Linux Virtualization - Apr 2018 - [PATCH v7 net-next 3/4] virtio_net: Extend virtio to use VF datapath when available

The main motivation for this patch is to enable cloud service providers
to provide an accelerated datapath to virtio-net enabled VMs in a 
transparent manner with no/minimal guest userspace changes. This also
enables hypervisor controlled live migration to be supported with VMs that
have direct attached SR-IOV VF devices.

Patch 1 introduces a new feature bit VIRTIO_NET_F_STANDBY that can be
used by hypervisor to indicate that virtio_net interface should act as
a standby for another device with the same MAC address.

Patch 2 introduces a failover module that provides a generic interface for 
paravirtual drivers to listen for netdev register/unregister/link change
events from pci ethernet devices with the same MAC and takeover their
datapath. The notifier and event handling code is based on the existing
netvsc implementation. It provides 2 sets of interfaces to paravirtual 
drivers to support 2-netdev(netvsc) and 3-netdev(virtio_net) models.

Patch 3 extends virtio_net to use alternate datapath when available and
registered. When STANDBY feature is enabled, virtio_net driver creates
an additional 'failover' netdev that acts as a master device and
controls
2 slave devices.  The original virtio_net netdev is registered as
'standby' netdev and a passthru/vf device with the same MAC gets
registered as 'primary' netdev. Both 'standby' and
'primary' netdevs are
associated with the same 'pci' device.  The user accesses the network
interface via 'failover' netdev. The 'failover' netdev chooses
'primary'
netdev as default for transmits when it is available with link up and
running.

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

As this patch series is initially focusing on usecases where hypervisor 
fully controls the VM networking and the guest is not expected to directly 
configure any hardware settings, it doesn't expose all the ndo/ethtool ops
that are supported by virtio_net at this time. To support additional usecases,
it should be possible to enable additional ops later by caching the state
in virtio netdev and replaying when the 'primary' netdev gets
registered.
 
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

v7
- Rename 'bypass/active/backup' terminology with
'failover/primary/standy'
  (jiri, mst)
- re-arranged dev_open() and dev_set_mtu() calls in the register routines
  so that they don't get called for 2-netdev model. (stephen)
- fixed select_queue() routine to do queue selection based on VF if it is
  registered as primary. (stephen)
-  minor bugfixes

v6 RFC:
  Simplified virtio_net changes by moving all the ndo_ops of the 
  bypass_netdev and create/destroy of bypass_netdev to 'bypass' module.
  avoided 2 phase registration(driver + instances).
  introduced IFF_BYPASS/IFF_BYPASS_SLAVE dev->priv_flags 
  replaced mutex with a spinlock

v5 RFC:
  Based on Jiri's comments, moved the common functionality to a
'bypass'
  module so that the same notifier and event handlers to handle child
  register/unregister/link change events can be shared between virtio_net
  and netvsc.
  Improved error handling based on Siwei's comments.
v4:
- Based on the review comments on the v3 version of the RFC patch and
  Jakub's suggestion for the naming issue with 3 netdev solution,
  proposed 3 netdev in-driver bonding solution for virtio-net.
v3 RFC:
- Introduced 3 netdev model and pointed out a couple of issues with
  that model and proposed 2 netdev model to avoid these issues.
- Removed broadcast/multicast optimization and only use virtio as
  backup path when VF is unplugged.
v2 RFC:
- Changed VIRTIO_NET_F_MASTER to VIRTIO_NET_F_BACKUP (mst)
- made a small change to the virtio-net xmit path to only use VF datapath
  for unicasts. Broadcasts/multicasts use virtio datapath. This avoids
  east-west broadcasts to go over the PCI link.
- added suppport for the feature bit in qemu

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

 drivers/net/Kconfig             |   1 +
 drivers/net/hyperv/Kconfig      |   1 +
 drivers/net/hyperv/hyperv_net.h |   2 +
 drivers/net/hyperv/netvsc_drv.c | 208 +++-------
 drivers/net/virtio_net.c        |  38 +-
 include/linux/netdevice.h       |  16 +
 include/net/failover.h          |  96 +++++
 include/uapi/linux/virtio_net.h |   3 +
 net/Kconfig                     |  18 +
 net/core/Makefile               |   1 +
 net/core/failover.c             | 844 ++++++++++++++++++++++++++++++++++++++++
 11 files changed, 1070 insertions(+), 158 deletions(-)
 create mode 100644 include/net/failover.h
 create mode 100644 net/core/failover.c

-- 
2.14.3

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

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

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

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7b187ec7411e..6f95719ede40 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_STANDBY
 
 static unsigned int features[] = {
 	VIRTNET_FEATURES,
diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index 5de6ed37695b..a3715a3224c1 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -57,6 +57,9 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_STANDBY	  62	/* Act as standby for another device
+					 * with the same MAC.
+					 */
 #define VIRTIO_NET_F_SPEED_DUPLEX 63	/* Device set linkspeed and duplex */
 
 #ifndef VIRTIO_NET_NO_LEGACY
-- 
2.14.3

This provides a generic interface for paravirtual drivers to listen
for netdev register/unregister/link change events from pci ethernet
devices with the same MAC and takeover their datapath. The notifier and
event handling code is based on the existing netvsc implementation.

It exposes 2 sets of interfaces to the paravirtual drivers.
1. existing netvsc driver that uses 2 netdev model. In this model, no
master netdev is created. The paravirtual driver registers each instance
of netvsc as a 'failover' instance  along with a set of ops to manage
the
slave events.
     failover_register()
     failover_unregister()
2. new virtio_net based solution that uses 3 netdev model. In this model,
the failover module provides interfaces to create/destroy additional master
netdev and all the slave events are managed internally.
      failover_create()
      failover_destroy()
These functions call failover_register()/failover_unregister() with the
master netdev created by the failover module.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 include/linux/netdevice.h |  16 +
 include/net/failover.h    |  96 ++++++
 net/Kconfig               |  18 +
 net/core/Makefile         |   1 +
 net/core/failover.c       | 844 ++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 975 insertions(+)
 create mode 100644 include/net/failover.h
 create mode 100644 net/core/failover.c

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cf44503ea81a..ed535b6724e1 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1401,6 +1401,8 @@ struct net_device_ops {
  *	entity (i.e. the master device for bridged veth)
  * @IFF_MACSEC: device is a MACsec device
  * @IFF_NO_RX_HANDLER: device doesn't support the rx_handler hook
+ * @IFF_FAILOVER: device is a failover master device
+ * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
  */
 enum netdev_priv_flags {
 	IFF_802_1Q_VLAN			= 1<<0,
@@ -1430,6 +1432,8 @@ enum netdev_priv_flags {
 	IFF_PHONY_HEADROOM		= 1<<24,
 	IFF_MACSEC			= 1<<25,
 	IFF_NO_RX_HANDLER		= 1<<26,
+	IFF_FAILOVER			= 1<<27,
+	IFF_FAILOVER_SLAVE		= 1<<28,
 };
 
 #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
@@ -1458,6 +1462,8 @@ enum netdev_priv_flags {
 #define IFF_RXFH_CONFIGURED		IFF_RXFH_CONFIGURED
 #define IFF_MACSEC			IFF_MACSEC
 #define IFF_NO_RX_HANDLER		IFF_NO_RX_HANDLER
+#define IFF_FAILOVER			IFF_FAILOVER
+#define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
 
 /**
  *	struct net_device - The DEVICE structure.
@@ -4308,6 +4314,16 @@ static inline bool netif_is_rxfh_configured(const struct
net_device *dev)
 	return dev->priv_flags & IFF_RXFH_CONFIGURED;
 }
 
