在onEventLocked中对DiskCreated处理，也是放在mDisks变量中

    private boolean onEventLocked(int code, String raw, String[] cooked) {
        switch (code) {
            case VoldResponseCode.DISK_CREATED: {
                if (cooked.length != 3) break;
                final String id = cooked[1];
                int flags = Integer.parseInt(cooked[2]);
                if (SystemProperties.getBoolean(StorageManager.PROP_FORCE_ADOPTABLE, false)
                        || mForceAdoptable) {
                    flags |= DiskInfo.FLAG_ADOPTABLE;
                }
                mDisks.put(id, new DiskInfo(id, flags));
                break;
            }

下面继续分析disk的create函数,看Disk::readMetadata函数

status_t Disk::readMetadata() {
    mSize = -1;
    mLabel.clear();

    int fd = open(mDevPath.c_str(), O_RDONLY | O_CLOEXEC);
    if (fd != -1) {
        if (ioctl(fd, BLKGETSIZE64, &mSize)) {
            mSize = -1;
        }
        close(fd);
    }

    switch (major(mDevice)) {
    case kMajorBlockScsiA: case kMajorBlockScsiB: case kMajorBlockScsiC: case kMajorBlockScsiD:
    case kMajorBlockScsiE: case kMajorBlockScsiF: case kMajorBlockScsiG: case kMajorBlockScsiH:
    case kMajorBlockScsiI: case kMajorBlockScsiJ: case kMajorBlockScsiK: case kMajorBlockScsiL:
    case kMajorBlockScsiM: case kMajorBlockScsiN: case kMajorBlockScsiO: case kMajorBlockScsiP: {
        std::string path(mSysPath + "/device/vendor");
        std::string tmp;
        if (!ReadFileToString(path, &tmp)) {
            PLOG(WARNING) << "Failed to read vendor from " << path;
            return -errno;
        }
        mLabel = tmp;
        break;
    }
    case kMajorBlockMmc: {
        std::string path(mSysPath + "/device/manfid");
        std::string tmp;
        if (!ReadFileToString(path, &tmp)) {
            PLOG(WARNING) << "Failed to read manufacturer from " << path;
            return -errno;
        }
        uint64_t manfid = strtoll(tmp.c_str(), nullptr, 16);
        // Our goal here is to give the user a meaningful label, ideally
        // matching whatever is silk-screened on the card.  To reduce
        // user confusion, this list doesn't contain white-label manfid.
        switch (manfid) {
        case 0x000003: mLabel = "SanDisk"; break;
        case 0x00001b: mLabel = "Samsung"; break;
        case 0x000028: mLabel = "Lexar"; break;
        case 0x000074: mLabel = "Transcend"; break;
        }
        break;
    }
    default: {
        LOG(WARNING) << "Unsupported block major type" << major(mDevice);
        return -ENOTSUP;
    }
    }

    notifyEvent(ResponseCode::DiskSizeChanged, StringPrintf("%" PRId64, mSize));
    notifyEvent(ResponseCode::DiskLabelChanged, mLabel);
    notifyEvent(ResponseCode::DiskSysPathChanged, mSysPath);
    return OK;
}

这个函数主要获取一些参数，然后发送给MountService,而MountService的处理如下，主要是把disk的参数修改下

            case VoldResponseCode.DISK_SIZE_CHANGED: {
                if (cooked.length != 3) break;
                final DiskInfo disk = mDisks.get(cooked[1]);
                if (disk != null) {
                    disk.size = Long.parseLong(cooked[2]);
                }
                break;
            }
            case VoldResponseCode.DISK_LABEL_CHANGED: {
                final DiskInfo disk = mDisks.get(cooked[1]);
                if (disk != null) {
                    final StringBuilder builder = new StringBuilder();
                    for (int i = 2; i < cooked.length; i++) {
                        builder.append(cooked[i]).append(' ');
                    }
                    disk.label = builder.toString().trim();
                }
                break;
            }
            case VoldResponseCode.DISK_SCANNED: {
                if (cooked.length != 2) break;
                final DiskInfo disk = mDisks.get(cooked[1]);
                if (disk != null) {
                    onDiskScannedLocked(disk);
                }
                break;
            }
            case VoldResponseCode.DISK_SYS_PATH_CHANGED: {
                if (cooked.length != 3) break;
                final DiskInfo disk = mDisks.get(cooked[1]);
                if (disk != null) {
                    disk.sysPath = cooked[2];
                }
                br

