OpenTelemetry tracing of Dbus calls

[Ralf Habacker]

Am 01.02.23 um 09:01 schrieb Umut Tezduyar Lindskog:
> Hi Ralf. Thanks for your work.
> 
> I have not used lttng extensively. Do these debug logs have some kind of 
> correlation between them to follow a journey of a dbus call or? 

The initial support provides the same information as you would get if 
you run dbus-daemon with DBUS_VERBOSE=1.

When running dbus-daemon with

DBUS_VERBOSE=1 ./bin/dbus-daemon --config-file=bus/session.conf 2>&1 | 
grep "pending\|incoming\|Initialized"

and in another terminal

DBUS_SESSION_BUS_ADDRESS=<address-from-dbus-daemon-log> bin/dbus-monitor 
--session

in the generated log there could be found for example

[dbus/dbus-connection.c(534):_dbus_connection_queue_received_message_link] 
Message 0x1b01e20 (method_call /org/freedesktop/DBus 
org.freedesktop.DBus Hello '' reply to 0) added to incoming queue 
0x1b07320, 1 incoming


[dbus/dbus-connection.c(2039):_dbus_connection_send_preallocated_unlocked_no_update] 
Message 0x1b08310 (method_return no path no interface no member 's') for 
:1.0 added to outgoing queue 0x1b07320, 1 pending to send

 
[dbus/dbus-connection.c(2039):_dbus_connection_send_preallocated_unlocked_no_update] 
Message 0x1b086b0 (signal /org/freedesktop/DBus org.freedesktop.DBus 
NameAcquired 's') for :1.0 added to outgoing queue 0x1b07320, 1 pending 
to send

  1675243246.984679 
[dbus/dbus-connection.c(534):_dbus_connection_queue_received_message_link] 
Message 0x1b08310 (method_call /org/freedesktop/DBus 
org.freedesktop.DBus.Monitoring BecomeMonitor 'asu' reply to 0) added to 
incoming queue 0x1b07320, 1 incoming


> While  you are implementing, if you have tried it out with LTTNG, it would be 
> very nice to see some screenshots.

Screenshots are not available, but there is an example session at 
https://gitlab.freedesktop.org/dbus/dbus/-/blob/7051e2a0506ea6be3fbd1294bc5561543f9f109a/README-lttng.md.

Regards
Ralf