+++ /dev/null
-Logging in U-Boot
-=================
-
-Introduction
-------------
-
-U-Boot's internal operation involves many different steps and actions. From
-setting up the board to displaying a start-up screen to loading an Operating
-System, there are many component parts each with many actions.
-
-Most of the time this internal detail is not useful. Displaying it on the
-console would delay booting (U-Boot's primary purpose) and confuse users.
-
-But for digging into what is happening in a particular area, or for debugging
-a problem it is often useful to see what U-Boot is doing in more detail than
-is visible from the basic console output.
-
-U-Boot's logging feature aims to satisfy this goal for both users and
-developers.
-
-
-Logging levels
---------------
-
-There are a number logging levels available, in increasing order of verbosity:
-
- LOGL_EMERG - Printed before U-Boot halts
- LOGL_ALERT - Indicates action must be taken immediate or U-Boot will crash
- LOGL_CRIT - Indicates a critical error that will cause boot failure
- LOGL_ERR - Indicates an error that may cause boot failure
- LOGL_WARNING - Warning about an unexpected condition
- LOGL_NOTE - Important information about progress
- LOGL_INFO - Information about normal boot progress
- LOGL_DEBUG - Debug information (useful for debugging a driver or subsystem)
- LOGL_DEBUG_CONTENT - Debug message showing full message content
- LOGL_DEBUG_IO - Debug message showing hardware I/O access
-
-
-Logging category
-----------------
-
-Logging can come from a wide variety of places within U-Boot. Each log message
-has a category which is intended to allow messages to be filtered according to
-their source.
-
-The following main categories are defined:
-
- LOGC_NONE - Unknown category (e.g. a debug() statement)
- UCLASS_... - Related to a particular uclass (e.g. UCLASS_USB)
- LOGC_ARCH - Related to architecture-specific code
- LOGC_BOARD - Related to board-specific code
- LOGC_CORE - Related to core driver-model support
- LOGC_DT - Related to device tree control
- LOGC_EFI - Related to EFI implementation
-
-
-Enabling logging
-----------------
-
-The following options are used to enable logging at compile time:
-
- CONFIG_LOG - Enables the logging system
- CONFIG_LOG_MAX_LEVEL - Max log level to build (anything higher is compiled
- out)
- CONFIG_LOG_CONSOLE - Enable writing log records to the console
-
-If CONFIG_LOG is not set, then no logging will be available.
-
-The above have SPL and TPL versions also, e.g. CONFIG_SPL_LOG_MAX_LEVEL and
-CONFIG_TPL_LOG_MAX_LEVEL.
-
-
-Temporary logging within a single file
---------------------------------------
-
-Sometimes it is useful to turn on logging just in one file. You can use this:
-
- #define LOG_DEBUG
-
-to enable building in of all logging statements in a single file. Put it at
-the top of the file, before any #includes. This overrides any log-level setting
-in U-Boot, including CONFIG_LOG_DEFAULT_LEVEL, but just for that file.
-
-
-Convenience functions
----------------------
-
-A number of convenience functions are available to shorten the code needed
-for logging:
-
- log_err(_fmt...)
- log_warning(_fmt...)
- log_notice(_fmt...)
- log_info(_fmt...)
- log_debug(_fmt...)
- log_content(_fmt...)
- log_io(_fmt...)
-
-With these the log level is implicit in the name. The category is set by
-LOG_CATEGORY, which you can only define once per file, above all #includes:
-
- #define LOG_CATEGORY LOGC_ALLOC
-
-or
-
- #define LOG_CATEGORY UCLASS_SPI
-
-Remember that all uclasses IDs are log categories too.
-
-
-Log commands
-------------
-
-The 'log' command provides access to several features:
-
- level - access the default log level
- format - access the console log format
- rec - output a log record
- test - run tests
-
-Type 'help log' for details.
-
-
-Using DEBUG
------------
-
-U-Boot has traditionally used a #define called DEBUG to enable debugging on a
-file-by-file basis. The debug() macro compiles to a printf() statement if
-DEBUG is enabled, and an empty statement if not.
-
-With logging enabled, debug() statements are interpreted as logging output
-with a level of LOGL_DEBUG and a category of LOGC_NONE.
-
-The logging facilities are intended to replace DEBUG, but if DEBUG is defined
-at the top of a file, then it takes precedence. This means that debug()
-statements will result in output to the console and this output will not be
-logged.
