Android7.0 Vold 進程工作機制分析之由Kernel發起掛載請求
一、MountService簡介
MountService是一個系統服務,負責與Vold進程通信的,運行在SystemServer進程,當收到Vold的掛載消息後,會通過廣播的方式通知上層應用.
它是在SystemServer的startOtherServices方法裏啓動的
SystemServer路徑——————/frameworks/base/services/java/com/android/server/SystemServer.java
private void startOtherServices() {
......
//如果不爲低級工廠測試
if (mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL) {
if (!disableStorage &&!"0".equals(SystemProperties.get("system_init.startmountservice"))) {
try {
//啓動MountService
mSystemServiceManager.startService(MOUNT_SERVICE_CLASS);
mountService = IMountService.Stub.asInterface(ServiceManager.getService("mount"));
} catch (Throwable e) {
reportWtf("starting Mount Service", e);
}
}
}
......
}
這裏並不打算詳細介紹MountService的啓動過程,只需關注它的構造方法即可(在啓動時會調用構造方法)
MountService路徑——————/frameworks/base/services/core/java/com/android/server/MountService.java
class MountService extends IMountService.Stub implements INativeDaemonConnectorCallbacks, Watchdog.Monitor {
......
public MountService(Context context) {
......
//創建並啓動一個帶消息循環的MountService工作線程
HandlerThread hthread = new HandlerThread(TAG);
hthread.start();
//爲MountService工作線程創建一個Handler
mHandler = new MountServiceHandler(hthread.getLooper());
......
/*
NativeDaemonConnector用於Socket通信,第二個參數“vold”表示將和Vold通信,也就是
和CL模塊中的那個socket建立通信連接。第一個參數爲INativeDaemonConnectorCallbacks
接口。它提供兩個回調函數:
onDaemonConnected:當NativeDaemonConnector連接上Vold後回調。
onEvent:當NativeDaemonConnector收到來自Vold的數據後回調。
*/
mConnector = new NativeDaemonConnector(this, "vold", MAX_CONTAINERS * 2, VOLD_TAG, 25,
null);
//創建線程名爲"VoldConnector"的線程,用於跟vold通信
mConnectorThread = new Thread(mConnector, VOLD_TAG);
......
}
主要做了以下幾件事
①創建並啓動一個帶消息循環的MountService工作線程 HandlerThread
②爲MountService工作線程創建一個Handler
③創建線程名爲”VoldConnector”的線程,用於跟vold通信
在MountService的start方法啓動這個線程
private void start() {
mConnectorThread.start();
}
這個VoldConnector線程在run方法裏會調用一個方法listenToSocket,監聽Vold進程發過來的Socket消息
NativeDaemonConnector路徑——/frameworks/base/services/core/java/com/android/server/NativeDaemonConnector.java
final class NativeDaemonConnector implements Runnable, Handler.Callback, Watchdog.Monitor {
......
@Override
public void run() {
mCallbackHandler = new Handler(mLooper, this);
while (true) {
try {
//監聽Vold進程發過來的socket消息
listenToSocket();
} catch (Exception e) {
loge("Error in NativeDaemonConnector: " + e);
SystemClock.sleep(5000);
}
}
}
......
}
在listenToSocket方法裏會建立Socket連接,把接收的消息解析成NativeDaemonEvent事件,通過mCallbackHandler處理這個事件
private void listenToSocket() throws IOException {
LocalSocket socket = null;
try {
socket = new LocalSocket();
LocalSocketAddress address = determineSocketAddress();
//建立與"/dev/socket/vold"的socket連接
socket.connect(address);
......
try {
//解析成 NativeDaemonEvent事件
final NativeDaemonEvent event = NativeDaemonEvent.parseRawEvent(rawEvent, fdList);
//當響應碼區間爲[600,700),則發送消息交由mCallbackHandler處理
Message msg = mCallbackHandler.obtainMessage( event.getCode(), uptimeMillisInt(), 0, event.getRawEvent());
......
}
}
關於MountService的簡介先到這裏,下面分析Kernel發起掛載請求的流程.
二、Kernel發起掛載請求的流程
上一篇文章Android7.0 Vold 進程工作機制分析之整體流程已經講了,Kernel是通過Netlink 進行通信的,Netlink 是一種特殊的Socket。
以下是上一篇文章的Vold 進程啓動時序圖(縮放瀏覽器可以放大查看或者在新標籤頁打開)
這裏以SD卡插入,Kernel掛載請求爲例,流程從NetlinkListener的onDataAvailable開始
1.NetlinkListener::onDataAvailable
bool NetlinkListener::onDataAvailable(SocketClient *cli)
{
int socket = cli->getSocket();
ssize_t count;
uid_t uid = -1;
......
