'\" t
.\"     Title: libtracefs
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 07/25/2024
.\"    Manual: libtracefs Manual
.\"    Source: libtracefs 1.8.1
.\"  Language: English
.\"
.TH "LIBTRACEFS" "3" "07/25/2024" "libtracefs 1\&.8\&.1" "libtracefs Manual"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
tracefs_synth_echo_cmd, tracefs_synth_get_start_hist, tracefs_synth_get_name, tracefs_synth_raw_fmt, tracefs_synth_show_event, tracefs_synth_show_start_hist, tracefs_synth_show_end_hist, tracefs_synth_get_event \- Retrieve data of synthetic events\&.
.SH "SYNOPSIS"
.sp
.nf
\fB#include <tracefs\&.h>\fR

int \fBtracefs_synth_echo_cmd\fR(struct trace_seq *\fIseq\fR, struct tracefs_synth *\fIsynth\fR);
struct tracefs_hist *\fBtracefs_synth_get_start_hist\fR(struct tracefs_synth *\fIsynth\fR);

const char *\fBtracefs_synth_get_name\fR(struct tracefs_synth *\fIsynth\fR);
int \fBtracefs_synth_raw_fmt\fR(struct trace_seq *\fIseq\fR, struct tracefs_synth *\fIsynth\fR);
const char *\fBtracefs_synth_show_event\fR(struct tracefs_synth *\fIsynth\fR);
const char *\fBtracefs_synth_show_start_hist\fR(struct tracefs_synth *\fIsynth\fR);
const char *\fBtracefs_synth_show_end_hist\fR(struct tracefs_synth *\fIsynth\fR);
struct tep_event *\fBtracefs_synth_get_event\fR(struct tep_handle *\fItep\fR, struct tracefs_synth *\fIsynth\fR);
.fi
.SH "DESCRIPTION"
.sp
Synthetic events are dynamic events that are created by matching two other events which triggers a synthetic event\&. One event is the starting event which some field is recorded, and when the second event is executed, if it has a field (or fields) that matches the starting event\(cqs field (or fields) then it will trigger the synthetic event\&. The field values other than the matching fields may be passed from the starting event to the end event to perform calculations on, or to simply pass as a parameter to the synthetic event\&.
.sp
One common use case is to set "sched_waking" as the starting event\&. This event is triggered when a process is awoken\&. Then set "sched_switch" as the ending event\&. This event is triggered when a new task is scheduled on the CPU\&. By setting the "common_pid" of both events as the matching fields, the time between the two events is considered the wake up latency of that process\&. Use \fBTRACEFS_TIMESTAMP\fR as a field for both events to calculate the delta in nanoseconds, or use \fBTRACEFS_TIMESTAMP_USECS\fR as the compare fields for both events to calculate the delta in microseconds\&. This is used as the example below\&.
.sp
See \fBtracefs_synth_alloc\fR(3) for allocation of synthetic events, and \fBtracefs_synth_create\fR() for creating the synthetic event on the system\&.
.sp
\fBtracefs_synth_echo_cmd\fR() acts like \fBtracefs_synth_create\fR(), but instead of creating the synthetic event in the system, it will write the echo commands to manually create it in the \fIseq\fR given\&.
.sp
\fBtracefs_synth_get_start_hist\fR() returns a struct tracefs_hist descriptor describing the histogram used to create the synthetic event\&.
.sp
.if n \{\
.RS 4
.\}
.nf
enum tracefs_synth_handler {
        \fBTRACEFS_SYNTH_HANDLE_MATCH\fR,
        \fBTRACEFS_SYNTH_HANDLE_MAX\fR,
        \fBTRACEFS_SYNTH_HANDLE_CHANGE\fR,
};
.fi
.if n \{\
.RE
.\}
.sp
\fBtracefs_synth_get_name\fR() returns the name of the synthetic event or NULL on error\&. The returned string belongs to the synth event object and is freed with the event by \fBtracefs_synth_free\fR()\&.
.sp
\fBtracefs_synth_raw_fmt\fR() writes the raw format strings (dynamic event and histograms) of the synthetic event in the \fIseq\fR given\&.
.sp
\fBtracefs_synth_show_event\fR() returns the format of the dynamic event used by the synthetic event or NULL on error\&. The returned string belongs to the synth event object and is freed with the event by \fBtracefs_synth_free\fR()\&.
.sp
\fBtracefs_synth_show_start_hist\fR() returns the format of the start histogram used by the synthetic event or NULL on error\&. The returned string belongs to the synth event object and is freed with the event by \fBtracefs_synth_free\fR()\&.
.sp
\fBtracefs_synth_show_end_hist\fR() returns the format of the end histogram used by the synthetic event or NULL on error\&. The returned string belongs to the synth event object and is freed with the event by \fBtracefs_synth_free\fR()\&.
.sp
The \fBtracefs_synth_get_event\fR() function returns a tep event, describing the given synthetic event\&. The API detects any newly created or removed dynamic events\&. The returned pointer to tep event is controlled by @tep and must not be freed\&.
.SH "RETURN VALUE"
.sp
\fBtracefs_synth_get_name\fR(), \fBtracefs_synth_show_event\fR(), \fBtracefs_synth_show_start_hist\fR() and \fBtracefs_synth_show_end_hist\fR() return a string owned by the synth event object\&.
.sp
The \fBtracefs_synth_get_event\fR() function returns a pointer to a tep event or NULL in case of an error or if the requested synthetic event is missing\&. The returned pointer to tep event is controlled by @tep and must not be freed\&.
.sp
All other functions return zero on success or \-1 on error\&.
.SH "ERRORS"
.sp
The following errors are for all the above calls:
.sp
\fBEPERM\fR Not run as root user when required\&.
.sp
\fBEINVAL\fR Either a parameter is not valid (NULL when it should not be) or a field that is not compatible for calculations\&.
.sp
\fBENODEV\fR An event or one of its fields is not found\&.
.sp
\fBEBADE\fR The fields of the start and end events are not compatible for either matching or comparing\&.
.sp
\fBENOMEM\fR not enough memory is available\&.
.sp
And more errors may have happened from the system calls to the system\&.
.SH "EXAMPLE"
.sp
See \fBtracefs_sql\fR(3) for a more indepth use of some of this code\&.
.sp
.if n \{\
.RS 4
.\}
.nf
#include <stdlib\&.h>
#include <tracefs\&.h>

