netdev - Re: [PATCH net-next 01/17] net/ipv6: Introduce payload

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Message-ID: <aNWIi0Ni-kwUmYul@mini-arch>
Date: Thu, 25 Sep 2025 11:23:07 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Maxim Mikityanskiy <maxtram95@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	David Ahern <dsahern@...nel.org>,
	Nikolay Aleksandrov <razor@...ckwall.org>, netdev@...r.kernel.org,
	tcpdump-workers@...ts.tcpdump.org, Guy Harris <gharris@...ic.net>,
	Michael Richardson <mcr@...delman.ca>,
	Denis Ovsienko <denis@...ienko.info>,
	Xin Long <lucien.xin@...il.com>,
	Maxim Mikityanskiy <maxim@...valent.com>
Subject: Re: [PATCH net-next 01/17] net/ipv6: Introduce payload_len helpers

On 09/23, Maxim Mikityanskiy wrote:
> From: Maxim Mikityanskiy <maxim@...valent.com>
> 
> From: Maxim Mikityanskiy <maxim@...valent.com>
> 
> 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: Maxim Mikityanskiy <maxim@...valent.com>
> ---
>  include/linux/ipv6.h                       | 20 ++++++++++++++++++++
>  include/net/ipv6.h                         |  2 --
>  include/net/netfilter/nf_tables_ipv6.h     |  4 ++--
>  net/bridge/br_netfilter_ipv6.c             |  2 +-
>  net/bridge/netfilter/nf_conntrack_bridge.c |  4 ++--
>  net/ipv6/ip6_input.c                       |  2 +-
>  net/ipv6/ip6_offload.c                     |  7 +++----
>  net/ipv6/output_core.c                     |  7 +------
>  net/netfilter/ipvs/ip_vs_xmit.c            |  2 +-
>  net/netfilter/nf_conntrack_ovs.c           |  2 +-
>  net/netfilter/nf_log_syslog.c              |  2 +-
>  net/sched/sch_cake.c                       |  2 +-
>  12 files changed, 34 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
> index 43b7bb828738..44c4b791eceb 100644
> --- a/include/linux/ipv6.h
> +++ b/include/linux/ipv6.h
> @@ -126,6 +126,26 @@ 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);

Any reason not to return skb->len - skb_network_offset(skb) - sizeof(struct ipv6hdr)
here unconditionally? Will it not work in some cases?