tep_register_event_handler - Man Page

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

Referenced By

The man page tep_unregister_event_handler(3) is an alias of tep_register_event_handler(3).

07/22/2021 libtraceevent 1.2.1 libtraceevent Manual