Re: [dpdk-dev] [PATCH] net: add support for UDP segmentation case

[Olivier Matz <olivier.matz@6wind.com>]

Hi Radu,

On Fri, Sep 03, 2021 at 11:59:42AM +0100, Radu Nicolau wrote:
> [PATCH] net: add support for UDP segmentation case

What about this title instead?

net: exclude IP len from phdr cksum if offloading UDP frag

> Add support to the ipv4/ipv6 pseudo-header function when TSO is enabled
> in the UDP case, eg  PKT_TX_UDP_SEG is set in the mbuf ol_flags

I think it would be clearer to say "UDP fragmentation" instead of
"TSO is enabled in the UDP case".

> Signed-off-by: Declan Doherty <declan.doherty@intel.com>
> Signed-off-by: Radu Nicolau <radu.nicolau@intel.com>
> ---
>  lib/net/rte_ip.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
> index 05948b69b7..c916ec1b09 100644
> --- a/lib/net/rte_ip.h
> +++ b/lib/net/rte_ip.h
> @@ -333,7 +333,7 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
>  	psd_hdr.dst_addr = ipv4_hdr->dst_addr;
>  	psd_hdr.zero = 0;
>  	psd_hdr.proto = ipv4_hdr->next_proto_id;
> -	if (ol_flags & PKT_TX_TCP_SEG) {
> +	if (ol_flags & (PKT_TX_TCP_SEG | PKT_TX_UDP_SEG)) {
>  		psd_hdr.len = 0;
>  	} else {
>  		l3_len = rte_be_to_cpu_16(ipv4_hdr->total_length);

Can you also update the API comment?

> @@ -474,7 +474,7 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>  	} psd_hdr;
>  
>  	psd_hdr.proto = (uint32_t)(ipv6_hdr->proto << 24);
> -	if (ol_flags & PKT_TX_TCP_SEG) {
> +	if (ol_flags & (PKT_TX_TCP_SEG | PKT_TX_UDP_SEG)) {
>  		psd_hdr.len = 0;
>  	} else {
>  		psd_hdr.len = ipv6_hdr->payload_len;
> -- 
> 2.25.1
> 

No objection for this patch, but I think we should consider removing
this ol_flags parameter from the pseudo header checksum calculation
functions in the future, because it is a bit confusing.

Historically, this was done in commit 4199fdea60c3 ("mbuf: generic
support for TCP segmentation offload") because we were expecting that
this pseudo-header checksum (required by Intel hw when doing checksum or
TSO) will be done in the same way for many drivers (i.e. without the IP
length for TSO). I don't know if it is the case.

Or maybe a 'use_0_length' parameter would make more sense than
'ol_flags'.

Thanks,
Olivier