SYNOPSIS

#include <tracefs.h>

enum tracefs_hist_key_type {
        TRACEFS_HIST_KEY_NORMAL = 0,
        TRACEFS_HIST_KEY_HEX,
        TRACEFS_HIST_KEY_SYM,
        TRACEFS_HIST_KEY_SYM_OFFSET,
        TRACEFS_HIST_KEY_SYSCALL,
        TRACEFS_HIST_KEY_EXECNAME,
        TRACEFS_HIST_KEY_LOG,
        TRACEFS_HIST_KEY_USECS,
        TRACEFS_HIST_KEY_MAX
};

struct tracefs_hist_axis {
        const char *key;
        enum tracefs_hist_key_type type;
};

struct tracefs_hist *tracefs_hist_alloc(struct tracefs_tep * tep,
                        const char *system, const char *event,
                        const char *key, enum tracefs_hist_key_type type);
struct tracefs_hist *tracefs_hist_alloc_2d(struct tracefs_tep * tep,
                        const char *system, const char *event,
                        const char *key1, enum tracefs_hist_key_type type1,
                        const char *key2, enum tracefs_hist_key_type type2));
struct tracefs_hist *tracefs_hist_alloc_nd(struct tracefs_tep * tep,
                        const char *system, const char *event,
                        struct tracefs_hist_axis *axes);
void tracefs_hist_free(struct tracefs_hist *hist);

int tracefs_hist_add_key(struct tracefs_hist *hist, const char *key,
                         enum tracefs_hist_key_type type);
int tracefs_hist_add_value(struct tracefs_hist *hist, const char *value);

DESCRIPTION

Event histograms are created by the trigger file in the event directory. The syntax can be complex and difficult to get correct. This API handles the syntax, and facilitates the creation and interaction with the event histograms. See https://www.kernel.org/doc/html/latest/trace/histogram.html for more information.

tracefs_hist_alloc() allocates a "struct tracefs_hist" descriptor of a one-dimensional histogram and returns the address of it. This descriptor must be freed by tracefs_hist_free(). The tep is a trace event handle (see tracefs_local_events(3)), that holds the system and event that the histogram will be attached to. The system is the system or group of the event. The event is the event to attach the histogram to. The key is a field of the event that will be used as the key(dimension) of the histogram. The type is the type of the key. See KEY TYPES below.

tracefs_hist_alloc_2d() allocates a "struct tracefs_hist" descriptor of a two-dimensional histogram and returns the address of it. This descriptor must be freed by tracefs_hist_free(). The tep is a trace event handle (see tracefs_local_events(3)), that holds the system and event that the histogram will be attached to. The system is the system or group of the event. The event is the event to attach the histogram to. The key1 is the first field of the event that will be used as the key(dimension) of the histogram. The type1 is the type of the key1. See KEY TYPES below. The key2 is the second field of the event that will be used as the key(dimension) of the histogram. The type2 is the type of the key2. See KEY TYPES below.

tracefs_hist_alloc_nd() allocates a "struct tracefs_hist" descriptor of an N-dimensional histogram and returns the address of it. This descriptor must be freed by tracefs_hist_free(). The tep is a trace event handle (see tracefs_local_events(3)), that holds the system and event that the histogram will be attached to. The system is the system or group of the event. The event is the event to attach the histogram to. The axes is an array of key / type pairs, defining the dimensions of the histogram.

tracefs_hist_free() frees the tracefs_hist descriptor. Note, it does not stop or disable the running histogram if it was started. tracefs_hist_destroy() needs to be called to do so.

tracefs_hist_add_key() Adds a secondary or tertiary key to the histogram. The key passed to tracefs_hist_alloc_nd() is the primary key of the histogram. The first time this function is called, it will add a secondary key (or two dimensional histogram). If this function is called again on the same histogram, it will add a tertiary key (or three dimensional histogram). The hist parameter is the histogram descriptor to add the key to. The type is the type of key to add (See KEY TYPES below).

tracefs_hist_add_value() will add a value to record. By default, the value is simply the "hitcount" of the number of times a instance of the histogram’s key was hit. The hist is the histogram descriptor to add the value to. The value is a field in the histogram to add to when an instance of the key is hit.

KEY TYPES

tracefs_hist_alloc_nd() and tracefs_hist_add_key() both add a key and requires that key to have a type. The types may be:

TRACEFS_HIST_KEY_NORMAL or zero (0) which is to not modify the type.

TRACEFS_HIST_KEY_HEX to display the key in hex.

TRACEFS_HIST_KEY_SYM to display the key as a kernel symbol (if found). If the key is an address, this is useful as it will display the function names instead of just a number.

TRACEFS_HIST_KEY_SYM_OFFSET similar to TRACEFS_HIST_KEY_SYM but will also include the offset of the function to match the exact address.

