bpf_ctx_init
ctx = bpf_ctx_init(kattr, sizeof(struct __sk_buff));
ctx = bpf_ctx_init(kattr, sizeof(struct xdp_md));
user_ctx = bpf_ctx_init(kattr, sizeof(struct bpf_flow_keys));
user_ctx = bpf_ctx_init(kattr, sizeof(*user_ctx));
user_ctx = bpf_ctx_init(kattr, sizeof(struct nf_hook_state));