-
-
-Logging destinations
---------------------
-
-If logging information goes nowhere then it serves no purpose. U-Boot provides
-several possible determinations for logging information, all of which can be
-enabled or disabled independently:
-
- console - goes to stdout
- syslog - broadcast RFC 3164 messages to syslog servers on UDP port 514
-
-The syslog driver sends the value of environmental variable 'log_hostname' as
-HOSTNAME if available.
-
-Log format
-----------
-
-You can control the log format using the 'log format' command. The basic
-format is:
-
- LEVEL.category,file.c:123-func() message
-
-In the above, file.c:123 is the filename where the log record was generated and
-func() is the function name. By default ('log format default') only the
-function name and message are displayed on the console. You can control which
-fields are present, but not the field order.
-
-
-Filters
--------
-
-Filters are attached to log drivers to control what those drivers emit. Only
-records that pass through the filter make it to the driver.
-
-Filters can be based on several criteria:
-
- - maximum log level
- - in a set of categories
- - in a set of files
-
-If no filters are attached to a driver then a default filter is used, which
-limits output to records with a level less than CONFIG_LOG_MAX_LEVEL.
-
-
-Logging statements
-------------------
-
-The main logging function is:
-
- log(category, level, format_string, ...)
-
-Also debug() and error() will generate log records - these use LOG_CATEGORY
-as the category, so you should #define this right at the top of the source
-file to ensure the category is correct.
-
-You can also define CONFIG_LOG_ERROR_RETURN to enable the log_ret() macro. This
-can be used whenever your function returns an error value:
-
- return log_ret(uclass_first_device(UCLASS_MMC, &dev));
-
-This will write a log record when an error code is detected (a value < 0). This
-can make it easier to trace errors that are generated deep in the call stack.
-
-
-Code size
----------
-
-Code size impact depends largely on what is enabled. The following numbers are
-generated by 'buildman -S' for snow, which is a Thumb-2 board (all units in
-bytes):
-
-This series: adds bss +20.0 data +4.0 rodata +4.0 text +44.0
-CONFIG_LOG: bss -52.0 data +92.0 rodata -635.0 text +1048.0
-CONFIG_LOG_MAX_LEVEL=7: bss +188.0 data +4.0 rodata +49183.0 text +98124.0
-
-The last option turns every debug() statement into a logging call, which
-bloats the code hugely. The advantage is that it is then possible to enable
-all logging within U-Boot.
-
-
-To Do
------
-
-There are lots of useful additions that could be made. None of the below is
-implemented! If you do one, please add a test in test/py/tests/test_log.py
-
-Convenience functions to support setting the category:
-
- log_arch(level, format_string, ...) - category LOGC_ARCH
- log_board(level, format_string, ...) - category LOGC_BOARD
- log_core(level, format_string, ...) - category LOGC_CORE
- log_dt(level, format_string, ...) - category LOGC_DT
-
-More logging destinations:
-
- device - goes to a device (e.g. serial)
- buffer - recorded in a memory buffer
-
-Convert debug() statements in the code to log() statements
-
-Support making printf() emit log statements a L_INFO level
-
-Convert error() statements in the code to log() statements
-
-Figure out what to do with BUG(), BUG_ON() and warn_non_spl()
-
-Figure out what to do with assert()
-
-Add a way to browse log records
-
-Add a way to record log records for browsing using an external tool
-
-Add commands to add and remove filters
-
-Add commands to add and remove log devices
-
-Allow sharing of printf format strings in log records to reduce storage size
-for large numbers of log records
-
-Add a command-line option to sandbox to set the default logging level
-
-Convert core driver model code to use logging
-
-Convert uclasses to use logging with the correct category
-
-Consider making log() calls emit an automatic newline, perhaps with a logn()
- function to avoid that
-
-Passing log records through to linux (e.g. via device tree /chosen)
-
-Provide a command to access the number of log records generated, and the
-number dropped due to them being generated before the log system was ready.
-
-Add a printf() format string pragma so that log statements are checked properly
-
-Enhance the log console driver to show level / category / file / line
-information
-
-Add a command to add new log records and delete existing records.
-
-Provide additional log() functions - e.g. logc() to specify the category
-
---
-Simon Glass <sjg@chromium.org>
-15-Sep-17
projects / u-boot.git / commitdiff