netdev - Re: netlink NETLINK_ROUTE failure & Can the kernel really handle IPv6 properly

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Date:	Thu, 2 Oct 2014 14:38:30 +0200
From:	Ulf samuelsson <netdev@...gii.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: netlink NETLINK_ROUTE  failure & Can the kernel really handle IPv6 properly

This is the significant code, and it is wrong.

static struct notifier_block my_ipv6_address_notifier =
 {
   my_ipv6_address_notifier_cb,
   NULL,
   0
 };

register_inet6addr_notifier (&my_ipv6_address_notifier );

int
my_ipv6_address_notifier_cb (struct notifier_block *self,
                                unsigned long event, void *val)
{
 struct inet6_ifaddr *ifaddr = (struct inet6_ifaddr *)val;


 /* We are only interested in address add/delete events */
 /* IPv6 address add comes as NETDEV_UP and delete comes as
  * NETDEV_DOWN
  */
 if ((event != NETDEV_UP) && (event != NETDEV_DOWN))
   return ret;

 if (ifaddr == NULL)
   return ret;
 /* Now that we are sure that it is a IPv6 address being added deleted,
  * verify that it is a link local address.
  */
 if (!IPV6_IS_ADDR_LINKLOCAL (&ifaddr->addr))
   {
     return ret;
   }
 ...
 send_message_to_app(LINK_LOCAL_UP, ip);
 ...
 return ret;
}


Application tries to send message to "ip" and fails, because the link-local adress is still
in "tentative state"

Best Regards
Ulf Samuelsson
ulf@...gii.com
+46  (722) 427 437


> 1 okt 2014 kl. 23:30 skrev Hannes Frederic Sowa <hannes@...essinduktion.org>:
> 
> Hello,
> 
>> On Wed, Oct 1, 2014, at 22:28, Ulf Samuelsson wrote:
>> BTW, the problem I am trying to solve is how to connect to an I/F with 
>> an IPv6 link-local address.
>> 
>> An existing kernel module waits for a NETDEV_UP event, and then tries to 
>> communicate
>> with the link-local address.
>> 
>> This will fail, because (according to a colleague) the I/F enters a 
>> "tentative" state,
>> where it is trying to decide if it is unique or not.
>> It will remain in that state for 1-2 seconds, and only afterwards is the 
>> link-local address
>> available for normal use.
>> 
>> The guys writing the module, claim that the kernel is using NETDEV_UP.
>> There is very little code in the kernel using NETLINK_ROUTE, even in 
>> latest stable.
>> It is using NETDEV_UP.
>> 
>> If my colleague is right, the kernel really cannot handle IPv6 
>> link-local addresses properly.
> 
> Sorry, I cannot really follow you, can you send example code or be a bit
> more precise?
> 
> Thanks,
> Hannes
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