Provided by: babeltrace2_2.0.6-2build1_amd64 
NAME
babeltrace2-intro - Introduction to Babeltrace 2
DESCRIPTION
This manual page is an introduction to the Babeltrace 2 project.
The “WHAT IS BABELTRACE 2?” section describes the parts of the project and shows the major
changes from Babeltrace 1 to Babeltrace 2 while the “BABELTRACE 2 CONCEPTS” section
defines the core concepts of Babeltrace 2.
The “TRACE PROCESSING GRAPH REPRESENTATION” section shows how some concepts are visually
represented in other Babeltrace 2 manual pages.
WHAT IS BABELTRACE 2?
Babeltrace 2 is an open-source software project of which the purpose is to process or
convert traces (see <https://en.wikipedia.org/wiki/Tracing_(software)>).
The Babeltrace 2 project includes the following parts:
Babeltrace 2 library (libbabeltrace2)
A shared library with a C API.
With libbabeltrace2, you can programmatically create plugins and component classes,
build and run trace processing graphs, and more (see the “BABELTRACE 2 CONCEPTS”
section for more details about those concepts).
All the other Babeltrace 2 parts rely on this library.
babeltrace2 command-line program
A command-line interface which uses libbabeltrace2 to load plugins, create a trace
processing graph, create components, connect their ports correctly, and run the graph.
You can also use babeltrace2 to list the available plugins or to query an object from
a component class.
See babeltrace2(1).
Babeltrace 2 Python bindings
A Python 3 package (bt2) which offers a Pythonic interface of libbabeltrace2.
You can perform the same operations which are available in libbabeltrace2 with the
Python bindings, but more conveniently and with less code. However, the Python
bindings are less performant than libbabeltrace2.
Babeltrace 2 project’s plugins
The Babeltrace 2 plugins shipped with the project.
Those plugins are not special in that they only rely on libbabeltrace2 and you don’t
need them to use libbabeltrace2, babeltrace2(1), or the Python bindings. However, the
project’s plugins provide many widely used trace format encoders/decoders as well as
common trace processing graph utilities.
The Babeltrace 2 project’s plugins are:
ctf
Common Trace Format (see <https://diamon.org/ctf/>) (CTF) input/output, including
the LTTng live source.
See babeltrace2-plugin-ctf(7).
lttng-utils
Graph utilities specific to LTTng (see <https://lttng.org/>) traces.
See babeltrace2-plugin-lttng-utils(7).
text
Plain text input/output.
See babeltrace2-plugin-text(7).
utils
Common graph utilities (muxer, trimmer, counter, dummy sink).
See babeltrace2-plugin-utils(7).
Changes since Babeltrace 1
This manual page is an introduction to Babeltrace 2, a rewrite of Babeltrace 1 with a
focus on extensibility, flexibility, and interoperability.
Babeltrace 1 exists since 2010.
You can install both projects on the same file system as there are no file name conflicts.
The major improvements brought by Babeltrace 2 are:
General
• Full plugin support: any user can distribute a Babeltrace 2 plugin and, as long as
libbabeltrace2 finds it, any application linked to libbabeltrace2 can load it and
use it.
Plugins are not just trace format encoders and decoders: they package source,
filter, and sink component classes so that you can connect specialized, reusable
components together in a trace processing graph to create a customized trace
conversion or analysis device.
This modular strategy is much like how the FFmpeg (see <https://www.ffmpeg.org/>),
GStreamer (see <https://gstreamer.freedesktop.org/>), and DirectShow (see
<https://en.wikipedia.org/wiki/DirectShow>) projects approach media stream
processing.
• All the parts of the Babeltrace 2 project run on the major operating systems,
including Windows and macOS.
• Some component classes, such as sink.text.pretty (similar to the text output
format of babeltrace(1)) and sink.text.details, can write color codes to the
standard output when it’s connected to a color-enabled terminal.
The Babeltrace 2 log, printed to the standard output, can also be colorized.
