base to be integrated with an upstream project.
.PP
+.SH "USAGE WITH TRACELOG"
+.PP
+If you want to migrate existing logging (info, errors, ...)
+to LTTng UST, you can use the tracelog() interface.
+To do it, in a nutshell:
+
+1) #include <lttng/tracelog.h>
+
+2) /* in your code, use like a printf, with extra loglevel info. */
+ tracelog(info, "Message with 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 "lttng_ust_tracelog:*"
+ lttng start
+ [... run your program ...]
+ lttng stop
+ lttng view
+
+That's it!
+
+You can replace the enable-event line above with a selection of
+loglevels, e.g.:
+
+ lttng enable-event -u -a --loglevel INFO
+
+Which will gather all events from INFO and more important loglevels.
+
+.PP
+
.SH "USAGE WITH TRACEPOINT"
.PP
The simple way to generate the lttng-ust tracepoint probes is to use the
the same provider and event name, it is recommended to use a
provider event name pair only once within the source code to help
map events back to their call sites when analyzing the trace.
+
+Sometimes arguments to the probe are expensive to compute (e.g.
+take call stack). To avoid the computation when the tracepoint is
+disabled one can use more 'low level' tracepoint_enabled() and
+do_tracepoint() macros as following:
+
+ if (tracepoint_enabled(ust_tests_hello, tptest)) {
+ /* prepare arguments */
+ do_tracepoint(ust_tests_hello, tptest, i, netint, values,
+ text, strlen(text), dbl, flt);
+ }
+
+Here do_tracepoint() doesn't contain check if the tracepoint is enabled.
+Using tracepoint() in such scenario is dangerous since it also contains
+enabled check and thus race condition is possible in the following code
+if the tracepoint has been enabled after check in tracepoint_enabled()
+but before tracepoint():
+
+ if (tracepoint_enabled(provider, name)) { /* tracepoint is disabled */
+ prepare(args);
+ }
+ /* tracepoint is enabled by 'lttng' tool */
+ tracepoint(provider, name, args); /* args wasn't prepared properly */
+
+Note also that neither tracepoint_enabled() nor do_tracepoint() have
+STAP_PROBEV() call so if you need it you should emit this call yourself.
+
.fi
.SH "BUILDING/LINKING THE TRACEPOINT PROVIDER"
.PP
.IP "LTTNG_UST_DEBUG"
-Activate liblttng-ust debug output.
+Activate liblttng-ust debug and error output.
.PP
.IP "LTTNG_UST_REGISTER_TIMEOUT"
The environment variable "LTTNG_UST_REGISTER_TIMEOUT" can be used to