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

[Jonathan Rajotte-Julien]

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
> Protection des systèmes et contremesures (PSC) | Systems Protection & Countermeasures (SPC)
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