netdev - Re: [PATCH] Hyperv: Trigger DHCP renew after host hibernation

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Message-ID: <53CCB944.8090709@nod.at>
Date:	Mon, 21 Jul 2014 08:55:00 +0200
From:	Richard Weinberger <richard@....at>
To:	"Yue Zhang (OSTC DEV)" <yuezha@...rosoft.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	KY Srinivasan <kys@...rosoft.com>,
	Thomas Shao <huishao@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH] Hyperv: Trigger DHCP renew after host hibernation

Yie,

Am 21.07.2014 04:44, schrieb Yue Zhang (OSTC DEV):
>> From: Richard Weinberger [mailto:richard.weinberger@...il.com]
>> Why 10? Is this a random number which works by accident for ifplugd?
>> What about other networking implementations, is 10 also ok for them?
>> --
>> Thanks,
>> //richard
> 
> Hi, Richard
> 
> I checked ifplugd's code. The deferring time is 5 seconds. That's how  comes 
> the "10s". I agree with you this is a magic number and should be avoid. However, 
> this is the only feasible solution right now. If there is a better solution, I will be 
> glad to switch to it.
> 
> I tested the fix in Redhat, Ubuntu and SUSE and it works in all of them.

The problem I see is that there is no good way to trigger a DHCP renew from
a network device drivers. You're on the wrong layer.
10 seconds may work but this is IMHO a hack which can easily break.
There are also more networking implementations than ifplugd.
Specially the systemd implementation looks promising.

Can't you propagate the RNDIS_STATUS_NETWORK_CHANGE event to userspace?
IIRC on HyperV guests already have a guest daemon. Let the daemon handle
the event such that distros can install their own hooks...

Thanks,
//richard
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