Linux Virtualization - Apr 2018 - [RFC PATCH net-next v6 4/4] netvsc: refactor notifier/event handling code to use the bypass framework

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_BACKUP that can be
used by hypervisor to indicate that virtio_net interface should act as
a backup for another device with the same MAC address.

Patch 2 introduces a bypass 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 BACKUP feature is enabled, virtio_net driver creates
an additional 'bypass' netdev that acts as a master device and controls
2 slave devices.  The original virtio_net netdev is registered as
'backup' netdev and a passthru/vf device with the same MAC gets
registered as 'active' netdev. Both 'bypass' and
'backup' netdevs are
associated with the same 'pci' device.  The user accesses the network
interface via 'bypass' netdev. The 'bypass' netdev chooses
'active' 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 bypass 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 'active' netdev gets registered.
 
The hypervisor needs to enable only one datapath at any time so that packets
don't get looped back to the VM over the other datapath. When a VF is
plugged, the virtio datapath link state can be marked as down.
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

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_BACKUP feature bit
  net: Introduce generic bypass module
  virtio_net: Extend virtio to use VF datapath when available
  netvsc: refactor notifier/event handling code to use the bypass
    framework

 drivers/net/Kconfig             |   1 +
 drivers/net/hyperv/Kconfig      |   1 +
 drivers/net/hyperv/netvsc_drv.c | 219 ++++----------
 drivers/net/virtio_net.c        | 614 +++++++++++++++++++++++++++++++++++++++-
 include/net/bypass.h            |  80 ++++++
 include/uapi/linux/virtio_net.h |   3 +
 net/Kconfig                     |  18 ++
 net/core/Makefile               |   1 +
 net/core/bypass.c               | 406 ++++++++++++++++++++++++++
 9 files changed, 1184 insertions(+), 159 deletions(-)
 create mode 100644 include/net/bypass.h
 create mode 100644 net/core/bypass.c

-- 
2.14.3

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

VIRTIO_NET_F_BACKUP 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 7b187ec7411e..befb5944f3fd 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2962,7 +2962,7 @@ 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_BACKUP
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index 5de6ed37695b..c7c35fd1a5ed 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_BACKUP	  62	/* Act as backup 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. existing netvsc driver that uses 2 netdev model. In this model, no
master netdev is created. The paravirtual driver registers each bypass
instance along with a set of ops to manage the slave events.
     bypass_master_register()
     bypass_master_unregister()
2. new virtio_net based solution that uses 3 netdev model. In this model,
the bypass module provides interfaces to create/destroy additional master
netdev and all the slave events are managed internally.
      bypass_master_create()
      bypass_master_destroy()

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 include/linux/netdevice.h |  14 +
 include/net/bypass.h      |  96 ++++++
 net/Kconfig               |  18 +
 net/core/Makefile         |   1 +
 net/core/bypass.c         | 844 ++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 973 insertions(+)
 create mode 100644 include/net/bypass.h
 create mode 100644 net/core/bypass.c

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cf44503ea81a..587293728f70 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1430,6 +1430,8 @@ enum netdev_priv_flags {
 	IFF_PHONY_HEADROOM		= 1<<24,
 	IFF_MACSEC			= 1<<25,
 	IFF_NO_RX_HANDLER		= 1<<26,
+	IFF_BYPASS			= 1 << 27,
+	IFF_BYPASS_SLAVE		= 1 << 28,
 };
 
 #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
@@ -1458,6 +1460,8 @@ 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_BYPASS			IFF_BYPASS
+#define IFF_BYPASS_SLAVE		IFF_BYPASS_SLAVE
 
 /**
  *	struct net_device - The DEVICE structure.
@@ -4308,6 +4312,16 @@ static inline bool netif_is_rxfh_configured(const struct
net_device *dev)
 	return dev->priv_flags & IFF_RXFH_CONFIGURED;
 }
 
+static inline bool netif_is_bypass_master(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_BYPASS;
+}
+
+static inline bool netif_is_bypass_slave(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_BYPASS_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/bypass.h b/include/net/bypass.h
new file mode 100644
index 000000000000..86b02cb894cf
--- /dev/null
+++ b/include/net/bypass.h
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2018, Intel Corporation. */
+
+#ifndef _NET_BYPASS_H
+#define _NET_BYPASS_H
+
+#include <linux/netdevice.h>
+
+struct bypass_ops {
+	int (*slave_pre_register)(struct net_device *slave_netdev,
+				  struct net_device *bypass_netdev);
+	int (*slave_join)(struct net_device *slave_netdev,
+			  struct net_device *bypass_netdev);
+	int (*slave_pre_unregister)(struct net_device *slave_netdev,
+				    struct net_device *bypass_netdev);
+	int (*slave_release)(struct net_device *slave_netdev,
+			     struct net_device *bypass_netdev);
+	int (*slave_link_change)(struct net_device *slave_netdev,
+				 struct net_device *bypass_netdev);
+	rx_handler_result_t (*handle_frame)(struct sk_buff **pskb);
+};
+
+struct bypass_master {
+	struct list_head list;
+	struct net_device __rcu *bypass_netdev;
+	struct bypass_ops __rcu *ops;
+};
+
+/* bypass state */
+struct bypass_info {
+	/* passthru netdev with same MAC */
+	struct net_device __rcu *active_netdev;
+
+	/* virtio_net netdev */
+	struct net_device __rcu *backup_netdev;
+
+	/* active netdev stats */
+	struct rtnl_link_stats64 active_stats;
+
+	/* backup netdev stats */
+	struct rtnl_link_stats64 backup_stats;
+
+	/* aggregated stats */
+	struct rtnl_link_stats64 bypass_stats;
+
+	/* spinlock while updating stats */
+	spinlock_t stats_lock;
+};
+
+#if IS_ENABLED(CONFIG_NET_BYPASS)
+
+int bypass_master_create(struct net_device *backup_netdev,
+			 struct bypass_master **pbypass_master);
+void bypass_master_destroy(struct bypass_master *bypass_master);
+
+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
+			   struct bypass_master **pbypass_master);
+void bypass_master_unregister(struct bypass_master *bypass_master);
+
+int bypass_slave_unregister(struct net_device *slave_netdev);
+
+#else
+
+static inline
+int bypass_master_create(struct net_device *backup_netdev,
+			 struct bypass_master **pbypass_master);
+{
+	return 0;
+}
+
+static inline
+void bypass_master_destroy(struct bypass_master *bypass_master)
+{
+}
+
+static inline
+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
+			   struct pbypass_master **pbypass_master);
+{
+	return 0;
+}
+
+static inline
+void bypass_master_unregister(struct bypass_master *bypass_master)
+{
+}
+
+static inline
+int bypass_slave_unregister(struct net_device *slave_netdev)
+{
+	return 0;
+}
+
+#endif
+
+#endif /* _NET_BYPASS_H */
diff --git a/net/Kconfig b/net/Kconfig
index 0428f12c25c2..994445f4a96a 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -423,6 +423,24 @@ config MAY_USE_DEVLINK
 	  on MAY_USE_DEVLINK to ensure they do not cause link errors when
 	  devlink is a loadable module and the driver using it is built-in.
 
