Re: [PATCH] tracing/ftrace: add the printk-msg-only option

[Frédéric Weisbecker]

2008/12/14 Steven Rostedt <rostedt@xxxxxxxxxxx>:
>
> On Sat, 13 Dec 2008, Frederic Weisbecker wrote:
>
>> Impact: display ftrace_printk messages "as is"
>>
>> By default, ftrace_printk() messages find their output with some other
>> informations like pid, caller, ...
>> Sometimes a developer just want to have the ftrace_printk left "as is", without
>> other information.
>>
>> This is done by providing a default-off option called printk-msg-only.
>> To enable it, just do `echo printk-msg-only > /debugfs/tracing/trace_options`
>>
>> Before the patch:
>>
>>            <...>-2739  [000]   145.692153: __might_sleep: I'm an ftrace_printk msg in __might_sleep
>>            <...>-2739  [000]   145.692155: __might_sleep: I'm another ftrace_printk msg in __might_sleep
>>
>> After the patch and the printk-msg-only option enabled:
>>
>> I'm an ftrace_printk msg in __might_sleep
>> I'm another ftrace_printk msg in __might_sleep
>>
>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>> Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
>> ---
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 8fd3c5a..cd4dbf2 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -287,6 +287,7 @@ static const char *trace_options[] = {
>>       "annotate",
>>       "userstacktrace",
>>       "sym-userobj",
>> +     "printk-msg-only",
>
> Hmm, I'm a bit apprehensive about this approach. We are adding a lot of
> options that I'm not sure will be used. Is this needed because you added a
> ftrace printk that you want to not have the header, or because there are
> ftrace printks that exist that you want to turn on and off. Or perhaps,
> you want to see the header sometimes and sometimes you do not?
>
> If it is the later two, then sure we could have this option. But if it is
> the former, then we probably should have another type of ftrace_printk
> that takes an option to make another event type to tell the output not to
> print?
>
> Oh well, I have patches in mind to clean up the output code anyway.
>
> -- Steve
>

Actually, it's not for my needs but Ingo requested it to have only the
message output without
the headers while debugging with ftrace_printk.
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