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Subject[PATCH] [171/275] arp_notify: unconditionally send gratuitous ARP for NETDEV_NOTIFY_PEERS.
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Ian Campbell <Ian.Campbell@citrix.com>

commit d11327ad6695db8117c78d70611e71102ceec2ac upstream.

NETDEV_NOTIFY_PEER is an explicit request by the driver to send a link
notification while NETDEV_UP/NETDEV_CHANGEADDR generate link
notifications as a sort of side effect.

In the later cases the sysctl option is present because link
notification events can have undesired effects e.g. if the link is
flapping. I don't think this applies in the case of an explicit
request from a driver.

This patch makes NETDEV_NOTIFY_PEER unconditional, if preferred we
could add a new sysctl for this case which defaults to on.

This change causes Xen post-migration ARP notifications (which cause
switches to relearn their MAC tables etc) to be sent by default.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
[reported to solve hyperv live migration problem - gkh]
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Mike Surcouf <mike@surcouf.co.uk>
Cc: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/ipv4/devinet.c | 30 ++++++++++++++++++++----------
1 file changed, 20 insertions(+), 10 deletions(-)

Index: linux-2.6.35.y/net/ipv4/devinet.c
===================================================================
--- linux-2.6.35.y.orig/net/ipv4/devinet.c 2011-03-29 22:50:55.819830128 -0700
+++ linux-2.6.35.y/net/ipv4/devinet.c 2011-03-29 23:03:01.802254055 -0700
@@ -1029,6 +1029,21 @@
return mtu >= 68;
}

+static void inetdev_send_gratuitous_arp(struct net_device *dev,
+ struct in_device *in_dev)
+
+{
+ struct in_ifaddr *ifa = in_dev->ifa_list;
+
+ if (!ifa)
+ return;
+
+ arp_send(ARPOP_REQUEST, ETH_P_ARP,
+ ifa->ifa_address, dev,
+ ifa->ifa_address, NULL,
+ dev->dev_addr, NULL);
+}
+
/* Called only under RTNL semaphore */

static int inetdev_event(struct notifier_block *this, unsigned long event,
@@ -1081,18 +1096,13 @@
}
ip_mc_up(in_dev);
/* fall through */
- case NETDEV_NOTIFY_PEERS:
case NETDEV_CHANGEADDR:
+ if (!IN_DEV_ARP_NOTIFY(in_dev))
+ break;
+ /* fall through */
+ case NETDEV_NOTIFY_PEERS:
/* Send gratuitous ARP to notify of link change */
- if (IN_DEV_ARP_NOTIFY(in_dev)) {
- struct in_ifaddr *ifa = in_dev->ifa_list;
-
- if (ifa)
- arp_send(ARPOP_REQUEST, ETH_P_ARP,
- ifa->ifa_address, dev,
- ifa->ifa_address, NULL,
- dev->dev_addr, NULL);
- }
+ inetdev_send_gratuitous_arp(dev, in_dev);
break;
case NETDEV_DOWN:
ip_mc_down(in_dev);

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