NetlinkEvent *evt = new NetlinkEvent();
//解析獲得NetlinkEvent實例
if (evt->decode(mBuffer, count, mFormat)) {
//傳入NetlinkEvent實例
onEvent(evt);
}
......
}
解析獲得NetlinkEvent實例,調用onEvent方法,onEvent由子類NetlinkHandler實現
2.NetlinkHandler::onEvent
void NetlinkHandler::onEvent(NetlinkEvent *evt) {
//獲取VolumeManager 單例對象
VolumeManager *vm = VolumeManager::Instance();
const char *subsys = evt->getSubsystem();
if (!strcmp(subsys, "block")) {
//調用VolumeManager 的handleBlockEvent方法
vm->handleBlockEvent(evt);
}
}
獲取VolumeManager 的單例然後調用handleBlockEvent方法
3.vm->handleBlockEvent
void VolumeManager::handleBlockEvent(NetlinkEvent *evt) {
switch (evt->getAction()) {
case NetlinkEvent::Action::kAdd: {
for (auto source : mDiskSources) {
if (source->matches(eventPath)) {
......
auto disk = new android::vold::Disk(eventPath, device,source->getNickname(), flags);
//調用disk 的create方法
disk->create();
mDisks.push_back(std::shared_ptr<android::vold::Disk>(disk));
break;
}
}
break;
}
case NetlinkEvent::Action::kChange: {
......
break;
}
case NetlinkEvent::Action::kRemove: {
......
break;
}
......
}
}
SD卡插入爲add事件。那麼調用了disk->create()方法。
4.disk->create()
路徑:
disk.cpp———————–system/vold/disk.cpp
status_t Disk::create() {
CHECK(!mCreated);
mCreated = true;
//調用notifyEvent方法
notifyEvent(ResponseCode::DiskCreated, StringPrintf("%d", mFlags));
readMetadata();
//讀取分區數據,創建Volume
readPartitions();
return OK;
}
在create方法裏調用notifyEvent通知DiskCreated事件,然後還有readMetadata方法創建Volume.所有這裏也要分兩條線5和6
5. Disk::notifyEvent
void Disk::notifyEvent(int event) {
VolumeManager::Instance()->getBroadcaster()->sendBroadcast(event,getId().c_str(), false);
}
獲取單例VolumeManager對象,然後獲取到SocketListener對象調用sendBroadcast方法
sendBroadcast方法的實現如下
在safelist列表中添加SocketClient,然後調用sendMsg方法
5. 1 SocketListener::sendBroadcast
void SocketListener::sendBroadcast(int code, const char *msg, bool addErrno) {
SocketClientCollection safeList;
//首先添加所有活動的SockClient到安全列表中
safeList.clear();
for (i = mClients->begin(); i != mClients->end(); ++i) {
SocketClient* c = *i;
c->incRef();
//添加
safeList.push_back(c);
}
while (!safeList.empty()) {
/* Pop the first item from the list */
i = safeList.begin();
SocketClient* c = *i;
safeList.erase(i);
//調用SockClient的sendMSg方法發送消息
if (c->sendMsg(code, msg, addErrno, false)) {
SLOGW("Error sending broadcast (%s)", strerror(errno));
}
c->decRef();
}
}
SockClient
路徑:
SockClient.cpp————————system/core/libsysutils/src/SockClient.cpp
調用sendMsg方法經過層層跳轉,到sendDataLockedv方法中,往Socket中寫入信息
5.2 sendDataLockedv
int SocketClient::sendDataLockedv(struct iovec *iov, int iovcnt) {
......
for (;;) {
ssize_t rc = TEMP_FAILURE_RETRY(
writev(mSocket, iov + current, iovcnt - current));
......
}
寫入到Socket之後,SystemServer中的MountService會收到,就是前面講到的NativeDaemonConnector的listenToSocket方法
5.3 NativeDaemonConnector::listenToSocket
在listenToSocket方法裏會建立Socket連接,把接收的消息解析成NativeDaemonEvent事件,通過mCallbackHandler處理這個事件
private void listenToSocket() throws IOException {
LocalSocket socket = null;
try {
socket = new LocalSocket();
LocalSocketAddress address = determineSocketAddress();
//建立與"/dev/socket/vold"的socket連接
socket.connect(address);
......
try {
//解析成 NativeDaemonEvent事件
final NativeDaemonEvent event = NativeDaemonEvent.parseRawEvent(rawEvent, fdList);
//當響應碼區間爲[600,700),則發送消息交由mCallbackHandler處理
Message msg = mCallbackHandler.obtainMessage( event.getCode(), uptimeMillisInt(), 0, event.getRawEvent());
......
