[PATCH net-next 2/4] 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.
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. 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)
+{
+	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