1.定义service

//src\webserver_run.cpp

int run()
{
    ...
    std::shared_ptr<sdbusplus::asio::connection> systemBus =
        std::make_shared<sdbusplus::asio::connection>(io);
    crow::connections::systemBus = systemBus.get();

    auto server = sdbusplus::asio::object_server(systemBus);

    std::shared_ptr<sdbusplus::asio::dbus_interface> iface =
        server.add_interface("/xyz/openbmc_project/bmcweb",
                             "xyz.openbmc_project.bmcweb");

    iface->register_method("SetLogLevel", setLogLevel);

    iface->initialize();
    ...

    systemBus->request_name("xyz.openbmc_project.bmcweb");
    ...
}

为BmcWeb定义了

Service:xyz.openbmc_project.bmcweb

ObjPath：/xyz/openbmc_project/bmcweb

Interface：xyz.openbmc_project.bmcweb

Method：SetLogLevel

 2.设置日志级别

//http\logging.hpp
constexpr std::array<std::string_view, 7> mapLogLevelFromName{
    "DISABLED", "CRITICAL", "ERROR", "WARNING", "INFO", "DEBUG", "ENABLED"};

constexpr crow::LogLevel getLogLevelFromName(std::string_view name)
{
    const auto* iter = std::ranges::find(mapLogLevelFromName, name);
    if (iter != mapLogLevelFromName.end())
    {
        return static_cast<LogLevel>(iter - mapLogLevelFromName.begin());
    }
    return crow::LogLevel::Disabled;
}

enum class LogLevel
{
    Disabled = 0,
    Critical,
    Error,
    Warning,
    Info,
    Debug,
    Enabled,
};

inline crow::LogLevel& getBmcwebCurrentLoggingLevel()
{
    static crow::LogLevel level = getLogLevelFromName(BMCWEB_LOGGING_LEVEL);
    return level;
}

//src\webserver_run.cpp
static void setLogLevel(const std::string& logLevel)
{
    const std::basic_string_view<char>* iter =
        std::ranges::find(crow::mapLogLevelFromName, logLevel);
    if (iter == crow::mapLogLevelFromName.end())
    {
        BMCWEB_LOG_ERROR("log-level {} not found", logLevel);
        return;
    }
    crow::getBmcwebCurrentLoggingLevel() = crow::getLogLevelFromName(logLevel);
    BMCWEB_LOG_INFO("Requested log-level change to: {}", logLevel);
}

BmcWeb被实现为一个service，目的只有一个就是设置日志级别

而日志级别被保存在函数getBmcwebCurrentLoggingLevel返回的单例对象中