Merge branch 'Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device'

Sridhar Samudrala says:

====================
Enable virtio_net to act as a standby for a passthru device

The main motivation for this patch is to enable cloud service providers
to provide an accelerated datapath to virtio-net enabled VMs in a
transparent manner with no/minimal guest userspace changes. This also
enables hypervisor controlled live migration to be supported with VMs that
have direct attached SR-IOV VF devices.

Patch 1 introduces a failover module that provides a generic interface for
paravirtual drivers to listen for netdev register/unregister/link change
events from pci ethernet devices with the same MAC and takeover their
datapath. The notifier and event handling code is based on the existing
netvsc implementation.

Patch 2 refactors netvsc to use the registration/notification framework
introduced by failover module.

Patch 3 introduces a net_failover driver that provides an automated
failover mechanism to paravirtual drivers via APIs to create and destroy
a failover master netdev and mananges a primary and standby slave netdevs
that get registered via the generic failover infrastructure.

Patch 4 introduces a new feature bit VIRTIO_NET_F_STANDBY to virtio-net
that can be used by hypervisor to indicate that virtio_net interface
should act as a standby for another device with the same MAC address.

Patch 5 extends virtio_net to use alternate datapath when available and
registered. When STANDBY feature is enabled, virtio_net driver uese the
net_failover API to create an additional 'failover' netdev that acts as
a master device and controls 2 slave devices.  The original virtio_net
netdev is registered as 'standby' netdev and a passthru/vf device with
the same MAC gets registered as 'primary' netdev. Both 'standby' and
'failover' netdevs are associated with the same 'pci' device.  The user
accesses the network interface via 'failover' netdev. The 'failover'
netdev chooses 'primary' netdev as default for transmits when it is
available with link up and running.

As this patch series is initially focusing on usecases where hypervisor
fully controls the VM networking and the guest is not expected to directly
configure any hardware settings, it doesn't expose all the ndo/ethtool ops
that are supported by virtio_net at this time. To support additional usecases,
it should be possible to enable additional ops later by caching the state
in failover netdev and replaying when the 'primary' netdev gets registered.

At the time of live migration, the hypervisor needs to unplug the VF device
from the guest on the source host and reset the MAC filter of the VF to
initiate failover of datapath to virtio before starting the migration. After
the migration is completed, the destination hypervisor sets the MAC filter
on the VF and plugs it back to the guest to switch over to VF datapath.

This patch is based on the discussion initiated by Jesse on this thread.
https://marc.info/?l=linux-virtualization&m=151189725224231&w=2

v12:
- Tested live migration with virtio-net/AVF(i40evf) configured in failover
  mode while running iperf in background. Tried static ip and dhcp
  configurations using 'network' scripts and Network Manager.
- Build tested netvsc module.
Updates:
- Extended generic failover module to do common functions like setting
  FAILOVER_SLAVE flag, registering rx-handler and linking to upper dev in
  the generic register/unregister handlers.
  This required adding 3 additional failover ops pre_register, pre_unregister
  and handle_frame.  netvsc and net_failover drivers are updated to support
  these ops.

v11:
- Split net_failover module into 2 components.
  1. 'failover' module that provides generic failover infrastructure
  to register a failover instance and listen for slave events.
  2. 'net_failover' driver that provides APIs to create/destroy upper
  netdev and supports 3-netdev model used by virtio-net.
- Added documentation

v10:
- fix net_failover_open() to update failover CARRIER correctly based on
  standby and primary states.
- fix net_failover_handle_frame() to handle frames received on standby
  when primary is present.
- replace netdev_upper_dev_link with netdev_master_upper_dev_link and
  handle lower dev state changes.
- fix net_failver_create() and net_failover_register() interfaces to
  use ERR_PTR and avoid arg **
- disable setting mac address when virtio-net in STANDBY mode
- document exported symbols
- added entry to MAINTAINERS file

v9:
Select NET_FAILOVER automatically when VIRTIO_NET/HYPERV_NET
are enabled. (stephen)

v8:
- Made the failover managment routines more robust by updating the feature
  bits/other fields in the failover netdev when slave netdevs are
  registered/unregistered. (mst)
- added support for handling vlans.
- Limited the changes in netvsc to only use the notifier/event/lookups
  from the failover module. The slave register/unregister/link-change
  handlers are only updated to use the getbymac routine to get the
  upper netdev. There is no change in their functionality. (stephen)
- renamed structs/function/file names to use net_failover prefix. (mst)

v7
- Rename 'bypass/active/backup' terminology with 'failover/primary/standy'
  (jiri, mst)
- re-arranged dev_open() and dev_set_mtu() calls in the register routines
  so that they don't get called for 2-netdev model. (stephen)
- fixed select_queue() routine to do queue selection based on VF if it is
  registered as primary. (stephen)
-  minor bugfixes

v6 RFC:
  Simplified virtio_net changes by moving all the ndo_ops of the
  bypass_netdev and create/destroy of bypass_netdev to 'bypass' module.
  avoided 2 phase registration(driver + instances).
  introduced IFF_BYPASS/IFF_BYPASS_SLAVE dev->priv_flags
  replaced mutex with a spinlock

v5 RFC:
  Based on Jiri's comments, moved the common functionality to a 'bypass'
  module so that the same notifier and event handlers to handle child
  register/unregister/link change events can be shared between virtio_net
  and netvsc.
  Improved error handling based on Siwei's comments.
v4:
- Based on the review comments on the v3 version of the RFC patch and
  Jakub's suggestion for the naming issue with 3 netdev solution,
  proposed 3 netdev in-driver bonding solution for virtio-net.
v3 RFC:
- Introduced 3 netdev model and pointed out a couple of issues with
  that model and proposed 2 netdev model to avoid these issues.
- Removed broadcast/multicast optimization and only use virtio as
  backup path when VF is unplugged.
v2 RFC:
- Changed VIRTIO_NET_F_MASTER to VIRTIO_NET_F_BACKUP (mst)
- made a small change to the virtio-net xmit path to only use VF datapath
  for unicasts. Broadcasts/multicasts use virtio datapath. This avoids
  east-west broadcasts to go over the PCI link.
- added suppport for the feature bit in qemu
====================
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/failover.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+========
+FAILOVER
+========
+
+Overview
+========
+
+The failover module provides a generic interface for paravirtual drivers
+to register a netdev and a set of ops with a failover instance. The ops
+are used as event handlers that get called to handle netdev register/
+unregister/link change/name change events on slave pci ethernet devices
+with the same mac address as the failover netdev.
+
+This enables paravirtual drivers to use a VF as an accelerated low latency
+datapath. It also allows live migration of VMs with direct attached VFs by
+failing over to the paravirtual datapath when the VF is unplugged.

