README.log 7.8 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251
  1. Logging in U-Boot
  2. =================
  3. Introduction
  4. ------------
  5. U-Boot's internal operation involves many different steps and actions. From
  6. setting up the board to displaying a start-up screen to loading an Operating
  7. System, there are many component parts each with many actions.
  8. Most of the time this internal detail is not useful. Displaying it on the
  9. console would delay booting (U-Boot's primary purpose) and confuse users.
  10. But for digging into what is happening in a particular area, or for debugging
  11. a problem it is often useful to see what U-Boot is doing in more detail than
  12. is visible from the basic console output.
  13. U-Boot's logging feature aims to satisfy this goal for both users and
  14. developers.
  15. Logging levels
  16. --------------
  17. There are a number logging levels available, in increasing order of verbosity:
  18. LOGL_EMERG - Printed before U-Boot halts
  19. LOGL_ALERT - Indicates action must be taken immediate or U-Boot will crash
  20. LOGL_CRIT - Indicates a critical error that will cause boot failure
  21. LOGL_ERR - Indicates an error that may cause boot failure
  22. LOGL_WARNING - Warning about an unexpected condition
  23. LOGL_NOTE - Important information about progress
  24. LOGL_INFO - Information about normal boot progress
  25. LOGL_DEBUG - Debug information (useful for debugging a driver or subsystem)
  26. LOGL_DEBUG_CONTENT - Debug message showing full message content
  27. LOGL_DEBUG_IO - Debug message showing hardware I/O access
  28. Logging category
  29. ----------------
  30. Logging can come from a wide variety of places within U-Boot. Each log message
  31. has a category which is intended to allow messages to be filtered according to
  32. their source.
  33. The following main categories are defined:
  34. LOGC_NONE - Unknown category (e.g. a debug() statement)
  35. UCLASS_... - Related to a particular uclass (e.g. UCLASS_USB)
  36. LOGC_ARCH - Related to architecture-specific code
  37. LOGC_BOARD - Related to board-specific code
  38. LOGC_CORE - Related to core driver-model support
  39. LOGC_DT - Related to device tree control
  40. LOGC_EFI - Related to EFI implementation
  41. Enabling logging
  42. ----------------
  43. The following options are used to enable logging at compile time:
  44. CONFIG_LOG - Enables the logging system
  45. CONFIG_MAX_LOG_LEVEL - Max log level to build (anything higher is compiled
  46. out)
  47. CONFIG_LOG_CONSOLE - Enable writing log records to the console
  48. If CONFIG_LOG is not set, then no logging will be available.
  49. The above have SPL versions also, e.g. CONFIG_SPL_MAX_LOG_LEVEL.
  50. Log commands
  51. ------------
  52. The 'log' command provides access to several features:
  53. level - access the default log level
  54. format - access the console log format
  55. rec - output a log record
  56. test - run tests
  57. Type 'help log' for details.
  58. Using DEBUG
  59. -----------
  60. U-Boot has traditionally used a #define called DEBUG to enable debugging on a
  61. file-by-file basis. The debug() macro compiles to a printf() statement if
  62. DEBUG is enabled, and an empty statement if not.
  63. With logging enabled, debug() statements are interpreted as logging output
  64. with a level of LOGL_DEBUG and a category of LOGC_NONE.
  65. The logging facilities are intended to replace DEBUG, but if DEBUG is defined
  66. at the top of a file, then it takes precedence. This means that debug()
  67. statements will result in output to the console and this output will not be
  68. logged.
  69. Logging destinations
  70. --------------------
  71. If logging information goes nowhere then it serves no purpose. U-Boot provides
  72. several possible determinations for logging information, all of which can be
  73. enabled or disabled independently:
  74. console - goes to stdout
  75. Log format
  76. ----------
  77. You can control the log format using the 'log format' command. The basic
  78. format is:
  79. LEVEL.category,file.c:123-func() message
  80. In the above, file.c:123 is the filename where the log record was generated and
  81. func() is the function name. By default ('log format default') only the
  82. function name and message are displayed on the console. You can control which
  83. fields are present, but not the field order.