Command-line interface
• Whereas you can convert traces from one format to another with Babeltrace 1’s CLI
tool, babeltrace(1), you can also execute a custom trace manipulation task with
babeltrace2(1) thanks to the babeltrace2-run(1) command.
• The babeltrace2-convert(1) command features an automatic source component
discovery algorithm to find the best suited components to create for a given
non-option argument (file or directory path, or custom string like an LTTng live
(see <https://lttng.org>) URL).
For example:
$ babeltrace2 /path/to/ctf/trace
$ babeltrace2 net://localhost/host/myhost/my-session
CTF (see <https://diamon.org/ctf/>) input/output
• The source.ctf.fs component class, which is more or less the equivalent of
Babeltrace 1’s ctf input format, has features not found in Babeltrace 1:
• The component handles many trace quirks which are the results of known tracer
bugs and corner cases (LTTng-UST, LTTng-modules, and barectf (see
<https://github.com/efficios/barectf>)), making it possible to decode
malformed packets.
• The component merges CTF traces sharing the same UUID into a single, logical
trace.
This feature supports LTTng 2.11’s tracing session rotation trace chunks.
• With a sink.ctf.fs component, you can create CTF traces on the file system.
With babeltrace2(1), you can use the --output-format=ctf and --output options to
create an implicit sink.ctf.fs component.
For example:
$ babeltrace2 /path/to/input/trace \
--output-format=ctf --output=trace-dir
LTTng live (see <https://lttng.org>) input
• The babeltrace(1) command exits successfully when it cannot find an LTTng live
(--input-format=lttng-live option) tracing session.
The session-not-found-action initialization parameter controls what a
source.ctf.lttng-live message iterator does when it cannot find the remote tracing
session.
If the action is end, the message iterator does like babeltrace(1) and simply ends
successfully.
If the action is continue (the default), the message iterator never ends: it keeps
on trying until the tracing session exists, indeed subscribing to the session.
Library
• libbabeltrace2 shares nothing with libbabeltrace.
The Babeltrace 2 library C API has features such as:
• A single header file.
• Function precondition and postcondition checking.
• Object-oriented model with shared and unique objects.
• Strict C typing and const correctness.
• User-extensible classes.
• Rich, thread-safe error reporting.
• Per-component and per-subsystem logging levels.
• Trace intermediate representation (IR) objects to make the API
trace-format-agnostic.
• A versioned protocol for message interchange between components to enable
forward and backward compatibility.
• You can build the library in developer mode to enable an extensive set of function
precondition and postcondition checks.
The developer mode can help detect programming errors early when you develop a
Babeltrace 2 plugin or an application using libbabeltrace2.
See the project’s README for build-time requirements and detailed build
instructions.
BABELTRACE 2 CONCEPTS
This section defines the main concepts of the Babeltrace 2 project.
These concepts translate into types and functions in libbabeltrace2 and its Python
bindings, but also as command-line actions and options in the babeltrace2 program. The
other Babeltrace 2 manual pages assume that you are familiar with the following
definitions.
Some Babeltrace 2 concepts are interdependent: it is normal to jump from one definition to
another to understand the big picture.
Component class
A reusable class which you can instantiate as one or more components within a trace
processing graph.
There are three types of component classes used to create the three types of
components: source, filter, and sink.
A component class implements methods, one of which is an initialization method, or
constructor, to create a component. You pass initialization parameters to this method
to customize the created component. For example, the initialization method of the
source.ctf.fs component class accepts a mandatory inputs parameter which is an array
of file system path(s) to the CTF trace(s). It also accepts an optional clock-class-
offset-ns parameter which is an offset, in nanoseconds, to add to all the clock
classes (descriptors of stream clocks) found in the traces’s metadata.
A component class can have a description and a help text.
Component
A node within a trace processing graph.
There are three types of components:
Source component
An input component which produces messages.
Examples: CTF files input, log file input, LTTng live input, random event
generator.