}
}
mCallbackHandler處理事件,HandleMessage方法如下
5.4 NativeDaemonConnector::handleMessage
@Override
public boolean handleMessage(Message msg) {
final String event = (String) msg.obj;
final int start = uptimeMillisInt();
final int sent = msg.arg1;
try {
if (!mCallbacks.onEvent(msg.what, event, NativeDaemonEvent.unescapeArgs(event))) {
log(String.format("Unhandled event '%s'", event));
}
}
......
return true;
}
在handleMessage方法裏會回調MountService的onEvent方法
5.5 MountService::onEvent
@Override
public boolean onEvent(int code, String raw, String[] cooked) {
synchronized (mLock) {
return onEventLocked(code, raw, cooked);
}
}
交給onEventLocked處理了
5.6 MountService::onEventLocked
private boolean onEventLocked(int code, String raw, String[] cooked) {
switch (code) {
//處理DISK_CREATED創建成功事件
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;
}
......
//這個事件就是之前4.disk->create()方法走第6條線最後回到這裏處理
//處理VOLUME_CREATED創建成功事件
case VoldResponseCode.VOLUME_CREATED: {
final String id = cooked[1];
final int type = Integer.parseInt(cooked[2]);
final String diskId = TextUtils.nullIfEmpty(cooked[3]);
final String partGuid = TextUtils.nullIfEmpty(cooked[4]);
final DiskInfo disk = mDisks.get(diskId);
final VolumeInfo vol = new VolumeInfo(id, type, disk, partGuid);
mVolumes.put(id, vol);
onVolumeCreatedLocked(vol);
break;
}
......
}
return true;
}
小結
在這裏處理了DISK_CREATED創建成功事件,至此這個事件傳遞就完了.我畫一張UML圖
(縮放瀏覽器可以放大查看或者在新標籤頁打開)
下面介紹的是從第6條線開始的流程
6 Disk::readPartitions()
在這個方法裏會讀取分區數據,然後創建Volume
status_t Disk::readPartitions() {
......
if (table == Table::kMbr) {
......
//6.2 創建PublicVolume
createPublicVolume(partDevice);
break;
}
} else if (table == Table::kGpt) {
......
if (!strcasecmp(typeGuid, kGptBasicData)) {
createPublicVolume(partDevice);
} else if (!strcasecmp(typeGuid, kGptAndroidExpand)) {
createPrivateVolume(partDevice, partGuid);
}
}
}
}
if (table == Table::kUnknown || !foundParts) {
......
if (ReadMetadataUntrusted(mDevPath, fsType, unused, unused) == OK) {
createPublicVolume(mDevice);
}
}
......
}
6.1 Disk::createPublicVolume()
void Disk::createPublicVolume(dev_t device) {
//獲取PublicVolume實例
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());
//調用VolumeBase的create方法
vol->create();
}
6.2 VolumeBase::create()
status_t VolumeBase::create() {
mCreated = true;
status_t res = doCreate();
//向VolumeManager發送VolumeCreated命令
notifyEvent(ResponseCode::VolumeCreated,StringPrintf("%d \"%s\" \"%s\"", mType, mDiskId.c_str(), mPartGuid.c_str()));
//設置已卸載狀態
setState(State::kUnmounted);
return res;
}
在這個方法裏通知VolumeManager創建了Volume,這個方法之後的步驟就和第5步以後一樣的了,就不重複介紹了.
之後走到5.6 MountService::onEventLocked方法裏的case VoldResponseCode.VOLUME_CREATED:處理,調用onVolumeCreatedLocked(vol)方法
6.3 MountService::onVolumeCreatedLocked()
class MountService extends IMountService.Stub implements INativeDaemonConnectorCallbacks, Watchdog.Monitor {
......
private void onVolumeCreatedLocked(VolumeInfo vol) {
......
if (vol.type == VolumeInfo.TYPE_EMULATED) {
final StorageManager storage = mContext.getSystemService(StorageManager.class);
final VolumeInfo privateVol = storage.findPrivateForEmulated(vol);
if (Objects.equals(StorageManager.UUID_PRIVATE_INTERNAL, mPrimaryStorageUuid)
&& VolumeInfo.ID_PRIVATE_INTERNAL.equals(privateVol.id)) {
Slog.v(TAG, "Found primary storage at " + vol);
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_PRIMARY;
vol.mountFlags |= VolumeInfo.MOUNT_FLAG_VISIBLE;
//handler發送消息
mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget();
......
}
}
之後走到Handler處理H_VOLUME_MOUNT消息
6.4 MountService::handleMessage()
class MountServiceHandler extends Handler {
public MountServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
......
case H_VOLUME_MOUNT: {
final VolumeInfo vol = (VolumeInfo) msg.obj;
if (isMountDisallowed(vol)) {
Slog.i(TAG, "Ignoring mount " + vol.getId() + " due to policy");
break;
}
try {
//執行mount(掛載)命令
mConnector.execute("volume", "mount", vol.id, vol.mountFlags,
vol.mountUserId);
} catch (NativeDaemonConnectorException ignored) {
}
break;
}
......