下面我们继续看Disk的readParttitions函数

status_t Disk::readPartitions() {
    int8_t maxMinors = getMaxMinors();
    if (maxMinors < 0) {
        return -ENOTSUP;
    }

    destroyAllVolumes();

    // Parse partition table

    std::vector<std::string> cmd;
    cmd.push_back(kSgdiskPath);
    cmd.push_back("--android-dump");
    cmd.push_back(mDevPath);

    std::vector<std::string> output;
    status_t res = ForkExecvp(cmd, output);
    if (res != OK) {
        LOG(WARNING) << "sgdisk failed to scan " << mDevPath;
        notifyEvent(ResponseCode::DiskScanned);
        mJustPartitioned = false;
        return res;
    }

    Table table = Table::kUnknown;
    bool foundParts = false;
    for (auto line : output) {
        char* cline = (char*) line.c_str();
        char* token = strtok(cline, kSgdiskToken);
        if (token == nullptr) continue;

        if (!strcmp(token, "DISK")) {
            const char* type = strtok(nullptr, kSgdiskToken);
            if (!strcmp(type, "mbr")) {
                table = Table::kMbr;
            } else if (!strcmp(type, "gpt")) {
                table = Table::kGpt;
            }
        } else if (!strcmp(token, "PART")) {
            foundParts = true;
            int i = strtol(strtok(nullptr, kSgdiskToken), nullptr, 10);
            if (i <= 0 || i > maxMinors) {
                LOG(WARNING) << mId << " is ignoring partition " << i
                        << " beyond max supported devices";
                continue;
            }
            dev_t partDevice = makedev(major(mDevice), minor(mDevice) + i);

            if (table == Table::kMbr) {
                const char* type = strtok(nullptr, kSgdiskToken);

                switch (strtol(type, nullptr, 16)) {
                case 0x06: // FAT16
                case 0x0b: // W95 FAT32 (LBA)
                case 0x0c: // W95 FAT32 (LBA)
                case 0x0e: // W95 FAT16 (LBA)
                    createPublicVolume(partDevice);
                    break;
                }
            } else if (table == Table::kGpt) {
                const char* typeGuid = strtok(nullptr, kSgdiskToken);
                const char* partGuid = strtok(nullptr, kSgdiskToken);

                if (!strcasecmp(typeGuid, kGptBasicData)) {
                    createPublicVolume(partDevice);
                } else if (!strcasecmp(typeGuid, kGptAndroidExpand)) {
                    createPrivateVolume(partDevice, partGuid);
                }
            }
        }
    }

    // Ugly last ditch effort, treat entire disk as partition
    if (table == Table::kUnknown || !foundParts) {
        LOG(WARNING) << mId << " has unknown partition table; trying entire device";

        std::string fsType;
        std::string unused;
        if (ReadMetadataUntrusted(mDevPath, fsType, unused, unused) == OK) {
            createPublicVolume(mDevice);
        } else {
            LOG(WARNING) << mId << " failed to identify, giving up";
        }
    }

    notifyEvent(ResponseCode::DiskScanned);
    mJustPartitioned = false;
    return OK;
}

这个函数就主要会createPublicVolume或者createPrivateVolume，然后会通知MountService DiskScanned消息。先看上层对这个消息的处理。

            case VoldResponseCode.DISK_SCANNED: {
                if (cooked.length != 2) break;
                final DiskInfo disk = mDisks.get(cooked[1]);
                if (disk != null) {
                    onDiskScannedLocked(disk);
                }
                break;
            }

