[RK3399][Android7.1] 調試筆記 --- sdcard守護程序啟動位置

Platform: RK3399

OS: Android 7.1

Kernel: v4.4.83

Board: Firefly-RK3399

之前版本sdcard守護程序都是放在init.rc中啟動:

service sdcard /system/bin/sdcard -u  -g  -l /data/media /mnt/shell/emulated
    class late_start
           

在Android7.1上被放在vold程序中啟動了：

status_t EmulatedVolume::doMount() {
    ......

    dev_t before = GetDevice(mFuseWrite);
    //kFusePath就是/system/bin/sdcard即守護程序的可執行檔案
    if (!(mFusePid = fork())) {
        if (execl(kFusePath, kFusePath,
                "-u", "1023", // AID_MEDIA_RW
                "-g", "1023", // AID_MEDIA_RW
                "-m",
                "-w",
                mRawPath.c_str(),
                label.c_str(),
                NULL)) {
            PLOG(ERROR) << "Failed to exec";
        }

        LOG(ERROR) << "FUSE exiting";
        _exit();
    }

    .....
    return OK;
}
           

那麼doMount()是如何調用到的呢？ 以下是調用流程：

main -> main.c //vold程序在rc檔案中啟動。
  vm->start ->
    VolumeManager::start -> VolumeManager.cpp
      new android::vold::EmulatedVolume("/data/media")); -> //資料是被存在/data/media路徑的
      mInternalEmulated->create -> //VolumeManager繼承了VolumeBase
        VolumeBase::create -> 
          notifyEvent -> //cmd是ResponseCode::VolumeCreated
            //vold是socket服務端，用戶端是MountService
            onEvent -> MountService.java
              onEventLocked ->   //cmd是名字改成VoldResponseCode.VOLUME_CREATED，但是值是一樣的。
                onVolumeCreatedLocked ->
                   mHandler.obtainMessage(H_VOLUME_MOUNT, vol).sendToTarget(); -> //交由MountServiceHandler類處理
                     handleMessage ->
                       mConnector.execute("volume", "mount",...); -> //利用NativeDaemonConnector中socket将消息發送給CommandListener
                         CommandListener::VolumeCmd::runCommand -> CommandListener.cpp //調用的類是VolumeCmd,cmd是mount
                           vol->mount -> 調用EmulatedVolume的基類VolumeBase ->
                             VolumeBase::mount -> VolumeBase.cpp
                               doMount -> //EmulatedVolume類實作了此虛函數
                                 EmulatedVolume::doMount //啟動sdcard程序
           

參考：

Android 7.0 Vold工作流程