[lttng-dev] [PATCH] tracepoint event exclusion

Woegerer, Paul Paul_Woegerer at mentor.com
Thu Jun 28 05:26:45 EDT 2012

On 06/27/2012 08:33 PM, Mathieu Desnoyers wrote:
> hrm, although possibly interesting, I don't think this semantic follows
> the lttng UI event enabling semantic. There are a few use-cases to
> cover:
> 1) enable tracepoints, start tracing, run app.
> 2) enable some tracepoints, start tracing, run app, enable more
>     tracepoints while app is running.
> 3) start tracing, run app, enable all tracepoints while app is running.
> AFAIU, your patch and proposed semantic covers use-case #1, but breaks
> the other 2. Basically, we have to apply a logical "or" between each
> enable-event command (rather than an "and" as your proposed semantic
> suggests), because they can be applied independently.

You are right, I only had use-case #1 in mind when I wrote this patch. I 
intentionally kept my modifications small not to break any of the the 
existing functionality if "!" is not used.

Let me provide a more elaborate description of what this patch is doing:

Original behavior:

    Check if a wildcard_entry matches the given lttng_event_desc name. 
If a mach is found and the loglevel also matches return the 
wildcard_entry. Otherwise return 0.

    If an event with the given name does not already exist create one, 
pass a pointer to it (via _event) and return 0. If an event with the 
given name already exists return -EEXIST.

Behavior after patch:

    First check if there is a wildcard_entry that starts with "!" that 
matches the given lttng_event_desc name. If a filter matches return 0 
(no match). If not proceed as before.

    If an event should be created that starts with "!" do not create it 
but instead add a new wildcard_entry (if not already existing in the 
wildcard_list). Otherwise as before.

Note that the change of ltt_event_create() was necessary to make sure 
that also things like:

lttng enable-event -u -c met_tools --tracepoint '!met_func:enter'

work (i.e. filters that do not have a '*' at the end).

> We could however try to come up with an event attribute that gets
> applied on a specific event, e.g.:
> lttng enable-event -u -a --exclude 'met_func:*' --exclude 'met_call:*'

I would prefer your "--exclude" over my solution but I doubt that I 
could implement it properly. Are you planning to add "--exclude" 
yourself or could you provide me with detailed instructions how to 
implement it (which functions and structures need to be adapted).


Paul Woegerer | SW Development Engineer
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