Both the server library and the client library include facilities to provide debugging and tracing information at runtime. This is achieved through component reports, which are sets of interesting events provided by many Mir components. A component report can be usually handled in a number of different ways, configured using command-line options and/or environment variables. By default, component reports are turned off.

Server reports

The way component reports are handled on the server can be configured using either command-line options or environment variables. The environment variables are prefixed with MIR_SERVER_ and contain underscores ('_') instead of dashes ('-'). The available component reports and handlers for the server are:

Environment variable	Command line option	Handlers
MIR_SERVER_COMPOSITOR_REPORT	–compositor-report	log,lttng
MIR_SERVER_DISPLAY_REPORT	–display-report	log,lttng
MIR_SERVER_INPUT_REPORT	–input-report	log,lttng
MIR_SERVER_LEGACY_INPUT_REPORT	–legacy-input-report	log
MIR_SERVER_SEAT_REPORT	–seat-report	log
MIR_SERVER_SCENE_REPORT	–scene-report	log,lttng
MIR_SERVER_SHARED_LIBRARY_PROBER_REPORT	–shared-library-prober-report	log,lttng

For example, to enable the LTTng input report, one could either use the --input-report=lttng command-line option to the server, or set the MIR_SERVER_INPUT_REPORT=lttng environment variable.

LTTng support

Mir provides LTTng tracepoints for various interesting events. You can enable LTTng tracing for a Mir component by using the corresponding command-line option or environment variable for that component's report:

$ lttng create mirsession -o /tmp/mirsession
$ lttng enable-event -u -a
$ lttng start
$ mir_demo_server --compositor-report=lttng
$ lttng stop
$ babeltrace /tmp/mirsession/<trace-subdir>

LTTng-UST versions up to and including 2.1.2, and up to and including 2.2-rc2 contain a bug (lttng #538) that prevents event recording if the tracepoint provider is dlopen()-ed at runtime, like in the case of Mir. If you have a version of LTTng affected by this bug, you need to preload the server tracepoint provider library:

$ LD_PRELOAD=libmirserverlttng.so mir_demo_server --compositor-report=lttng