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

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Message-ID: <4E2ADB39.9070409@gmail.com>
Date:	Sat, 23 Jul 2011 16:31:21 +0200
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	David Miller <davem@...emloft.net>, jbohac@...e.cz,
	netdev@...r.kernel.org, shemminger@...tta.com
Subject: Re: IPv6: autoconfiguration and suspend/resume or link down/up

Le 22/07/2011 11:21, Herbert Xu a écrit :
> On Fri, Jul 22, 2011 at 01:06:28AM -0700, David Miller wrote:
>>
>> Suspend is even more important because while we were suspended we
>> could be on the same network but the routers present and available
>> might have changed completely.
>
> Unfortunately virtual machine live migration also uses the suspend
> &  resume mechanism.  In that case we don't wish to renegotiate
> everything, since the goal is to minimise the outage window.
>
> This would suggest that putting the policy in user-space may be the
> best option.

For the particular situation where we use suspend/resume to migrate a virtual machine, we might have 
a kernel parameter or sysfs entry that instruct the kernel not to renegotiate anything on resume.

That being said, the time to renegotiate a network setup sounds very short, compared to the time for 
a full suspend-migrate-resume cycle. I'm not sure VM migration would really suffer from such 
renegotiation.

And because the local network may change while we migrate the VM (in particular if the migration 
happens because of some failover), I think we should enforce renegotiation on resume anyway.

	Nicolas.
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