Filter component
An intermediate component which can transform the messages it consumes, augment
them, sort them, discard them, or create new ones.
Examples: filter which removes messages based on an expression, filter which adds
debugging information to selected events, message muxer, trace trimmer.
Sink component
An output component which consumes messages and usually writes them to one or more
formatted files.
Examples: log file output, CTF files output, pretty-printed plain text output.
Components are connected together within a trace processing graph through their ports.
Source components have output ports, sink components have input ports, and filter
components have both.
A component is the instance of a component class. The terms component and component
class instance are equivalent.
Within a trace processing graph, each component has a unique name. This is not the
name of its component class, but an instance name. If human is a component class name,
than Nancy and John could be component names.
Once a graph is configured (the first time it runs), you cannot add components to it
for the remaining graph’s lifetime.
Port
A connection point, on a component, from which are sent or where are received messages
when the trace processing graph runs.
An output port is from where messages are sent. An input port is where messages are
received. Source components have output ports, sink components have input ports, and
filter components have both.
You can only connect an output port to a single input port.
All ports do not need to be connected.
A filter or sink component receiving messages from its input ports is said to consume
messages.
The link between an output port and input port is a connection.
Once a graph is configured (the first time it runs), you cannot connect ports for the
remaining graph’s lifetime.
Connection
The link between an output port and an input port through which messages flow when a
trace processing graph runs.
Message iterator
An iterator on an input port of which the returned elements are messages.
A component or another message iterator can create many message iterators on a single
input port, before or while the trace processing graph runs.
Message
The element of a message iterator.
Messages flow from output ports to input ports.
A source component message iterator produces messages, while a sink component consumes
them. A filter component message iterator can both consume and produce messages.
The main types of messages are:
Event
A trace event record within a packet or within a stream.
Packet beginning
The beginning of a packet within a stream.
A packet is a conceptual container of events.
Packet end
The end of a packet within a stream.
Stream beginning
The beginning of a stream.
A stream is a conceptual container of packets and/or events.
Usually, a given source component’s output port sends packet and event messages
which belong to a single stream, but it’s not required.
Stream end
The end of a stream.
Discarded events
A count of discarded events within a given time interval for a given stream.
Discarded packets
A count of discarded packets within a given time interval for a given stream.
Trace processing graph
A filter graph (see <https://en.wikipedia.org/wiki/Filter_graph>) where nodes are
components and messages flow from output ports to input ports.
You can build a trace processing graph with libbabeltrace2, with the Babeltrace 2
Python bindings, or with the babeltrace2-run(1) and babeltrace2-convert(1) CLI
commands.
When a trace processing graph runs, the sink components consume messages from their
input ports, making all the graph’s message iterators work one message at a time to
perform the trace conversion or analysis duty.
Plugin
A container, or package, of component classes as a shared library or Python module.
Each component class within a plugin has a type (source, filter, or sink) and a name.
The type and name pair is unique within a given plugin.
libbabeltrace2 can load a plugin (.so, .dll, or .py file) at run time: the result is a
plugin object in which you can find a specific component class and instantiate it
within a trace processing graph as a component.
The babeltrace2 program uses the COMP-CLS-TYPE.PLUGIN-NAME.COMP-CLS-NAME format to
identify a specific component class within a specific plugin. COMP-CLS-TYPE is either
source (or src), filter (or flt), or sink.
You can list the available Babeltrace 2 plugins with the babeltrace2-list-plugins(1)
command.
Query
An operation with which you can get a named object from a component class, possibly
with custom query parameters.
The plain text metadata stream of a CTF trace and the available LTTng live sessions of
a given LTTng relay daemon are examples of query objects.
You can use libbabeltrace2, the Babeltrace 2 Python bindings, or the
babeltrace2-query(1) CLI command to query a component class’s object.
TRACE PROCESSING GRAPH REPRESENTATION
In the Babeltrace 2 manual pages, a component is represented with a box. The box has the
component class type, plugin name, and component class name at the top. Just below,
between square brackets, is its component name within the trace processing graph. Each
port is represented with an @ symbol on the border(s) of the component box with its name
inside the box. Output ports are on the box’s right border while input ports are on the
box’s left border.
