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MountService作为Vold的客户端，会接收来自vold的消息，并且内部定义保存了各种Volume相关的状态定义： 1、VolumeState
class VolumeState {
public static final int Init = -1;
public static final int NoMedia = 0;
public static final int Idle = 1;
public static final int Pending = 2;
public static final int Checking = 3;
public static final int Mounted = 4;
public static final int Unmounting = 5;
public static final int Formatting = 6;
public static final int Shared = 7;
public static final int SharedMnt = 8;
}VoldResponseCode
class VoldResponseCode {
/*
* 100 series - Requestion action was initiated; expect another reply
* before proceeding with a new command.
*/
public static final int VolumeListResult = 110;
public static final int AsecListResult = 111;
public static final int StorageUsersListResult = 112;
public static final int CryptfsGetfieldResult = 113;
/*
* 200 series - Requestion action has been successfully completed.
*/
public static final int ShareStatusResult = 210;
public static final int AsecPathResult = 211;
public static final int ShareEnabledResult = 212;
/*
* 400 series - Command was accepted, but the requested action
* did not take place.
*/
public static final int OpFailedNoMedia = 401;
public static final int OpFailedMediaBlank = 402;
public static final int OpFailedMediaCorrupt = 403;
public static final int OpFailedVolNotMounted = 404;
public static final int OpFailedStorageBusy = 405;
public static final int OpFailedStorageNotFound = 406;
/*
* 600 series - Unsolicited broadcasts.
*/
public static final int VolumeStateChange = 605;
public static final int VolumeUuidChange = 613;
public static final int VolumeUserLabelChange = 614;
public static final int VolumeDiskInserted = 630;
public static final int VolumeDiskRemoved = 631;
public static final int VolumeBadRemoval = 632;
/*
* 700 series - fstrim
*/
public static final int FstrimCompleted = 700;
}1、MountService构造方法： 1.1、初始化MountService静态对象sSelf以及PackageManagerService，readStoregeListLocked方法会读取系统配置文件，初始化mVolumes对象。
sSelf = this;
mContext = context;
synchronized (mVolumesLock) {
readStorageListLocked();
}
// XXX: This will go away soon in favor of IMountServiceObserver
mPms = (PackageManagerService) ServiceManager.getService("package");readStorageListLocked方法，读取storage_list.xml文件。
private void readStorageListLocked() {
mVolumes.clear();
mVolumeStates.clear();
Resources resources = mContext.getResources();
int id = com.android.internal.R.xml.storage_list;
XmlResourceParser parser = resources.getXml(id);
AttributeSet attrs = Xml.asAttributeSet(parser);我这边的手机读取结果为：
04-21 21:50:36.230 D/MountService( 1269): got storage path: /storage/sdcard0 description: 内部存储设备 primary: true removable: false emulated: true mtpReserve: 100 allowMassStorage: false maxFileSize: 0 allowMtp: true如果是模拟分区，则：
if (emulated) {
// For devices with emulated storage, we create separate
// volumes for each known user.
mEmulatedTemplate = new StorageVolume(null, descriptionId, true, false,
true, mtpReserve, false, maxFileSize, null, allowMtp);
final UserManagerService userManager = UserManagerService.getInstance();
for (UserInfo user : userManager.getUsers(false)) {
createEmulatedVolumeForUserLocked(user.getUserHandle());
}
} 即：初始化mEmulatedTemplate。 如果不为 ：则构建StorageVolume，并加入到mVolumes中。
else {
if (path == null || description == null) {
Slog.e(TAG, "Missing storage path or description in readStorageList");
} else {
final StorageVolume volume = new StorageVolume(new File(path),
descriptionId, primary, removable, emulated, mtpReserve,
allowMassStorage, maxFileSize, null, allowMtp);
addVolumeLocked(volume);
// Until we hear otherwise, treat as unmounted
mVolumeStates.put(volume.getPath(), Environment.MEDIA_UNMOUNTED);
volume.setState(Environment.MEDIA_UNMOUNTED);
}1.2、开辟MountServcieHandler子线程
HandlerThread hthread = new HandlerThread(TAG);
hthread.start();
mHandler = new MountServiceHandler(hthread.getLooper());1.3、注册用户相关广播，多用户相关。
final IntentFilter userFilter = new IntentFilter();
userFilter.addAction(Intent.ACTION_USER_ADDED);
userFilter.addAction(Intent.ACTION_USER_REMOVED);
mContext.registerReceiver(mUserReceiver, userFilter, null, mHandler);1.4、如果主Volume设备允许massStorage，则监听usb状态：
// Watch for USB changes on primary volume
final StorageVolume primary = getPrimaryPhysicalVolume();
if ((primary != null && primary.allowMassStorage()) ||
//ignore primary config, force to register if property is true
SystemProperties.getBoolean("persist.sys.ums", true)) {
mContext.registerReceiver(
mUsbReceiver, new IntentFilter(UsbManager.ACTION_USB_STATE), null, mHandler);
}1.5、构建NativeDaemonConnector，用户和vold进行socket通信。并为其开辟单独线程：
mConnector = new NativeDaemonConnector(this, "vold", MAX_CONTAINERS * 2, VOLD_TAG, 25,
null);
Thread thread = new Thread(mConnector, VOLD_TAG);
thread.start();NativeDaemonConnector将会和vold进程的CommandListener进行通信，第二个参数为vold，标示和vold进行通信，第一个参数为INativeDaemonConnectorCallbacks，其有三个回调：
void onDaemonConnected();
boolean onCheckHoldWakeLock(int code);
boolean onEvent(int code, String raw, String[] cooked);在和vold通信过程中，会回调执行onEvent方法。
