[lttng-dev] make a trace_event in a module (driver)

[Daniel.Thibault@drdc-rddc.gc.ca (Thibault, Daniel)]

> Date: Sun, 24 Nov 2013 19:26:05 +0100
> From: Klaus Dannecker <klaus.dannecker@gmx.de>
>
> > Interesting. Would you mind running "lttng start" in verbose mode and 
> > provide the output?
> > lttng -vvv start
> klaus at ubuntu:~$ sudo lttng -vvv start
> DEBUG2 [2854/2854]: Config file path found: /home/klaus (in get_session_name() at utils.c:57)
> DEBUG1 [2854/2854]: Session name found: auto-20131124-091639 (in get_session_name() at utils.c:58)
> DEBUG1 [2854/2854]: Starting tracing for session auto-20131124-091639 (in start_tracing() at commands/start.c:81)
> DEBUG1 [2854/2854]: LSM cmd type : 16 (in send_session_msg() at lttng-ctl.c:131)
> 'ctrl c'
> klaus at ubuntu:~$

Definitely looks like a module loading problem.

> > lttng-modules does not define an "uninstall" make target. I guess 
> > you'll have to delete the modules manually under /lib/modules/$(uname 
> > -r)/extra /lib/modules/$(uname -r)/extra/lib /lib/modules/$(uname 
> > -r)/extra/probes
> >
> > I'm wondering if it could be a conflict with your distribution's 
> > lttng-modules-dkms package... Could you verify that it is not 
> > installed?
>
> now i make two experiments:
> first:
> install ubuntu 12.04 in vmware
> $ git clone git://git.lttng.org/lttng-tools.git
> $ git clone git://git.lttng.org/lttng-modules.git
> $ git clone git://git.lttng.org/lttng-ust.git
> $ git clone git://git.lttng.org/userspace-rcu.git
> compile and install all like:
> https://www.ibm.com/developerworks/community/blogs/fe313521-2e95-46f2-817d-44a4f27eba32/entry/howto_tracing_with_lttng?lang=en
> now i have the same problem.

   Aha!  There is one crucial mistake in the ibm.com document: he installs the packages in the wrong order.  lttng-tools must be installed AFTER lttng-modules and lttng-ust.  lttng-modules can be installed before, during or after lttng-ust, but userspace-rcu must be installed before lttng-ust.
   The problem is that the configure of lttng-tools detects the presence or absence of lttng-modules and also detects the presence or absence of lttng-ust, and adjusts to both.  By installing lttng-tools before lttng-modules, you've built an lttng-tools set that CANNOT be used to trace the kernel.

   So, try again from scratch, making sure to install lttng-tools last.

> second:
> install ubuntu 12.04 in vmware
> sudo apt-get install lttng-tools
>...
> Building only for 3.8.0-29-generic
> Building initial module for 3.8.0-29-generic
> Error! Bad return status for module build on kernel: 3.8.0-29-generic (i686)
> Consult /var/lib/dkms/lttng-modules/2.0.2/build/make.log for more information.
> Setting up lttng-tools (2.0.1-0ubuntu1) ...
> /usr/sbin/addgroup
> lttng-sessiond start/running, process 5515
> Processing triggers for libc-bin ...
> ldconfig deferred processing now taking place
> klaus at ubuntu:~$

   The Ubuntu lttng 2.0.1 install will very likely run into trouble against kernel 3.8 because of the new module signing requirements.

> $ git clone git://git.lttng.org/lttng-modules.git
> compile and install lttng_modules
>
> now works lttng start, stop and destroy!
>
> Klaus

Daniel U. Thibault
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