Subject: Re: [PATCH bpf-next v3 4/4] selftests/bpf: add icmp_send_unreach kfunc tests

From: Martin KaFai Lau <[email-masked]>
Date: Mon, 28 Jul 2025 18:18:11 -0700

On 7/28/25 2:43 AM, Mahe Tardy wrote:
> +SEC("cgroup_skb/egress")
> +int egress(struct __sk_buff *skb)
> +{
> +	void *data = (void *)(long)skb->data;
> +	void *data_end = (void *)(long)skb->data_end;
> +	struct iphdr *iph;
> +	struct tcphdr *tcph;
> +
> +	iph = data;
> +	if ((void *)(iph + 1) > data_end || iph->version != 4 ||
> +	    iph->protocol != IPPROTO_TCP || iph->daddr != bpf_htonl(SERVER_IP))
> +		return SK_PASS;
> +
> +	tcph = (void *)iph + iph->ihl * 4;
> +	if ((void *)(tcph + 1) > data_end ||
> +	    tcph->dest != bpf_htons(SERVER_PORT))
> +		return SK_PASS;
> +
> +	kfunc_ret = bpf_icmp_send_unreach(skb, unreach_code);
> +
> +	/* returns SK_PASS to execute the test case quicker */

Do you know why the user space is slower if 0 (SK_DROP) is used?

> +	return SK_PASS;