diff mbox series

[net-next,v10,2/4] net: Introduce generic failover module

Message ID 1525731046-10989-3-git-send-email-sridhar.samudrala@intel.com
State Changes Requested, archived
Delegated to: David Miller
Headers show
Series Enable virtio_net to act as a standby for a passthru device | expand

Commit Message

Samudrala, Sridhar May 7, 2018, 10:10 p.m. UTC 
This 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.

It exposes 2 sets of interfaces to the paravirtual drivers.
1. For paravirtual drivers like virtio_net that use 3 netdev model, the
   the failover module provides interfaces to create/destroy additional
   master netdev and all the slave events are managed internally.
          net_failover_create()
          net_failover_destroy()
   A failover netdev is created that acts 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.
2. For existing netvsc driver that uses 2 netdev model, no master netdev
   is created. The paravirtual driver registers each instance of netvsc
   as a 'failover' netdev  along with a set of ops to manage the slave
   events. There is no 'standby' netdev in this model. A passthru/vf device
   with the same MAC gets registered as 'primary' netdev.
          net_failover_register()
          net_failover_unregister()

Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
---
 MAINTAINERS                |    7 +
 include/linux/netdevice.h  |   16 +
 include/net/net_failover.h |   52 +++
 net/Kconfig                |   10 +
 net/core/Makefile          |    1 +
 net/core/net_failover.c    | 1044 ++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 1130 insertions(+)
 create mode 100644 include/net/net_failover.h
 create mode 100644 net/core/net_failover.c

Comments

Randy Dunlap May 7, 2018, 10:39 p.m. UTC | #1 
Hi,

On 05/07/2018 03:10 PM, Sridhar Samudrala wrote:
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
> ---
>  MAINTAINERS                |    7 +
>  include/linux/netdevice.h  |   16 +
>  include/net/net_failover.h |   52 +++
>  net/Kconfig                |   10 +
>  net/core/Makefile          |    1 +
>  net/core/net_failover.c    | 1044 ++++++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 1130 insertions(+)
>  create mode 100644 include/net/net_failover.h
>  create mode 100644 net/core/net_failover.c


> diff --git a/net/Kconfig b/net/Kconfig
> index b62089fb1332..0540856676de 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -429,6 +429,16 @@ config MAY_USE_DEVLINK
>  config PAGE_POOL
>         bool
>  
> +config NET_FAILOVER
> +	tristate "Failover interface"
> +	default m

Need some justification for default m (as opposed to n).

> +	help
> +	  This provides a generic interface for paravirtual drivers to listen
> +	  for netdev register/unregister/link change events from pci ethernet

	                                                         PCI

> +	  devices with the same MAC and takeover their datapath. This also
> +	  enables live migration of a VM with direct attached VF 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.

> diff --git a/net/core/net_failover.c b/net/core/net_failover.c
> new file mode 100644
> index 000000000000..8d60e74e3034
> --- /dev/null
> +++ b/net/core/net_failover.c
> @@ -0,0 +1,1044 @@
> +// 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 and failover
> + * netdev management routines are based on bond/team driver.
> + *
> + */


> +/**
> + * net_failover_create - Create and register a failover instance
> + *
> + * @dev: standby netdev

    * @standby_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 net_failover *net_failover_create(struct net_device *standby_dev)
> +{
> +	struct device *dev = standby_dev->dev.parent;
> +	struct net_device *failover_dev;
> +	struct net_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 = net_failover_register(failover_dev, NULL);
> +	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);
Stephen Hemminger May 7, 2018, 11:46 p.m. UTC | #2 
On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:

> This 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.
> 
> It exposes 2 sets of interfaces to the paravirtual drivers.
> 1. For paravirtual drivers like virtio_net that use 3 netdev model, the
>    the failover module provides interfaces to create/destroy additional
>    master netdev and all the slave events are managed internally.
>           net_failover_create()
>           net_failover_destroy()
>    A failover netdev is created that acts 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.
> 2. For existing netvsc driver that uses 2 netdev model, no master netdev
>    is created. The paravirtual driver registers each instance of netvsc
>    as a 'failover' netdev  along with a set of ops to manage the slave
>    events. There is no 'standby' netdev in this model. A passthru/vf device
>    with the same MAC gets registered as 'primary' netdev.
>           net_failover_register()
>           net_failover_unregister()
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>

