Re: [dpdk-dev] [PATCH] examples/ipsec-secgw: update incremental checksum

["Nicolau, Radu" <radu.nicolau@intel.com>]

> -----Original Message-----
> From: Akhil Goyal [mailto:akhil.goyal@nxp.com]
> Sent: Monday, January 15, 2018 12:48 PM
> To: dev@dpdk.org
> Cc: De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>;
> hemant.agrawal@nxp.com; Nicolau, Radu <radu.nicolau@intel.com>
> Subject: Re: [PATCH] examples/ipsec-secgw: update incremental checksum
> 
> On 1/15/2018 6:12 PM, Akhil Goyal wrote:
> > When TTL is decremented or ecn is updated in IP header before
> > forwarding the packet, checksum needs to be updated.
> >
> > In this patch an incremental checksum is added for ipv4 case.
> >
> > Signed-off-by: Akhil Goyal <akhil.goyal@nxp.com>
> > ---
> This patch is an update to a very old patch which was rejected earlier.
> http://dpdk.org/dev/patchwork/patch/16113/
> 
> >   examples/ipsec-secgw/ipip.h | 19 ++++++++++++++++++-
> >   1 file changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/examples/ipsec-secgw/ipip.h b/examples/ipsec-secgw/ipip.h
> > index fb6a6fa..13b8455 100644
> > --- a/examples/ipsec-secgw/ipip.h
> > +++ b/examples/ipsec-secgw/ipip.h
> > @@ -27,6 +27,10 @@ ipip_outbound(struct rte_mbuf *m, uint32_t offset,
> uint32_t is_ipv6,
> >   	if (inip4->ip_v == IPVERSION) {
> >   		/* XXX This should be done by the forwarding engine instead
> */
> >   		inip4->ip_ttl -= 1;
> > +		if (inip4->ip_sum >= rte_cpu_to_be_16(0xffff - 0x100))
> > +			inip4->ip_sum += rte_cpu_to_be_16(0x100) + 1;
> > +		else
> > +			inip4->ip_sum += rte_cpu_to_be_16(0x100);
> >   		ds_ecn = inip4->ip_tos;
> >   	} else {
> >   		inip6 = (struct ip6_hdr *)inip4;
> > @@ -95,8 +99,17 @@ ip6ip_outbound(struct rte_mbuf *m, uint32_t offset,
> >   static inline void
> >   ip4_ecn_setup(struct ip *ip4)
> >   {
> > -	if (ip4->ip_tos & IPTOS_ECN_MASK)
> > +	if (ip4->ip_tos & IPTOS_ECN_MASK) {
> > +		unsigned long sum;
> > +		uint8_t old;
> > +
> > +		old = ip4->ip_tos;
> >   		ip4->ip_tos |= IPTOS_ECN_CE;
> > +		sum = old + (~(*(uint8_t *)&ip4->ip_tos) & 0xff);
> > +		sum += rte_be_to_cpu_16(ip4->ip_sum);
> > +		sum = (sum & 0xffff) + (sum >> 16);
> > +		ip4->ip_sum = rte_cpu_to_be_16(sum + (sum >> 16));
> > +	}
> >   }
> >
> >   static inline void
> > @@ -140,6 +153,10 @@ ipip_inbound(struct rte_mbuf *m, uint32_t offset)
> >   			ip4_ecn_setup(inip4);
> >   		/* XXX This should be done by the forwarding engine instead
> */
> >   		inip4->ip_ttl -= 1;
> > +		if (inip4->ip_sum >= rte_cpu_to_be_16(0xffff - 0x100))
> > +			inip4->ip_sum += rte_cpu_to_be_16(0x100) + 1;
> > +		else
> > +			inip4->ip_sum += rte_cpu_to_be_16(0x100);
> >   		m->packet_type &= ~RTE_PTYPE_L4_MASK;
> >   		if (inip4->ip_p == IPPROTO_UDP)
> >   			m->packet_type |= RTE_PTYPE_L4_UDP;
> >

I think instead of manipulating the checksum in this way it will be better to use rte_ipv4_cksum to re-compute it, unless the performance penalty is too significant.