net: Introduce generic failover module

The failover module provides a generic interface for paravirtual drivers
to register a netdev and a set of ops with a failover instance. The ops
are used as event handlers that get called to handle netdev register/
unregister/link change/name change events on slave pci ethernet devices
with the same mac address as the failover netdev.

This enables paravirtual drivers to use a VF as an accelerated low latency
datapath. It also allows migration of VMs with direct attached VFs by
failing over to the paravirtual datapath when the VF is unplugged.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 329 insertions, 0 deletions

diff --git a/net/Kconfig b/net/Kconfig
index ba554cedb615..f738a6f27665 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -432,6 +432,19 @@ config MAY_USE_DEVLINK
 config PAGE_POOL
        bool
 
+config FAILOVER
+	tristate "Generic failover module"
+	help
+	  The failover module provides a generic interface for paravirtual
+	  drivers to register a netdev and a set of ops with a failover
+	  instance. The ops are used as event handlers that get called to
+	  handle netdev register/unregister/link change/name change events
+	  on slave pci ethernet devices with the same mac address as the
+	  failover netdev. This enables paravirtual drivers to use a
+	  VF as an accelerated low latency datapath. It also allows live
+	  migration of VMs with direct attached VFs by failing over to the
+	  paravirtual datapath when the VF is unplugged.
+
 endif   # if NET
 
