linux-kernel - Re: [PATCH v2 net-next v2 2/5] net: add support for segmenting TCP fraglist GSO packets

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Message-ID: <89c406c9-9017-49cb-9084-c0a0fc3ad6f3@nbd.name>
Date: Thu, 25 Apr 2024 17:22:59 +0200
From: Felix Fietkau <nbd@....name>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next v2 2/5] net: add support for segmenting TCP
 fraglist GSO packets

On 25.04.24 17:17, Willem de Bruijn wrote:
> Felix Fietkau wrote:
>> Preparation for adding TCP fraglist GRO support. It expects packets to be
>> combined in a similar way as UDP fraglist GSO packets.
>> For IPv4 packets, NAT is handled in the same way as UDP fraglist GSO.
>> 
>> Signed-off-by: Felix Fietkau <nbd@....name>
>> ---
>>  net/ipv4/tcp_offload.c   | 69 ++++++++++++++++++++++++++++++++++++++++
>>  net/ipv6/tcpv6_offload.c |  3 ++
>>  2 files changed, 72 insertions(+)
>> 
>> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
>> index fab0973f995b..e455f884190c 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -28,6 +28,72 @@ static void tcp_gso_tstamp(struct sk_buff *skb, unsigned int ts_seq,
>>  	}
>>  }
>>  
>> +static void __tcpv4_gso_segment_csum(struct sk_buff *seg,
>> +				     __be32 *oldip, __be32 *newip,
>> +				     __be16 *oldport, __be16 *newport)
>> +{
>> +	struct tcphdr *th;
>> +	struct iphdr *iph;
>> +
>> +	if (*oldip == *newip && *oldport == *newport)
>> +		return;
>> +
>> +	th = tcp_hdr(seg);
>> +	iph = ip_hdr(seg);
>> +
>> +	inet_proto_csum_replace4(&th->check, seg, *oldip, *newip, true);
>> +	inet_proto_csum_replace2(&th->check, seg, *oldport, *newport, false);
>> +	*oldport = *newport;
>> +
>> +	csum_replace4(&iph->check, *oldip, *newip);
>> +	*oldip = *newip;
>> +}
>> +
>> +static struct sk_buff *__tcpv4_gso_segment_list_csum(struct sk_buff *segs)
>> +{
>> +	struct sk_buff *seg;
>> +	struct tcphdr *th, *th2;
>> +	struct iphdr *iph, *iph2;
>> +	__be32 flags, flags2;
>> +
>> +	seg = segs;
>> +	th = tcp_hdr(seg);
>> +	iph = ip_hdr(seg);
>> +	flags = tcp_flag_word(th);
>> +	flags2 = tcp_flag_word(tcp_hdr(seg->next));
> 
> Vestigial, now that flag overwrite is removed in v2?

Will fix, thanks.

> All this code is very similar to __udpv4_gso_segment_list_csum. But
> the zero checksum handling in __udpv4_gso_segment_csum makes it just
> different enough that I also do not immediately see a straightforward
> way to avoid duplicating.

Also, the checksum field is in a different location in the udp header. I 
don't think avoiding duplication makes sense here.

- Felix