TRACEFS_HIST_KEY_SYSCALL If the key is a system call "id" (the number passed from user space to the kernel to tell it what system call it is calling), then the name of the system call is displayed.

TRACEFS_HIST_KEY_EXECNAME If "common_pid" is the key (the pid of the executing task), instead of showing the number, show the name of the running task.

TRACEFS_HIST_KEY_LOG will display the key in a binary logarithmic scale.

TRACEFS_HIST_KEY_USECS for use with "common_timestamp" or TRACEFS_HIST_TIMESTAMP, in which case it will show the timestamp in microseconds instead of nanoseconds.

RETURN VALUE

tracefs_hist_alloc_nd() returns an allocated histogram descriptor which must be freed by tracefs_hist_free() or NULL on error.

All the other functions return zero on success or -1 on error.

If tracefs_hist_start() returns an error, a message may be displayed in the kernel that can be retrieved by tracefs_error_last().

EXAMPLE

#include <stdlib.h>
#include <unistd.h>
#include <tracefs.h>

enum commands {
        START,
        PAUSE,
        CONT,
        RESET,
        DELETE,
        SHOW,
};

static void parse_system_event(char *group, char **system, char **event)
{
        *system = strtok(group, "/");
        *event = strtok(NULL, "/");
        if (!*event) {
                *event = *system;
                *system = NULL;
        }
}

static int parse_keys(char *keys, struct tracefs_hist_axis **axes)
{
        char *sav = NULL;
        char *key;
        int cnt = 0;

        for (key = strtok_r(keys, ",", &sav); key; key = strtok_r(NULL, ",", &sav)) {
                struct tracefs_hist_axis *ax;
                char *att;

                ax = realloc(*axes, sizeof(*ax) * (cnt + 2));
                if (!ax) {
                        perror("Failed to allocate axes");
                        exit(-1);
                }
                ax[cnt].key = key;
                ax[cnt].type = 0;
                ax[cnt + 1].key = NULL;
                ax[cnt + 1].type = 0;

                *axes = ax;

                att = strchr(key, '.');
                if (att) {
                        *att++ = '\0';
                        if (strcmp(att, "hex") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_HEX;
                        else if (strcmp(att, "sym") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_SYM;
                        else if (strcmp(att, "sym_offset") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_SYM_OFFSET;
                        else if (strcmp(att, "syscall") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_SYSCALL;
                        else if (strcmp(att, "exec") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_EXECNAME;
                        else if (strcmp(att, "log") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_LOG;
                        else if (strcmp(att, "usecs") == 0)
                                ax[cnt].type = TRACEFS_HIST_KEY_USECS;
                        else {
                                fprintf(stderr, "Undefined attribute '%s'\n", att);
                                fprintf(stderr,"  Acceptable attributes:\n");
                                fprintf(stderr,"    hex, sym, sym_offset, syscall, exe, log, usecs\n");
                                exit(-1);
                        }
                }
                cnt++;
        }
        return cnt;
}

static void process_hist(enum commands cmd, const char *instance_name,
                         char *group, char *keys, char *vals, char *sort,
                         char *ascend, char *desc)
{
        struct tracefs_instance *instance = NULL;
        struct tracefs_hist *hist;
        struct tep_handle *tep;
        struct tracefs_hist_axis *axes = NULL;
        char *system;
        char *event;
        char *sav;
        char *val;
        int ret;
        int cnt;

        if (instance_name) {
                instance = tracefs_instance_create(instance_name);
                if (!instance) {
                        fprintf(stderr, "Failed instance create\n");
                        exit(-1);
                }
        }

        tep = tracefs_local_events(NULL);
        if (!tep) {
                perror("Could not read events");
                exit(-1);
        }

        parse_system_event(group, &system, &event);

        if (cmd == SHOW) {
                char *content;
                content = tracefs_event_file_read(instance, system, event,
                                                  "hist", NULL);
                if (!content) {
                        perror("Reading hist file");
                        exit(-1);
                }
                printf("%s\n", content);
                free(content);
                return;
        }

        if (!keys) {
                fprintf(stderr, "Command needs -k option\n");
                exit(-1);
        }

        cnt = parse_keys(keys, &axes);
        if (!cnt) {
                fprintf(stderr, "No keys??\n");
                exit(-1);
        }

