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    SubjectRe: [PATCH -tip -v10 7/7] tracing: add kprobe-based event tracer
    On Tue, Jul 07, 2009 at 04:42:32PM -0400, Masami Hiramatsu wrote:
    > 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,


    Ok. Btw, why do you need to define those two anonymous events?
    Actually your event types are always dynamically created.
    Those you defined through TRACE_FORMAT_EVENT are only "ghost events",
    they only stand there as a abstract pattern, right?



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