Re: [PATCH -tip -v10 7/7] tracing: add kprobe-based event tracer

[Masami Hiramatsu <mhiramat@redhat.com>]

Frederic Weisbecker wrote:
> On Tue, Jul 07, 2009 at 03:55:28PM -0400, Masami Hiramatsu wrote:
>> Frederic Weisbecker wrote:
>>>> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
>>>> index 206cb7d..65945eb 100644
>>>> --- a/kernel/trace/trace.h
>>>> +++ b/kernel/trace/trace.h
>>>> @@ -45,6 +45,8 @@ enum trace_type {
>>>>  	TRACE_POWER,
>>>>  	TRACE_BLK,
>>>>  	TRACE_KSYM,
>>>> +	TRACE_KPROBE,
>>>> +	TRACE_KRETPROBE,
>>>>  
>>>>  	__TRACE_LAST_TYPE,
>>>>  };
>>>> @@ -227,6 +229,22 @@ struct trace_ksym {
>>>>  	char			ksym_name[KSYM_NAME_LEN];
>>>>  	char			p_name[TASK_COMM_LEN];
>>>>  };
>>>> +#define TRACE_KPROBE_ARGS 6
>>>> +
>>>> +struct kprobe_trace_entry {
>>>> +	struct trace_entry	ent;
>>>> +	unsigned long		ip;
>>>> +	int			nargs;
>>>> +	unsigned long		args[TRACE_KPROBE_ARGS];
>>>
>>>
>>> I see that you actually make use of arg as a dynamic sizeable
>>> array.
>>> For clarity, args[TRACE_KPROBE_ARGS] could be args[0].
>>>
>>> It's just a neat and wouldn't affect the code nor the data
>>> but would be clearer for readers of that code.
>> Hmm. In that case, I think we'll need a new macro for field
>> definition, like TRACE_FIELD_ZERO(type, item).
> 
> 
> 
> You mean that for trace_define_field() to describe fields of events?
> Actually the fields should be defined dynamically depending on how
> is built the kprobe event (which arguments are requested, how many,
> etc..).

Yeah, if you specified a probe point with its event name, the tracer
will make a corresponding event dynamically. There are also anonymous
probes which don't have corresponding events. For those anonymous
probes, I need to define two generic event types(kprobe and kretprobe).

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com