Init rc 文件解析

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调用LoadBootScripts方法加载/解析rc文件。先创建一个解析器，支持解析’service’, ‘on’, ‘import’。
若ro.boot.init_rc为空，则开始解析init.rc文件。
然后依次解析/system,/product,/odm,/vendor/etc/init目录rc文件。

一、加载rc文件

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static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
    Parser parser = CreateParser(action_manager, service_list);
    std::string bootscript = GetProperty("ro.boot.init_rc", "");
    if (bootscript.empty()) {
        parser.ParseConfig("/init.rc");
        if (!parser.ParseConfig("/system/etc/init")) {
            late_import_paths.emplace_back("/system/etc/init");
        }
        if (!parser.ParseConfig("/product/etc/init")) {
            late_import_paths.emplace_back("/product/etc/init");
        }
        if (!parser.ParseConfig("/odm/etc/init")) {
            late_import_paths.emplace_back("/odm/etc/init");
        }
        if (!parser.ParseConfig("/vendor/etc/init")) {
            late_import_paths.emplace_back("/vendor/etc/init");
        }
    } else {
        parser.ParseConfig(bootscript);
    }
}

二、创建解析器

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Parser CreateParser(ActionManager& action_manager, ServiceList& service_list) {
    Parser parser;
    parser.AddSectionParser("service", std::make_unique<ServiceParser>(&service_list, subcontexts));
    parser.AddSectionParser("on", std::make_unique<ActionParser>(&action_manager, subcontexts));
    parser.AddSectionParser("import", std::make_unique<ImportParser>(&parser));
    return parser;
}
void Parser::AddSectionParser(const std::string& name, std::unique_ptr<SectionParser> parser) {
    section_parsers_[name] = std::move(parser);
}

三、解析config

调用ParseConfig方法解析rc文件时，先判断路径是目录还是文件，若是目录则先调用ParseConfigDir方法，否则直接调用ParseConfigFile方法。

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bool Parser::ParseConfig(const std::string& path) {
    size_t parse_errors;
    return ParseConfig(path, &parse_errors);
}

bool Parser::ParseConfig(const std::string& path, size_t* parse_errors) {
    *parse_errors = 0;
    if (is_dir(path.c_str())) {
        return ParseConfigDir(path, parse_errors);
    }
    return ParseConfigFile(path, parse_errors);
}

四、解析config目录

ParseConfigDir方法先判断给定的路径是不是目录，若是目录则再判断该目录下是否包含子目录，若是子目录则直接忽略，而只处理当前路径下rc文件。
为了便于处理，会先对该目录文件进行排序处理，然后再调用ParseConfigFile方法按顺序加载/解析。

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bool Parser::ParseConfigDir(const std::string& path, size_t* parse_errors) {
    LOG(INFO) << "Parsing directory " << path << "...";
    std::unique_ptr<DIR, decltype(&closedir)> config_dir(opendir(path.c_str()), closedir);
    if (!config_dir) {
        PLOG(ERROR) << "Could not import directory '" << path << "'";
        return false;
    }
    dirent* current_file;
    std::vector<std::string> files;
    while ((current_file = readdir(config_dir.get()))) {
        // 忽略目录并仅处理常规文件。
        if (current_file->d_type == DT_REG) {
            std::string current_path =
                android::base::StringPrintf("%s/%s", path.c_str(), current_file->d_name);
            files.emplace_back(current_path);
        }
    }
    // 先排序，然后按顺序加载文件
    std::sort(files.begin(), files.end());
    for (const auto& file : files) {
        if (!ParseConfigFile(file, parse_errors)) {
            LOG(ERROR) << "could not import file '" << file << "'";
        }
    }
    return true;
}

五、解析config文件

ParseConfigFile方法解析文件时会先读取文件内容，然后将数据传给ParseData方法。
紧接着再遍历section_parser调用其EndFile方法，然后再分析。

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bool Parser::ParseConfigFile(const std::string& path, size_t* parse_errors) {
    LOG(INFO) << "Parsing file " << path << "...";
    android::base::Timer t;
    auto config_contents = ReadFile(path);
    if (!config_contents) {
        LOG(ERROR) << "Unable to read config file '" << path << "': " << config_contents.error();
        return false;
    }
    config_contents->push_back('\n');
    ParseData(path, *config_contents, parse_errors);
    for (const auto& [section_name, section_parser] : section_parsers_) {
        section_parser->EndFile();
    }
    LOG(VERBOSE) << "(Parsing " << path << " took " << t << ".)";
    return true;
}