Documentation/networking/net_failover.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+============
+NET_FAILOVER
+============
+
+Overview
+========
+
+The net_failover driver provides an automated failover mechanism via APIs
+to create and destroy a failover master netdev and mananges a primary and
+standby slave netdevs that get registered via the generic failover
+infrastructrure.
+
+The failover netdev acts a master device and controls 2 slave devices. The
+original paravirtual interface is registered as 'standby' slave netdev and
+a passthru/vf device with the same MAC gets registered as 'primary' slave
+netdev. Both 'standby' and 'failover' netdevs are associated with the same
+'pci' device. The user accesses the network interface via 'failover' netdev.
+The 'failover' netdev chooses 'primary' netdev as default for transmits when
+it is available with link up and running.
+
+This can be used by paravirtual drivers to enable an alternate low latency
+datapath. It also enables hypervisor controlled live migration of a VM with
+direct attached VF by failing over to the paravirtual datapath when the VF
+is unplugged.
+
+virtio-net accelerated datapath: STANDBY mode
+=============================================
+
+net_failover enables hypervisor controlled accelerated datapath to virtio-net
+enabled VMs in a transparent manner with no/minimal guest userspace chanages.
+
+To support this, the hypervisor needs to enable VIRTIO_NET_F_STANDBY
+feature on the virtio-net interface and assign the same MAC address to both
+virtio-net and VF interfaces.
+
+Here is an example XML snippet that shows such configuration.
+
+ <interface type='network'>
+   <mac address='52:54:00:00:12:53'/>
+   <source network='enp66s0f0_br'/>
+   <target dev='tap01'/>
+   <model type='virtio'/>
+   <driver name='vhost' queues='4'/>
+   <link state='down'/>
+   <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
+ </interface>
+ <interface type='hostdev' managed='yes'>
+   <mac address='52:54:00:00:12:53'/>
+   <source>
+     <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
+   </source>
+   <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
+ </interface>
+
+Booting a VM with the above configuration will result in the following 3
+netdevs created in the VM.
+
+4: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
+    link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
+    inet 192.168.12.53/24 brd 192.168.12.255 scope global dynamic ens10
+       valid_lft 42482sec preferred_lft 42482sec
+    inet6 fe80::97d8:db2:8c10:b6d6/64 scope link
+       valid_lft forever preferred_lft forever
+5: ens10nsby: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master ens10 state UP group default qlen 1000
+    link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
+7: ens11: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ens10 state UP group default qlen 1000
+    link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
+
+ens10 is the 'failover' master netdev, ens10nsby and ens11 are the slave
+'standby' and 'primary' netdevs respectively.
+
+Live Migration of a VM with SR-IOV VF & virtio-net in STANDBY mode
+==================================================================
+
+net_failover also enables hypervisor controlled live migration to be supported
+with VMs that have direct attached SR-IOV VF devices by automatic failover to
+the paravirtual datapath when the VF is unplugged.
+
+Here is a sample script that shows the steps to initiate live migration on
+the source hypervisor.
+
+# cat vf_xml
+<interface type='hostdev' managed='yes'>
+  <mac address='52:54:00:00:12:53'/>
+  <source>
+    <address type='pci' domain='0x0000' bus='0x42' slot='0x02' function='0x5'/>
+  </source>
+  <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
+</interface>
+
+# Source Hypervisor
+#!/bin/bash
+
+DOMAIN=fedora27-tap01
+PF=enp66s0f0
+VF_NUM=5
+TAP_IF=tap01
+VF_XML=
+
+MAC=52:54:00:00:12:53
+ZERO_MAC=00:00:00:00:00:00
+
+virsh domif-setlink $DOMAIN $TAP_IF up
+bridge fdb del $MAC dev $PF master
+virsh detach-device $DOMAIN $VF_XML
+ip link set $PF vf $VF_NUM mac $ZERO_MAC
+
+virsh migrate --live $DOMAIN qemu+ssh://$REMOTE_HOST/system
+
+# Destination Hypervisor
+#!/bin/bash
+
+virsh attach-device $DOMAIN $VF_XML
+virsh domif-setlink $DOMAIN $TAP_IF down

MAINTAINERS

@@ -5411,6 +5411,14 @@ S:	Maintained
 F:	Documentation/hwmon/f71805f
 F:	drivers/hwmon/f71805f.c
 
+FAILOVER MODULE
+M:	Sridhar Samudrala <sridhar.samudrala@intel.com>
+L:	netdev@vger.kernel.org
+S:	Supported
+F:	net/core/failover.c
+F:	include/net/failover.h
+F:	Documentation/networking/failover.rst
+
 FANOTIFY
 M:	Jan Kara <jack@suse.cz>
 R:	Amir Goldstein <amir73il@gmail.com>
@@ -9646,6 +9654,14 @@ S:	Maintained
 F:	Documentation/hwmon/nct6775
 F:	drivers/hwmon/nct6775.c
 
+NET_FAILOVER MODULE
+M:	Sridhar Samudrala <sridhar.samudrala@intel.com>
+L:	netdev@vger.kernel.org
+S:	Supported
+F:	driver/net/net_failover.c
+F:	include/net/net_failover.h
+F:	Documentation/networking/net_failover.rst
+
 NETEFFECT IWARP RNIC DRIVER (IW_NES)
 M:	Faisal Latif <faisal.latif@intel.com>
 L:	linux-rdma@vger.kernel.org

drivers/net/Kconfig

@@ -332,6 +332,7 @@ config VETH
 config VIRTIO_NET
 	tristate "Virtio network driver"
 	depends on VIRTIO
+	select NET_FAILOVER
 	---help---
 	  This is the virtual network driver for virtio.  It can be used with
 	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
@@ -510,4 +511,16 @@ config NETDEVSIM
 	  To compile this driver as a module, choose M here: the module
 	  will be called netdevsim.
 
+config NET_FAILOVER
+	tristate "Failover driver"
+	select FAILOVER
+	help
+	  This provides an automated failover mechanism via APIs to create
+	  and destroy a failover master netdev and manages a primary and
+	  standby slave netdevs that get registered via the generic failover
+	  infrastructure. This can be used by paravirtual drivers to enable
+	  an alternate low latency datapath. It alsoenables live migration of
+	  a VM with direct attached VF by failing over to the paravirtual
+	  datapath when the VF is unplugged.
+
 endif # NETDEVICES

drivers/net/Makefile

@@ -78,3 +78,4 @@ obj-$(CONFIG_FUJITSU_ES) += fjes/
 thunderbolt-net-y += thunderbolt.o
 obj-$(CONFIG_THUNDERBOLT_NET) += thunderbolt-net.o
 obj-$(CONFIG_NETDEVSIM) += netdevsim/
+obj-$(CONFIG_NET_FAILOVER) += net_failover.o

drivers/net/hyperv/Kconfig

@@ -2,5 +2,6 @@ config HYPERV_NET
 	tristate "Microsoft Hyper-V virtual network driver"
 	depends on HYPERV
 	select UCS2_STRING
+	select FAILOVER
 	help
 	  Select this option to enable the Hyper-V virtual network driver.

drivers/net/hyperv/hyperv_net.h

@@ -932,6 +932,8 @@ struct net_device_context {
 	u32 vf_alloc;
 	/* Serial number of the VF to team with */
 	u32 vf_serial;
+
+	struct failover *failover;
 };
 
 /* Per channel data */

drivers/net/hyperv/netvsc_drv.c

@@ -43,6 +43,7 @@
 #include <net/pkt_sched.h>
 #include <net/checksum.h>
 #include <net/ip6_checksum.h>
+#include <net/failover.h>
 
 #include "hyperv_net.h"
 
@@ -1779,46 +1780,6 @@ static void netvsc_link_change(struct work_struct *w)
 	rtnl_unlock();
 }
 
-static struct net_device *get_netvsc_bymac(const u8 *mac)
-{
-	struct net_device *dev;
-
-	ASSERT_RTNL();
-
-	for_each_netdev(&init_net, dev) {
-		if (dev->netdev_ops != &device_ops)
-			continue;	/* not a netvsc device */
-
-		if (ether_addr_equal(mac, dev->perm_addr))
-			return dev;
-	}
-
-	return NULL;
-}
-
-static struct net_device *get_netvsc_byref(struct net_device *vf_netdev)
-{
-	struct net_device *dev;
-
-	ASSERT_RTNL();
-
-	for_each_netdev(&init_net, dev) {
-		struct net_device_context *net_device_ctx;
-
-		if (dev->netdev_ops != &device_ops)
-			continue;	/* not a netvsc device */
-
-		net_device_ctx = netdev_priv(dev);
-		if (!rtnl_dereference(net_device_ctx->nvdev))
-			continue;	/* device is removed */
-
-		if (rtnl_dereference(net_device_ctx->vf_netdev) == vf_netdev)
-			return dev;	/* a match */
-	}
-
-	return NULL;
-}
-
 /* Called when VF is injecting data into network stack.
  * Change the associated network device from VF to netvsc.
  * note: already called with rcu_read_lock
@@ -1841,46 +1802,6 @@ static rx_handler_result_t netvsc_vf_handle_frame(struct sk_buff **pskb)
 	return RX_HANDLER_ANOTHER;
 }
 
-static int netvsc_vf_join(struct net_device *vf_netdev,
-			  struct net_device *ndev)
-{
-	struct net_device_context *ndev_ctx = netdev_priv(ndev);
-	int ret;
-
-	ret = netdev_rx_handler_register(vf_netdev,
-					 netvsc_vf_handle_frame, ndev);
-	if (ret != 0) {
-		netdev_err(vf_netdev,
-			   "can not register netvsc VF receive handler (err = %d)\n",
-			   ret);
-		goto rx_handler_failed;
-	}
-
-	ret = netdev_master_upper_dev_link(vf_netdev, ndev,
-					   NULL, NULL, NULL);
-	if (ret != 0) {
-		netdev_err(vf_netdev,
-			   "can not set master device %s (err = %d)\n",
-			   ndev->name, ret);
-		goto upper_link_failed;
-	}
-
-	/* set slave flag before open to prevent IPv6 addrconf */
-	vf_netdev->flags |= IFF_SLAVE;
-
-	schedule_delayed_work(&ndev_ctx->vf_takeover, VF_TAKEOVER_INT);
-
-	call_netdevice_notifiers(NETDEV_JOIN, vf_netdev);
-
-	netdev_info(vf_netdev, "joined to %s\n", ndev->name);
-	return 0;
-
-upper_link_failed:
-	netdev_rx_handler_unregister(vf_netdev);
-rx_handler_failed:
-	return ret;
-}
-
 static void __netvsc_vf_setup(struct net_device *ndev,
 			      struct net_device *vf_netdev)
 {
@@ -1931,85 +1852,95 @@ static void netvsc_vf_setup(struct work_struct *w)
 	rtnl_unlock();
 }
 