+static inline bool netif_is_failover(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_FAILOVER;
+}
+
+static inline bool netif_is_failover_slave(const struct net_device *dev)
+{
+	return dev->priv_flags & IFF_FAILOVER_SLAVE;
+}
+
 /* This device needs to keep skb dst for qdisc enqueue or ndo_start_xmit() */
 static inline void netif_keep_dst(struct net_device *dev)
 {
diff --git a/include/net/failover.h b/include/net/failover.h
new file mode 100644
index 000000000000..0b8601043d90
--- /dev/null
+++ b/include/net/failover.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (c) 2018, Intel Corporation. */
+
+#ifndef _NET_FAILOVER_H
+#define _NET_FAILOVER_H
+
+#include <linux/netdevice.h>
+
+struct failover_ops {
+	int (*slave_pre_register)(struct net_device *slave_dev,
+				  struct net_device *failover_dev);
+	int (*slave_join)(struct net_device *slave_dev,
+			  struct net_device *failover_dev);
+	int (*slave_pre_unregister)(struct net_device *slave_dev,
+				    struct net_device *failover_dev);
+	int (*slave_release)(struct net_device *slave_dev,
+			     struct net_device *failover_dev);
+	int (*slave_link_change)(struct net_device *slave_dev,
+				 struct net_device *failover_dev);
+	rx_handler_result_t (*handle_frame)(struct sk_buff **pskb);
+};
+
+struct failover {
+	struct list_head list;
+	struct net_device __rcu *failover_dev;
+	struct failover_ops __rcu *ops;
+};
+
+/* failover state */
+struct failover_info {
+	/* primary netdev with same MAC */
+	struct net_device __rcu *primary_dev;
+
+	/* standby netdev */
+	struct net_device __rcu *standby_dev;
+
+	/* primary netdev stats */
+	struct rtnl_link_stats64 primary_stats;
+
+	/* standby netdev stats */
+	struct rtnl_link_stats64 standby_stats;
+
+	/* aggregated stats */
+	struct rtnl_link_stats64 failover_stats;
+
+	/* spinlock while updating stats */
+	spinlock_t stats_lock;
+};
+
+#if IS_ENABLED(CONFIG_NET_FAILOVER)
+
+int failover_create(struct net_device *standby_dev,
+		    struct failover **pfailover);
+void failover_destroy(struct failover *failover);
+
+int failover_register(struct net_device *standby_dev, struct failover_ops *ops,
+		      struct failover **pfailover);
+void failover_unregister(struct failover *failover);
+
+int failover_slave_unregister(struct net_device *slave_dev);
+
+#else
+
+static inline
+int failover_create(struct net_device *standby_dev,
+		    struct failover **pfailover);
+{
+	return 0;
+}
+
+static inline
+void failover_destroy(struct failover *failover)
+{
+}
+
+static inline
+int failover_register(struct net_device *standby_dev, struct failover_ops *ops,
+		      struct pfailover **pfailover);
+{
+	return 0;
+}
+
+static inline
+void failover_unregister(struct failover *failover)
+{
+}
+
+static inline
+int failover_slave_unregister(struct net_device *slave_dev)
+{
+	return 0;
+}
+
+#endif
+
+#endif /* _NET_FAILOVER_H */
diff --git a/net/Kconfig b/net/Kconfig
index 0428f12c25c2..388b99dfee10 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_FAILOVER
+	tristate "Failover 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_FAILOVER
+	tristate
+	default m if NET_FAILOVER=m
+	default y if NET_FAILOVER=y || NET_FAILOVER=n
+	help
+	  Drivers using the failover infrastructure should have a dependency
+	  on MAY_USE_FAILOVER to ensure they do not cause link errors when
+	  failover 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..cef17518bb7d 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_FAILOVER) += failover.o
diff --git a/net/core/failover.c b/net/core/failover.c
new file mode 100644
index 000000000000..7bee762cb737
--- /dev/null
+++ b/net/core/failover.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/failover.h>
+
+static LIST_HEAD(failover_list);
+static DEFINE_SPINLOCK(failover_lock);
+
+static int failover_slave_pre_register(struct net_device *slave_dev,
+				       struct net_device *failover_dev,
+				       struct failover_ops *failover_ops)
+{
+	struct failover_info *finfo;
+	bool standby;
+
+	if (failover_ops) {
+		if (!failover_ops->slave_pre_register)
+			return -EINVAL;
+
+		return failover_ops->slave_pre_register(slave_dev,
+							failover_dev);
+	}
+
+	finfo = netdev_priv(failover_dev);
+	standby = (slave_dev->dev.parent == failover_dev->dev.parent);
+	if (standby ? rtnl_dereference(finfo->standby_dev) :
+			rtnl_dereference(finfo->primary_dev)) {
+		netdev_err(failover_dev, "%s attempting to register as slave dev when %s
already present\n",
+			   slave_dev->name, standby ? "standby" : "primary");
+		return -EEXIST;
+	}
+
+	/* Avoid non pci devices as primary netdev */
+	if (!standby && (!slave_dev->dev.parent ||
+			 !dev_is_pci(slave_dev->dev.parent)))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int failover_slave_join(struct net_device *slave_dev,
+			       struct net_device *failover_dev,
+			       struct failover_ops *failover_ops)
+{
+	struct failover_info *finfo;
+	int err, orig_mtu;
+	bool standby;
+
+	if (failover_ops) {
+		if (!failover_ops->slave_join)
+			return -EINVAL;
+
+		return failover_ops->slave_join(slave_dev, failover_dev);
+	}
+
+	if (netif_running(failover_dev)) {
+		err = dev_open(slave_dev);
+		if (err && (err != -EBUSY)) {
+			netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
+				   slave_dev->name, err);
+			goto err_dev_open;
+		}
+	}
+
+	/* Align MTU of slave with failover dev */
+	orig_mtu = slave_dev->mtu;
+	err = dev_set_mtu(slave_dev, failover_dev->mtu);
+	if (err) {
+		netdev_err(failover_dev, "unable to change mtu of %s to %u register
failed\n",
+			   slave_dev->name, failover_dev->mtu);
+		goto err_set_mtu;
+	}
+
+	finfo = netdev_priv(failover_dev);
+	standby = (slave_dev->dev.parent == failover_dev->dev.parent);
+
+	dev_hold(slave_dev);
+
+	if (standby) {
+		rcu_assign_pointer(finfo->standby_dev, slave_dev);
+		dev_get_stats(finfo->standby_dev, &finfo->standby_stats);
+	} else {
+		rcu_assign_pointer(finfo->primary_dev, slave_dev);
+		dev_get_stats(finfo->primary_dev, &finfo->primary_stats);
+		failover_dev->min_mtu = slave_dev->min_mtu;
+		failover_dev->max_mtu = slave_dev->max_mtu;
+	}
+
+	netdev_info(failover_dev, "failover slave:%s joined\n",
+		    slave_dev->name);
+
+	return 0;
+
+err_set_mtu:
+	dev_close(slave_dev);
+err_dev_open:
+	return err;
+}
+
+/* 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 failover_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 *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;
+}
+
+static int failover_slave_register(struct net_device *slave_dev)
+{
+	struct failover_ops *failover_ops;
+	struct net_device *failover_dev;
+	int ret;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &failover_ops);
+	if (!failover_dev)
+		goto done;
+
+	ret = failover_slave_pre_register(slave_dev, failover_dev,
+					  failover_ops);
+	if (ret)
+		goto done;
+
+	ret = netdev_rx_handler_register(slave_dev, failover_ops ?
+					 failover_ops->handle_frame :
+					 failover_handle_frame, failover_dev);
+	if (ret) {
+		netdev_err(slave_dev, "can not register failover rx handler (err =
%d)\n",
+			   ret);
+		goto done;
+	}
+
+	ret = netdev_upper_dev_link(slave_dev, failover_dev, NULL);
+	if (ret) {
+		netdev_err(slave_dev, "can not set failover device %s (err =
%d)\n",
+			   failover_dev->name, ret);
+		goto upper_link_failed;
+	}
+
+	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
+
+	ret = failover_slave_join(slave_dev, failover_dev, failover_ops);
+	if (ret)
+		goto err_join;
+
+	call_netdevice_notifiers(NETDEV_JOIN, slave_dev);
+
+	netdev_info(failover_dev, "failover slave:%s registered\n",
+		    slave_dev->name);
+
+	goto done;
+
+err_join:
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+upper_link_failed:
+	netdev_rx_handler_unregister(slave_dev);
+done:
+	return NOTIFY_DONE;
+}
+
+static int failover_slave_pre_unregister(struct net_device *slave_dev,
+					 struct net_device *failover_dev,
+					 struct failover_ops *failover_ops)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct failover_info *finfo;
+
+	if (failover_ops) {
+		if (!failover_ops->slave_pre_unregister)
+			return -EINVAL;
+
+		return failover_ops->slave_pre_unregister(slave_dev,
+							  failover_dev);
+	}
+
+	finfo = netdev_priv(failover_dev);
+	primary_dev = rtnl_dereference(finfo->primary_dev);
+	standby_dev = rtnl_dereference(finfo->standby_dev);
+
+	if (slave_dev != primary_dev && slave_dev != standby_dev)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int failover_slave_release(struct net_device *slave_dev,
+				  struct net_device *failover_dev,
+				  struct failover_ops *failover_ops)
+{
+	struct net_device *standby_dev, *primary_dev;
+	struct failover_info *finfo;
+
+	if (failover_ops) {
+		if (!failover_ops->slave_release)
+			return -EINVAL;
+
+		return failover_ops->slave_release(slave_dev, failover_dev);
+	}
+
+	finfo = netdev_priv(failover_dev);
+	primary_dev = rtnl_dereference(finfo->primary_dev);
+	standby_dev = rtnl_dereference(finfo->standby_dev);
+
+	if (slave_dev == standby_dev) {
+		RCU_INIT_POINTER(finfo->standby_dev, NULL);
+	} else {
+		RCU_INIT_POINTER(finfo->primary_dev, NULL);
+		if (standby_dev) {
+			failover_dev->min_mtu = standby_dev->min_mtu;
+			failover_dev->max_mtu = standby_dev->max_mtu;
+		}
+	}
+
+	dev_put(slave_dev);
+
+	netdev_info(failover_dev, "failover slave:%s released\n",
+		    slave_dev->name);
+
+	return 0;
+}
+
+int failover_slave_unregister(struct net_device *slave_dev)
+{
+	struct failover_ops *failover_ops;
+	struct net_device *failover_dev;
+	int ret;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &failover_ops);
+	if (!failover_dev)
+		goto done;
+
+	ret = failover_slave_pre_unregister(slave_dev, failover_dev,
+					    failover_ops);
+	if (ret)
+		goto done;
+
+	netdev_rx_handler_unregister(slave_dev);
+	netdev_upper_dev_unlink(slave_dev, failover_dev);
+	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+
+	failover_slave_release(slave_dev, failover_dev, failover_ops);
+
+	netdev_info(failover_dev, "failover slave:%s unregistered\n",
+		    slave_dev->name);
+
+done:
+	return NOTIFY_DONE;
+}
+EXPORT_SYMBOL_GPL(failover_slave_unregister);
+
+static bool failover_xmit_ready(struct net_device *dev)
+{
+	return netif_running(dev) && netif_carrier_ok(dev);
+}
+
+static int failover_slave_link_change(struct net_device *slave_dev)
+{
+	struct net_device *failover_dev, *primary_dev, *standby_dev;
+	struct failover_ops *failover_ops;
+	struct failover_info *finfo;
+
+	if (!netif_is_failover_slave(slave_dev))
+		goto done;
+
+	ASSERT_RTNL();
+
+	failover_dev = failover_get_bymac(slave_dev->perm_addr, &failover_ops);
+	if (!failover_dev)
+		goto done;
+
+	if (failover_ops) {
+		if (!failover_ops->slave_link_change)
+			goto done;
+
+		return failover_ops->slave_link_change(slave_dev, failover_dev);
+	}
+
+	if (!netif_running(failover_dev))
+		return 0;
+
+	finfo = netdev_priv(failover_dev);
+
+	primary_dev = rtnl_dereference(finfo->primary_dev);
+	standby_dev = rtnl_dereference(finfo->standby_dev);
+
+	if (slave_dev != primary_dev && slave_dev != standby_dev)
+		goto done;
+
+	if ((primary_dev && failover_xmit_ready(primary_dev)) ||
+	    (standby_dev && failover_xmit_ready(standby_dev))) {
+		netif_carrier_on(failover_dev);
+		netif_tx_wake_all_queues(failover_dev);
+	} else {
+		netif_carrier_off(failover_dev);
+		netif_tx_stop_all_queues(failover_dev);
+	}
+
+done:
+	return NOTIFY_DONE;
+}
+
+static bool failover_validate_event_dev(struct net_device *dev)
+{
+	/* Skip parent events */
+	if (netif_is_failover(dev))
