MountService、vold(4)大容量ストレージ、MountServiceのメッセージメカニズムに深く入り込む(and 5.1)

大容量ストレージのインタフェースStorageManagerのコードは次のとおりです.

    public void enableUsbMassStorage() {
        try {
            mMountService.setUsbMassStorageEnabled(true);
        } catch (Exception ex) {
            Log.e(TAG, "Failed to enable UMS", ex);
        }
    }

    /**
     * Disables USB Mass Storage (UMS) on the device.
     *
     * @hide
     */
    public void disableUsbMassStorage() {
        try {
            mMountService.setUsbMassStorageEnabled(false);
        } catch (Exception ex) {
            Log.e(TAG, "Failed to disable UMS", ex);
        }
    }

MountServiceでのインタフェース

    public void setUsbMassStorageEnabled(boolean enable) {
        waitForReady();
        validatePermission(android.Manifest.permission.MOUNT_UNMOUNT_FILESYSTEMS);
        validateUserRestriction(UserManager.DISALLOW_USB_FILE_TRANSFER);
        final StorageVolume primary = getPhysicalVolume();
        if (primary == null){
            return;
        }
        // TODO: Add support for multiple share methods

        /*
         * If the volume is mounted and we're enabling then unmount it
         */
        String path = primary.getPath();
        String vs = getVolumeState(path);
        String method = "ums";
        if (enable && vs.equals(Environment.MEDIA_MOUNTED)) {//       ，        
            // Override for isUsbMassStorageEnabled()
            setUmsEnabling(enable);
            UmsEnableCallBack umscb = new UmsEnableCallBack(path, method, true);//    ，    
            mHandler.sendMessage(mHandler.obtainMessage(H_UNMOUNT_PM_UPDATE, umscb));
            // Clear override
            setUmsEnabling(false);
        }
        /*
         * If we disabled UMS then mount the volume
         */
        if (!enable) {//    
            doShareUnshareVolume(path, method, enable);//     ，          sd 
            if (doMountVolume(path) != StorageResultCode.OperationSucceeded) {
                Slog.e(TAG, "Failed to remount " + path +
                        " after disabling share method " + method);
                /*
                 * Even though the mount failed, the unshare didn't so don't indicate an error.
                 * The mountVolume() call will have set the storage state and sent the necessary
                 * broadcasts.
                 */
            }
        }
    }

次にdoShareUnshareVolumeインタフェースを見てみましょう

    private void doShareUnshareVolume(String path, String method, boolean enable) {
        // TODO: Add support for multiple share methods
        if (!method.equals("ums")) {
            throw new IllegalArgumentException(String.format("Method %s not supported", method));
        }

        try {
            mConnector.execute("volume", enable ? "share" : "unshare", path, method);//    
        } catch (NativeDaemonConnectorException e) {
            Slog.e(TAG, "Failed to share/unshare", e);
        }
    }

大容量オープンを実行すると、まずメッセージが送信され、MountServiceのメッセージメカニズムも分析されます.

        if (enable && vs.equals(Environment.MEDIA_MOUNTED)) {//       ，        
            // Override for isUsbMassStorageEnabled()
            setUmsEnabling(enable);
            UmsEnableCallBack umscb = new UmsEnableCallBack(path, method, true);//    
            mHandler.sendMessage(mHandler.obtainMessage(H_UNMOUNT_PM_UPDATE, umscb));
            // Clear override
            setUmsEnabling(false);
        }

MountServiceのメッセージを分析し、H_を送信します.UNMOUNT_PM_UPDATEメッセージの後、handlerは処理し、そのUnmountCallBackオブジェクトをmForceUnmountsリストに追加します.

    class MountServiceHandler extends Handler {
        ArrayList mForceUnmounts = new ArrayList();
        boolean mUpdatingStatus = false;

