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:
- BPF_PROG_TYPE_CGROUP_DEVICE
- BPF_PROG_TYPE_CGROUP_SKB
- BPF_PROG_TYPE_CGROUP_SOCK
- BPF_PROG_TYPE_CGROUP_SOCKOPT
- BPF_PROG_TYPE_CGROUP_SOCK_ADDR
- BPF_PROG_TYPE_CGROUP_SYSCTL
- BPF_PROG_TYPE_FLOW_DISSECTOR
- BPF_PROG_TYPE_KPROBE
- BPF_PROG_TYPE_LIRC_MODE2
- BPF_PROG_TYPE_LSM
- BPF_PROG_TYPE_LWT_IN
- BPF_PROG_TYPE_LWT_OUT
- BPF_PROG_TYPE_LWT_SEG6LOCAL
- BPF_PROG_TYPE_LWT_XMIT
- BPF_PROG_TYPE_PERF_EVENT
- BPF_PROG_TYPE_RAW_TRACEPOINT
- BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE
- BPF_PROG_TYPE_SCHED_ACT
- BPF_PROG_TYPE_SCHED_CLS
- BPF_PROG_TYPE_SK_LOOKUP
- BPF_PROG_TYPE_SK_MSG
- BPF_PROG_TYPE_SK_REUSEPORT
- BPF_PROG_TYPE_SK_SKB
- BPF_PROG_TYPE_SOCKET_FILTER
- BPF_PROG_TYPE_SOCK_OPS
- BPF_PROG_TYPE_SYSCALL
- BPF_PROG_TYPE_TRACEPOINT
- BPF_PROG_TYPE_TRACING
- BPF_PROG_TYPE_XDP
Map types
This helper call can be used with the following map types:
- BPF_MAP_TYPE_ARRAY
- BPF_MAP_TYPE_HASH
- BPF_MAP_TYPE_LPM_TRIE
- BPF_MAP_TYPE_LRU_HASH
- BPF_MAP_TYPE_LRU_PERCPU_HASH
- BPF_MAP_TYPE_PERCPU_ARRAY
- BPF_MAP_TYPE_PERCPU_HASH
- BPF_MAP_TYPE_SOCKHASH
- BPF_MAP_TYPE_SOCKMAP
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);