LIBTRACECMD(3)

NAME
tracecmd_get_first_ts, tracecmd_add_ts_offset - Handle time stamps from a trace file.

SYNOPSIS

#include <trace-cmd.h>
unsigned long long tracecmd_get_first_ts(struct tracecmd_input *handle);
void tracecmd_add_ts_offset(struct tracecmd_input *handle, long long offset);

DESCRIPTION

This set of APIs can be used to read tracing data from a trace file opened with tracecmd_open()(3), tracecmd_open_fd()(3) or tracecmd_open_head()(3).

The tracecmd_get_first_ts() function returns the time stamp of the first record in the handle.

The tracecmd_add_ts_offset() function adds an offset to each of the records in the handle that represents a trace file. This is useful for associating two different tracing files by their offset (for example a trace file from a host and a trace file from a guest that were not synchronized when created).

RETURN VALUE

The tracecmd_get_first_ts() function returns the timestamp of the first record in a trace file for the given handle.

EXAMPLE

    #include <stdlib.h>
    #include <trace-cmd.h>
    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);
            const char *file = tracecmd_get_private(handle);
            if (!seq.buffer)
                    trace_seq_init(&seq);
            trace_seq_reset(&seq);
            trace_seq_printf(&seq, "%s: ", 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;
    }
    int main(int argc, char **argv)
    {
            struct tracecmd_input **handles = NULL;
            unsigned long long ts, first_ts = 0;
            int nr_handles = 0;
            int i;
            if (argc < 2) {
                    printf("usage: %s trace.dat [trace.dat ...]\n", argv[0]);
                    exit(-1);
            }
            for (i = 1; 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])
                            exit(-1);
                    tracecmd_set_private(handles[nr_handles], argv[i]);
                    ts = tracecmd_get_first_ts(handles[nr_handles]);
                    if (!first_ts || ts < first_ts)
                            first_ts = ts;
                    nr_handles++;
            }
            /* Set the time stamp to start at the first record found */
            for (i = 0; i < nr_handles; i++)
                    tracecmd_add_ts_offset(handles[i], -first_ts);
            tracecmd_iterate_events_multi(handles, nr_handles, print_events, NULL);
            for (i = 0; i < nr_handles; i++)
                    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