Re: [net-next] ipv6: Enable netlink notification for tentative addresses.

[Brian Haley <brian.haley@hp.com>]

On 08/26/2010 02:50 PM, Ben Greear wrote:
> On 08/25/2010 09:24 PM, David Miller wrote:
>> From: Ben Greear<greearb@candelatech.com>
>> Date: Wed, 25 Aug 2010 11:26:17 -0700
>>
>>> By default, netlink messages are not sent when an IPv6 address
>>> is added if it is in tentative state.  This makes it harder
>>> for user-space applications to know the current state of the
>>> IPv6 addresses.  This patch adds an ipv6 sysctl that will
>>> allow tentative address notifications to be sent.  The sysctl
>>> is off by default.
>>>
>>> Signed-off-by: Ben Greear<greearb@candelatech.com>
>>
>> It's inconsistent to send two NEWADDR events for the same add.
>>
>> I would advise that we unconditionally do the NEWADDR once,
>> when the tentative state address is added, and completely
>> elide the one we current send when it leaves tentative state.

But then we get a message for an address that can't be used because
it hasn't passed DAD, I'm not so sure that is a good thing,
especially if we don't get notified when it passes DAD.

> @@ -697,9 +698,10 @@ ipv6_add_addr(struct inet6_dev *idev, const struct
> in6_addr *addr, int pfxlen,
>  out2:
>         rcu_read_unlock_bh();
> 
> -       if (likely(err == 0))
> +       if (likely(err == 0)) {
>                 atomic_notifier_call_chain(&inet6addr_chain, NETDEV_UP,
> ifa);
> -       else {
> +               inet6_ifa_notify(RTM_NEWADDR, ifa);
> +       } else {
>                 kfree(ifa);
>                 ifa = ERR_PTR(err);
>         }

This will generate two messages in some cases, for example, when lo is
configured, or a SIT tunnel is added, see add_addr() in addrconf.c.

-Brian