---
name: "tracefs_hist_add_value"
section: "3"
platform: "linux"
package: "libtracefs-doc"
version: "1.8.1-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/tracefs_hist_alloc"
---

# tracefs\_hist\_add\_value(3)

Create and destroy event histograms

Part of [tracefs\_hist\_alloc(3)](/tracefs_hist_alloc/3.md).

## NAME

tracefs\_hist\_alloc, tracefs\_hist\_alloc\_2d, tracefs\_hist\_alloc\_nd, tracefs\_hist\_alloc\_nd\_cnt, tracefs\_hist\_free, tracefs\_hist\_add\_key, tracefs\_hist\_add\_key\_cnt, tracefs\_hist\_add\_value - Create and destroy event histograms

## 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);
struct tracefs_hist *tracefs_hist_alloc_nd_cnt(struct tep_handle *tep,
                          const char *system, const char *event_name,
                          struct tracefs_hist_axis_cnt *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_key_cnt(struct tracefs_hist *hist, const char *key,
                         enum tracefs_hist_key_type type, int cnt);
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)](/tracefs_local_events/3.md)), 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)](/tracefs_local_events/3.md)), 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)](/tracefs_local_events/3.md)), 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\_alloc\_nd\_cnt**() will initialize a histogram descriptor that will be attached to the *system*/*event*. This only initializes the descriptor with the given *axes* keys as primaries. This only initializes the descriptor, it does not start the histogram in the kernel. The difference between this and **tracefs\_hist\_alloc\_nd()** is that the *axes* parameter is of type **struct tracefs\_hist\_axis\_cnt** and not **struct tracefs\_hist\_axis**.

**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).

The **tracefs\_hist\_add\_key\_cnt**() is the same as **tracefs\_hist\_add\_key**() except that it allows to add a counter for the given type. Currently, there’s only the **buckets** type that requires a counter. When adding a key with the buckets type, **tracefs\_hist\_add\_key**() is not sufficient, as the **buckets** type requires a counter or bucket size. Use **tracefs\_hist\_add\_key\_cnt**() when specifing a key that is broken up into buckets, and pass in the size of those buckets into *cnt*.

**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 <ctype.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_cnt **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_cnt *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 if (strncmp(att, "buckets", 7) == 0) {
                                if (att[7] != '=' && !isdigit(att[8])) {
                                        fprintf(stderr, "'buckets' key type requires '=<size>'\n");
                                        exit(-1);
                                }
                                ax[cnt].type = TRACEFS_HIST_KEY_BUCKETS;
                                ax[cnt].cnt = atoi(&att[8]);
                        } 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_cnt *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);
        }
        /* buckets require the nd_cnt function */
        switch (cnt) {
        case 2:
                if (axes[1].type == TRACEFS_HIST_KEY_BUCKETS)
                        cnt = -1;
                /* fall through */
        case 1:
                if (axes[0].type == TRACEFS_HIST_KEY_BUCKETS)
                        cnt = -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_cnt(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)](/libtracefs/3.md), [**libtraceevent**(3)](/libtraceevent/3.md), [**trace-cmd**(1)](/trace-cmd/1.md), [**tracefs\_hist\_pause**(3)](/tracefs_hist_pause/3.md), [**tracefs\_hist\_continue**(3)](/tracefs_hist_continue/3.md), [**tracefs\_hist\_reset**(3)](/tracefs_hist_reset/3.md)

## AUTHOR

```
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>
```

## REPORTING BUGS

Report bugs to \<**linux-trace-devel@vger.kernel.org**\[4\]\>

## LICENSE

libtracefs is Free Software licensed under the GNU LGPL 2.1

## RESOURCES

**https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.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\.

  sameeruddin.shaik8@gmail.com

  mailto:sameeruddin.shaik8@gmail.com

- 4\.

  linux-trace-devel@vger.kernel.org

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