[lttng-dev] Correct way to use the tpl file

[John O'Sullivan]

Hi Mathieu,
Thank you for the reply and my apologies for the confusion. Let me try and clarify.

I understood that the use of the class and instance concepts in the tpl file was to be able to declare a class with as you say a number of fields and then create instances of that class that provided a way of defining specific variants of that class.

For example
TRACEPOINT_EVENT_CLASS(
    /* Tracepoint provider name */
    core_event_trace,

    /* Tracepoint class name */
    core_event_tracepoint_class,

/* Input arguments */
    TP_ARGS(
      int, event_type
     int, second_field
     int, third_field
     int, fourth_field
    ),

    /* Output event fields */
    TP_FIELDS(
        ctf_integer(int, event_type, event_type)
        ctf_integer(int, second_field, second_field)
       ctf_integer(int, third_field, third_field)
    )
)


Then we declare an instance

TRACEPOINT_EVENT_INSTANCE(
    core_event_trace,
    core_event_tracepoint_class,
    first_event_tracepoint,
    TP_ARGS(
      int, event_type
      Int, first_field

    )
)

And a second one

TRACEPOINT_EVENT_INSTANCE(
    core_event_trace,
    core_event_tracepoint_class,
    second_event_tracepoint,
    TP_ARGS(
      int, event_type
      Int, second_field

    )
)

So the two instances do not define all of the fields in the class definition, the first only defines first_field and the second only defines second_field, will this work or do the field in the instance always have to match the fields in the class?

From: Mathieu Desnoyers [mailto:mathieu.desnoyers at efficios.com]
Sent: 30 November 2018 17:13
To: John O'Sullivan
Cc: lttng-dev
Subject: [EXTERNAL] Re: [lttng-dev] Correct way to use the tpl file



----- On Nov 30, 2018, at 11:09 AM, John OSullivan <John.OSullivan at BlackBox.com> wrote:


Hi,

I am looking for some advice on the best way to manage the tracing of some user space events.



I have a series of events that are fed to queues, they look something like the following sample





EventEnd* event_end_new()
{
    EventEnd* event_end = bb_xnew(EventEnd,__func__);

    if (event_end != NULL)
    {
        event_end->type = EQ_EVENT_END;
    .   .. other event specific fields here

        ..
    }
#ifdef LTTNG_TRACE
    tracepoint(core_event_trace, end_event_tracepoint, EQ_EVENT_END);
#endif
    return event_end;
}







I want to try and trace these so created the following template shown below. My question is, does the class have to have all of the possible members that the different instances will have, as each unique event is likely to have different members will the class have to have all of these members defines, and if this is the case is it okay for an instance to just implement a subset of the members the class defines?

I am a bit confused by your use of the word "members" here. A tracepoint class has a provider name,
a class name, input argument, and output fields.

The event instance refers to the class by provider and class name, defines its own name, and needs to
have a compatible input argument prototype (same number of arguments, same types). It will serialize
the output fields in the exact layout described by the event class.

I know it does not directly answer your question, but I'm really unsure about what you mean
by "members".

Thanks,

Mathieu










TRACEPOINT_EVENT_CLASS(
    /* Tracepoint provider name */
    core_event_trace,

    /* Tracepoint class name */
    core_event_tracepoint_class,

/* Input arguments */
    TP_ARGS(
      int, event_type

    ),

    /* Output event fields */
    TP_FIELDS(
        ctf_integer(int, event_type, event_type)

    )
)





TRACEPOINT_EVENT_INSTANCE(
    core_event_trace,
    core_event_tracepoint_class,
    end_event_tracepoint,
    TP_ARGS(
      int, event_type

    )
)

TRACEPOINT_EVENT_INSTANCE(
    core_event_trace,
    core_event_tracepoint_class,
    start_event_tracepoint,
    TP_ARGS(
      int, event_type
    )
)



TRACEPOINT_EVENT_INSTANCE(
    core_event_trace,
    core_event_tracepoint_class,
    foo_event_tracepoint,
    TP_ARGS(
      int, event_type
    )
)

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--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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