From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> Move most of the hist trigger extended error documentation to ftrace.rst and expand on it to fully document tracing/error_log. Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx> --- Documentation/trace/ftrace.rst | 31 +++++++++++++++++++++++++++++++ Documentation/trace/histogram.rst | 16 ++-------------- 2 files changed, 33 insertions(+), 14 deletions(-) diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index 7c5e6d6ab5d1..809b39d066ee 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -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 ---------------------------- diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index 0ea59d45aef1..7612c7ad5715 100644 --- a/Documentation/trace/histogram.rst +++ b/Documentation/trace/histogram.rst @@ -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 --------------------------- -- 2.14.1
