harmony 鸿蒙Log Management

2022-12-22
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Log Management

Overview

Function Introduction

Basic functions of a log include recording key nodes and troubleshooting faults during the init startup process. - Logs help troubleshoot faults, check the startup duration of each subsystem, command execution duration, and more. - Log tags (including param, uevent, and module) for different modules can be viewed. - Logs can be printed for key phases, for example, the startup of the first phase, a required partition and its device node, uevent creation, service startup, and more. - Log levels are configurable. Available log levels include INIT_DEBUG, INIT_INFO, INIT_WARN, INIT_ERROR, and INIT_FATAL.

Basic Concepts

The implementation of the init log function varies according to the OpenHarmony version. - OpenHarmony standard system: The init log function is implemented via dmesg log of the Linux kernel. - For the OpenHarmony LiteOS small system, the init log function is implemented by using the hilog API. - For the OpenHarmony LiteOS mini system, the init log function is implemented by using the printf API.

Log Type

init logs are classified into hilog and demsg logs. The hilog log records information related to system service processes, and the demsg log records information related to the kernel.

Log Level

init logs are classified into five levels, which can be set by the (INIT_DEBUG_LEVEL)persist.init.debug.loglevel parameter.

  InitLogLevel:
    INIT_DEBUG = 0,
    INIT_INFO,
    INIT_WARN,
    INIT_ERROR,
    INIT_FATAL

Kmsg log level. The options are as follows:

  "<7>" =====> "DEBUG"
  "<6>" =====> "INFO"
  "<4>" =====> "WARNING"
  "<3>" =====> "ERROR"
  "<3>" =====> "FATAL"

Key Macros for Log Control

INIT_DMESG specifies whether to record kernel logs in /dev/kmsg. INIT_FILE specifies whether to write log information to the /data/init_agent/begetctl.log file. INIT_AGENT specifies whether to use hilog to record log information.

Key APIs:

    void EnableInitLog (InitLogLevel level) Enables the init log function.
  
    void SetInitLogLevel(InitLogLevel level) Sets the log level to control log output.

    void StartupLog(InitLogLevel logLevel, uint32_t domain, const char *tag, const char *fmt, ...) Provides an entry to the init log function.

STARTUP_LOGI is a macro defined for StartupLog, which is defined in the /base/startup/init/interfaces/innerkits/include/beget_ext.h file. Other logs are redefined based on the STARTUP_LOGI macro.

deviceInfo module (init/device_info/idevice_info.h): DINFO_LOGI DINFO_LOGE DINFO_LOGV
Param JS API module (init/interfaces/kits/jskits/src/native_parameters_js.h): PARAM_JS_LOGI PARAM_JS_LOGE PARAM_JS_LOGV PARAM_JS_LOGW
Shell module (init/services/begetctl/shell/shell_utils.h): BSH_LOGI BSH_LOGE BSH_LOGV
LoopEvent module (init/services/loopevent/utils/le_utils.h): LE_LOGI LE_LOGE LE_LOGV
Plug-in module (init/services/modules/plugin_adapter.h): PLUGIN_LOGI PLUGIN_LOGE PLUGIN_LOGV PLUGIN_LOGW
Param module (init/services/param/include/param_utils.h): PARAM_LOGI PARAM_LOGE PARAM_LOGV PARAM_LOGW
ParamWatcher module (init/services/param/watcher/include/watcher_utils.h): WATCHER_LOGI WATCHER_LOGE WATCHER_LOGV
init log module implemented based on the macros defined by StartupLog (init/services/log/init_log.h) INIT_LOGV INIT_LOGI INIT_LOGW INIT_LOGE INIT_LOGF

Constraints

N/A

How to Develop

Use Cases

init logs are mainly used to start modules (like param, ueventd, and module) during init startup, and are used in the open API begetutils.

Available APIs

Development Example

Call an API to print the log.

For example, call INIT_LOGI(“Start init first stage.”) in //base/startup/init/services/init/standard/init.c to print the log.

   void SystemPrepare(void)
   {
      MountBasicFs();
      CreateDeviceNode();
      LogInit();
      // Make sure init log always output to /dev/kmsg.
      EnableDevKmsg();
      INIT_LOGI("Start init first stage.");
      // Only ohos normal system support
      // two stages of init.
      // If we are in updater mode, only one stage of init.
      if (InUpdaterMode() == 0) {
          StartInitSecondStage();
      }
   }

Run dmesg to check the printed log Start init first stage.

Set the log level by running the begetctl setloglevel level command.

In the command, set level to one of the following log levels: 0 (INIT_DEBUG), 1 (INIT_INFO), 2 (INIT_WARN), 3 (INIT_ERROR), and 4 (INIT_FATAL).

After the setting is complete, the level set via g_logLevel of init takes effect immediately, and log APIs can print logs only when their log levels are higher than or equal to this level. For example, begetctl setloglevel 3 sets the log level to INIT_ERROR. In this case, only INIT_LOGE and INIT_LOGF will print logs.

After the system is restarted, the configured log level will take effect after the load_persist_params command in the init.cfg file is executed.