找到DiskInfo后，调用了onDiskScannedLocked函数

    private void onDiskScannedLocked(DiskInfo disk) {
        int volumeCount = 0;
        for (int i = 0; i < mVolumes.size(); i++) {
            final VolumeInfo vol = mVolumes.valueAt(i);
            if (Objects.equals(disk.id, vol.getDiskId())) {
                volumeCount++;
            }
        }

        final Intent intent = new Intent(DiskInfo.ACTION_DISK_SCANNED);
        intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);
        intent.putExtra(DiskInfo.EXTRA_DISK_ID, disk.id);
        intent.putExtra(DiskInfo.EXTRA_VOLUME_COUNT, volumeCount);
        mHandler.obtainMessage(H_INTERNAL_BROADCAST, intent).sendToTarget();

        final CountDownLatch latch = mDiskScanLatches.remove(disk.id);
        if (latch != null) {
            latch.countDown();
        }

        disk.volumeCount = volumeCount;
        mCallbacks.notifyDiskScanned(disk, volumeCount);
    }

这个函数中发送了广播，然后通知了回调。

三、CreatePublicVolume

接下来我们主要分析下createPublicVolume和createPrivateVolume两个函数。

先看createPublicVolume函数：

void Disk::createPublicVolume(dev_t device) {
    auto vol = std::shared_ptr<VolumeBase>(new PublicVolume(device));
    if (mJustPartitioned) {
        LOG(DEBUG) << "Device just partitioned; silently formatting";
        vol->setSilent(true);
        vol->create();
        vol->format("auto");
        vol->destroy();
        vol->setSilent(false);
    }

    mVolumes.push_back(vol);
    vol->setDiskId(getId());
    vol->create();
}

这个函数中，先新建了一个PublicVolume，然后让如了Disk的mVolumes中，最后调用了volume的create函数

status_t VolumeBase::create() {
    CHECK(!mCreated);

    mCreated = true;
    status_t res = doCreate();
    notifyEvent(ResponseCode::VolumeCreated,
            StringPrintf("%d \"%s\" \"%s\"", mType, mDiskId.c_str(), mPartGuid.c_str()));
    setState(State::kUnmounted);
    return res;
}

create函数又回调之前分析过得，给上层发送VolumeCreated消息
只是这个create的doCreate函数在PublicVolume中有实现：

status_t PublicVolume::doCreate() {
    return CreateDeviceNode(mDevPath, mDevice);
}

然后往MountService发送VolumeCreated后，MountService会往vold发送mount。

status_t VolumeBase::mount() {
    if ((mState != State::kUnmounted) && (mState != State::kUnmountable)) {
        LOG(WARNING) << getId() << " mount requires state unmounted or unmountable";
        return -EBUSY;
    }

    setState(State::kChecking);
    status_t res = doMount();
    if (res == OK) {
        setState(State::kMounted);
    } else {
        setState(State::kUnmountable);
    }

    return res;
}

在Volumebase执行mount函数的时候，到doMount是一个虚函数会到PublicVolume的doMount函数

status_t PublicVolume::doMount() {
    // TODO: expand to support mounting other filesystems
    readMetadata();

    if (mFsType != "vfat") {
        LOG(ERROR) << getId() << " unsupported filesystem " << mFsType;
        return -EIO;
    }

    if (vfat::Check(mDevPath)) {
        LOG(ERROR) << getId() << " failed filesystem check";
        return -EIO;
    }

    // Use UUID as stable name, if available
    std::string stableName = getId();
    if (!mFsUuid.empty()) {
        stableName = mFsUuid;
    }

    mRawPath = StringPrintf("/mnt/media_rw/%s", stableName.c_str());//挂载地址，stableName为uuid

    mFuseDefault = StringPrintf("/mnt/runtime/default/%s", stableName.c_str());
    mFuseRead = StringPrintf("/mnt/runtime/read/%s", stableName.c_str());
    mFuseWrite = StringPrintf("/mnt/runtime/write/%s", stableName.c_str());

    setInternalPath(mRawPath);
    if (getMountFlags() & MountFlags::kVisible) {
        setPath(StringPrintf("/storage/%s", stableName.c_str()));
    } else {
        setPath(mRawPath);
    }

