[lttng-dev] application changes to support lttng

[Mathieu Desnoyers]

----- On Jun 30, 2015, at 8:08 PM, jamie explorer <jamieexplorer at gmail.com> wrote: 

> Hi lttng-dev,
> sorry for asking basic questions.
> Can you guys point me to any documentation which has this info. lttng.org
> documentation doesnt have info about this.

> How does the app register to use lttng?

It awaits on a futex in a shared memory area, and then connects to the session 
daemon through a unix socket. 

> how do sessiond, app and lttng-ust interact? is there any socket from every app
> to sessiond?

Through unix sockets. Yes, there are two unix sockets between each instrumented 
application and each session daemon. One for commands (sent by session daemon, 
reply received from application), the other for notifications (send by app, reply received 
by session daemon). 

> How is the app modified when instrumented using lttng? are there any threads
> added?

Yes, 2 threads are added. One interacts with root sessiond (if there is one 
active), the other with per-user sessiond (if one is active). If no sessiond is 
active, those threads simply wait on futexes. 

> Are there any powerful tools for analysis on collected traces.

Trace Compass (Eclipse UI) 
lttng-analyses 
lttngtop 
and of course babeltrace for the event-by-event text output. 

Best regards, 

Mathieu 

> /Jam

> On Mon, Jun 29, 2015 at 10:03 AM, jamie explorer < jamieexplorer at gmail.com >
> wrote:

>> Hello,
>> I have just started using lttng and still looking at documentation.
>> Can you help me with some info.

>> How does the app register to use lttng?
>> how do sessiond, app and lttng-ust interact? is there any socket from every app
>> to sessiond?
>> How is the app modified when instrumented using lttng? are there any threads
>> added?
>> when lttng instrumentation is linked along with app
>> Are there any powerful tools for analysis on collected traces.

>> /Jam

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