+		return false;
+
+	/* Avoid non-Ethernet type devices */
+	if (dev->type != ARPHRD_ETHER)
+		return false;
+
+	return true;
+}
+
+static int
+failover_event(struct notifier_block *this, unsigned long event, void *ptr)
+{
+	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
+
+	if (!failover_validate_event_dev(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);
+	default:
+		return NOTIFY_DONE;
+	}
+}
+
+static struct notifier_block failover_notifier = {
+	.notifier_call = failover_event,
+};
+
+static int failover_open(struct net_device *dev)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+	int err;
+
+	netif_carrier_off(dev);
+	netif_tx_wake_all_queues(dev);
+
+	primary_dev = rtnl_dereference(finfo->primary_dev);
+	if (primary_dev) {
+		err = dev_open(primary_dev);
+		if (err)
+			goto err_primary_open;
+	}
+
+	standby_dev = rtnl_dereference(finfo->standby_dev);
+	if (standby_dev) {
+		err = dev_open(standby_dev);
+		if (err)
+			goto err_standby_open;
+	}
+
+	return 0;
+
+err_standby_open:
+	dev_close(primary_dev);
+err_primary_open:
+	netif_tx_disable(dev);
+	return err;
+}
+
+static int failover_close(struct net_device *dev)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	netif_tx_disable(dev);
+
+	slave_dev = rtnl_dereference(finfo->primary_dev);
+	if (slave_dev)
+		dev_close(slave_dev);
+
+	slave_dev = rtnl_dereference(finfo->standby_dev);
+	if (slave_dev)
+		dev_close(slave_dev);
+
+	return 0;
+}
+
+static netdev_tx_t failover_drop_xmit(struct sk_buff *skb,
+				      struct net_device *dev)
+{
+	atomic_long_inc(&dev->tx_dropped);
+	dev_kfree_skb_any(skb);
+	return NETDEV_TX_OK;
+}
+
+static netdev_tx_t failover_start_xmit(struct sk_buff *skb,
+				       struct net_device *dev)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *xmit_dev;
+
+	/* Try xmit via primary netdev followed by standby netdev */
+	xmit_dev = rcu_dereference_bh(finfo->primary_dev);
+	if (!xmit_dev || !failover_xmit_ready(xmit_dev)) {
+		xmit_dev = rcu_dereference_bh(finfo->standby_dev);
+		if (!xmit_dev || !failover_xmit_ready(xmit_dev))
+			return failover_drop_xmit(skb, dev);
+	}
+
+	skb->dev = xmit_dev;
+	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
+
+	return dev_queue_xmit(skb);
+}
+
+static u16 failover_select_queue(struct net_device *dev, struct sk_buff *skb,
+				 void *accel_priv,
+				 select_queue_fallback_t fallback)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *primary_dev;
+	u16 txq;
+
+	rcu_read_lock();
+	primary_dev = rcu_dereference(finfo->primary_dev);
+	if (primary_dev) {
+		const struct net_device_ops *ops = primary_dev->netdev_ops;
+
+		if (ops->ndo_select_queue)
+			txq = ops->ndo_select_queue(primary_dev, skb,
+						    accel_priv, fallback);
+		else
+			txq = fallback(primary_dev, skb);
+
+		qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
+
+		return txq;
+	}
+
+	txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) : 0;
+
+	/* Save the original txq to restore before passing to the driver */
+	qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
+
+	if (unlikely(txq >= dev->real_num_tx_queues)) {
+		do {
+			txq -= dev->real_num_tx_queues;
+		} while (txq >= dev->real_num_tx_queues);
+	}
+
+	return txq;
+}
+
+/* fold stats, assuming all rtnl_link_stats64 fields are u64, but
+ * that some drivers can provide 32finfot values only.
+ */
+static void failover_fold_stats(struct rtnl_link_stats64 *_res,
+				const struct rtnl_link_stats64 *_new,
+				const struct rtnl_link_stats64 *_old)
+{
+	const u64 *new = (const u64 *)_new;
+	const u64 *old = (const u64 *)_old;
+	u64 *res = (u64 *)_res;
+	int i;
+
+	for (i = 0; i < sizeof(*_res) / sizeof(u64); i++) {
+		u64 nv = new[i];
+		u64 ov = old[i];
+		s64 delta = nv - ov;
+
+		/* detects if this particular field is 32bit only */
+		if (((nv | ov) >> 32) == 0)
+			delta = (s64)(s32)((u32)nv - (u32)ov);
+
+		/* filter anomalies, some drivers reset their stats
+		 * at down/up events.
+		 */
+		if (delta > 0)
+			res[i] += delta;
+	}
+}
+
+static void failover_get_stats(struct net_device *dev,
+			       struct rtnl_link_stats64 *stats)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	const struct rtnl_link_stats64 *new;
+	struct rtnl_link_stats64 temp;
+	struct net_device *slave_dev;
+
+	spin_lock(&finfo->stats_lock);
+	memcpy(stats, &finfo->failover_stats, sizeof(*stats));
+
+	rcu_read_lock();
+
+	slave_dev = rcu_dereference(finfo->primary_dev);
+	if (slave_dev) {
+		new = dev_get_stats(slave_dev, &temp);
+		failover_fold_stats(stats, new, &finfo->primary_stats);
+		memcpy(&finfo->primary_stats, new, sizeof(*new));
+	}
+
+	slave_dev = rcu_dereference(finfo->standby_dev);
+	if (slave_dev) {
+		new = dev_get_stats(slave_dev, &temp);
+		failover_fold_stats(stats, new, &finfo->standby_stats);
+		memcpy(&finfo->standby_stats, new, sizeof(*new));
+	}
+
+	rcu_read_unlock();
+
+	memcpy(&finfo->failover_stats, stats, sizeof(*stats));
+	spin_unlock(&finfo->stats_lock);
+}
+
+static int failover_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *primary_dev, *standby_dev;
+	int ret = 0;
+
+	primary_dev = rcu_dereference(finfo->primary_dev);
+	if (primary_dev) {
+		ret = dev_set_mtu(primary_dev, new_mtu);
+		if (ret)
+			return ret;
+	}
+
+	standby_dev = rcu_dereference(finfo->standby_dev);
+	if (standby_dev) {
+		ret = dev_set_mtu(standby_dev, new_mtu);
+		if (ret) {
+			dev_set_mtu(primary_dev, dev->mtu);
+			return ret;
+		}
+	}
+
+	dev->mtu = new_mtu;
+	return 0;
+}
+
+static void failover_set_rx_mode(struct net_device *dev)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	rcu_read_lock();
+
+	slave_dev = rcu_dereference(finfo->primary_dev);
+	if (slave_dev) {
+		dev_uc_sync_multiple(slave_dev, dev);
+		dev_mc_sync_multiple(slave_dev, dev);
+	}
+
+	slave_dev = rcu_dereference(finfo->standby_dev);
+	if (slave_dev) {
+		dev_uc_sync_multiple(slave_dev, dev);
+		dev_mc_sync_multiple(slave_dev, dev);
+	}
+
+	rcu_read_unlock();
+}
+
+static const struct net_device_ops failover_dev_ops = {
+	.ndo_open		= failover_open,
+	.ndo_stop		= failover_close,
+	.ndo_start_xmit		= failover_start_xmit,
+	.ndo_select_queue	= failover_select_queue,
+	.ndo_get_stats64	= failover_get_stats,
+	.ndo_change_mtu		= failover_change_mtu,
+	.ndo_set_rx_mode	= failover_set_rx_mode,
+	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_features_check	= passthru_features_check,
+};
+
+#define FAILOVER_NAME "failover"
+#define FAILOVER_VERSION "0.1"
+
+static void failover_ethtool_get_drvinfo(struct net_device *dev,
+					 struct ethtool_drvinfo *drvinfo)
+{
+	strlcpy(drvinfo->driver, FAILOVER_NAME, sizeof(drvinfo->driver));
+	strlcpy(drvinfo->version, FAILOVER_VERSION, sizeof(drvinfo->version));
+}
+
+int failover_ethtool_get_link_ksettings(struct net_device *dev,
+					struct ethtool_link_ksettings *cmd)
+{
+	struct failover_info *finfo = netdev_priv(dev);
+	struct net_device *slave_dev;
+
+	slave_dev = rtnl_dereference(finfo->primary_dev);
+	if (!slave_dev || !failover_xmit_ready(slave_dev)) {
+		slave_dev = rtnl_dereference(finfo->standby_dev);
+		if (!slave_dev || !failover_xmit_ready(slave_dev)) {
+			cmd->base.duplex = DUPLEX_UNKNOWN;
+			cmd->base.port = PORT_OTHER;
+			cmd->base.speed = SPEED_UNKNOWN;
+
+			return 0;
+		}
+	}
+
+	return __ethtool_get_link_ksettings(slave_dev, cmd);
+}
+EXPORT_SYMBOL_GPL(failover_ethtool_get_link_ksettings);
+
+static const struct ethtool_ops failover_ethtool_ops = {
+	.get_drvinfo            = failover_ethtool_get_drvinfo,
+	.get_link               = ethtool_op_get_link,
+	.get_link_ksettings     = failover_ethtool_get_link_ksettings,
+};
+
+static void failover_register_existing_slave(struct net_device *failover_dev)
+{
+	struct net *net = dev_net(failover_dev);
+	struct net_device *dev;
+
+	rtnl_lock();
+	for_each_netdev(net, dev) {
+		if (dev == failover_dev)
+			continue;
+		if (!failover_validate_event_dev(dev))
+			continue;
+		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
+			failover_slave_register(dev);
+	}
+	rtnl_unlock();
+}
+
+int failover_register(struct net_device *dev, struct failover_ops *ops,
+		      struct failover **pfailover)
+{
+	struct failover *failover;
+
+	failover = kzalloc(sizeof(*failover), GFP_KERNEL);
+	if (!failover)
+		return -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);
+
+	failover_register_existing_slave(dev);
+
+	*pfailover = failover;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(failover_register);
+
+void failover_unregister(struct failover *failover)
+{
+	struct net_device *failover_dev;
+
+	failover_dev = rcu_dereference(failover->failover_dev);
+
+	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);
+
+int failover_create(struct net_device *standby_dev, struct failover
**pfailover)
+{
+	struct device *dev = standby_dev->dev.parent;
+	struct net_device *failover_dev;
+	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.
+	 */
+	failover_dev = alloc_etherdev_mq(sizeof(struct failover_info), 16);
+	if (!failover_dev) {
+		dev_err(dev, "Unable to allocate failover_netdev!\n");
+		return -ENOMEM;
+	}
+
+	dev_net_set(failover_dev, dev_net(standby_dev));
+	SET_NETDEV_DEV(failover_dev, dev);
+
+	failover_dev->netdev_ops = &failover_dev_ops;
+	failover_dev->ethtool_ops = &failover_ethtool_ops;
+
+	/* Initialize the device options */
+	failover_dev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
+	failover_dev->priv_flags &= ~(IFF_XMIT_DST_RELEASE |
+				       IFF_TX_SKB_SHARING);
+
+	/* don't acquire failover netdev's netif_tx_lock when transmitting */
+	failover_dev->features |= NETIF_F_LLTX;
+
+	/* Don't allow failover devices to change network namespaces. */
+	failover_dev->features |= NETIF_F_NETNS_LOCAL;
+
+	failover_dev->hw_features = NETIF_F_HW_CSUM | NETIF_F_SG |
+				    NETIF_F_FRAGLIST | NETIF_F_ALL_TSO |
+				    NETIF_F_HIGHDMA | NETIF_F_LRO;
+
+	failover_dev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
+	failover_dev->features |= failover_dev->hw_features;
+
+	memcpy(failover_dev->dev_addr, standby_dev->dev_addr,
+	       failover_dev->addr_len);
+
+	failover_dev->min_mtu = standby_dev->min_mtu;
+	failover_dev->max_mtu = standby_dev->max_mtu;
+
+	err = register_netdev(failover_dev);
+	if (err < 0) {
+		dev_err(dev, "Unable to register failover_dev!\n");
+		goto err_register_netdev;
+	}
+
+	netif_carrier_off(failover_dev);
+
+	err = failover_register(failover_dev, NULL, pfailover);
+	if (err < 0)
+		goto err_failover;
+
+	return 0;
+
+err_failover:
+	unregister_netdev(failover_dev);
+err_register_netdev:
+	free_netdev(failover_dev);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(failover_create);
+
+void failover_destroy(struct failover *failover)
+{
+	struct net_device *failover_dev;
+	struct net_device *slave_dev;
+	struct failover_info *finfo;
+
+	if (!failover)
+		return;
+
+	failover_dev = rcu_dereference(failover->failover_dev);
+	finfo = netdev_priv(failover_dev);
+
+	netif_device_detach(failover_dev);
+
+	rtnl_lock();
+
+	slave_dev = rtnl_dereference(finfo->primary_dev);
+	if (slave_dev)
+		failover_slave_unregister(slave_dev);
+
+	slave_dev = rtnl_dereference(finfo->standby_dev);
+	if (slave_dev)
+		failover_slave_unregister(slave_dev);
+
+	failover_unregister(failover);
+
+	unregister_netdevice(failover_dev);
+
+	rtnl_unlock();
+
+	free_netdev(failover_dev);
+}
+EXPORT_SYMBOL_GPL(failover_destroy);
+
+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("Failover infrastructure/interface for Paravirtual
drivers");
+MODULE_LICENSE("GPL v2");
-- 
2.14.3