+config NET_BYPASS
+	tristate "Bypass interface"
+	---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.
+
+config MAY_USE_BYPASS
+	tristate
+	default m if NET_BYPASS=m
+	default y if NET_BYPASS=y || NET_BYPASS=n
+	help
+	  Drivers using the bypass infrastructure should have a dependency
+	  on MAY_USE_BYPASS to ensure they do not cause link errors when
+	  bypass is a loadable module and the driver using it is built-in.
+
 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 6dbbba8c57ae..a9727ed1c8fc 100644
--- a/net/core/Makefile
+++ b/net/core/Makefile
@@ -30,3 +30,4 @@ 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_BYPASS) += bypass.o
diff --git a/net/core/bypass.c b/net/core/bypass.c
new file mode 100644
index 000000000000..b5b9cb554c3f
--- /dev/null
+++ b/net/core/bypass.c
@@ -0,0 +1,844 @@
+// 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/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/bypass.h>
+
+static LIST_HEAD(bypass_master_list);
+static DEFINE_SPINLOCK(bypass_lock);
+
+static int bypass_slave_pre_register(struct net_device *slave_netdev,
+				     struct net_device *bypass_netdev,
+				     struct bypass_ops *bypass_ops)
+{
+	struct bypass_info *bi;
+	bool backup;
+
+	if (bypass_ops) {
+		if (!bypass_ops->slave_pre_register)
+			return -EINVAL;
+
+		return bypass_ops->slave_pre_register(slave_netdev,
+						      bypass_netdev);
+	}
+
+	bi = netdev_priv(bypass_netdev);
+	backup = (slave_netdev->dev.parent == bypass_netdev->dev.parent);
+	if (backup ? rtnl_dereference(bi->backup_netdev) :
+			rtnl_dereference(bi->active_netdev)) {
+		netdev_err(bypass_netdev, "%s attempting to register as slave dev when
%s already present\n",
+			   slave_netdev->name, backup ? "backup" : "active");
+		return -EEXIST;
+	}
+
+	/* Avoid non pci devices as active netdev */
+	if (!backup && (!slave_netdev->dev.parent ||
+			!dev_is_pci(slave_netdev->dev.parent)))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int bypass_slave_join(struct net_device *slave_netdev,
+			     struct net_device *bypass_netdev,
+			     struct bypass_ops *bypass_ops)
+{
+	struct bypass_info *bi;
+	bool backup;
+
+	if (bypass_ops) {
+		if (!bypass_ops->slave_join)
+			return -EINVAL;
+
+		return bypass_ops->slave_join(slave_netdev, bypass_netdev);
+	}
+
+	bi = netdev_priv(bypass_netdev);
+	backup = (slave_netdev->dev.parent == bypass_netdev->dev.parent);
+
+	dev_hold(slave_netdev);
+
+	if (backup) {
+		rcu_assign_pointer(bi->backup_netdev, slave_netdev);
+		dev_get_stats(bi->backup_netdev, &bi->backup_stats);
+	} else {
+		rcu_assign_pointer(bi->active_netdev, slave_netdev);
+		dev_get_stats(bi->active_netdev, &bi->active_stats);
+		bypass_netdev->min_mtu = slave_netdev->min_mtu;
+		bypass_netdev->max_mtu = slave_netdev->max_mtu;
+	}
+
+	netdev_info(bypass_netdev, "bypass slave:%s joined\n",
+		    slave_netdev->name);
+
+	return 0;
+}
+
+/* Called when slave dev is injecting data into network stack.
+ * Change the associated network device from lower dev to virtio.
+ * note: already called with rcu_read_lock
+ */
+static rx_handler_result_t bypass_handle_frame(struct sk_buff **pskb)
+{
+	struct sk_buff *skb = *pskb;
+	struct net_device *ndev = rcu_dereference(skb->dev->rx_handler_data);
+
+	skb->dev = ndev;
+
+	return RX_HANDLER_ANOTHER;
+}
+
+static struct net_device *bypass_master_get_bymac(u8 *mac,
+						  struct bypass_ops **ops)
+{
+	struct bypass_master *bypass_master;
+	struct net_device *bypass_netdev;
+
+	spin_lock(&bypass_lock);
+	list_for_each_entry(bypass_master, &bypass_master_list, list) {
+		bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
+		if (ether_addr_equal(bypass_netdev->perm_addr, mac)) {
+			*ops = rcu_dereference(bypass_master->ops);
+			spin_unlock(&bypass_lock);
+			return bypass_netdev;
+		}
+	}
+	spin_unlock(&bypass_lock);
+	return NULL;
+}
+
+static int bypass_slave_register(struct net_device *slave_netdev)
+{
+	struct net_device *bypass_netdev;
+	struct bypass_ops *bypass_ops;
+	int ret, orig_mtu;
+
+	ASSERT_RTNL();
+
+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
+						&bypass_ops);
+	if (!bypass_netdev)
+		goto done;
+
+	ret = bypass_slave_pre_register(slave_netdev, bypass_netdev,
+					bypass_ops);
+	if (ret != 0)
+		goto done;
+
+	ret = netdev_rx_handler_register(slave_netdev,
+					 bypass_ops ? bypass_ops->handle_frame :
+					 bypass_handle_frame, bypass_netdev);
+	if (ret != 0) {
+		netdev_err(slave_netdev, "can not register bypass rx handler (err =
%d)\n",
+			   ret);
+		goto done;
+	}
+
+	ret = netdev_upper_dev_link(slave_netdev, bypass_netdev, NULL);
+	if (ret != 0) {
+		netdev_err(slave_netdev, "can not set master device %s (err =
%d)\n",
+			   bypass_netdev->name, ret);
+		goto upper_link_failed;
+	}
+
+	slave_netdev->priv_flags |= IFF_BYPASS_SLAVE;
+
+	if (netif_running(bypass_netdev)) {
+		ret = dev_open(slave_netdev);
+		if (ret && (ret != -EBUSY)) {
+			netdev_err(bypass_netdev, "Opening slave %s failed ret:%d\n",
+				   slave_netdev->name, ret);
+			goto err_interface_up;
+		}
+	}
+
+	/* Align MTU of slave with master */
+	orig_mtu = slave_netdev->mtu;
+	ret = dev_set_mtu(slave_netdev, bypass_netdev->mtu);
+	if (ret != 0) {
+		netdev_err(bypass_netdev, "unable to change mtu of %s to %u register
failed\n",
+			   slave_netdev->name, bypass_netdev->mtu);
+		goto err_set_mtu;
+	}
+
+	ret = bypass_slave_join(slave_netdev, bypass_netdev, bypass_ops);
+	if (ret != 0)
+		goto err_join;
+
+	call_netdevice_notifiers(NETDEV_JOIN, slave_netdev);
+
+	netdev_info(bypass_netdev, "bypass slave:%s registered\n",
+		    slave_netdev->name);
+
+	goto done;
+
+err_join:
+	dev_set_mtu(slave_netdev, orig_mtu);
+err_set_mtu:
+	dev_close(slave_netdev);
+err_interface_up:
+	netdev_upper_dev_unlink(slave_netdev, bypass_netdev);
+	slave_netdev->priv_flags &= ~IFF_BYPASS_SLAVE;
+upper_link_failed:
+	netdev_rx_handler_unregister(slave_netdev);
+done:
+	return NOTIFY_DONE;
+}
+
+static int bypass_slave_pre_unregister(struct net_device *slave_netdev,
+				       struct net_device *bypass_netdev,
+				       struct bypass_ops *bypass_ops)
+{
+	struct net_device *backup_netdev, *active_netdev;
+	struct bypass_info *bi;
+
+	if (bypass_ops) {
+		if (!bypass_ops->slave_pre_unregister)
+			return -EINVAL;
+
+		return bypass_ops->slave_pre_unregister(slave_netdev,
+							bypass_netdev);
+	}
+
+	bi = netdev_priv(bypass_netdev);
+	active_netdev = rtnl_dereference(bi->active_netdev);
+	backup_netdev = rtnl_dereference(bi->backup_netdev);
+
+	if (slave_netdev != active_netdev && slave_netdev != backup_netdev)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int bypass_slave_release(struct net_device *slave_netdev,
+				struct net_device *bypass_netdev,
+				struct bypass_ops *bypass_ops)
+{
+	struct net_device *backup_netdev, *active_netdev;
+	struct bypass_info *bi;
+
+	if (bypass_ops) {
+		if (!bypass_ops->slave_release)
+			return -EINVAL;
+
+		return bypass_ops->slave_release(slave_netdev, bypass_netdev);
+	}
+
+	bi = netdev_priv(bypass_netdev);
+	active_netdev = rtnl_dereference(bi->active_netdev);
+	backup_netdev = rtnl_dereference(bi->backup_netdev);
+
+	if (slave_netdev == backup_netdev) {
+		RCU_INIT_POINTER(bi->backup_netdev, NULL);
+	} else {
+		RCU_INIT_POINTER(bi->active_netdev, NULL);
+		if (backup_netdev) {
+			bypass_netdev->min_mtu = backup_netdev->min_mtu;
+			bypass_netdev->max_mtu = backup_netdev->max_mtu;
+		}
+	}
+
+	dev_put(slave_netdev);
+
+	netdev_info(bypass_netdev, "bypass slave:%s released\n",
+		    slave_netdev->name);
+
+	return 0;
+}
+
+int bypass_slave_unregister(struct net_device *slave_netdev)
+{
+	struct net_device *bypass_netdev;
+	struct bypass_ops *bypass_ops;
+	int ret;
+
+	if (!netif_is_bypass_slave(slave_netdev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
+						&bypass_ops);
+	if (!bypass_netdev)
+		goto done;
+
+	ret = bypass_slave_pre_unregister(slave_netdev, bypass_netdev,
+					  bypass_ops);
+	if (ret != 0)
+		goto done;
+
+	netdev_rx_handler_unregister(slave_netdev);
+	netdev_upper_dev_unlink(slave_netdev, bypass_netdev);
+	slave_netdev->priv_flags &= ~IFF_BYPASS_SLAVE;
+
+	bypass_slave_release(slave_netdev, bypass_netdev, bypass_ops);
+
+	netdev_info(bypass_netdev, "bypass slave:%s unregistered\n",
+		    slave_netdev->name);
+
+done:
+	return NOTIFY_DONE;
+}
+EXPORT_SYMBOL_GPL(bypass_slave_unregister);
+
+static bool bypass_xmit_ready(struct net_device *dev)
+{
+	return netif_running(dev) && netif_carrier_ok(dev);
+}
+
+static int bypass_slave_link_change(struct net_device *slave_netdev)
+{
+	struct net_device *bypass_netdev, *active_netdev, *backup_netdev;
+	struct bypass_ops *bypass_ops;
+	struct bypass_info *bi;
+
+	if (!netif_is_bypass_slave(slave_netdev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
+						&bypass_ops);
+	if (!bypass_netdev)
+		goto done;
+
+	if (bypass_ops) {
+		if (!bypass_ops->slave_link_change)
+			goto done;
+
+		return bypass_ops->slave_link_change(slave_netdev,
+						     bypass_netdev);
+	}
+
+	if (!netif_running(bypass_netdev))
+		return 0;
+
+	bi = netdev_priv(bypass_netdev);
+
+	active_netdev = rtnl_dereference(bi->active_netdev);
+	backup_netdev = rtnl_dereference(bi->backup_netdev);
+
+	if (slave_netdev != active_netdev && slave_netdev != backup_netdev)
+		goto done;
+
+	if ((active_netdev && bypass_xmit_ready(active_netdev)) ||
+	    (backup_netdev && bypass_xmit_ready(backup_netdev))) {
+		netif_carrier_on(bypass_netdev);
+		netif_tx_wake_all_queues(bypass_netdev);
+	} else {
+		netif_carrier_off(bypass_netdev);
+		netif_tx_stop_all_queues(bypass_netdev);
+	}
+
+done:
+	return NOTIFY_DONE;
+}
+
+static bool bypass_validate_event_dev(struct net_device *dev)
+{
+	/* Skip parent events */
+	if (netif_is_bypass_master(dev))
+		return false;
+
+	/* Avoid non-Ethernet type devices */
+	if (dev->type != ARPHRD_ETHER)
+		return false;
+
+	/* Avoid Vlan dev with same MAC registering as VF */
+	if (is_vlan_dev(dev))
+		return false;
+
+	/* Avoid Bonding master dev with same MAC registering as slave dev */
+	if ((dev->priv_flags & IFF_BONDING) && (dev->flags &
IFF_MASTER))
+		return false;
+
+	return true;
+}
+
+static int
+bypass_event(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
+
+	if (!bypass_validate_event_dev(event_dev))
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case NETDEV_REGISTER:
+		return bypass_slave_register(event_dev);
+	case NETDEV_UNREGISTER:
+		return bypass_slave_unregister(event_dev);
+	case NETDEV_UP:
+	case NETDEV_DOWN:
+	case NETDEV_CHANGE:
+		return bypass_slave_link_change(event_dev);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block bypass_notifier = {
+	.notifier_call = bypass_event,
+};
+
+int bypass_open(struct net_device *dev)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	struct net_device *active_netdev, *backup_netdev;
+	int err;
+
+	netif_carrier_off(dev);
+	netif_tx_wake_all_queues(dev);
+
+	active_netdev = rtnl_dereference(bi->active_netdev);
+	if (active_netdev) {
+		err = dev_open(active_netdev);
+		if (err)
+			goto err_active_open;
+	}
+
+	backup_netdev = rtnl_dereference(bi->backup_netdev);
+	if (backup_netdev) {
+		err = dev_open(backup_netdev);
+		if (err)
+			goto err_backup_open;
+	}
+
+	return 0;
+
+err_backup_open:
+	dev_close(active_netdev);
+err_active_open:
+	netif_tx_disable(dev);
+	return err;
+}
+EXPORT_SYMBOL_GPL(bypass_open);
+
+int bypass_close(struct net_device *dev)
