kbuffer_timestamp(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | NOTES | COLOPHON

LIBTRACEEVENT(3)          libtraceevent Manual          LIBTRACEEVENT(3)

NAME         top

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

SYNOPSIS         top

       #include <kbuffer.h>

       unsigned long long kbuffer_timestamp(struct kbuffer *kbuf);
       unsigned long long kbuffer_subbuf_timestamp(struct kbuffer *kbuf, void *subbuf);

DESCRIPTION         top

       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         top

       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         top

           #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         top

           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         top

       libtraceevent(3), trace-cmd(1)

AUTHOR         top

           Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.

REPORTING BUGS         top

       Report bugs to <linux-trace-devel@vger.kernel.org[2]>

LICENSE         top

       libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES         top

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

NOTES         top

        1. rostedt@goodmis.org
           mailto:rostedt@goodmis.org

        2. linux-trace-devel@vger.kernel.org
           mailto:linux-trace-devel@vger.kernel.org

COLOPHON         top

       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 1.7.3            09/24/2023               LIBTRACEEVENT(3)