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(TRACE_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 TRACE_INFO
+
+Which will gather all events from TRACE_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
*/
ctf_float(float, floatfield, floatarg)
ctf_float(double, doublefield, doublearg)
+
+ /*
+ * ctf_enum: a field using a previously declared
+ * enumeration args: (provider, enum name, container
+ * type, field name, argument expression). The
+ * enumeration itself and its values must have been
+ * defined previously with the TRACEPOINT_ENUM macro,
+ * described below.
+ */
+ ctf_enum(sample_component, enumeration_name, int,
+ enumfield, enumarg)
)
)
application, but they must each have their own provider name. Duplicate
provider names are not allowed.
+The CTF specification also supports enumerations that can be declared
+inside a tracepoint provider and used as fields in the tracepoint. This
+shows how to specify enumerations and what they can be used for:
+
+The enumeration is a mapping between an integer, or a range of integers, and a
+string. It can be used to have a more compact trace in cases where the possible
+values for a field are limited:
+
+TRACEPOINT_ENUM(
+ /*
+ * The provider name, as described in the TRACEPOINT_EVENT macro.
+ */
+ sample_component,
+
+ /*
+ * The name of this enumeration, that will be used when using this
+ * global type in tracepoint fields.
+ */
+ enumeration_name,
+
+ /*
+ * TP_ENUM_VALUES describe the values of this enumeration and what they
+ * map to.
+ */
+ TP_ENUM_VALUES(
+ /*
+ * Maps an integer with this string value. By default, enumerations
+ * start at 0 and increment 1 for each entry.
+ */
+ ctf_enum_value(string_value)
+
+ /*
+ * Maps the string value to integers in the range 'start' to 'end'
+ * inclusively. If 'start' == 'end', then the string is mapped to
+ * a specific value.
+ * Enumeration ranges may overlap, but the behavior is
+ * implementation-defined, each trace reader will handle overlapping
+ * as it wishes.
+ */
+ ctf_enum_range(start, end, string_value)
+ )
+)
+
.fi
.SH "ASSIGNING LOGLEVEL TO EVENTS"
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"
.IP "LTTNG_UST_WITHOUT_BADDR_STATEDUMP"
Prevent liblttng-ust to perform a base-address statedump on session-enable.
.PP
+.IP "LTTNG_UST_GETCPU_PLUGIN"
+Used by the getcpu override plugin system. The environment variable
+provides the path to the shared object which will act as the getcpu override
+plugin. An example can be found in the lttng-ust documentation under
+examples/getcpu-override .
+.PP
+.IP "LTTNG_UST_CLOCK_PLUGIN"
+Used by the clock override plugin system. The environment variable
+provides the path to the shared object wich will act as the clock override
+plugin. An example can be found in the lttng-ust documentation under
+doc/examples/clock-override .
+.PP
.SH "SEE ALSO"
projects / deliverable / lttng-ust.git / blobdiff