Re: [PATCH net-next v2 1/5] net: gro: remove is_ipv6 from napi_gro_cb

[Eric Dumazet]

On Mon, Aug 18, 2025 at 11:32 PM Richard Gobert
<richardbgobert@xxxxxxxxx> wrote:
>
> Remove is_ipv6 from napi_gro_cb and use sk->sk_family instead.
> This frees up space for another ip_fixedid bit that will be added
> in the next commit.
>
> Using sk->sk_family is reliable since udp_sock_create always
> creates either a AF_INET or a AF_INET6 socket, and IPv6-FOU
> doesn't support receiving IPv4 packets.
>
> Signed-off-by: Richard Gobert <richardbgobert@xxxxxxxxx>
> ---
>  include/net/gro.h      |  3 ---
>  net/ipv4/fou_core.c    | 31 +++++++++++++------------------
>  net/ipv4/udp_offload.c |  2 --
>  net/ipv6/udp_offload.c |  2 --
>  4 files changed, 13 insertions(+), 25 deletions(-)
>
> diff --git a/include/net/gro.h b/include/net/gro.h
> index a0fca7ac6e7e..87c68007f949 100644
> --- a/include/net/gro.h
> +++ b/include/net/gro.h
> @@ -71,9 +71,6 @@ struct napi_gro_cb {
>                 /* Free the skb? */
>                 u8      free:2;
>
> -               /* Used in foo-over-udp, set in udp[46]_gro_receive */
> -               u8      is_ipv6:1;
> -
>                 /* Used in GRE, set in fou/gue_gro_receive */
>                 u8      is_fou:1;
>
> diff --git a/net/ipv4/fou_core.c b/net/ipv4/fou_core.c
> index 3e30745e2c09..261ea2cf460f 100644
> --- a/net/ipv4/fou_core.c
> +++ b/net/ipv4/fou_core.c
> @@ -228,21 +228,26 @@ static int gue_udp_recv(struct sock *sk, struct sk_buff *skb)
>         return 0;
>  }
>
> +static inline const struct net_offload *fou_gro_ops(struct sock *sk, int proto)

const struct sock *sk

> +{
> +       const struct net_offload __rcu **offloads;
> +
> +       /* FOU doesn't allow IPv4 on IPv6 sockets. */
> +       offloads = sk->sk_family == AF_INET6 ? inet6_offloads : inet_offloads;


Do we have a guarantee sk->sk_family can not change under us ?

IPV6_ADDRFORM is available to UDP sockets after all.