linux-kernel - Re: [PATCH v3 net-next v3 2/6] net: add support for segmenting TCP fraglist GSO packets

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Date: Fri, 26 Apr 2024 09:44:40 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Felix Fietkau <nbd@....name>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	willemdebruijn.kernel@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next v3 2/6] net: add support for segmenting TCP
 fraglist GSO packets

On Fri, Apr 26, 2024 at 8:51 AM Felix Fietkau <nbd@....name> 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@....name>
> ---
>  net/ipv4/tcp_offload.c   | 65 ++++++++++++++++++++++++++++++++++++++++
>  net/ipv6/tcpv6_offload.c |  3 ++
>  2 files changed, 68 insertions(+)
>
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index fab0973f995b..c493e95e09a5 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -28,6 +28,68 @@ 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)


Do we really need pointers for newip and 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)
> +{
> +       struct sk_buff *seg;
> +       struct tcphdr *th, *th2;
> +       struct iphdr *iph, *iph2;

I would probably add a const qualifier to th and iph

> +
> +       seg = segs;
> +       th = tcp_hdr(seg);
> +       iph = ip_hdr(seg);
> +       th2 = tcp_hdr(seg->next);
> +       iph2 = ip_hdr(seg->next);
> +
> +       if (!(*(u32 *)&th->source ^ *(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;
> +}
>