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

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Date:	Mon, 21 Jul 2014 12:17:36 -0500
From:	Dan Williams <dcbw@...hat.com>
To:	Lennart Poettering <mzxreary@...inter.de>
Cc:	"Yue Zhang (OSTC DEV)" <yuezha@...rosoft.com>,
	Tom Gundersen <teg@...m.no>, netdev <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 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

On Mon, 2014-07-21 at 15:11 +0200, Lennart Poettering wrote:
> On Mon, 21.07.14 10:21, Yue Zhang (OSTC DEV) (yuezha@...rosoft.com) wrote:
> 
> > Some network monitoring daemon, like ifplugd has a deferring mechanism.
> > When it detects carriers is offline, it doesn't trigger DHCP renew immediately. 
> > Instead it will wait for another 5 seconds to check whether carrier is back to 
> > online status. In that case, it will avoid renew DHCP lease.
> 
> ifplugd doesn't renew DHCP leases anyway, one of the scripts it invokes
> does.
> 
> ifplugd is obsolete software. I wrote it more than 10 years ago, and
> haven't really updated it since. it's sounds seriously wrong to add
> multi-second waits to the kernel just to make this crappy, obsolete
> software work.
> 
> Please fix this properly, and work with the PM guys, so that we get a
> sane userspace how the kernel can notify userspace about
> suspends/hibernations triggered from the outside, so that userspace
> daemons can subscribe to that and then refresh the DHCP leases on their
> own.

Yeah, like I've said before, there have been other cases where a "hey,
my L3 address might be wrong now, so please confirm it" message would be
useful.  Carrier on/off doesn't necessarily mean that, but even if it
did, the off interval is a really bad mechanism for that too.  So I'd
really like some kind of event for this that's distinct from carrier
that userspace could use.

Dan

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