[lttng-dev] How to disable an event that's been enabled by a wildcard selection or -a?

[David OShea]

Hi,

My understanding (hopefully someone will correct me if I'm wrong) is that each time you invoke 'lttng enable-event', your specification for the events you want enabled is stored and applied, and/or potentially applied later if a new application connects to the session daemon.  All 'lttng disable-event' does is remove one of the specifications you previously provided to 'lttng enable-event', so you can't say 'enable-event *' and then 'disable-event foo:*' to get all events except 'foo:*'.

If you could constrain the application to use a particular trace provider name for all of its tracepoints, say "app", then you could just do 'lttng enable-event app:*'.  If you can't do that, then I think you need to fall back on getting a list of all the available tracepoints using 'lttng list -u', parsing this to find all of the available tracepoints, extracting the trace provider name from them, then using 'lttng enable-event <provider>:*' for each provider other than the provider from your uninteresting library.  I think there are APIs that can be used instead of issuing the 'lttng' commands.

I would certainly also like a way to be able to, say, enable all events other than foo:* and bar:* using one command.

Regards,
David

> -----Original Message-----
> From: Ikaheimonen, JP [mailto:jp_ikaheimonen at mentor.com]
> Sent: Friday, 8 February 2013 7:56 PM
> To: lttng-dev at lists.lttng.org
> Subject: [lttng-dev] How to disable an event that's been enabled by a
> wildcard selection or -a?
> 
> Consider the following scenario.
> I want to write a script that traces all UST tracepoints of a given
> application. I have no idea what the names of these tracepoints are.
> Also, I know that the application uses a library that contains some
> tracepoints I am not interested about. Now I want to trace all UST
> tracepoints except the ones I already know about. Is this possible with
> the lttng commands?
> 
> If I enable all tracepoints with "lttng enable-event -u -a" I get all
> events, even those I do not want. I've tried using "lttng disable-
> event", and "lttng enable-event" with a filter, but I cannot seem to be
> able to get rid of the specific events.
> 
> Thank you,
> 
> JP Ikaheimonen
> Mentor Graphics Embedded Systems Division
> Nucleus(r) | Linux(r) | Android(tm) | Services | UI | Multi-OS
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