[radvd-devel-l] how is the length field calcuted for the radvd options

[Magesh mannar]

Hi
   
  I am going through the radvd src code. In send.c program, i find the send_ra() fn which creates the various options and sends the ra using sendmsg.
  I suppose the msgs are created in the TLV format. I am wondering how the length filed is calculated. For example, while creating the prefix info option, the length field is set to 4 (pinfo->nd_opt_pi_len = 4;). Can you please let me know how the length field is calculated and how it is 4 for the prefix option
   
  while(prefix)
  {
  dlog(LOG_DEBUG, 3, "Adding prefix on %p", prefix);
  if( prefix->enabled )
  {
  struct nd_opt_prefix_info *pinfo;
  
  pinfo = (struct nd_opt_prefix_info *) (buff + len);
  pinfo->nd_opt_pi_type = ND_OPT_PREFIX_INFORMATION;
  pinfo->nd_opt_pi_len = 4;
  pinfo->nd_opt_pi_prefix_len = prefix->PrefixLen;
  
  pinfo->nd_opt_pi_flags_reserved = 
  (prefix->AdvOnLinkFlag)?ND_OPT_PI_FLAG_ONLINK:0;
  pinfo->nd_opt_pi_flags_reserved |=
  (prefix->AdvAutonomousFlag)?ND_OPT_PI_FLAG_AUTO:0;
  /* Mobile IPv6 ext */
  pinfo->nd_opt_pi_flags_reserved |=
  (prefix->AdvRouterAddr)?ND_OPT_PI_FLAG_RADDR:0;
  pinfo->nd_opt_pi_valid_time = htonl(prefix->AdvValidLifetime);
  pinfo->nd_opt_pi_preferred_time = htonl(prefix->AdvPreferredLifetime);
  pinfo->nd_opt_pi_reserved2 = 0;
  
  memcpy(&pinfo->nd_opt_pi_prefix, &prefix->Prefix,
  sizeof(struct in6_addr));
  len += sizeof(*pinfo);
  }
   
   
  Sorry for troubling with a trivial doubt.
   
  Many thanks
   
  Magesh

		
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