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

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

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

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/Kconfig      |  1 +
 drivers/net/virtio_net.c | 36 +++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 891846655000..5abe328973da 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_FAILOVER
 	---help---
 	  This is the virtual network driver for virtio.  It can be used with
 	  QEMU based VMMs (like KVM or Xen).  Say Y or M.
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6f95719ede40..42b9f9bff48b 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/failover.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;
+
+	/* failover when STANDBY feature enabled */
+	struct failover *failover;
 };
 
 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_STANDBY))
+		return -EOPNOTSUPP;
+
+	ret = snprintf(buf, len, "_sby");
+	if (ret >= len)
+		return -EOPNOTSUPP;
+
+	return 0;
+}
+
 static const struct net_device_ops virtnet_netdev = {
 	.ndo_open            = virtnet_open,
 	.ndo_stop   	     = virtnet_close,
@@ -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_STANDBY)) {
+		err = failover_create(vi->dev, &vi->failover);
+		if (err)
+			goto free_vqs;
+	}
+
 	err = register_netdev(dev);
 	if (err) {
 		pr_debug("virtio_net: registering device failed\n");
-		goto free_vqs;
+		goto free_failover;
 	}
 
 	virtio_device_ready(vdev);
@@ -2879,6 +2908,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	vi->vdev->config->reset(vdev);
 
 	unregister_netdev(dev);
+free_failover:
+	failover_destroy(vi->failover);
 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);
 
+	failover_destroy(vi->failover);
+
 	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
failover infrastructure.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
---
 drivers/net/hyperv/Kconfig      |   1 +
 drivers/net/hyperv/hyperv_net.h |   2 +
 drivers/net/hyperv/netvsc_drv.c | 208 ++++++++++------------------------------
 3 files changed, 55 insertions(+), 156 deletions(-)

diff --git a/drivers/net/hyperv/Kconfig b/drivers/net/hyperv/Kconfig
index 936968d23559..56099d10beed 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_FAILOVER
 	help
 	  Select this option to enable the Hyper-V virtual network driver.
diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index 960f06141472..d8c2ff698693 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 failover *failover;
 };
 
 /* Per channel data */
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index ecc84954c511..8404c22de32b 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/failover.h>
 
 #include "hyperv_net.h"
 
@@ -1763,46 +1764,6 @@ static void netvsc_link_change(struct work_struct *w)
 	rtnl_unlock();
 }
 
-static struct net_device *get_netvsc_bymac(const u8 *mac)
-{
-	struct net_device *dev;
-
-	ASSERT_RTNL();
-
-	for_each_netdev(&init_net, dev) {
-		if (dev->netdev_ops != &device_ops)
-			continue;	/* not a netvsc device */
-
-		if (ether_addr_equal(mac, dev->perm_addr))
-			return dev;
-	}
-
-	return NULL;
-}
-
-static struct net_device *get_netvsc_byref(struct net_device *vf_netdev)
-{
-	struct net_device *dev;
-
-	ASSERT_RTNL();
-
-	for_each_netdev(&init_net, dev) {
-		struct net_device_context *net_device_ctx;
-
-		if (dev->netdev_ops != &device_ops)
-			continue;	/* not a netvsc device */
-
-		net_device_ctx = netdev_priv(dev);
-		if (!rtnl_dereference(net_device_ctx->nvdev))
-			continue;	/* device is removed */
-
-		if (rtnl_dereference(net_device_ctx->vf_netdev) == vf_netdev)
-			return dev;	/* a match */
-	}
-
-	return NULL;
-}
-
 /* Called when VF is injecting data into network stack.
  * Change the associated network device from VF to netvsc.
  * note: already called with rcu_read_lock
@@ -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 failover_ops netvsc_failover_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 = failover_register(net, &netvsc_failover_ops,
+				&net_device_ctx->failover);
+	if (ret != 0)
+		goto err_failover;
+
 	return ret;
 
+err_failover:
+	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);
+		failover_slave_unregister(vf_netdev);
 
 	if (nvdev)
 		rndis_filter_device_remove(dev, nvdev);
 
 	unregister_netdevice(net);
 
+	failover_unregister(ndev_ctx->failover);
+
 	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 Thu, Apr 19, 2018 at 06:42:02PM -0700, Sridhar Samudrala
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 instance
> of netvsc as a 'failover' instance  along with a set of ops to
manage the
> slave events.
>      failover_register()
>      failover_unregister()
> 2. new virtio_net based solution that uses 3 netdev model. In this model,
> the failover module provides interfaces to create/destroy additional master
> netdev and all the slave events are managed internally.
>       failover_create()
>       failover_destroy()
> These functions call failover_register()/failover_unregister() with the
> master netdev created by the failover module.
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
I like this patch. Yes something to improve (see below)
> ---
>  include/linux/netdevice.h |  16 +
>  include/net/failover.h    |  96 ++++++
>  net/Kconfig               |  18 +
>  net/core/Makefile         |   1 +
>  net/core/failover.c       | 844
++++++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 975 insertions(+)
>  create mode 100644 include/net/failover.h
>  create mode 100644 net/core/failover.c
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index cf44503ea81a..ed535b6724e1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1401,6 +1401,8 @@ struct net_device_ops {
>   *	entity (i.e. the master device for bridged veth)
>   * @IFF_MACSEC: device is a MACsec device
>   * @IFF_NO_RX_HANDLER: device doesn't support the rx_handler hook
> + * @IFF_FAILOVER: device is a failover master device
> + * @IFF_FAILOVER_SLAVE: device is lower dev of a failover master device
>   */
>  enum netdev_priv_flags {
>  	IFF_802_1Q_VLAN			= 1<<0,
> @@ -1430,6 +1432,8 @@ enum netdev_priv_flags {
>  	IFF_PHONY_HEADROOM		= 1<<24,
>  	IFF_MACSEC			= 1<<25,
>  	IFF_NO_RX_HANDLER		= 1<<26,
> +	IFF_FAILOVER			= 1<<27,
> +	IFF_FAILOVER_SLAVE		= 1<<28,
>  };
>  
>  #define IFF_802_1Q_VLAN			IFF_802_1Q_VLAN
> @@ -1458,6 +1462,8 @@ enum netdev_priv_flags {
>  #define IFF_RXFH_CONFIGURED		IFF_RXFH_CONFIGURED
>  #define IFF_MACSEC			IFF_MACSEC
>  #define IFF_NO_RX_HANDLER		IFF_NO_RX_HANDLER
> +#define IFF_FAILOVER			IFF_FAILOVER
> +#define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
>  
>  /**
>   *	struct net_device - The DEVICE structure.
> @@ -4308,6 +4314,16 @@ static inline bool netif_is_rxfh_configured(const
struct net_device *dev)
>  	return dev->priv_flags & IFF_RXFH_CONFIGURED;
>  }
>  
> +static inline bool netif_is_failover(const struct net_device *dev)
> +{
> +	return dev->priv_flags & IFF_FAILOVER;
> +}
> +
> +static inline bool netif_is_failover_slave(const struct net_device *dev)
> +{
> +	return dev->priv_flags & IFF_FAILOVER_SLAVE;
> +}
> +
>  /* This device needs to keep skb dst for qdisc enqueue or ndo_start_xmit()
*/
>  static inline void netif_keep_dst(struct net_device *dev)
>  {
> diff --git a/include/net/failover.h b/include/net/failover.h
> new file mode 100644
> index 000000000000..0b8601043d90
> --- /dev/null
> +++ b/include/net/failover.h
> @@ -0,0 +1,96 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2018, Intel Corporation. */
> +
> +#ifndef _NET_FAILOVER_H
> +#define _NET_FAILOVER_H
> +
> +#include <linux/netdevice.h>
> +
> +struct failover_ops {
> +	int (*slave_pre_register)(struct net_device *slave_dev,
> +				  struct net_device *failover_dev);
> +	int (*slave_join)(struct net_device *slave_dev,
> +			  struct net_device *failover_dev);
> +	int (*slave_pre_unregister)(struct net_device *slave_dev,
> +				    struct net_device *failover_dev);
> +	int (*slave_release)(struct net_device *slave_dev,
> +			     struct net_device *failover_dev);
> +	int (*slave_link_change)(struct net_device *slave_dev,
> +				 struct net_device *failover_dev);
> +	rx_handler_result_t (*handle_frame)(struct sk_buff **pskb);
> +};
> +
> +struct failover {
> +	struct list_head list;
> +	struct net_device __rcu *failover_dev;
> +	struct failover_ops __rcu *ops;
> +};
> +
> +/* failover state */
> +struct failover_info {
> +	/* primary netdev with same MAC */
> +	struct net_device __rcu *primary_dev;
> +
> +	/* standby netdev */
> +	struct net_device __rcu *standby_dev;
> +
> +	/* primary netdev stats */
> +	struct rtnl_link_stats64 primary_stats;
> +
> +	/* standby netdev stats */
> +	struct rtnl_link_stats64 standby_stats;
> +
> +	/* aggregated stats */
> +	struct rtnl_link_stats64 failover_stats;
> +
> +	/* spinlock while updating stats */
> +	spinlock_t stats_lock;
> +};
> +
> +#if IS_ENABLED(CONFIG_NET_FAILOVER)
> +
> +int failover_create(struct net_device *standby_dev,
> +		    struct failover **pfailover);
> +void failover_destroy(struct failover *failover);
> +
> +int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
> +		      struct failover **pfailover);
> +void failover_unregister(struct failover *failover);
> +
> +int failover_slave_unregister(struct net_device *slave_dev);
> +
> +#else
> +
> +static inline
> +int failover_create(struct net_device *standby_dev,
> +		    struct failover **pfailover);
> +{
> +	return 0;
> +}
> +
> +static inline
> +void failover_destroy(struct failover *failover)
> +{
> +}
> +
> +static inline
> +int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
> +		      struct pfailover **pfailover);
> +{
> +	return 0;
> +}
> +
> +static inline
> +void failover_unregister(struct failover *failover)
> +{
> +}
> +
> +static inline
> +int failover_slave_unregister(struct net_device *slave_dev)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +#endif /* _NET_FAILOVER_H */
> diff --git a/net/Kconfig b/net/Kconfig
> index 0428f12c25c2..388b99dfee10 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_FAILOVER
> +	tristate "Failover 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_FAILOVER
> +	tristate
> +	default m if NET_FAILOVER=m
> +	default y if NET_FAILOVER=y || NET_FAILOVER=n
> +	help
> +	  Drivers using the failover infrastructure should have a dependency
> +	  on MAY_USE_FAILOVER to ensure they do not cause link errors when
> +	  failover 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..cef17518bb7d 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_FAILOVER) += failover.o
> diff --git a/net/core/failover.c b/net/core/failover.c
> new file mode 100644
> index 000000000000..7bee762cb737
> --- /dev/null
> +++ b/net/core/failover.c
> @@ -0,0 +1,844 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2018, Intel Corporation. */