六、解析数据

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void Parser::ParseData(const std::string& filename, const std::string& data, size_t* parse_errors) {
    // 将data中内容拷贝到data_copy中，并添加结束符'\0'
    std::vector<char> data_copy(data.begin(), data.end());
    data_copy.push_back('\0');
    parse_state state;
    state.line = 0;
    state.ptr = &data_copy[0];
    state.nexttoken = 0;
    SectionParser* section_parser = nullptr;
    int section_start_line = -1;
    std::vector<std::string> args;
    auto end_section = [&] {
        if (section_parser == nullptr) return;
        if (auto result = section_parser->EndSection(); !result) {
            (*parse_errors)++;
            LOG(ERROR) << filename << ": " << section_start_line << ": " << result.error();
        }
        section_parser = nullptr;
        section_start_line = -1;
    };
    for (;;) {
        // 遍历data_copy中每个字符
        switch (next_token(&state)) {
            case T_EOF:
                end_section();
                return;
            case T_NEWLINE:
                state.line++;
                if (args.empty()) break;
                // 如果我们有识别到相匹配前缀的行，则调用它的回调并取消设置当前部分解析器。
                // 意味着/sys/和/dev/行条目是用于uevent的
                for (const auto& [prefix, callback] : line_callbacks_) {
                    if (android::base::StartsWith(args[0], prefix)) {
                        end_section();
                        if (auto result = callback(std::move(args)); !result) {
                            (*parse_errors)++;
                            LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                        }
                        break;
                    }
                }
                // 判断是否包含service,on,import
                if (section_parsers_.count(args[0])) {
                    end_section();
                    section_parser = section_parsers_[args[0]].get();
                    section_start_line = state.line;
                    // 解析对应的section
                    if (auto result =
                            section_parser->ParseSection(std::move(args), filename, state.line);
                        !result) {
                        (*parse_errors)++;
                        LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                        section_parser = nullptr;
                    }
                } else if (section_parser) {
                    if (auto result = section_parser->ParseLineSection(std::move(args), state.line);
                        !result) {
                        (*parse_errors)++;
                        LOG(ERROR) << filename << ": " << state.line << ": " << result.error();
                    }
                }
                args.clear();
                break;
            case T_TEXT:
                args.emplace_back(state.text);
                break;
        }
    }
}

七、解析服务

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Result<Success> ServiceParser::EndSection() {
    if (service_) {
        Service* old_service = service_list_->FindService(service_->name());
        if (old_service) {
            if (!service_->is_override()) {
                return Error() << "ignored duplicate definition of service '" << service_->name()
                               << "'";
            }

            service_list_->RemoveService(*old_service);
            old_service = nullptr;
        }
        service_list_->AddService(std::move(service_));
    }
    return Success();
}

void ServiceList::AddService(std::unique_ptr<Service> service) {
    services_.emplace_back(std::move(service));
}

Result<Success> ServiceParser::ParseSection(std::vector<std::string>&& args,
                                            const std::string& filename, int line) {
    if (args.size() < 3) {
        return Error() << "services must have a name and a program";
    }
    const std::string& name = args[1];
    if (!IsValidName(name)) {
        return Error() << "invalid service name '" << name << "'";
    }
    Subcontext* restart_action_subcontext = nullptr;
    if (subcontexts_) {
        for (auto& subcontext : *subcontexts_) {
            if (StartsWith(filename, subcontext.path_prefix())) {
                restart_action_subcontext = &subcontext;
                break;
            }
        }
    }
    std::vector<std::string> str_args(args.begin() + 2, args.end());
    service_ = std::make_unique<Service>(name, restart_action_subcontext, str_args);
    return Success();
}

Result<Success> ServiceParser::ParseLineSection(std::vector<std::string>&& args, int line) {
    return service_ ? service_->ParseLine(std::move(args)) : Success();
}

Result<Success> Service::ParseLine(const std::vector<std::string>& args) {
    static const OptionParserMap parser_map;
    auto parser = parser_map.FindFunction(args);
    if (!parser) return parser.error();
    return std::invoke(*parser, this, args);
}