LIBTRACEEVENT(3) libtraceevent Manual LIBTRACEEVENT(3) NAME tep_register_event_handler, tep_unregister_event_handler - Register / unregisters a callback function to parse an event information. SYNOPSIS #include enum tep_reg_handler { TEP_REGISTER_SUCCESS, TEP_REGISTER_SUCCESS_OVERWRITE, }; 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); 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); typedef int (*tep_event_handler_func)(struct trace_seq *s, struct tep_record *record, struct tep_event *event, void *context); DESCRIPTION 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 registered. 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. RETURN VALUE 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, TEP_ERRNO__MEM_ALLOC_FAILED is returned. 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. EXAMPLE #include #include ... 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) { case TEP_REGISTER_SUCCESS: printf ("Registered handler for hrtimer_expire_entry\n"); break; case TEP_REGISTER_SUCCESS_OVERWRITE: 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"); FILES event-parse.h Header file to include in order to have access to the library APIs. trace-seq.h 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. -ltraceevent Linker switch to add when building a program that uses the library. SEE ALSO libtraceevent(3), trace-cmd(1) AUTHOR Steven Rostedt , author of libtraceevent. Tzvetomir Stoyanov , author of this man page. REPORTING BUGS Report bugs to LICENSE libtraceevent is Free Software licensed under the GNU LGPL 2.1 RESOURCES https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/ NOTES 1. rostedt@goodmis.org mailto:rostedt@goodmis.org 2. tz.stoyanov@gmail.com mailto:tz.stoyanov@gmail.com 3. linux-trace-devel@vger.kernel.org mailto:linux-trace-devel@vger.kernel.org libtraceevent 01/13/2024 LIBTRACEEVENT(3)