[lttng-dev] Error: opening metadata failed (LTTng on OpenWRT)

Thu Nov 23 17:20:24 UTC 2017

Hi Jonathan,

The lttng-sessiond.log that I provided was actually from a second time that I started 'lttng-sessiond'  (did not realize that there is a difference), which resulted in the already loaded error. When I captured the output from a fresh start of 'lttng-sessiond' I noticed lots of modprobe errors with modules that could not be loaded.

Turns out that the modprobe on my OpenWrt system can only handle modules with a name of max 32 characters (!). The first mandatory core module ("lttng-ring-buffer-client-discard") is still loaded as its name is exactly 32 chars, the other 5 core modules do not get loaded as their names are longer than 32 chars. I will modify modprobe as a proper fix, but shortening the names of the lttng-*.ko modules and manually loading each core module already showed that this solves the issue.

Thanks for your reply! This helped in pointing me in the right direction.

Kind regards,
Robin

-----Original Message-----
From: Jonathan Rajotte-Julien [mailto:jonathan.rajotte-julien at efficios.com] 
Sent: Wednesday, 22 November, 2017 19:55
To: Robin Michielsen
Cc: lttng-dev at lists.lttng.org
Subject: Re: [lttng-dev] Error: opening metadata failed (LTTng on OpenWRT)

Hi,

On Wed, Nov 22, 2017 at 06:39:11PM +0100, Robin Michielsen wrote:
> Hi all,
> 
>Any suggestions from anyone on what to check and/or how to debug the issue that I described in my mail from last week?

>From lttng-sessiond.log:

lttng-ring-buffer-client-discard is already loaded
Error: Unable to load required module lttng-ring-buffer-client-discard

Is there any particular reason why some modules are already loaded ?

Did you perform a "depmod -a" on the target?

Cheers

> 
> Kind regards,
> Robin
> 
> -----Original Message-----
> From: jeremie.galarneau at gmail.com [mailto:jeremie.galarneau at gmail.com] 
> On Behalf Of Jérémie Galarneau
> Sent: Tuesday, 14 November, 2017 22:14
> To: Robin Michielsen
> Cc: lttng-dev at lists.lttng.org
> Subject: Re: [lttng-dev] Error: opening metadata failed (LTTng on 
> OpenWRT)
> 
> On 14 November 2017 at 12:09, Robin Michielsen <robin.michielsen.1 at gmail.com> wrote:
> > Hi Jérémie,
> >
> > Maybe I misunderstood how to create a session, but are the commands that I listed not sufficient for this?
> >
> > •       lttng create
> > •       lttng enable-event --kernel --syscall open,close
> > •       lttng start
> >
> 
> Yes, sorry. I missed it on the first read through.
> 
> Jérémie
> 
> > Kind regards,
> > Robin
> >
> > -----Original Message-----
> > From: jeremie.galarneau at gmail.com 
> > [mailto:jeremie.galarneau at gmail.com]
> > On Behalf Of Jérémie Galarneau
> > Sent: Tuesday, 14 November, 2017 17:09
> > To: Robin Michielsen
> > Cc: lttng-dev at lists.lttng.org
> > Subject: Re: [lttng-dev] Error: opening metadata failed (LTTng on
> > OpenWRT)
> >
> > Hi Robin,
> >
> > Can you add the commands you use to create the session?
> >
> > Thanks,
> > Jérémie
> >
> > On 14 November 2017 at 04:41, Robin Michielsen <robin.michielsen.1 at gmail.com> wrote:
> >> Hi all,
> >>
> >>
> >>
> >> I am trying to trace the Linux kernel (system calls) using LTTng on 
> >> a platform that is running OpenWRT. I have cross compiled the 
> >> latest versions
> >> (2.10.x) of the lttng-modules, lttng-tools and lttng-ust packages 
> >> and installed these on my OpenWRT system. Now when I start a kernel 
> >> trace then the lttng tool returns the error "LTTng transport 
> >> relay-metadata not found /
> >> Error: Opening metadata failed". Does anybody know what might cause 
> >> this error, or have a hint on what to check?
> >>
> >>
> >>
> >> I have attached the captured output of ‘lttng-sessiond -vvv 
> >> --verbose-consumer’. Here is some more context:
> >>
> >> ·         MIPS platform running Linux 3.18.29
> >>
> >> ·         Package versions:
> >>
> >> o   lttng-modules-2.10.4
> >>
> >> o   lttng-tools-2.10.1
> >>
> >> o   lttng-ust-2.10.0
> >>
> >> ·         lsmod shows that the following modules have been loaded:
> >>
> >> o   lttng_clock
> >>
> >> o   lttng_lib_ring_buffer
> >>
> >> o   lttng_ring_buffer_client_discard
> >>
> >> o   lttng_statedump
> >>
> >> o   lttng_tracer
> >>
> >> ·         Commands to create and start a session:
> >>
> >> o   lttng create
> >>
> >> o   lttng enable-event --kernel --syscall open,close
> >>
> >> o   lttng start
> >>
> >>
> >>
> >> When ‘lttng start’ is called then lttng-sessiond’s debug output 
> >> shows “Closing metadata fd -1 (in trace_kernel_destroy_metadata() 
> >> at trace-kernel.c:569)” followed by “Sending response (size: 20, retcode:
> >> Opening metadata failed (45)) (in thread_manage_clients() at main.c:4641)”.
> >> I assume that the error that I’m seeing is because for some reason 
> >> metadata fd is being closed.
> >>
> >>
> >>
> >> Does anybody know what may cause this issue, or have a hint on to check?
> >>
> >>
> >>
> >> Kind regards,
> >>
> >> Robin
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> lttng-dev mailing list
> >> lttng-dev at lists.lttng.org
> >> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >>
> >
> >
> >
> > --
> > Jérémie Galarneau
> > EfficiOS Inc.
> > http://www.efficios.com
> >
> 
> 
> 
> --
> Jérémie Galarneau
> EfficiOS Inc.
> http://www.efficios.com
> 
> _______________________________________________
> lttng-dev mailing list
> lttng-dev at lists.lttng.org
> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

--
Jonathan Rajotte-Julien
EfficiOS