xref: /aosp_15_r20/external/libtraceevent/Documentation/libtraceevent-kbuffer-timestamp.txt (revision 436bf2bcd5202612ffffe471bbcc1f277cc8d28e)

libtraceevent(3)
================

NAME
----
kbuffer_timestamp, kbuffer_subbuf_timestamp -
Functions that read various data of a kbuffer descriptor

SYNOPSIS
--------
[verse]
--
*#include <kbuffer.h>*

unsigned long long *kbuffer_timestamp*(struct kbuffer pass:[*]_kbuf_);
unsigned long long *kbuffer_subbuf_timestamp*(struct kbuffer pass:[*]_kbuf_, void pass:[*]_subbuf_);
--

DESCRIPTION
-----------
The function *kbuffer_timestamp()* returns the timestamp of the current event of _kbuf_.

The function *kbuffer_subbuf_timestamp()* returns the timestamp for the sub-buffer
that was loaded in _kbuf_. This usually is (but not guaranteed to be) the timestamp
of the first event on the sub-buffer.

The function *kbuffer_start_of_data()* returns the offset of where the delta

RETURN VALUE
------------
*kbuffer_read_event()* returns the event that the _kbuf_ descriptor is currently at,
or NULL if the last event was passed (by *kbuffer_next_event()*).

*kbuffer_next_event()* returns the next event after the current event or NULL if there
are no more events.

*kbuffer_read_at_offset()* returns the event at a given _offset_ from the start of
the sub-buffer stored in _kbuf_, or NULL if there exists no event. Note, _offset_
only needs to be an offset that lands on the record, or is at the start of it. It does
not need to be exactly at the beginning of the record.

*kbuffer_missed_events()* returns 0 if there were no missed events before loaded sub-buffer.
Returns -1 if there were an unknown number of missed events, or if the number of missed events
is known, that number will be returned.

*kbuffer_event_size()* returns the size of the data payload of the current event of _kbuf_.

*kbuffer_curr_size()* returns the size of the entire record of the current event of _kbuf_.
This includes the size of the meta data for that record.

*kbuf_curr_offset()* returns the offset of the current record from the beginning of the _kbuf_
sub-buffer.

*kbuf_curr_index()* returns the index of the current record from the beginning of the _kbuf_
data section.

EXAMPLE
-------
[source,c]
--
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>

#include <kbuffer.h>

int main (int argc, char **argv)
{
	unsigned long long ts;
	struct kbuffer *kbuf;
	struct stat st;
	char *buf;
	void *event;
	int save_offset = -1;
	int record_size;
	int offset;
	int index;
	int size;
	int ret;
	int fd;
	int i = 0;

	if (argc < 2) {
		printf("usage: %s raw-subbuffer-page\n", argv[0]);
		printf(" Try: dd count=1 bs=4096 if=/sys/kernel/tracing/per_cpu/cpu0/trace_pipe_raw of=/tmp/file\n");
		exit(0);
	}

	if (stat(argv[1], &st) < 0) {
		perror("stat");
		exit(-1);
	}

	buf = malloc(st.st_size);
	if (!buf) {
		perror("Allocating buffer");
		exit(-1);
	}

	fd = open(argv[1], O_RDONLY);
	if (fd < 0) {
		perror(argv[1]);
		exit(-1);
	}

	ret = read(fd, buf, st.st_size);
	if (ret < 0) {
		perror("Reading buffer");
		exit(-1);
	}
	close(fd);

	kbuf = kbuffer_alloc(KBUFFER_ENDIAN_SAME_AS_HOST,
			     KBUFFER_LSIZE_SAME_AS_HOST);
	if (!kbuf) {
		perror("Creating kbuffer");
		exit(-1);
	}
	ret = kbuffer_load_subbuffer(kbuf, buf);
	if (ret < 0) {
		perror("Loading sub bufer");
		exit(-1);
	}

	if (kbuffer_subbuffer_size(kbuf) > st.st_size) {
		fprintf(stderr, "kbuffer is bigger than raw size %d > %ld\n",
			kbuffer_subbuffer_size(kbuf), st.st_size);
		exit(-1);
	}

	ret = kbuffer_missed_events(kbuf);
	if (ret) {
		if (ret > 0)
			printf("Missed %d events before this buffer\n", ret);
		else
			printf("Missed unknown number of events before this buffer\n");
	}
	do {
		event = kbuffer_read_event(kbuf, &ts);
		if (event) {
			record_size = kbuffer_curr_size(kbuf);
			offset = kbuffer_curr_offset(kbuf);
			index = kbuffer_curr_index(kbuf);
			size = kbuffer_event_size(kbuf);

			if (i == 20)
				save_offset = offset;
			printf(" event %3d ts:%lld\trecord_size:%d size:%d\tindex:%d offset:%d\n",
			       i++, ts, record_size, size, index, offset);
			event = kbuffer_next_event(kbuf, NULL);
		}
	} while (event);

	if (!event)
		printf("Finished sub buffer\n");

	if (save_offset > 0) {
		event = kbuffer_read_at_offset(kbuf, save_offset, &ts);
		if (!event) {
			fprintf(stderr, "Funny, can't find event 20 at offset %d\n", save_offset);
			exit(-1);
		}
		record_size = kbuffer_curr_size(kbuf);
		offset = kbuffer_curr_offset(kbuf);
		index = kbuffer_curr_index(kbuf);
		size = kbuffer_event_size(kbuf);

		printf("\n saved event 20 ts:%lld\trecord_size:%d size:%d\tindex:%d offset:%d\n\n",
		       ts, record_size, size, index, offset);
	}
	kbuffer_free(kbuf);

	return 0;
}
--
FILES
-----
[verse]
--
*event-parse.h*
	Header file to include in order to have access to the library APIs.
*-ltraceevent*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
*libtraceevent*(3), *trace-cmd*(1)

AUTHOR
------
[verse]
--
*Steven Rostedt* <[email protected]>, author of *libtraceevent*.
--
REPORTING BUGS
--------------
Report bugs to  <[email protected]>

LICENSE
-------
libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/