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Date:	Mon, 21 Jul 2014 02:44:35 +0000
From:	"Yue Zhang (OSTC DEV)" <yuezha@...rosoft.com>
To:	Richard Weinberger <richard.weinberger@...il.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

> From: Richard Weinberger [mailto:richard.weinberger@...il.com]
> Sent: Friday, July 18, 2014 9:41 PM
> 
> On Fri, Jul 18, 2014 at 12:55 PM, Yue Zhang <yuezha@...rosoft.com> wrote:
> > From: Yue Zhang <yuezha@...rosoft.com>
> >
> > This patch addresses the comment from Olaf Hering and Greg KH
> > for a previous commit 3a494e710367 ("hyperv: Add handler for
> > RNDIS_STATUS_NETWORK_CHANGE event")
> >
> > In previous solution, the driver calls "network restart" to
> > force a DHCP renew when the host is back from hibernation.
> >
> > In this fix, the driver will keep network carrier offline for
> > 10 seconds and then bring it back. So that ifplugd daemon will
> > notice this change and refresh DHCP lease.
> >
> > Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> > Cc: K. Y. Srinivasan <kys@...rosoft.com>
> >
> > Signed-off-by: Yue Zhang <yuezha@...rosoft.com>
> > ---
> >  drivers/net/hyperv/netvsc_drv.c | 21 +++++++++++++++++----
> >  1 file changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> > index a9c5eaa..559c97d 100644
> > --- a/drivers/net/hyperv/netvsc_drv.c
> > +++ b/drivers/net/hyperv/netvsc_drv.c
> > @@ -33,6 +33,7 @@
> >  #include <linux/if_vlan.h>
> >  #include <linux/in.h>
> >  #include <linux/slab.h>
> > +#include <linux/delay.h>
> >  #include <net/arp.h>
> >  #include <net/route.h>
> >  #include <net/sock.h>
> > @@ -792,8 +793,7 @@ static void netvsc_link_change(struct work_struct
> *w)
> >         struct netvsc_device *net_device;
> >         struct rndis_device *rdev;
> >         bool notify, refresh = false;
> > -       char *argv[] = { "/etc/init.d/network", "restart", NULL };
> > -       char *envp[] = { "HOME=/", "PATH=/sbin:/usr/sbin:/bin:/usr/bin",
> NULL };
> > +       int delay;
> >
> >         rtnl_lock();
> >
> > @@ -816,8 +816,21 @@ static void netvsc_link_change(struct work_struct
> *w)
> >
> >         rtnl_unlock();
> >
> > -       if (refresh)
> > -               call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
> > +       if (refresh) {
> > +               /*
> > +                * Keep the carrier offline for 10 seconds
> > +                * to notify ifplugd daemon network change
> > +                */
> 
> 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.

Thanks
Yie

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