-static int netvsc_register_vf(struct net_device *vf_netdev)
+static int netvsc_pre_register_vf(struct net_device *vf_netdev,
+				  struct net_device *ndev)
 {
-	struct net_device *ndev;
 	struct net_device_context *net_device_ctx;
 	struct netvsc_device *netvsc_dev;
 
-	if (vf_netdev->addr_len != ETH_ALEN)
-		return NOTIFY_DONE;
-
-	/*
-	 * We will use the MAC address to locate the synthetic interface to
-	 * associate with the VF interface. If we don't find a matching
-	 * synthetic interface, move on.
-	 */
-	ndev = get_netvsc_bymac(vf_netdev->perm_addr);
-	if (!ndev)
-		return NOTIFY_DONE;
-
 	net_device_ctx = netdev_priv(ndev);
 	netvsc_dev = rtnl_dereference(net_device_ctx->nvdev);
 	if (!netvsc_dev || rtnl_dereference(net_device_ctx->vf_netdev))
-		return NOTIFY_DONE;
+		return -ENODEV;
+
+	return 0;
+}
+
+static int netvsc_register_vf(struct net_device *vf_netdev,
+			      struct net_device *ndev)
+{
+	struct net_device_context *ndev_ctx = netdev_priv(ndev);
 
-	if (netvsc_vf_join(vf_netdev, ndev) != 0)
-		return NOTIFY_DONE;
+	/* set slave flag before open to prevent IPv6 addrconf */
+	vf_netdev->flags |= IFF_SLAVE;
 
-	netdev_info(ndev, "VF registering: %s\n", vf_netdev->name);
+	schedule_delayed_work(&ndev_ctx->vf_takeover, VF_TAKEOVER_INT);
+
+	call_netdevice_notifiers(NETDEV_JOIN, vf_netdev);
+
+	netdev_info(vf_netdev, "joined to %s\n", ndev->name);
 
 	dev_hold(vf_netdev);
-	rcu_assign_pointer(net_device_ctx->vf_netdev, vf_netdev);
-	return NOTIFY_OK;
+	rcu_assign_pointer(ndev_ctx->vf_netdev, vf_netdev);
+
+	return 0;
 }
 
 /* VF up/down change detected, schedule to change data path */
-static int netvsc_vf_changed(struct net_device *vf_netdev)
+static int netvsc_vf_changed(struct net_device *vf_netdev,
+			     struct net_device *ndev)
 {
 	struct net_device_context *net_device_ctx;
 	struct netvsc_device *netvsc_dev;
-	struct net_device *ndev;
 	bool vf_is_up = netif_running(vf_netdev);
 
-	ndev = get_netvsc_byref(vf_netdev);
-	if (!ndev)
-		return NOTIFY_DONE;
-
 	net_device_ctx = netdev_priv(ndev);
 	netvsc_dev = rtnl_dereference(net_device_ctx->nvdev);
 	if (!netvsc_dev)
-		return NOTIFY_DONE;
+		return -ENODEV;
 
 	netvsc_switch_datapath(ndev, vf_is_up);
 	netdev_info(ndev, "Data path switched %s VF: %s\n",
 		    vf_is_up ? "to" : "from", vf_netdev->name);
 
-	return NOTIFY_OK;
+	return 0;
 }
 
-static int netvsc_unregister_vf(struct net_device *vf_netdev)
+static int netvsc_pre_unregister_vf(struct net_device *vf_netdev,
+				    struct net_device *ndev)
 {
-	struct net_device *ndev;
 	struct net_device_context *net_device_ctx;
 
-	ndev = get_netvsc_byref(vf_netdev);
-	if (!ndev)
-		return NOTIFY_DONE;
-
 	net_device_ctx = netdev_priv(ndev);
 	cancel_delayed_work_sync(&net_device_ctx->vf_takeover);
 
+	return 0;
+}
+
+static int netvsc_unregister_vf(struct net_device *vf_netdev,
+				struct net_device *ndev)
+{
+	struct net_device_context *net_device_ctx;
+
+	net_device_ctx = netdev_priv(ndev);
+
 	netdev_info(ndev, "VF unregistering: %s\n", vf_netdev->name);
 
-	netdev_rx_handler_unregister(vf_netdev);
-	netdev_upper_dev_unlink(vf_netdev, ndev);
 	RCU_INIT_POINTER(net_device_ctx->vf_netdev, NULL);
 	dev_put(vf_netdev);
 
-	return NOTIFY_OK;
+	return 0;
 }
 
+static struct failover_ops netvsc_failover_ops = {
+	.slave_pre_register	= netvsc_pre_register_vf,
+	.slave_register		= netvsc_register_vf,
+	.slave_pre_unregister	= netvsc_pre_unregister_vf,
+	.slave_unregister	= netvsc_unregister_vf,
+	.slave_link_change	= netvsc_vf_changed,
+	.slave_handle_frame	= netvsc_vf_handle_frame,
+};
+
 static int netvsc_probe(struct hv_device *dev,
 			const struct hv_vmbus_device_id *dev_id)
 {
@@ -2099,8 +2030,14 @@ static int netvsc_probe(struct hv_device *dev,
 		goto register_failed;
 	}
 
+	net_device_ctx->failover = failover_register(net, &netvsc_failover_ops);
+	if (IS_ERR(net_device_ctx->failover))
+		goto err_failover;
+
 	return ret;
 
+err_failover:
+	unregister_netdev(net);
 register_failed:
 	rndis_filter_device_remove(dev, nvdev);
 rndis_failed:
@@ -2141,13 +2078,15 @@ static int netvsc_remove(struct hv_device *dev)
 	rtnl_lock();
 	vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
 	if (vf_netdev)
-		netvsc_unregister_vf(vf_netdev);
+		failover_slave_unregister(vf_netdev);
 
 	if (nvdev)
 		rndis_filter_device_remove(dev, nvdev);
 
 	unregister_netdevice(net);
 
+	failover_unregister(ndev_ctx->failover);
+
 	rtnl_unlock();
 	rcu_read_unlock();
 
@@ -2174,54 +2113,8 @@ static struct  hv_driver netvsc_drv = {
 	.remove = netvsc_remove,
 };
 
-/*
- * On Hyper-V, every VF interface is matched with a corresponding
- * synthetic interface. The synthetic interface is presented first
- * to the guest. When the corresponding VF instance is registered,
- * we will take care of switching the data path.
- */
-static int netvsc_netdev_event(struct notifier_block *this,
-			       unsigned long event, void *ptr)
-{
-	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
-
-	/* Skip our own events */
-	if (event_dev->netdev_ops == &device_ops)
-		return NOTIFY_DONE;
-
-	/* Avoid non-Ethernet type devices */
-	if (event_dev->type != ARPHRD_ETHER)
-		return NOTIFY_DONE;
-
-	/* Avoid Vlan dev with same MAC registering as VF */
-	if (is_vlan_dev(event_dev))
-		return NOTIFY_DONE;
-
-	/* Avoid Bonding master dev with same MAC registering as VF */
-	if ((event_dev->priv_flags & IFF_BONDING) &&
-	    (event_dev->flags & IFF_MASTER))
-		return NOTIFY_DONE;
-
-	switch (event) {
-	case NETDEV_REGISTER:
-		return netvsc_register_vf(event_dev);
-	case NETDEV_UNREGISTER:
-		return netvsc_unregister_vf(event_dev);
-	case NETDEV_UP:
-	case NETDEV_DOWN:
-		return netvsc_vf_changed(event_dev);
-	default:
-		return NOTIFY_DONE;
-	}
-}
-
-static struct notifier_block netvsc_netdev_notifier = {
-	.notifier_call = netvsc_netdev_event,
-};
-
 static void __exit netvsc_drv_exit(void)
 {
-	unregister_netdevice_notifier(&netvsc_netdev_notifier);
 	vmbus_driver_unregister(&netvsc_drv);
 }
 
@@ -2241,7 +2134,6 @@ static int __init netvsc_drv_init(void)
 	if (ret)
 		return ret;
 
