1LIBTRACEEVENT(3) libtraceevent Manual LIBTRACEEVENT(3)
2
6 tep_register_event_handler, tep_unregister_event_handler - Register /
7 unregisters a callback function to parse an event information.
8
10 #include <event-parse.h>
11 enum tep_reg_handler {
13 TEP_REGISTER_SUCCESS,
14 TEP_REGISTER_SUCCESS_OVERWRITE,
15 };
16 int tep_register_event_handler(struct tep_handle *tep, int id, const char *sys_name, const char *event_name, tep_event_handler_func func, void *context);
18 int tep_unregister_event_handler(struct tep_handle *tep, int id, const char *sys_name, const char *event_name, tep_event_handler_func func, void *context);
19 typedef int (*tep_event_handler_func)(struct trace_seq *s, struct tep_record *record, struct tep_event *event, void *context);
21
23 The tep_register_event_handler() function registers a handler function,
24 which is going to be called to parse the information for a given event.
25 The tep argument is the trace event parser context. The id argument is
26 the id of the event. The sys_name argument is the name of the system,
27 the event belongs to. The event_name argument is the name of the event.
28 If id is >= 0, it is used to find the event, otherwise sys_name and
29 event_name are used. The func is a pointer to the function, which is
30 going to be called to parse the event information. The context argument
31 is a pointer to the context data, which will be passed to the func. If
32 a handler function for the same event is already registered, it will be
33 overridden with the new one. This mechanism allows a developer to
34 override the parsing of a given event. If for some reason the default
35 print format is not sufficient, the developer can register a function
36 for an event to be used to parse the data instead.
37 The tep_unregister_event_handler() function unregisters the handler
39 function, previously registered with tep_register_event_handler(). The
40 tep argument is the trace event parser context. The id, sys_name,
41 event_name, func, and context are the same arguments, as when the
42 callback function func was registered.
43 The tep_event_handler_func is the type of the custom event handler
45 function. The s argument is the trace sequence, it can be used to
46 create a custom string, describing the event. A record to get the event
47 from is passed as input parameter and also the event - the handle to
48 the record’s event. The context is custom context, set when the custom
49 event handler is registered.
50
52 The tep_register_event_handler() function returns TEP_REGISTER_SUCCESS
53 if the new handler is registered successfully or
54 TEP_REGISTER_SUCCESS_OVERWRITE if an existing handler is overwritten.
55 If there is not enough memory to complete the registration,
56 TEP_ERRNO__MEM_ALLOC_FAILED is returned.
57 The tep_unregister_event_handler() function returns 0 if func was
59 removed successful or, -1 if the event was not found.
60 The tep_event_handler_func should return -1 in case of an error, or 0
62 otherwise.
63
65 #include <event-parse.h>
66 #include <trace-seq.h>
67 ...
68 struct tep_handle *tep = tep_alloc();
69 ...
70 int timer_expire_handler(struct trace_seq *s, struct tep_record *record,
71 struct tep_event *event, void *context)
72 {
73 trace_seq_printf(s, "hrtimer=");
74 if (tep_print_num_field(s, "0x%llx", event, "timer", record, 0) == -1)
76 tep_print_num_field(s, "0x%llx", event, "hrtimer", record, 1);
77 trace_seq_printf(s, " now=");
79 tep_print_num_field(s, "%llu", event, "now", record, 1);
81 tep_print_func_field(s, " function=%s", event, "function", record, 0);
83 return 0;
85 }
86 ...
87 int ret;
88 ret = tep_register_event_handler(tep, -1, "timer", "hrtimer_expire_entry",
90 timer_expire_handler, NULL);
91 if (ret < 0) {
92 char buf[32];
93 tep_strerror(tep, ret, buf, 32)
95 printf("Failed to register handler for hrtimer_expire_entry: %s\n", buf);
96 } else {
97 switch (ret) {
98 case TEP_REGISTER_SUCCESS:
99 printf ("Registered handler for hrtimer_expire_entry\n");
100 break;
101 case TEP_REGISTER_SUCCESS_OVERWRITE:
102 printf ("Overwrote handler for hrtimer_expire_entry\n");
103 break;
104 }
105 }
106 ...
107 ret = tep_unregister_event_handler(tep, -1, "timer", "hrtimer_expire_entry",
108 timer_expire_handler, NULL);
109 if ( ret )
110 printf ("Failed to unregister handler for hrtimer_expire_entry\n");
111
113 event-parse.h
114 Header file to include in order to have access to the library APIs.
115 trace-seq.h
116 Header file to include in order to have access to trace sequences
117 related APIs. Trace sequences are used to allow a function to call
118 several other functions to create a string of data to use.
119 -ltraceevent
120 Linker switch to add when building a program that uses the library.
121
123 libtraceevent(3), trace-cmd(1)
124
126 Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.
127 Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>, author of this man page.
128
130 Report bugs to <linux-trace-devel@vger.kernel.org[3]>
131
133 libtraceevent is Free Software licensed under the GNU LGPL 2.1
134
136 https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/
137
139 1. rostedt@goodmis.org
140 mailto:rostedt@goodmis.org
141 2. tz.stoyanov@gmail.com
143 mailto:tz.stoyanov@gmail.com
144 3. linux-trace-devel@vger.kernel.org
146 mailto:linux-trace-devel@vger.kernel.org
147libtraceevent 1.5.3 07/21/2022 LIBTRACEEVENT(3)