+{
+	struct bypass_info *vi = netdev_priv(dev);
+	struct net_device *slave_netdev;
+
+	netif_tx_disable(dev);
+
+	slave_netdev = rtnl_dereference(vi->active_netdev);
+	if (slave_netdev)
+		dev_close(slave_netdev);
+
+	slave_netdev = rtnl_dereference(vi->backup_netdev);
+	if (slave_netdev)
+		dev_close(slave_netdev);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(bypass_close);
+
+static netdev_tx_t bypass_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;
+}
+
+netdev_tx_t bypass_start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	struct net_device *xmit_dev;
+
+	/* Try xmit via active netdev followed by backup netdev */
+	xmit_dev = rcu_dereference_bh(bi->active_netdev);
+	if (!xmit_dev || !bypass_xmit_ready(xmit_dev)) {
+		xmit_dev = rcu_dereference_bh(bi->backup_netdev);
+		if (!xmit_dev || !bypass_xmit_ready(xmit_dev))
+			return bypass_drop_xmit(skb, dev);
+	}
+
+	skb->dev = xmit_dev;
+	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
+
+	return dev_queue_xmit(skb);
+}
+EXPORT_SYMBOL_GPL(bypass_start_xmit);
+
+u16 bypass_select_queue(struct net_device *dev, struct sk_buff *skb,
+			void *accel_priv, select_queue_fallback_t fallback)
+{
+	/* This helper function exists to help dev_pick_tx get the correct
+	 * destination queue.  Using a helper function skips a call to
+	 * skb_tx_hash and will put the skbs in the queue we expect on their
+	 * way down to the bonding driver.
+	 */
+	u16 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;
+}
+EXPORT_SYMBOL_GPL(bypass_select_queue);
+
+/* fold stats, assuming all rtnl_link_stats64 fields are u64, but
+ * that some drivers can provide 32bit values only.
+ */
+static void bypass_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;
+	}
+}
+
+void bypass_get_stats(struct net_device *dev, struct rtnl_link_stats64 *stats)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	const struct rtnl_link_stats64 *new;
+	struct rtnl_link_stats64 temp;
+	struct net_device *slave_netdev;
+
+	spin_lock(&bi->stats_lock);
+	memcpy(stats, &bi->bypass_stats, sizeof(*stats));
+
+	rcu_read_lock();
+
+	slave_netdev = rcu_dereference(bi->active_netdev);
+	if (slave_netdev) {
+		new = dev_get_stats(slave_netdev, &temp);
+		bypass_fold_stats(stats, new, &bi->active_stats);
+		memcpy(&bi->active_stats, new, sizeof(*new));
+	}
+
+	slave_netdev = rcu_dereference(bi->backup_netdev);
+	if (slave_netdev) {
+		new = dev_get_stats(slave_netdev, &temp);
+		bypass_fold_stats(stats, new, &bi->backup_stats);
+		memcpy(&bi->backup_stats, new, sizeof(*new));
+	}
+
+	rcu_read_unlock();
+
+	memcpy(&bi->bypass_stats, stats, sizeof(*stats));
+	spin_unlock(&bi->stats_lock);
+}
+EXPORT_SYMBOL_GPL(bypass_get_stats);
+
+int bypass_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	struct net_device *active_netdev, *backup_netdev;
+	int ret = 0;
+
+	active_netdev = rcu_dereference(bi->active_netdev);
+	if (active_netdev) {
+		ret = dev_set_mtu(active_netdev, new_mtu);
+		if (ret)
+			return ret;
+	}
+
+	backup_netdev = rcu_dereference(bi->backup_netdev);
+	if (backup_netdev) {
+		ret = dev_set_mtu(backup_netdev, new_mtu);
+		if (ret) {
+			dev_set_mtu(active_netdev, dev->mtu);
+			return ret;
+		}
+	}
+
+	dev->mtu = new_mtu;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(bypass_change_mtu);
+
+void bypass_set_rx_mode(struct net_device *dev)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	struct net_device *slave_netdev;
+
+	rcu_read_lock();
+
+	slave_netdev = rcu_dereference(bi->active_netdev);
+	if (slave_netdev) {
+		dev_uc_sync_multiple(slave_netdev, dev);
+		dev_mc_sync_multiple(slave_netdev, dev);
+	}
+
+	slave_netdev = rcu_dereference(bi->backup_netdev);
+	if (slave_netdev) {
+		dev_uc_sync_multiple(slave_netdev, dev);
+		dev_mc_sync_multiple(slave_netdev, dev);
+	}
+
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(bypass_set_rx_mode);
+
+static const struct net_device_ops bypass_netdev_ops = {
+	.ndo_open		= bypass_open,
+	.ndo_stop		= bypass_close,
+	.ndo_start_xmit		= bypass_start_xmit,
+	.ndo_select_queue	= bypass_select_queue,
+	.ndo_get_stats64	= bypass_get_stats,
+	.ndo_change_mtu		= bypass_change_mtu,
+	.ndo_set_rx_mode	= bypass_set_rx_mode,
+	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_features_check	= passthru_features_check,
+};
+
+#define BYPASS_DRV_NAME "bypass"
+#define BYPASS_DRV_VERSION "0.1"
+
+static void bypass_ethtool_get_drvinfo(struct net_device *dev,
+				       struct ethtool_drvinfo *drvinfo)
+{
+	strlcpy(drvinfo->driver, BYPASS_DRV_NAME, sizeof(drvinfo->driver));
+	strlcpy(drvinfo->version, BYPASS_DRV_VERSION, sizeof(drvinfo->version));
+}
+
+int bypass_ethtool_get_link_ksettings(struct net_device *dev,
+				      struct ethtool_link_ksettings *cmd)
+{
+	struct bypass_info *bi = netdev_priv(dev);
+	struct net_device *slave_netdev;
+
+	slave_netdev = rtnl_dereference(bi->active_netdev);
+	if (!slave_netdev || !bypass_xmit_ready(slave_netdev)) {
+		slave_netdev = rtnl_dereference(bi->backup_netdev);
+		if (!slave_netdev || !bypass_xmit_ready(slave_netdev)) {
+			cmd->base.duplex = DUPLEX_UNKNOWN;
+			cmd->base.port = PORT_OTHER;
+			cmd->base.speed = SPEED_UNKNOWN;
+
+			return 0;
+		}
+	}
+
+	return __ethtool_get_link_ksettings(slave_netdev, cmd);
+}
+EXPORT_SYMBOL_GPL(bypass_ethtool_get_link_ksettings);
+
+static const struct ethtool_ops bypass_ethtool_ops = {
+	.get_drvinfo            = bypass_ethtool_get_drvinfo,
+	.get_link               = ethtool_op_get_link,
+	.get_link_ksettings     = bypass_ethtool_get_link_ksettings,
+};
+
+static void bypass_register_existing_slave(struct net_device *bypass_netdev)
+{
+	struct net *net = dev_net(bypass_netdev);
+	struct net_device *dev;
+
+	rtnl_lock();
+	for_each_netdev(net, dev) {
+		if (dev == bypass_netdev)
+			continue;
+		if (!bypass_validate_event_dev(dev))
+			continue;
+		if (ether_addr_equal(bypass_netdev->perm_addr, dev->perm_addr))
+			bypass_slave_register(dev);
+	}
+	rtnl_unlock();
+}
+
+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
+			   struct bypass_master **pbypass_master)
+{
+	struct bypass_master *bypass_master;
+
+	bypass_master = kzalloc(sizeof(*bypass_master), GFP_KERNEL);
+	if (!bypass_master)
+		return -ENOMEM;
+
+	rcu_assign_pointer(bypass_master->ops, ops);
+	dev_hold(dev);
+	dev->priv_flags |= IFF_BYPASS;
+	rcu_assign_pointer(bypass_master->bypass_netdev, dev);
+
+	spin_lock(&bypass_lock);
+	list_add_tail(&bypass_master->list, &bypass_master_list);
+	spin_unlock(&bypass_lock);
+
+	bypass_register_existing_slave(dev);
+
+	*pbypass_master = bypass_master;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(bypass_master_register);
+
+void bypass_master_unregister(struct bypass_master *bypass_master)
+{
+	struct net_device *bypass_netdev;
+
+	bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
+
+	bypass_netdev->priv_flags &= ~IFF_BYPASS;
+	dev_put(bypass_netdev);
+
+	spin_lock(&bypass_lock);
+	list_del(&bypass_master->list);
+	spin_unlock(&bypass_lock);
+
+	kfree(bypass_master);
+}
+EXPORT_SYMBOL_GPL(bypass_master_unregister);
+
+int bypass_master_create(struct net_device *backup_netdev,
+			 struct bypass_master **pbypass_master)
+{
+	struct device *dev = backup_netdev->dev.parent;
+	struct net_device *bypass_netdev;
+	int err;
+
+	/* Alloc at least 2 queues, for now we are going with 16 assuming
+	 * that most devices being bonded won't have too many queues.
+	 */
+	bypass_netdev = alloc_etherdev_mq(sizeof(struct bypass_info), 16);
+	if (!bypass_netdev) {
+		dev_err(dev, "Unable to allocate bypass_netdev!\n");
+		return -ENOMEM;
+	}
+
+	dev_net_set(bypass_netdev, dev_net(backup_netdev));
+	SET_NETDEV_DEV(bypass_netdev, dev);
+
+	bypass_netdev->netdev_ops = &bypass_netdev_ops;
+	bypass_netdev->ethtool_ops = &bypass_ethtool_ops;
+
+	/* Initialize the device options */
+	bypass_netdev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
+	bypass_netdev->priv_flags &= ~(IFF_XMIT_DST_RELEASE |
+				       IFF_TX_SKB_SHARING);
+
+	/* don't acquire bypass netdev's netif_tx_lock when transmitting */
+	bypass_netdev->features |= NETIF_F_LLTX;
+
+	/* Don't allow bypass devices to change network namespaces. */
+	bypass_netdev->features |= NETIF_F_NETNS_LOCAL;
+
+	bypass_netdev->hw_features = NETIF_F_HW_CSUM | NETIF_F_SG |
+				     NETIF_F_FRAGLIST | NETIF_F_ALL_TSO |
+				     NETIF_F_HIGHDMA | NETIF_F_LRO;
+
+	bypass_netdev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
+	bypass_netdev->features |= bypass_netdev->hw_features;
+
+	memcpy(bypass_netdev->dev_addr, backup_netdev->dev_addr,
+	       bypass_netdev->addr_len);
+
+	bypass_netdev->min_mtu = backup_netdev->min_mtu;
+	bypass_netdev->max_mtu = backup_netdev->max_mtu;
+
+	err = register_netdev(bypass_netdev);
+	if (err < 0) {
+		dev_err(dev, "Unable to register bypass_netdev!\n");
+		goto err_register_netdev;
+	}
+
+	netif_carrier_off(bypass_netdev);
+
+	err = bypass_master_register(bypass_netdev, NULL, pbypass_master);
+	if (err < 0)
+		goto err_bypass;
+
+	return 0;
+
+err_bypass:
+	unregister_netdev(bypass_netdev);
+err_register_netdev:
+	free_netdev(bypass_netdev);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(bypass_master_create);
+
+void bypass_master_destroy(struct bypass_master *bypass_master)
+{
+	struct net_device *bypass_netdev;
+	struct net_device *slave_netdev;
+	struct bypass_info *bi;
+
+	if (!bypass_master)
+		return;
+
+	bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
+	bi = netdev_priv(bypass_netdev);
+
+	netif_device_detach(bypass_netdev);
+
+	rtnl_lock();
+
+	slave_netdev = rtnl_dereference(bi->active_netdev);
+	if (slave_netdev)
+		bypass_slave_unregister(slave_netdev);
+
+	slave_netdev = rtnl_dereference(bi->backup_netdev);
+	if (slave_netdev)
+		bypass_slave_unregister(slave_netdev);
+
+	bypass_master_unregister(bypass_master);
+
+	unregister_netdevice(bypass_netdev);
+
+	rtnl_unlock();
+
+	free_netdev(bypass_netdev);
+}
+EXPORT_SYMBOL_GPL(bypass_master_destroy);
+
+static __init int
+bypass_init(void)
+{
+	register_netdevice_notifier(&bypass_notifier);
+
+	return 0;
+}
+module_init(bypass_init);
+
+static __exit
+void bypass_exit(void)
+{
+	unregister_netdevice_notifier(&bypass_notifier);
+}
+module_exit(bypass_exit);
+
+MODULE_DESCRIPTION("Bypass 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 enable only one datapath at any time so that
packets don't get looped back to the VM over the other datapath. When a VF
is plugged, the virtio datapath link state can be marked as down. 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 bypass framework that provides 2 functions to create
and destroy a master bypass netdev. When BACKUP feature is enabled, an
additional netdev(bypass 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 'backup' netdev and a passthru device with the same MAC is
registered as 'active' 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 | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 891846655000..9e2cf61fd1c1 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -331,6 +331,7 @@ config VETH
 config VIRTIO_NET
 	tristate "Virtio network driver"
 	depends on VIRTIO
+	depends on MAY_USE_BYPASS
 	---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 befb5944f3fd..99aa52d5ac9b 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/bypass.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -206,6 +209,9 @@ struct virtnet_info {
 	u32 speed;
 
