From b2936b4fd56294e49d6c8e9152ea6c4982757c7d Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Thu, 5 Feb 2026 15:39:14 +0200 Subject: net/ipv6: Introduce payload_len helpers The next commits will transition away from using the hop-by-hop extension header to encode packet length for BIG TCP. Add wrappers around ip6->payload_len that return the actual value if it's non-zero, and calculate it from skb->len if payload_len is set to zero (and a symmetrical setter). The new helpers are used wherever the surrounding code supports the hop-by-hop jumbo header for BIG TCP IPv6, or the corresponding IPv4 code uses skb_ip_totlen (e.g., in include/net/netfilter/nf_tables_ipv6.h). No behavioral change in this commit. Signed-off-by: Alice Mikityanska Acked-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260205133925.526371-2-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- include/linux/ipv6.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'include/linux') diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h index 20aae8357dd1..57ab6c97ee7e 100644 --- a/include/linux/ipv6.h +++ b/include/linux/ipv6.h @@ -126,6 +126,28 @@ static inline unsigned int ipv6_transport_len(const struct sk_buff *skb) skb_network_header_len(skb); } +static inline unsigned int +ipv6_payload_len(const struct sk_buff *skb, const struct ipv6hdr *ip6) +{ + u32 len = ntohs(ip6->payload_len); + + return (len || !skb_is_gso(skb) || !skb_is_gso_tcp(skb)) ? + len : + skb->len - skb_network_offset(skb) - sizeof(struct ipv6hdr); +} + +static inline unsigned int skb_ipv6_payload_len(const struct sk_buff *skb) +{ + return ipv6_payload_len(skb, ipv6_hdr(skb)); +} + +#define IPV6_MAXPLEN 65535 + +static inline void ipv6_set_payload_len(struct ipv6hdr *ip6, unsigned int len) +{ + ip6->payload_len = len <= IPV6_MAXPLEN ? htons(len) : 0; +} + /* This structure contains results of exthdrs parsing as offsets from skb->nh. -- cgit v1.2.3 From 741d069aa488866ae8425f87ad270ed3815ccaac Mon Sep 17 00:00:00 2001 From: Alice Mikityanska Date: Thu, 5 Feb 2026 15:39:15 +0200 Subject: net/ipv6: Drop HBH for BIG TCP on TX side BIG TCP IPv6 inserts a hop-by-hop extension header to indicate the real IPv6 payload length when it doesn't fit into the 16-bit field in the IPv6 header itself. While it helps tools parse the packet, it also requires every driver that supports TSO and BIG TCP to remove this 8-byte extension header. It might not sound that bad until we try to apply it to tunneled traffic. Currently, the drivers don't attempt to strip HBH if skb->encapsulation = 1. Moreover, trying to do so would require dissecting different tunnel protocols and making corresponding adjustments on case-by-case basis, which would slow down the fastpath (potentially also requiring adjusting checksums in outer headers). At the same time, BIG TCP IPv4 doesn't insert any extra headers and just calculates the payload length from skb->len, significantly simplifying implementing BIG TCP for tunnels. Stop inserting HBH when building BIG TCP GSO SKBs. Signed-off-by: Alice Mikityanska Acked-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260205133925.526371-3-alice.kernel@fastmail.im Signed-off-by: Jakub Kicinski --- include/linux/ipv6.h | 1 - 1 file changed, 1 deletion(-) (limited to 'include/linux') diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h index 57ab6c97ee7e..bdbd63f9a85e 100644 --- a/include/linux/ipv6.h +++ b/include/linux/ipv6.h @@ -177,7 +177,6 @@ struct inet6_skb_parm { #define IP6SKB_L3SLAVE 64 #define IP6SKB_JUMBOGRAM 128 #define IP6SKB_SEG6 256 -#define IP6SKB_FAKEJUMBO 512 #define IP6SKB_MULTIPATH 1024 #define IP6SKB_MCROUTE 2048 }; -- cgit v1.2.3