Provided by: trace-cmd_3.1.6-1_amd64 
NAME
tracecmd_iterate_events, tracecmd_iterate_events_multi, tracecmd_follow_event,
tracecmd_follow_missed_events, tracecmd_filter_add - Read events from a trace file
SYNOPSIS
#include <trace-cmd.h>
int tracecmd_iterate_events(struct tracecmd_input *handle,
cpu_set_t *cpus, int cpu_size,
int (*callback)(struct tracecmd_input *,
struct tep_record *,
int, void *),
void *callback_data);
int tracecmd_iterate_events_multi(struct tracecmd_input **handles,
int nr_handles,
int (*callback)(struct tracecmd_input *,
struct tep_record *,
int, void *),
void *callback_data);
int tracecmd_follow_event(struct tracecmd_input *handle,
const char *system, const char *event_name,
int (*callback)(struct tracecmd_input *,
struct tep_event *,
struct tep_record *,
int, void *),
void *callback_data);
int tracecmd_follow_missed_events(struct tracecmd_input *handle,
int (*callback)(struct tracecmd_input *,
struct tep_event *,
struct tep_record *,
int, void *),
void *callback_data);
struct tracecmd_filter *tracecmd_filter_add(struct tracecmd_input *handle,
const char *filter_str, bool neg);
DESCRIPTION
This set of APIs can be used to iterate over events after opening a trace file using one
of the open functions like tracecmd_open(3) or tracecmd_open_fd(3).
The function tracecmd_iterate_events() will iterate through all the events in the trace
file defined by handle, where handle is returned from one of the tracecmd_open(3)
functions. It will call the callback() function on the events on the CPUs defined by cpus.
The cpu_size must be the size of cpus (see CPU_SET(3)). If cpus is NULL, then cpu_size is
ignored and callback() will be called for all events on all CPUs in the trace file. The
callback_data is passed to the callback() as its last parameter. callback may be NULL,
which is useful if tracecmd_follow_event() is used, but note if callback is NULL, then
callback_data is ignored and not sent to the callback of tracecmd_follow_event().
The function tracecmd_iterate_events_multi() is similar to tracecmd_iterate_events()
except that it allows to iterate over more than one trace file. If tracecmd agent(1) is
used to get a trace file for both the host and guest, make sure that the host trace file
is the first entry in handles and tracecmd_iterate_events_multi() will do the
synchronization of the meta data for the guest files that come later in handles. handles
is an array of trace file descriptors that were opened by tracecmd_open(3) and friends.
Note, unlike tracecmd_iterate_events(), tracecmd_iterate_events_multi() does not filter on
CPUs, as it will cause the API to become too complex in knowing which handle to filter the
CPUs on. If CPU filtering is desired, then the callback should check the record→cpu to and
return 0 if it is not the desired CPU to process. nr_handles denotes the number of
elements in handles. The callback_data is passed to the callback as its last parameter.
callback may be NULL, which is useful if tracecmd_follow_event() is used, but note if
callback is NULL, then callback_data is ignored and not sent to the callback of
tracecmd_follow_event().
The callback() for both tracecmd_iterate_events() and tracecmd_iterate_events_multi() is
of the prototype:
int callback()(struct tracecmd_input *handle, struct tep_record *record, int cpu, void
*data);
The handle is the same handle passed to tracecmd_iterate_events() or the current handle of
handles passed to tracecmd_iterate_events_multi() that the record belongs to. The record
is the current event record. The cpu is the current CPU being processed. Note, for
tracecmd_iterate_events_multi() it may not be the actual CPU of the file, but the nth CPU
of all the handles put together. Use record→cpu to get the actual CPU that the event is
on.
The tracecmd_follow_event() function will attach to a trace file descriptor handle and
call the callback when the event described by system and name matches an event in the
iteration of tracecmd_iterate_events() or tracecmd_iterate_events_multi(). Note, the cpu
is the nth CPU for both tracecmd_iterate_events() and tracecmd_iterate_events_multi(). If
the actual CPU of the record is needed, use record→cpu. For
tracecmd_iterate_events_multi(), the callback is only called if the handle matches the
current trace file descriptor within handles. The callback_data is passed as the last
parameter to the callback() function. Note, this callback() function will be called before
the callback() function of either tracecmd_iterate_events() or
tracecmd_iterate_events_multi().
The callback() prototype for *tracecmd_follow_event()_ is:
int callback()(struct tracecmd_input *handle, struct tep_event *event, struct tep_record
*_record, int cpu, void *data);
The tracecmd_follow_missed_events() function will attach to a trace file descriptor handle
and call the callback when missed events are detected. The event will hold the type of
event that the record is. The record will hold the information of the missed events. The
cpu is the nth CPU for both tracecmd_iterate_events() and tracecmd_iterate_events_multi().
If the CPU that the missed events are for is needed, use record→cpu. If
record→missed_events is a positive number, then it holds the number of missed events since
the last event on its CPU, otherwise it will be negative, and that will mean that the
number of missed events is unknown but missed events exist since the last event on the
CPU. The callback and callback_data is the same format as tracecmd_follow_event() above.
The missed events callback is called before any of the other callbacks and any filters
that were added by tracecmd_filter_add() are ignored. If callback returns a non zero, it
will stop the iterator before it calls any of the other iterator callbacks for the given
record.
The tracecmd_filter_add() function, adds a filter to handle that affects both
tracecmd_iterate_events() and tracecmd_iterate_events_multi(). The filter_str is a
character string defining a filter in a format that is defined by
tep_filter_add_filter_str(3). If neg is true, then the events that match the filter will
be skipped, otherwise the events that match will execute the callback() function in the
iterators.
