[AndroidContainer]sdcard分区挂载问题已知点分析

最新推荐文章于 2025-03-02 00:02:32 发布

b178903294

最新推荐文章于 2025-03-02 00:02:32 发布

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分类专栏： chrome os 文章标签： linux android chrome os

本文链接：https://blog.youkuaiyun.com/b178903294/article/details/115395826

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本文分析了ChromiumOS与Android容器之间的sdcard挂载问题，探讨了从Android的EmulatedVolume到ChromiumOS的挂载流程，涉及到esdfs、mount --bind、VoldNativeService以及binder通信。在ChromiumOS中，通过arc-setup将Android的数据目录挂载到容器内的相应位置，解决了权限和文件系统格式的问题。

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由 b178903294创建, 最后修改于1月 15, 2020 , 版权所有，谢绝转载

前言： chromiumOS与安卓容器之间不仅需要有数据沟通的桥梁ArcBridgeService 还要有文件交换的通道，那就是我们两个系统的下载目录。

chromiumOS这边编译时在build_packages添加esdfs USE标志并且在platform2/arc/setup/etc/config.json 中设置为"USE_ESDFS": true,

在/src/overlays/overlay-variant-coral-cvte/profiles/base/make.defaults中添加USE="${USE} esdfs"

即可由arc-setup 将/opt/google/containers/android/rootfs/android-data/media 挂载到/run/arc/sdcrd/(default || write || read)/emulated 并绑定挂载到/home/chronos/user/Downloads

*原生安卓*执行挂载流程，是由/system/vold/model/EmulatedVolume.cpp 中执行execl system/bin/sdcard 来执行挂载的。sdcard里面的挂载逻辑是判断安卓系统编译属性来确定是挂载哪种格式，详见代码/system/sdcard/sdcard.cpp

由于看见谷歌网上论坛的一个回帖： https://groups.google.com/a/chromium.org/forum/#!searchin/chromium-os-reviews/vold-sdcard%7Csort:date/chromium-os-reviews/DSsvjJupI_I/MtrIg-JjBwAJ 里面写道：

The current Android upstream design is that

vold -> sdcard.cpp (responsible for mounting) -> esdfs

The ARC++ design could be

vold -> sdcard.cpp (running outside of Android container) -> esdfs

我就坚信了是由sdcard.cpp实现的挂载操作。然后就遇到了权限问题，一头扎进了内核，寻找许久未果。

后来把fydeos 中的sdcard 文件加进自己编译的包中运行，发现报错如下：

failed to open fuse device: No such file or directory

failed to fuse_setup: No such file or directory

然后再谷歌和fydeos的机器上手动运行也同样报错：

sdcard E 11-22 19:45:18 1153 1153 sdcard.cpp:295] setting RLIMIT_NOFILE failed: Operation not permitted  （有时没有这句）

sdcard E 11-22 19:45:18 1153 1153 run_fuse.cpp:178] failed to open fuse device: No such file or directory

sdcard F 11-22 19:45:18 1153 1153 run_fuse.cpp:301] failed to fuse_setup: No such file or directory

既然是挂载esdfs 但是显然谷歌的sdcard文件还是在进行挂载fuse的逻辑中，并且同样会报错。因为没有/dev/fuse这个设备可以来进行挂载。

然后想到是vold调取sdcard文件的所以就查看了谷歌安卓容器中vold的log:

11-22 19:42:00.411 19 19 I vold : Vold 3.0 (the awakening) firing up

11-22 19:42:00.411 19 19 V vold : Detected support for: ext4

11-22 19:42:00.430 19 19 E vold : Failed open: No such file or directory

11-22 19:42:00.430 19 19 E vold : Failed to opendir: No such file or directory

11-22 19:42:00.437 19 19 I vold : [libfs_mgr]fs_mgr_read_fstab_dt(): failed to read fstab from dt

11-22 19:42:00.441 19 19 D vold : ArcVoldNativeService::start() completed OK

11-22 19:42:00.441 19 19 D vold : VoldNativeService::start() completed OK

11-22 19:42:00.456 19 21 D vold : e4crypt_init_user0

11-22 19:42:00.456 19 21 D vold : e4crypt_prepare_user_storage for volume null, user 0, serial 0, flags 1

11-22 19:42:00.456 19 21 D vold : Preparing: /data/system/users/0

11-22 19:42:00.456 19 21 E vold : Failed to prepare /data/system/users/0: No such file or directory

11-22 19:42:00.456 19 21 E vold : Failed to prepare user 0 storage

11-22 19:42:08.030 19 23 D vold : e4crypt_init_user0

11-22 19:42:08.030 19 23 D vold : e4crypt_prepare_user_storage for volume null, user 0, serial 0, flags 1

