Logging system of Android

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explain internal of logging system of Android.

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Logging system of Android

  1. 1. Logging System of Android 2010.8.27 2010.9.2 updated Tetsuyuki Kobayashi 1
  2. 2. Who am I?  20+ years involved in embedded systems  10 years in real time OS, such as iTRON  10 years in embedded Java Virtual Machine  Now GCC, Linux, QEMU, Android, …  Blogs  http://d.hatena.ne.jp/embedded/ (Personal)  http://blog.kmckk.com/ (Corporate)  Twitter  @tetsu_koba 2
  3. 3. Today's topic  Log from Java program  Log from native program  Overview of Android Logging system  Tips 3
  4. 4. Log from Java program  android.util.Log class  System.out, System.err
  5. 5. android.util.Log  Static methods  Log.e, Log.w, Log.i, Log.d, Log.v  e,w,i,d,v mean priority/log level  writing log with tag, priority  Tag and priority is used by filtering Static final String LOG_TAG = ”Hello”; ... Log.i(LOG_TAG, ”Hello to log”);
  6. 6. System.out/System.err  Default instance is com.android.internal.os.AndroidPri ntStream  These connects to android.util.Log Tips: How to identify instance of System.out System.out.println(”System.out=” + System.out.toString());
  7. 7. Log from native program  Use liblog library  Include <android/log.h>  __android_log_print  Writing log with tag, priority #include <android/log.h> #define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARG S__) … LIGI(”i=%d, name=%sn”, i, name);
  8. 8. Stdout/stderr of native program  These are NOT connected to logging system.  Init process set stdout/stderr to /dev/null for its child processes.  All Java processes, too.  JNI native libs, too.  Do not use printf (to stdout) in JNI native libs.
  9. 9. How to read logs  Logcat command  Adb logcat  Logcat pane in ADT, Eclipse  Filtering by tag and priority
  10. 10. Log device files  4 channels, each have ring buffer  /dev/log/radio – radio-related messages (64KB)  /dev/log/event – system/hardware events (256KB)  /dev/log/system – system/framwork messages (64KB)  /dev/log/main – everything else (64KB)  File permission of each is 0662  owner/group RW, other Write only  owner=root, group=log  Anyone can write logs, root or log group can read them
  11. 11. Overview of Android Logging System Target Java program Java program System.out /System.err com.android.internal.os Native program android.util.Log com.android.internal.os Host Native program android.util.Log AndroidPrintStream AndroidPrintStream ADT in Eclipse stdout logcat logcat stdout liblog /stderr liblog adbserver adbd adbd adbserver User Kernel adb logcat main 64KB radio logger logger 64KB /dev/log/main /dev/log/main /dev/log/radio event /dev/log/radio system /dev/log/event 256KB /dev/log/event /dev/log/system 64KB /dev/log/system
  12. 12. Where to read in source code  android.util.Log  frameworks/base/core/java/android/util/Log.java  com.android.internal.os.AndroidPrintStream  frameworks/base/core/java/com/android/internal/os/Android PrintStream.java  Liblog  system/core/liblog/  Logcat command  system/core/logcat/  Adb command  system/core/adb/  Kernel log driver  drivers/staging/android/logger.c
  13. 13. Tips  Dumping stack trace  Character Encoding  Logwrapper  Log at init process
  14. 14. Dumping stack trace  3 arguments fuctions in android.util.Log class You can put 'new Throwable()'  For example:  Log.e(String tag, String msg, Throwable tr)  Throwable.printStacktrace() also works  Dump to System.err  See also  http://blog.kmckk.com/archives/2902690.html
  15. 15. Character Encoding  Fixed to Utf-8  Not Shift-JIS, Not EUC  Use Utf-8 encoding terminal/window to use logcat  adb logcat  invoke 'logcat' at serial console  Logcat pane in ADT in Eclipse seems bug.  Can not show Japanese character correctly.
  16. 16. Logwrapper  Logwrapper redirects stdout/stderr to Android Logging system  Easy way to add 'usual' command as Android service lunched from init.  See also  http://blog.kmckk.com/archives/2918551.html
  17. 17. Log at init process  The first process 'init' does not use Android Logging System.  Init writes log to (the same node as) '/dev/kmsg'  The same way as 'printk' : kernel log
  18. 18. Q&A Thank you for listening! Any comments to blogs are welcome. 18
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