Re: [PATCH net-next 2/4] net: add support for segmenting TCP fraglist GSO packets

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

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.
> One difference is the fact that this code assumes that the TCP flags of
> all packets have the same value. This allows simple handling of flags
> mutations.

Can you clarify this some more? We expect potentially different flags
on first and last packet in a TSO train. With fraglist, the segments
keep their original flags, as the headers are only pulled. When do
segment flags need to be replaced with those of the first segment?

> 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   | 74 ++++++++++++++++++++++++++++++++++++++++
>  net/ipv6/tcpv6_offload.c | 37 ++++++++++++++++++++
>  2 files changed, 111 insertions(+)
> 
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index fab0973f995b..06dbb2e2b2f3 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -28,6 +28,77 @@ 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)
> +{
> +	struct sk_buff *seg;
> +	struct tcphdr *th, *th2;
> +	struct iphdr *iph, *iph2;
> +	__be32 flags, flags2;
> +
> +	seg = segs;
> +	th = tcp_hdr(seg);
> +	iph = ip_hdr(seg);
> +	flags = tcp_flag_word(th);
> +	flags2 = tcp_flag_word(tcp_hdr(seg->next));
> +
> +	if ((tcp_hdr(seg)->dest == tcp_hdr(seg->next)->dest) &&
> +	    (tcp_hdr(seg)->source == tcp_hdr(seg->next)->source) &&
> +	    (ip_hdr(seg)->daddr == ip_hdr(seg->next)->daddr) &&
> +	    (ip_hdr(seg)->saddr == ip_hdr(seg->next)->saddr) &&
> +	    (flags == flags2))
> +		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);
> +		if (flags == flags2)
> +			continue;
> +
> +		inet_proto_csum_replace4(&th2->check, seg, flags2, flags, false);
> +		tcp_flag_word(th2) = flags;
> +	}
> +
> +	return segs;
> +}
> +
> +static struct sk_buff *__tcp_gso_segment_list(struct sk_buff *skb,
> +					      netdev_features_t features)

For consistency and to avoid having the same name in ipv6,
add the 4/6 suffix here too.

> +{
> +	skb = skb_segment_list(skb, features, skb_mac_header_len(skb));
> +	if (IS_ERR(skb))
> +		return skb;
> +
> +	return __tcpv4_gso_segment_list_csum(skb);
> +}
> +
>  static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
>  					netdev_features_t features)
>  {
> @@ -37,6 +108,9 @@ static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
>  	if (!pskb_may_pull(skb, sizeof(struct tcphdr)))
>  		return ERR_PTR(-EINVAL);
>  
> +	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST)
> +		return __tcp_gso_segment_list(skb, features);
> +
>  	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
>  		const struct iphdr *iph = ip_hdr(skb);
>  		struct tcphdr *th = tcp_hdr(skb);
> diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
> index 4b07d1e6c952..12fe79cb2c10 100644
> --- a/net/ipv6/tcpv6_offload.c
> +++ b/net/ipv6/tcpv6_offload.c
> @@ -40,6 +40,40 @@ INDIRECT_CALLABLE_SCOPE int tcp6_gro_complete(struct sk_buff *skb, int thoff)
>  	return 0;
>  }
>  
> +static struct sk_buff *__tcpv6_gso_segment_list_csum(struct sk_buff *segs)
> +{
> +	struct tcphdr *th, *th2;
> +	__be32 flags, flags2;
> +	struct sk_buff *seg;
> +
> +	seg = segs;
> +	th = tcp_hdr(seg);
> +	flags = tcp_flag_word(th);
> +	flags2 = tcp_flag_word(tcp_hdr(seg->next));
> +
> +	if (flags == flags2)
> +		return segs;
> +
> +	while ((seg = seg->next)) {
> +		th2 = tcp_hdr(seg);
> +
> +		inet_proto_csum_replace4(&th2->check, seg, flags2, flags, false);
> +		tcp_flag_word(th2) = flags;
> +	}
> +
> +	return segs;
> +}
> +
> +static struct sk_buff *__tcp_gso_segment_list(struct sk_buff *skb,
> +					      netdev_features_t features)
> +{
> +	skb = skb_segment_list(skb, features, skb_mac_header_len(skb));
> +	if (IS_ERR(skb))
> +		return skb;
> +
> +	return __tcpv6_gso_segment_list_csum(skb);
> +}
> +
>  static struct sk_buff *tcp6_gso_segment(struct sk_buff *skb,
>  					netdev_features_t features)
>  {
> @@ -51,6 +85,9 @@ static struct sk_buff *tcp6_gso_segment(struct sk_buff *skb,
>  	if (!pskb_may_pull(skb, sizeof(*th)))
>  		return ERR_PTR(-EINVAL);
>  
> +	if (skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST)
> +		return __tcp_gso_segment_list(skb, features);
> +
>  	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
>  		const struct ipv6hdr *ipv6h = ipv6_hdr(skb);
>  		struct tcphdr *th = tcp_hdr(skb);
> -- 
> 2.44.0
> 
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