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

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Message-ID: <6533e1fa-2528-4bee-92fa-6f2d1a44d906@gmail.com>
Date: Tue, 19 Aug 2025 14:26:47 +0200
From: Richard Gobert <richardbgobert@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
 pabeni@...hat.com, horms@...nel.org, corbet@....net, shenjian15@...wei.com,
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 saeedm@...dia.com, tariqt@...dia.com, mbloch@...dia.com, leon@...nel.org,
 ecree.xilinx@...il.com, dsahern@...nel.org, ncardwell@...gle.com,
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 aleksander.lobakin@...el.com, florian.fainelli@...adcom.com,
 willemdebruijn.kernel@...il.com, linux-kernel@...r.kernel.org,
 linux-net-drivers@....com
Subject: Re: [PATCH net-next v2 1/5] net: gro: remove is_ipv6 from napi_gro_cb

Eric Dumazet wrote:
> On Mon, Aug 18, 2025 at 11:32 PM Richard Gobert
> <richardbgobert@...il.com> 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@...il.com>
>> ---
>>  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.

This is a kernel socket, and FOU doesn't use IPV6_ADDRFORM.