I think you should copy the header from bond_main.c upon which
some of the code seems to be based.
> +
> +/* 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/failover.h>
> +
> +static LIST_HEAD(failover_list);
> +static DEFINE_SPINLOCK(failover_lock);
> +
> +static int failover_slave_pre_register(struct net_device *slave_dev,
> +				       struct net_device *failover_dev,
> +				       struct failover_ops *failover_ops)
> +{
> +	struct failover_info *finfo;
> +	bool standby;
> +
> +	if (failover_ops) {
> +		if (!failover_ops->slave_pre_register)
> +			return -EINVAL;
> +
> +		return failover_ops->slave_pre_register(slave_dev,
> +							failover_dev);
> +	}
> +
> +	finfo = netdev_priv(failover_dev);
> +	standby = (slave_dev->dev.parent == failover_dev->dev.parent);
> +	if (standby ? rtnl_dereference(finfo->standby_dev) :
> +			rtnl_dereference(finfo->primary_dev)) {
> +		netdev_err(failover_dev, "%s attempting to register as slave dev
when %s already present\n",
> +			   slave_dev->name, standby ? "standby" :
"primary");
> +		return -EEXIST;
> +	}
> +
> +	/* Avoid non pci devices as primary netdev */
Why? Pls change this comment so it explains the motivation
rather than just repeat what the code does.
> +	if (!standby && (!slave_dev->dev.parent ||
> +			 !dev_is_pci(slave_dev->dev.parent)))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int failover_slave_join(struct net_device *slave_dev,
> +			       struct net_device *failover_dev,
> +			       struct failover_ops *failover_ops)
> +{
> +	struct failover_info *finfo;
> +	int err, orig_mtu;
> +	bool standby;
> +
> +	if (failover_ops) {
> +		if (!failover_ops->slave_join)
> +			return -EINVAL;
> +
> +		return failover_ops->slave_join(slave_dev, failover_dev);
> +	}
> +
> +	if (netif_running(failover_dev)) {
> +		err = dev_open(slave_dev);
> +		if (err && (err != -EBUSY)) {
> +			netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
> +				   slave_dev->name, err);
> +			goto err_dev_open;
> +		}
> +	}
> +
> +	/* Align MTU of slave with failover dev */
> +	orig_mtu = slave_dev->mtu;
I suspect this was copied from bond. this variable is never
used and I'm even surprised gcc did not warn about this.

> +	err = dev_set_mtu(slave_dev, failover_dev->mtu);
How do we know slave supports this MTU? same applies to
failover_change_mtu.



> +	if (err) {
> +		netdev_err(failover_dev, "unable to change mtu of %s to %u register
failed\n",
> +			   slave_dev->name, failover_dev->mtu);
> +		goto err_set_mtu;
> +	}
> +
> +	finfo = netdev_priv(failover_dev);
> +	standby = (slave_dev->dev.parent == failover_dev->dev.parent);
> +
> +	dev_hold(slave_dev);
> +
> +	if (standby) {
> +		rcu_assign_pointer(finfo->standby_dev, slave_dev);
> +		dev_get_stats(finfo->standby_dev, &finfo->standby_stats);
> +	} else {
> +		rcu_assign_pointer(finfo->primary_dev, slave_dev);
> +		dev_get_stats(finfo->primary_dev, &finfo->primary_stats);
> +		failover_dev->min_mtu = slave_dev->min_mtu;
> +		failover_dev->max_mtu = slave_dev->max_mtu;
> +	}
> +
> +	netdev_info(failover_dev, "failover slave:%s joined\n",
> +		    slave_dev->name);
> +
> +	return 0;
> +
> +err_set_mtu:
> +	dev_close(slave_dev);
> +err_dev_open:
> +	return err;
> +}
> +
> +/* 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 failover_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 *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;
> +}
> +
> +static int failover_slave_register(struct net_device *slave_dev)
> +{
> +	struct failover_ops *failover_ops;
> +	struct net_device *failover_dev;
> +	int ret;
> +
> +	ASSERT_RTNL();
> +
> +	failover_dev = failover_get_bymac(slave_dev->perm_addr,
&failover_ops);
> +	if (!failover_dev)
> +		goto done;
> +
> +	ret = failover_slave_pre_register(slave_dev, failover_dev,
> +					  failover_ops);
> +	if (ret)
> +		goto done;
> +
> +	ret = netdev_rx_handler_register(slave_dev, failover_ops ?
> +					 failover_ops->handle_frame :
> +					 failover_handle_frame, failover_dev);
> +	if (ret) {
> +		netdev_err(slave_dev, "can not register failover rx handler (err =
%d)\n",
> +			   ret);
> +		goto done;
> +	}
> +
> +	ret = netdev_upper_dev_link(slave_dev, failover_dev, NULL);
> +	if (ret) {
> +		netdev_err(slave_dev, "can not set failover device %s (err =
%d)\n",
> +			   failover_dev->name, ret);
> +		goto upper_link_failed;
> +	}
> +
> +	slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
> +
> +	ret = failover_slave_join(slave_dev, failover_dev, failover_ops);
> +	if (ret)
> +		goto err_join;
> +
> +	call_netdevice_notifiers(NETDEV_JOIN, slave_dev);
> +
> +	netdev_info(failover_dev, "failover slave:%s registered\n",
> +		    slave_dev->name);
> +
> +	goto done;
> +
> +err_join:
> +	netdev_upper_dev_unlink(slave_dev, failover_dev);
> +	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
> +upper_link_failed:
> +	netdev_rx_handler_unregister(slave_dev);
> +done:
> +	return NOTIFY_DONE;
> +}
> +
> +static int failover_slave_pre_unregister(struct net_device *slave_dev,
> +					 struct net_device *failover_dev,
> +					 struct failover_ops *failover_ops)
> +{
> +	struct net_device *standby_dev, *primary_dev;
> +	struct failover_info *finfo;
> +
> +	if (failover_ops) {
> +		if (!failover_ops->slave_pre_unregister)
> +			return -EINVAL;
> +
> +		return failover_ops->slave_pre_unregister(slave_dev,
> +							  failover_dev);
> +	}
> +
> +	finfo = netdev_priv(failover_dev);
> +	primary_dev = rtnl_dereference(finfo->primary_dev);
> +	standby_dev = rtnl_dereference(finfo->standby_dev);
> +
> +	if (slave_dev != primary_dev && slave_dev != standby_dev)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int failover_slave_release(struct net_device *slave_dev,
> +				  struct net_device *failover_dev,
> +				  struct failover_ops *failover_ops)
> +{
> +	struct net_device *standby_dev, *primary_dev;
> +	struct failover_info *finfo;
> +
> +	if (failover_ops) {
> +		if (!failover_ops->slave_release)
> +			return -EINVAL;
> +
> +		return failover_ops->slave_release(slave_dev, failover_dev);
> +	}
> +
> +	finfo = netdev_priv(failover_dev);
> +	primary_dev = rtnl_dereference(finfo->primary_dev);
> +	standby_dev = rtnl_dereference(finfo->standby_dev);
> +
> +	if (slave_dev == standby_dev) {
> +		RCU_INIT_POINTER(finfo->standby_dev, NULL);
> +	} else {
> +		RCU_INIT_POINTER(finfo->primary_dev, NULL);
> +		if (standby_dev) {
> +			failover_dev->min_mtu = standby_dev->min_mtu;
> +			failover_dev->max_mtu = standby_dev->max_mtu;
> +		}
> +	}
> +
> +	dev_put(slave_dev);
> +
> +	netdev_info(failover_dev, "failover slave:%s released\n",
> +		    slave_dev->name);
> +
> +	return 0;
> +}
> +
> +int failover_slave_unregister(struct net_device *slave_dev)
> +{
> +	struct failover_ops *failover_ops;
> +	struct net_device *failover_dev;
> +	int ret;
> +
> +	if (!netif_is_failover_slave(slave_dev))
> +		goto done;
> +
> +	ASSERT_RTNL();
> +
> +	failover_dev = failover_get_bymac(slave_dev->perm_addr,
&failover_ops);
> +	if (!failover_dev)
> +		goto done;
> +
> +	ret = failover_slave_pre_unregister(slave_dev, failover_dev,
> +					    failover_ops);
> +	if (ret)
> +		goto done;
> +
> +	netdev_rx_handler_unregister(slave_dev);
> +	netdev_upper_dev_unlink(slave_dev, failover_dev);
> +	slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
> +
> +	failover_slave_release(slave_dev, failover_dev, failover_ops);

Don't you need to get stats from it? This device is going away ...
> +
> +	netdev_info(failover_dev, "failover slave:%s unregistered\n",
> +		    slave_dev->name);
> +
> +done:
> +	return NOTIFY_DONE;
> +}
> +EXPORT_SYMBOL_GPL(failover_slave_unregister);
> +
> +static bool failover_xmit_ready(struct net_device *dev)
> +{
> +	return netif_running(dev) && netif_carrier_ok(dev);
> +}
> +
> +static int failover_slave_link_change(struct net_device *slave_dev)
> +{
> +	struct net_device *failover_dev, *primary_dev, *standby_dev;
> +	struct failover_ops *failover_ops;
> +	struct failover_info *finfo;
> +
> +	if (!netif_is_failover_slave(slave_dev))
> +		goto done;
> +
> +	ASSERT_RTNL();
> +
> +	failover_dev = failover_get_bymac(slave_dev->perm_addr,
&failover_ops);
> +	if (!failover_dev)
> +		goto done;
> +
> +	if (failover_ops) {
> +		if (!failover_ops->slave_link_change)
> +			goto done;
> +
> +		return failover_ops->slave_link_change(slave_dev, failover_dev);
> +	}
> +
> +	if (!netif_running(failover_dev))
> +		return 0;
> +
> +	finfo = netdev_priv(failover_dev);
> +
> +	primary_dev = rtnl_dereference(finfo->primary_dev);
> +	standby_dev = rtnl_dereference(finfo->standby_dev);
> +
> +	if (slave_dev != primary_dev && slave_dev != standby_dev)
> +		goto done;
> +
> +	if ((primary_dev && failover_xmit_ready(primary_dev)) ||
> +	    (standby_dev && failover_xmit_ready(standby_dev))) {
> +		netif_carrier_on(failover_dev);
> +		netif_tx_wake_all_queues(failover_dev);
> +	} else {
> +		netif_carrier_off(failover_dev);
> +		netif_tx_stop_all_queues(failover_dev);
And I think it's a good idea to get stats from device here too.