For example, here’s a source component box:
+------------+
| src.ctf.fs |
| [my-src] |
| |
| stream0 @
| stream1 @
| stream2 @
+------------+
This one is an instance of the source.ctf.fs component class named my-src. It has three
output ports named stream0, stream1, and stream2.
A trace processing graph is represented with multiple component boxes connected together.
The connections are arrows from output ports to input ports.
For example, here’s a simple conversion graph:
+------------+ +-----------------+ +------------------+
| src.ctf.fs | | flt.utils.muxer | | sink.text.pretty |
| [ctf] | | [muxer] | | [text] |
| | | | | |
| stream0 @--->@ in0 out @--->@ in |
| stream1 @--->@ in1 | +------------------+
| stream2 @--->@ in2 |
+------------+ @ in3 |
+-----------------+
Note that input port in3 of component muxer is not connected in this example.
Sometimes, we symbolically represent other resources which are consumed from or produced
by components. In this case, arrows are used, but they do not go to or from port symbols
(@), except for messages. For example, in the graph above, the ctf source component
consumes a CTF trace and the text sink component prints plain text to the terminal, so
here’s a more complete diagram:
CTF trace
|
| +------------+ +-----------------+ +------------------+
| | src.ctf.fs | | flt.utils.muxer | | sink.text.pretty |
'-->| [ctf] | | [muxer] | | [text] |
| | | | | |
| stream0 @--->@ in0 out @--->@ in |
| stream1 @--->@ in1 | +-----+------------+
| stream2 @--->@ in2 | |
+------------+ @ in3 | '--> Terminal
+-----------------+
Here’s another example of a more complex graph which splits a specific stream using some
criteria:
+------------+ +-----------------+ +------------------+
| src.ctf.fs | | flt.utils.muxer | | sink.text.pretty |
| [ctf-in] | | [muxer] | | [text] |
| | | | | |
| stream0 @--->@ in0 out @--->@ in |
| stream1 @--->@ in1 | +------------------+
| stream2 @-. @ in2 |
+------------+ | +-----------------+ +-------------+
| | sink.ctf.fs |
| | [ctf-out0] |
| +-------------------+ | |
| | flt.some.splitter | .->@ in |
| | [splitter] | | +-------------+
| | | |
'->@ in A @-' +-------------+
| B @-. | sink.ctf.fs |
+-------------------+ | | [ctf-out1] |
| | |
'->@ in |
+-------------+
BUGS
If you encounter any issue or usability problem, please report it on the Babeltrace bug
tracker (see <https://bugs.lttng.org/projects/babeltrace>).
RESOURCES
The Babeltrace project shares some communication channels with the LTTng project (see
<https://lttng.org/>).
• Babeltrace website (see <https://babeltrace.org/>)
• Mailing list (see <https://lists.lttng.org>) for support and development: lttng-
dev@lists.lttng.org
• IRC channel (see <irc://irc.oftc.net/lttng>): #lttng on irc.oftc.net
• Bug tracker (see <https://bugs.lttng.org/projects/babeltrace>)
• Git repository (see <https://git.efficios.com/?p=babeltrace.git>)
• GitHub project (see <https://github.com/efficios/babeltrace>)
• Continuous integration (see <https://ci.lttng.org/view/Babeltrace/>)
• Code review (see <https://review.lttng.org/q/project:babeltrace>)
AUTHORS
The Babeltrace 2 project is the result of hard work by many regular developers and
occasional contributors.
The current project maintainer is Jérémie Galarneau
<mailto:jeremie.galarneau@efficios.com>.
COPYRIGHT
This manual page is part of the Babeltrace 2 project.
Babeltrace is distributed under the MIT license (see
<https://opensource.org/licenses/MIT>).
SEE ALSO
babeltrace2(1)