Helper function `bpf_timer_set_callback`

This helper sets the callback function for a timer.

Definition

Copyright (c) 2015 The Libbpf Authors. All rights reserved.

Configure the timer to call callback_fn static function.

Returns

0 on success. -EINVAL if timer was not initialized with bpf_timer_init() earlier. -EPERM if timer is in a map that doesn't have any user references. The user space should either hold a file descriptor to a map with timers or pin such map in bpffs. When map is unpinned or file descriptor is closed all timers in the map will be cancelled and freed.

static long (* const bpf_timer_set_callback)(struct bpf_timer *timer, void *callback_fn) = (void *) 170;

The function passed to callback_fn should have the following signature:

static int callback_fn(void *map, {map key type} *key, {map value type} *value)

Usage

Docs could be improved

This part of the docs is incomplete, contributions are very welcome

Example

#include <linux/bpf.h>
#include <time.h>
#include <stdbool.h>
#include <errno.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

struct elem {
    struct bpf_timer t;
};

struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __uint(max_entries, 1);
    __type(key, int);
    __type(value, struct elem);
} hmap SEC(".maps");

static int timer_callback(void* hmap, int* key, struct bpf_timer *timer)
{
        bpf_printk("Callback was invoked do something useful");
    return 0;
}

SEC("cgroup_skb/egress")
int bpf_prog1(void *ctx)
{
    struct bpf_timer *timer;
    int err, key = 0;
    struct elem init;
    struct elem* ele;

    __builtin_memset(&init, 0, sizeof(struct elem));
    bpf_map_update_elem(&hmap, &key, &init, BPF_ANY);

    ele = bpf_map_lookup_elem(&hmap, &key);
    if (!ele)
        return 1;

    timer = &ele->t;
    err = bpf_timer_init(timer, &hmap, CLOCK_MONOTONIC);
    if (err && err != -EBUSY)
        return 1;

    bpf_timer_set_callback(timer, timer_callback);
    bpf_timer_start(timer, 0, 0);
    bpf_timer_cancel(timer);

    return 0;
}

char _license[] SEC("license") = "GPL";

Helper function bpf_timer_set_callback