Android4.4KitKat支持u盤功能

作者：??發布日期：2014-05-14 23:16:13 我來說兩句(0) 0 Tag標簽：功能??

• Android?U 盤功能實現和分析

  
  

  u 盤功能實現結果：

  u 盤會當成 usb storage 在 Settings Storage 里面顯示。?
  

  準備工作

  內核需支持 usb host，需支持 FUSE 文件系統，在 FS 選項里面配置即可（CONFIG_FUSE_FS=y）。?
  

  Android 的配置

  配置 init.<board>.rc

  mkdir /storage/udisk0 0000 system systemmkdir /mnt/media_rw/udisk0 0700 media_rw media_rw
  service fuse_udisk0 /system/bin/sdcard -u 1023 -g 1023 -w 1023 -d /mnt/media_rw/udisk0 /storage/udisk0class late_startdisabled
  

  配置 fstab.<board>

  /block/sda /mnt/media_rw/udisk0 vfat defaults voldmanaged=udisk0:auto
  

  配置 overlay

  <storage android:mountPoint="/storage/udisk0"android:storageDescription="@string/storage_usb"android:primary="false"android:removable="true" />
  

  掛載過程：

  /dev/block/vold/8:1 /mnt/media_rw/udisk0 vfat rw,dirsync,nosuid,nodev,noexec,relatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro 0 0 /dev/fuse /storage/udisk0 fuse rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other 0 0
  root@android:/ # logcat -s Vold MountService --------- beginning of /dev/log/main --------- beginning of /dev/log/system I/Vold ( 820): Vold 2.1 (the revenge) firing up D/Vold ( 820): Volume sdcard1 state changing -1 (Initializing) -> 0 (No-Media) D/Vold ( 820): Volume sdcard1 state changing -1 (Initializing) -> 0 (No-Media) D/Vold ( 820): Volume udisk0 state changing -1 (Initializing) -> 0 (No-Media) D/Vold ( 820): Volume udisk0 state changing 0 (No-Media) -> 2 (Pending) D/Vold ( 820): Volume udisk0 state changing 2 (Pending) -> 1 (Idle-Unmounted) D/Vold ( 820): Volume sdcard1 state changing 0 (No-Media) -> 2 (Pending) D/Vold ( 820): Volume sdcard1 state changing 2 (Pending) -> 1 (Idle-Unmounted) D/MountService( 1587): got storage path: /storage/sdcard0 description: Internal storage primary: true removable: false emulated: true mtpReserve: 50 allowMassStorage: false maxFileSize: 0 D/MountService( 1587): addVolumeLocked() StorageVolume: D/MountService( 1587): mStorageId=65537 mPath=/storage/emulated/0 mDescriptionId=17040662 D/MountService( 1587): mPrimary=true mRemovable=false mEmulated=true mMtpReserveSpace=50 D/MountService( 1587): mAllowMassStorage=false mMaxFileSize=0 mOwner=UserHandle{0} mUuid=null D/MountService( 1587): mUserLabel=null mState=null D/MountService( 1587): got storage path: /storage/sdcard1 description: SD card primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 4294967296 D/MountService( 1587): addVolumeLocked() StorageVolume: D/MountService( 1587): mStorageId=0 mPath=/storage/sdcard1 mDescriptionId=17040663 mPrimary=false D/MountService( 1587): mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=false D/MountService( 1587): mMaxFileSize=4294967296 mOwner=null mUuid=null mUserLabel=null mState=null D/MountService( 1587): got storage path: /storage/udisk0 description: USB storage primary: false removable: true emulated: false mtpReserve: 0 allowMassStorage: false maxFileSize: 0 D/MountService( 1587): addVolumeLocked() StorageVolume: D/MountService( 1587): mStorageId=0 mPath=/storage/udisk0 mDescriptionId=17040664 mPrimary=false D/MountService( 1587): mRemovable=true mEmulated=false mMtpReserveSpace=0 mAllowMassStorage=false D/MountService( 1587): mMaxFileSize=0 mOwner=null mUuid=null mUserLabel=null mState=null W/MountService( 1587): Duplicate state transition (unmounted -> unmounted) for /storage/sdcard1 D/MountService( 1587): volume state changed for /storage/sdcard1 (unmounted -> removed) W/MountService( 1587): Duplicate state transition (unmounted -> unmounted) for /storage/udisk0 I/Vold ( 820): /dev/block/vold/8:1 being considered for volume udisk0 D/Vold ( 820): Volume udisk0 state changing 1 (Idle-Unmounted) -> 3 (Checking) D/MountService( 1587): volume state changed for /storage/udisk0 (unmounted -> checking) D/MountService( 1587): sendStorageIntent Intent { act=android.intent.action.MEDIA_CHECKING dat=file:///storage/udisk0 (has extras) } to UserHandle{-1} I/Vold ( 820): Filesystem check completed OK D/Vold ( 820): blkid identified as /dev/block/vold/8:1: UUID="402E-0EE3" TYPE="vfat" D/Vold ( 820): Volume udisk0 state changing 3 (Checking) -> 4 (Mounted) D/MountService( 1587): volume state changed for /storage/udisk0 (checking -> mounted) D/MountService( 1587): sendStorageIntent Intent { act=android.intent.action.MEDIA_MOUNTED dat=file:///storage/udisk0 (has extras) } to UserHandle{-1} W/MountService( 1587): Duplicate state transition (mounted -> mounted) for /storage/emulated/0
  

