libtraceevent(3) ================ NAME ---- tep_register_event_handler, tep_unregister_event_handler - Register / unregisters a callback function to parse an event information. SYNOPSIS -------- [verse] -- *#include * enum *tep_reg_handler* { _TEP_REGISTER_SUCCESS_, _TEP_REGISTER_SUCCESS_OVERWRITE_, }; 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); -- 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 ------- [source,c] -- #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 ----- [verse] -- *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 ------ [verse] -- *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/linux/kernel/git/torvalds/linux.git