#define start_event "sched_waking"
#define start_field "pid"

#define end_event "sched_switch"
#define end_field "next_pid"

#define match_name "pid"

static struct tracefs_synth *synth;

static void make_event(void)
{
        struct tep_handle *tep;

        /* Load all events from the system */
        tep = tracefs_local_events(NULL);

        /* Initialize the synthetic event */
        synth = tracefs_synth_alloc(tep, "wakeup_lat",
                                    NULL, start_event,
                                    NULL, end_event,
                                    start_field, end_field,
                                    match_name);

        /* The tep is no longer needed */
        tep_free(tep);


        /* Save the "prio" field as "prio" from the start event */
        tracefs_synth_add_start_field(synth, "prio", NULL);

        /* Save the "next_comm" as "comm" from the end event */
        tracefs_synth_add_end_field(synth, "next_comm", "comm");

        /* Save the "prev_prio" as "prev_prio" from the end event */
        tracefs_synth_add_end_field(synth, "prev_prio", NULL);

        /*
         * Take a microsecond time difference between end and start
         * and record as "delta"
         */
        tracefs_synth_add_compare_field(synth, TRACEFS_TIMESTAMP_USECS,
                                        TRACEFS_TIMESTAMP_USECS,
                                        TRACEFS_SYNTH_DELTA_END, "delta");

        /* Only record if start event "prio" is less than 100 */
        tracefs_synth_append_start_filter(synth, TRACEFS_FILTER_COMPARE,
                                          "prio", TRACEFS_COMPARE_LT, "100");

        /*
         * Only record if end event "next_prio" is less than 50
         * or the previous task\*(Aqs prio was not greater than or equal to 100\&.
         *   next_prio < 50 || !(prev_prio >= 100)
         */
        tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_COMPARE,
                                        "next_prio", TRACEFS_COMPARE_LT, "50");
        tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_OR, NULL, 0, NULL);
        tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_NOT, NULL, 0, NULL);
        tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_OPEN_PAREN, NULL, 0, NULL);
        tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_COMPARE,
                                        "prev_prio", TRACEFS_COMPARE_GE, "100");
        /*
         * Note, the above only added: "next_prio < 50 || !(prev_prio >= 100"
         * That\*(Aqs because, when the synth is executed, the remaining close parenthesis
         * will be added\&. That is, the string will end up being:
         * "next_prio < 50 || !(prev_prio >= 100)" when one of tracefs_sync_create()
         * or tracefs_sync_echo_cmd() is run\&.
         */
}