  Vold 解析 fstab 文件

  在?Android?4.4 中，?Vold 會解析 vold.<hardware> 文件 property_get("ro.hardware", propbuf, "");snprintf(fstab_filename, sizeof(fstab_filename), FSTAB_PREFIX"%s", propbuf);fstab = fs_mgr_read_fstab(fstab_filename);if (!fstab) {SLOGE("failed to open %s\n", fstab_filename);return -1;}
  其中 #define FSTAB_PREFIX "/fstab." 所以，配置的 fatab 文件必須放在根目錄，?Vold 是 android 的后臺進程，將會一直監聽 fatab 里面標記為 voldmanaged 的項目 如果沒有標記，則略過。沒有標記的項目。可以交給 init 的 mount 命令處理，但是不會監聽，所以你可以將recovery 和 cache 目錄這樣只需啟動是掛載的目錄項放在 fatab 里面交給 init 的 mount 命令處理，例如三星 device/samsung/manta/fstab.manta # Android fstab file. #<src> <mnt_point> <type> <mnt_flags and opt ions> <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/dw_mmc.0/by-name/system /system ext4 rowait /dev/block/platform/dw_mmc.0/by-name/cache /cache ext4 noatime,nosuid,nodev,nombl k_io_submit,errors=panic wait,check /dev/block/platform/dw_mmc.0/by-name/userdata /data ext4 noatime,nosuid,nodev,nombl k_io_submit,errors=panic wait,check,encryptable=/dev/block/platform/dw_mmc.0/by-name/metadata /dev/block/platform/dw_mmc.0/by-name/efs /factory ext4 noatime,nosuid,nodev,rowait /dev/block/platform/dw_mmc.0/by-name/boot /boot emmc defaultsdefaults /dev/block/platform/dw_mmc.0/by-name/recovery /recovery emmc defaultsdefaults /dev/block/platform/dw_mmc.0/by-name/misc /misc emmc defaultsdefaults /dev/block/mmcblk0boot0 /bootloader emmc defaultsdefaults
  在系統啟動調用 mount ： on fsmkdir /factory 0775 radio radiomount_all /fstab.manta
  同理，?init 的 mount 也會忽略標記為 voldmanaged 的項目 init 的 mount 命令與 vold 的 mount 管理大有不同，兩者不能混用。?
  

  MountService 與 Vold 聯合掛載 u 盤

  MountService 與 Vold 會建立 socket 通信，具體的掛載操作都是下發命令，交給 Vold 去完成。 MountService 會解析我們配置的 storage_list.xml 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);try {XmlUtils.beginDocument(parser, TAG_STORAGE_LIST);while (true) {XmlUtils.nextElement(parser);
  Vold 獲取到 list 里面的設備變化時將會發送 state change event，?MountService 在 onEvent 處理各種不同 state?，其中獲取到設備插入，將會執行掛載操作： if (code == VoldResponseCode.VolumeDiskInserted) {new Thread("MountService#VolumeDiskInserted") {@Overridepublic void run() {try {int rc;if ((rc = doMountVolume(path)) != StorageResultCode.OperationSucceeded) {Slog.w(TAG, String.format("Insertion mount failed (%d)", rc));}} catch (Exception ex) {Slog.w(TAG, "Failed to mount media on insertion", ex);}}}.start();
  doMountVolume 只是發送 mount 命令給 Vold private int doMountVolume(String path) {int rc = StorageResultCode.OperationSucceeded;final StorageVolume volume;synchronized (mVolumesLock) {volume = mVolumesByPath.get(path);}if (DEBUG_EVENTS) Slog.i(TAG, "doMountVolume: Mouting " + path);try {mConnector.execute("volume", "mount", path);
  最終 Vold 里面執行相應的 mount 操作，我們的 u 盤是 vfat 格式，我只測試了這個格式，?Linux?下的格式沒有測試，因為 Vold 只支持 fat 和 ext4 int VolumeManager::mountVolume(const char *label) {Volume *v = lookupVolume(label);if (!v) {errno = ENOENT;return -1;}return v->mountVol(); }
  if (Fat::doMount(devicePath, getMountpoint(), false, false, false,AID_MEDIA_RW, AID_MEDIA_RW, 0007, true)) {SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno));continue;

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