Re: ifconfig not waiting for DAD completion

[Roy Marples <roy%marples.name@localhost>]

Hi

On 27/11/2015 00:29, Anthony Mallet wrote:
> When my wm(4) interface goes from down to up, it first enters a 'detached'
> state for 1s or so, then the carrier is detected and the interface goes to the
> ipv6 'tentative' state.

I believe this behaviour is true for all interfaces, it's not specific
to wm(4).

The best way of fixing this is to reduce this window to zero because
it's a small lie - kernel is telling userland the link is down when it's
really up.
I don't know how to start doing that though .... I suspect each driver
would need to be touched somewhere.

> The detached state is long enough for ifconfig -w in /etc/rc.d/network to not
> wait at all for DAD (the interface is still 'detached' when ifconfig -w runs).
> 
> This then leads to unexpected delays (~30s) in e.g. /etc/rc.d/mountall with an
> NFS filesystem. (The machine is in ip6mode=host).
> 
> I tried the following quick patch to ifconfig(8) so that ifconfig -w waits for
> DAD completion only once DAD has started. Does this look like the proper fix?
> 
> Index: sbin/ifconfig/af_inet6.c
> ===================================================================
> RCS file: /cvsroot/src/sbin/ifconfig/af_inet6.c,v
> retrieving revision 1.33
> diff -u -r1.33 af_inet6.c
> --- sbin/ifconfig/af_inet6.c  12 May 2015 14:05:29 -0000      1.33
> +++ sbin/ifconfig/af_inet6.c  27 Nov 2015 00:05:46 -0000
> @@ -489,7 +489,7 @@
>         ifr.ifr_addr = *(struct sockaddr_in6 *)ifa->ifa_addr;
>         if (prog_ioctl(s, SIOCGIFAFLAG_IN6, &ifr) == -1)
>                 err(EXIT_FAILURE, "SIOCGIFAFLAG_IN6");
> -       return ifr.ifr_ifru.ifru_flags6 & IN6_IFF_TENTATIVE ? true : false;
> +       return ifr.ifr_ifru.ifru_flags6 & (IN6_IFF_TENTATIVE|IN6_IFF_DETACHED) ? true : false;
>  }
>  
>  static void

Any fix like this would also be needed in af_inet.c as IPv4 has similar
flags.
But if we do this then I think that ifconfig.c:wait_dad_exec() needs to
test the interface flags for IFF_UP as well.

Not that it helps because when you add an address, the interface is
brought up right away.

I avoided detached originally because I didn't want to wait for a
configured interface without an attached cable because that would just
timeout needlessly. But is that actually desireable behaviour?
This also affects wireless interfaces, so it's not entirely optimal either.

Roy