NAME

       tep_register_event_handler, tep_unregister_event_handler - Register / unregisters a
       callback function to parse an event information.

SYNOPSIS

       #include <event-parse.h>

       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 <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) {
                           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 <rostedt@goodmis.org[1]>, author of libtraceevent.
           Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>, author of this man page.

REPORTING BUGS

       Report bugs to <linux-trace-devel@vger.kernel.org[3]>

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