11-22 19:42:08.030 19 23 D vold : Preparing: /data/system/users/0

11-22 19:42:08.030 19 23 D vold : Preparing: /data/misc/profiles/cur/0

11-22 19:42:08.047 19 23 D vold : Preparing: /data/system_de/0

11-22 19:42:08.056 19 23 D vold : Preparing: /data/misc_de/0

11-22 19:42:08.102 19 23 D vold : Preparing: /data/vendor_de/0

11-22 19:42:08.114 19 23 D vold : Preparing: /data/user_de/0

11-22 19:42:08.122 19 23 V vold : /system/bin/vold_prepare_subdirs

11-22 19:42:08.122 19 23 V vold : prepare

11-22 19:42:08.122 19 23 V vold :

11-22 19:42:08.122 19 23 V vold : 0

11-22 19:42:08.122 19 23 V vold : 1

11-22 19:42:08.231 19 23 I vold_prepare_subdirs: SELinux: Loaded file_contexts

11-22 19:42:08.234   111   111 D vold_prepare_subdirs: Setting up mode 700 uid 0 gid 0 context u:object_r:vold_data_file:s0 on path:

/data/misc_de/0/vold

11-22 19:42:08.248   111   111 D vold_prepare_subdirs: Setting up mode 700 uid 0 gid 0 context u:object_r:storaged_data_file:s0 on path:

/data/misc_de/0/storaged

11-22 19:42:08.248   111   111 D vold_prepare_subdirs: Setting up mode 700 uid 1000 gid 1000 context u:object_r:fingerprint_vendor_data_file:s0 on path:

/data/vendor_de/0/fpdata

11-22 19:42:08.284 19 23 D vold : e4crypt_unlock_user_key 0 serial=0 token_present=0

11-22 19:42:12.683 19 23 D vold : e4crypt_unlock_user_key 0 serial=0 token_present=0

11-22 19:42:12.684   137   212 I ActivityManager: Force stopping com.android.providers.media appid=10006 user=-1: vold reset

11-22 19:42:12.687 19 23 I vold : Polling...: /var/run/arc/sdcard/write/emulated // 注意这两句

11-22 19:42:12.687 19 23 I vold : sdcard has been mounted

11-22 19:42:14.545 19 23 D vold : e4crypt_prepare_user_storage for volume null, user 0, serial 0, flags 2

11-22 19:42:14.545 19 23 D vold : Preparing: /data/system_ce/0

11-22 19:42:14.545 19 23 D vold : Preparing: /data/misc_ce/0

11-22 19:42:14.545 19 23 D vold : Preparing: /data/vendor_ce/0

11-22 19:42:14.545 19 23 D vold : Preparing: /data/media/0

11-22 19:42:14.545 19 23 D vold : Preparing: /data/data

11-22 19:42:14.545 19 23 V vold : Starting restorecon of /data/system_ce/0

11-22 19:42:14.592 19 23 V vold : Finished restorecon of /data/system_ce/0

11-22 19:42:14.592 19 23 V vold : Starting restorecon of /data/misc_ce/0

11-22 19:42:14.602 19 23 V vold : Finished restorecon of /data/misc_ce/0

11-22 19:42:14.602 19 23 V vold : /system/bin/vold_prepare_subdirs

看到了挂载成功的log,但是相关log在我们的代码中并没有。并且谷歌安卓容器里面的log 并没有看到任何sdcard的信息，即使最初的挂载格式提示也没有:

static bool should_use_sdcardfs(void

) {

char property[PROPERTY_VALUE_MAX];

// Allow user to have a strong opinion about state

property_get(PROP_SDCARDFS_USER, property, "");

if (!strcmp(property, "force_on"

)) {

LOG(WARNING) << "User explicitly enabled sdcardfs";

return true;

} else if (!strcmp(property, "force_off"

)) {

LOG(WARNING) << "User explicitly disabled sdcardfs";

return !supports_esdfs();

}

// Fall back to device opinion about state

if (property_get_bool(PROP_SDCARDFS_DEVICE, true

)) {

LOG(WARNING) << "Device explicitly enabled sdcardfs";

return true;

} else

LOG(WARNING) << "Device explicitly disabled sdcardfs";

return !supports_esdfs();

}

这段代码在https://chromium.googlesource.com/aosp/platform/system/core/+/refs/heads/upstream/sdcard/sdcard.cpp 无论是master分支和upstream分支都有这段代码，所以就想知道为什么没有打印这段代码。所以就把谷歌的sdcard文件直接二进制打开然后读里面的log字符，发现确实没有这几句。可能谷歌的这个sdcard就是直接挂载fuse的。二进制文件读出的log如下：

sdcard.txt ：sdcard

接着读谷歌vold二进制文件：

vold.txt ：vold

发现了几个点：

ArcVoldNativeService::start.