You are conflating the net_failover device (3 device model) with
the generic network failover infrastructure into one file. There should be two
seperate files net/core/failover.c and drivers/net/failover.c which splits
the work into two parts (and acts a check for the api).
Stephen Hemminger May 7, 2018, 11:53 p.m. UTC | #3 
On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:

> +static struct net_device *net_failover_get_bymac(u8 *mac,
> +						 struct net_failover_ops **ops)
> +{
> +	struct net_device *failover_dev;
> +	struct net_failover *failover;
> +
> +	spin_lock(&net_failover_lock);
> +	list_for_each_entry(failover, &net_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(&net_failover_lock);
> +			return failover_dev;
> +		}
> +	}
> +	spin_unlock(&net_failover_lock);
> +	return NULL;
> +}

This is broken if non-ethernet devices such as Infiniband are present.
Stephen Hemminger May 7, 2018, 11:59 p.m. UTC | #4 
On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:

> +	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);
> +

The order of these is backwards, you want to sync addresses before bringing up.
Also, doing it this way does not allow udev/systemd the chance to rename VF devices.

The complexity of this whole failover mechanism does not make life easier,
more reliable, or safer for netvsc. I though that was the whole reason for having
common code.
Samudrala, Sridhar May 8, 2018, 12:11 a.m. UTC | #5 
On 5/7/2018 4:59 PM, Stephen Hemminger wrote:
> On Mon,  7 May 2018 15:10:44 -0700
> Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:
>
>> +	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);
>> +
> The order of these is backwards, you want to sync addresses before bringing up.
> Also, doing it this way does not allow udev/systemd the chance to rename VF devices.

During my testing, i noticed that dev_open() may fail with EBUSY in certain scenarios,
If so, the opening of the slave is handled after the rename via the NETDEV_CHANGENAME
event handler.

>
> The complexity of this whole failover mechanism does not make life easier,
> more reliable, or safer for netvsc. I though that was the whole reason for having
> common code.

netvsc doesn't go through this code.

	if (nfo_ops && nfo_ops->slave_register)
                 return nfo_ops->slave_register(slave_dev, failover_dev);

So there is no change in event handling for netvsc 2-netdev model.
Samudrala, Sridhar May 8, 2018, 12:24 a.m. UTC | #6 
On 5/7/2018 4:53 PM, Stephen Hemminger wrote:
> On Mon,  7 May 2018 15:10:44 -0700
> Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:
>
>> +static struct net_device *net_failover_get_bymac(u8 *mac,
>> +						 struct net_failover_ops **ops)
>> +{
>> +	struct net_device *failover_dev;
>> +	struct net_failover *failover;
>> +
>> +	spin_lock(&net_failover_lock);
>> +	list_for_each_entry(failover, &net_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(&net_failover_lock);
>> +			return failover_dev;
>> +		}
>> +	}
>> +	spin_unlock(&net_failover_lock);
>> +	return NULL;
>> +}
> This is broken if non-ethernet devices such as Infiniband are present.

There is check to make sure that a slave and failover devices are of the same type in
net_failover_slave_register()

	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
         if (!failover_dev)
                 goto done;

         if (failover_dev->type != slave_dev->type)
                 goto done;

Do you think this is not good enough? I had an explicit check for ARPHRD_ETHER in
earlier patchsets, but removed it based on Jiri's comment.
kernel test robot May 8, 2018, 9:02 a.m. UTC | #7 
Hi Sridhar,

I love your patch! Perhaps something to improve:

[auto build test WARNING on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Sridhar-Samudrala/Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device/20180508-123531
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

>> net/core/net_failover.c:868:16: sparse: Using plain integer as NULL pointer
   net/core/net_failover.c:115:12: sparse: context imbalance in 'net_failover_select_queue' - wrong count at exit