        MountServiceHandler(Looper l) {
            super(l);
        }

        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case H_UNMOUNT_PM_UPDATE: {
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "H_UNMOUNT_PM_UPDATE");
                    UnmountCallBack ucb = (UnmountCallBack) msg.obj;
                    mForceUnmounts.add(ucb);
                    if (DEBUG_UNMOUNT) Slog.i(TAG, " registered = " + mUpdatingStatus);
                    // Register only if needed.
                    if (!mUpdatingStatus) {
                        if (DEBUG_UNMOUNT) Slog.i(TAG, "Updating external media status on PackageManager");
                        mUpdatingStatus = true;
                        mPms.updateExternalMediaStatus(false, true);
                    }
                    break;
                }
                case H_UNMOUNT_PM_DONE: {
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "H_UNMOUNT_PM_DONE");
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "Updated status. Processing requests");
                    mUpdatingStatus = false;
                    int size = mForceUnmounts.size();
                    int sizeArr[] = new int[size];
                    int sizeArrN = 0;
                    // Kill processes holding references first
                    ActivityManagerService ams = (ActivityManagerService)
                    ServiceManager.getService("activity");
                    for (int i = 0; i < size; i++) {
                        UnmountCallBack ucb = mForceUnmounts.get(i);
                        String path = ucb.path;
                        boolean done = false;
                        if (!ucb.force) {
                            done = true;
                        } else {
                            int pids[] = getStorageUsers(path);
                            if (pids == null || pids.length == 0) {
                                done = true;
                            } else {
                                // Eliminate system process here?
                                ams.killPids(pids, "unmount media", true);
                                // Confirm if file references have been freed.
                                pids = getStorageUsers(path);
                                if (pids == null || pids.length == 0) {
                                    done = true;
                                }
                            }
                        }
                        if (!done && (ucb.retries < MAX_UNMOUNT_RETRIES)) {
                            // Retry again
                            Slog.i(TAG, "Retrying to kill storage users again");
                            mHandler.sendMessageDelayed(
                                    mHandler.obtainMessage(H_UNMOUNT_PM_DONE,
                                            ucb.retries++),
                                    RETRY_UNMOUNT_DELAY);
                        } else {
                            if (ucb.retries >= MAX_UNMOUNT_RETRIES) {
                                Slog.i(TAG, "Failed to unmount media inspite of " +
                                        MAX_UNMOUNT_RETRIES + " retries. Forcibly killing processes now");
                            }
                            sizeArr[sizeArrN++] = i;
                            mHandler.sendMessage(mHandler.obtainMessage(H_UNMOUNT_MS,
                                    ucb));
                        }
                    }
                    // Remove already processed elements from list.
                    for (int i = (sizeArrN-1); i >= 0; i--) {
                        mForceUnmounts.remove(sizeArr[i]);
                    }
                    break;
                }
                case H_UNMOUNT_MS: {
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "H_UNMOUNT_MS");
                    UnmountCallBack ucb = (UnmountCallBack) msg.obj;
                    ucb.handleFinished();
                    break;
                }

hander処理H_UNMOUNT_PM_UPDATEメッセージ、最後にPMSのupdateExternalMediaStatusインタフェースを呼び出します.その役割を分析しないで、UPDATEDを送信したのを見てみましょう.MEDIA_STATUSというニュース

    @Override
    public void updateExternalMediaStatus(final boolean mediaStatus, final boolean reportStatus) {
        int callingUid = Binder.getCallingUid();
        if (callingUid != 0 && callingUid != Process.SYSTEM_UID) {
            throw new SecurityException("Media status can only be updated by the system");
        }
        // reader; this apparently protects mMediaMounted, but should probably
        // be a different lock in that case.
        synchronized (mPackages) {
            Log.i(TAG, "Updating external media status from "
                    + (mMediaMounted ? "mounted" : "unmounted") + " to "
                    + (mediaStatus ? "mounted" : "unmounted"));
            if (DEBUG_SD_INSTALL)
                Log.i(TAG, "updateExternalMediaStatus:: mediaStatus=" + mediaStatus
                        + ", mMediaMounted=" + mMediaMounted);
            if (mediaStatus == mMediaMounted) {
                final Message msg = mHandler.obtainMessage(UPDATED_MEDIA_STATUS, reportStatus ? 1
                        : 0, -1);
                mHandler.sendMessage(msg);//    
                return;
            }
            mMediaMounted = mediaStatus;
        }
        // Queue up an async operation since the package installation may take a
        // little while.
        mHandler.post(new Runnable() {
            public void run() {
                updateExternalMediaStatusInner(mediaStatus, reportStatus, true);
            }
        });
    }

