[for-next][PATCH 15/19] tracing: Add tracing/error_log Documentation

Steven Rostedt
2019-04-04T01:38:14Z

From: Tom Zanussi <tom.zanussi@linux.intel.com>

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>
---
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
---------------------------
--
2.20.1