CODEWITHSUNDEEP
clinuxnetwork-programmingmapsebpf
imawful
imawful

Reputation: 135

bpf_map_lookup_elem not working when key is struct

I am creating an entry into the map of type BPF_MAP_TYPE_HASH in one SEC in the program and trying to access that entry in another SEC. The key is defined as a struct.

struct map_key
{
    __u16 key_1;
    __u16 key_2;
}

struct map_value
{
    __u16 value_1;
    __u16 value_2;
}

struct
{
    __uint(type, BPF_MAP_TYPE_HASH);
    __type(key, struct map_key);
    __type(value, struct map_value);
    __uint(max_entries, 1024);
} bpf_map SEC(".maps");

SEC("sec1")
int sec1_func(struct __sk_buff *skb)
{
    struct map_key key = {0}
    key.key1 = 10;
    key.key2 = 20;
    check = bpf_map_lookup_elem(&bpf_map, &key);
    if (check == NULL) {
        bpf_trace_printk("Trouble.", sizeof("Trouble"));
    }
}

SEC("sec2")
{
    struct map_key key = {0}
    key.key1 = 10;
    key.key2 = 20;

    struct map_value value = {0}
    value.value1 = 15
    value.value2 = 25

    bpf_map_update_elem(&map_key, &key, &value, BPF_NOEXIST);
}

sec2 is executed before sec1, so the map is definitely created before bpf_map_lookup_elem is called. But still, i'm getting null value returned from it when i call this function in sec1.

Upvotes: 0

Views: 787

Answers (1)

imawful
imawful

Reputation: 135

So the fix is,

struct map_key
{
    __u16 key_1;
    __u16 key_2;
}

struct map_value
{
    __u16 value_1;
    __u16 value_2;
}

struct
{
    __uint(type, BPF_MAP_TYPE_HASH);
    __type(key, struct map_key);
    __type(value, struct map_value);
    __uint(max_entries, 1024);
    __uint(pinning, 1);
} bpf_map SEC(".maps");

SEC("sec1")
int sec1_func(struct __sk_buff *skb)
{
    struct map_key key = {0}
    key.key1 = 10;
    key.key2 = 20;
    check = bpf_map_lookup_elem(&bpf_map, &key);
    if (check == NULL) {
        bpf_trace_printk("Trouble.", sizeof("Trouble"));
    }
}

SEC("sec2")
{
    struct map_key key = {0}
    key.key1 = 10;
    key.key2 = 20;

    struct map_value value = {0}
    value.value1 = 15
    value.value2 = 25

    bpf_map_update_elem(&map_key, &key, &value, BPF_NOEXIST);
}

The additional pin field allows me to use the map in different elf sections within the same object file.

Upvotes: 1

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