Re: IPv6: autoconfiguration and suspend/resume or link down/up

From: Dan Williams <dcbw@redhat.com>
To: Jiri Bohac <jbohac@suse.cz>
Cc: netdev@vger.kernel.org, Herbert Xu <herbert@gondor.hengli.com.au>,
	"David S. Miller" <davem@davemloft.net>,
	stephen hemminger <shemminger@vyatta.com>
Subject: Re: IPv6: autoconfiguration and suspend/resume or link down/up
Date: Thu, 21 Jul 2011 00:30:53 -0500	[thread overview]
Message-ID: <1311226254.3140.52.camel@dcbw.foobar.com> (raw)
In-Reply-To: <20110720163656.GD11692@midget.suse.cz>

On Wed, 2011-07-20 at 18:36 +0200, Jiri Bohac wrote:
> On Wed, Jul 20, 2011 at 11:21:43AM -0500, Dan Williams wrote:
> > ... and in the resume handler use that value to age anything
> > that needs to know about time spent in suspend, and then do what needs
> > to be done with that.  So something like that may work for IPv6
> > addrconf; on suspend save current time, and on resume check the current
> > time, subtract the time you saved on suspend, and magically add that to
> > the lifetime counts and then run any expiry stuff.
> 
> IPv6 (by specification) does not send any RS when an IP address
> or route expires. So only subtracting the supend time from the
> lifetimes and possibly expiring the routes/IP addresses won't fix
> the problem.

Well, the prefix option of the RA includes the Valid Lifetime (in
seconds, no less) so I'd assume the kernel starts a timer when it
receives the RA and updates any addresses configured as a result of
receiving that RA+prefix, such that when the timer expires, the
autoconfigured address is deleted.  That timer can be used as a base for
the expiry mechanism that I've noted above, no?  This fixes problem #1
from your first mail.

For problem #2, shouldn't a new RS be sent whenever the interface
changes it's IFF_LOWER_UP bit?  IFF_LOWER_UP indicates a carrier on/off
event and thus indicates possible disconnect/reconnect to a new network.
I don't specifically know how it works now, but if RS isn't triggered
from IFF_LOWER_UP, I'd imagine that either (a) something didn't get
updated when IFF_LOWER_UP became how carrier was indicated in 2.6.17
(commit b00055aacdb172c05067612278ba27265fcd05ce) or (b) there's a
reason IFF_LOWER_UP isn't used as the trigger for sending an RS and I'm
qualified to say why.

Dan

> When I move to a new network, I need to restart the
> autoconfiguration. This does not currently happen - neither for
> an alive system where the ethernet link goes down/up, nor for a
> system that gets suspended, moved and then resumed.
> 