babeltrace2-source.ctf.lttng-live(7)

NAME

babeltrace2-source.ctf.lttng-live — Babeltrace 2: LTTng live source component class

DESCRIPTION

A Babeltrace 2 source.ctf.lttng-live message iterator connects to a local or remote LTTng relay daemon, receives the streams of a specific tracing session, and emits corresponding messages.

CTF streams over
LTTng live (TCP)
  |
  |   +--------------------+
  |   | src.ctf.lttng-live |
  '-->|                    |
      |                out @--> Sorted messages of one
      +--------------------+    or more streams

More information about LTTng live is available in the LTTng Documentation.

See babeltrace2-intro(7) to learn more about the Babeltrace 2 project and its core concepts.

A source.ctf.lttng-live component has a single output port: its message iterator muxes (sorts) the messages from the various CTF data streams internally.

A source.ctf.lttng-live message iterator handles the messages of one, and only one LTTng tracing session. A single LTTng tracing session can contain one or more traces, depending on the active tracing domains and the configured user space buffering scheme.

The component connects to an LTTng relay daemon using the inputs parameter. This is an array of exactly one string which is the URL of the LTTng relay daemon to connect to.

By default, if the remote tracing session name doesn’t exist, then the message iterator returns "try again later". This default mode makes the message iterator never end: even if the remote tracing session is destroyed, the message iterator keeps on waiting for a tracing session with the same name to exist. You can change this behaviour with the session-not-found-action initialization parameter.

NoteAs of this version, you can only create one message iterator per source.ctf.lttng-live component. This is because the LTTng live protocol accepts at most one client per tracing session per LTTng relay daemon.

As of this version, a source.ctf.lttng-live component can connect to an LTTng relay daemon using the LTTng 2.4 or LTTng 2.15 protocol. The latter is required for CTF 2 support.

The "get supported MIP versions" method of source.ctf.lttng-live always reports to support MIP versions 0 and 1. If you attempt to make a source.ctf.lttng-live component read a CTF 2 recording session within a trace processing graph configured with MIP 0, then the message iterator will fail at initialization or "next" method call time.

INITIALIZATION PARAMETERS

inputs=URL [array of one string]

Use URL to connect to the LTTng relay daemon.

URL is an array of exactly one string of which the format is:

net[4]://RDHOST[:RDPORT]/host/TGTHOST/SESSION

RDHOST

Host name or IP address of the LTTng relay daemon.

RDPORT

Listening port of the LTTng relay daemon.

If not specified, then the component uses the default port (5344).

TGTHOST

Target host name or IP address.

SESSION

Name of the LTTng tracing session from which to receive data.

session-not-found-action=(continue | fail | end) [optional string]

When the message iterator doesn’t find the specified remote tracing session (SESSION part of the inputs parameter), do one of:

continue (default)

Keep on trying, returning "try again later" to the downstream user until the tracing session exists.

With this action, the message iterator never ends, as the LTTng live protocol cannot currently indicate that a tracing session will never exist.

fail

Fail.

end

End.

PORTS

+--------------------+
| src.ctf.lttng-live |
|                    |
|                out @
+--------------------+

Output

out: Single output port.

QUERY OBJECTS

`babeltrace.support-info`

See babeltrace2-query-babeltrace.support-info(7) to learn more about this query object.

For a string input which honors the LTTng live URL format (see the inputs parameter), the result object is 0.75.

`sessions`

You can query the sessions object to get a list of available LTTng tracing sessions for a given LTTng relay daemon URL.

Parameters:

url=URL [string]

Use URL to connect to the LTTng relay daemon.

The format of URL is:

net[4]://RDHOST[:RDPORT]

RDHOST

Host name or IP address of the LTTng relay daemon.

RDPORT

Listening port of the LTTng relay daemon.

If not specified, then the query operation uses the default port (5344).

Result object (array of maps, one element for each available tracing session):

client-count [unsigned integer]

Current number of LTTng live clients connected to the relay daemon to receive data from this tracing session.

session-name [string]

Tracing session name.

stream-count [unsigned integer]

Current number of CTF streams in this tracing sessions, including the metadata streams.

target-hostname [string]

Hostname of the tracing session.

This isn’t necessarily the hostname of the relay daemon.

timer-us [unsigned integer]

Configured period (µs) of the live timer of the tracing session (see lttng-create(1)).

trace-format [string]

Format of the trace(s) of the tracing session amongst:

ctf-1.8: CTF 1.8
ctf-2.0: CTF 2

url [string]

URL to use as the first element of the inputs parameter to connect to the same LTTng relay daemon and receive data from this tracing session.