[ovs-dev] [PATCH] ovn: remove the dead code.

[Numan Siddique]

On Sun, Jul 24, 2016 at 6:26 AM, Ryan Moats <rmoats at us.ibm.com> wrote:

> "dev" <dev-bounces at openvswitch.org> wrote on 07/21/2016 05:36:13 AM:
>
> > From: nickcooper-zhangtonghao <nickcooper-zhangtonghao at opencloud.tech>
> > To: dev at openvswitch.org
> > Cc: nickcooper-zhangtonghao <nickcooper-zhangtonghao at opencloud.tech>
> > Date: 07/21/2016 05:36 AM
> > Subject: [ovs-dev] [PATCH] ovn: remove the dead code.
> > Sent by: "dev" <dev-bounces at openvswitch.org>
> >
> > It is not necessary to assign 0 to ip_csum.
> >
> > Signed-off-by: nickcooper-zhangtonghao <nickcooper-
> > zhangtonghao at opencloud.tech>
> > ---
> >  ovn/controller/pinctrl.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/ovn/controller/pinctrl.c b/ovn/controller/pinctrl.c
> > index 7893872..b35576a 100644
> > --- a/ovn/controller/pinctrl.c
> > +++ b/ovn/controller/pinctrl.c
> > @@ -349,7 +349,6 @@ pinctrl_handle_put_dhcp_opts(
> >      struct ip_header *out_ip = dp_packet_l3(&pkt_out);
> >      out_ip->ip_tot_len = htons(pkt_out.l4_ofs - pkt_out.l3_ofs +
> > new_l4_size);
> >      udp->udp_csum = 0;
> > -    out_ip->ip_csum = 0;
>

​This is not a dead code. It is required. The reason it is required is
because the DHCPv4 response packet is constructed by copying the DHCPv4
request packet and then adding the dhcp options. So the ip_csum needs to be
set to 0 before calling "csum", otherwise, csum() will calculate wrong
checksum. because of which the VM will reject the DHCPv4 response packet.

​You can verify yourself by applying the ovn-northd DHCP patch [1].

​[1] - https://patchwork.ozlabs.org/patch/651958/

​

>      out_ip->ip_csum = csum(out_ip, sizeof *out_ip);
> >
> >      pin->packet = dp_packet_data(&pkt_out);
>
> lgtm...
>
> Acked-by: Ryan Moats <rmoats at us.ibm.com>
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