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authorTom Zanussi <tom.zanussi@linux.intel.com>2019-03-31 18:48:24 -0500
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2019-04-08 09:22:50 -0400
commit26a944917989d57c0dddec284b3088fa31127717 (patch)
treef00b6bbbc91e2b7634d8bc6c44574faf2cbd9a93 /Documentation/trace/ftrace.rst
parent4eab1cc461a6e820eddf88ac63eed98793c96a7c (diff)
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: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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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
----------------------------