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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | NOTES | COLOPHON |
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LIBTRACEEVENT(3) libtraceevent Manual LIBTRACEEVENT(3)
kbuffer_read_event, kbuffer_next_event, kbuffer_missed_events,
kbuffer_event_size, kbuffer_curr_size, kbuffer_curr_offset,
kbuffer_curr_index, kbuffer_read_buffer - Functions to read
through the kbuffer sub buffer.
#include <kbuffer.h>
void *kbuffer_read_event(struct kbuffer *kbuf, unsigned long long *ts);
void *kbuffer_next_event(struct kbuffer *kbuf, unsigned long long *ts);
void *kbuffer_read_at_offset(struct kbuffer *kbuf, int offset, unsigned long long *ts);
int kbuffer_missed_events(struct kbuffer *kbuf);
int kbuffer_event_size(struct kbuffer *kbuf);
int kbuffer_curr_size(struct kbuffer *kbuf);
int kbuffer_curr_offset(struct kbuffer *kbuf);
int kbuffer_curr_index(struct kbuffer *kbuf);
int kbuffer_read_buffer(struct kbuffer *kbuf, void *buffer, int len);
The function kbuffer_read_event() reads the next event in the
kbuf descriptor and if ts is non NULL, will place its timestamp
into it. This does not modify the kbuf descriptor, and calling
this function mulitple times will return the same result.
The function kbuffer_next_event() will return the next event in
the kbuf descriptor. It will also set the ts to the timestamp of
the returned event. NULL is returned if there are no more events
and ts will be undefined. Note, if this is called directly after
a kbuffer_load_subbuffer() then it will likely give an unexpected
result, as it will return the second event and not the first
event. Usually this function is only used to move to the next
event and to know if there’s any more events to read, and
kbuffer_read_event() is always called first.
The function kbuffer_read_at_offset() returns the event located
at a given offset from the beginning of the sub-buffer. This
offset can be retrieved by kbuffer_curr_offset(). If ts points to
an unsigned long long, then it will be set to the event at the
given offset’s timestamp.
If the sub-buffer had missed events before it, then
kbuffer_missed_events() will return the non zero. If it returns
-1, that means there were missed events, but the exact number of
missed events is unknown. If it returns a positive number, then
the number of missed events is the return value.
The kbuffer_event_size() function returns the size of the data
portion of the current event (the one that would be returned by
kbuffer_read_event().
The kbuffer_curr_size() function returns the entire record size
of the current event (the one that would be returned by
kbuffer_read_event(). The difference here is that the return
value includes the size of the event record meta data that is not
part of what is returned by kbuffer_read_event().
The kbuffer_curr_offset() function returns the offset from the
beginning of the sub-buffer of where the current event’s meta
data for the record begins. The first event will not be at offset
zero. This offset can be used to retrieve the event with
kbuffer_read_at_offset().
The kbuffer_curr_index() function returns the index from the
beginning of the data portion of the sub-buffer where the current
evnet’s meta data is located. The first event will likely be
zero, but may not be if there’s a timestamp attached to it.
The kbuffer_read_buffer() function will fill the given buffer
from the kbuf the same way the kernel would do a read system
call. That is, if the length len is less than the sub buffer
size, or the kbuffer current index is non-zero, it will start
copying from the kbuf current event and create buffer as a new
sub buffer (with a timestamp and commit header) with that event
that was found and including all events after that can fit within
len. The len must include the size of the sub buffer header as
well as the events to include. That is, len is the allocate size
of buffer that can be filled. The return from this function is
the index of the end of the last event that was added. If there
are no more events then zero is returned, and if the buffer can
not copy any events because len was too small, then -1 is
returned.
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.
kbuf_read_buffer() returns the index of the end of the last event
that was filled in buffer. If there are no more events to copy
from start then 0 is returned. If len is not big enough to hold
any events, then -1 is returned.
#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;
}
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.
libtraceevent(3), trace-cmd(1)
Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.
Report bugs to <linux-trace-devel@vger.kernel.org[2]>
libtraceevent is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
2. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org
This page is part of the libtraceevent (Linux kernel trace event
library) project. Information about the project can be found at
⟨https://www.trace-cmd.org/⟩. If you have a bug report for this
manual page, see ⟨https://www.trace-cmd.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git⟩
on 2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
libtraceevent 1.8.2 06/07/2024 LIBTRACEEVENT(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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