 	unsigned long guest_offloads;
+
+	/* bypass_master created when BACKUP feature enabled */
+	struct bypass_master *bypass_master;
 };
 
 struct padded_vnet_hdr {
@@ -2275,6 +2281,22 @@ 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_BACKUP))
+		return -EOPNOTSUPP;
+
+	ret = snprintf(buf, len, "_bkup");
+	if (ret >= len)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -2292,6 +2314,7 @@ 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)
@@ -2839,10 +2862,16 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	virtnet_init_settings(dev);
 
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_BACKUP)) {
+		err = bypass_master_create(vi->dev, &vi->bypass_master);
+		if (err)
+			goto free_vqs;
+	}
+
 	err = register_netdev(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");
-		goto free_vqs;
+		goto free_bypass;
 	}
 
 	virtio_device_ready(vdev);
@@ -2879,6 +2908,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	vi->vdev->config->reset(vdev);
 
 	unregister_netdev(dev);
+free_bypass:
+	bypass_master_destroy(vi->bypass_master);
 free_vqs:
 	cancel_delayed_work_sync(&vi->refill);
 	free_receive_page_frags(vi);
@@ -2913,6 +2944,8 @@ static void virtnet_remove(struct virtio_device *vdev)
 
 	unregister_netdev(vi->dev);
 
+	bypass_master_destroy(vi->bypass_master);
+
 	remove_vq_common(vi);
 
 	free_netdev(vi->dev);
@@ -3010,6 +3043,7 @@ static __init int virtio_net_driver_init(void)
         ret = register_virtio_driver(&virtio_net_driver);
 	if (ret)
 		goto err_virtio;
+
 	return 0;
 err_virtio:
 	cpuhp_remove_multi_state(CPUHP_VIRT_NET_DEAD);
-- 
2.14.3

Use the registration/notification framework supported by the generic
bypass 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 | 208 ++++++++++------------------------------
 3 files changed, 55 insertions(+), 156 deletions(-)

diff --git a/drivers/net/hyperv/Kconfig b/drivers/net/hyperv/Kconfig
index 936968d23559..cc3a721baa18 100644
--- a/drivers/net/hyperv/Kconfig
+++ b/drivers/net/hyperv/Kconfig
@@ -1,5 +1,6 @@
 config HYPERV_NET
 	tristate "Microsoft Hyper-V virtual network driver"
 	depends on HYPERV
+	depends on MAY_USE_BYPASS
 	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 960f06141472..5f8137bc5c1c 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -768,6 +768,8 @@ struct net_device_context {
 	u32 vf_alloc;
 	/* Serial number of the VF to team with */
 	u32 vf_serial;
+
+	struct bypass_master *bypass_master;
 };
 
 /* Per channel data */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index ecc84954c511..87c2a276e62f 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/bypass.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
@@ -1829,39 +1790,15 @@ static int netvsc_vf_join(struct net_device *vf_netdev,
 			  struct net_device *ndev)
 {
 	struct net_device_context *ndev_ctx = netdev_priv(ndev);
-	int ret;
-
-	ret = netdev_rx_handler_register(vf_netdev,
-					 netvsc_vf_handle_frame, ndev);
-	if (ret != 0) {
-		netdev_err(vf_netdev,
-			   "can not register netvsc VF receive handler (err = %d)\n",
-			   ret);
-		goto rx_handler_failed;
-	}
-
-	ret = netdev_upper_dev_link(vf_netdev, ndev, NULL);
-	if (ret != 0) {
-		netdev_err(vf_netdev,
-			   "can not set master device %s (err = %d)\n",
-			   ndev->name, ret);
-		goto upper_link_failed;
-	}
-
-	/* set slave flag before open to prevent IPv6 addrconf */
-	vf_netdev->flags |= IFF_SLAVE;
 
 	schedule_delayed_work(&ndev_ctx->vf_takeover, VF_TAKEOVER_INT);
 
-	call_netdevice_notifiers(NETDEV_JOIN, vf_netdev);
-
 	netdev_info(vf_netdev, "joined to %s\n", ndev->name);
-	return 0;
 
-upper_link_failed:
-	netdev_rx_handler_unregister(vf_netdev);
-rx_handler_failed:
-	return ret;
+	dev_hold(vf_netdev);
+	rcu_assign_pointer(ndev_ctx->vf_netdev, vf_netdev);
+
+	return 0;
 }
 
 static void __netvsc_vf_setup(struct net_device *ndev,
@@ -1914,85 +1851,82 @@ static void netvsc_vf_setup(struct work_struct *w)
 	rtnl_unlock();
 }
 
-static int netvsc_register_vf(struct net_device *vf_netdev)
+static int netvsc_vf_pre_register(struct net_device *vf_netdev,
+				  struct net_device *ndev)
 {
-	struct net_device *ndev;
 	struct net_device_context *net_device_ctx;
 	struct netvsc_device *netvsc_dev;
 
-	if (vf_netdev->addr_len != ETH_ALEN)
-		return NOTIFY_DONE;
-
-	/*
-	 * We will use the MAC address to locate the synthetic interface to
-	 * associate with the VF interface. If we don't find a matching
-	 * synthetic interface, move on.
-	 */
-	ndev = get_netvsc_bymac(vf_netdev->perm_addr);
-	if (!ndev)
-		return NOTIFY_DONE;
-
 	net_device_ctx = netdev_priv(ndev);
 	netvsc_dev = rtnl_dereference(net_device_ctx->nvdev);
 	if (!netvsc_dev || rtnl_dereference(net_device_ctx->vf_netdev))
-		return NOTIFY_DONE;
-
-	if (netvsc_vf_join(vf_netdev, ndev) != 0)
-		return NOTIFY_DONE;
+		return -EEXIST;
 
 	netdev_info(ndev, "VF registering: %s\n", vf_netdev->name);
 
-	dev_hold(vf_netdev);
-	rcu_assign_pointer(net_device_ctx->vf_netdev, vf_netdev);
-	return NOTIFY_OK;
+	return 0;
 }
 
 /* VF up/down change detected, schedule to change data path */
-static int netvsc_vf_changed(struct net_device *vf_netdev)
+static int netvsc_vf_changed(struct net_device *vf_netdev,
+			     struct net_device *ndev)
 {
 	struct net_device_context *net_device_ctx;
 	struct netvsc_device *netvsc_dev;
-	struct net_device *ndev;
 	bool vf_is_up = netif_running(vf_netdev);
 
-	ndev = get_netvsc_byref(vf_netdev);
-	if (!ndev)
-		return NOTIFY_DONE;
-
 	net_device_ctx = netdev_priv(ndev);
 	netvsc_dev = rtnl_dereference(net_device_ctx->nvdev);
 	if (!netvsc_dev)
-		return NOTIFY_DONE;
+		return -EINVAL;
 
 	netvsc_switch_datapath(ndev, vf_is_up);
 	netdev_info(ndev, "Data path switched %s VF: %s\n",
 		    vf_is_up ? "to" : "from", vf_netdev->name);
 
