[V2] xen-netback notify DomU to send ARP.

[jianhai luan <jianhai.luan@oracle.com>]

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By Jan and Ian's advice, I have modified the former patch and test some 
platform, the below is test result:
   Linux       Pass (Send  gratuitous ARP )
   Window   Pass (don't send ARP, but no other issue occur)
   Solaris     Pass (don't send ARP, but no other issue occur)
    NetBsd    Pass (don't send ARP, but no other issue occur)

Thanks,
Jason

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>From c70af311cc22a1bb04004b03bd5973573360b942 Mon Sep 17 00:00:00 2001
From: Jason Luan <jianhai.luan@oracle.com>
Date: Fri, 28 Dec 2012 15:43:06 +0800
Subject: [PATCH] xen-netback notify frontend to send gratuitous ARP.

In the real network environment, some cause will lead
to Active-Backup mode bonding chose new actived port.
After that, the trffic, destinated to DomU by inactived
port (former actived port), will be unreachable at now.
DomU should send gratutious ARP initialtivly to find the
new corrected path.

By netback's Connected->Connected transition, frontend
will watch the change, and send gratuitous ARP.

Signed-off-by: Jason Luan <jianhai.luan@oracle.com>
---
 drivers/net/xen-netback/xenbus.c |   51 ++++++++++++++++++++++++++++++++++++++
 1 files changed, 51 insertions(+), 0 deletions(-)

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 410018c..23e3679 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -26,6 +26,7 @@ struct backend_info {
 	struct xenvif *vif;
 	enum xenbus_state frontend_state;
 	struct xenbus_watch hotplug_status_watch;
+	struct notifier_block vif_notifier;
 	u8 have_hotplug_status_watch:1;
 };
 
@@ -34,11 +35,57 @@ static void connect(struct backend_info *);
 static void backend_create_xenvif(struct backend_info *be);
 static void unregister_hotplug_status_watch(struct backend_info *be);
 
+/*
+ * By Connected->Connected transition, netfront will watch the change and
+ * send gratuitous ARP.
+ */
+static void notify_front_arping(struct xenbus_device *dev)
+{
+	int err;
+
+	if (dev->state != XenbusStateConnected)
+		return;
+
+	err = xenbus_printf(XBT_NIL, dev->nodename, "state", "%d", dev->state);
+	if (err) {
+		pr_fmt("Error writing the state");
+	}
+
+	return;
+}
+
+#define nb_to_backend(nb) container_of(nb, struct backend_info, vif_notifier)
+/**
+ * When network condition of vif change, notify the frontend.
+ */
+static int netback_netdev_event(struct notifier_block *this,
+				unsigned long event, void *ptr)
+{
+	struct net_device *event_dev = ptr;
+	struct backend_info *be = nb_to_backend(this);
+
+	pr_debug("event_dev: %s, event: %lx\n",
+		 event_dev ? event_dev->name : "None", event);
+
+	if (!be->vif)
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_NOTIFY_PEERS:
+		/* Notify frontend to Send gratuitous ARP */
+		notify_front_arping(be->dev);
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int netback_remove(struct xenbus_device *dev)
 {
 	struct backend_info *be = dev_get_drvdata(&dev->dev);
 
 	unregister_hotplug_status_watch(be);
+	unregister_netdevice_notifier(&be->vif_notifier);
 	if (be->vif) {
 		kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
 		xenbus_rm(XBT_NIL, dev->nodename, "hotplug-status");
@@ -129,6 +176,10 @@ static int netback_probe(struct xenbus_device *dev,
 	/* This kicks hotplug scripts, so do it immediately. */
 	backend_create_xenvif(be);
 
+	/* Register Frontend Event Notify */
+	be->vif_notifier.notifier_call = netback_netdev_event;
+	register_netdevice_notifier(&be->vif_notifier);
+
 	return 0;
 
 abort_transaction:
-- 
1.7.6.5


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