[lttng-dev] custom probe for loadable device driver - no output?

[Joe VanAndel]

Sorry, I’m answering my own question:

When I built a new kernel with “CONFIG_MODULE_SIG” disabled, the probes in
my loadable driver started working.

It would be helpful to have this documented in the tutorial on kernel
tracing.

On Tue, Aug 4, 2015 at 3:46 PM, Joe VanAndel <vanandel at ucar.edu> wrote:

> I’m trying to add LTTng probes to a driver module, but I don’t get any
> output from my probe in the LTTng session.
>
>
> Any idea what else I need to configure to get the output from my probe?
>
>
> Kernel: 3.10.0
>
> OS:  Centos 7.1.1503
>
> LTTng tools : from EfficiOS-RHEL7-x86-64 repository
>
> lttng-modules:  2.6.2
>
>
> The running kernel has the following enabled:
>
> CONFIG_MODULES
>
> CONFIG_KALLSYMS
>
> CONFIG_HIGH_RES_TIMERS
>
> CONFIG_TRACEPOINTS
>
>
> I’ve defined/used tracepoints in my driver with the mainline TRACE_EVENT()
> macros.  My tracepoints are on the open/close entry points of the device.
>
>
> I’ve added the LTTng adaptation layer for my probe in LTTng-modules.
>
>
> I’ve started the daemon to load my custom probe
>
>  lttng-sessiond -d --extra-kmod-probes=db2k
>
>
> I’ve verified that my event is available, by running
>
>
> lttng list --kernel | grep db2k
>
>       db2k_hello (loglevel: TRACE_EMERG (0)) (type: tracepoint)
>
>
> There’s an entry for my probe in
>
> /sys/kernel/debug/tracing/events/db2k/db2k_hello
>
>
> When I run the following as root:
>
> lttng create trace_db2k
>
> lttng enable-event --kernel --tracepoint db2k_hello --tracepoint
> kmem_kmalloc --tracepoint kmem_kfree \
>
>      --tracepoint timer_start --tracepoint timer_cancel
>
> lttng start
>
> ———————
>
> the output is:
>
> Session trace_db2k created.
>
> Traces will be written in /root/lttng-traces/trace_db2k-20150804-193318
>
> Kernel event db2k_hello created in channel channel0
>
> Tracing started for session trace_db2k
>
> ===========
>
>  I run a test program that uses the driver, and then stop the session.
>
> # lttng stop
>
> Waiting for data availability.
>
> Tracing stopped for session trace_db2k
>
> # lttng view
>
> Trace directory: /root/lttng-traces/trace_db2k-20150804-193318
>
> <No output>
>
>
> Here is the “mainline” db2k.h
>
> http://pastebin.com/0i8eWF1a
>
>
> Here is the
>
> LTTng adaptation db2k.h
>
> http://pastebin.com/fXW9ppqM
>
>
> Here is the
>
> lttng-probe-db2k.c
>
> http://pastebin.com/WHuWKpPZ
>
>
> The drive contains the lines:
>
> #define CREATE_TRACE_POINTS
>
> #include "trace/events/db2k.h"
>
> static int
> db2k_open(struct inode *inode, struct file *file)
> {
>     int minor = MINOR(inode->i_rdev);
>     int stat = 0;
>     DEVICE_EXTENSION *pde = NULL;
>     dbg("db2k_open called");
>     trace_db2k_hello(minor, "open");
> .
> .
> }
>
> --
> Joe VanAndel
> NCAR/EOL
>



-- 
Joe VanAndel
NCAR/EOL
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