-	return NOTIFY_OK;
+	return 0;
 }
 
-static int netvsc_unregister_vf(struct net_device *vf_netdev)
+static int netvsc_vf_release(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);
+	if (vf_netdev != rtnl_dereference(net_device_ctx->vf_netdev))
+		return -EINVAL;
 
-	netdev_info(ndev, "VF unregistering: %s\n", vf_netdev->name);
+	cancel_delayed_work_sync(&net_device_ctx->vf_takeover);
 
-	netdev_rx_handler_unregister(vf_netdev);
-	netdev_upper_dev_unlink(vf_netdev, ndev);
 	RCU_INIT_POINTER(net_device_ctx->vf_netdev, NULL);
 	dev_put(vf_netdev);
 
-	return NOTIFY_OK;
+	return 0;
 }
 
+static int netvsc_vf_pre_unregister(struct net_device *vf_netdev,
+				    struct net_device *ndev)
+{
+	struct net_device_context *net_device_ctx;
+
+	net_device_ctx = netdev_priv(ndev);
+	if (vf_netdev != rtnl_dereference(net_device_ctx->vf_netdev))
+		return -EINVAL;
+
+	netdev_info(ndev, "VF unregistering: %s\n", vf_netdev->name);
+
+	return 0;
+}
+
+static struct bypass_ops netvsc_bypass_ops = {
+	.slave_pre_register	= netvsc_vf_pre_register,
+	.slave_join		= netvsc_vf_join,
+	.slave_pre_unregister	= netvsc_vf_pre_unregister,
+	.slave_release		= netvsc_vf_release,
+	.slave_link_change	= netvsc_vf_changed,
+	.handle_frame		= netvsc_vf_handle_frame,
+};
+
 static int netvsc_probe(struct hv_device *dev,
 			const struct hv_vmbus_device_id *dev_id)
 {
@@ -2082,8 +2016,15 @@ static int netvsc_probe(struct hv_device *dev,
 		goto register_failed;
 	}
 
+	ret = bypass_master_register(net, &netvsc_bypass_ops,
+				     &net_device_ctx->bypass_master);
+	if (ret != 0)
+		goto err_bypass;
+
 	return ret;
 
+err_bypass:
+	unregister_netdev(net);
 register_failed:
 	rndis_filter_device_remove(dev, nvdev);
 rndis_failed:
@@ -2124,13 +2065,15 @@ 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);
+		bypass_slave_unregister(vf_netdev);
 
 	if (nvdev)
 		rndis_filter_device_remove(dev, nvdev);
 
 	unregister_netdevice(net);
 
+	bypass_master_unregister(ndev_ctx->bypass_master);
+
 	rtnl_unlock();
 	rcu_read_unlock();
 
@@ -2157,54 +2100,8 @@ 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 +2121,6 @@ static int __init netvsc_drv_init(void)
 	if (ret)
 		return ret;
 
-	register_netdevice_notifier(&netvsc_netdev_notifier);
 	return 0;
 }
 
-- 
2.14.3

On Tue, 10 Apr 2018 11:59:50 -0700
Sridhar Samudrala <sridhar.samudrala at intel.com> wrote:
> Use the registration/notification framework supported by the generic
> bypass infrastructure.
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
> ---
Thanks for doing this.  Your current version has couple show stopper
issues.

First, the slave device is instantly taking over the slave.
This doesn't allow udev/systemd to do its device rename of the slave
device. Netvsc uses a delayed work to workaround this.

Secondly, the select queue needs to call queue selection in VF.
The bonding/teaming logic doesn't work well for UDP flows.
Commit b3bf5666a510 ("hv_netvsc: defer queue selection to VF")
fixed this performance problem.

Lastly, more indirection is bad in current climate.

I am not completely adverse to this but it needs to be fast, simple
and completely transparent.

Tue, Apr 10, 2018 at 08:59:48PM CEST, 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. existing netvsc driver that uses 2 netdev model. In this model, no
>master netdev is created. The paravirtual driver registers each bypass
>instance along with a set of ops to manage the slave events.
>     bypass_master_register()
>     bypass_master_unregister()
>2. new virtio_net based solution that uses 3 netdev model. In this model,
>the bypass module provides interfaces to create/destroy additional master
>netdev and all the slave events are managed internally.
>      bypass_master_create()
>      bypass_master_destroy()
>
>Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
>---
> include/linux/netdevice.h |  14 +
> include/net/bypass.h      |  96 ++++++
> net/Kconfig               |  18 +
> net/core/Makefile         |   1 +
> net/core/bypass.c         | 844
++++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 973 insertions(+)
> create mode 100644 include/net/bypass.h
> create mode 100644 net/core/bypass.c
>
>diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>index cf44503ea81a..587293728f70 100644
>--- a/include/linux/netdevice.h
>+++ b/include/linux/netdevice.h
>@@ -1430,6 +1430,8 @@ enum netdev_priv_flags {
> 	IFF_PHONY_HEADROOM		= 1<<24,
> 	IFF_MACSEC			= 1<<25,
> 	IFF_NO_RX_HANDLER		= 1<<26,
>+	IFF_BYPASS			= 1 << 27,
>+	IFF_BYPASS_SLAVE		= 1 << 28,
I wonder, why you don't follow the existing coding style... Also, please
add these to into the comment above.

> };
> 
> #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
>@@ -1458,6 +1460,8 @@ 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_BYPASS			IFF_BYPASS
>+#define IFF_BYPASS_SLAVE		IFF_BYPASS_SLAVE
> 
> /**
>  *	struct net_device - The DEVICE structure.
>@@ -4308,6 +4312,16 @@ static inline bool netif_is_rxfh_configured(const
struct net_device *dev)
> 	return dev->priv_flags & IFF_RXFH_CONFIGURED;
> }
> 
>+static inline bool netif_is_bypass_master(const struct net_device *dev)
>+{
>+	return dev->priv_flags & IFF_BYPASS;
>+}
>+
>+static inline bool netif_is_bypass_slave(const struct net_device *dev)
>+{
>+	return dev->priv_flags & IFF_BYPASS_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/bypass.h b/include/net/bypass.h
>new file mode 100644
>index 000000000000..86b02cb894cf
>--- /dev/null
>+++ b/include/net/bypass.h
>@@ -0,0 +1,96 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/* Copyright (c) 2018, Intel Corporation. */
>+
>+#ifndef _NET_BYPASS_H
>+#define _NET_BYPASS_H
>+
>+#include <linux/netdevice.h>
>+
>+struct bypass_ops {
>+	int (*slave_pre_register)(struct net_device *slave_netdev,
>+				  struct net_device *bypass_netdev);
>+	int (*slave_join)(struct net_device *slave_netdev,
>+			  struct net_device *bypass_netdev);
>+	int (*slave_pre_unregister)(struct net_device *slave_netdev,
>+				    struct net_device *bypass_netdev);
>+	int (*slave_release)(struct net_device *slave_netdev,
>+			     struct net_device *bypass_netdev);
>+	int (*slave_link_change)(struct net_device *slave_netdev,
>+				 struct net_device *bypass_netdev);
>+	rx_handler_result_t (*handle_frame)(struct sk_buff **pskb);
>+};
>+
>+struct bypass_master {
>+	struct list_head list;
>+	struct net_device __rcu *bypass_netdev;
>+	struct bypass_ops __rcu *ops;
>+};
>+
>+/* bypass state */
>+struct bypass_info {
>+	/* passthru netdev with same MAC */
>+	struct net_device __rcu *active_netdev;
You still use "active"/"backup" names which is highly
misleading as
it has completely different meaning that in bond for example.
I noted that in my previous review already. Please change it.

