Re: [PATCH v4 net-next v4 2/6] net: add support for segmenting TCP fraglist GSO packets

[Paolo Abeni <pabeni@redhat.com>]

On Sat, 2024-04-27 at 20:22 +0200, Felix Fietkau wrote:
> Preparation for adding TCP fraglist GRO support. It expects packets to be
> combined in a similar way as UDP fraglist GSO packets.
> For IPv4 packets, NAT is handled in the same way as UDP fraglist GSO.
> 
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>  net/ipv4/tcp_offload.c   | 67 ++++++++++++++++++++++++++++++++++++++++
>  net/ipv6/tcpv6_offload.c | 58 ++++++++++++++++++++++++++++++++++
>  2 files changed, 125 insertions(+)
> 
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index fab0973f995b..affd4ed28cfe 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -28,6 +28,70 @@ static void tcp_gso_tstamp(struct sk_buff *skb, unsigned int ts_seq,
>  	}
>  }
>  
> +static void __tcpv4_gso_segment_csum(struct sk_buff *seg,
> +				     __be32 *oldip, __be32 newip,
> +				     __be16 *oldport, __be16 newport)
> +{
> +	struct tcphdr *th;
> +	struct iphdr *iph;
> +
> +	if (*oldip == newip && *oldport == newport)
> +		return;
> +
> +	th = tcp_hdr(seg);
> +	iph = ip_hdr(seg);
> +
> +	inet_proto_csum_replace4(&th->check, seg, *oldip, newip, true);
> +	inet_proto_csum_replace2(&th->check, seg, *oldport, newport, false);
> +	*oldport = newport;
> +
> +	csum_replace4(&iph->check, *oldip, newip);
> +	*oldip = newip;
> +}
> +
> +static struct sk_buff *__tcpv4_gso_segment_list_csum(struct sk_buff *segs)
> +{
> +	const struct tcphdr *th;
> +	const struct iphdr *iph;
> +	struct sk_buff *seg;
> +	struct tcphdr *th2;
> +	struct iphdr *iph2;
> +
> +	seg = segs;
> +	th = tcp_hdr(seg);
> +	iph = ip_hdr(seg);
> +	th2 = tcp_hdr(seg->next);
> +	iph2 = ip_hdr(seg->next);
> +
> +	if (!(*(const u32 *)&th->source ^ *(const u32 *)&th2->source) &&
> +	    iph->daddr == iph2->daddr && iph->saddr == iph2->saddr)
> +		return segs;
> +
> +	while ((seg = seg->next)) {
> +		th2 = tcp_hdr(seg);
> +		iph2 = ip_hdr(seg);
> +
> +		__tcpv4_gso_segment_csum(seg,
> +					 &iph2->saddr, iph->saddr,
> +					 &th2->source, th->source);
> +		__tcpv4_gso_segment_csum(seg,
> +					 &iph2->daddr, iph->daddr,
> +					 &th2->dest, th->dest);
> +	}
> +
> +	return segs;
> +}

AFAICS, all the above is really alike the UDP side, except for the
transport header zero csum.

What about renaming the udp version of this helpers as 'tcpudpv4_...',
move them in common code, add an explicit argument for
'zerocsum_allowed' and reuse such helper for both tcp and udp?

The same for the ipv6 variant. 

Cheers,

Paolo