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

[Ferruh Yigit]

On 11/10/2020 2:46 PM, Ferruh Yigit wrote:
> 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 at 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 
> '~' ?

This seems correct, this is related to what cksum functions return and how to 
verify cksum, I will proceed with the patch.