Unable to start ArcVoldNativeService.

ArcVoldNativeService::start() completed OK.

上面这个显然是重写了VoldNativeService.cpp 文件

102

103

104

105

106

107

108

mountAppFuse.arc_app_fuse_mounter_service. 参考(VoldNativeService.cpp +503)

system/vold/VoldNativeService.cpp.

Can not get ArcAppFuseMounterService.

unmountAppFuse.

open AppFuseFile.

这里应该是用到了AppFuseMount mojom。

158

159

arc_volume_mounter_service.

Could not get ArcVolumeMounterService.VolumeManager::updateVirtualDisk.

这里使用VolumeMounter mojom 进行mountevent 更新。

system/vold/model/ArcEmulatedVolume.cpp .Polling...: .sdcard has been mounted.

这里原来调用sdcard的EmulatedVolume.cpp文件重写了。所以考虑到没有看到sdcard挂载fuse失败的log ，严重怀疑就是在这里面执行了挂载逻辑而并没有使用sdcard程序。具体怎样绕过内核权限和mount namespace 将/opt/google/containers/android/rootfs/android-data/media 挂载到安卓rootfs 里的/mnt/runtime/(default || write || read)/emulated 都应该是在这里面实现的。

目前了解到的几个点都在这里。

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~下面分析vold sdcard挂载流程~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Volume Daemon,用于管理和控制Android平台外部存储设备的后台进程,这些管理和控制,包括SD卡的插拔事件检测/SD卡挂载/卸载/格式化等.

9.0以前framework java层(StorageManagerService)和native层(Vold)的通信是socket,9.0以后使用binder通信. 通过SD卡挂载流程,分析binder在vold服务中的使用.

vold服务在开机的时候会启动.定义于system/vold/vold.rc文件中：

service vold /system/bin/vold \

--blkid_context=u:r:blkid:s0 --blkid_untrusted_context=u:r:blkid_untrusted:s0 \

--fsck_context=u:r:fsck:s0 --fsck_untrusted_context=u:r:fsck_untrusted:s0

class core

ioprio be 2

writepid /dev/cpuset/foreground/tasks

shutdown critical

group reserved_disk

被init进程启动后，将调用system/vold/main.cpp中的main函数,然后初始化VolumeManager,NetlinkManager等等.初始化Vold服务.

在看下StorageManagerService的初始化.StorageManagerService由SystemServer启动，我们简单看看它的启动流程：

//调用SystemServiceManager的startService

mSystemServiceManager.startService(STORAGE_MANAGER_SERVICE_CLASS);

最终的实现如下:

public void

startService(@NonNull final SystemService service) {

// Register it.

mServices.add(service);

// Start it.

long time = SystemClock.elapsedRealtime();

try

//调用服务的onStart方法.

service.onStart();

} catch

(RuntimeException ex) {

throw new RuntimeException("Failed to start service " + service.getClass().getName()

+ ": onStart threw an exception", ex);

}

warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");

}

//StorageManagerService的onStart方法如下:

@Override

public void

onStart() {

//创建StorageManagerService

mStorageManagerService = new StorageManagerService(getContext());

//将StorageManagerService注册到ServiceManager中

publishBinderService("mount", mStorageManagerService);

//调用StorageManagerService的start方法

mStorageManagerService.start();

}

private void

start() {

connect();

}

//主要建立和Vold的通信,获取mVold对象,与Vold进程通信.

private void

connect() {

IBinder binder = ServiceManager.getService("storaged");

if

(binder != null) {

try

//为binder对象设置死亡代理。当binder死亡后重新建立连接.

binder.linkToDeath(new

DeathRecipient() {

@Override

public void

binderDied() {

Slog.w(TAG, "storaged died; reconnecting");

mStoraged = null;

connect();

}

}, 0);

} catch

(RemoteException e) {

binder = null;

}

if

(binder != null) {

mStoraged = IStoraged.Stub.asInterface(binder);

} else

Slog.w(TAG, "storaged not found; trying again");

}

binder = ServiceManager.getService("vold");

if

(binder != null) {

try

//为binder对象设置死亡代理。当binder死亡后重新建立连接.

binder.linkToDeath(new

DeathRecipient() {

@Override

public void

binderDied() {

Slog.w(TAG, "vold died; reconnecting");

mVold = null;

connect();

}

}, 0);

} catch

(RemoteException e) {

binder = null;

}

if

(binder != null) {

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