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

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Message-Id: <20140811002210.2a697052767e9ec1989cb219@mindspring.com>
Date:	Mon, 11 Aug 2014 00:22:10 -0400
From:	Bill Fink <billfink@...dspring.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Dexuan Cui <decui@...rosoft.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	Richard Weinberger <richard.weinberger@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Shao <huishao@...rosoft.com>,
	"Yue Zhang (OSTC DEV)" <yuezha@...rosoft.com>,
	David Miller <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH] Hyperv: Trigger DHCP renew after host hibernation

On Sun, 10 Aug 2014, Florian Fainelli wrote:

> Le 10/08/2014 20:23, Dexuan Cui a écrit :
> >> -----Original Message-----
> >> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> >>>>>
> >>>>> IMO the most feasible and need-the-least-change solution may be:
> >>>>> the hyperv network VSC driver passes the event
> >>>>> RNDIS_STATUS_NETWORK_CHANGE to the udev daemon?
> >>>>>
> >>>> No, don't do that, again, act like any other network device, drop the
> >>>> link and bring it up when it comes back.
> >>>>
> >>> Hi Greg,
> >>> Do you mean tearing down the net device and re-creating it (by
> >>> register_netdev() and unregister_netdev)?
> >>
> >> No, don't you have link-detect for your network device?  Toggle that, I
> >> thought patches to do this were posted a while ago...
> >>
> >> But if you really want to tear the whole network device down and then
> >> back up again, sure, that would also work.
> > Hi Greg, Stephen,
> >
> > Thanks for the comments!
> >
> > I suppose you meant the below logic:
> > if (refresh) {
> >          rtnl_lock();
> >          netif_carrier_off(net);
> >          netif_carrier_on(net);
> >          rtnl_unlock();
> > }
> >
> > We have discussed this in the previous mails of this thread itself:
> > e.g., http://marc.info/?l=linux-driver-devel&m=140593811715975&w=2
> >
> > Unluckily this logic doesn't work because the user-space daemons
> > like ifplugd, usually don't renew the DHCP immediately as long as they
> > receive a link-down message: they usually wait for some seconds and if
> > they find the link becomes up soon, they won't trigger renew operations.
> > (I guess this behavior can be somewhat reasonable: maybe the daemons
> > try to not trigger DHCP renew on temporary link instability)
> 
> Is that such a big deal? If you know you spend much of your time in 
> ifplugd, why not use something different that triggers a DHCP renewal 
> faster, or fix ifplugd?

In the case of ifplugd, it has parameters -u | --delay-up= which
defaults to 0 seconds, and -d | --delay-down= which defaults to
5 seconds.  Maybe for hyperv you could specify --delay-down=0.
I don't know if other daemons such as systemd have similar options.
It might still be good to have some modest delay between the
netif_carrier_off(net) and netif_carrier_on(net).

						-Bill
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