-	register_netdevice_notifier(&netvsc_netdev_notifier);
 	return 0;
 }
 

drivers/net/net_failover.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018, Intel Corporation. */
+
+/* This provides a net_failover interface for paravirtual drivers to
+ * provide an alternate datapath by exporting APIs to create and
+ * destroy a upper 'net_failover' netdev. The upper dev manages the
+ * original paravirtual interface as a 'standby' netdev and uses the
+ * generic failover infrastructure to register and manage a direct
+ * attached VF as a 'primary' netdev. This enables live migration of
+ * a VM with direct attached VF by failing over to the paravirtual
+ * datapath when the VF is unplugged.
+ *
+ * Some of the netdev management routines are based on bond/team driver as
+ * this driver provides active-backup functionality similar to those drivers.
+ */
+
+#include <linux/netdevice.h>
+#include <linux/etherdevice.h>
+#include <linux/ethtool.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/netdevice.h>
+#include <linux/netpoll.h>
+#include <linux/rtnetlink.h>
+#include <linux/if_vlan.h>
+#include <linux/pci.h>
+#include <net/sch_generic.h>
+#include <uapi/linux/if_arp.h>
+#include <net/net_failover.h>
+
+static bool net_failover_xmit_ready(struct net_device *dev)
+{
+	return netif_running(dev) && netif_carrier_ok(dev);
+}
+
+static int net_failover_open(struct net_device *dev)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+	int err;
+
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	if (primary_dev) {
+		err = dev_open(primary_dev);
+		if (err)
+			goto err_primary_open;
+	}
+
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+	if (standby_dev) {
+		err = dev_open(standby_dev);
+		if (err)
+			goto err_standby_open;
+	}
+
+	if ((primary_dev && net_failover_xmit_ready(primary_dev)) ||
+	    (standby_dev && net_failover_xmit_ready(standby_dev))) {
+		netif_carrier_on(dev);
+		netif_tx_wake_all_queues(dev);
+	}
+
+	return 0;
+
+err_standby_open:
+	dev_close(primary_dev);
+err_primary_open:
+	netif_tx_disable(dev);
+	return err;
+}
+
+static int net_failover_close(struct net_device *dev)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	netif_tx_disable(dev);
+
+	slave_dev = rtnl_dereference(nfo_info->primary_dev);
+	if (slave_dev)
+		dev_close(slave_dev);
+
+	slave_dev = rtnl_dereference(nfo_info->standby_dev);
+	if (slave_dev)
+		dev_close(slave_dev);
+
+	return 0;
+}
+
+static netdev_tx_t net_failover_drop_xmit(struct sk_buff *skb,
+					  struct net_device *dev)
+{
+	atomic_long_inc(&dev->tx_dropped);
+	dev_kfree_skb_any(skb);
+	return NETDEV_TX_OK;
+}
+
+static netdev_tx_t net_failover_start_xmit(struct sk_buff *skb,
+					   struct net_device *dev)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *xmit_dev;
+
+	/* Try xmit via primary netdev followed by standby netdev */
+	xmit_dev = rcu_dereference_bh(nfo_info->primary_dev);
+	if (!xmit_dev || !net_failover_xmit_ready(xmit_dev)) {
+		xmit_dev = rcu_dereference_bh(nfo_info->standby_dev);
+		if (!xmit_dev || !net_failover_xmit_ready(xmit_dev))
+			return net_failover_drop_xmit(skb, dev);
+	}
+
+	skb->dev = xmit_dev;
+	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
+
+	return dev_queue_xmit(skb);
+}
+
+static u16 net_failover_select_queue(struct net_device *dev,
+				     struct sk_buff *skb, void *accel_priv,
+				     select_queue_fallback_t fallback)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev;
+	u16 txq;
+
+	primary_dev = rcu_dereference(nfo_info->primary_dev);
+	if (primary_dev) {
+		const struct net_device_ops *ops = primary_dev->netdev_ops;
+
+		if (ops->ndo_select_queue)
+			txq = ops->ndo_select_queue(primary_dev, skb,
+						    accel_priv, fallback);
+		else
+			txq = fallback(primary_dev, skb);
+
+		qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
+
+		return txq;
+	}
+
+	txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) : 0;
+
+	/* Save the original txq to restore before passing to the driver */
+	qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
+
+	if (unlikely(txq >= dev->real_num_tx_queues)) {
+		do {
+			txq -= dev->real_num_tx_queues;
+		} while (txq >= dev->real_num_tx_queues);
+	}
+
+	return txq;
+}
+
+/* fold stats, assuming all rtnl_link_stats64 fields are u64, but
+ * that some drivers can provide 32bit values only.
+ */
+static void net_failover_fold_stats(struct rtnl_link_stats64 *_res,
+				    const struct rtnl_link_stats64 *_new,
+				    const struct rtnl_link_stats64 *_old)
+{
+	const u64 *new = (const u64 *)_new;
+	const u64 *old = (const u64 *)_old;
+	u64 *res = (u64 *)_res;
+	int i;
+
+	for (i = 0; i < sizeof(*_res) / sizeof(u64); i++) {
+		u64 nv = new[i];
+		u64 ov = old[i];
+		s64 delta = nv - ov;
+
+		/* detects if this particular field is 32bit only */
+		if (((nv | ov) >> 32) == 0)
+			delta = (s64)(s32)((u32)nv - (u32)ov);
+
+		/* filter anomalies, some drivers reset their stats
+		 * at down/up events.
+		 */
+		if (delta > 0)
+			res[i] += delta;
+	}
+}
+
+static void net_failover_get_stats(struct net_device *dev,
+				   struct rtnl_link_stats64 *stats)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	const struct rtnl_link_stats64 *new;
+	struct rtnl_link_stats64 temp;
+	struct net_device *slave_dev;
+
+	spin_lock(&nfo_info->stats_lock);
+	memcpy(stats, &nfo_info->failover_stats, sizeof(*stats));
+
+	rcu_read_lock();
+
+	slave_dev = rcu_dereference(nfo_info->primary_dev);
+	if (slave_dev) {
+		new = dev_get_stats(slave_dev, &temp);
+		net_failover_fold_stats(stats, new, &nfo_info->primary_stats);
+		memcpy(&nfo_info->primary_stats, new, sizeof(*new));
+	}
+
+	slave_dev = rcu_dereference(nfo_info->standby_dev);
+	if (slave_dev) {
+		new = dev_get_stats(slave_dev, &temp);
+		net_failover_fold_stats(stats, new, &nfo_info->standby_stats);
+		memcpy(&nfo_info->standby_stats, new, sizeof(*new));
+	}
+
+	rcu_read_unlock();
+
+	memcpy(&nfo_info->failover_stats, stats, sizeof(*stats));
+	spin_unlock(&nfo_info->stats_lock);
+}
+
+static int net_failover_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+	int ret = 0;
+
+	primary_dev = rcu_dereference(nfo_info->primary_dev);
+	if (primary_dev) {
+		ret = dev_set_mtu(primary_dev, new_mtu);
+		if (ret)
+			return ret;
+	}
+
+	standby_dev = rcu_dereference(nfo_info->standby_dev);
+	if (standby_dev) {
+		ret = dev_set_mtu(standby_dev, new_mtu);
+		if (ret) {
+			if (primary_dev)
+				dev_set_mtu(primary_dev, dev->mtu);
+			return ret;
+		}
+	}
+
+	dev->mtu = new_mtu;
+
+	return 0;
+}
+
+static void net_failover_set_rx_mode(struct net_device *dev)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	rcu_read_lock();
+
+	slave_dev = rcu_dereference(nfo_info->primary_dev);
+	if (slave_dev) {
+		dev_uc_sync_multiple(slave_dev, dev);
+		dev_mc_sync_multiple(slave_dev, dev);
+	}
+
+	slave_dev = rcu_dereference(nfo_info->standby_dev);
+	if (slave_dev) {
+		dev_uc_sync_multiple(slave_dev, dev);
+		dev_mc_sync_multiple(slave_dev, dev);
+	}
+
+	rcu_read_unlock();
+}
+
+static int net_failover_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
+					u16 vid)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+	int ret = 0;
+
+	primary_dev = rcu_dereference(nfo_info->primary_dev);
+	if (primary_dev) {
+		ret = vlan_vid_add(primary_dev, proto, vid);
+		if (ret)
+			return ret;
+	}
+
+	standby_dev = rcu_dereference(nfo_info->standby_dev);
+	if (standby_dev) {
+		ret = vlan_vid_add(standby_dev, proto, vid);
+		if (ret)
+			if (primary_dev)
+				vlan_vid_del(primary_dev, proto, vid);
+	}
+
+	return ret;
+}
+
+static int net_failover_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,
+					 u16 vid)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	slave_dev = rcu_dereference(nfo_info->primary_dev);
+	if (slave_dev)
+		vlan_vid_del(slave_dev, proto, vid);
+
+	slave_dev = rcu_dereference(nfo_info->standby_dev);
+	if (slave_dev)
+		vlan_vid_del(slave_dev, proto, vid);
+
+	return 0;
+}
