netdev - Re: [PATCH net v2 1/3] net: gro: add {inner_}network_offset to napi_gro

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Date: Mon, 22 Apr 2024 10:32:16 +0200
From: Richard Gobert <richardbgobert@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, dsahern@...nel.org,
 alexander.duyck@...il.com, aleksander.lobakin@...el.com,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 1/3] net: gro: add {inner_}network_offset to
 napi_gro_cb

Willem de Bruijn wrote:
> Richard Gobert wrote:
>> This patch adds network_offset and inner_network_offset to napi_gro_cb, and
>> makes sure both are set correctly. In the common path there's only one
>> write (skb_gro_reset_offset, which replaces skb_set_network_header).
>>
>> Signed-off-by: Richard Gobert <richardbgobert@...il.com>
>> ---
>>  drivers/net/geneve.c           |  1 +
>>  drivers/net/vxlan/vxlan_core.c |  1 +
>>  include/net/gro.h              | 18 ++++++++++++++++--
>>  net/8021q/vlan_core.c          |  2 ++
>>  net/core/gro.c                 |  1 +
>>  net/ethernet/eth.c             |  1 +
>>  net/ipv4/af_inet.c             |  5 +----
>>  net/ipv4/gre_offload.c         |  1 +
>>  net/ipv6/ip6_offload.c         |  8 ++++----
>>  9 files changed, 28 insertions(+), 10 deletions(-)
>>
> 
>> +static inline int skb_gro_network_offset(const struct sk_buff *skb)
>> +{
>> +	return NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark];
>> +}
>> +
> 
> 
>> @@ -236,8 +236,6 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
>>  	if (unlikely(!iph))
>>  		goto out;
>>  
>> -	skb_set_network_header(skb, off);
>> -
> 
> Especially for net, this is still a large patch.
> 
> Can we avoid touching all those tunnel callbacks and just set the
> offsets in inet_gro_receive and ipv6_gro_receive themselves, just
> as skb_set_network_header now:
> 
> @@ -236,7 +236,7 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
>         if (unlikely(!iph))
>                 goto out;
>  
> -       skb_set_network_header(skb, off);
> +       NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark] = off;
> 

Thanks for the reply!

Setting network_offset on dev_gro_receive and inner_network_offset only
in the tunnel callbacks is the best option IMO. I agree that
we want a small patch to net that solves the problem, although I 
think always using ->encap_mark in the common path is not ideal. 

We can avoid changing all the tunnel callbacks by always setting
inner_network_offset in {ipv6,inet}_gro_receive and initialize
network_offset to 0 in dev_gro_receive. It will result in a small
change, without using ->encap_mark.

What are your thoughts?