Re: [dpdk-dev] [PATCH] net/tap: Allow all-zero checksum for UDP over IPv4

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

On 11/9/2020 2:22 PM, Michael Pfeiffer wrote:
> Unlike TCP, UDP checksums are optional and may be zero to indicate "not
> set" [RFC 768] (except for IPv6, where this prohibited [RFC 8200]). Add
> this special case to the checksum offload emulation in net/tap.
> 
> Signed-off-by: Michael Pfeiffer <michael.pfeiffer@tu-ilmenau.de>
> ---
>   drivers/net/tap/rte_eth_tap.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index 2f8abb12c..e486b41c5 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -303,6 +303,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
>   	uint16_t cksum = 0;
>   	void *l3_hdr;
>   	void *l4_hdr;
> +	struct rte_udp_hdr *udp_hdr;
>   
>   	if (l2 == RTE_PTYPE_L2_ETHER_VLAN)
>   		l2_len += 4;
> @@ -349,10 +350,18 @@ tap_verify_csum(struct rte_mbuf *mbuf)
>   		/* Don't verify checksum for multi-segment packets. */
>   		if (mbuf->nb_segs > 1)
>   			return;
> -		if (l3 == RTE_PTYPE_L3_IPV4)
> +		if (l3 == RTE_PTYPE_L3_IPV4) {
> +			if (l4 == RTE_PTYPE_L4_UDP) {
> +				udp_hdr = (struct rte_udp_hdr *)l4_hdr;
> +				if (udp_hdr->dgram_cksum == 0) {
> +					mbuf->ol_flags |= PKT_RX_L4_CKSUM_NONE;
> +					return;
> +				}
> +			}
>   			cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
> -		else if (l3 == RTE_PTYPE_L3_IPV6)
> +		} else if (l3 == RTE_PTYPE_L3_IPV6) {
>   			cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
> +		}
>   		mbuf->ol_flags |= cksum ?
>   			PKT_RX_L4_CKSUM_BAD :
>   			PKT_RX_L4_CKSUM_GOOD;
> 

While checking this I stuck with following part:

  cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
  ...
   mbuf->ol_flags |= cksum ?
   	PKT_RX_L4_CKSUM_BAD :
  	PKT_RX_L4_CKSUM_GOOD;


Is this correct, or am I missing something, can intention be '!' here instead of 
'~' ?