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(
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.
#
# 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 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(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 cmd;
cmd.push_back(kSgdiskPath);
cmd.push_back("--android-dump");
cmd.push_back(mDevPath);
std::vector 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(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(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(
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！