[lttng-dev] Question about TRACEPOINT_EVENT_CLASS and TRACEPOINT_EVENT_INSTANCE

[Thibault, Daniel]

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Date: Fri, 21 Nov 2014 15:28:30 +0400
From: Eugene Ivanov <eiva at tbricks.com>

>>    Normally you use TRACEPOINT_EVENT_CLASS and _INSTANCE within the same
>> provider, but you could theoretically have varying instances rely on
>> different providers.  I guess this would allow you some flexibility in
>> picking which sets of instances to enable/disable by picking which provider
>> shared objects (.so) to preload or not.
>
>Thanks for the explanation, Daniel! Unfortunately using class defined in
>another provider doesn't work. I get an error about undefined
>__event_probe__instance_provider_name___class_name_from_another_provider?.
>Connecting it with your description, I guess it's probably a feature and
>intended behaviour. Though it would be a nice feature to be able to specify
>provider of class separately from provider of instance.

   Would LTTng-delvers more versed in these innards care to comment on the following?

   If the provider argument to the macros is not intended to ever point at anything else than the provider block it is declared in (the #define TRACEPOINT_PROVIDER line), this should be documented and ideally the macros should hide this implicit argument.

   On the other hand, if the intent is to allow cross-provider usage of some form, this also needs to be documented.  What is the recipe supposed to be?

Daniel U. Thibault
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