  84. Filters
  85. -------
  86. Filters are attached to log drivers to control what those drivers emit. Only
  87. records that pass through the filter make it to the driver.
  88. Filters can be based on several criteria:
  89. - maximum log level
  90. - in a set of categories
  91. - in a set of files
  92. If no filters are attached to a driver then a default filter is used, which
  93. limits output to records with a level less than CONFIG_LOG_MAX_LEVEL.
  94. Logging statements
  95. ------------------
  96. The main logging function is:
  97. log(category, level, format_string, ...)
  98. Also debug() and error() will generate log records - these use LOG_CATEGORY
  99. as the category, so you should #define this right at the top of the source
  100. file to ensure the category is correct.
  101. You can also define CONFIG_LOG_ERROR_RETURN to enable the log_ret() macro. This
  102. can be used whenever your function returns an error value:
  103. return log_ret(uclass_first_device(UCLASS_MMC, &dev));
  104. This will write a log record when an error code is detected (a value < 0). This
  105. can make it easier to trace errors that are generated deep in the call stack.
  106. Code size
  107. ---------
  108. Code size impact depends largely on what is enabled. The following numbers are
  109. generated by 'buildman -S' for snow, which is a Thumb-2 board (all units in
  110. bytes):
  111. This series: adds bss +20.0 data +4.0 rodata +4.0 text +44.0
  112. CONFIG_LOG: bss -52.0 data +92.0 rodata -635.0 text +1048.0
  113. CONFIG_LOG_MAX_LEVEL=7: bss +188.0 data +4.0 rodata +49183.0 text +98124.0
  114. The last option turns every debug() statement into a logging call, which
  115. bloats the code hugely. The advantage is that it is then possible to enable
  116. all logging within U-Boot.
  117. To Do
  118. -----
  119. There are lots of useful additions that could be made. None of the below is
  120. implemented! If you do one, please add a test in test/py/tests/test_log.py
  121. Convenience functions to support setting the category:
  122. log_arch(level, format_string, ...) - category LOGC_ARCH
  123. log_board(level, format_string, ...) - category LOGC_BOARD
  124. log_core(level, format_string, ...) - category LOGC_CORE
  125. log_dt(level, format_string, ...) - category LOGC_DT
  126. Convenience functions to support a category defined for a single file, for
  127. example:
  128. #define LOG_CATEGORY UCLASS_USB
  129. all of these can use LOG_CATEGORY as the category, and a log level
  130. corresponding to the function name:
  131. logc(level, format_string, ...)
  132. More logging destinations:
  133. device - goes to a device (e.g. serial)
  134. buffer - recorded in a memory buffer
  135. Convert debug() statements in the code to log() statements
  136. Support making printf() emit log statements a L_INFO level
  137. Convert error() statements in the code to log() statements
  138. Figure out what to do with BUG(), BUG_ON() and warn_non_spl()
  139. Figure out what to do with assert()
  140. Add a way to browse log records
  141. Add a way to record log records for browsing using an external tool
  142. Add commands to add and remove filters
  143. Add commands to add and remove log devices
  144. Allow sharing of printf format strings in log records to reduce storage size
  145. for large numbers of log records
  146. Add a command-line option to sandbox to set the default logging level
  147. Convert core driver model code to use logging
  148. Convert uclasses to use logging with the correct category
  149. Consider making log() calls emit an automatic newline, perhaps with a logn()
  150. function to avoid that
  151. Passing log records through to linux (e.g. via device tree /chosen)
  152. Provide a command to access the number of log records generated, and the
  153. number dropped due to them being generated before the log system was ready.
  154. Add a printf() format string pragma so that log statements are checked properly
  155. Enhance the log console driver to show level / category / file / line
  156. information
  157. Add a command to add new log records and delete existing records.
  158. Provide additional log() functions - e.g. logc() to specify the category
  159. --
  160. Simon Glass <sjg@chromium.org>
  161. 15-Sep-17