    if (fs_prepare_dir(mRawPath.c_str(), 0700, AID_ROOT, AID_ROOT) ||
            fs_prepare_dir(mFuseDefault.c_str(), 0700, AID_ROOT, AID_ROOT) ||
            fs_prepare_dir(mFuseRead.c_str(), 0700, AID_ROOT, AID_ROOT) ||
            fs_prepare_dir(mFuseWrite.c_str(), 0700, AID_ROOT, AID_ROOT)) {
        PLOG(ERROR) << getId() << " failed to create mount points";
        return -errno;
    }

    if (vfat::Mount(mDevPath, mRawPath, false, false, false,//挂载sd卡
            AID_MEDIA_RW, AID_MEDIA_RW, 0007, true)) {
        PLOG(ERROR) << getId() << " failed to mount " << mDevPath;
        return -EIO;
    }

    if (getMountFlags() & MountFlags::kPrimary) {
        initAsecStage();
    }

    if (!(getMountFlags() & MountFlags::kVisible)) {
        // Not visible to apps, so no need to spin up FUSE
        return OK;
    }

    dev_t before = GetDevice(mFuseWrite);

    if (!(mFusePid = fork())) {
        if (getMountFlags() & MountFlags::kPrimary) {//开启fuse文件系统，让storage下面的sd卡读取直接到mnt下挂载的地址
            if (execl(kFusePath, kFusePath,
                    "-u", "1023", // AID_MEDIA_RW
                    "-g", "1023", // AID_MEDIA_RW
                    "-U", std::to_string(getMountUserId()).c_str(),
                    "-w",
                    mRawPath.c_str(),
                    stableName.c_str(),
                    NULL)) {
                PLOG(ERROR) << "Failed to exec";
            }
        } else {
            if (execl(kFusePath, kFusePath,
                    "-u", "1023", // AID_MEDIA_RW
                    "-g", "1023", // AID_MEDIA_RW
                    "-U", std::to_string(getMountUserId()).c_str(),
                    mRawPath.c_str(),
                    stableName.c_str(),
                    NULL)) {
                PLOG(ERROR) << "Failed to exec";
            }
        }

        LOG(ERROR) << "FUSE exiting";
        _exit(1);
    }

    if (mFusePid == -1) {
        PLOG(ERROR) << getId() << " failed to fork";
        return -errno;
    }

    while (before == GetDevice(mFuseWrite)) {
        LOG(VERBOSE) << "Waiting for FUSE to spin up...";
        usleep(50000); // 50ms
    }

    return OK;
}

这个函数我们先看readMetadata函数，会读取各个参数，然后发送到MountService中，在上层会把这些参数保存在DiskInfo中

status_t PublicVolume::readMetadata() {
    status_t res = ReadMetadataUntrusted(mDevPath, mFsType, mFsUuid, mFsLabel);
    notifyEvent(ResponseCode::VolumeFsTypeChanged, mFsType);
    notifyEvent(ResponseCode::VolumeFsUuidChanged, mFsUuid);
    notifyEvent(ResponseCode::VolumeFsLabelChanged, mFsLabel);
    return res;
}

再看下面这段代码，当uuid不为空，statbleName为uuid

    if (!mFsUuid.empty()) {
        stableName = mFsUuid;
    }

doMount就是把sd卡设备挂载到mnt/media_rw下面创建一个uuid的目录。然后在Storage下面也有一个uuid的目录，用fuse文件系统连接起来。大家可以看上面代码的注释。

四、createPrivateVolume

下面我们再来看Disk的createPrivateVolume方法

void Disk::createPrivateVolume(dev_t device, const std::string& partGuid) {
    std::string normalizedGuid;
    if (NormalizeHex(partGuid, normalizedGuid)) {
        LOG(WARNING) << "Invalid GUID " << partGuid;
        return;
    }

    std::string keyRaw;
    if (!ReadFileToString(BuildKeyPath(normalizedGuid), &keyRaw)) {
        PLOG(ERROR) << "Failed to load key for GUID " << normalizedGuid;
        return;
    }