>+
>+	/* virtio_net netdev */
>+	struct net_device __rcu *backup_netdev;
>+
>+	/* active netdev stats */
>+	struct rtnl_link_stats64 active_stats;
>+
>+	/* backup netdev stats */
>+	struct rtnl_link_stats64 backup_stats;
>+
>+	/* aggregated stats */
>+	struct rtnl_link_stats64 bypass_stats;
>+
>+	/* spinlock while updating stats */
>+	spinlock_t stats_lock;
>+};
>+
>+#if IS_ENABLED(CONFIG_NET_BYPASS)
>+
>+int bypass_master_create(struct net_device *backup_netdev,
>+			 struct bypass_master **pbypass_master);
>+void bypass_master_destroy(struct bypass_master *bypass_master);
>+
>+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
>+			   struct bypass_master **pbypass_master);
>+void bypass_master_unregister(struct bypass_master *bypass_master);
>+
>+int bypass_slave_unregister(struct net_device *slave_netdev);
>+
>+#else
>+
>+static inline
>+int bypass_master_create(struct net_device *backup_netdev,
>+			 struct bypass_master **pbypass_master);
>+{
>+	return 0;
>+}
>+
>+static inline
>+void bypass_master_destroy(struct bypass_master *bypass_master)
>+{
>+}
>+
>+static inline
>+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
>+			   struct pbypass_master **pbypass_master);
>+{
>+	return 0;
>+}
>+
>+static inline
>+void bypass_master_unregister(struct bypass_master *bypass_master)
>+{
>+}
>+
>+static inline
>+int bypass_slave_unregister(struct net_device *slave_netdev)
>+{
>+	return 0;
>+}
>+
>+#endif
>+
>+#endif /* _NET_BYPASS_H */
>diff --git a/net/Kconfig b/net/Kconfig
>index 0428f12c25c2..994445f4a96a 100644
>--- a/net/Kconfig
>+++ b/net/Kconfig
>@@ -423,6 +423,24 @@ config MAY_USE_DEVLINK
> 	  on MAY_USE_DEVLINK to ensure they do not cause link errors when
> 	  devlink is a loadable module and the driver using it is built-in.
> 
>+config NET_BYPASS
>+	tristate "Bypass interface"
>+	---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.
>+
>+config MAY_USE_BYPASS
>+	tristate
>+	default m if NET_BYPASS=m
>+	default y if NET_BYPASS=y || NET_BYPASS=n
>+	help
>+	  Drivers using the bypass infrastructure should have a dependency
>+	  on MAY_USE_BYPASS to ensure they do not cause link errors when
>+	  bypass is a loadable module and the driver using it is built-in.
>+
> 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 6dbbba8c57ae..a9727ed1c8fc 100644
>--- a/net/core/Makefile
>+++ b/net/core/Makefile
>@@ -30,3 +30,4 @@ 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_BYPASS) += bypass.o
>diff --git a/net/core/bypass.c b/net/core/bypass.c
>new file mode 100644
>index 000000000000..b5b9cb554c3f
>--- /dev/null
>+++ b/net/core/bypass.c
>@@ -0,0 +1,844 @@
>+// 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/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/bypass.h>
>+
>+static LIST_HEAD(bypass_master_list);
>+static DEFINE_SPINLOCK(bypass_lock);
>+
>+static int bypass_slave_pre_register(struct net_device *slave_netdev,
>+				     struct net_device *bypass_netdev,
>+				     struct bypass_ops *bypass_ops)
>+{
>+	struct bypass_info *bi;
>+	bool backup;
>+
>+	if (bypass_ops) {
>+		if (!bypass_ops->slave_pre_register)
>+			return -EINVAL;
>+
>+		return bypass_ops->slave_pre_register(slave_netdev,
>+						      bypass_netdev);
>+	}
>+
>+	bi = netdev_priv(bypass_netdev);
>+	backup = (slave_netdev->dev.parent == bypass_netdev->dev.parent);
>+	if (backup ? rtnl_dereference(bi->backup_netdev) :
>+			rtnl_dereference(bi->active_netdev)) {
>+		netdev_err(bypass_netdev, "%s attempting to register as slave dev
when %s already present\n",
>+			   slave_netdev->name, backup ? "backup" :
"active");
>+		return -EEXIST;
>+	}
>+
>+	/* Avoid non pci devices as active netdev */
>+	if (!backup && (!slave_netdev->dev.parent ||
>+			!dev_is_pci(slave_netdev->dev.parent)))
>+		return -EINVAL;
>+
>+	return 0;
>+}
>+
>+static int bypass_slave_join(struct net_device *slave_netdev,
>+			     struct net_device *bypass_netdev,
>+			     struct bypass_ops *bypass_ops)
>+{
>+	struct bypass_info *bi;
>+	bool backup;
>+
>+	if (bypass_ops) {
>+		if (!bypass_ops->slave_join)
>+			return -EINVAL;
>+
>+		return bypass_ops->slave_join(slave_netdev, bypass_netdev);
>+	}
>+
>+	bi = netdev_priv(bypass_netdev);
>+	backup = (slave_netdev->dev.parent == bypass_netdev->dev.parent);
>+
>+	dev_hold(slave_netdev);
>+
>+	if (backup) {
>+		rcu_assign_pointer(bi->backup_netdev, slave_netdev);
>+		dev_get_stats(bi->backup_netdev, &bi->backup_stats);
>+	} else {
>+		rcu_assign_pointer(bi->active_netdev, slave_netdev);
>+		dev_get_stats(bi->active_netdev, &bi->active_stats);
>+		bypass_netdev->min_mtu = slave_netdev->min_mtu;
>+		bypass_netdev->max_mtu = slave_netdev->max_mtu;
>+	}
>+
>+	netdev_info(bypass_netdev, "bypass slave:%s joined\n",
>+		    slave_netdev->name);
>+
>+	return 0;
>+}
>+
>+/* Called when slave dev is injecting data into network stack.
>+ * Change the associated network device from lower dev to virtio.
>+ * note: already called with rcu_read_lock
>+ */
>+static rx_handler_result_t bypass_handle_frame(struct sk_buff **pskb)
>+{
>+	struct sk_buff *skb = *pskb;
>+	struct net_device *ndev =
rcu_dereference(skb->dev->rx_handler_data);
>+
>+	skb->dev = ndev;
>+
>+	return RX_HANDLER_ANOTHER;
>+}
>+
>+static struct net_device *bypass_master_get_bymac(u8 *mac,
>+						  struct bypass_ops **ops)
>+{
>+	struct bypass_master *bypass_master;
>+	struct net_device *bypass_netdev;
>+
>+	spin_lock(&bypass_lock);
>+	list_for_each_entry(bypass_master, &bypass_master_list, list) {
As I wrote the last time, you don't need this list, spinlock.
You can do just something like:
        for_each_net(net) {
                for_each_netdev(net, dev) {
			if (netif_is_bypass_master(dev)) {



>+		bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
>+		if (ether_addr_equal(bypass_netdev->perm_addr, mac)) {
>+			*ops = rcu_dereference(bypass_master->ops);
I don't see how rcu_dereference is ok here.
1) I don't see rcu_read_lock taken
2) Looks like bypass_master->ops has the same value across the whole
   existence.

>+			spin_unlock(&bypass_lock);
>+			return bypass_netdev;
>+		}
>+	}
>+	spin_unlock(&bypass_lock);
>+	return NULL;
>+}
>+
>+static int bypass_slave_register(struct net_device *slave_netdev)
>+{
>+	struct net_device *bypass_netdev;
>+	struct bypass_ops *bypass_ops;
>+	int ret, orig_mtu;
>+
>+	ASSERT_RTNL();
>+
>+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
>+						&bypass_ops);
For master, could you use word "master" in the variables so it is
clear?
Also, "dev" is fine instead of "netdev".
Something like "bpmaster_dev"

>+	if (!bypass_netdev)
>+		goto done;
>+
>+	ret = bypass_slave_pre_register(slave_netdev, bypass_netdev,
>+					bypass_ops);
>+	if (ret != 0)
	Just "if (ret)" will do. You have this on more places.

>+		goto done;
>+
>+	ret = netdev_rx_handler_register(slave_netdev,
>+					 bypass_ops ? bypass_ops->handle_frame :
>+					 bypass_handle_frame, bypass_netdev);
>+	if (ret != 0) {
>+		netdev_err(slave_netdev, "can not register bypass rx handler (err =
%d)\n",
>+			   ret);
>+		goto done;
>+	}
>+
>+	ret = netdev_upper_dev_link(slave_netdev, bypass_netdev, NULL);
>+	if (ret != 0) {
>+		netdev_err(slave_netdev, "can not set master device %s (err =
%d)\n",
>+			   bypass_netdev->name, ret);
>+		goto upper_link_failed;
>+	}
>+
>+	slave_netdev->priv_flags |= IFF_BYPASS_SLAVE;
>+
>+	if (netif_running(bypass_netdev)) {
>+		ret = dev_open(slave_netdev);
>+		if (ret && (ret != -EBUSY)) {
>+			netdev_err(bypass_netdev, "Opening slave %s failed ret:%d\n",
>+				   slave_netdev->name, ret);
>+			goto err_interface_up;
>+		}
>+	}
>+
>+	/* Align MTU of slave with master */
>+	orig_mtu = slave_netdev->mtu;
>+	ret = dev_set_mtu(slave_netdev, bypass_netdev->mtu);
>+	if (ret != 0) {
>+		netdev_err(bypass_netdev, "unable to change mtu of %s to %u register
failed\n",
>+			   slave_netdev->name, bypass_netdev->mtu);
>+		goto err_set_mtu;
>+	}
>+
>+	ret = bypass_slave_join(slave_netdev, bypass_netdev, bypass_ops);
>+	if (ret != 0)
>+		goto err_join;
>+
>+	call_netdevice_notifiers(NETDEV_JOIN, slave_netdev);
>+
>+	netdev_info(bypass_netdev, "bypass slave:%s registered\n",
>+		    slave_netdev->name);
>+
>+	goto done;
>+
>+err_join:
>+	dev_set_mtu(slave_netdev, orig_mtu);
>+err_set_mtu:
>+	dev_close(slave_netdev);
>+err_interface_up:
>+	netdev_upper_dev_unlink(slave_netdev, bypass_netdev);
>+	slave_netdev->priv_flags &= ~IFF_BYPASS_SLAVE;
>+upper_link_failed:
>+	netdev_rx_handler_unregister(slave_netdev);
>+done:
>+	return NOTIFY_DONE;
>+}
>+
>+static int bypass_slave_pre_unregister(struct net_device *slave_netdev,
>+				       struct net_device *bypass_netdev,
>+				       struct bypass_ops *bypass_ops)
>+{
>+	struct net_device *backup_netdev, *active_netdev;
>+	struct bypass_info *bi;
>+
>+	if (bypass_ops) {
>+		if (!bypass_ops->slave_pre_unregister)
>+			return -EINVAL;
>+
>+		return bypass_ops->slave_pre_unregister(slave_netdev,
>+							bypass_netdev);
>+	}
>+
>+	bi = netdev_priv(bypass_netdev);
>+	active_netdev = rtnl_dereference(bi->active_netdev);
>+	backup_netdev = rtnl_dereference(bi->backup_netdev);
>+
>+	if (slave_netdev != active_netdev && slave_netdev !=
backup_netdev)
>+		return -EINVAL;
>+
>+	return 0;
>+}
>+
>+static int bypass_slave_release(struct net_device *slave_netdev,
>+				struct net_device *bypass_netdev,
>+				struct bypass_ops *bypass_ops)
>+{
>+	struct net_device *backup_netdev, *active_netdev;
>+	struct bypass_info *bi;
>+
>+	if (bypass_ops) {
>+		if (!bypass_ops->slave_release)
>+			return -EINVAL;
I think it would be good to make the API to the driver more strict and
have a separate set of ops for "active" and "backup"
netdevices.
That should stop people thinking about extending this to more slaves in
the future.


