Re: [dpdk-dev] [PATCH v3] app/testpmd: fix l4 sw csum over multi segments

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/20/2021 11:12 AM, Xiaoyun Li wrote:
> In csum forwarding mode, software UDP/TCP csum calculation only takes
> the first segment into account while using the whole packet length so
> the calculation will read invalid memory region with multi-segments
> packets and will get wrong value.
> This patch fixes this issue.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Xiaoyun Li <xiaoyun.li@intel.com>
> ---
> v3:
>   * Use rte_raw_cksum() for multi-segs case instead of copying the whole
>   * packet.
> v2:
>   * Use static stack memory instead of dynamic allocating in datapath
> ---
>   app/test-pmd/csumonly.c | 68 ++++++++++++++++++++++++++++++++---------
>   1 file changed, 53 insertions(+), 15 deletions(-)
> 
> diff --git a/app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c
> index 090797318a..f3e60eb3c3 100644
> --- a/app/test-pmd/csumonly.c
> +++ b/app/test-pmd/csumonly.c
> @@ -91,12 +91,41 @@ struct simple_gre_hdr {
>   } __rte_packed;
>   
>   static uint16_t
> -get_udptcp_checksum(void *l3_hdr, void *l4_hdr, uint16_t ethertype)
> +get_udptcp_checksum(void *l3_hdr, struct rte_mbuf *m, uint16_t l4_off,
> +		    uint16_t ethertype)
>   {
> +	uint16_t off = l4_off;
> +	uint32_t cksum = 0;
> +	char *buf;
> +
> +	while (m != NULL) {
> +		buf = rte_pktmbuf_mtod_offset(m, char *, off);
> +		cksum += rte_raw_cksum(buf, m->data_len - off);
> +		off = 0;
> +		m = m->next;
> +	}
>   	if (ethertype == _htons(RTE_ETHER_TYPE_IPV4))
> -		return rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
> +		cksum += rte_ipv4_phdr_cksum(l3_hdr, 0);
>   	else /* assume ethertype == RTE_ETHER_TYPE_IPV6 */
> -		return rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
> +		cksum += rte_ipv6_phdr_cksum(l3_hdr, 0);
> +

Hi Xiaoyun,

I can see 'rte_ipv[46]_udptcp_cksum()' is not taking multi segment mbuf
into account, so this fix is required,
but instead of implementing this logic into testpmd, what do you think
to have APIs to support multi segment mbufs?
This way other applications also benefit from it and we don't need to
maintain ip4/6 checksum related code in testpmd.

btw, how are you testing this?