Linux Virtualization - May 2018 - [PATCH net-next v10 0/4] 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 new feature bit VIRTIO_NET_F_STANDBY 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 2 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. It provides 2 sets of interfaces to paravirtual 
drivers to support 2-netdev(netvsc) and 3-netdev(virtio_net) models.

Patch 3 extends virtio_net to use alternate datapath when available and
registered. When STANDBY feature is enabled, virtio_net driver creates
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.

Patch 4 refactors netvsc to use the registration/notification framework
supported by failover module.

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 virtio 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

v10:
- 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.
  - To avoid dhcp requests to be sent over the lower 'standby' and
'primary'
    netdevs, ifcfg-xxx scripts for the lower devices can be created.
- Build tested netvsc module.
Updates:
- 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

Sridhar Samudrala (4):
  virtio_net: Introduce VIRTIO_NET_F_STANDBY feature bit
  net: Introduce generic failover module
  virtio_net: Extend virtio to use VF datapath when available
  netvsc: refactor notifier/event handling code to use the failover
    framework

 MAINTAINERS                     |    7 +
 drivers/net/Kconfig             |    1 +
 drivers/net/hyperv/Kconfig      |    1 +
 drivers/net/hyperv/hyperv_net.h |    2 +
 drivers/net/hyperv/netvsc_drv.c |  134 +----
 drivers/net/virtio_net.c        |   40 +-
 include/linux/netdevice.h       |   16 +
 include/net/net_failover.h      |   52 ++
 include/uapi/linux/virtio_net.h |    3 +
 net/Kconfig                     |   10 +
 net/core/Makefile               |    1 +
 net/core/net_failover.c         | 1044 +++++++++++++++++++++++++++++++++++++++
 12 files changed, 1198 insertions(+), 113 deletions(-)
 create mode 100644 include/net/net_failover.h
 create mode 100644 net/core/net_failover.c

-- 
2.14.3

This feature bit can be used by hypervisor to indicate virtio_net device to
act as a standby for another device with the same MAC address.

VIRTIO_NET_F_STANDBY is defined as bit 62 as it is a device feature bit.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/virtio_net.c        | 2 +-
 include/uapi/linux/virtio_net.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f34794a76c4d..213fddc70fd0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2999,7 +2999,7 @@ 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,
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index 5de6ed37695b..a3715a3224c1 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/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
-- 
2.14.3

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 at 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/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 at intel.com>
+L:	netdev at 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 at intel.com>
 L:	linux-rdma at 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");
-- 
2.14.3

This patch enables virtio_net to switch over to a VF datapath when a VF
netdev is present with the same MAC address. It allows live migration
of a VM with a direct attached VF without the need to setup a bond/team
between a VF and virtio net device in the guest.

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.

It uses the generic failover framework that provides 2 functions to create
and destroy a master failover netdev. When STANDBY feature is enabled, an
additional netdev(failover netdev) is created that acts as a master device
and tracks the state of the 2 lower netdevs. The original virtio_net netdev
is marked as 'standby' netdev and a passthru device with the same MAC is
registered as 'primary' netdev.

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

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/Kconfig      |  1 +
 drivers/net/virtio_net.c | 38 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index a029b27fd002..30e3bb0532e4 100644
--- a/drivers/net/Kconfig
+++ b/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.
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 213fddc70fd0..e7428d20763c 100644
--- a/drivers/net/virtio_net.c
+++ b/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 net_failover *failover;
 };
 
 struct padded_vnet_hdr {
@@ -1523,6 +1529,9 @@ 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;
@@ -2306,6 +2315,22 @@ 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,
@@ -2323,6 +2348,7 @@ 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)
@@ -2876,10 +2902,16 @@ 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);
@@ -2916,6 +2948,8 @@ 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);
@@ -2950,6 +2984,8 @@ 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);
-- 
2.14.3

Use the registration/notification framework supported by the generic
failover infrastructure.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/hyperv/Kconfig      |   1 +
 drivers/net/hyperv/hyperv_net.h |   2 +
 drivers/net/hyperv/netvsc_drv.c | 134 +++++++---------------------------------
 3 files changed, 26 insertions(+), 111 deletions(-)

diff --git a/drivers/net/hyperv/Kconfig b/drivers/net/hyperv/Kconfig
index 0765d5f61714..1f8419fc7c7f 100644
--- a/drivers/net/hyperv/Kconfig
+++ b/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 NET_FAILOVER
 	help
 	  Select this option to enable the Hyper-V virtual network driver.
diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index 6ebe39a3dde6..2ec18344c0e8 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/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 net_failover *failover;
 };
 
 /* Per channel data */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index ecc84954c511..f852b3a9403a 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/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/net_failover.h>
 
 #include "hyperv_net.h"
 
@@ -1763,46 +1764,6 @@ 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
@@ -1914,24 +1875,15 @@ static void netvsc_vf_setup(struct work_struct *w)
 	rtnl_unlock();
 }
 
-static int netvsc_register_vf(struct net_device *vf_netdev)
+static int netvsc_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))
@@ -1948,17 +1900,13 @@ static int netvsc_register_vf(struct net_device
*vf_netdev)
 }
 
 /* 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)
@@ -1971,15 +1919,11 @@ static int netvsc_vf_changed(struct net_device
*vf_netdev)
 	return NOTIFY_OK;
 }
 
-static int netvsc_unregister_vf(struct net_device *vf_netdev)
+static int netvsc_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);
 
@@ -1993,6 +1937,12 @@ static int netvsc_unregister_vf(struct net_device
*vf_netdev)
 	return NOTIFY_OK;
 }
 
+static struct net_failover_ops netvsc_failover_ops = {
+	.slave_register		= netvsc_register_vf,
+	.slave_unregister	= netvsc_unregister_vf,
+	.slave_link_change	= netvsc_vf_changed,
+};
+
 static int netvsc_probe(struct hv_device *dev,
 			const struct hv_vmbus_device_id *dev_id)
 {
@@ -2082,8 +2032,15 @@ static int netvsc_probe(struct hv_device *dev,
 		goto register_failed;
 	}
 
+	net_device_ctx->failover = net_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:
@@ -2124,13 +2081,15 @@ 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);
+		net_failover_slave_unregister(vf_netdev);
 
 	if (nvdev)
 		rndis_filter_device_remove(dev, nvdev);
 
 	unregister_netdevice(net);
 
+	net_failover_unregister(ndev_ctx->failover);
+
 	rtnl_unlock();
 	rcu_read_unlock();
 
@@ -2157,54 +2116,8 @@ 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);
 }
 
@@ -2224,7 +2137,6 @@ static int __init netvsc_drv_init(void)
 	if (ret)
 		return ret;
 
-	register_netdevice_notifier(&netvsc_netdev_notifier);
 	return 0;
 }
 
-- 
2.14.3

Hi,

On 05/07/2018 03:10 PM, Sridhar Samudrala wrote:
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at 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);


-- 
~Randy

On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala at 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 at 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).

On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala at 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.

On Mon,  7 May 2018 15:10:44 -0700
Sridhar Samudrala <sridhar.samudrala at 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.

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	

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