Re: [dpdk-dev] [dpdk-stable] [PATCH 1/4] net/tap: fix Rx cksum flags on IP options packets

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 6/8/21 3:29 PM, Olivier Matz wrote:
> Hi Ferruh, Andrew,
> 
> On Tue, Jun 08, 2021 at 01:13:59PM +0300, Andrew Rybchenko wrote:
>> On 4/30/21 5:48 PM, Ferruh Yigit wrote:
>>> On 4/27/2021 2:57 PM, Olivier Matz wrote:
>>>> When packet type is IPV4_EXT, the checksum is always marked as good in
>>>> the mbuf offload flags.
>>>>
>>>> Since we know the header lengths, we can easily call
>>>> rte_ipv4_udptcp_cksum() in this case too.
>>>>
>>>> Fixes: 8ae3023387e9 ("net/tap: add Rx/Tx checksum offload support")
>>>> Cc: stable@dpdk.org
>>>>
>>>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>>>> ---
>>>>  drivers/net/tap/rte_eth_tap.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
>>>> index 68baa18523..e7b185a4b5 100644
>>>> --- a/drivers/net/tap/rte_eth_tap.c
>>>> +++ b/drivers/net/tap/rte_eth_tap.c
>>>> @@ -350,7 +350,7 @@ 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 || l3 == RTE_PTYPE_L3_IPV4_EXT) {
>>>
>>> Should we take 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN' into account?
>>
>> I think we should.
> 
> I think 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN' cannot happen here:
> 
> - mbuf->packet_type is generated by 

(), which cannot
>   return 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN'

My question if it is guaranteed and the only possible branch.
Can application set packet_type itself and do not call
rte_net_get_ptype(). Yes, typically application knows
if it has IPv4 options in the header or not, but theoretically
could be unaware as well.

> - right above this code, we already returned if l3 is not in
>   (RTE_PTYPE_L3_IPV4, RTE_PTYPE_L3_IPV4_EXT, RTE_PTYPE_L3_IPV6)

If so, it sounds like it should be allowed above as well.

> 
>>>
>>>>  			if (l4 == RTE_PTYPE_L4_UDP) {
>>>>  				udp_hdr = (struct rte_udp_hdr *)l4_hdr;
>>>>  				if (udp_hdr->dgram_cksum == 0) {
>>>> @@ -364,7 +364,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
>>>>  				}
>>>>  			}
>>>>  			cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
>>>> -		} else if (l3 == RTE_PTYPE_L3_IPV6) {
>>>> +		} else { /* l3 == RTE_PTYPE_L3_IPV6, checked above */
>>>>  			cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
>>>>  		}
>>>>  		mbuf->ol_flags |= cksum ?
>>>>
>>