2、在系统启动时，还会执行器systemReady方法：
public void systemReady() {
mSystemReady = true;
mHandler.obtainMessage(H_SYSTEM_READY).sendToTarget();
}case H_SYSTEM_READY: {
try {
handleSystemReady();
} catch (Exception ex) {
Slog.e(TAG, "Boot-time mount exception", ex);
}
break;
}在handleSystemReady中，会遍历当前存储块区，并更新其状态：
// Push mounted state for all emulated storage
synchronized (mVolumesLock) {
for (StorageVolume volume : mVolumes) {
if (volume.isEmulated()) {
updatePublicVolumeState(volume, Environment.MEDIA_MOUNTED);
}
}
}3、和vold进程通信，MountService会执行其onEvent方法：
public boolean onEvent(int code, String raw, String[] cooked) {
if (code == VoldResponseCode.VolumeStateChange) {
} else if (code == VoldResponseCode.VolumeUuidChange) {
} else if (code == VoldResponseCode.VolumeUserLabelChange) {
} else if ((code == VoldResponseCode.VolumeDiskInserted) ||
(code == VoldResponseCode.VolumeDiskRemoved) ||
(code == VoldResponseCode.VolumeBadRemoval)) {
} else if (code == VoldResponseCode.VolumeDiskRemoved) {
} else if (code == VoldResponseCode.VolumeBadRemoval) {
} else if (code == VoldResponseCode.FstrimCompleted) {
}
。。。。
}4、附storate_list.xml文件内容：
<StorageList xmlns:android="http://schemas.android.com/apk/res/android">
<!-- internal emulated storage -->
<storage android:mountPoint="/storage/sdcard0"
android:storageDescription="@string/storage_internal"
android:primary="true"
android:emulated="true"
android:removable="false"
android:mtpReserve="100" />
<storage android:mountPoint="/storage/sdcard1"
android:storageDescription="@string/storage_sd_card"
android:primary="false"
android:emulated="false"
android:removable="true"
android:allowMassStorage="true" />
<storage android:mountPoint="/storage/uicc0"
android:storageDescription="@string/storage_uicc"
android:primary="false"
android:emulated="false"
android:removable="true"
android:allowMassStorage="true" />
<storage android:mountPoint="/storage/uicc1"
android:storageDescription="@string/storage_uicc"
android:primary="false"
android:emulated="false"
android:removable="true"
android:allowMassStorage="false"
android:allowMtp="false" />
<storage android:mountPoint="/storage/usbotg"
android:storageDescription="@string/storage_usb"
android:primary="false"
android:emulated="false"
android:removable="true"
android:allowMassStorage="false" />
</StorageList>log描述：
04-21 21:50:36.230 D/MountService( 1269): got storage path: /storage/sdcard0 description: 内部存储设备 primary: true removable: false emulated: true mtpReserve: 100 allowMassStorage: false maxFileSize: 0 allowMtp: true
04-21 21:50:36.232 D/MountService( 1269): addVolumeLocked() StorageVolume:
04-21 21:50:36.232 D/MountService( 1269): mStorageId=65537 mPath=/storage/emulated/0 mDescriptionId=17040809
04-21 21:50:36.232 D/MountService( 1269): mPrimary=true mRemovable=false mEmulated=true mMtpReserveSpace=100
04-21 21:50:36.232 D/MountService( 1269): mAllowMassStorage=false mMaxFileSize=0 mOwner=UserHandle{0} mUuid=null
04-21 21:50:36.232 D/MountService( 1269): mUserLabel=null mState=null mAllowMtp=true
04-21 21:50:36.232 D/MountService( 1269): got storage path: /storage/sdcard1 description: SD卡 primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: true maxFileSize: 0 allowMtp: true
04-21 21:50:36.232 D/MountService( 1269): addVolumeLocked() StorageVolume:
04-21 21:50:36.232 D/MountService( 1269): mStorageId=0 mPath=/storage/sdcard1 mDescriptionId=17040810 mPrimary=false
04-21 21:50:36.232 D/MountService( 1269): mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=true
04-21 21:50:36.232 D/MountService( 1269): mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null
04-21 21:50:36.232 D/MountService( 1269): mAllowMtp=true
04-21 21:50:36.232 D/MountService( 1269): got storage path: /storage/uicc0 description: 电话卡存储设备 primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: true maxFileSize: 0 allowMtp: true
04-21 21:50:36.232 D/MountService( 1269): addVolumeLocked() StorageVolume:
04-21 21:50:36.232 D/MountService( 1269): mStorageId=0 mPath=/storage/uicc0 mDescriptionId=17040812 mPrimary=false
04-21 21:50:36.232 D/MountService( 1269): mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=true
04-21 21:50:36.232 D/MountService( 1269): mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null
04-21 21:50:36.232 D/MountService( 1269): mAllowMtp=true
04-21 21:50:36.232 D/MountService( 1269): got storage path: /storage/uicc1 description: 电话卡存储设备 primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0 allowMtp: false
04-21 21:50:36.233 D/MountService( 1269): addVolumeLocked() StorageVolume:
04-21 21:50:36.233 D/MountService( 1269): mStorageId=0 mPath=/storage/uicc1 mDescriptionId=17040812 mPrimary=false
04-21 21:50:36.233 D/MountService( 1269): mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=false
04-21 21:50:36.233 D/MountService( 1269): mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null
04-21 21:50:36.233 D/MountService( 1269): mAllowMtp=false
04-21 21:50:36.233 D/MountService( 1269): got storage path: /storage/usbotg description: USB存储器 primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0 allowMtp: true