> +	}
> +
> +done:
> +	return NOTIFY_DONE;
> +}
> +
> +static bool failover_validate_event_dev(struct net_device *dev)
> +{
> +	/* Skip parent events */
> +	if (netif_is_failover(dev))
> +		return false;
> +
> +	/* Avoid non-Ethernet type devices */
... for now. It would be possible easy to make this generic -
just copy things like type and addr_len from slave.
> +	if (dev->type != ARPHRD_ETHER)
> +		return false;
> +
> +	return true;
> +}
> +
> +static int
> +failover_event(struct notifier_block *this, unsigned long event, void
*ptr)
> +{
> +	struct net_device *event_dev = netdev_notifier_info_to_dev(ptr);
> +
> +	if (!failover_validate_event_dev(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);
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +}
> +
> +static struct notifier_block failover_notifier = {
> +	.notifier_call = failover_event,
> +};
> +
> +static int failover_open(struct net_device *dev)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *primary_dev, *standby_dev;
> +	int err;
> +
> +	netif_carrier_off(dev);
> +	netif_tx_wake_all_queues(dev);
> +
> +	primary_dev = rtnl_dereference(finfo->primary_dev);
> +	if (primary_dev) {
> +		err = dev_open(primary_dev);
> +		if (err)
> +			goto err_primary_open;
> +	}
> +
> +	standby_dev = rtnl_dereference(finfo->standby_dev);
> +	if (standby_dev) {
> +		err = dev_open(standby_dev);
> +		if (err)
> +			goto err_standby_open;
> +	}
> +
> +	return 0;
> +
> +err_standby_open:
> +	dev_close(primary_dev);
> +err_primary_open:
> +	netif_tx_disable(dev);
> +	return err;
> +}
> +
> +static int failover_close(struct net_device *dev)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *slave_dev;
> +
> +	netif_tx_disable(dev);
> +
> +	slave_dev = rtnl_dereference(finfo->primary_dev);
> +	if (slave_dev)
> +		dev_close(slave_dev);
> +
> +	slave_dev = rtnl_dereference(finfo->standby_dev);
> +	if (slave_dev)
> +		dev_close(slave_dev);
> +
> +	return 0;
> +}
> +
> +static netdev_tx_t failover_drop_xmit(struct sk_buff *skb,
> +				      struct net_device *dev)
> +{
> +	atomic_long_inc(&dev->tx_dropped);
> +	dev_kfree_skb_any(skb);
> +	return NETDEV_TX_OK;
> +}
> +
> +static netdev_tx_t failover_start_xmit(struct sk_buff *skb,
> +				       struct net_device *dev)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *xmit_dev;
> +
> +	/* Try xmit via primary netdev followed by standby netdev */
> +	xmit_dev = rcu_dereference_bh(finfo->primary_dev);
> +	if (!xmit_dev || !failover_xmit_ready(xmit_dev)) {
> +		xmit_dev = rcu_dereference_bh(finfo->standby_dev);
> +		if (!xmit_dev || !failover_xmit_ready(xmit_dev))
> +			return failover_drop_xmit(skb, dev);
> +	}
> +
> +	skb->dev = xmit_dev;
> +	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
> +
> +	return dev_queue_xmit(skb);
> +}
Is this going through qdisc twice? Won't this hurt performance
measureably?
> +
> +static u16 failover_select_queue(struct net_device *dev, struct sk_buff
*skb,
> +				 void *accel_priv,
> +				 select_queue_fallback_t fallback)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *primary_dev;
> +	u16 txq;
> +
> +	rcu_read_lock();
> +	primary_dev = rcu_dereference(finfo->primary_dev);
> +	if (primary_dev) {
> +		const struct net_device_ops *ops = primary_dev->netdev_ops;
> +
> +		if (ops->ndo_select_queue)
> +			txq = ops->ndo_select_queue(primary_dev, skb,
> +						    accel_priv, fallback);
> +		else
> +			txq = fallback(primary_dev, skb);
> +
> +		qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
> +
> +		return txq;
> +	}
> +
> +	txq = skb_rx_queue_recorded(skb) ? skb_get_rx_queue(skb) : 0;
> +
> +	/* Save the original txq to restore before passing to the driver */
> +	qdisc_skb_cb(skb)->slave_dev_queue_mapping = skb->queue_mapping;
> +
> +	if (unlikely(txq >= dev->real_num_tx_queues)) {
> +		do {
> +			txq -= dev->real_num_tx_queues;
> +		} while (txq >= dev->real_num_tx_queues);
> +	}
> +
> +	return txq;
> +}
> +
> +/* fold stats, assuming all rtnl_link_stats64 fields are u64, but
> + * that some drivers can provide 32finfot values only.
> + */
> +static void failover_fold_stats(struct rtnl_link_stats64 *_res,
> +				const struct rtnl_link_stats64 *_new,
> +				const struct rtnl_link_stats64 *_old)
> +{
> +	const u64 *new = (const u64 *)_new;
> +	const u64 *old = (const u64 *)_old;
> +	u64 *res = (u64 *)_res;
> +	int i;
> +
> +	for (i = 0; i < sizeof(*_res) / sizeof(u64); i++) {
> +		u64 nv = new[i];
> +		u64 ov = old[i];
> +		s64 delta = nv - ov;
> +
> +		/* detects if this particular field is 32bit only */
> +		if (((nv | ov) >> 32) == 0)
> +			delta = (s64)(s32)((u32)nv - (u32)ov);
> +
> +		/* filter anomalies, some drivers reset their stats
> +		 * at down/up events.
> +		 */
> +		if (delta > 0)
> +			res[i] += delta;
> +	}
> +}
> +
> +static void failover_get_stats(struct net_device *dev,
> +			       struct rtnl_link_stats64 *stats)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	const struct rtnl_link_stats64 *new;
> +	struct rtnl_link_stats64 temp;
> +	struct net_device *slave_dev;
> +
> +	spin_lock(&finfo->stats_lock);
> +	memcpy(stats, &finfo->failover_stats, sizeof(*stats));
> +
> +	rcu_read_lock();
> +
> +	slave_dev = rcu_dereference(finfo->primary_dev);
> +	if (slave_dev) {
> +		new = dev_get_stats(slave_dev, &temp);
> +		failover_fold_stats(stats, new, &finfo->primary_stats);
> +		memcpy(&finfo->primary_stats, new, sizeof(*new));
> +	}
> +
> +	slave_dev = rcu_dereference(finfo->standby_dev);
> +	if (slave_dev) {
> +		new = dev_get_stats(slave_dev, &temp);
> +		failover_fold_stats(stats, new, &finfo->standby_stats);
> +		memcpy(&finfo->standby_stats, new, sizeof(*new));
> +	}
> +
> +	rcu_read_unlock();
> +
> +	memcpy(&finfo->failover_stats, stats, sizeof(*stats));
> +	spin_unlock(&finfo->stats_lock);
> +}
> +
> +static int failover_change_mtu(struct net_device *dev, int new_mtu)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *primary_dev, *standby_dev;
> +	int ret = 0;
> +
> +	primary_dev = rcu_dereference(finfo->primary_dev);
> +	if (primary_dev) {
> +		ret = dev_set_mtu(primary_dev, new_mtu);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	standby_dev = rcu_dereference(finfo->standby_dev);
> +	if (standby_dev) {
> +		ret = dev_set_mtu(standby_dev, new_mtu);
> +		if (ret) {
> +			dev_set_mtu(primary_dev, dev->mtu);
> +			return ret;
> +		}
> +	}
> +
> +	dev->mtu = new_mtu;
> +	return 0;
> +}
> +
> +static void failover_set_rx_mode(struct net_device *dev)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *slave_dev;
> +
> +	rcu_read_lock();
> +
> +	slave_dev = rcu_dereference(finfo->primary_dev);
> +	if (slave_dev) {
> +		dev_uc_sync_multiple(slave_dev, dev);
> +		dev_mc_sync_multiple(slave_dev, dev);
> +	}
> +
> +	slave_dev = rcu_dereference(finfo->standby_dev);
> +	if (slave_dev) {
> +		dev_uc_sync_multiple(slave_dev, dev);
> +		dev_mc_sync_multiple(slave_dev, dev);
> +	}
> +
> +	rcu_read_unlock();
> +}
> +
> +static const struct net_device_ops failover_dev_ops = {
> +	.ndo_open		= failover_open,
> +	.ndo_stop		= failover_close,
> +	.ndo_start_xmit		= failover_start_xmit,
> +	.ndo_select_queue	= failover_select_queue,
> +	.ndo_get_stats64	= failover_get_stats,
> +	.ndo_change_mtu		= failover_change_mtu,
> +	.ndo_set_rx_mode	= failover_set_rx_mode,
> +	.ndo_validate_addr	= eth_validate_addr,
> +	.ndo_features_check	= passthru_features_check,
xdp support?
> +};
> +
> +#define FAILOVER_NAME "failover"
> +#define FAILOVER_VERSION "0.1"
> +
> +static void failover_ethtool_get_drvinfo(struct net_device *dev,
> +					 struct ethtool_drvinfo *drvinfo)
> +{
> +	strlcpy(drvinfo->driver, FAILOVER_NAME, sizeof(drvinfo->driver));
> +	strlcpy(drvinfo->version, FAILOVER_VERSION,
sizeof(drvinfo->version));
> +}
> +
> +int failover_ethtool_get_link_ksettings(struct net_device *dev,
> +					struct ethtool_link_ksettings *cmd)
> +{
> +	struct failover_info *finfo = netdev_priv(dev);
> +	struct net_device *slave_dev;
> +
> +	slave_dev = rtnl_dereference(finfo->primary_dev);
> +	if (!slave_dev || !failover_xmit_ready(slave_dev)) {
> +		slave_dev = rtnl_dereference(finfo->standby_dev);
> +		if (!slave_dev || !failover_xmit_ready(slave_dev)) {
> +			cmd->base.duplex = DUPLEX_UNKNOWN;
> +			cmd->base.port = PORT_OTHER;
> +			cmd->base.speed = SPEED_UNKNOWN;
> +
> +			return 0;
> +		}
> +	}
> +
> +	return __ethtool_get_link_ksettings(slave_dev, cmd);
> +}
> +EXPORT_SYMBOL_GPL(failover_ethtool_get_link_ksettings);
> +
> +static const struct ethtool_ops failover_ethtool_ops = {
> +	.get_drvinfo            = failover_ethtool_get_drvinfo,
> +	.get_link               = ethtool_op_get_link,
> +	.get_link_ksettings     = failover_ethtool_get_link_ksettings,
> +};
> +
> +static void failover_register_existing_slave(struct net_device
*failover_dev)
> +{
> +	struct net *net = dev_net(failover_dev);
> +	struct net_device *dev;
> +
> +	rtnl_lock();
> +	for_each_netdev(net, dev) {
> +		if (dev == failover_dev)
> +			continue;
> +		if (!failover_validate_event_dev(dev))
> +			continue;
> +		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
> +			failover_slave_register(dev);
> +	}
> +	rtnl_unlock();
> +}
> +
> +int failover_register(struct net_device *dev, struct failover_ops *ops,
> +		      struct failover **pfailover)
> +{
> +	struct failover *failover;
> +
> +	failover = kzalloc(sizeof(*failover), GFP_KERNEL);
> +	if (!failover)
> +		return -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);
> +
> +	failover_register_existing_slave(dev);
> +
> +	*pfailover = failover;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(failover_register);
> +
> +void failover_unregister(struct failover *failover)
> +{
> +	struct net_device *failover_dev;
> +
> +	failover_dev = rcu_dereference(failover->failover_dev);
> +
> +	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);
> +
> +int failover_create(struct net_device *standby_dev, struct failover
**pfailover)
> +{
> +	struct device *dev = standby_dev->dev.parent;
> +	struct net_device *failover_dev;
> +	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.
> +	 */
> +	failover_dev = alloc_etherdev_mq(sizeof(struct failover_info), 16);
> +	if (!failover_dev) {
> +		dev_err(dev, "Unable to allocate failover_netdev!\n");
> +		return -ENOMEM;
> +	}
> +
> +	dev_net_set(failover_dev, dev_net(standby_dev));
> +	SET_NETDEV_DEV(failover_dev, dev);
> +
> +	failover_dev->netdev_ops = &failover_dev_ops;
> +	failover_dev->ethtool_ops = &failover_ethtool_ops;
> +
> +	/* Initialize the device options */
> +	failover_dev->priv_flags |= IFF_UNICAST_FLT | IFF_NO_QUEUE;
> +	failover_dev->priv_flags &= ~(IFF_XMIT_DST_RELEASE |
> +				       IFF_TX_SKB_SHARING);
> +
> +	/* don't acquire failover netdev's netif_tx_lock when
transmitting */
> +	failover_dev->features |= NETIF_F_LLTX;
> +
> +	/* Don't allow failover devices to change network namespaces. */
> +	failover_dev->features |= NETIF_F_NETNS_LOCAL;
> +
> +	failover_dev->hw_features = NETIF_F_HW_CSUM | NETIF_F_SG |
> +				    NETIF_F_FRAGLIST | NETIF_F_ALL_TSO |
> +				    NETIF_F_HIGHDMA | NETIF_F_LRO;
OK but then you must make sure your primary and standby both
support these features.
> +
> +	failover_dev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
> +	failover_dev->features |= failover_dev->hw_features;
> +
> +	memcpy(failover_dev->dev_addr, standby_dev->dev_addr,
> +	       failover_dev->addr_len);
> +
> +	failover_dev->min_mtu = standby_dev->min_mtu;
> +	failover_dev->max_mtu = standby_dev->max_mtu;
OK MTU is copied, fine. But is this always enough?