    LOG(DEBUG) << "Found key for GUID " << normalizedGuid;

    auto vol = std::shared_ptr<VolumeBase>(new PrivateVolume(device, keyRaw));
    if (mJustPartitioned) {
        LOG(DEBUG) << "Device just partitioned; silently formatting";
        vol->setSilent(true);
        vol->create();
        vol->format("auto");
        vol->destroy();
        vol->setSilent(false);
    }

    mVolumes.push_back(vol);
    vol->setDiskId(getId());
    vol->setPartGuid(partGuid);
    vol->create();
}

和PublicVolume类似我们就直接看privateVolume的doMount函数

tatus_t PrivateVolume::doMount() {
    if (readMetadata()) {
        LOG(ERROR) << getId() << " failed to read metadata";
        return -EIO;
    }

    mPath = StringPrintf("/mnt/expand/%s", mFsUuid.c_str());//mount地址
    setPath(mPath);

    if (PrepareDir(mPath, 0700, AID_ROOT, AID_ROOT)) {
        PLOG(ERROR) << getId() << " failed to create mount point " << mPath;
        return -EIO;
    }

    if (mFsType == "ext4") {//fs类型
        int res = ext4::Check(mDmDevPath, mPath);
        if (res == 0 || res == 1) {
            LOG(DEBUG) << getId() << " passed filesystem check";
        } else {
            PLOG(ERROR) << getId() << " failed filesystem check";
            return -EIO;
        }

        if (ext4::Mount(mDmDevPath, mPath, false, false, true)) {
            PLOG(ERROR) << getId() << " failed to mount";
            return -EIO;
        }

    } else if (mFsType == "f2fs") {
        int res = f2fs::Check(mDmDevPath);
        if (res == 0) {
            LOG(DEBUG) << getId() << " passed filesystem check";
        } else {
            PLOG(ERROR) << getId() << " failed filesystem check";
            return -EIO;
        }

        if (f2fs::Mount(mDmDevPath, mPath)) {
            PLOG(ERROR) << getId() << " failed to mount";
            return -EIO;
        }

    } else {
        LOG(ERROR) << getId() << " unsupported filesystem " << mFsType;
        return -EIO;
    }

    LOG(VERBOSE) << "Starting restorecon of " << mPath;

    // TODO: find a cleaner way of waiting for restorecon to finish
    property_set("selinux.restorecon_recursive", "");
    property_set("selinux.restorecon_recursive", mPath.c_str());

    char value[PROPERTY_VALUE_MAX];
    while (true) {
        property_get("selinux.restorecon_recursive", value, "");
        if (strcmp(mPath.c_str(), value) == 0) {
            break;
        }
        sleep(1);
        LOG(VERBOSE) << "Waiting for restorecon...";
    }

    LOG(VERBOSE) << "Finished restorecon of " << mPath;

    // Verify that common directories are ready to roll
    if (PrepareDir(mPath + "/app", 0771, AID_SYSTEM, AID_SYSTEM) ||//创建了各个目录
            PrepareDir(mPath + "/user", 0711, AID_SYSTEM, AID_SYSTEM) ||
            PrepareDir(mPath + "/media", 0770, AID_MEDIA_RW, AID_MEDIA_RW) ||
            PrepareDir(mPath + "/media/0", 0770, AID_MEDIA_RW, AID_MEDIA_RW) ||
            PrepareDir(mPath + "/local", 0751, AID_ROOT, AID_ROOT) ||
            PrepareDir(mPath + "/local/tmp", 0771, AID_SHELL, AID_SHELL)) {
        PLOG(ERROR) << getId() << " failed to prepare";
        return -EIO;
    }

    // Create a new emulated volume stacked above us, it will automatically
    // be destroyed during unmount
    std::string mediaPath(mPath + "/media");//只把media传过去，fuse给storage
    auto vol = std::shared_ptr<VolumeBase>(
            new EmulatedVolume(mediaPath, mRawDevice, mFsUuid));
    addVolume(vol);
    vol->create();

    return OK;
}

当然最后完成后setState（kMounted）会通知MountService，上层只会调用onVolumeStateChangedLocked会发送广播并且通知回调。

这样整个vold主要的流程分析完了，当然这边没有分析fuse的相关内容，等以后再分析吧！