SYNOPSIS

#include <tracefs.h>

char **tracefs_event_systems(const char *tracing_dir);
char **tracefs_system_events(const char *tracing_dir, const char *system);
int tracefs_event_enable(struct tracefs_instance *instance, const char *system,
                           const char *event);
int tracefs_event_disable(struct tracefs_instance *instance, const char *system,
                            const char *event);
int tracefs_iterate_raw_events(struct tep_handle *tep, struct tracefs_instance *instance,
                                 cpu_set_t *cpus, int cpu_size,
                                 int (*callback)(struct tep_event *, struct tep_record *, int, void *),
                                 void *callback_context);
void tracefs_iterate_stop(struct tracefs_instance *instance);

DESCRIPTION

Trace systems and events related APIs.

The tracefs_event_systems() function returns array of strings with the names of all registered trace systems, located in the given tracing_dir directory. This could be NULL or the location of the tracefs mount point for the trace systems of the local machine, or it may be a path to a copy of the tracefs directory from another machine. The last entry in the array is a NULL pointer. The array must be freed with tracefs_list_free() API.

The tracefs_system_events() function returns array of strings with the names of all registered trace events for given trace system specified by system, located in the given tracing_dir directory. This could be NULL or the location of the tracefs mount point for the trace systems of the local machine, or it may be a path to a copy of the tracefs directory from another machine. The last entry in the array as a NULL pointer. The array must be freed with tracefs_list_free() API.

The tracefs_event_enable() function enables a given event based on the system and event passed in for the given instance. If instance is NULL, then the top level tracing directory is used. If system and event are both NULL, then all events are enabled for the instance. If event is NULL then all events within the system are enabled. If system is NULL, then all systems are searched and any event within a system that matches event is enabled. Both system and event may be regular expressions as defined by regex(3).

The tracefs_event_disable() function disables the events that match the system and event parameters for the given instance. What events are disable follow the same rules as tracefs_event_enable() for matching events. That is, if instance is NULL, then the top level tracing directory is used. If both system and event are NULL then all events are disabled for the given instance, and so on.

The tracefs_iterate_raw_events() function will read the tracefs raw data buffers and call the specified callback function for every event it encounters. Events are iterated in sorted order: oldest first. An initialized tep handler is required (See tracefs_local_events(3)). If instance is NULL, then the toplevel tracefs buffer is used, otherwise the buffer for the corresponding instance is read. To filter only on a subset of CPUs, cpus and cpu_size may be set to only call callback with events that occurred on the CPUs specified, otherwise if cpus is NULL then the callback function will be called for all events, and cpu_size is ignored. The callback function will be called with the following parameters: A pointer to a struct tep_event that corresponds to the type of event the record is; The record representing the event; The CPU that the event occurred on; and a pointer to user specified callback_context. If the callback returns non-zero, the iteration stops.

Use tracefs_iterate_stop() to force a executing tracefs_iterate_raw_events() to halt. This can be called from either a callback that is called by the iterator (even though a return of non-zero will stop it), or from another thread.

RETURN VALUE

The tracefs_event_systems() and tracefs_system_events() functions return an array of strings. The last element in that array is a NULL pointer. The array must be freed with tracefs_list_free() API. In case of an error, NULL is returned.

Both tracefs_event_enable() and tracefs_event_disable() return 0 if they found any matching events (Note it does not check the previous status of the event. If tracefs_event_enable() finds an event that is already enabled, and there are no other errors, then it will return 0). If an error occurs, even if other events were found, it will return -1 and errno will be set. If no errors occur, but no events are found that match the system and event parameters, then -1 is returned and errno is not set.

The tracefs_iterate_raw_events() function returns -1 in case of an error or 0 otherwise.

EXAMPLE

#include <tracefs.h>

char **systems = tracefs_event_systems(NULL);

        if (systems) {
                int i = 0;
                /* Got registered trace systems from the top trace instance */
                while (systems[i]) {
                        char **events = tracefs_system_events(NULL, systems[i]);
                        if (events) {
                                /* Got registered events in system[i] from the top trace instance */
                                int j = 0;

                                while (events[j]) {
                                        /* Got event[j] in system[i] from the top trace instance */
                                        j++;
                                }
                                tracefs_list_free(events);
                        }
                        i++;
                }
                tracefs_list_free(systems);
        }
....
static int records_walk(struct tep_event *tep, struct tep_record *record, int cpu, void *context)
{
        /* Got recorded event on cpu */
        return 0;
}
...
struct tep_handle *tep = tracefs_local_events(NULL);

        if (!tep) {
                /* Failed to initialise tep handler with local events */
                ...
        }

        errno = 0;
        ret = tracefs_event_enable(NULL, "sched", NULL);
        if (ret < 0 && !errno)
                printf("Could not find 'sched' events\n");
        tracefs_event_enable(NULL, "irq", "irq_handler_\(enter\|exit\)");

        if (tracefs_iterate_raw_events(tep, NULL, NULL, 0, records_walk, NULL) < 0) {
                /* Error walking through the recorded raw events */
        }

        /* Disable all events */
        tracefs_event_disable(NULL, NULL, NULL);
        tep_free(tep);

FILES

tracefs.h
        Header file to include in order to have access to the library APIs.
-ltracefs
        Linker switch to add when building a program that uses the library.

SEE ALSO

libtracefs(3), libtraceevent(3), trace-cmd(1)

AUTHOR

Steven Rostedt <rostedt@goodmis.org>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com>

REPORTING BUGS

LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES

COPYING

Copyright (C) 2020 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).