>+
>+		return bypass_ops->slave_release(slave_netdev, bypass_netdev);
>+	}
>+
>+	bi = netdev_priv(bypass_netdev);
>+	active_netdev = rtnl_dereference(bi->active_netdev);
>+	backup_netdev = rtnl_dereference(bi->backup_netdev);
>+
>+	if (slave_netdev == backup_netdev) {
>+		RCU_INIT_POINTER(bi->backup_netdev, NULL);
>+	} else {
>+		RCU_INIT_POINTER(bi->active_netdev, NULL);
>+		if (backup_netdev) {
>+			bypass_netdev->min_mtu = backup_netdev->min_mtu;
>+			bypass_netdev->max_mtu = backup_netdev->max_mtu;
>+		}
>+	}
>+
>+	dev_put(slave_netdev);
>+
>+	netdev_info(bypass_netdev, "bypass slave:%s released\n",
>+		    slave_netdev->name);
>+
>+	return 0;
>+}
>+
>+int bypass_slave_unregister(struct net_device *slave_netdev)
>+{
>+	struct net_device *bypass_netdev;
>+	struct bypass_ops *bypass_ops;
>+	int ret;
>+
>+	if (!netif_is_bypass_slave(slave_netdev))
>+		goto done;
>+
>+	ASSERT_RTNL();
>+
>+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
>+						&bypass_ops);
>+	if (!bypass_netdev)
>+		goto done;
>+
>+	ret = bypass_slave_pre_unregister(slave_netdev, bypass_netdev,
>+					  bypass_ops);
>+	if (ret != 0)
>+		goto done;
>+
>+	netdev_rx_handler_unregister(slave_netdev);
>+	netdev_upper_dev_unlink(slave_netdev, bypass_netdev);
>+	slave_netdev->priv_flags &= ~IFF_BYPASS_SLAVE;
>+
>+	bypass_slave_release(slave_netdev, bypass_netdev, bypass_ops);
>+
>+	netdev_info(bypass_netdev, "bypass slave:%s unregistered\n",
>+		    slave_netdev->name);
>+
>+done:
>+	return NOTIFY_DONE;
>+}
>+EXPORT_SYMBOL_GPL(bypass_slave_unregister);
>+
>+static bool bypass_xmit_ready(struct net_device *dev)
>+{
>+	return netif_running(dev) && netif_carrier_ok(dev);
>+}
>+
>+static int bypass_slave_link_change(struct net_device *slave_netdev)
>+{
>+	struct net_device *bypass_netdev, *active_netdev, *backup_netdev;
>+	struct bypass_ops *bypass_ops;
>+	struct bypass_info *bi;
>+
>+	if (!netif_is_bypass_slave(slave_netdev))
>+		goto done;
>+
>+	ASSERT_RTNL();
>+
>+	bypass_netdev = bypass_master_get_bymac(slave_netdev->perm_addr,
>+						&bypass_ops);
>+	if (!bypass_netdev)
>+		goto done;
>+
>+	if (bypass_ops) {
>+		if (!bypass_ops->slave_link_change)
>+			goto done;
>+
>+		return bypass_ops->slave_link_change(slave_netdev,
>+						     bypass_netdev);
>+	}
>+
>+	if (!netif_running(bypass_netdev))
>+		return 0;
>+
>+	bi = netdev_priv(bypass_netdev);
>+
>+	active_netdev = rtnl_dereference(bi->active_netdev);
>+	backup_netdev = rtnl_dereference(bi->backup_netdev);
>+
>+	if (slave_netdev != active_netdev && slave_netdev !=
backup_netdev)
>+		goto done;
You don't need this check. "if
(!netif_is_bypass_slave(slave_netdev))"
above is enough.

>+
>+	if ((active_netdev && bypass_xmit_ready(active_netdev)) ||
>+	    (backup_netdev && bypass_xmit_ready(backup_netdev))) {
>+		netif_carrier_on(bypass_netdev);
>+		netif_tx_wake_all_queues(bypass_netdev);
>+	} else {
>+		netif_carrier_off(bypass_netdev);
>+		netif_tx_stop_all_queues(bypass_netdev);
>+	}
>+
>+done:
>+	return NOTIFY_DONE;
>+}
>+
>+static bool bypass_validate_event_dev(struct net_device *dev)
>+{
>+	/* Skip parent events */
>+	if (netif_is_bypass_master(dev))
>+		return false;
>+
>+	/* Avoid non-Ethernet type devices */
>+	if (dev->type != ARPHRD_ETHER)
>+		return false;
>+
>+	/* Avoid Vlan dev with same MAC registering as VF */
>+	if (is_vlan_dev(dev))
>+		return false;
>+
>+	/* Avoid Bonding master dev with same MAC registering as slave dev */
>+	if ((dev->priv_flags & IFF_BONDING) && (dev->flags &
IFF_MASTER))
Yeah, this is certainly incorrect. One thing is, you should be using the
helpers netif_is_bond_master().
But what about the rest? macsec, macvlan, team, bridge, ovs and others?

You need to do it not by blacklisting, but with whitelisting. You need
to whitelist VF devices. My port flavours patchset might help with this.

>+		return false;
>+
>+	return true;
>+}
>+
>+static int
>+bypass_event(struct notifier_block *this, unsigned long event, void *ptr)
>+{
>+	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
>+
>+	if (!bypass_validate_event_dev(event_dev))
>+		return NOTIFY_DONE;
>+
>+	switch (event) {
>+	case NETDEV_REGISTER:
>+		return bypass_slave_register(event_dev);
>+	case NETDEV_UNREGISTER:
>+		return bypass_slave_unregister(event_dev);
>+	case NETDEV_UP:
>+	case NETDEV_DOWN:
>+	case NETDEV_CHANGE:
>+		return bypass_slave_link_change(event_dev);
>+	default:
>+		return NOTIFY_DONE;
>+	}
>+}
>+
>+static struct notifier_block bypass_notifier = {
>+	.notifier_call = bypass_event,
>+};
>+
>+int bypass_open(struct net_device *dev)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
>+	struct net_device *active_netdev, *backup_netdev;
>+	int err;
>+
>+	netif_carrier_off(dev);
>+	netif_tx_wake_all_queues(dev);
>+
>+	active_netdev = rtnl_dereference(bi->active_netdev);
>+	if (active_netdev) {
>+		err = dev_open(active_netdev);
>+		if (err)
>+			goto err_active_open;
>+	}
>+
>+	backup_netdev = rtnl_dereference(bi->backup_netdev);
>+	if (backup_netdev) {
>+		err = dev_open(backup_netdev);
>+		if (err)
>+			goto err_backup_open;
>+	}
>+
>+	return 0;
>+
>+err_backup_open:
>+	dev_close(active_netdev);
>+err_active_open:
>+	netif_tx_disable(dev);
>+	return err;
>+}
>+EXPORT_SYMBOL_GPL(bypass_open);
>+
>+int bypass_close(struct net_device *dev)
>+{
>+	struct bypass_info *vi = netdev_priv(dev);
This should be probably "bi"

>+	struct net_device *slave_netdev;
>+
>+	netif_tx_disable(dev);
>+
>+	slave_netdev = rtnl_dereference(vi->active_netdev);
>+	if (slave_netdev)
>+		dev_close(slave_netdev);
>+
>+	slave_netdev = rtnl_dereference(vi->backup_netdev);
>+	if (slave_netdev)
>+		dev_close(slave_netdev);
>+
>+	return 0;
>+}
>+EXPORT_SYMBOL_GPL(bypass_close);
>+
>+static netdev_tx_t bypass_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;
>+}
>+
>+netdev_tx_t bypass_start_xmit(struct sk_buff *skb, struct net_device *dev)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
If you rename the other variable to "bpmaster_dev", it would be nice
to
rename this to bpinfo or something more descriptive. "bi" is too short
to know what that is right away.

>+	struct net_device *xmit_dev;
Don't mix "dev" and "netdev" in one .c file. Just use
"dev" for all.


>+
>+	/* Try xmit via active netdev followed by backup netdev */
>+	xmit_dev = rcu_dereference_bh(bi->active_netdev);
>+	if (!xmit_dev || !bypass_xmit_ready(xmit_dev)) {
>+		xmit_dev = rcu_dereference_bh(bi->backup_netdev);
>+		if (!xmit_dev || !bypass_xmit_ready(xmit_dev))
>+			return bypass_drop_xmit(skb, dev);
>+	}
>+
>+	skb->dev = xmit_dev;
>+	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
>+
>+	return dev_queue_xmit(skb);
>+}
>+EXPORT_SYMBOL_GPL(bypass_start_xmit);
>+
>+u16 bypass_select_queue(struct net_device *dev, struct sk_buff *skb,
>+			void *accel_priv, select_queue_fallback_t fallback)
>+{
>+	/* This helper function exists to help dev_pick_tx get the correct
>+	 * destination queue.  Using a helper function skips a call to
>+	 * skb_tx_hash and will put the skbs in the queue we expect on their
>+	 * way down to the bonding driver.
>+	 */
>+	u16 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;
>+}
>+EXPORT_SYMBOL_GPL(bypass_select_queue);
>+
>+/* fold stats, assuming all rtnl_link_stats64 fields are u64, but
>+ * that some drivers can provide 32bit values only.
>+ */
>+static void bypass_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;
>+	}
>+}
>+
>+void bypass_get_stats(struct net_device *dev, struct rtnl_link_stats64
*stats)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
You can WARN_ON and return in case the dev is not bypass master, just
to catch buggy drivers. Same with other helpers.

>+	const struct rtnl_link_stats64 *new;
>+	struct rtnl_link_stats64 temp;
>+	struct net_device *slave_netdev;
>+
>+	spin_lock(&bi->stats_lock);
>+	memcpy(stats, &bi->bypass_stats, sizeof(*stats));
>+
>+	rcu_read_lock();
>+
>+	slave_netdev = rcu_dereference(bi->active_netdev);
>+	if (slave_netdev) {
>+		new = dev_get_stats(slave_netdev, &temp);
>+		bypass_fold_stats(stats, new, &bi->active_stats);
>+		memcpy(&bi->active_stats, new, sizeof(*new));
>+	}
>+
>+	slave_netdev = rcu_dereference(bi->backup_netdev);
>+	if (slave_netdev) {
>+		new = dev_get_stats(slave_netdev, &temp);
>+		bypass_fold_stats(stats, new, &bi->backup_stats);
>+		memcpy(&bi->backup_stats, new, sizeof(*new));
>+	}
>+
>+	rcu_read_unlock();
>+
>+	memcpy(&bi->bypass_stats, stats, sizeof(*stats));
>+	spin_unlock(&bi->stats_lock);
>+}
>+EXPORT_SYMBOL_GPL(bypass_get_stats);
>+
>+int bypass_change_mtu(struct net_device *dev, int new_mtu)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
>+	struct net_device *active_netdev, *backup_netdev;
>+	int ret = 0;
Pointless initialization.

