libtracecmd(3)
=============

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
--------
[verse]
--
*#include <trace-cmd.h>*

int *tracecmd_iterate_events*(struct tracecmd_input pass:[*]_handle_,
			    cpu_set_t pass:[*]_cpus_, int _cpu_size_,
			    int (pass:[*]_callback_)(struct tracecmd_input pass:[*],
					    struct tep_record pass:[*],
					    int, void pass:[*]),
			    void pass:[*]_callback_data_);
int *tracecmd_iterate_events_multi*(struct tracecmd_input pass:[**]_handles_,
				  int _nr_handles_,
				  int (pass:[*]_callback_)(struct tracecmd_input pass:[*],
							   struct tep_record pass:[*],
							   int, void pass:[*]),
				  void pass:[*]_callback_data_);
int *tracecmd_follow_event*(struct tracecmd_input pass:[*]_handle_,
			  const char pass:[*]_system_, const char pass:[*]_event_name_,
			  int (pass:[*]_callback_)(struct tracecmd_input pass:[*],
					  struct tep_event pass:[*],
					  struct tep_record pass:[*],
					  int, void pass:[*]),
			  void pass:[*]_callback_data_);
int *tracecmd_follow_missed_events*(struct tracecmd_input pass:[*]_handle_,
				   int (pass:[*]_callback_)(struct tracecmd_input pass:[*],
						   struct tep_event pass:[*],
						   struct tep_record pass:[*],
						   int, void pass:[*]),
				   void pass:[*]_callback_data_);
struct tracecmd_filter pass:[*]*tracecmd_filter_add*(struct tracecmd_input *_handle_,
					    const char pass:[*]_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 pass:[*]_handle_, struct tep_record pass:[*]_record_,
		 int _cpu_, void pass:[*]_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 pass:[*]_handle_, struct tep_event pass:[*]_event,
		 struct tep_record pass:[*]_record_, int _cpu_, void pass:[*]_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
-------
[source,c]
--
#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
-----
[verse]
--
*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
------
[verse]
--
*Steven Rostedt* <rostedt@goodmis.org>
*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
--
REPORTING BUGS
--------------
Report bugs to  <linux-trace-devel@vger.kernel.org>

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).
