[lttng-dev] Can tracepoint be listed before app registered?

[Mathieu Desnoyers]

----- Original Message -----
> From: "Jérémie Galarneau" <jeremie.galarneau at efficios.com>
> To: "zlynus" <302590304 at qq.com>
> Cc: "lttng-dev" <lttng-dev at lists.lttng.org>
> Sent: Friday, March 7, 2014 1:23:01 PM
> Subject: Re: [lttng-dev] Can tracepoint be listed before app registered?
> 
> On Fri, Mar 7, 2014 at 12:26 PM, zlynus <302590304 at qq.com> wrote:
> > Hi,
> > Sorry to bother you guys. The lttng-tool man page dosen't make it clear
> > that
> > when the tracepoints of user-space application can be listed. So I did a
> > little test. As far as I can tell ,the tracepoint information is only
> > available during the application is running.
> >
> 
> Correct.
> 
> > So is it possible that the tracepoint can be available *before* app get
> > running, specifically, before enable-event subcommand? I think it can be
> > quite convenient to output the list when specify which events to trace. If
> > it is not for now,
> > maybe it's a feature worth working on. My idea is lttng-tool could read
> > tracer provider library and get the info,and  add a option after 'list'
> > subcommand which let user specify the provider library to read. Just a
> > personal opion from a new comer :-)
> >
> 
> You can enable an event before the app is started. However, as you
> pointed out, the session daemon has no knowledge of application events
> before they are launched.
> 
> My understanding of your suggestion is that we should define a public
> provider API on which the lttng client could hook itself to list
> events. It would be of limited use in the case of statically linked
> providers, but It's an interesting problem... Do you have a specific
> use-case in mind?

Another option that would take care of statically linked providers
would be to let a lttng library look at all the executables on the system
(or from a certain path in the system), as well as .so, and list a specific
"tracepoint provider" section that we could specify. We'd need to parse
ELF for this.

Thoughts ?

Thanks,

Mathieu

> 
> Regards,
> Jérémie
> 
> > Best regards,
> > Lingyu Zhu
> >
> >
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> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >
> 
> 
> 
> --
> Jérémie Galarneau
> EfficiOS Inc.
> http://www.efficios.com
> 
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> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com