        /* Show examples of hist1d and hist2d */
        switch (cnt) {
        case 1:
                hist = tracefs_hist_alloc(tep, system, event,
                                          axes[0].key, axes[0].type);
                break;
        case 2:
                hist = tracefs_hist_alloc_2d(tep, system, event,
                                             axes[0].key, axes[0].type,
                                             axes[1].key, axes[1].type);
                break;
        default:
                /* Really, 1 and 2 could use this too */
                hist = tracefs_hist_alloc_nd(tep, system, event, axes);
        }
        if (!hist) {
                fprintf(stderr, "Failed hist create\n");
                exit(-1);
        }

        if (vals) {
                sav = NULL;
                for (val = strtok_r(vals, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) {
                        ret = tracefs_hist_add_value(hist, val);
                        if (ret) {
                                fprintf(stderr, "Failed to add value %s\n", val);
                                exit(-1);
                        }
                }
        }

        if (sort) {
                sav = NULL;
                for (val = strtok_r(sort, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) {
                        ret = tracefs_hist_add_sort_key(hist, val);
                        if (ret) {
                                fprintf(stderr, "Failed to add sort key/val %s\n", val);
                                exit(-1);
                        }
                }
        }

        if (ascend) {
                sav = NULL;
                for (val = strtok_r(ascend, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) {
                        ret = tracefs_hist_sort_key_direction(hist, val, TRACEFS_HIST_SORT_ASCENDING);
                        if (ret) {
                                fprintf(stderr, "Failed to add ascending key/val %s\n", val);
                                exit(-1);
                        }
                }
        }

        if (desc) {
                sav = NULL;
                for (val = strtok_r(desc, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) {
                        ret = tracefs_hist_sort_key_direction(hist, val, TRACEFS_HIST_SORT_DESCENDING);
                        if (ret) {
                                fprintf(stderr, "Failed to add descending key/val %s\n", val);
                                exit(-1);
                        }
                }
        }

        tracefs_error_clear(instance);

        switch (cmd) {
        case START:
                ret = tracefs_hist_start(instance, hist);
                if (ret) {
                        char *err = tracefs_error_last(instance);
                        if (err)
                                fprintf(stderr, "\n%s\n", err);
                }
                break;
        case PAUSE:
                ret = tracefs_hist_pause(instance, hist);
                break;
        case CONT:
                ret = tracefs_hist_continue(instance, hist);
                break;
        case RESET:
                ret = tracefs_hist_reset(instance, hist);
                break;
        case DELETE:
                ret = tracefs_hist_destroy(instance, hist);
                break;
        case SHOW:
                /* Show was already done */
                break;
        }
        if (ret)
                fprintf(stderr, "Failed: command\n");
        exit(ret);
}

int main (int argc, char **argv, char **env)
{
        enum commands cmd;
        char *instance = NULL;
        char *cmd_str;
        char *event = NULL;
        char *keys = NULL;
        char *vals = NULL;
        char *sort = NULL;
        char *desc = NULL;
        char *ascend = NULL;

        if (argc < 2) {
                fprintf(stderr, "usage: %s command [-B instance][-e [system/]event][-k keys][-v vals][-s sort]\n", argv[0]);
                fprintf(stderr, "      [-a ascending][-d descending]\n");
                exit(-1);
        }

        cmd_str = argv[1];

        if (!strcmp(cmd_str, "start"))
                cmd = START;
        else if (!strcmp(cmd_str, "pause"))
                cmd = PAUSE;
        else if (!strcmp(cmd_str, "cont"))
                cmd = CONT;
        else if (!strcmp(cmd_str, "reset"))
                cmd = RESET;
        else if (!strcmp(cmd_str, "delete"))
                cmd = DELETE;
        else if (!strcmp(cmd_str, "show"))
                cmd = SHOW;
        else {
                fprintf(stderr, "Unknown command %s\n", cmd_str);
                exit(-1);
        }

        for (;;) {
                int c;

                c = getopt(argc - 1, argv + 1, "e:k:v:B:s:d:a:");
                if (c == -1)
                        break;

                switch (c) {
                case 'e':
                        event = optarg;
                        break;
                case 'k':
                        keys = optarg;
                        break;
                case 'v':
                        vals = optarg;
                        break;
                case 'B':
                        instance = optarg;
                        break;
                case 's':
                        sort = optarg;
                        break;
                case 'd':
                        desc = optarg;
                        break;
                case 'a':
                        ascend = optarg;
                        break;
                }
        }
        if (!event) {
                event = "kmem/kmalloc";
                if (!keys)
                        keys = "call_site.sym,bytes_req";
                if (!vals)
                        vals = "bytes_alloc";
                if (!sort)
                        sort = "bytes_req,bytes_alloc";
                if (!desc)
                        desc = "bytes_alloc";
        }
        process_hist(cmd, instance, event, keys, vals, sort, ascend, desc);
}

FILES

tracefs.h
        Header file to include in order to have access to the library APIs.
-ltracefs
        Linker switch to add when building a program that uses the library.

SEE ALSO

libtracefs(3), libtraceevent(3), trace-cmd(1), tracefs_hist_pause(3), tracefs_hist_continue(3), tracefs_hist_reset(3)

AUTHOR

Steven Rostedt <rostedt@goodmis.org>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
sameeruddin shaik <sameeruddin.shaik8@gmail.com>

REPORTING BUGS

LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES

COPYING

Copyright (C) 2020 VMware, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).