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

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

On Tue, Jun 08, 2021 at 04:57:00PM +0300, Andrew Rybchenko wrote:
> On 6/8/21 3:49 PM, Olivier Matz wrote:
> > On Tue, Jun 08, 2021 at 03:34:36PM +0300, Andrew Rybchenko wrote:
> >> 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.
> > 
> > This function is called on the Rx path from pmd_rx_burst(), so
> > the application does not have access to the mbuf.
> > 
> > The software parser that sets the packet type returns either
> > RTE_PTYPE_L3_IPV4 if there is no option, or RTE_PTYPE_L3_IPV4_EXT
> > else. The value RTE_PTYPE_L3_IPV4_EXT_UNKNOWN is used by PMDs that don't
> > know if there are options.
> 
> I see. What I'm trying to say that there are non
> obvious assumptions here on rte_net_get_ptype()
> behaviour which can be changed. May be it makes
> sense to add comments here to highlight it.

Ok, I'll add some words about it.

Thanks!

> 
> > 
> >>> - 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 ?
> >>>>>>
> >>>>
> >>
>