[PATCH v2 net-next v2 2/5] net: add support for segmenting TCP fraglist GSO packets

[Felix Fietkau <nbd@nbd.name>]

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   | 69 ++++++++++++++++++++++++++++++++++++++++
 net/ipv6/tcpv6_offload.c |  3 ++
 2 files changed, 72 insertions(+)

diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
index fab0973f995b..e455f884190c 100644
--- a/net/ipv4/tcp_offload.c
+++ b/net/ipv4/tcp_offload.c
@@ -28,6 +28,72 @@ 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);
+	}
+
+	return segs;
+}
+
+static struct sk_buff *__tcp4_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 __tcpv4_gso_segment_list_csum(skb);
+}
+
 static struct sk_buff *tcp4_gso_segment(struct sk_buff *skb,
 					netdev_features_t features)
 {
@@ -37,6 +103,9 @@ 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 __tcp4_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..b3b8e1f6b92a 100644
--- a/net/ipv6/tcpv6_offload.c
+++ b/net/ipv6/tcpv6_offload.c
@@ -51,6 +51,9 @@ 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 skb_segment_list(skb, features, skb_mac_header_len(skb));
+
 	if (unlikely(skb->ip_summed != CHECKSUM_PARTIAL)) {
 		const struct ipv6hdr *ipv6h = ipv6_hdr(skb);
 		struct tcphdr *th = tcp_hdr(skb);
-- 
2.44.0