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

[Mathieu Desnoyers]

* Woegerer, Paul (Paul_Woegerer at mentor.com) wrote:
> On 05/02/2013 03:40 PM, Mathieu Desnoyers wrote:
> > Hi Paul,
> > 
> > I would be interested to see this feature upstream. Previously was not a
> > good timing to pull it in, because we were adding the concept of event
> > "enablers" within lttng-ust.
> 
> Sounds great. I will port our patch to master.
> 
> > 
> > One thing I'm curious about is how you present the logical combination
> > with exlusion match are present. For instance, if we only have
> > inclusion, we get:
> > 
> > lttng enable-event 'a'
> > lttng enable-event 'c'
> > lttng enable-event 'zc*'
> > 
> > it turns into :   (a || c || zc*)
> > 
> > I expect that negation would look like:
> > 
> > lttng enable-event 'a'
> > lttng enable-event '!abc*'
> > lttng enable-event 'c'
> > lttng enable-event '!cxx'
> 
> Our current solution does not handle '!cxx' correctly.
> I will fix that.
> 
> > lttng enable-event 'zc*'
> > 
> > ->  !(abc* || cxx) || (a || c || zc*)
> 
> Exactly. The "!something" wildcards are always first and will prevent further matching with non-! wildcards.
> 
> > 
> > Am I correct ? If yes, we should expand lttng-tools lttng(1) manpage and
> > cmd help with this info.
> 
> I will take care of documentation updates as well.
> 
> > 
> > Can you make sure it works well with lttng-ust master branch ?
> 
> Once I have a working, tested patch against master I will send it to you.

One thing I just remembered: Please make sure that the order of
evaluation of filter expressions stays the same, because we plan to add
"actions" associated with the filter expressions in the future.

Therefore, if we have:

lttng enable-event 'a' --filter 'fielname==1'           (1)
lttng enable-event '!abc*' --filter 'somename>2'        (2)
lttng enable-event 'c' --filter 'othername==3'          (3)
lttng enable-event '!cxx' --filter 'thisname="abc"'     (4)

We want to interpret the filter expressions in this order:

(1), then (2), then (3), then (4) within lttng-ust.

We also have to assign a clear semantic to those exclusions when a
filter is applied. Same for loglevels.

This is one of the reasons why I waited to pull your modification: I was
implementing the filter, and "enablers", back then. So now there
everything is in place, it should become clearer what needs to be done.

Thanks,

Mathieu



> 
> Thanks,
> Paul
> 
> -- 
> Paul Woegerer | SW Development Engineer
> http://go.mentor.com/sourceryanalyzer
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com