+
+static const struct net_device_ops failover_dev_ops = {
+	.ndo_open		= net_failover_open,
+	.ndo_stop		= net_failover_close,
+	.ndo_start_xmit		= net_failover_start_xmit,
+	.ndo_select_queue	= net_failover_select_queue,
+	.ndo_get_stats64	= net_failover_get_stats,
+	.ndo_change_mtu		= net_failover_change_mtu,
+	.ndo_set_rx_mode	= net_failover_set_rx_mode,
+	.ndo_vlan_rx_add_vid	= net_failover_vlan_rx_add_vid,
+	.ndo_vlan_rx_kill_vid	= net_failover_vlan_rx_kill_vid,
+	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_features_check	= passthru_features_check,
+};
+
+#define FAILOVER_NAME "net_failover"
+#define FAILOVER_VERSION "0.1"
+
+static void nfo_ethtool_get_drvinfo(struct net_device *dev,
+				    struct ethtool_drvinfo *drvinfo)
+{
+	strlcpy(drvinfo->driver, FAILOVER_NAME, sizeof(drvinfo->driver));
+	strlcpy(drvinfo->version, FAILOVER_VERSION, sizeof(drvinfo->version));
+}
+
+static int nfo_ethtool_get_link_ksettings(struct net_device *dev,
+					  struct ethtool_link_ksettings *cmd)
+{
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	slave_dev = rtnl_dereference(nfo_info->primary_dev);
+	if (!slave_dev || !net_failover_xmit_ready(slave_dev)) {
+		slave_dev = rtnl_dereference(nfo_info->standby_dev);
+		if (!slave_dev || !net_failover_xmit_ready(slave_dev)) {
+			cmd->base.duplex = DUPLEX_UNKNOWN;
+			cmd->base.port = PORT_OTHER;
+			cmd->base.speed = SPEED_UNKNOWN;
+
+			return 0;
+		}
+	}
+
+	return __ethtool_get_link_ksettings(slave_dev, cmd);
+}
+
+static const struct ethtool_ops failover_ethtool_ops = {
+	.get_drvinfo            = nfo_ethtool_get_drvinfo,
+	.get_link               = ethtool_op_get_link,
+	.get_link_ksettings     = nfo_ethtool_get_link_ksettings,
+};
+
+/* Called when slave dev is injecting data into network stack.
+ * Change the associated network device from lower dev to failover dev.
+ * note: already called with rcu_read_lock
+ */
+static rx_handler_result_t net_failover_handle_frame(struct sk_buff **pskb)
+{
+	struct sk_buff *skb = *pskb;
+	struct net_device *dev = rcu_dereference(skb->dev->rx_handler_data);
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+
+	primary_dev = rcu_dereference(nfo_info->primary_dev);
+	standby_dev = rcu_dereference(nfo_info->standby_dev);
+
+	if (primary_dev && skb->dev == standby_dev)
+		return RX_HANDLER_EXACT;
+
+	skb->dev = dev;
+
+	return RX_HANDLER_ANOTHER;
+}
+
+static void net_failover_compute_features(struct net_device *dev)
+{
+	u32 vlan_features = FAILOVER_VLAN_FEATURES & NETIF_F_ALL_FOR_ALL;
+	netdev_features_t enc_features  = FAILOVER_ENC_FEATURES;
+	unsigned short max_hard_header_len = ETH_HLEN;
+	unsigned int dst_release_flag = IFF_XMIT_DST_RELEASE |
+					IFF_XMIT_DST_RELEASE_PERM;
+	struct net_failover_info *nfo_info = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+
+	primary_dev = rcu_dereference(nfo_info->primary_dev);
+	if (primary_dev) {
+		vlan_features =
+			netdev_increment_features(vlan_features,
+						  primary_dev->vlan_features,
+						  FAILOVER_VLAN_FEATURES);
+		enc_features =
+			netdev_increment_features(enc_features,
+						  primary_dev->hw_enc_features,
+						  FAILOVER_ENC_FEATURES);
+
+		dst_release_flag &= primary_dev->priv_flags;
+		if (primary_dev->hard_header_len > max_hard_header_len)
+			max_hard_header_len = primary_dev->hard_header_len;
+	}
+
+	standby_dev = rcu_dereference(nfo_info->standby_dev);
+	if (standby_dev) {
+		vlan_features =
+			netdev_increment_features(vlan_features,
+						  standby_dev->vlan_features,
+						  FAILOVER_VLAN_FEATURES);
+		enc_features =
+			netdev_increment_features(enc_features,
+						  standby_dev->hw_enc_features,
+						  FAILOVER_ENC_FEATURES);
+
+		dst_release_flag &= standby_dev->priv_flags;
+		if (standby_dev->hard_header_len > max_hard_header_len)
+			max_hard_header_len = standby_dev->hard_header_len;
+	}
+
+	dev->vlan_features = vlan_features;
+	dev->hw_enc_features = enc_features | NETIF_F_GSO_ENCAP_ALL;
+	dev->hard_header_len = max_hard_header_len;
+
+	dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
+	if (dst_release_flag == (IFF_XMIT_DST_RELEASE |
+				 IFF_XMIT_DST_RELEASE_PERM))
+		dev->priv_flags |= IFF_XMIT_DST_RELEASE;
+
+	netdev_change_features(dev);
+}
+
+static void net_failover_lower_state_changed(struct net_device *slave_dev,
+					     struct net_device *primary_dev,
+					     struct net_device *standby_dev)
+{
+	struct netdev_lag_lower_state_info info;
+
+	if (netif_carrier_ok(slave_dev))
+		info.link_up = true;
+	else
+		info.link_up = false;
+
+	if (slave_dev == primary_dev) {
+		if (netif_running(primary_dev))
+			info.tx_enabled = true;
+		else
+			info.tx_enabled = false;
+	} else {
+		if ((primary_dev && netif_running(primary_dev)) ||
+		    (!netif_running(standby_dev)))
+			info.tx_enabled = false;
+		else
+			info.tx_enabled = true;
+	}
+
+	netdev_lower_state_changed(slave_dev, &info);
+}
+
+static int net_failover_slave_pre_register(struct net_device *slave_dev,
+					   struct net_device *failover_dev)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct net_failover_info *nfo_info;
+	bool slave_is_standby;
+
+	nfo_info = netdev_priv(failover_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	slave_is_standby = slave_dev->dev.parent == failover_dev->dev.parent;
+	if (slave_is_standby ? standby_dev : primary_dev) {
+		netdev_err(failover_dev, "%s attempting to register as slave dev when %s already present\n",
+			   slave_dev->name,
+			   slave_is_standby ? "standby" : "primary");
+		return -EINVAL;
+	}
+
+	/* We want to allow only a direct attached VF device as a primary
+	 * netdev. As there is no easy way to check for a VF device, restrict
+	 * this to a pci device.
+	 */
+	if (!slave_is_standby && (!slave_dev->dev.parent ||
+				  !dev_is_pci(slave_dev->dev.parent)))
+		return -EINVAL;
+
+	if (failover_dev->features & NETIF_F_VLAN_CHALLENGED &&
+	    vlan_uses_dev(failover_dev)) {
+		netdev_err(failover_dev, "Device %s is VLAN challenged and failover device has VLAN set up\n",
+			   failover_dev->name);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int net_failover_slave_register(struct net_device *slave_dev,
+				       struct net_device *failover_dev)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct net_failover_info *nfo_info;
+	bool slave_is_standby;
+	u32 orig_mtu;
+	int err;
+
+	/* Align MTU of slave with failover dev */
+	orig_mtu = slave_dev->mtu;
+	err = dev_set_mtu(slave_dev, failover_dev->mtu);
+	if (err) {
+		netdev_err(failover_dev, "unable to change mtu of %s to %u register failed\n",
+			   slave_dev->name, failover_dev->mtu);
+		goto done;
+	}
+
+	dev_hold(slave_dev);
+
+	if (netif_running(failover_dev)) {
+		err = dev_open(slave_dev);
+		if (err && (err != -EBUSY)) {
+			netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
+				   slave_dev->name, err);
+			goto err_dev_open;
+		}
+	}
+
+	netif_addr_lock_bh(failover_dev);
+	dev_uc_sync_multiple(slave_dev, failover_dev);
+	dev_uc_sync_multiple(slave_dev, failover_dev);
+	netif_addr_unlock_bh(failover_dev);
+
+	err = vlan_vids_add_by_dev(slave_dev, failover_dev);
+	if (err) {
+		netdev_err(failover_dev, "Failed to add vlan ids to device %s err:%d\n",
+			   slave_dev->name, err);
+		goto err_vlan_add;
+	}
+
+	nfo_info = netdev_priv(failover_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	slave_is_standby = slave_dev->dev.parent == failover_dev->dev.parent;
+
+	if (slave_is_standby) {
+		rcu_assign_pointer(nfo_info->standby_dev, slave_dev);
+		standby_dev = slave_dev;
+		dev_get_stats(standby_dev, &nfo_info->standby_stats);
+	} else {
+		rcu_assign_pointer(nfo_info->primary_dev, slave_dev);
+		primary_dev = slave_dev;
+		dev_get_stats(primary_dev, &nfo_info->primary_stats);
+		failover_dev->min_mtu = slave_dev->min_mtu;
+		failover_dev->max_mtu = slave_dev->max_mtu;
+	}
+
+	net_failover_lower_state_changed(slave_dev, primary_dev, standby_dev);
+	net_failover_compute_features(failover_dev);
