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

[Joe VanAndel]

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
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