PMSのhandler処理を見て、MountServiceのfinishMediaUpdateメソッドを呼び出しました

                case UPDATED_MEDIA_STATUS: {
                    if (DEBUG_SD_INSTALL) Log.i(TAG, "Got message UPDATED_MEDIA_STATUS");
                    boolean reportStatus = msg.arg1 == 1;
                    boolean doGc = msg.arg2 == 1;
                    if (DEBUG_SD_INSTALL) Log.i(TAG, "reportStatus=" + reportStatus + ", doGc = " + doGc);
                    if (doGc) {
                        // Force a gc to clear up stale containers.
                        Runtime.getRuntime().gc();
                    }
                    if (msg.obj != null) {
                        @SuppressWarnings("unchecked")
                        Set args = (Set) msg.obj;
                        if (DEBUG_SD_INSTALL) Log.i(TAG, "Unloading all containers");
                        // Unload containers
                        unloadAllContainers(args);
                    }
                    if (reportStatus) {
                        try {
                            if (DEBUG_SD_INSTALL) Log.i(TAG, "Invoking MountService call back");
                            PackageHelper.getMountService().finishMediaUpdate();
                        } catch (RemoteException e) {
                            Log.e(TAG, "MountService not running?");
                        }
                    }
                } break;

MountServiceで最後にH_を送信しましたUNMOUNT_PM_DONEメッセージ

    public void finishMediaUpdate() {
        mHandler.sendEmptyMessage(H_UNMOUNT_PM_DONE);
    }

次はhandler対H_UNMOUNT_PM_DONEメッセージの処理

                case H_UNMOUNT_PM_DONE: {
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "H_UNMOUNT_PM_DONE");
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "Updated status. Processing requests");
                    mUpdatingStatus = false;
                    int size = mForceUnmounts.size();
                    int sizeArr[] = new int[size];
                    int sizeArrN = 0;
                    // Kill processes holding references first
                    ActivityManagerService ams = (ActivityManagerService)
                    ServiceManager.getService("activity");
                    for (int i = 0; i < size; i++) {//     mForceUnmounts
                        UnmountCallBack ucb = mForceUnmounts.get(i);
                        String path = ucb.path;
                        boolean done = false;
                        if (!ucb.force) {//ucb      force true            volume   ，  kill
                            done = true;
                        } else {
                            int pids[] = getStorageUsers(path);
                            if (pids == null || pids.length == 0) {//    pid，   volume  
                                done = true;
                            } else {
                                // Eliminate system process here?
                                ams.killPids(pids, "unmount media", true);
                                // Confirm if file references have been freed.
                                pids = getStorageUsers(path);
                                if (pids == null || pids.length == 0) {
                                    done = true;//     done  true
                                }
                            }
                        }
                        if (!done && (ucb.retries < MAX_UNMOUNT_RETRIES)) {
                            // Retry again
                            Slog.i(TAG, "Retrying to kill storage users again");
                            mHandler.sendMessageDelayed(//  done  true，      ，     MAX_UNMOUNT_RETRIES
                                    mHandler.obtainMessage(H_UNMOUNT_PM_DONE,
                                            ucb.retries++),
                                    RETRY_UNMOUNT_DELAY);
                        } else {
                            if (ucb.retries >= MAX_UNMOUNT_RETRIES) {
                                Slog.i(TAG, "Failed to unmount media inspite of " +
                                        MAX_UNMOUNT_RETRIES + " retries. Forcibly killing processes now");
                            }
                            sizeArr[sizeArrN++] = i;
                            mHandler.sendMessage(mHandler.obtainMessage(H_UNMOUNT_MS,
                                    ucb));//     H_UNMOUNT_MS  
                        }
                    }
                    // Remove already processed elements from list.
                    for (int i = (sizeArrN-1); i >= 0; i--) {
                        mForceUnmounts.remove(sizeArr[i]);
                    }
                    break;
                }

H_UNMOUNT_MSメッセージは、ucbを実行するhandleFinished関数です.

                case H_UNMOUNT_MS: {
                    if (DEBUG_UNMOUNT) Slog.i(TAG, "H_UNMOUNT_MS");
                    UnmountCallBack ucb = (UnmountCallBack) msg.obj;
                    ucb.handleFinished();
                    break;
                }

前に大容量のnewを開いたUmsEnableCallBackオブジェクトを見てみましょう

        if (enable && vs.equals(Environment.MEDIA_MOUNTED)) {
            // Override for isUsbMassStorageEnabled()
            setUmsEnabling(enable);
            UmsEnableCallBack umscb = new UmsEnableCallBack(path, method, true);
            mHandler.sendMessage(mHandler.obtainMessage(H_UNMOUNT_PM_UPDATE, umscb));
            // Clear override
            setUmsEnabling(false);
        }

