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LTTng Toolchain 2.5.0 RC1 Now Available

Christian Babeux on 28 May 2014

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A new release candidate of the LTTng toolchain is now available.

This release adds multiple fixes and new features detailed below.

LTTng-tools

Save and Load sessions

This introduce two new commands along with API's functions allowing the user to save/load a session to/from an XML file.

lttng save [OPTIONS] [SESSION]

(lttng_save_session_*() in lttng/save.h).

lttng load [OPTIONS] [SESSION]

(lttng_load_session*() in lttng/load.h).

The XML format of the session file is described in the tarball in src/common/config/session.xsd. Note that this adds a new dependency to libxml2.

User space Perf counter support

With the lttng add-context command you can now use perf context perf:thread:* along with the -u/--userspace option. See --help for a full list.

Daemon configuration files

A configuration file can be used for each daemon to control their options. Three configuration files are available:

  • lttng-sessiond.conf
  • lttng-relayd.conf
  • lttng-consumerd.conf

These are simple INI format and can be placed in the system-wide directory /etc/lttng, ~/$HOME/.lttng/ or user-defined with:

  -f  --config                       Load daemon configuration file

User-defined list of kernel probe modules

Thanks to Jan Glauber, it's now possible to load a user-defined list of LTTng probe modules with the new option of the session daemon or by using an environment variable. For instance:

lttng-sessiond --kmod-probes ext4,btrfs,kvm

or

LTTNG_KMOD_PROBES=ext4,btrfs,kvm lttng-sessiond

These are the major features added for this release. A couple of things also have changed that are worth mentioning.

The lttng.h header file has been split into several components like event.h, session.h, and so on. If you are using lttng.h directly in your application, this should not affect you at all because including lttng.h also includes every other components.

The deprecated lttng_enable_consumer(), lttng_disable_consumer(), and lttng_health_check() API functions have been removed for good.

The list command now prints the log level of JUL events.

Debug logs now have a timestamp (YAMAN!).

LTTng-UST

New tracef() instrumentation facility

Excerpt from the lttng-ust(3) man page:

USAGE WITH TRACEF

  The simplest way to add instrumentation to your  code  is  by  far  the
  tracef() API. To do it, in a nutshell:

  1) #include <lttng/tracef.h>

  2) /* in your code, use like a printf */
    tracef("my message, this integer %d", 1234);

  3) Link your program against liblttng-ust.so.

  4) Enable  UST events when tracing with the following sequence of commands
    from lttng-tools:

    lttng create
    lttng enable-event -u -a
    lttng start
    [... run your program ...]
    lttng stop
    lttng view

If you want to have more flexibility and control on the event names, payload typing, etc, you can continue reading on and use the tracepoints below. tracef() is there for quick and dirty ad hoc instrumentation, whereas tracepoint.h is meant for thorough instrumentation of a code base to be integrated with an upstream project.

LTTng-modules

New and noteworthy:

  • State dump of block devices
  • State dump of file descriptor flags and modes
  • 3.15 Linux kernel support
  • v4lv2 instrumentation support
  • MIPS32 system call tracing
  • New /proc/lttng-logger ABI

Here's how to use the new /proc/lttng-logger ABI:

From the command line (for instance), start lttng-sessiond as root:

sudo lttng-sessiond

Start tracing from root or from a user belonging to the tracing group:

lttng create
lttng enable-event --kernel lttng-logger

Write event payload data to /proc/lttng-logger (from any user, does not need to be in any group):

echo -n "Some message" > /proc/lttng-logger

Stop tracing, view the trace:

lttng stop
lttng view

You should see:

[10:44:24.810273367] (+?.?????????) thinkos lttng_logger: { cpu_id = 3 }, { _msg_length = 12, msg = "Some message" }

It is a quick and easy way to trace some events from user space through the kernel tracer. It is much more basic than UST: lttng-logger is slower (involves system call round-trip to the kernel) and only supports logging strings. But it's very quick and easy to use, especially from scripts.

  • 2014-05-28 lttng-tools 2.5.0-rc1 (changelog)
  • 2014-05-28 lttng-ust 2.5.0-rc1 (changelog)
  • 2014-05-28 lttng-modules 2.5.0-rc1 (changelog)

Available in the Download section.