vim +868 net/core/net_failover.c

   828	
   829	/**
   830	 * net_failover_register - Register a failover instance
   831	 *
   832	 * @dev: failover or standby netdev
   833	 * @ops: failover ops
   834	 *
   835	 * Paravirtual drivers supporting 3-netdev model call this routine indirectly
   836	 * via net_failover_create(). It passes failover netdev and ops will be NULL
   837	 * as the slave events are handled internally.
   838	 * Paravirtual drivers supporting 2-netdev model call this routine by passing
   839	 * standby netdev and ops that are called to handle slave register/unregister/
   840	 * link change events.
   841	 *
   842	 * Return: pointer to failover instance
   843	 */
   844	struct net_failover *net_failover_register(struct net_device *dev,
   845						   struct net_failover_ops *ops)
   846	{
   847		struct net_failover *failover;
   848	
   849		failover = kzalloc(sizeof(*failover), GFP_KERNEL);
   850		if (!failover)
   851			return ERR_PTR(-ENOMEM);
   852	
   853		rcu_assign_pointer(failover->ops, ops);
   854		dev_hold(dev);
   855		dev->priv_flags |= IFF_FAILOVER;
   856		rcu_assign_pointer(failover->failover_dev, dev);
   857	
   858		spin_lock(&net_failover_lock);
   859		list_add_tail(&failover->list, &net_failover_list);
   860		spin_unlock(&net_failover_lock);
   861	
   862		netdev_info(dev, "failover master:%s registered\n", dev->name);
   863	
   864		net_failover_existing_slave_register(dev);
   865	
   866		return failover;
   867	
 > 868		return 0;
   869	}
   870	EXPORT_SYMBOL_GPL(net_failover_register);
   871	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
Samudrala, Sridhar May 11, 2018, 3:40 p.m. UTC | #8 
On 5/7/2018 4:46 PM, Stephen Hemminger wrote:
> On Mon,  7 May 2018 15:10:44 -0700
> Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:
>
>> This 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.
>>
>> It exposes 2 sets of interfaces to the paravirtual drivers.
>> 1. For paravirtual drivers like virtio_net that use 3 netdev model, the
>>     the failover module provides interfaces to create/destroy additional
>>     master netdev and all the slave events are managed internally.
>>            net_failover_create()
>>            net_failover_destroy()
>>     A failover netdev is created that acts 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.
>> 2. For existing netvsc driver that uses 2 netdev model, no master netdev
>>     is created. The paravirtual driver registers each instance of netvsc
>>     as a 'failover' netdev  along with a set of ops to manage the slave
>>     events. There is no 'standby' netdev in this model. A passthru/vf device
>>     with the same MAC gets registered as 'primary' netdev.
>>            net_failover_register()
>>            net_failover_unregister()
>>
>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
> You are conflating the net_failover device (3 device model) with
> the generic network failover infrastructure into one file. There should be two
> seperate files net/core/failover.c and drivers/net/failover.c which splits
> the work into two parts (and acts a check for the api).

OK. I started splitting net_failover.c into 2 files.

net/core/failover.c (CONFIG_FAILOVER)
- implements the generic failover infrastructure that exports failover_register(),
   failover_unregister() and failover_slave_unregister() as the API that will be
   used by netvsc and the net_failover drivers(3 netdev model)

drivers/net/net_failover.c (CONFIG_NET_FAILOVER)
- implements the net_failover netdev as the upper dev for the 3-netdev model and
   exports net_failover_create() and net_failover_destroy() as the API that is
   used by virtio_net.

HYPERV_NET and NET_FAILOVER selects FAILOVER
VIRTIO_NET selects NET_FAILOVER

Does this look good? Any better suggestion for the prefix to be used for generic
network failover api rather than 'failover'?
Samudrala, Sridhar May 11, 2018, 3:43 p.m. UTC | #9 
On 5/7/2018 3:39 PM, Randy Dunlap wrote:
> Hi,
>
> On 05/07/2018 03:10 PM, Sridhar Samudrala wrote:
>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
>> ---
>>   MAINTAINERS                |    7 +
>>   include/linux/netdevice.h  |   16 +
>>   include/net/net_failover.h |   52 +++
>>   net/Kconfig                |   10 +
>>   net/core/Makefile          |    1 +
>>   net/core/net_failover.c    | 1044 ++++++++++++++++++++++++++++++++++++++++++++
>>   6 files changed, 1130 insertions(+)
>>   create mode 100644 include/net/net_failover.h
>>   create mode 100644 net/core/net_failover.c
>
>> diff --git a/net/Kconfig b/net/Kconfig
>> index b62089fb1332..0540856676de 100644
>> --- a/net/Kconfig
>> +++ b/net/Kconfig
>> @@ -429,6 +429,16 @@ config MAY_USE_DEVLINK
>>   config PAGE_POOL
>>          bool
>>   
>> +config NET_FAILOVER
>> +	tristate "Failover interface"
>> +	default m
> Need some justification for default m (as opposed to n).

default n should be fine.  It will get selected automatically when virtio_net or
netvsc are enabled. will fix in the next revision.


