Re: gateway field missing in netlink message

["Magesh M P" <magesh@digitizethings.com>]

Hi Dave,

Thanks for responding.

The librtnl/netns.c contains the parser code as below which parses the MULTIPATH attribute. Could you please take a look at the code and see if anything is wrong ?
static int
rtnl_parse_rtattr(struct rtattr *db[], size_t max,
                  struct rtattr *rta, size_t len) {
int attrlen;
  for(; RTA_OK(rta, len); rta = RTA_NEXT(rta, len)) {
    if (rta->rta_type <= max){
                clib_warning("rattr type [%d] ",rta->rta_type);
         if (rta->rta_type == RTA_TABLE) {
           unsigned int rtable=*(unsigned int*)RTA_DATA(rta);
            clib_warning("RTA_RTABLE type rtable %x\n",rtable);
           }
         if (rta->rta_type == RTA_OIF) {
           unsigned int oif=*(unsigned int*)RTA_DATA(rta);
            clib_warning("RTA_OIF type oif %x\n",oif);
           }
         if (rta->rta_type == RTA_GATEWAY) {
           unsigned int gw=*(unsigned int*)RTA_DATA(rta);
            clib_warning("RTA_GATEWAY type gateway %x\n",gw);
           }
         if (rta->rta_type == RTA_DST) {
           unsigned int destip=*(unsigned int*)RTA_DATA(rta);
            clib_warning("RTA_DST type destip %x\n",destip);
           }
         if (rta->rta_type == RTA_MULTIPATH){
          struct rtnexthop *nhptr = (struct rtnexthop*)RTA_DATA(rta);
          int rtnhp_len = RTA_PAYLOAD(rta);
                 clib_warning("RTA_MULTIPATH type\n");
           if (rtnhp_len < (int) sizeof (*nhptr) ||
              nhptr->rtnh_len > rtnhp_len){
                continue;
               }
          attrlen = rtnhp_len - sizeof(struct rtnexthop);
           if (attrlen) {
              struct rtattr *attr = RTNH_DATA(nhptr);
                for(; RTA_OK(attr,attrlen);attr=RTA_NEXT(attr, attrlen)){
                 clib_warning("attr->rta_type %d\n",attr->rta_type);
                 if (attr->rta_type == RTA_GATEWAY) {
                 unsigned int nh= *(unsigned int*) RTA_DATA(attr);
                 clib_warning("gateway %x\n",nh);
                  }
                }
             }
          }
      db[rta->rta_type] = rta;
        }
#ifdef RTNL_CHECK
    else
      clib_warning("RTA type too high: %d", rta->rta_type);
#endif
  }

  if(len) {
    clib_warning("rattr lenght mistmatch %d %d len",
                 (int) len, (int) rta->rta_len);
    return -1;
  }
  return 0;
}



From: David Ahern <dsahern@kernel.org>
Sent: Thursday, May 5, 2022 4:01 AM
To: Magesh M P <magesh@digitizethings.com>
Cc: netdev@vger.kernel.org <netdev@vger.kernel.org>
Subject: Re: gateway field missing in netlink message 
 
On Wed, May 04, 2022 at 06:46:05AM +0000, Magesh  M P wrote:
> Hi
> 
> I am trying to configure dual gateways with ip route command.
> 
> Ip route show command shows the dual gateway information.
> 
> I got a vpp stack that is running. The communication of route entries between Linux kernel and vpp stack is through netlink messages.
> 
> On parsing the netlink message for the route entry with dual gateways, we see that the message carries only single gateway. Is this a known bug ? Please suggest a solution to resolve this.
> 

If `ip route show` lists a multipath route, the bug is in your app. Are
you handling RTA_MULTIPATH attribute?