>+
>+	active_netdev = rcu_dereference(bi->active_netdev);
>+	if (active_netdev) {
>+		ret = dev_set_mtu(active_netdev, new_mtu);
>+		if (ret)
>+			return ret;
>+	}
>+
>+	backup_netdev = rcu_dereference(bi->backup_netdev);
>+	if (backup_netdev) {
>+		ret = dev_set_mtu(backup_netdev, new_mtu);
>+		if (ret) {
>+			dev_set_mtu(active_netdev, dev->mtu);
>+			return ret;
>+		}
>+	}
>+
>+	dev->mtu = new_mtu;
>+	return 0;
>+}
>+EXPORT_SYMBOL_GPL(bypass_change_mtu);
>+
>+void bypass_set_rx_mode(struct net_device *dev)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
>+	struct net_device *slave_netdev;
>+
>+	rcu_read_lock();
>+
>+	slave_netdev = rcu_dereference(bi->active_netdev);
>+	if (slave_netdev) {
>+		dev_uc_sync_multiple(slave_netdev, dev);
>+		dev_mc_sync_multiple(slave_netdev, dev);
>+	}
>+
>+	slave_netdev = rcu_dereference(bi->backup_netdev);
>+	if (slave_netdev) {
>+		dev_uc_sync_multiple(slave_netdev, dev);
>+		dev_mc_sync_multiple(slave_netdev, dev);
>+	}
>+
>+	rcu_read_unlock();
>+}
>+EXPORT_SYMBOL_GPL(bypass_set_rx_mode);
>+
>+static const struct net_device_ops bypass_netdev_ops = {
>+	.ndo_open		= bypass_open,
>+	.ndo_stop		= bypass_close,
>+	.ndo_start_xmit		= bypass_start_xmit,
>+	.ndo_select_queue	= bypass_select_queue,
>+	.ndo_get_stats64	= bypass_get_stats,
>+	.ndo_change_mtu		= bypass_change_mtu,
>+	.ndo_set_rx_mode	= bypass_set_rx_mode,
>+	.ndo_validate_addr	= eth_validate_addr,
>+	.ndo_features_check	= passthru_features_check,
>+};
>+
>+#define BYPASS_DRV_NAME "bypass"
>+#define BYPASS_DRV_VERSION "0.1"
>+
>+static void bypass_ethtool_get_drvinfo(struct net_device *dev,
>+				       struct ethtool_drvinfo *drvinfo)
>+{
>+	strlcpy(drvinfo->driver, BYPASS_DRV_NAME, sizeof(drvinfo->driver));
>+	strlcpy(drvinfo->version, BYPASS_DRV_VERSION,
sizeof(drvinfo->version));
>+}
>+
>+int bypass_ethtool_get_link_ksettings(struct net_device *dev,
>+				      struct ethtool_link_ksettings *cmd)
>+{
>+	struct bypass_info *bi = netdev_priv(dev);
>+	struct net_device *slave_netdev;
>+
>+	slave_netdev = rtnl_dereference(bi->active_netdev);
>+	if (!slave_netdev || !bypass_xmit_ready(slave_netdev)) {
>+		slave_netdev = rtnl_dereference(bi->backup_netdev);
>+		if (!slave_netdev || !bypass_xmit_ready(slave_netdev)) {
>+			cmd->base.duplex = DUPLEX_UNKNOWN;
>+			cmd->base.port = PORT_OTHER;
>+			cmd->base.speed = SPEED_UNKNOWN;
>+
>+			return 0;
>+		}
>+	}
>+
>+	return __ethtool_get_link_ksettings(slave_netdev, cmd);
>+}
>+EXPORT_SYMBOL_GPL(bypass_ethtool_get_link_ksettings);
>+
>+static const struct ethtool_ops bypass_ethtool_ops = {
>+	.get_drvinfo            = bypass_ethtool_get_drvinfo,
>+	.get_link               = ethtool_op_get_link,
>+	.get_link_ksettings     = bypass_ethtool_get_link_ksettings,
>+};
>+
>+static void bypass_register_existing_slave(struct net_device
*bypass_netdev)
>+{
>+	struct net *net = dev_net(bypass_netdev);
>+	struct net_device *dev;
>+
>+	rtnl_lock();
>+	for_each_netdev(net, dev) {
>+		if (dev == bypass_netdev)
>+			continue;
>+		if (!bypass_validate_event_dev(dev))
>+			continue;
>+		if (ether_addr_equal(bypass_netdev->perm_addr, dev->perm_addr))
>+			bypass_slave_register(dev);
>+	}
>+	rtnl_unlock();
>+}
>+
>+int bypass_master_register(struct net_device *dev, struct bypass_ops *ops,
>+			   struct bypass_master **pbypass_master)
>+{
>+	struct bypass_master *bypass_master;
>+
>+	bypass_master = kzalloc(sizeof(*bypass_master), GFP_KERNEL);
>+	if (!bypass_master)
>+		return -ENOMEM;
>+
>+	rcu_assign_pointer(bypass_master->ops, ops);
>+	dev_hold(dev);
>+	dev->priv_flags |= IFF_BYPASS;
>+	rcu_assign_pointer(bypass_master->bypass_netdev, dev);
>+
>+	spin_lock(&bypass_lock);
>+	list_add_tail(&bypass_master->list, &bypass_master_list);
>+	spin_unlock(&bypass_lock);
>+
>+	bypass_register_existing_slave(dev);
>+
>+	*pbypass_master = bypass_master;
>+	return 0;
>+}
>+EXPORT_SYMBOL_GPL(bypass_master_register);
>+
>+void bypass_master_unregister(struct bypass_master *bypass_master)
>+{
>+	struct net_device *bypass_netdev;
>+
>+	bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
>+
>+	bypass_netdev->priv_flags &= ~IFF_BYPASS;
>+	dev_put(bypass_netdev);
>+
>+	spin_lock(&bypass_lock);
>+	list_del(&bypass_master->list);
>+	spin_unlock(&bypass_lock);
>+
>+	kfree(bypass_master);
>+}
>+EXPORT_SYMBOL_GPL(bypass_master_unregister);
>+
>+int bypass_master_create(struct net_device *backup_netdev,
>+			 struct bypass_master **pbypass_master)
>+{
>+	struct device *dev = backup_netdev->dev.parent;
>+	struct net_device *bypass_netdev;
>+	int err;
>+
>+	/* Alloc at least 2 queues, for now we are going with 16 assuming
>+	 * that most devices being bonded won't have too many queues.
>+	 */
>+	bypass_netdev = alloc_etherdev_mq(sizeof(struct bypass_info), 16);
>+	if (!bypass_netdev) {
>+		dev_err(dev, "Unable to allocate bypass_netdev!\n");
>+		return -ENOMEM;
>+	}
>+
>+	dev_net_set(bypass_netdev, dev_net(backup_netdev));
>+	SET_NETDEV_DEV(bypass_netdev, dev);
>+
>+	bypass_netdev->netdev_ops = &bypass_netdev_ops;
>+	bypass_netdev->ethtool_ops = &bypass_ethtool_ops;
>+
>+	/* Initialize the device options */
>+	bypass_netdev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
>+	bypass_netdev->priv_flags &= ~(IFF_XMIT_DST_RELEASE |
>+				       IFF_TX_SKB_SHARING);
>+
>+	/* don't acquire bypass netdev's netif_tx_lock when transmitting
*/
>+	bypass_netdev->features |= NETIF_F_LLTX;
>+
>+	/* Don't allow bypass devices to change network namespaces. */
>+	bypass_netdev->features |= NETIF_F_NETNS_LOCAL;
>+
>+	bypass_netdev->hw_features = NETIF_F_HW_CSUM | NETIF_F_SG |
>+				     NETIF_F_FRAGLIST | NETIF_F_ALL_TSO |
>+				     NETIF_F_HIGHDMA | NETIF_F_LRO;
>+
>+	bypass_netdev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
>+	bypass_netdev->features |= bypass_netdev->hw_features;
>+
>+	memcpy(bypass_netdev->dev_addr, backup_netdev->dev_addr,
>+	       bypass_netdev->addr_len);
>+
>+	bypass_netdev->min_mtu = backup_netdev->min_mtu;
>+	bypass_netdev->max_mtu = backup_netdev->max_mtu;
>+
>+	err = register_netdev(bypass_netdev);
>+	if (err < 0) {
>+		dev_err(dev, "Unable to register bypass_netdev!\n");
>+		goto err_register_netdev;
>+	}
>+
>+	netif_carrier_off(bypass_netdev);
>+
>+	err = bypass_master_register(bypass_netdev, NULL, pbypass_master);
>+	if (err < 0)
just "if (err)" would do.

>+		goto err_bypass;
>+
>+	return 0;
>+
>+err_bypass:
>+	unregister_netdev(bypass_netdev);
>+err_register_netdev:
>+	free_netdev(bypass_netdev);
>+
>+	return err;
>+}
>+EXPORT_SYMBOL_GPL(bypass_master_create);
>+
>+void bypass_master_destroy(struct bypass_master *bypass_master)
>+{
>+	struct net_device *bypass_netdev;
>+	struct net_device *slave_netdev;
>+	struct bypass_info *bi;
>+
>+	if (!bypass_master)
>+		return;
>+
>+	bypass_netdev = rcu_dereference(bypass_master->bypass_netdev);
>+	bi = netdev_priv(bypass_netdev);
>+
>+	netif_device_detach(bypass_netdev);
>+
>+	rtnl_lock();
>+
>+	slave_netdev = rtnl_dereference(bi->active_netdev);
>+	if (slave_netdev)
>+		bypass_slave_unregister(slave_netdev);
>+
>+	slave_netdev = rtnl_dereference(bi->backup_netdev);
>+	if (slave_netdev)
>+		bypass_slave_unregister(slave_netdev);
>+
>+	bypass_master_unregister(bypass_master);
>+
>+	unregister_netdevice(bypass_netdev);
>+
>+	rtnl_unlock();
>+
>+	free_netdev(bypass_netdev);
>+}
>+EXPORT_SYMBOL_GPL(bypass_master_destroy);
>+
>+static __init int
>+bypass_init(void)
>+{
>+	register_netdevice_notifier(&bypass_notifier);
>+
>+	return 0;
>+}
>+module_init(bypass_init);
>+
>+static __exit
>+void bypass_exit(void)
>+{
>+	unregister_netdevice_notifier(&bypass_notifier);
>+}
>+module_exit(bypass_exit);
>+
>+MODULE_DESCRIPTION("Bypass infrastructure/interface for Paravirtual
drivers");
>+MODULE_LICENSE("GPL v2");
>-- 
>2.14.3
>