tools/testing/selftests/bpf/progs/test_sockmap_drop_prog.c

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

struct {
	__uint(type, BPF_MAP_TYPE_SOCKMAP);
	__uint(max_entries, 20);
	__type(key, int);
	__type(value, int);
} sock_map_rx SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_SOCKMAP);
	__uint(max_entries, 20);
	__type(key, int);
	__type(value, int);
} sock_map_tx SEC(".maps");

struct {
	__uint(type, BPF_MAP_TYPE_SOCKMAP);
	__uint(max_entries, 20);
	__type(key, int);
	__type(value, int);
} sock_map_msg SEC(".maps");

SEC("sk_skb")
int prog_skb_verdict(struct __sk_buff *skb)
{
	return SK_DROP;
}

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