Recovery过程

Recovery升级过程–（一）

recovery 从bootloader中启动

1. recovery程序入口

//bootable\recovery\recovery_main.cpp
int main(int argc, char** argv) {
    ...
    load_volume_table();//加载system/etc/recovery.fstab，结果如下：
    //[    0.002447]   0 /vendor  ext4 /dev/block/platform/soc/7824900.sdhci/by-name/vendor 0
    //[    0.002453]   1 /  ext4 /dev/block/bootdevice/by-name/system 0
    //[    0.002458]   2 /cache  ext4 /dev/block/bootdevice/by-name/cache 0
    //[    0.002466]   3 /vendor  ext4 /dev/block/bootdevice/by-name/vendor 0
    //[    0.002471]   4 /data  ext4 /dev/block/bootdevice/by-name/userdata 0
    //[    0.002476]   5 /sdcard  vfat /dev/block/mmcblk1p1 0
    //[    0.002481]   6 /boot  emmc /dev/block/bootdevice/by-name/boot 0
    //[    0.002485]   7 /recovery  emmc /dev/block/bootdevice/by-name/recovery 0
    //[    0.002491]   8 /misc  emmc /dev/block/bootdevice/by-name/misc 0
    //[    0.002496]   9 /tmp  ramdisk ramdisk 0
    has_cache = volume_for_mount_point(CACHE_ROOT) != nullptr;//检查Fstab中是否包含cache分区 true
    ...
    auto ret = fastboot ? StartFastboot(device, args) : start_recovery(device, args);//是否进入fastboot ,根据启动recover参数而定。升级执行start_recovery
    ...
}

2. 开始升级

//bootable\recovery\recovery.cpp
Device::BuiltinAction start_recovery(Device* device, const std::vector<std::string>& args){
	//解析参数,如下：
    //Command: "/system/bin/recovery" "--update_package=@/cache/recovery/block.map" "--locale=en-US"
    ...
    status = install_package(update_package, should_wipe_cache, true, retry_count, ui);//调用install_package安装
    ...
}

3. 安装逻辑

//bootable\recovery\install\install.cpp
int install_package(const std::string& path, bool should_wipe_cache, bool needs_mount,int retry_count, RecoveryUI* ui) {
	...
    if (needs_mount == true)
        result = setup_install_mounts();//挂载/tmp及cache 分区
    //调用really_install_package安装
    result = really_install_package(path, &updater_wipe_cache, needs_mount, &log_buffer,
                                    retry_count, &max_temperature, ui);
    ...
    int result =
      try_update_binary(path, zip, wipe_cache, log_buffer, retry_count, max_temperature, ui);
    ...
}

//bootable\recovery\install\install.cpp
static int try_update_binary(const std::string& package, ZipArchiveHandle zip, bool* wipe_cache,
                             std::vector<std::string>* log_buffer, int retry_count,
                             int* max_temperature, RecoveryUI* ui) {
    //1.检查是否AB升级还是BLOCK升级
    bool is_ab = android::base::GetBoolProperty("ro.build.ab_update", false);
    ...
    //创建升级命令保存到args，如：
    //"META-INF/com/google/android/update-binary" ,3,...
   	if (int update_status =is_ab ? SetUpAbUpdateCommands(package, zip, pipe_write.get(), &args) update_status != 0) {
         log_buffer->push_back(android::base::StringPrintf("error: %d", kUpdateBinaryCommandFailure));
   		return update_status;
    }
    //fork一个update-binary进程升级
    
                             
}

查源码中可以看到update-binary二进制文件是从bootable\recovery\updater编译得出

4. update-binary入口

int main(int argc, char** argv) {
	//解析META-INF/com/google/android/updater-script脚本
   	ZipString script_name(SCRIPT_NAME);
    int find_err = FindEntry(za, script_name, &script_entry);
    ...
    std::string script;
    script.resize(script_entry.uncompressed_length);
    int extract_err = ExtractToMemory(za, &script_entry, reinterpret_cast<uint8_t*>(&script[0]),
                                    script_entry.uncompressed_length);
    ...
    RegisterBuiltins();//注册控制流程的语句，如ifelse、assert、abort、stdout等
    RegisterInstallFunctions();//mount、is_mounted、unmount、format等
    RegisterBlockImageFunctions();//block_image_verify、block_image_update、block_image_recover、check_first_block、range_sha1
    RegisterDynamicPartitionsFunctions();//unmap_partition、map_partition、update_dynamic_partitions
    RegisterDeviceExtensions();//暂未实现
    ...
    int error = ParseString(script, &root, &error_count);
    State state(script, &updater_info);
    //执行升级脚本
    bool status = Evaluate(&state, root, &result);
}

5. 脚本语法介绍：

#bootable\recovery\edify\expr.cpp
- The && and || operators can be used similarly; they evaluate their
  second argument only if it's needed to determine the truth of the
  expression.  Their value is the value of the last-evaluated
  argument:
     file_exists("/data/system/bad") && delete("/data/system/bad")
     file_exists("/data/system/missing") || create("/data/system/missing")
     get_it() || "xxx"     # returns value of get_it() if that value is
                           # true, otherwise returns "xxx"