[lttng-dev] Creating custom application

[Jonathan Rajotte-Julien]

On Wed, Apr 03, 2019 at 09:08:45AM -0400, Mosleh Uddin wrote:
> Hello,
> 
> Sorry, I should be more specific. I am creating a custom yocto build. I
> have seen some examples where systemd is utilized to start the sessiond as
> a service. The limitation I have is that I don't want to include the whole
> lttng-tools librray in my build. I understand that the sessiond is an

You will have to if you plan on tracing any applications on your resulting
image. Why is it a limitation? Size constraint?

lttng-tools is already part of OE-core (the meta/ layer). Use this recipe to
build it [1] or as a base for a custom one.

[1] https://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta/recipes-kernel/lttng/lttng-tools_2.10.6.bb

You can add the following to your local.conf file to build only lttng-ust and
lttng-tools.

CORE_IMAGE_EXTRA_INSTALL += "lttng-ust lttng-tools"
PACKAGECONFIG_pn-lttng-tools_append = " lttng-ust"

By default a systemd service file is installed but is not activated (which seems
to be what you want).

Cheers


> executable, I am just unsure how I could build or get this in my build.
> Moving forward from this I could use fork/exec to daemonize which would be
> simple.
> Is there perhaps a existing recipe?
> 
> Regards,
> Mosleh
> 
> On Tue, Apr 2, 2019 at 6:01 PM Mosleh Uddin <mosleh1235 at gmail.com> wrote:
> 
> > Hi,
> >
> > That makes complete sense. I was more curious about the sessiond
> > executable. I'm guessing this is something I will have to create along with
> > my build?
> >
> > Regards,
> > Mosleh
> >
> > On Tue, Apr 2, 2019 at 5:18 PM Jonathan Rajotte-Julien <
> > jonathan.rajotte-julien at efficios.com> wrote:
> >
> >> On Tue, Apr 02, 2019 at 04:54:00PM -0400, Mosleh Uddin wrote:
> >> > Hello,
> >> >
> >> > Could you give me some more insight into spawning my own sessiond? Sorry
> >> > I'm not completely clear on the topic.
> >> > Thank you for all your assistance.
> >>
> >> Normally lttng-sessiond is treated as a "server/service/daemon" (think
> >> http
> >> server as apache) and is *normally* launched as a daemon
> >> (systemd/sysVinit) at
> >> boot time.
> >>
> >> Managing manually the lifetime of a lttng-sessiond process is done the
> >> same way
> >> as any other process. You can manage it via the command line
> >> (./lttng-sessiond), via a
> >> service manager (systemd/upstart etc.) or with a custom service manager (a
> >> python script/c etc.).
> >>
> >> You could spawn a lttng-sessiond from your application with the
> >> appropriate
> >> parameters set to isolate it if you need. LTTNG_HOME is an important one.
> >> The
> >> output directory also can be manipulated. See man lttng-sessiond for more
> >> details. You will need to manage the process or leave it to a system
> >> administrator and only active tracing when a sessiond is present for
> >> example.
> >>
> >> Cheers
> >>
> >> >
> >> > Regards,
> >> > Mosleh
> >> >
> >> > On Wed, Mar 27, 2019 at 1:52 PM Jonathan Rajotte-Julien <
> >> > jonathan.rajotte-julien at efficios.com> wrote:
> >> >
> >> > > Hi Mosleh,
> >> > >
> >> > > On Wed, Mar 27, 2019 at 12:09:54PM -0400, Mosleh Uddin wrote:
> >> > > > Hello,
> >> > > >
> >> > > > Thank you for the quick response. I was able to use the
> >> documentation you
> >> > > > provided to start a session and get tracepoint list. I do have some
> >> > > > follow-up questions:
> >> > > >
> >> > > > 1) I needed to create a session daemon before executing my custom
> >> > > > application. In the API I did see functionality to see if a daemon
> >> is
> >> > > > active, however, it is possible to spawn a session daemon in my
> >> custom
> >> > > app?
> >> > >
> >> > > liblttng-ctl does not expose a lttng-sessiond spawning function since
> >> by
> >> > > definition it is a daemon executable (think apache,mysql etc.), you
> >> will
> >> > > have to
> >> > > use system/popen/exec.. to spawn the lttng-sessiond process etc. if
> >> you
> >> > > want to
> >> > > control its lifetime using your custom application.
> >> > >
> >> > > >
> >> > > > 2) I am able to get a list of active traces lttng can see in
> >> userspace, I
> >> > > > enable all the traces and start tracing. The traces however seem to
> >> not
> >> > > be
> >> > > > written anywhere on my filesystem. Do I have to specify a location?
> >> Or
> >> > > am I
> >> > > > missing something? My current flow is:
> >> > >
> >> > > Please refer to the create command. If outputting locally you will
> >> need to
> >> > > pass
> >> > > a "file://...." url to lttng_create_session.
> >> > >
> >> > > You can check on the result for each steps using "lttng list" and
> >> "lttng
> >> > > list
> >> > > <session_name>" as you go to troubleshot your setup script.
> >> > >
> >> > > While debugging you can also start the lttng-sessiond in verbose mode
> >> to
> >> > > understand what is going on.
> >> > >
> >> > > Also note that you could also use the lttng "load" api if the session
> >> you
> >> > > are
> >> > > trying to load is "static" and always the same. You would only need to
> >> > > ship an
> >> > > xml file with your application.
> >> > >
> >> > > Cheers
> >> > >
> >> > > >
> >> > > >    - Creating a session
> >> > > >    - Specifying the domain
> >> > > >    - Creating a handle
> >> > > >    - Creating a channel (with default attributes)
> >> > > >    - Enabling the channel
> >> > > >    - Enabling event (for all traces)
> >> > > >    - Start tracing
> >> > > >
> >> > > > Thanks again for all the assistance.
> >> > > >
> >> > > > Regards,
> >> > > > Mosleh
> >> > > >
> >> > > > On Tue, Mar 26, 2019 at 11:29 AM Jonathan Rajotte-Julien <
> >> > > > jonathan.rajotte-julien at efficios.com> wrote:
> >> > > >
> >> > >
> >>
> >> --
> >> Jonathan Rajotte-Julien
> >> EfficiOS
> >>
> >

-- 
Jonathan Rajotte-Julien
EfficiOS