+
+	call_netdevice_notifiers(NETDEV_JOIN, slave_dev);
+
+	netdev_info(failover_dev, "failover %s slave:%s registered\n",
+		    slave_is_standby ? "standby" : "primary", slave_dev->name);
+
+	return 0;
+
+err_vlan_add:
+	dev_uc_unsync(slave_dev, failover_dev);
+	dev_mc_unsync(slave_dev, failover_dev);
+	dev_close(slave_dev);
+err_dev_open:
+	dev_put(slave_dev);
+	dev_set_mtu(slave_dev, orig_mtu);
+done:
+	return err;
+}
+
+static int net_failover_slave_pre_unregister(struct net_device *slave_dev,
+					     struct net_device *failover_dev)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct net_failover_info *nfo_info;
+
+	nfo_info = netdev_priv(failover_dev);
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+
+	if (slave_dev != primary_dev && slave_dev != standby_dev)
+		return -ENODEV;
+
+	return 0;
+}
+
+static int net_failover_slave_unregister(struct net_device *slave_dev,
+					 struct net_device *failover_dev)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct net_failover_info *nfo_info;
+	bool slave_is_standby;
+
+	nfo_info = netdev_priv(failover_dev);
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+
+	vlan_vids_del_by_dev(slave_dev, failover_dev);
+	dev_uc_unsync(slave_dev, failover_dev);
+	dev_mc_unsync(slave_dev, failover_dev);
+	dev_close(slave_dev);
+
+	nfo_info = netdev_priv(failover_dev);
+	dev_get_stats(failover_dev, &nfo_info->failover_stats);
+
+	slave_is_standby = slave_dev->dev.parent == failover_dev->dev.parent;
+	if (slave_is_standby) {
+		RCU_INIT_POINTER(nfo_info->standby_dev, NULL);
+	} else {
+		RCU_INIT_POINTER(nfo_info->primary_dev, NULL);
+		if (standby_dev) {
+			failover_dev->min_mtu = standby_dev->min_mtu;
+			failover_dev->max_mtu = standby_dev->max_mtu;
+		}
+	}
+
+	dev_put(slave_dev);
+
+	net_failover_compute_features(failover_dev);
+
+	netdev_info(failover_dev, "failover %s slave:%s unregistered\n",
+		    slave_is_standby ? "standby" : "primary", slave_dev->name);
+
+	return 0;
+}
+
+static int net_failover_slave_link_change(struct net_device *slave_dev,
+					  struct net_device *failover_dev)
+{
+	struct net_device *primary_dev, *standby_dev;
+	struct net_failover_info *nfo_info;
+
+	nfo_info = netdev_priv(failover_dev);
+
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+
+	if (slave_dev != primary_dev && slave_dev != standby_dev)
+		return -ENODEV;
+
+	if ((primary_dev && net_failover_xmit_ready(primary_dev)) ||
+	    (standby_dev && net_failover_xmit_ready(standby_dev))) {
+		netif_carrier_on(failover_dev);
+		netif_tx_wake_all_queues(failover_dev);
+	} else {
+		dev_get_stats(failover_dev, &nfo_info->failover_stats);
+		netif_carrier_off(failover_dev);
+		netif_tx_stop_all_queues(failover_dev);
+	}
+
+	net_failover_lower_state_changed(slave_dev, primary_dev, standby_dev);
+
+	return 0;
+}
+
+static int net_failover_slave_name_change(struct net_device *slave_dev,
+					  struct net_device *failover_dev)
+{
+	struct net_device *primary_dev, *standby_dev;
+	struct net_failover_info *nfo_info;
+
+	nfo_info = netdev_priv(failover_dev);
+
+	primary_dev = rtnl_dereference(nfo_info->primary_dev);
+	standby_dev = rtnl_dereference(nfo_info->standby_dev);
+
+	if (slave_dev != primary_dev && slave_dev != standby_dev)
+		return -ENODEV;
+
+	/* We need to bring up the slave after the rename by udev in case
+	 * open failed with EBUSY when it was registered.
+	 */
+	dev_open(slave_dev);
+
+	return 0;
+}
+
+static struct failover_ops net_failover_ops = {
+	.slave_pre_register	= net_failover_slave_pre_register,
+	.slave_register		= net_failover_slave_register,
+	.slave_pre_unregister	= net_failover_slave_pre_unregister,
+	.slave_unregister	= net_failover_slave_unregister,
+	.slave_link_change	= net_failover_slave_link_change,
+	.slave_name_change	= net_failover_slave_name_change,
+	.slave_handle_frame	= net_failover_handle_frame,
+};
+
+/**
+ * net_failover_create - Create and register a failover instance
+ *
+ * @dev: standby netdev
+ *
+ * Creates a failover netdev and registers a failover instance for a standby
+ * netdev. Used by paravirtual drivers that use 3-netdev model.
+ * The failover netdev acts as a master device and controls 2 slave devices -
+ * the original standby netdev and a VF netdev with the same MAC gets
+ * registered as primary netdev.
+ *
+ * Return: pointer to failover instance
+ */
+struct failover *net_failover_create(struct net_device *standby_dev)
+{
+	struct device *dev = standby_dev->dev.parent;
+	struct net_device *failover_dev;
+	struct failover *failover;
+	int err;
+
+	/* Alloc at least 2 queues, for now we are going with 16 assuming
+	 * that VF devices being enslaved won't have too many queues.
+	 */
+	failover_dev = alloc_etherdev_mq(sizeof(struct net_failover_info), 16);
+	if (!failover_dev) {
+		dev_err(dev, "Unable to allocate failover_netdev!\n");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	dev_net_set(failover_dev, dev_net(standby_dev));
+	SET_NETDEV_DEV(failover_dev, dev);
+
+	failover_dev->netdev_ops = &failover_dev_ops;
+	failover_dev->ethtool_ops = &failover_ethtool_ops;
+
+	/* Initialize the device options */
+	failover_dev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
+	failover_dev->priv_flags &= ~(IFF_XMIT_DST_RELEASE |
+				       IFF_TX_SKB_SHARING);
+
+	/* don't acquire failover netdev's netif_tx_lock when transmitting */
+	failover_dev->features |= NETIF_F_LLTX;
+
+	/* Don't allow failover devices to change network namespaces. */
+	failover_dev->features |= NETIF_F_NETNS_LOCAL;
+
+	failover_dev->hw_features = FAILOVER_VLAN_FEATURES |
+				    NETIF_F_HW_VLAN_CTAG_TX |
+				    NETIF_F_HW_VLAN_CTAG_RX |
+				    NETIF_F_HW_VLAN_CTAG_FILTER;
+
+	failover_dev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
+	failover_dev->features |= failover_dev->hw_features;
+
+	memcpy(failover_dev->dev_addr, standby_dev->dev_addr,
+	       failover_dev->addr_len);
+
+	failover_dev->min_mtu = standby_dev->min_mtu;
+	failover_dev->max_mtu = standby_dev->max_mtu;
+
+	err = register_netdev(failover_dev);
+	if (err) {
+		dev_err(dev, "Unable to register failover_dev!\n");
+		goto err_register_netdev;
+	}
+
+	netif_carrier_off(failover_dev);
+
+	failover = failover_register(failover_dev, &net_failover_ops);
+	if (IS_ERR(failover))
+		goto err_failover_register;
+
+	return failover;
+
+err_failover_register:
+	unregister_netdev(failover_dev);
+err_register_netdev:
+	free_netdev(failover_dev);
+
+	return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(net_failover_create);
+
+/**
+ * net_failover_destroy - Destroy a failover instance
+ *
+ * @failover: pointer to failover instance
+ *
+ * Unregisters any slave netdevs associated with the failover instance by
+ * calling failover_slave_unregister().
+ * unregisters the failover instance itself and finally frees the failover
+ * netdev. Used by paravirtual drivers that use 3-netdev model.
+ *
+ */
+void net_failover_destroy(struct failover *failover)
+{
+	struct net_failover_info *nfo_info;
+	struct net_device *failover_dev;
+	struct net_device *slave_dev;
+
+	if (!failover)
+		return;
+
+	failover_dev = rcu_dereference(failover->failover_dev);
+	nfo_info = netdev_priv(failover_dev);
+
+	netif_device_detach(failover_dev);
+
+	rtnl_lock();
+
+	slave_dev = rtnl_dereference(nfo_info->primary_dev);
+	if (slave_dev)
+		failover_slave_unregister(slave_dev);
+
+	slave_dev = rtnl_dereference(nfo_info->standby_dev);
+	if (slave_dev)
+		failover_slave_unregister(slave_dev);
+
+	failover_unregister(failover);
+
+	unregister_netdevice(failover_dev);
+
+	rtnl_unlock();
+
+	free_netdev(failover_dev);
+}
+EXPORT_SYMBOL_GPL(net_failover_destroy);
+
+static __init int
+net_failover_init(void)
+{
+	return 0;
+}
+module_init(net_failover_init);
+
+static __exit
+void net_failover_exit(void)
+{
+}
+module_exit(net_failover_exit);
+
+MODULE_DESCRIPTION("Failover driver for Paravirtual drivers");
+MODULE_LICENSE("GPL v2");