RETURN VALUE
Both tracecmd_iterate_events() and tracecmd_iterate_events_multi() return zero if they
successfully iterated all events (handling the follow and filters appropriately). Or an
error value, which can include returning a non-zero result from the callback() function.
EXAMPLE
#define _GNU_SOURCE
#include <sched.h>
#include <stdlib.h>
#include <getopt.h>
#include <trace-cmd.h>
struct private_data {
int cpu;
const char *file;
};
static int print_events(struct tracecmd_input *handle, struct tep_record *record, int cpu, void *data)
{
static struct trace_seq seq;
struct tep_handle *tep = tracecmd_get_tep(handle);
struct private_data *pdata = tracecmd_get_private(handle);
/* For multi handles we need this */
if (pdata->cpu >= 0 && pdata->cpu != record->cpu)
return 0;
if (!seq.buffer)
trace_seq_init(&seq);
trace_seq_reset(&seq);
trace_seq_printf(&seq, "%s: ", pdata->file);
tep_print_event(tep, &seq, record, "%6.1000d [%03d] %s-%d %s: %s\n",
TEP_PRINT_TIME, TEP_PRINT_CPU, TEP_PRINT_COMM, TEP_PRINT_PID,
TEP_PRINT_NAME, TEP_PRINT_INFO);
trace_seq_terminate(&seq);
trace_seq_do_printf(&seq);
return 0;
}
static int print_event(struct tracecmd_input *handle, struct tep_event *event,
struct tep_record *record, int cpu, void *data)
{
return print_events(handle, record, cpu, data);
}
static int missed_events(struct tracecmd_input *handle, struct tep_event *event,
struct tep_record *record, int cpu, void *data)
{
if (record->missed_events > 0)
printf("CPU [%03d] has %d missed events\n",
record->cpu, record->missed_events);
else
printf("CPU [%03d] has missed events\n", record->cpu);
return 0;
}
static void usage(const char *argv0)
{
printf("usage: [-c cpu][-f filter][-e event] %s trace.dat [trace.dat ...]\n",
argv0);
exit(-1);
}
int main(int argc, char **argv)
{
struct tracecmd_input **handles = NULL;
const char *filter_str = NULL;
const char *argv0 = argv[0];
struct private_data *priv;
cpu_set_t *cpuset = NULL;
char *event = NULL;
size_t cpusize = 0;
int nr_handles = 0;
int cpu = -1;
int i;
int c;
while ((c = getopt(argc, argv, "c:f:e:")) >= 0) {
switch (c) {
case 'c':
/* filter all trace data to this one CPU. */
cpu = atoi(optarg);
break;
case 'f':
filter_str = optarg;
break;
case 'e':
event = optarg;
break;
default:
usage(argv0);
}
}
argc -= optind;
argv += optind;
if (argc == 0)
usage(argv0);
for (i = 0; i < argc; i++) {
handles = realloc(handles, sizeof(*handles) * (nr_handles + 1));
if (!handles)
exit(-1);
handles[nr_handles] = tracecmd_open(argv[i], 0);
if (!handles[nr_handles]) {
perror(argv[i]);
exit(-1);
}
if (filter_str) {
if (tracecmd_filter_add(handles[nr_handles], filter_str, false) == NULL) {
perror("adding filter");
exit(-1);
}
}
priv = calloc(1, sizeof(*priv));
if (!priv)
exit(-1);
priv->file = argv[i];
priv->cpu = cpu;
tracecmd_set_private(handles[nr_handles], priv);
if (event) {
if (tracecmd_follow_event(handles[nr_handles], NULL, event, print_event, NULL) < 0) {
printf("Could not follow event %s for file %s\n", event, argv[i]);
exit(-1);
}
}
tracecmd_follow_missed_events(handles[nr_handles], missed_events, NULL);
nr_handles++;
}
/* Shortcut */
if (nr_handles == 1) {
if (cpu >= 0) {
cpuset = CPU_ALLOC(cpu + 1);
if (!cpuset)
exit(-1);
cpusize = CPU_ALLOC_SIZE(cpu + 1);
CPU_SET_S(cpu, cpusize, cpuset);
}
if (event)
tracecmd_iterate_events(handles[0], cpuset, cpusize, NULL, NULL);
else
tracecmd_iterate_events(handles[0], cpuset, cpusize, print_events, NULL);
} else {
if (event)
tracecmd_iterate_events_multi(handles, nr_handles, NULL, NULL);
else
tracecmd_iterate_events_multi(handles, nr_handles, print_events, NULL);
}
for (i = 0; i < nr_handles; i++) {
priv = tracecmd_get_private(handles[i]);
free(priv);
tracecmd_close(handles[i]);
}
free(handles);
}
FILES
trace-cmd.h
Header file to include in order to have access to the library APIs.
-ltracecmd
Linker switch to add when building a program that uses the library.
SEE ALSO
libtracefs(3), libtraceevent(3), trace-cmd(1) trace-cmd.dat(5)
AUTHOR
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
REPORTING BUGS
Report bugs to <linux-trace-devel@vger.kernel.org[3]>
LICENSE
libtracecmd is Free Software licensed under the GNU LGPL 2.1
RESOURCES
https://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git/
COPYING
Copyright (C) 2020 VMware, Inc. Free use of this software is granted under the terms of
the GNU Public License (GPL).
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