Helper function `bpf_map_update_elem`

The update map element helper call is used to write values from maps.

Definition

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

static long (* const bpf_map_update_elem)(void *map, const void *key, const void *value, __u64 flags) = (void *) 2;

Usage

Arguments of this helper are map which is a pointer to a map definition, key which is a pointer to the key you wish to write to, value which is a pointer to the value you wish to write to the map, and flags which are described below.

The flags argument can be one of the following values:

BPF_NOEXIST - If set the update will only happen if the key doesn't exist yet, to prevent overwriting existing data.
BPF_EXIST - If set the update will only happen if the key exists, to ensure an update and no new key creation.
BPF_ANY - It doesn't matter, an update will be attempted in both cases.

Info

BPF_NOEXIST isn't supported for array type maps since all keys always exist.

The return value will be 0 on success or a negative valued error number indicating a failure.

Program types

This helper call can be used in the following program types:

Map types

This helper call can be used with the following map types:

Example

int key, value, result;

key = 1, value = 5678;

result = bpf_map_update_elem(&my_map, &key, &value, BPF_NOEXIST);
if (result == 0)
    bpf_printk("Map updated with new element\n");
else
    bpf_printk("Failed to update map with new value: %d\n", result);

Helper function bpf_map_update_elem