Re: [dpdk-dev] [PATCH v3] net: fix Intel-specific Prepare the outer ipv4 hdr for checksum

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

On Wed, Jul 28, 2021 at 06:46:53PM +0300, Andrew Rybchenko wrote:
> On 7/7/21 12:40 PM, Mohsin Kazmi wrote:
> > Preparation the headers for the hardware offload
> > misses the outer ipv4 checksum offload.
> > It results in bad checksum computed by hardware NIC.
> > 
> > This patch fixes the issue by setting the outer ipv4
> > checksum field to 0.
> > 
> > Fixes: 4fb7e803eb1a ("ethdev: add Tx preparation")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Mohsin Kazmi <mohsin.kazmi14@gmail.com>
> > Acked-by: Qi Zhang <qi.z.zhang@intel.com>
> > ---
> > v3:
> >     * Update the conditional test with PKT_TX_OUTER_IP_CKSUM.
> >     * Update the commit title with "Intel-specific".
> > 
> > v2:
> >     * Update the commit message with Fixes.
> > 
> >   lib/net/rte_net.h | 15 +++++++++++++--
> >   1 file changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/net/rte_net.h b/lib/net/rte_net.h
> > index 434435ffa2..3f4c8c58b9 100644
> > --- a/lib/net/rte_net.h
> > +++ b/lib/net/rte_net.h
> > @@ -125,11 +125,22 @@ rte_net_intel_cksum_flags_prepare(struct rte_mbuf *m, uint64_t ol_flags)
> >   	 * Mainly it is required to avoid fragmented headers check if
> >   	 * no offloads are requested.
> >   	 */
> > -	if (!(ol_flags & (PKT_TX_IP_CKSUM | PKT_TX_L4_MASK | PKT_TX_TCP_SEG)))
> > +	if (!(ol_flags & (PKT_TX_IP_CKSUM | PKT_TX_L4_MASK | PKT_TX_TCP_SEG |
> > +			  PKT_TX_OUTER_IP_CKSUM)))
> >   		return 0;
> > -	if (ol_flags & (PKT_TX_OUTER_IPV4 | PKT_TX_OUTER_IPV6))
> > +	if (ol_flags & (PKT_TX_OUTER_IPV4 | PKT_TX_OUTER_IPV6)) {
> >   		inner_l3_offset += m->outer_l2_len + m->outer_l3_len;
> > +		/*
> > +		 * prepare outer ipv4 header checksum by setting it to 0,
> > +		 * in order to be computed by hardware NICs.
> > +		 */
> > +		if (ol_flags & PKT_TX_OUTER_IP_CKSUM) {
> > +			ipv4_hdr = rte_pktmbuf_mtod_offset(m,
> > +					struct rte_ipv4_hdr *, m->outer_l2_len);
> > +			ipv4_hdr->hdr_checksum = 0;
> 
> Here we assume that the field is located in the first segment.
> Unlikely but it still could be false. We must handle it properly.

This is specified in the API comment, so I think it has to be checked
by the caller.

> > +		}
> > +	}
> >   	/*
> >   	 * Check if headers are fragmented.
> > 
>