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Diffstat (limited to 'Documentation/trace/ftrace.rst')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index c3b9bd2fd512..f60079259669 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 ---------------------------- |