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

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/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

+ *
+ * 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);