Android4.4KitKat支持u盘功能

时间:2022-09-06 18:18:28

Android4.4KitKat支持u盘功能

作者:  发布日期:2014-05-14 23:16:13
Tag标签:功能  
  • Android U 盘功能实现和分析

    u 盘功能实现结果:

    Android4.4KitKat支持u盘功能

    u 盘会当成 usb storage 在 Settings Storage 里面显示。

    准备工作

    内核需支持 usb host需支持 FUSE 文件系统在 FS 选项里面配置即可(CONFIG_FUSE_FS=y)。

    Android 的配置

    配置 init.<board>.rc

        mkdir /storage/udisk0 0000 system system
    mkdir /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/udisk0
    class late_start
    disabled

    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" />

    挂载过程:

    /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 会解析 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 文件必须放在根目录 Vold 是 android 的后台进程将会一直监听 fatab 里面标记为 voldmanaged 的项目 如果没有标记则略过。没有标记的项目。可以交给 init 的 mount 命令处理但是不会监听所以你可以将recovery 和 cache 目录这样只需启动是挂载的目录项放在 fatab 里面交给 init 的 mount 命令处理例如三星 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 ro
    wait
    /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,ro
    wait
    /dev/block/platform/dw_mmc.0/by-name/boot /boot emmc defaults
    defaults
    /dev/block/platform/dw_mmc.0/by-name/recovery /recovery emmc defaults
    defaults
    /dev/block/platform/dw_mmc.0/by-name/misc /misc emmc defaults
    defaults
    /dev/block/mmcblk0boot0 /bootloader emmc defaults
    defaults

    在系统启动调用 mount :

    on fs
    mkdir /factory 0775 radio radio mount_all /fstab.manta

    同理 init 的 mount 也会忽略标记为 voldmanaged 的项目 init 的 mount 命令与 vold 的 mount 管理大有不同两者不能混用。

    MountService 与 Vold 联合挂载 u 盘

    MountService 与 Vold 会建立 socket 通信具体的挂载操作都是下发命令交给 Vold 去完成。 MountService 会解析我们配置的 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 获取到 list 里面的设备变化时将会发送 state change event MountService 在 onEvent 处理各种不同 state 其中获取到设备插入将会执行挂载操作:

                if (code == VoldResponseCode.VolumeDiskInserted) {
    new Thread("MountService#VolumeDiskInserted") {
    @Override
    public 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 只是发送 mount 命令给 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);

    最终 Vold 里面执行相应的 mount 操作我们的 u 盘是 vfat 格式我只测试了这个格式 Linux 下的格式没有测试因为 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;