tep_register_event_handler - Man Page

#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);

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​.

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​.

#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");

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​.

libtraceevent(3), trace-cmd(1)

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

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

libtraceevent is Free Software licensed under the GNU LGPL 2​.1

https://git​.kernel​.org/pub/scm/libs/libtrace/libtraceevent​.git/

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