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

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Message-ID: <4E2BD96E.4090101@gmail.com>
Date:	Sun, 24 Jul 2011 10:35:58 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>, jbohac@...e.cz,
	netdev@...r.kernel.org
Subject: Re: IPv6: autoconfiguration and suspend/resume or link down/up

Le 24/07/2011 02:18, Herbert Xu a écrit :
> On Sat, Jul 23, 2011 at 09:37:43AM -0700, Stephen Hemminger wrote:
>>
>> Would it be possible to do live migration without dropping carrier
>> or setting interface down?
>
> I think LM uses the same mechanism as suspend and resume so whatever
> happens in one case will happen in the other case as well.

So we need to distinguish between two kind of link events:

1/ Really having the link goes down then up. This should trigger a renegotiation.

2/ Having the system suspend then resume :
2a/ This should trigger link down/link up events to force a renegotiation, for normal suspend/resume 
where the network might have changed between suspend and resume.
2/ This should *not* trigger link down/link up events to avoid a renegotiation (for live migration) 
because it is assumed that the network didn't change while suspended.

Can't we allow the user to set a global "link-down-link-up-timeout" and only force a renegotiation 
if the time between link down and link up events is longer than this timeout? Normal user would set 
this timeout close to 0 (default value). Live migration user would set this timeout to about twice 
the time it normally takes to do a live migration. That way, in a VM environment, if the 
suspend/resume cycle happens to take far more than a normal live migration time, the kernel would 
renegotiate, which sounds reasonable, from my point of view.

Does this make sense?

	Nicolas.
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