linux-kernel - [17/18] arp_notify: unconditionally send gratuitous ARP for NETDEV_NOTIFY

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Date:	Fri, 04 Mar 2011 17:03:11 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Ian Campbell <ian.campbell@...rix.com>,
	"David S. Miller" <davem@...emloft.net>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Mike Surcouf <mike@...couf.co.uk>,
	Hank Janssen <hjanssen@...rosoft.com>
Subject: [17/18] arp_notify: unconditionally send gratuitous ARP for NETDEV_NOTIFY_PEERS.

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Ian Campbell <Ian.Campbell@...rix.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@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[reported to solve hyperv live migration problem - gkh]
Cc: Haiyang Zhang <haiyangz@...rosoft.com>
Cc: Mike Surcouf <mike@...couf.co.uk>
Cc: Hank Janssen <hjanssen@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1025,6 +1025,21 @@ static inline bool inetdev_valid_mtu(uns
 	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,
@@ -1076,18 +1091,13 @@ static int inetdev_event(struct notifier
 		}
 		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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