そのhandleFinishedインタフェースはdoShareUnshareVolumeを呼び出し、voldにshareコマンドを送信します.

    class UmsEnableCallBack extends UnmountCallBack {
        final String method;

        UmsEnableCallBack(String path, String method, boolean force) {
            super(path, force, false);
            this.method = method;
        }

        @Override
        void handleFinished() {
            super.handleFinished();
            doShareUnshareVolume(path, method, true);
        }
    }

MountServiceでは、Unmountと大容量ストレージがオンの場合にのみ、このメッセージが送信されます.この2つの動作は他のpidを許さず,このvolumeの下のpathを用いることを説明する.voldでは、Unmountの場合もこのpathを使用するpidをすべてkillします.しかし、大容量ストレージを開くと、どのpidがこのvolumeのpathを使用しているかはチェックされません.
次に、大容量ストレージvoldとMountServiceのインタラクションを開く方法を見てみましょう.
voldはMountServiceからshareコマンドを受け取り、CommandListenerからコマンドを配布し、最後にVolumeManagement::shareVolume

int VolumeManager::shareVolume(const char *label, const char *method) {
    Volume *v = lookupVolume(label);//  volume

    if (!v) {
        errno = ENOENT;
        return -1;
    }

    /*
     * Eventually, we'll want to support additional share back-ends,
     * some of which may work while the media is mounted. For now,
     * we just support UMS
     */
    if (strcmp(method, "ums")) {
        errno = ENOSYS;
        return -1;
    }

    if (v->getState() == Volume::State_NoMedia) {
        errno = ENODEV;
        return -1;
    }

    if (v->getState() != Volume::State_Idle) {
        // You need to unmount manually befoe sharing
        errno = EBUSY;
        return -1;
    }

    if (mVolManagerDisabled) {
        errno = EBUSY;
        return -1;
    }

    dev_t d = v->getShareDevice();
    if ((MAJOR(d) == 0) && (MINOR(d) == 0)) {
        // This volume does not support raw disk access
        errno = EINVAL;
        return -1;
    }

    int fd;
    char nodepath[255];
    int written = snprintf(nodepath,//nodepath       
             sizeof(nodepath), "/dev/block/vold/%d:%d",
             major(d), minor(d));//

    if ((written < 0) || (size_t(written) >= sizeof(nodepath))) {
        SLOGE("shareVolume failed: couldn't construct nodepath");
        return -1;
    }

    if ((fd = open(MASS_STORAGE_FILE_PATH, O_WRONLY)) < 0) {
        SLOGE("Unable to open ums lunfile (%s)", strerror(errno));
        return -1;
    }

    if (write(fd, nodepath, strlen(nodepath)) < 0) {// "/sys/class/android_usb/android0/f_mass_storage/lun/file"      
        SLOGE("Unable to write to ums lunfile (%s)", strerror(errno));
        close(fd);
        return -1;
    }

    close(fd);
    v->handleVolumeShared();//       State_Shared，    MountService。    setState(Volume::State_Shared);
    if (mUmsSharingCount++ == 0) {
        FILE* fp;
        mSavedDirtyRatio = -1; // in case we fail
        if ((fp = fopen("/proc/sys/vm/dirty_ratio", "r+"))) {
            char line[16];
            if (fgets(line, sizeof(line), fp) && sscanf(line, "%d", &mSavedDirtyRatio)) {
                fprintf(fp, "%d
", mUmsDirtyRatio);
            } else {
                SLOGE("Failed to read dirty_ratio (%s)", strerror(errno));
            }
            fclose(fp);
        } else {
            SLOGE("Failed to open /proc/sys/vm/dirty_ratio (%s)", strerror(errno));
        }
    }
    return 0;
}

MountServiceはOnEventでvoldからStateを受信しましたSharedステータスではnotifyVolumeStateChange関数が呼び出されます.updatePublicVolumeStateという関数では各listenerに通知されます.