How about e.g. hard_header_len? min_header_len? needed_headroom?
needed_tailroom? I'd worry that even if you cover existing ones more
might be added with time.  A function copying config between devices
probably belongs in some central place IMHO.


> +
> +	err = register_netdev(failover_dev);
> +	if (err < 0) {
> +		dev_err(dev, "Unable to register failover_dev!\n");
> +		goto err_register_netdev;
> +	}
> +
> +	netif_carrier_off(failover_dev);
> +
> +	err = failover_register(failover_dev, NULL, pfailover);
> +	if (err < 0)
> +		goto err_failover;
> +
> +	return 0;
> +
> +err_failover:
> +	unregister_netdev(failover_dev);
> +err_register_netdev:
> +	free_netdev(failover_dev);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(failover_create);
> +
> +void failover_destroy(struct failover *failover)
> +{
> +	struct net_device *failover_dev;
> +	struct net_device *slave_dev;
> +	struct failover_info *finfo;
> +
> +	if (!failover)
> +		return;
> +
> +	failover_dev = rcu_dereference(failover->failover_dev);
> +	finfo = netdev_priv(failover_dev);
> +
> +	netif_device_detach(failover_dev);
> +
> +	rtnl_lock();
> +
> +	slave_dev = rtnl_dereference(finfo->primary_dev);
> +	if (slave_dev)
> +		failover_slave_unregister(slave_dev);
> +
> +	slave_dev = rtnl_dereference(finfo->standby_dev);
> +	if (slave_dev)
> +		failover_slave_unregister(slave_dev);
> +
> +	failover_unregister(failover);
> +
> +	unregister_netdevice(failover_dev);
> +
> +	rtnl_unlock();
> +
> +	free_netdev(failover_dev);
> +}
> +EXPORT_SYMBOL_GPL(failover_destroy);
> +
> +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("Failover infrastructure/interface for Paravirtual
drivers");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.14.3

On Thu, Apr 19, 2018 at 06:42:03PM -0700, Sridhar Samudrala
wrote:
> @@ -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);
I'd rather you didn't let's not mix in whitespace changes.
> -- 
> 2.14.3

On Thu, Apr 19, 2018 at 06:42:02PM -0700, Sridhar Samudrala
wrote:
> +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;
> +}
So it bothers me that this ties to just any device at all.

I thought hard about it, and I see a nice solution.
Here goes:

QEMU has a pci-bridge-seat device. It is used currently to
group e.g. input devices for multiseat support.

Now if you squint at it hard enough, you can see we are also
in a grouping problem. So how about the following:

1. allocate a virtio pci bridge device failover grouping id (reserve through
virtio TC).
2. only group two devices in a failover configuration if both
   are under the same bridge with this id (in addition to a mac check).

In particular a bridged configuration makes it easier to
make sure the standby is enumerated before the primary.
In fact we could fail init of failover if we see
appear standby *after* primary.

And this allows many devices with the same ethernet address
without any issues - just under separate bridges.

Further if we ever want to enumerate in parallel this can
be supported by adding a driver for the bridge.

In fact, I see how down the road such a device could
be the beginning of the more ambitious plan to
expose a powerful switchdev interface for
more advanced 


So far so good, but I see a couple of issues:

- it is PCI specific
	 Not a big deal: we limit ourselves to PCI anyway ATM.

- does not work across PCI domains - which are helpful for NUMA
  (e.g. we want to be able to move to primary
   which is on a different numa
   node without losing connectivity).

	Idea: add a "group ID" register to each of these pci bridge
	devices (e.g. in device specific config space).
	Match two bridges if they have the same group ID.

- all these extra bridges slow enumeration down somewhat

	Idea: as a fallback if no bridge is found,
	just assume all devices match, which will result
	in falling back on the "match by mac" logic like in
	this patchset. Will be fine for simple setups.
	

Thoughts?

-- 
MST

On Thu, 19 Apr 2018 18:42:04 -0700
Sridhar Samudrala <sridhar.samudrala at intel.com> wrote:
> Use the registration/notification framework supported by the generic
> failover infrastructure.
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala at intel.com>
Do what you want to other devices but leave netvsc alone.
Adding these failover ops does not reduce the code size, and really is
no benefit.  The netvsc device driver needs to be backported to several
other distributions and doing this makes that harder.

I will NAK patches to change to common code for netvsc especially the
three device model.  MS worked hard with distro vendors to support transparent
mode, ans we really can't have a new model; or do backport.

Plus, DPDK is now dependent on existing model.

Hi Sridhar,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net/master]
[also build test ERROR on v4.17-rc1]
[cannot apply to net-next/master next-20180420]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system]

url:   
https://github.com/0day-ci/linux/commits/Sridhar-Samudrala/Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device/20180422-210557
config: x86_64-allyesdebian (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All error/warnings (new ones prefixed by >>):

   In file included from drivers/net/hyperv/netvsc_drv.c:46:0:
   include/net/failover.h:67:1: error: expected identifier or '(' before
'{' token
    {
    ^
   include/net/failover.h:78:16: warning: 'struct pfailover' declared
inside parameter list will not be visible outside of this definition or
declaration
            struct pfailover **pfailover);
                   ^~~~~~~~~
   include/net/failover.h:79:1: error: expected identifier or '(' before
'{' token
    {
    ^
   drivers/net/hyperv/netvsc_drv.c: In function
'netvsc_probe':
>> drivers/net/hyperv/netvsc_drv.c:2020:5: error: passing argument 3 of
'failover_register' from incompatible pointer type
[-Werror=incompatible-pointer-types]
        &net_device_ctx->failover);
        ^
   In file included from drivers/net/hyperv/netvsc_drv.c:46:0:
   include/net/failover.h:77:5: note: expected 'struct pfailover **' but
argument is of type 'struct failover **'
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^~~~~~~~~~~~~~~~~
   drivers/net/hyperv/netvsc_drv.c: At top level:
   include/net/failover.h:65:5: warning: 'failover_create' declared
'static' but never defined [-Wunused-function]
    int failover_create(struct net_device *standby_dev,
        ^~~~~~~~~~~~~~~
>> include/net/failover.h:77:5: warning: 'failover_register' used
but never defined
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors
--
   In file included from drivers/net//hyperv/netvsc_drv.c:46:0:
   include/net/failover.h:67:1: error: expected identifier or '(' before
'{' token
    {
    ^
   include/net/failover.h:78:16: warning: 'struct pfailover' declared
inside parameter list will not be visible outside of this definition or
declaration
            struct pfailover **pfailover);
                   ^~~~~~~~~
   include/net/failover.h:79:1: error: expected identifier or '(' before
'{' token
    {
    ^
   drivers/net//hyperv/netvsc_drv.c: In function 'netvsc_probe':
   drivers/net//hyperv/netvsc_drv.c:2020:5: error: passing argument 3 of
'failover_register' from incompatible pointer type
[-Werror=incompatible-pointer-types]
        &net_device_ctx->failover);
        ^
   In file included from drivers/net//hyperv/netvsc_drv.c:46:0:
   include/net/failover.h:77:5: note: expected 'struct pfailover **' but
argument is of type 'struct failover **'
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^~~~~~~~~~~~~~~~~
   drivers/net//hyperv/netvsc_drv.c: At top level:
   include/net/failover.h:65:5: warning: 'failover_create' declared
'static' but never defined [-Wunused-function]
    int failover_create(struct net_device *standby_dev,
        ^~~~~~~~~~~~~~~
>> include/net/failover.h:77:5: warning: 'failover_register' used
but never defined
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/failover_register +2020 drivers/net/hyperv/netvsc_drv.c

