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tracing: Add tracing/error_log Documentation

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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>
This commit is contained in:
Tom Zanussi 2019-03-31 18:48:24 -05:00 committed by Steven Rostedt (VMware)
parent 4eab1cc461
commit 26a9449179
2 changed files with 33 additions and 14 deletions
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31
Documentation/trace/ftrace.rst
View File

@ -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
----------------------------

16
Documentation/trace/histogram.rst
View File

@ -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
---------------------------