netdev - Re: [PATCH v4 net-next v4 2/6] net: add support for segmenting TCP fraglist GSO packets

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Message-ID: <9e686cb4-ed1f-4886-a0b7-328367e62757@nbd.name>
Date: Tue, 30 Apr 2024 12:27:40 +0200
From: Felix Fietkau <nbd@....name>
To: Paolo Abeni <pabeni@...hat.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>
Cc: willemdebruijn.kernel@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 net-next v4 2/6] net: add support for segmenting TCP
 fraglist GSO packets

On 30.04.24 12:19, Paolo Abeni wrote:
> On Sat, 2024-04-27 at 20:22 +0200, 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   | 67 ++++++++++++++++++++++++++++++++++++++++
>>  net/ipv6/tcpv6_offload.c | 58 ++++++++++++++++++++++++++++++++++
>>  2 files changed, 125 insertions(+)
>> 
>> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
>> index fab0973f995b..affd4ed28cfe 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -28,6 +28,70 @@ 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)
>> +{
>> +	const struct tcphdr *th;
>> +	const struct iphdr *iph;
>> +	struct sk_buff *seg;
>> +	struct tcphdr *th2;
>> +	struct iphdr *iph2;
>> +
>> +	seg = segs;
>> +	th = tcp_hdr(seg);
>> +	iph = ip_hdr(seg);
>> +	th2 = tcp_hdr(seg->next);
>> +	iph2 = ip_hdr(seg->next);
>> +
>> +	if (!(*(const u32 *)&th->source ^ *(const u32 *)&th2->source) &&
>> +	    iph->daddr == iph2->daddr && iph->saddr == iph2->saddr)
>> +		return segs;
>> +
>> +	while ((seg = seg->next)) {
>> +		th2 = tcp_hdr(seg);
>> +		iph2 = ip_hdr(seg);
>> +
>> +		__tcpv4_gso_segment_csum(seg,
>> +					 &iph2->saddr, iph->saddr,
>> +					 &th2->source, th->source);
>> +		__tcpv4_gso_segment_csum(seg,
>> +					 &iph2->daddr, iph->daddr,
>> +					 &th2->dest, th->dest);
>> +	}
>> +
>> +	return segs;
>> +}
> 
> AFAICS, all the above is really alike the UDP side, except for the
> transport header zero csum.
> 
> What about renaming the udp version of this helpers as 'tcpudpv4_...',
> move them in common code, add an explicit argument for
> 'zerocsum_allowed' and reuse such helper for both tcp and udp?
> 
> The same for the ipv6 variant.

Wouldn't that make it more convoluted when taking into account that the 
checksum field offset is different for tcp vs udp?
How would you handle that?

- Felix