drivers/net/virtio_net.c

@@ -30,8 +30,11 @@
 #include <linux/cpu.h>
 #include <linux/average.h>
 #include <linux/filter.h>
+#include <linux/netdevice.h>
+#include <linux/pci.h>
 #include <net/route.h>
 #include <net/xdp.h>
+#include <net/net_failover.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -210,6 +213,9 @@ struct virtnet_info {
 	u32 speed;
 
 	unsigned long guest_offloads;
+
+	/* failover when STANDBY feature enabled */
+	struct failover *failover;
 };
 
 struct padded_vnet_hdr {
@@ -1554,6 +1560,9 @@ static int virtnet_set_mac_address(struct net_device *dev, void *p)
 	struct sockaddr *addr;
 	struct scatterlist sg;
 
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STANDBY))
+		return -EOPNOTSUPP;
+
 	addr = kmemdup(p, sizeof(*addr), GFP_KERNEL);
 	if (!addr)
 		return -ENOMEM;
@@ -2337,6 +2346,22 @@ static int virtnet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
 	}
 }
 
+static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
+				      size_t len)
+{
+	struct virtnet_info *vi = netdev_priv(dev);
+	int ret;
+
+	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_STANDBY))
+		return -EOPNOTSUPP;
+
+	ret = snprintf(buf, len, "sby");
+	if (ret >= len)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -2354,6 +2379,7 @@ static const struct net_device_ops virtnet_netdev = {
 	.ndo_xdp_xmit		= virtnet_xdp_xmit,
 	.ndo_xdp_flush		= virtnet_xdp_flush,
 	.ndo_features_check	= passthru_features_check,
+	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
 };
 
 static void virtnet_config_changed_work(struct work_struct *work)
@@ -2907,10 +2933,16 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	virtnet_init_settings(dev);
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_STANDBY)) {
+		vi->failover = net_failover_create(vi->dev);
+		if (IS_ERR(vi->failover))
+			goto free_vqs;
+	}
+
 	err = register_netdev(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");
-		goto free_vqs;
+		goto free_failover;
 	}
 
 	virtio_device_ready(vdev);
@@ -2947,6 +2979,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	vi->vdev->config->reset(vdev);
 
 	unregister_netdev(dev);
+free_failover:
+	net_failover_destroy(vi->failover);
 free_vqs:
 	cancel_delayed_work_sync(&vi->refill);
 	free_receive_page_frags(vi);
@@ -2981,6 +3015,8 @@ static void virtnet_remove(struct virtio_device *vdev)
 
 	unregister_netdev(vi->dev);
 
+	net_failover_destroy(vi->failover);
+
 	remove_vq_common(vi);
 
 	free_netdev(vi->dev);
@@ -3030,7 +3066,7 @@ static struct virtio_device_id id_table[] = {
 	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
 	VIRTIO_NET_F_CTRL_MAC_ADDR, \
 	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
-	VIRTIO_NET_F_SPEED_DUPLEX
+	VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_STANDBY
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,

include/linux/netdevice.h

@@ -1425,6 +1425,8 @@ struct net_device_ops {
  *	entity (i.e. the master device for bridged veth)
  * @IFF_MACSEC: device is a MACsec device
  * @IFF_NO_RX_HANDLER: device doesn't support the rx_handler hook
+ * @IFF_FAILOVER: device is a failover master device
+ * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
  */
 enum netdev_priv_flags {
 	IFF_802_1Q_VLAN			= 1<<0,
@@ -1454,6 +1456,8 @@ enum netdev_priv_flags {
 	IFF_PHONY_HEADROOM		= 1<<24,
 	IFF_MACSEC			= 1<<25,
 	IFF_NO_RX_HANDLER		= 1<<26,
+	IFF_FAILOVER			= 1<<27,
+	IFF_FAILOVER_SLAVE		= 1<<28,
 };
 
 #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
@@ -1482,6 +1486,8 @@ enum netdev_priv_flags {
 #define IFF_RXFH_CONFIGURED		IFF_RXFH_CONFIGURED
 #define IFF_MACSEC			IFF_MACSEC
 #define IFF_NO_RX_HANDLER		IFF_NO_RX_HANDLER
+#define IFF_FAILOVER			IFF_FAILOVER
+#define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
 
 /**
  *	struct net_device - The DEVICE structure.
@@ -4336,6 +4342,16 @@ static inline bool netif_is_rxfh_configured(const struct net_device *dev)
 	return dev->priv_flags & IFF_RXFH_CONFIGURED;
 }
 
+static inline bool netif_is_failover(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_FAILOVER;
+}
+
+static inline bool netif_is_failover_slave(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_FAILOVER_SLAVE;
+}
+
 /* This device needs to keep skb dst for qdisc enqueue or ndo_start_xmit() */
 static inline void netif_keep_dst(struct net_device *dev)
 {

include/net/failover.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2018, Intel Corporation. */
+
+#ifndef _FAILOVER_H
+#define _FAILOVER_H
+
+#include <linux/netdevice.h>
+
+struct failover_ops {
+	int (*slave_pre_register)(struct net_device *slave_dev,
+				  struct net_device *failover_dev);
+	int (*slave_register)(struct net_device *slave_dev,
+			      struct net_device *failover_dev);
+	int (*slave_pre_unregister)(struct net_device *slave_dev,
+				    struct net_device *failover_dev);
+	int (*slave_unregister)(struct net_device *slave_dev,
+				struct net_device *failover_dev);
+	int (*slave_link_change)(struct net_device *slave_dev,
+				 struct net_device *failover_dev);
+	int (*slave_name_change)(struct net_device *slave_dev,
+				 struct net_device *failover_dev);
+	rx_handler_result_t (*slave_handle_frame)(struct sk_buff **pskb);
+};
+
+struct failover {
+	struct list_head list;
+	struct net_device __rcu *failover_dev;
+	struct failover_ops __rcu *ops;
+};
+
+struct failover *failover_register(struct net_device *dev,
+				   struct failover_ops *ops);
+void failover_unregister(struct failover *failover);
+int failover_slave_unregister(struct net_device *slave_dev);
+
+#endif /* _FAILOVER_H */

include/net/net_failover.h

+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2018, Intel Corporation. */
+
+#ifndef _NET_FAILOVER_H
+#define _NET_FAILOVER_H
+
+#include <net/failover.h>
+
+/* failover state */
+struct net_failover_info {
+	/* primary netdev with same MAC */
+	struct net_device __rcu *primary_dev;
+
+	/* standby netdev */
+	struct net_device __rcu *standby_dev;
+
+	/* primary netdev stats */
+	struct rtnl_link_stats64 primary_stats;
+
+	/* standby netdev stats */
+	struct rtnl_link_stats64 standby_stats;
+
+	/* aggregated stats */
+	struct rtnl_link_stats64 failover_stats;
+
+	/* spinlock while updating stats */
+	spinlock_t stats_lock;
+};
+
+struct failover *net_failover_create(struct net_device *standby_dev);
+void net_failover_destroy(struct failover *failover);
+
+#define FAILOVER_VLAN_FEATURES	(NETIF_F_HW_CSUM | NETIF_F_SG | \
+				 NETIF_F_FRAGLIST | NETIF_F_ALL_TSO | \
+				 NETIF_F_HIGHDMA | NETIF_F_LRO)
+
+#define FAILOVER_ENC_FEATURES	(NETIF_F_HW_CSUM | NETIF_F_SG | \
+				 NETIF_F_RXCSUM | NETIF_F_ALL_TSO)
+
+#endif /* _NET_FAILOVER_H */

include/uapi/linux/virtio_net.h

@@ -57,6 +57,9 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_STANDBY	  62	/* Act as standby for another device
+					 * with the same MAC.
+					 */
 #define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
 
