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Commit 26a94491 authored by Tom Zanussi's avatar Tom Zanussi Committed by Steven Rostedt (VMware)
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tracing: Add tracing/error_log Documentation 

Move most of the hist trigger extended error documentation to
ftrace.rst and expand on it to fully document tracing/error_log.

Link: http://lkml.kernel.org/r/c5d53c8f643ef6844d6ad8d0200c116936730b01.1554072478.git.tom.zanussi@linux.intel.com



Acked-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Acked-by: default avatarNamhyung Kim <namhyung@kernel.org>
Signed-off-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 4eab1cc4

Documentation/trace/ftrace.rst

+31 −0
Original line number Diff line number Diff line
@@ -765,6 +765,37 @@ Here is the list of current tracers that may be configured. 
	tracers from tracing simply echo "nop" into

	current_tracer.



Error conditions

----------------



  For most ftrace commands, failure modes are obvious and communicated

  using standard return codes.



  For other more involved commands, extended error information may be

  available via the tracing/error_log file.  For the commands that

  support it, reading the tracing/error_log file after an error will

  display more detailed information about what went wrong, if

  information is available.  The tracing/error_log file is a circular

  error log displaying a small number (currently, 8) of ftrace errors

  for the last (8) failed commands.



  The extended error information and usage takes the form shown in

  this example::



    # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger

    echo: write error: Invalid argument



    # cat /sys/kernel/debug/tracing/error_log

    [ 5348.887237] location: error: Couldn't yyy: zzz

      Command: xxx

               ^

    [ 7517.023364] location: error: Bad rrr: sss

      Command: ppp qqq

                   ^



  To clear the error log, echo the empty string into it::



    # echo > /sys/kernel/debug/tracing/error_log



Examples of using the tracer

----------------------------

Documentation/trace/histogram.rst

+2 −14
Original line number Diff line number Diff line
@@ -199,20 +199,8 @@ Extended error information 


  For some error conditions encountered when invoking a hist trigger

  command, extended error information is available via the

  corresponding event's 'hist' file.  Reading the hist file after an

  error will display more detailed information about what went wrong,

  if information is available.  This extended error information will

  be available until the next hist trigger command for that event.



  If available for a given error condition, the extended error

  information and usage takes the following form::



    # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger

    echo: write error: Invalid argument



    # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist

    ERROR: Couldn't yyy: zzz

      Last command: xxx

  tracing/error_log file.  See Error Conditions in

  :file:`Documentation/trace/ftrace.rst` for details.



6.2 'hist' trigger examples

---------------------------