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

[Mathieu Desnoyers]

----- 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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