/* Display how to create the synthetic event */
static void show_event(void)
{
        struct trace_seq s;

        trace_seq_init(&s);

        tracefs_synth_echo_cmd(&s, synth);
        trace_seq_terminate(&s);
        trace_seq_do_printf(&s);
        trace_seq_destroy(&s);
}

int main (int argc, char **argv)
{
        make_event();

        if (argc > 1) {
                if (!strcmp(argv[1], "create")) {
                        /* Create the synthetic event */
                        tracefs_synth_create(synth);
                } else if (!strcmp(argv[1], "delete")) {
                        /* Delete the synthetic event */
                        tracefs_synth_destroy(synth);
                } else {
                        printf("usage: %s [create|delete]\en", argv[0]);
                        exit(\-1);
                }
        } else
                show_event();

        tracefs_synth_free(synth);

        return 0;
}
.fi
.if n \{\
.RE
.\}
.SH "FILES"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBtracefs\&.h\fR
        Header file to include in order to have access to the library APIs\&.
\fB\-ltracefs\fR
        Linker switch to add when building a program that uses the library\&.
.fi
.if n \{\
.RE
.\}
.SH "SEE ALSO"
.sp
\fBlibtracefs\fR(3), \fBlibtraceevent\fR(3), \fBtrace\-cmd\fR(1), \fBtracefs_hist_alloc\fR(3), \fBtracefs_hist_alloc_2d\fR(3), \fBtracefs_hist_alloc_nd\fR(3), \fBtracefs_hist_free\fR(3), \fBtracefs_hist_add_key\fR(3), \fBtracefs_hist_add_value\fR(3), \fBtracefs_hist_add_name\fR(3), \fBtracefs_hist_start\fR(3), \fBtracefs_hist_destory\fR(3), \fBtracefs_hist_add_sort_key\fR(3), \fBtracefs_hist_sort_key_direction\fR(3), \fBtracefs_synth_alloc\fR(3), \fBtracefs_synth_add_match_field\fR(3), \fBtracefs_synth_add_compare_field\fR(3), \fBtracefs_synth_add_start_field\fR(3), \fBtracefs_synth_add_end_field\fR(3), \fBtracefs_synth_append_start_filter\fR(3), \fBtracefs_synth_append_end_filter\fR(3), \fBtracefs_synth_free\fR(3), \fBtracefs_synth_create\fR(3), \fBtracefs_synth_destroy\fR(3), \fBtracefs_synth_complete\fR(3), \fBtracefs_synth_trace\fR(3), \fBtracefs_synth_snapshot\fR(3), \fBtracefs_synth_save\fR(3),
.SH "AUTHOR"
.sp
.if n \{\
.RS 4
.\}
.nf
\fBSteven Rostedt\fR <\m[blue]\fBrostedt@goodmis\&.org\fR\m[]\&\s-2\u[1]\d\s+2>
\fBTzvetomir Stoyanov\fR <\m[blue]\fBtz\&.stoyanov@gmail\&.com\fR\m[]\&\s-2\u[2]\d\s+2>
\fBsameeruddin shaik\fR <\m[blue]\fBsameeruddin\&.shaik8@gmail\&.com\fR\m[]\&\s-2\u[3]\d\s+2>
.fi
.if n \{\
.RE
.\}
.SH "REPORTING BUGS"
.sp
Report bugs to <\m[blue]\fBlinux\-trace\-devel@vger\&.kernel\&.org\fR\m[]\&\s-2\u[4]\d\s+2>
.SH "LICENSE"
.sp
libtracefs is Free Software licensed under the GNU LGPL 2\&.1
.SH "RESOURCES"
.sp
\m[blue]\fBhttps://git\&.kernel\&.org/pub/scm/libs/libtrace/libtracefs\&.git/\fR\m[]
.SH "COPYING"
.sp
Copyright (C) 2020 VMware, Inc\&. Free use of this software is granted under the terms of the GNU Public License (GPL)\&.
.SH "NOTES"
.IP " 1." 4
rostedt@goodmis.org
.RS 4
\%mailto:rostedt@goodmis.org
.RE
.IP " 2." 4
tz.stoyanov@gmail.com
.RS 4
\%mailto:tz.stoyanov@gmail.com
.RE
.IP " 3." 4
sameeruddin.shaik8@gmail.com
.RS 4
\%mailto:sameeruddin.shaik8@gmail.com
.RE
.IP " 4." 4
linux-trace-devel@vger.kernel.org
.RS 4
\%mailto:linux-trace-devel@vger.kernel.org
.RE