[lttng-dev] How to check is tracepoint is currently enabled (UST)

[Dmitri Shubin]

Daniel and Jonathan,

Thanks for your replies!

Sorry I wasn't clear enough -- I want to check it in my application to
avoid 'heavy' calculation of probe arguments when the probe is actually
disabled.
Please see this blog entry for description of dtrace feature in question --
http://dtrace.org/blogs/ahl/2006/05/08/user-land-tracing-gets-better-and-better/


On Wed, Jun 25, 2014 at 6:49 PM, Jonathan Rajotte-Julien <
jonathan.rajotte-julien at ericsson.com> wrote:

> You can also list all ust events available for tracing via the command
> "lttng list -u".
>
> Make sure that the application you want to trace is running.
>
> On 06/25/2014 10:40 AM, Thibault, Daniel wrote:
> > ----------------------------------------------------------------------
> > Date: Sun, 22 Jun 2014 19:27:31 +0400
> > From: Dmitri Shubin <sbn at tbricks.com>
> >
> >> In dtrace it's possible to check if some probe is currently enabled or
> not (to avoid argument preparation for disabled probes).
> >> But I'm unable to find similar feature in lttng-ust (at least it's not
> mentioned in lttng-ust man page).
> >>
> >> Am I missed it or it's not implemented on purpose?
> >
> >    Use the list command.  A command such as 'lttng list <session_name>'
> will list the known events and their enabled/disabled status.  You can
> filter the command's output by specifying a domain (--userspace) and/or a
> channel (--channel <channel_name>).  For example:
> >
> > (begin example)
> > $ lttng create some_session
> > Session some_session created.
> > Traces will be written in /home/username/lttng-traces/
> some_session-20140625-102709
> > $ lttng enable-event -u some_event
> > UST event some_event created in channel channel0
> > $ lttng list some_session -u --channel channel0
> > Tracing session some_session: [inactive]
> >     Trace path: /home/username/lttng-traces/ some_session-20140625-102709
> >
> > === Domain: UST global ===
> >
> > Buffer type: per UID
> >
> > - channel0: [enabled]
> >
> >     Attributes:
> >       overwrite mode: 0
> >       subbuffers size: 131072
> >       number of subbufers: 4
> >       switch time interval: 0
> >       read time interval: 0
> >       output: mmap()
> >
> >     Events:
> >       some_event (type: tracepoint) [enabled]
> > (end example)
> >
> >    You can take a look at
> /usr/src/lttng-tools/src/bin/lttng/commands/list.c to see how the
> information is obtained.
> >
> > Daniel U. Thibault
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