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Subject[PATCH 30/73] tools lib traceevent: Man pages for event handler APIs
From: Tzvetomir Stoyanov <>

Create man pages for libtraceevent APIs:


Signed-off-by: Tzvetomir Stoyanov <>
Cc: Andrew Morton <>
Cc: Jiri Olsa <>
Cc: Namhyung Kim <>
Signed-off-by: Steven Rostedt (VMware) <>
Signed-off-by: Arnaldo Carvalho de Melo <>
.../libtraceevent-reg_event_handler.txt | 156 ++++++++++++++++++
1 file changed, 156 insertions(+)
create mode 100644 tools/lib/traceevent/Documentation/libtraceevent-reg_event_handler.txt

diff --git a/tools/lib/traceevent/Documentation/libtraceevent-reg_event_handler.txt b/tools/lib/traceevent/Documentation/libtraceevent-reg_event_handler.txt
new file mode 100644
index 000000000000..53d37d72a1c1
--- /dev/null
+++ b/tools/lib/traceevent/Documentation/libtraceevent-reg_event_handler.txt
@@ -0,0 +1,156 @@
+tep_register_event_handler, tep_unregister_event_handler - Register /
+unregisters a callback function to parse an event information.
+*#include <event-parse.h>*
+enum *tep_reg_handler* {
+int *tep_register_event_handler*(struct tep_handle pass:[*]_tep_, int _id_, const char pass:[*]_sys_name_, const char pass:[*]_event_name_, tep_event_handler_func _func_, void pass:[*]_context_);
+int *tep_unregister_event_handler*(struct tep_handle pass:[*]tep, int id, const char pass:[*]sys_name, const char pass:[*]event_name, tep_event_handler_func func, void pass:[*]_context_);
+typedef int (*pass:[*]tep_event_handler_func*)(struct trace_seq pass:[*]s, struct tep_record pass:[*]record, struct tep_event pass:[*]event, void pass:[*]context);
+The _tep_register_event_handler()_ function registers a handler function,
+which is going to be called to parse the information for a given event.
+The _tep_ argument is the trace event parser context. The _id_ argument is
+the id of the event. The _sys_name_ argument is the name of the system,
+the event belongs to. The _event_name_ argument is the name of the event.
+If _id_ is >= 0, it is used to find the event, otherwise _sys_name_ and
+_event_name_ are used. The _func_ is a pointer to the function, which is going
+to be called to parse the event information. The _context_ argument is a pointer
+to the context data, which will be passed to the _func_. If a handler function
+for the same event is already registered, it will be overridden with the new
+one. This mechanism allows a developer to override the parsing of a given event.
+If for some reason the default print format is not sufficient, the developer
+can register a function for an event to be used to parse the data instead.
+The _tep_unregister_event_handler()_ function unregisters the handler function,
+previously registered with _tep_register_event_handler()_. The _tep_ argument
+is the trace event parser context. The _id_, _sys_name_, _event_name_, _func_,
+and _context_ are the same arguments, as when the callback function _func_ was
+The _tep_event_handler_func_ is the type of the custom event handler
+function. The _s_ argument is the trace sequence, it can be used to create a
+custom string, describing the event. A _record_ to get the event from is passed
+as input parameter and also the _event_ - the handle to the record's event. The
+_context_ is custom context, set when the custom event handler is registered.
+The _tep_register_event_handler()_ function returns _TEP_REGISTER_SUCCESS_
+if the new handler is registered successfully or
+_TEP_REGISTER_SUCCESS_OVERWRITE_ if an existing handler is overwritten.
+If there is not enough memory to complete the registration,
+The _tep_unregister_event_handler()_ function returns 0 if _func_ was removed
+successful or, -1 if the event was not found.
+The _tep_event_handler_func_ should return -1 in case of an error,
+or 0 otherwise.
+#include <event-parse.h>
+#include <trace-seq.h>
+struct tep_handle *tep = tep_alloc();
+int timer_expire_handler(struct trace_seq *s, struct tep_record *record,
+ struct tep_event *event, void *context)
+ trace_seq_printf(s, "hrtimer=");
+ if (tep_print_num_field(s, "0x%llx", event, "timer", record, 0) == -1)
+ tep_print_num_field(s, "0x%llx", event, "hrtimer", record, 1);
+ trace_seq_printf(s, " now=");
+ tep_print_num_field(s, "%llu", event, "now", record, 1);
+ tep_print_func_field(s, " function=%s", event, "function", record, 0);
+ return 0;
+ int ret;
+ ret = tep_register_event_handler(tep, -1, "timer", "hrtimer_expire_entry",
+ timer_expire_handler, NULL);
+ if (ret < 0) {
+ char buf[32];
+ tep_strerror(tep, ret, buf, 32)
+ printf("Failed to register handler for hrtimer_expire_entry: %s\n", buf);
+ } else {
+ switch (ret) {
+ printf ("Registered handler for hrtimer_expire_entry\n");
+ break;
+ printf ("Overwrote handler for hrtimer_expire_entry\n");
+ break;
+ }
+ }
+ ret = tep_unregister_event_handler(tep, -1, "timer", "hrtimer_expire_entry",
+ timer_expire_handler, NULL);
+ if ( ret )
+ printf ("Failed to unregister handler for hrtimer_expire_entry\n");
+ Header file to include in order to have access to the library APIs.
+ Header file to include in order to have access to trace sequences
+ related APIs. Trace sequences are used to allow a function to call
+ several other functions to create a string of data to use.
+ Linker switch to add when building a program that uses the library.
+_libtraceevent(3)_, _trace-cmd(1)_
+*Steven Rostedt* <>, author of *libtraceevent*.
+*Tzvetomir Stoyanov* <>, author of this man page.
+Report bugs to <>
+libtraceevent is Free Software licensed under the GNU LGPL 2.1
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