>
>
Michael S. Tsirkin May 11, 2018, 5:15 p.m. UTC | #10 
On Mon, May 07, 2018 at 05:24:27PM -0700, Samudrala, Sridhar wrote:
> 
> 
> On 5/7/2018 4:53 PM, Stephen Hemminger wrote:
> > On Mon,  7 May 2018 15:10:44 -0700
> > Sridhar Samudrala <sridhar.samudrala@intel.com> wrote:
> > 
> > > +static struct net_device *net_failover_get_bymac(u8 *mac,
> > > +						 struct net_failover_ops **ops)
> > > +{
> > > +	struct net_device *failover_dev;
> > > +	struct net_failover *failover;
> > > +
> > > +	spin_lock(&net_failover_lock);
> > > +	list_for_each_entry(failover, &net_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(&net_failover_lock);
> > > +			return failover_dev;
> > > +		}
> > > +	}
> > > +	spin_unlock(&net_failover_lock);
> > > +	return NULL;
> > > +}
> > This is broken if non-ethernet devices such as Infiniband are present.
> 
> There is check to make sure that a slave and failover devices are of the same type in
> net_failover_slave_register()
> 
> 	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
>         if (!failover_dev)
>                 goto done;
> 
>         if (failover_dev->type != slave_dev->type)
>                 goto done;
> 
> Do you think this is not good enough? I had an explicit check for ARPHRD_ETHER in
> earlier patchsets, but removed it based on Jiri's comment.

Right but how is ether_addr_equal supposed to work if types are
identical but not ethernet?

This can also benefit from a comment referring to the check in
net_failover_slave_register.
Michael S. Tsirkin May 11, 2018, 6:09 p.m. UTC | #11 
On Mon, May 07, 2018 at 03:39:19PM -0700, Randy Dunlap wrote:
> Hi,
> 
> On 05/07/2018 03:10 PM, Sridhar Samudrala wrote:
> > 
> > Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
> > ---
> >  MAINTAINERS                |    7 +
> >  include/linux/netdevice.h  |   16 +
> >  include/net/net_failover.h |   52 +++
> >  net/Kconfig                |   10 +
> >  net/core/Makefile          |    1 +
> >  net/core/net_failover.c    | 1044 ++++++++++++++++++++++++++++++++++++++++++++
> >  6 files changed, 1130 insertions(+)
> >  create mode 100644 include/net/net_failover.h
> >  create mode 100644 net/core/net_failover.c
> 
> 
> > diff --git a/net/Kconfig b/net/Kconfig
> > index b62089fb1332..0540856676de 100644
> > --- a/net/Kconfig
> > +++ b/net/Kconfig
> > @@ -429,6 +429,16 @@ config MAY_USE_DEVLINK
> >  config PAGE_POOL
> >         bool
> >  
> > +config NET_FAILOVER
> > +	tristate "Failover interface"
> > +	default m
> 
> Need some justification for default m (as opposed to n).

Or one can just leave the default line out.
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index ebe0b9ed7805..83cbd99d8efa 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9638,6 +9638,13 @@  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:	net/core/net_failover.c
+F:	include/net/net_failover.h
+
 NETEFFECT IWARP RNIC DRIVER (IW_NES)
 M:	Faisal Latif <faisal.latif@intel.com>
 L:	linux-rdma@vger.kernel.org
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 46dcb5f7522f..4fff9b5d079e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1421,6 +1421,8 @@  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,
@@ -1450,6 +1452,8 @@  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
@@ -1478,6 +1482,8 @@  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.
@@ -4320,6 +4326,16 @@  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)
 {
diff --git a/include/net/net_failover.h b/include/net/net_failover.h
new file mode 100644
index 000000000000..221c2aff7531
--- /dev/null
+++ b/include/net/net_failover.h
@@ -0,0 +1,52 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2018, Intel Corporation. */
+
+#ifndef _NET_FAILOVER_H
+#define _NET_FAILOVER_H
+
+#include <linux/netdevice.h>
+
+struct net_failover_ops {
+	int (*slave_register)(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);
+};
+
+struct net_failover {
+	struct list_head list;
+	struct net_device __rcu *failover_dev;
+	struct net_failover_ops __rcu *ops;
+};
+
+/* 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 net_failover *net_failover_create(struct net_device *standby_dev);
+void net_failover_destroy(struct net_failover *failover);
+struct net_failover *net_failover_register(struct net_device *dev,
+					   struct net_failover_ops *ops);
+void net_failover_unregister(struct net_failover *failover);
+int net_failover_slave_unregister(struct net_device *slave_dev);
+
+#endif /* _NET_FAILOVER_H */
diff --git a/net/Kconfig b/net/Kconfig
index b62089fb1332..0540856676de 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -429,6 +429,16 @@  config MAY_USE_DEVLINK
 config PAGE_POOL
        bool
 
