| libtracefs(3) |
| ============= |
| |
| NAME |
| ---- |
| tracefs_iterate_raw_events, tracefs_iterate_stop, tracefs_follow_event, tracefs_follow_missed_events - Iterate over events in the ring buffer |
| |
| SYNOPSIS |
| -------- |
| [verse] |
| -- |
| *#include <tracefs.h>* |
| |
| int *tracefs_iterate_raw_events*(struct tep_handle pass:[*]_tep_, struct tracefs_instance pass:[*]_instance_, |
| cpu_set_t pass:[*]_cpus_, int _cpu_size_, |
| int (pass:[*]_callback_)(struct tep_event pass:[*], struct tep_record pass:[*], int, void pass:[*]), |
| void pass:[*]_callback_context_); |
| void *tracefs_iterate_stop*(struct tracefs_instance pass:[*]_instance_); |
| |
| int *tracefs_follow_event*(struct tep_handle pass:[*]_tep_, struct tracefs_instance pass:[*]_instance_, |
| const char pass:[*]_system_, const char pass:[*]_event_name_, |
| int (pass:[*]_callback_)(struct tep_event pass:[*], |
| struct tep_record pass:[*], |
| int, void pass:[*]), |
| void pass:[*]_callback_data_); |
| int *tracefs_follow_missed_events*(struct tracefs_instance pass:[*]_instance_, |
| int (pass:[*]_callback_)(struct tep_event pass:[*], |
| struct tep_record pass:[*], |
| int, void pass:[*]), |
| void pass:[*]_callback_data_); |
| -- |
| |
| DESCRIPTION |
| ----------- |
| Trace iterator over raw events. |
| |
| 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. |
| |
| The *tracefs_follow_event()* is used with *tracefs_iterate_raw_events()* but |
| intead of the callback being called for every event, it is only called for the |
| specified _system_ / _event_name_ given to the function. The _callback_ is the |
| same as for *tracefs_iterate_raw_events()*, and the passed in _callback_context_ |
| will be passed to the _callback_ as well. Note, if it returns something other |
| than 0, it will stop the loop before the _callback_ of *tracefs_iterate_raw_events()* |
| is called. |
| |
| The *tracefs_follow_missed_events()* will call the _callback_ when missed |
| events are detected. It will set the _record_ parameter of the callback to the |
| record that came after the missed events and _event_ will be of the type of |
| event _record_ is. _cpu_ will be set to the CPU that missed the events, and |
| _callback_data_ will be the content that was passed in to the function. |
| |
| RETURN VALUE |
| ------------ |
| The *tracefs_iterate_raw_events()* function returns -1 in case of an error or |
| 0 otherwise. |
| |
| EXAMPLE |
| ------- |
| [source,c] |
| -- |
| #include <unistd.h> |
| #include <tracefs.h> |
| #include <stdbool.h> |
| #include <signal.h> |
| |
| struct my_struct { |
| bool stopped; |
| }; |
| |
| #define MAX_COUNT 500000 |
| static int counter; |
| |
| static int callback(struct tep_event *event, struct tep_record *record, |
| int cpu, void *data) |
| { |
| struct my_struct *my_data = data; |
| static struct trace_seq seq; |
| |
| if (counter++ > MAX_COUNT) { |
| my_data->stopped = true; |
| return 1; |
| } |
| |
| if (!seq.buffer) |
| trace_seq_init(&seq); |
| |
| tep_print_event(event->tep, &seq, record, "%16s-%-5d [%03d] %6.1000d %s: %s\n", |
| TEP_PRINT_COMM, TEP_PRINT_PID, TEP_PRINT_CPU, |
| TEP_PRINT_TIME, TEP_PRINT_NAME, TEP_PRINT_INFO); |
| trace_seq_terminate(&seq); |
| trace_seq_do_printf(&seq); |
| trace_seq_reset(&seq); |
| return 0; |
| } |
| |
| static int sched_callback(struct tep_event *event, struct tep_record *record, |
| int cpu, void *data) |
| { |
| static struct tep_format_field *prev_pid; |
| static struct tep_format_field *next_pid; |
| unsigned long long pid; |
| int this_pid = *(int *)data; |
| |
| if (!prev_pid) { |
| prev_pid = tep_find_field(event, "prev_pid"); |
| next_pid = tep_find_field(event, "next_pid"); |
| if (!prev_pid || !next_pid) { |
| fprintf(stderr, "No pid fields??\n"); |
| return -1; |
| } |
| } |
| |
| tep_read_number_field(prev_pid, record->data, &pid); |
| if (pid == this_pid) |
| printf("WE ARE LEAVING!\n"); |
| tep_read_number_field(next_pid, record->data, &pid); |
| if (pid == this_pid) |
| printf("WE ARE ARRIVING!\n"); |
| return 0; |
| } |
| |
| static int missed_callback(struct tep_event *event, struct tep_record *record, |
| int cpu, void *data) |
| { |
| printf("OOPS! cpu %d dropped ", cpu); |
| if (record->missed_events > 0) |
| printf("%lld ", record->missed_events); |
| printf("events\n"); |
| return 0; |
| } |
| |
| static struct tracefs_instance *instance; |
| static struct my_struct my_data; |
| |
| static void sig(int s) |
| { |
| tracefs_iterate_stop(instance); |
| my_data.stopped = true; |
| } |
| |
| int main (int argc, char **argv, char **env) |
| { |
| struct tep_handle *tep; |
| int this_pid = getpid(); |
| |
| instance = tracefs_instance_create("my-buffer"); |
| if (!instance) |
| return -1; |
| |
| signal(SIGINT, sig); |
| |
| tracefs_event_enable(instance, NULL, NULL); |
| sleep(1); |
| tracefs_event_disable(instance, NULL, NULL); |
| tep = tracefs_local_events(NULL); |
| tep_load_plugins(tep); |
| tracefs_follow_missed_events(instance, missed_callback, NULL); |
| tracefs_follow_event(tep, instance, "sched", "sched_switch", sched_callback, &this_pid); |
| tracefs_iterate_raw_events(tep, instance, NULL, 0, callback, &my_data); |
| tracefs_instance_destroy(instance); |
| |
| if (my_data.stopped) { |
| if (counter > MAX_COUNT) |
| printf("Finished max count\n"); |
| else |
| printf("Finished via signal\n"); |
| } |
| |
| return 0; |
| } |
| -- |
| FILES |
| ----- |
| [verse] |
| -- |
| *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 |
| ------ |
| [verse] |
| -- |
| *Steven Rostedt* <rostedt@goodmis.org> |
| *Tzvetomir Stoyanov* <tz.stoyanov@gmail.com> |
| -- |
| REPORTING BUGS |
| -------------- |
| Report bugs to <linux-trace-devel@vger.kernel.org> |
| |
| LICENSE |
| ------- |
| libtracefs is Free Software licensed under the GNU LGPL 2.1 |
| |
| RESOURCES |
| --------- |
| https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/ |
| |
| COPYING |
| ------- |
| Copyright \(C) 2020 VMware, Inc. Free use of this software is granted under |
| the terms of the GNU Public License (GPL). |