 #ifndef VIRTIO_NET_NO_LEGACY

net/Kconfig

@@ -432,6 +432,19 @@ config MAY_USE_DEVLINK
 config PAGE_POOL
        bool
 
+config FAILOVER
+	tristate "Generic failover module"
+	help
+	  The failover module provides a generic interface for paravirtual
+	  drivers to register a netdev and a set of ops with a failover
+	  instance. The ops are used as event handlers that get called to
+	  handle netdev register/unregister/link change/name change events
+	  on slave pci ethernet devices with the same mac address as the
+	  failover netdev. This enables paravirtual drivers to use a
+	  VF as an accelerated low latency datapath. It also allows live
+	  migration of VMs with direct attached VFs by failing over to the
+	  paravirtual datapath when the VF is unplugged.
+
 endif   # if NET
 
 # Used by archs to tell that they support BPF JIT compiler plus which flavour.

net/core/Makefile

@@ -31,3 +31,4 @@ obj-$(CONFIG_DST_CACHE) += dst_cache.o
 obj-$(CONFIG_HWBM) += hwbm.o
 obj-$(CONFIG_NET_DEVLINK) += devlink.o
 obj-$(CONFIG_GRO_CELLS) += gro_cells.o
+obj-$(CONFIG_FAILOVER) += failover.o

net/core/failover.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018, Intel Corporation. */
+
+/* A common module to handle registrations and notifications for paravirtual
+ * drivers to enable accelerated datapath and support VF live migration.
+ *
+ * The notifier and event handling code is based on netvsc driver.
+ */
+
+#include <linux/module.h>
+#include <linux/etherdevice.h>
+#include <uapi/linux/if_arp.h>
+#include <linux/rtnetlink.h>
+#include <linux/if_vlan.h>
+#include <net/failover.h>
+
+static LIST_HEAD(failover_list);
+static DEFINE_SPINLOCK(failover_lock);
+
+static struct net_device *failover_get_bymac(u8 *mac, struct failover_ops **ops)
+{
+	struct net_device *failover_dev;
+	struct failover *failover;
+
+	spin_lock(&failover_lock);
+	list_for_each_entry(failover, &failover_list, list) {
+		failover_dev = rtnl_dereference(failover->failover_dev);
+		if (ether_addr_equal(failover_dev->perm_addr, mac)) {
+			*ops = rtnl_dereference(failover->ops);
+			spin_unlock(&failover_lock);
+			return failover_dev;
+		}
+	}
+	spin_unlock(&failover_lock);
+	return NULL;
+}
+
+/**
+ * failover_slave_register - Register a slave netdev
+ *
+ * @slave_dev: slave netdev that is being registered
+ *
+ * Registers a slave device to a failover instance. Only ethernet devices
+ * are supported.
+ */
+static int failover_slave_register(struct net_device *slave_dev)
+{
+	struct netdev_lag_upper_info lag_upper_info;
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+	int err;
+
+	if (slave_dev->type != ARPHRD_ETHER)
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (fops && fops->slave_pre_register &&
+	    fops->slave_pre_register(slave_dev, failover_dev))
+		goto done;
+
+	err = netdev_rx_handler_register(slave_dev, fops->slave_handle_frame,
+					 failover_dev);
+	if (err) {
+		netdev_err(slave_dev, "can not register failover rx handler (err = %d)\n",
+			   err);
+		goto done;
+	}
+
+	lag_upper_info.tx_type = NETDEV_LAG_TX_TYPE_ACTIVEBACKUP;
+	err = netdev_master_upper_dev_link(slave_dev, failover_dev, NULL,
+					   &lag_upper_info, NULL);
+	if (err) {
+		netdev_err(slave_dev, "can not set failover device %s (err = %d)\n",
+			   failover_dev->name, err);
+		goto err_upper_link;
+	}
+
+	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
+
+	if (fops && fops->slave_register &&
+	    !fops->slave_register(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+err_upper_link:
+	netdev_rx_handler_unregister(slave_dev);
+done:
+	return NOTIFY_DONE;
+}
+
+/**
+ * failover_slave_unregister - Unregister a slave netdev
+ *
+ * @slave_dev: slave netdev that is being unregistered
+ *
+ * Unregisters a slave device from a failover instance.
+ */
+int failover_slave_unregister(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (fops && fops->slave_pre_unregister &&
+	    fops->slave_pre_unregister(slave_dev, failover_dev))
+		goto done;
+
+	netdev_rx_handler_unregister(slave_dev);
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+
+	if (fops && fops->slave_unregister &&
+	    !fops->slave_unregister(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+EXPORT_SYMBOL_GPL(failover_slave_unregister);
+
+static int failover_slave_link_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	if (fops && fops->slave_link_change &&
+	    !fops->slave_link_change(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int failover_slave_name_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	if (fops && fops->slave_name_change &&
+	    !fops->slave_name_change(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int
+failover_event(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
+
+	/* Skip parent events */
+	if (netif_is_failover(event_dev))
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_REGISTER:
+		return failover_slave_register(event_dev);
+	case NETDEV_UNREGISTER:
+		return failover_slave_unregister(event_dev);
+	case NETDEV_UP:
+	case NETDEV_DOWN:
+	case NETDEV_CHANGE:
+		return failover_slave_link_change(event_dev);
+	case NETDEV_CHANGENAME:
+		return failover_slave_name_change(event_dev);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block failover_notifier = {
+	.notifier_call = failover_event,
+};
+
+static void
+failover_existing_slave_register(struct net_device *failover_dev)
+{
+	struct net *net = dev_net(failover_dev);
+	struct net_device *dev;
+
+	rtnl_lock();
+	for_each_netdev(net, dev) {
+		if (netif_is_failover(dev))
+			continue;
+		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
+			failover_slave_register(dev);
+	}
+	rtnl_unlock();
+}
+
+/**
+ * failover_register - Register a failover instance
+ *
+ * @dev: failover netdev
+ * @ops: failover ops
+ *
+ * Allocate and register a failover instance for a failover netdev. ops
+ * provides handlers for slave device register/unregister/link change/
+ * name change events.
+ *
+ * Return: pointer to failover instance
+ */
+struct failover *failover_register(struct net_device *dev,
+				   struct failover_ops *ops)
+{
+	struct failover *failover;
+
+	if (dev->type != ARPHRD_ETHER)
+		return ERR_PTR(-EINVAL);
+
+	failover = kzalloc(sizeof(*failover), GFP_KERNEL);
+	if (!failover)
+		return ERR_PTR(-ENOMEM);
+
+	rcu_assign_pointer(failover->ops, ops);
+	dev_hold(dev);
+	dev->priv_flags |= IFF_FAILOVER;
+	rcu_assign_pointer(failover->failover_dev, dev);
+
+	spin_lock(&failover_lock);
+	list_add_tail(&failover->list, &failover_list);
+	spin_unlock(&failover_lock);
+
+	netdev_info(dev, "failover master:%s registered\n", dev->name);
+
+	failover_existing_slave_register(dev);
+
+	return failover;
+}
+EXPORT_SYMBOL_GPL(failover_register);
+
+/**
+ * failover_unregister - Unregister a failover instance
+ *
+ * @failover: pointer to failover instance
+ *
+ * Unregisters and frees a failover instance.
+ */
+void failover_unregister(struct failover *failover)
+{
+	struct net_device *failover_dev;
+
+	failover_dev = rcu_dereference(failover->failover_dev);
+
+	netdev_info(failover_dev, "failover master:%s unregistered\n",
+		    failover_dev->name);
+
+	failover_dev->priv_flags &= ~IFF_FAILOVER;
+	dev_put(failover_dev);
+
+	spin_lock(&failover_lock);
+	list_del(&failover->list);
+	spin_unlock(&failover_lock);
+
+	kfree(failover);
+}
+EXPORT_SYMBOL_GPL(failover_unregister);
+
+static __init int
+failover_init(void)
+{
+	register_netdevice_notifier(&failover_notifier);
+
+	return 0;
+}
+module_init(failover_init);
+
+static __exit
+void failover_exit(void)
+{
+	unregister_netdevice_notifier(&failover_notifier);
+}
+module_exit(failover_exit);
+
+MODULE_DESCRIPTION("Generic failover infrastructure/interface");
+MODULE_LICENSE("GPL v2");