Android6.0 MountService和vold詳解（三） vold SD卡、otg
阿新 • • 發佈：2019-02-02
既上面兩篇部落格，繼續分析vold、對外接SD卡和OTG的分析：
一、process_config函式
上一篇我們再main函式中分析了VolumeManager的start函式，這次我們接下來分析process_config函式
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函式就是遍歷fstab檔案，下面就是fstab檔案
# 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
簡單說上面的函式就是遍歷fstab檔案中有voldmanaged的那項，然後新建一個DiskSource物件，加入volumeManager。
我們再來看看上面加的log的列印
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
一個nickname是sdcard1，另一個是usbotg。
二、Disk的建立
下面我們來看下kernel對sdcard的檢測到之後，通知vold後，vold如何操作。
kernel收到插入sd或者otg的event後，先到NetlinkHandler的onEvent函式，這個在之前分析android5.1的時候分析過了，不再詳述。
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);
}
}
然後就到VolumeManager的handleBlockEvent函式，我們先看add的處理
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的資源遍歷，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;
}遍歷之前在process_config函式中放入VolumeManager的DiskSource，看看是否有匹配的。匹配的新建一個Disk物件，放入VolumeManager的mDisks中。並且呼叫disk的create函式：
status_t Disk::create() {
CHECK(!mCreated);
mCreated = true;
notifyEvent(ResponseCode::DiskCreated, StringPrintf("%d", mFlags));
readMetadata();
readPartitions();
return OK;
}在create函式中，先給MountService傳送了DiskCreated的訊息，我們看看MountService是如何處理的？
在MountService中在onEventLocked中對DiskCreated處理，也是放在mDisks變數中
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;
}下面繼續分析disk的create函式,看Disk::readMetadata函式
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;
}
這個函式主要獲取一些引數，然後傳送給MountService,而MountService的處理如下，主要是把disk的引數修改下
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下面我們繼續看Disk的readParttitions函式
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;
}這個函式就主要會createPublicVolume或者createPrivateVolume，然後會通知MountService DiskScanned訊息。先看上層對這個訊息的處理。
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後，呼叫了onDiskScannedLocked函式
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);
}這個函式中傳送了廣播，然後通知了回撥。
三、CreatePublicVolume
接下來我們主要分析下createPublicVolume和createPrivateVolume兩個函式。
先看createPublicVolume函式：
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();
}這個函式中，先新建了一個PublicVolume，然後讓如了Disk的mVolumes中，最後呼叫了volume的create函式
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函式又回撥之前分析過得，給上層傳送VolumeCreated訊息
只是這個create的doCreate函式在PublicVolume中有實現：
status_t PublicVolume::doCreate() {
return CreateDeviceNode(mDevPath, mDevice);
}
然後往MountService傳送VolumeCreated後，MountService會往vold傳送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執行mount函式的時候，到doMount是一個虛擬函式會到PublicVolume的doMount函式
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());//掛載地址，stableName為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,//掛載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) {//開啟fuse檔案系統，讓storage下面的sd卡讀取直接到mnt下掛載的地址
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;
}這個函式我們先看readMetadata函式，會讀取各個引數，然後傳送到MountService中，在上層會把這些引數儲存在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;
}再看下面這段程式碼，當uuid不為空，statbleName為uuid
if (!mFsUuid.empty()) {
stableName = mFsUuid;
}doMount就是把sd卡裝置掛載到mnt/media_rw下面建立一個uuid的目錄。然後在Storage下面也有一個uuid的目錄，用fuse檔案系統連線起來。大家可以看上面程式碼的註釋。
四、createPrivateVolume
下面我們再來看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類似我們就直接看privateVolume的doMount函式
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型別
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) ||//建立了各個目錄
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傳過去，fuse給storage
auto vol = std::shared_ptr<VolumeBase>(
new EmulatedVolume(mediaPath, mRawDevice, mFsUuid));
addVolume(vol);
vol->create();
return OK;
}當然最後完成後setState（kMounted）會通知MountService，上層只會呼叫onVolumeStateChangedLocked會發送廣播並且通知回撥。
這樣整個vold主要的流程分析完了，當然這邊沒有分析fuse的相關內容，等以後再分析吧！