        } else if (newState == VolumeState.Shared) {
            if (DEBUG_EVENTS) Slog.i(TAG, "Updating volume state media mounted");
            /* Send the media unmounted event first */
            updatePublicVolumeState(volume, Environment.MEDIA_UNMOUNTED);//       MEDIA_UNMOUNTED，
            sendStorageIntent(Intent.ACTION_MEDIA_UNMOUNTED, volume, UserHandle.ALL);

            if (DEBUG_EVENTS) Slog.i(TAG, "Updating media shared");
            updatePublicVolumeState(volume, Environment.MEDIA_SHARED);//     MEDIA_SHARED
            action = Intent.ACTION_MEDIA_SHARED;
            if (LOCAL_LOGD) Slog.d(TAG, "Sending ACTION_MEDIA_SHARED intent");
        }

voldのunshareに対する処理を見てみると、その経路の下に0と書いて、上位のStateを送信しただけです.Idleステータス

int VolumeManager::unshareVolume(const char *label, const char *method) {
    Volume *v = lookupVolume(label);

    if (!v) {
        errno = ENOENT;
        return -1;
    }

    if (strcmp(method, "ums")) {
        errno = ENOSYS;
        return -1;
    }

    if (v->getState() != Volume::State_Shared) {
        errno = EINVAL;
        return -1;
    }

    int fd;
    if ((fd = open(MASS_STORAGE_FILE_PATH, O_WRONLY)) < 0) {//        
        SLOGE("Unable to open ums lunfile (%s)", strerror(errno));
        return -1;
    }

    char ch = 0;
    if (write(fd, &ch, 1) < 0) {//     0
        SLOGE("Unable to write to ums lunfile (%s)", strerror(errno));
        close(fd);
        return -1;
    }

    close(fd);
    v->handleVolumeUnshared();//  setState(Volume::State_Idle);
    if (--mUmsSharingCount == 0 && mSavedDirtyRatio != -1) {
        FILE* fp;
        if ((fp = fopen("/proc/sys/vm/dirty_ratio", "r+"))) {
            fprintf(fp, "%d
", mSavedDirtyRatio);
            fclose(fp);
        } else {
            SLOGE("Failed to open /proc/sys/vm/dirty_ratio (%s)", strerror(errno));
        }
        mSavedDirtyRatio = -1;
    }
    return 0;
}

MountServiceはまずブロードキャストを送信し、Volumeの状態をMEDIA_に設定します.UNMOUNTED

        if (oldState == VolumeState.Shared && newState != oldState) {
            if (LOCAL_LOGD) Slog.d(TAG, "Sending ACTION_MEDIA_UNSHARED intent");
            sendStorageIntent(Intent.ACTION_MEDIA_UNSHARED, volume, UserHandle.ALL);//    
        }

        if (newState == VolumeState.Init) {
        } else if (newState == VolumeState.NoMedia) {
            // NoMedia is handled via Disk Remove events
        } else if (newState == VolumeState.Idle) {
            /*
             * Don't notify if we're in BAD_REMOVAL, NOFS, UNMOUNTABLE, or
             * if we're in the process of enabling UMS
             */
            if (!state.equals(
                    Environment.MEDIA_BAD_REMOVAL) && !state.equals(
                            Environment.MEDIA_NOFS) && !state.equals(
                                    Environment.MEDIA_UNMOUNTABLE) && !getUmsEnabling()) {
                if (DEBUG_EVENTS) Slog.i(TAG, "updating volume state for media bad removal nofs and unmountable");
                updatePublicVolumeState(volume, Environment.MEDIA_UNMOUNTED);
                action = Intent.ACTION_MEDIA_UNMOUNTED;
            }
        }

大容量がオンになっているかどうかを確認

    private boolean doGetVolumeShared(String path, String method) {
        final NativeDaemonEvent event;
        try {
            event = mConnector.execute("volume", "shared", path, method);
        } catch (NativeDaemonConnectorException ex) {
            Slog.e(TAG, "Failed to read response to volume shared " + path + " " + method);
            return false;
        }

        if (event.getCode() == VoldResponseCode.ShareEnabledResult) {
            return event.getMessage().endsWith("enabled");
        } else {
            return false;
        }
    }

voldはVolumeの状態がStateかどうかを見るShared

int VolumeManager::shareEnabled(const char *label, const char *method, bool *enabled) {
    Volume *v = lookupVolume(label);

    if (!v) {
        errno = ENOENT;
        return -1;
    }

    if (strcmp(method, "ums")) {
        errno = ENOSYS;
        return -1;
    }

    if (v->getState() != Volume::State_Shared) {
        *enabled = false;
    } else {
        *enabled = true;
    }
    return 0;
}

これで大容量でMountServiceに格納された解析は終了しますが、UsbDeviceManagerでもこの内容があるので、次回分析しましょう!
MountServiceのメッセージメカニズムは参考になり、メッセージメカニズムを利用してエラー遅延処理を行うことができます.