Subject: Re: [PATCH bpf-next v2 11/13] selftests/bpf: add network helpers to generate udp checksums

From: Stanislav Fomichev <[email-masked]>
Date: Fri, 15 Nov 2024 07:54:05 -0800

On 11/14, Alexis Lothoré (eBPF Foundation) wrote:
> network_helpers.c provides some helpers to generate ip checksums or ip
> pseudo-header checksums, but not for upper layers (eg: udp checksums)
> 
> Add helpers for udp checksum to allow manually building udp packets.
> 
> Signed-off-by: Alexis Lothoré (eBPF Foundation) <[email-masked]>
> ---
> Changes in v2:
> - new patch
> ---
>  tools/testing/selftests/bpf/network_helpers.h | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
> index 6d1ae56080c56a65c437899c32566f0e4c496c33..fa82269f7a169a518ba210fa8641eba02f262333 100644
> --- a/tools/testing/selftests/bpf/network_helpers.h
> +++ b/tools/testing/selftests/bpf/network_helpers.h
> @@ -161,6 +161,33 @@ build_ipv6_pseudo_header_csum(const struct in6_addr *saddr,
>  	return csum_fold((__u32)s);
>  }
>  
> +static inline __sum16 build_udp_v4_csum(const struct iphdr *iph, __u8 l4_proto,
> +					__u16 l4_len, const void *l4_start,
> +					int num_words)
> +{
> +	unsigned long pseudo_sum;
> +	int num_u16 = sizeof(iph->saddr); /* halfwords: twice byte len */
> +
> +	pseudo_sum = add_csum_hword((void *)&iph->saddr, num_u16);
> +	pseudo_sum += htons(l4_proto);
> +	pseudo_sum += l4_len;
> +	pseudo_sum += add_csum_hword(l4_start, num_words);
> +	return csum_fold(pseudo_sum);

I was expecting to see a call to csum_tcpudp_magic here. And csum_ipv6_magic
down below. These build pseudo header csum, so no need to manually do it
again.

> +}
> +
> +static inline __sum16 build_udp_v6_csum(const struct ipv6hdr *ip6h,
> +					const void *l4_start, int num_words)
> +{
> +	unsigned long pseudo_sum;
> +	int num_u16 = sizeof(ip6h->saddr); /* halfwords: twice byte len */
> +
> +	pseudo_sum = add_csum_hword((void *)&ip6h->saddr, num_u16);
> +	pseudo_sum += htons(ip6h->nexthdr);
> +	pseudo_sum += ip6h->payload_len;
> +	pseudo_sum += add_csum_hword(l4_start, num_words);
> +	return csum_fold(pseudo_sum);
> +}
> +
>  struct tmonitor_ctx;
>  
>  #ifdef TRAFFIC_MONITOR
> 
> -- 
> 2.47.0
>