}
會調用NativeDaemonConnector的execute方法,經過跳轉到executeForList方法
6.5 NativeDaemonConnector::executeForList()
final class NativeDaemonConnector implements Runnable, Handler.Callback, Watchdog.Monitor {
......
public NativeDaemonEvent[] executeForList(long timeoutMs, String cmd, Object... args)
throws NativeDaemonConnectorException {
......
synchronized (mDaemonLock) {
if (mOutputStream == null) {
throw new NativeDaemonConnectorException("missing output stream");
} else {
try {
//往Socket 輸出流寫入命令
mOutputStream.write(rawCmd.getBytes(StandardCharsets.UTF_8));
} catch (IOException e) {
throw new NativeDaemonConnectorException("problem sending command", e);
}
}
......
}
往Socket寫入輸出流之後,Vold中FrameWorkListener的onDataAvailable會收到
6.6 FrameWorkListener::onDataAvailable()
bool FrameworkListener::onDataAvailable(SocketClient *c) {
char buffer[CMD_BUF_SIZE];
int len;
//讀取socket消息
len = TEMP_FAILURE_RETRY(read(c->getSocket(), buffer, sizeof(buffer)));
.....
int i;
for (i = 0; i < len; i++) {
if (buffer[i] == '\0') {
//根據消息內容 派發命令
dispatchCommand(c, buffer + offset);
offset = i + 1;
}
}
return true;
}
在onDataAvailable方法裏會先讀取Socket消息,然後分發命令
6.7 FrameWorkListener::dispatchCommand()
void FrameworkListener::dispatchCommand(SocketClient *cli, char *data) {
......
//執行對應的消息
for (i = mCommands->begin(); i != mCommands->end(); ++i) {
FrameworkCommand *c = *i;
//匹配命令
if (!strcmp(argv[0], c->getCommand())) {
//執行命令
if (c->runCommand(cli, argc, argv)) {
SLOGW("Handler '%s' error (%s)", c->getCommand(), strerror(errno));
}
goto out;
}
}
......
}
會調用FrameworkCommand 的runCommand方法,之前在CommandListener的構造方法裏註冊的這些指令,就是FrameWorkCommand類型,如下
FrameworkListener.cpp
void FrameworkListener::registerCmd(FrameworkCommand *cmd) {
//添加元素
mCommands->push_back(cmd);
}
CommandListener.cpp
CommandListener::CommandListener() :FrameworkListener("vold", true) {
//註冊多條指令
registerCmd(new DumpCmd());
registerCmd(new VolumeCmd());
registerCmd(new AsecCmd());
registerCmd(new ObbCmd());
registerCmd(new StorageCmd());
registerCmd(new FstrimCmd());
registerCmd(new AppFuseCmd());
}
這裏插入SD卡是掛載指令,即VolumeCmd指令,會進入到VolumeCmd的runCommand方法
6.8 CommandListener::runCommand()
CommandListener.cpp
int CommandListener::VolumeCmd::runCommand(SocketClient *cli, int argc, char **argv) {
......
} else if (cmd == "mount" && argc > 2) {
// mount [volId] [flags] [user]
std::string id(argv[2]);
auto vol = vm->findVolume(id);
if (vol == nullptr) {
return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume", false);
}
int mountFlags = (argc > 3) ? atoi(argv[3]) : 0;
userid_t mountUserId = (argc > 4) ? atoi(argv[4]) : -1;
vol->setMountFlags(mountFlags);
vol->setMountUserId(mountUserId);
//執行真正的掛載操作
int res = vol->mount();
if (mountFlags & android::vold::VolumeBase::MountFlags::kPrimary) {
vm->setPrimary(vol);
}
//發送應答消息給MountService
return sendGenericOkFail(cli, res);
......
}
}
會執行實際的mount操作
6.9 vol->mount()
vol是VolumeBase的實例,VolumeBase的mount方法由具體的子類EmulatedVolume、PublicVolume、PrivateVolume等實現
執行操作之後會發送應答消息給MountService.
status_t VolumeBase::mount() {
......
setState(State::kChecking);
//doMount由子類實現實際掛載操作
status_t res = doMount();
if (res == OK) {
setState(State::kMounted);
} else {
setState(State::kUnmountable);
}
return res;
}
6.10 PublicVolume->doMount()
PublicVolume.cpp
status_t PublicVolume::doMount() {
......
}
三、小結
至此,這個掛載操作就完成了.時序圖如下:
下一篇講解從上層MountService發起掛載請求的流程.