+config NET_FAILOVER
+	tristate "Failover interface"
+	default m
+	help
+	  This 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. This also
+	  enables live migration of a VM with direct attached VF 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.
diff --git a/net/core/Makefile b/net/core/Makefile
index 7080417f8bc8..283ed9b0e581 100644
--- a/net/core/Makefile
+++ b/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_NET_FAILOVER) += net_failover.o
diff --git a/net/core/net_failover.c b/net/core/net_failover.c
new file mode 100644
index 000000000000..8d60e74e3034
--- /dev/null
+++ b/net/core/net_failover.c
@@ -0,0 +1,1044 @@ 
+// 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 and failover
+ * netdev management routines are based on bond/team driver.
+ *
+ */
+
+#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 LIST_HEAD(net_failover_list);
+static DEFINE_SPINLOCK(net_failover_lock);
+
+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;
+
+	rcu_read_lock();
+	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,
+};
+
+static struct net_device *net_failover_get_bymac(u8 *mac,
+						 struct net_failover_ops **ops)
+{
+	struct net_device *failover_dev;
+	struct net_failover *failover;
+
+	spin_lock(&net_failover_lock);
+	list_for_each_entry(failover, &net_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(&net_failover_lock);
+			return failover_dev;
+		}
+	}
+	spin_unlock(&net_failover_lock);
+	return NULL;
+}
+
+/* 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;
+}
+
+#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)
+
+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);
+}
+
+/**
+ * net_failover_slave_register - Register a slave netdev
+ *
+ * @slave_dev: slave netdev that is being registered
+ *
+ * Registers a slave device to a failover instance. For a 2 netdev model,
+ * this will be primary netdev. In case of a 3 netdev model, it can be a
+ * standby or a primary netdev.
+ *
+ */
+static int net_failover_slave_register(struct net_device *slave_dev)
+{
+	struct net_device *standby_dev, *primary_dev, *failover_dev;
+	struct netdev_lag_upper_info lag_upper_info;
+	struct net_failover_info *nfo_info;
+	struct net_failover_ops *nfo_ops;
+	bool slave_is_standby;
+	u32 orig_mtu;
+	int err;
+
+	ASSERT_RTNL();
+
+	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
+	if (!failover_dev)
+		goto done;
+
+	if (failover_dev->type != slave_dev->type)
+		goto done;
+
+	if (nfo_ops && nfo_ops->slave_register)
+		return nfo_ops->slave_register(slave_dev, failover_dev);
+
+	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");
+		goto done;
+	}
+
+	/* 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)))
+		goto done;
+
+	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);
+		goto done;
+	}
+
+	/* 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;
+	}
+
+	err = netdev_rx_handler_register(slave_dev, net_failover_handle_frame,
+					 failover_dev);
+	if (err) {
+		netdev_err(slave_dev, "can not register failover rx handler (err = %d)\n",
+			   err);
+		goto err_handler_register;
+	}
+
+	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 (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);
+
+	goto done;
+
+err_upper_link:
+	netdev_rx_handler_unregister(slave_dev);
+err_handler_register:
+	vlan_vids_del_by_dev(slave_dev, failover_dev);
+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 NOTIFY_DONE;
+}
+
+/**
+ * net_failover_slave_unregister - Unregister a slave netdev
+ *
+ * @slave_dev: slave netdev that is being unregistered
+ *
+ * Unregisters a slave device from a failover instance. For a 2 netdev model,
+ * this will be primary netdev. In case of a 3 netdev model, it can be a
+ * standby or a primary netdev.
+ *
+ */
+int net_failover_slave_unregister(struct net_device *slave_dev)
+{
+	struct net_device *standby_dev, *primary_dev, *failover_dev;
+	struct net_failover_info *nfo_info;
+	struct net_failover_ops *nfo_ops;
+	bool slave_is_standby;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
+	if (!failover_dev)
+		goto done;
+
+	if (nfo_ops && nfo_ops->slave_unregister)
+		return nfo_ops->slave_unregister(slave_dev, failover_dev);
+
+	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)
+		goto done;
+
+	slave_is_standby = slave_dev->dev.parent == failover_dev->dev.parent;
+
+	netdev_rx_handler_unregister(slave_dev);
+	netdev_upper_dev_unlink(slave_dev, failover_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);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+
+	nfo_info = netdev_priv(failover_dev);
+	net_failover_get_stats(failover_dev, &nfo_info->failover_stats);
+
