Android 11属性系统初始化流程

在init进程启动的第二阶段，调用PropertyInit 对属性系统进行初始化

int SecondStageMain(int argc, char** argv) {
	//省略
	PropertyInit();
	//省略
}

PropertyInit函数在system\core\init\property_service.cpp 中实现

void PropertyInit() {
   //省略
    mkdir("/dev/__properties__", S_IRWXU | S_IXGRP | S_IXOTH); //1
    CreateSerializedPropertyInfo();//2
    if (__system_property_area_init()) {//3
        LOG(FATAL) 
        LOG(FATAL) 
    auto property_infos = std::vector
        if (!LoadPropertyInfoFromFile("/system/etc/selinux/plat_property_contexts",
                                      &property_infos)) {
            return;
        }
        // Don't check for failure here, so we always have a sane list of properties.
        // E.g. In case of recovery, the vendor partition will not have mounted and we
        // still need the system / platform properties to function.
        if (access("/system_ext/etc/selinux/system_ext_property_contexts", R_OK) != -1) {
            LoadPropertyInfoFromFile("/system_ext/etc/selinux/system_ext_property_contexts",
                                     &property_infos);
        }
        if (!LoadPropertyInfoFromFile("/vendor/etc/selinux/vendor_property_contexts",
                                      &property_infos)) {
            // Fallback to nonplat_* if vendor_* doesn't exist.
            LoadPropertyInfoFromFile("/vendor/etc/selinux/nonplat_property_contexts",
                                     &property_infos);
        }
        if (access("/product/etc/selinux/product_property_contexts", R_OK) != -1) {
            LoadPropertyInfoFromFile("/product/etc/selinux/product_property_contexts",
                                     &property_infos);
        }
        if (access("/odm/etc/selinux/odm_property_contexts", R_OK) != -1) {
            LoadPropertyInfoFromFile("/odm/etc/selinux/odm_property_contexts", &property_infos);
        }
    } 
    //省略
    auto serialized_contexts = std::string();
    auto error = std::string();
    if (!BuildTrie(property_infos, "u:object_r:default_prop:s0", "string", &serialized_contexts,
                   &error)) {
        LOG(ERROR) 
        PLOG(ERROR) 
  bool fsetxattr_failed = false;
  return system_properties.AreaInit(PROP_FILENAME, &fsetxattr_failed) && !fsetxattr_failed ? 0 : -1;
}

  if (strlen(filename) = PROP_FILENAME_MAX) {
    return false;
  }
  strcpy(property_filename_, filename);
  contexts_ = new (contexts_data_) ContextsSerialized();
  if (!contexts_-Initialize(true, property_filename_, fsetxattr_failed)) {
    return false;
  }
  initialized_ = true;
  return true;
}

  filename_ = filename;
  if (!InitializeProperties()) {
    return false;
  }
  if (writable) {
    mkdir(filename_, S_IRWXU | S_IXGRP | S_IXOTH);
    bool open_failed = false;
    if (fsetxattr_failed) {
      *fsetxattr_failed = false;
    }
    for (size_t i = 0; i d_name;
        android::base::ReadFileToString(file_name, &dt_file);
        std::replace(dt_file.begin(), dt_file.end(), ',', '.');
        InitPropertySet("ro.boot."s + dp->d_name, dt_file);
    }
}

首先检查compatible属性的值是"android,firmware"如果不是，函数直接返回。如果是的话，再打开目录下的dts文件，并读取其内容。其中 get_android_dt_dir是在cmdline中指定

static std::string init_android_dt_dir() {
    // Use the standard procfs-based path by default
    std::string android_dt_dir = kDefaultAndroidDtDir;
    // The platform may specify a custom Android DT path in kernel cmdline
    ImportKernelCmdline([&](const std::string& key, const std::string& value) {
        if (key == "androidboot.android_dt_dir") {
            android_dt_dir = value;
        }
    });
    LOG(INFO) 
    // Set once and saves time for subsequent calls to this function
    static const std::string kAndroidDtDir = init_android_dt_dir();
    return kAndroidDtDir;
}

    bool for_emulator = false;
    ImportKernelCmdline([&](const std::string& key, const std::string& value) {
        if (key == "qemu") {
            for_emulator = true;
        } else if (StartsWith(key, "androidboot.")) {
            InitPropertySet("ro.boot." + key.substr(12), value);
        }
    });
    if (for_emulator) {
        ImportKernelCmdline([&](const std::string& key, const std::string& value) {
            // In the emulator, export any kernel option with the "ro.kernel." prefix.
            InitPropertySet("ro.kernel." + key, value);
        });
    }
}

    constexpr const char* UNSET = "";
    struct {
        const char* src_prop;
        const char* dst_prop;
        const char* default_value;
    } prop_map[] = {
            // clang-format off
        { "ro.boot.serialno",   "ro.serialno",   UNSET, },
        { "ro.boot.mode",       "ro.bootmode",   "unknown", },
        { "ro.boot.baseband",   "ro.baseband",   "unknown", },
        { "ro.boot.bootloader", "ro.bootloader", "unknown", },
        { "ro.boot.hardware",   "ro.hardware",   "unknown", },
        { "ro.boot.revision",   "ro.revision",   "0", },
            // clang-format on
    };
    for (const auto& prop : prop_map) {
        std::string value = GetProperty(prop.src_prop, prop.default_value);
        if (value != UNSET) InitPropertySet(prop.dst_prop, value);
    }
}