 # Used by archs to tell that they support BPF JIT compiler plus which flavour.
diff --git a/net/core/Makefile b/net/core/Makefile
index 7080417f8bc8..80175e6a2eb8 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_FAILOVER) += failover.o
diff --git a/net/core/failover.c b/net/core/failover.c
new file mode 100644
index 000000000000..4a92a98ccce9
--- /dev/null
+++ b/net/core/failover.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018, Intel Corporation. */
+
+/* A common module to handle registrations and notifications for paravirtual
+ * drivers to enable accelerated datapath and support VF live migration.
+ *
+ * The notifier and event handling code is based on netvsc driver.
+ */
+
+#include <linux/module.h>
+#include <linux/etherdevice.h>
+#include <uapi/linux/if_arp.h>
+#include <linux/rtnetlink.h>
+#include <linux/if_vlan.h>
+#include <net/failover.h>
+
+static LIST_HEAD(failover_list);
+static DEFINE_SPINLOCK(failover_lock);
+
+static struct net_device *failover_get_bymac(u8 *mac, struct failover_ops **ops)
+{
+	struct net_device *failover_dev;
+	struct failover *failover;
+
+	spin_lock(&failover_lock);
+	list_for_each_entry(failover, &failover_list, list) {
+		failover_dev = rtnl_dereference(failover->failover_dev);
+		if (ether_addr_equal(failover_dev->perm_addr, mac)) {
+			*ops = rtnl_dereference(failover->ops);
+			spin_unlock(&failover_lock);
+			return failover_dev;
+		}
+	}
+	spin_unlock(&failover_lock);
+	return NULL;
+}
+
+/**
+ * failover_slave_register - Register a slave netdev
+ *
+ * @slave_dev: slave netdev that is being registered
+ *
+ * Registers a slave device to a failover instance. Only ethernet devices
+ * are supported.
+ */
+static int failover_slave_register(struct net_device *slave_dev)
+{
+	struct netdev_lag_upper_info lag_upper_info;
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+	int err;
+
+	if (slave_dev->type != ARPHRD_ETHER)
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (fops && fops->slave_pre_register &&
+	    fops->slave_pre_register(slave_dev, failover_dev))
+		goto done;
+
+	err = netdev_rx_handler_register(slave_dev, fops->slave_handle_frame,
+					 failover_dev);
+	if (err) {
+		netdev_err(slave_dev, "can not register failover rx handler (err = %d)\n",
+			   err);
+		goto done;
+	}
+
+	lag_upper_info.tx_type = NETDEV_LAG_TX_TYPE_ACTIVEBACKUP;
+	err = netdev_master_upper_dev_link(slave_dev, failover_dev, NULL,
+					   &lag_upper_info, NULL);
+	if (err) {
+		netdev_err(slave_dev, "can not set failover device %s (err = %d)\n",
+			   failover_dev->name, err);
+		goto err_upper_link;
+	}
+
+	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
+
+	if (fops && fops->slave_register &&
+	    !fops->slave_register(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+err_upper_link:
+	netdev_rx_handler_unregister(slave_dev);
+done:
+	return NOTIFY_DONE;
+}
+
+/**
+ * failover_slave_unregister - Unregister a slave netdev
+ *
+ * @slave_dev: slave netdev that is being unregistered
+ *
+ * Unregisters a slave device from a failover instance.
+ */
+int failover_slave_unregister(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (fops && fops->slave_pre_unregister &&
+	    fops->slave_pre_unregister(slave_dev, failover_dev))
+		goto done;
+
+	netdev_rx_handler_unregister(slave_dev);
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+
+	if (fops && fops->slave_unregister &&
+	    !fops->slave_unregister(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+EXPORT_SYMBOL_GPL(failover_slave_unregister);
+
+static int failover_slave_link_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	if (fops && fops->slave_link_change &&
+	    !fops->slave_link_change(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int failover_slave_name_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev;
+	struct failover_ops *fops;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+	if (!failover_dev)
+		goto done;
+
+	if (!netif_running(failover_dev))
+		goto done;
+
+	if (fops && fops->slave_name_change &&
+	    !fops->slave_name_change(slave_dev, failover_dev))
+		return NOTIFY_OK;
+
+done:
+	return NOTIFY_DONE;
+}
+
+static int
+failover_event(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
+
+	/* Skip parent events */
+	if (netif_is_failover(event_dev))
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_REGISTER:
+		return failover_slave_register(event_dev);
+	case NETDEV_UNREGISTER:
+		return failover_slave_unregister(event_dev);
+	case NETDEV_UP:
+	case NETDEV_DOWN:
+	case NETDEV_CHANGE:
+		return failover_slave_link_change(event_dev);
+	case NETDEV_CHANGENAME:
+		return failover_slave_name_change(event_dev);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block failover_notifier = {
+	.notifier_call = failover_event,
+};
+
+static void
+failover_existing_slave_register(struct net_device *failover_dev)
+{
+	struct net *net = dev_net(failover_dev);
+	struct net_device *dev;
+
+	rtnl_lock();
+	for_each_netdev(net, dev) {
+		if (netif_is_failover(dev))
+			continue;
+		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
+			failover_slave_register(dev);
+	}
+	rtnl_unlock();
+}
+
+/**
+ * failover_register - Register a failover instance
+ *
+ * @dev: failover netdev
+ * @ops: failover ops
+ *
+ * Allocate and register a failover instance for a failover netdev. ops
+ * provides handlers for slave device register/unregister/link change/
+ * name change events.
+ *
+ * Return: pointer to failover instance
+ */
+struct failover *failover_register(struct net_device *dev,
+				   struct failover_ops *ops)
+{
+	struct failover *failover;
+
+	if (dev->type != ARPHRD_ETHER)
+		return ERR_PTR(-EINVAL);
+
+	failover = kzalloc(sizeof(*failover), GFP_KERNEL);
+	if (!failover)
+		return ERR_PTR(-ENOMEM);
+
+	rcu_assign_pointer(failover->ops, ops);
+	dev_hold(dev);
+	dev->priv_flags |= IFF_FAILOVER;
+	rcu_assign_pointer(failover->failover_dev, dev);
+
+	spin_lock(&failover_lock);
+	list_add_tail(&failover->list, &failover_list);
+	spin_unlock(&failover_lock);
+
+	netdev_info(dev, "failover master:%s registered\n", dev->name);
+
+	failover_existing_slave_register(dev);
+
+	return failover;
+}
+EXPORT_SYMBOL_GPL(failover_register);
+
+/**
+ * failover_unregister - Unregister a failover instance
+ *
+ * @failover: pointer to failover instance
+ *
+ * Unregisters and frees a failover instance.
+ */
+void failover_unregister(struct failover *failover)
+{
+	struct net_device *failover_dev;
+
+	failover_dev = rcu_dereference(failover->failover_dev);
+
+	netdev_info(failover_dev, "failover master:%s unregistered\n",
+		    failover_dev->name);
+
+	failover_dev->priv_flags &= ~IFF_FAILOVER;
+	dev_put(failover_dev);
+
+	spin_lock(&failover_lock);
+	list_del(&failover->list);
+	spin_unlock(&failover_lock);
+
+	kfree(failover);
+}
+EXPORT_SYMBOL_GPL(failover_unregister);
+
+static __init int
+failover_init(void)
+{
+	register_netdevice_notifier(&failover_notifier);
+
+	return 0;
+}
+module_init(failover_init);
+
+static __exit
+void failover_exit(void)
+{
+	unregister_netdevice_notifier(&failover_notifier);
+}
+module_exit(failover_exit);
+
+MODULE_DESCRIPTION("Generic failover infrastructure/interface");
+MODULE_LICENSE("GPL v2");