+	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);
+
+done:
+	return NOTIFY_DONE;
+}
+EXPORT_SYMBOL_GPL(net_failover_slave_unregister);
+
+static int net_failover_slave_link_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev, *primary_dev, *standby_dev;
+	struct net_failover_info *nfo_info;
+	struct net_failover_ops *nfo_ops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
+	if (!failover_dev)
+		goto done;
+
+	if (nfo_ops && nfo_ops->slave_link_change)
+		return nfo_ops->slave_link_change(slave_dev, failover_dev);
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	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)
+		goto done;
+
+	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 {
+		net_failover_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);
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int net_failover_slave_change_name(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev, *primary_dev, *standby_dev;
+	struct net_failover_info *nfo_info;
+	struct net_failover_ops *nfo_ops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = net_failover_get_bymac(slave_dev->perm_addr, &nfo_ops);
+	if (!failover_dev)
+		goto done;
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	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)
+		goto done;
+
+	/* 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);
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int
+net_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 net_failover_slave_register(event_dev);
+	case NETDEV_UNREGISTER:
+		return net_failover_slave_unregister(event_dev);
+	case NETDEV_UP:
+	case NETDEV_DOWN:
+	case NETDEV_CHANGE:
+		return net_failover_slave_link_change(event_dev);
+	case NETDEV_CHANGENAME:
+		return net_failover_slave_change_name(event_dev);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block net_failover_notifier = {
+	.notifier_call = net_failover_event,
+};
+
+static void
+net_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))
+			net_failover_slave_register(dev);
+	}
+	rtnl_unlock();
+}
+
+/**
+ * net_failover_register - Register a failover instance
+ *
+ * @dev: failover or standby netdev
+ * @ops: failover ops
+ *
+ * Paravirtual drivers supporting 3-netdev model call this routine indirectly
+ * via net_failover_create(). It passes failover netdev and ops will be NULL
+ * as the slave events are handled internally.
+ * Paravirtual drivers supporting 2-netdev model call this routine by passing
+ * standby netdev and ops that are called to handle slave register/unregister/
+ * link change events.
+ *
+ * Return: pointer to failover instance
+ */
+struct net_failover *net_failover_register(struct net_device *dev,
+					   struct net_failover_ops *ops)
+{
+	struct net_failover *failover;
+
+	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(&net_failover_lock);
+	list_add_tail(&failover->list, &net_failover_list);
+	spin_unlock(&net_failover_lock);
+
+	netdev_info(dev, "failover master:%s registered\n", dev->name);
+
+	net_failover_existing_slave_register(dev);
+
+	return failover;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(net_failover_register);
+
+/**
+ * net_failover_unregister - Unregister a failover instance
+ *
+ * @failover: pointer to failover instance
+ *
+ * Unregisters and frees a failover instance.
+ */
+void net_failover_unregister(struct net_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(&net_failover_lock);
+	list_del(&failover->list);
+	spin_unlock(&net_failover_lock);
+
+	kfree(failover);
+}
+EXPORT_SYMBOL_GPL(net_failover_unregister);
+
+/**
+ * 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 net_failover *net_failover_create(struct net_device *standby_dev)
+{
+	struct device *dev = standby_dev->dev.parent;
+	struct net_device *failover_dev;
+	struct net_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 = net_failover_register(failover_dev, NULL);
+	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 net_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 net_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)
+		net_failover_slave_unregister(slave_dev);
+
+	slave_dev = rtnl_dereference(nfo_info->standby_dev);
+	if (slave_dev)
+		net_failover_slave_unregister(slave_dev);
+
+	net_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)
+{
+	register_netdevice_notifier(&net_failover_notifier);
+
+	return 0;
+}
+module_init(net_failover_init);
+
+static __exit
+void net_failover_exit(void)
+{
+	unregister_netdevice_notifier(&net_failover_notifier);
+}
+module_exit(net_failover_exit);
+
+MODULE_DESCRIPTION("Failover infrastructure/interface for Paravirtual drivers");
+MODULE_LICENSE("GPL v2");