  1929	
  1930	static int netvsc_probe(struct hv_device *dev,
  1931				const struct hv_vmbus_device_id *dev_id)
  1932	{
  1933		struct net_device *net = NULL;
  1934		struct net_device_context *net_device_ctx;
  1935		struct netvsc_device_info device_info;
  1936		struct netvsc_device *nvdev;
  1937		int ret = -ENOMEM;
  1938	
  1939		net = alloc_etherdev_mq(sizeof(struct net_device_context),
  1940					VRSS_CHANNEL_MAX);
  1941		if (!net)
  1942			goto no_net;
  1943	
  1944		netif_carrier_off(net);
  1945	
  1946		netvsc_init_settings(net);
  1947	
  1948		net_device_ctx = netdev_priv(net);
  1949		net_device_ctx->device_ctx = dev;
  1950		net_device_ctx->msg_enable = netif_msg_init(debug, default_msg);
  1951		if (netif_msg_probe(net_device_ctx))
  1952			netdev_dbg(net, "netvsc msg_enable: %d\n",
  1953				   net_device_ctx->msg_enable);
  1954	
  1955		hv_set_drvdata(dev, net);
  1956	
  1957		INIT_DELAYED_WORK(&net_device_ctx->dwork, netvsc_link_change);
  1958	
  1959		spin_lock_init(&net_device_ctx->lock);
  1960		INIT_LIST_HEAD(&net_device_ctx->reconfig_events);
  1961		INIT_DELAYED_WORK(&net_device_ctx->vf_takeover, netvsc_vf_setup);
  1962	
  1963		net_device_ctx->vf_stats
  1964			= netdev_alloc_pcpu_stats(struct netvsc_vf_pcpu_stats);
  1965		if (!net_device_ctx->vf_stats)
  1966			goto no_stats;
  1967	
  1968		net->netdev_ops = &device_ops;
  1969		net->ethtool_ops = &ethtool_ops;
  1970		SET_NETDEV_DEV(net, &dev->device);
  1971	
  1972		/* We always need headroom for rndis header */
  1973		net->needed_headroom = RNDIS_AND_PPI_SIZE;
  1974	
  1975		/* Initialize the number of queues to be 1, we may change it if more
  1976		 * channels are offered later.
  1977		 */
  1978		netif_set_real_num_tx_queues(net, 1);
  1979		netif_set_real_num_rx_queues(net, 1);
  1980	
  1981		/* Notify the netvsc driver of the new device */
  1982		memset(&device_info, 0, sizeof(device_info));
  1983		device_info.num_chn = VRSS_CHANNEL_DEFAULT;
  1984		device_info.send_sections = NETVSC_DEFAULT_TX;
  1985		device_info.send_section_size = NETVSC_SEND_SECTION_SIZE;
  1986		device_info.recv_sections = NETVSC_DEFAULT_RX;
  1987		device_info.recv_section_size = NETVSC_RECV_SECTION_SIZE;
  1988	
  1989		nvdev = rndis_filter_device_add(dev, &device_info);
  1990		if (IS_ERR(nvdev)) {
  1991			ret = PTR_ERR(nvdev);
  1992			netdev_err(net, "unable to add netvsc device (ret %d)\n",
ret);
  1993			goto rndis_failed;
  1994		}
  1995	
  1996		memcpy(net->dev_addr, device_info.mac_adr, ETH_ALEN);
  1997	
  1998		/* hw_features computed in rndis_netdev_set_hwcaps() */
  1999		net->features = net->hw_features |
  2000			NETIF_F_HIGHDMA | NETIF_F_SG |
  2001			NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_CTAG_RX;
  2002		net->vlan_features = net->features;
  2003	
  2004		netdev_lockdep_set_classes(net);
  2005	
  2006		/* MTU range: 68 - 1500 or 65521 */
  2007		net->min_mtu = NETVSC_MTU_MIN;
  2008		if (nvdev->nvsp_version >= NVSP_PROTOCOL_VERSION_2)
  2009			net->max_mtu = NETVSC_MTU - ETH_HLEN;
  2010		else
  2011			net->max_mtu = ETH_DATA_LEN;
  2012	
  2013		ret = register_netdev(net);
  2014		if (ret != 0) {
  2015			pr_err("Unable to register netdev.\n");
  2016			goto register_failed;
  2017		}
  2018	
  2019		ret = failover_register(net,
&netvsc_failover_ops,
> 2020					&net_device_ctx->failover);
  2021		if (ret != 0)
  2022			goto err_failover;
  2023	
  2024		return ret;
  2025	
  2026	err_failover:
  2027		unregister_netdev(net);
  2028	register_failed:
  2029		rndis_filter_device_remove(dev, nvdev);
  2030	rndis_failed:
  2031		free_percpu(net_device_ctx->vf_stats);
  2032	no_stats:
  2033		hv_set_drvdata(dev, NULL);
  2034		free_netdev(net);
  2035	no_net:
  2036		return ret;
  2037	}
  2038	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
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Hi Sridhar,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on net/master]
[also build test ERROR on v4.17-rc1]
[cannot apply to net-next/master next-20180420]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system]

url:   
https://github.com/0day-ci/linux/commits/Sridhar-Samudrala/Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device/20180422-210557
config: i386-randconfig-x071-201816 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All error/warnings (new ones prefixed by >>):

   In file included from drivers//net/virtio_net.c:37:0:
>> include/net/failover.h:67:1: error: expected identifier or '('
before '{' token
    {
    ^
>> include/net/failover.h:78:16: warning: 'struct pfailover'
declared inside parameter list will not be visible outside of this definition or
declaration
            struct pfailover **pfailover);
                   ^~~~~~~~~
   include/net/failover.h:79:1: error: expected identifier or '(' before
'{' token
    {
    ^
>> include/net/failover.h:65:5: warning: 'failover_create' used
but never defined
    int failover_create(struct net_device *standby_dev,
        ^~~~~~~~~~~~~~~
   include/net/failover.h:77:5: warning: 'failover_register' declared
'static' but never defined [-Wunused-function]
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^~~~~~~~~~~~~~~~~

vim +67 include/net/failover.h

891cac68 Sridhar Samudrala 2018-04-19  63  
891cac68 Sridhar Samudrala 2018-04-19  64  static inline
891cac68 Sridhar Samudrala 2018-04-19 @65  int failover_create(struct net_device
*standby_dev,
891cac68 Sridhar Samudrala 2018-04-19  66  		    struct failover **pfailover);
891cac68 Sridhar Samudrala 2018-04-19 @67  {
891cac68 Sridhar Samudrala 2018-04-19  68  	return 0;
891cac68 Sridhar Samudrala 2018-04-19  69  }
891cac68 Sridhar Samudrala 2018-04-19  70  
891cac68 Sridhar Samudrala 2018-04-19  71  static inline
891cac68 Sridhar Samudrala 2018-04-19  72  void failover_destroy(struct failover
*failover)
891cac68 Sridhar Samudrala 2018-04-19  73  {
891cac68 Sridhar Samudrala 2018-04-19  74  }
891cac68 Sridhar Samudrala 2018-04-19  75  
891cac68 Sridhar Samudrala 2018-04-19  76  static inline
891cac68 Sridhar Samudrala 2018-04-19  77  int failover_register(struct
net_device *standby_dev, struct failover_ops *ops,
891cac68 Sridhar Samudrala 2018-04-19 @78  		      struct pfailover
**pfailover);
891cac68 Sridhar Samudrala 2018-04-19  79  {
891cac68 Sridhar Samudrala 2018-04-19  80  	return 0;
891cac68 Sridhar Samudrala 2018-04-19  81  }
891cac68 Sridhar Samudrala 2018-04-19  82  

:::::: The code at line 67 was first introduced by commit
:::::: 891cac68e9283c9561d0097af77e7189b9752719 net: Introduce generic failover
module

:::::: TO: Sridhar Samudrala <sridhar.samudrala at intel.com>
:::::: CC: 0day robot <fengguang.wu at intel.com>

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Hi Sridhar,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net/master]
[also build test WARNING on v4.17-rc1]
[cannot apply to net-next/master next-20180420]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system]

url:   
https://github.com/0day-ci/linux/commits/Sridhar-Samudrala/Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device/20180422-210557
config: i386-randconfig-a1-04221429 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.4-2) 4.9.4
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   In file included from drivers//net/virtio_net.c:37:0:
   include/net/failover.h:67:1: error: expected identifier or '(' before
'{' token
    {
    ^
>> include/net/failover.h:78:16: warning: 'struct pfailover'
declared inside parameter list
            struct pfailover **pfailover);
                   ^
>> include/net/failover.h:78:16: warning: its scope is only this
definition or declaration, which is probably not what you want
   include/net/failover.h:79:1: error: expected identifier or '(' before
'{' token
    {
    ^
   include/net/failover.h:65:5: warning: 'failover_create' used but
never defined
    int failover_create(struct net_device *standby_dev,
        ^
   include/net/failover.h:77:5: warning: 'failover_register' declared
'static' but never defined [-Wunused-function]
    int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
        ^

vim +78 include/net/failover.h

891cac68 Sridhar Samudrala 2018-04-19  63  
891cac68 Sridhar Samudrala 2018-04-19  64  static inline
891cac68 Sridhar Samudrala 2018-04-19  65  int failover_create(struct net_device
*standby_dev,
891cac68 Sridhar Samudrala 2018-04-19  66  		    struct failover **pfailover);
891cac68 Sridhar Samudrala 2018-04-19 @67  {
891cac68 Sridhar Samudrala 2018-04-19  68  	return 0;
891cac68 Sridhar Samudrala 2018-04-19  69  }
891cac68 Sridhar Samudrala 2018-04-19  70  
891cac68 Sridhar Samudrala 2018-04-19  71  static inline
891cac68 Sridhar Samudrala 2018-04-19  72  void failover_destroy(struct failover
*failover)
891cac68 Sridhar Samudrala 2018-04-19  73  {
891cac68 Sridhar Samudrala 2018-04-19  74  }
891cac68 Sridhar Samudrala 2018-04-19  75  
891cac68 Sridhar Samudrala 2018-04-19  76  static inline
891cac68 Sridhar Samudrala 2018-04-19  77  int failover_register(struct
net_device *standby_dev, struct failover_ops *ops,
891cac68 Sridhar Samudrala 2018-04-19 @78  		      struct pfailover
**pfailover);
891cac68 Sridhar Samudrala 2018-04-19  79  {
891cac68 Sridhar Samudrala 2018-04-19  80  	return 0;
891cac68 Sridhar Samudrala 2018-04-19  81  }
891cac68 Sridhar Samudrala 2018-04-19  82  

:::::: The code at line 78 was first introduced by commit
:::::: 891cac68e9283c9561d0097af77e7189b9752719 net: Introduce generic failover
module

:::::: TO: Sridhar Samudrala <sridhar.samudrala at intel.com>
:::::: CC: 0day robot <fengguang.wu at intel.com>

---
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On Thu, Apr 19, 2018 at 06:42:02PM -0700, Sridhar Samudrala
wrote:
> +#if IS_ENABLED(CONFIG_NET_FAILOVER)
> +
> +int failover_create(struct net_device *standby_dev,
> +		    struct failover **pfailover);
Should we rename all these structs net_failover?
It's possible to extend the concept to storage I think.
> +void failover_destroy(struct failover *failover);
> +
> +int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
> +		      struct failover **pfailover);
> +void failover_unregister(struct failover *failover);
> +
> +int failover_slave_unregister(struct net_device *slave_dev);
> +
> +#else
> +
> +static inline
> +int failover_create(struct net_device *standby_dev,
> +		    struct failover **pfailover);
> +{
> +	return 0;
Does this make callers do something sane?
Shouldn't these return an error?
> +}
> +
> +static inline
> +void failover_destroy(struct failover *failover)
> +{
> +}
> +
> +static inline
> +int failover_register(struct net_device *standby_dev, struct failover_ops
*ops,
> +		      struct pfailover **pfailover);
> +{
> +	return 0;
> +}
struct pfailover seems like a typo.
> +
> +static inline
> +void failover_unregister(struct failover *failover)
> +{
> +}
> +
> +static inline
> +int failover_slave_unregister(struct net_device *slave_dev)
> +{
> +	return 0;
> +}
Does anyone test return value of unregister?
should this be void?
> +
> +#endif
> +
> +#endif /* _NET_FAILOVER_H */

Hi Sridhar,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net/master]
[also build test WARNING on v4.17-rc1]
[cannot apply to net-next/master next-20180420]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system]

url:   
https://github.com/0day-ci/linux/commits/Sridhar-Samudrala/Enable-virtio_net-to-act-as-a-standby-for-a-passthru-device/20180422-210557
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)
>> net/core/failover.c:99:36: sparse: incorrect type in argument 1
(different address spaces) @@    expected struct net_device *dev @@    got
struct net_devicestruct net_device *dev @@
   net/core/failover.c:99:36:    expected struct net_device *dev
   net/core/failover.c:99:36:    got struct net_device [noderef]
<asn:4>*standby_dev
   net/core/failover.c:102:36: sparse: incorrect type in argument 1 (different
address spaces) @@    expected struct net_device *dev @@    got struct
net_devicestruct net_device *dev @@
   net/core/failover.c:102:36:    expected struct net_device *dev
   net/core/failover.c:102:36:    got struct net_device [noderef]
<asn:4>*primary_dev
>> net/core/failover.c:468:12: sparse: context imbalance in
'failover_select_queue' - wrong count at exit
vim +99 net/core/failover.c

    58	
    59	static int failover_slave_join(struct net_device *slave_dev,
    60				       struct net_device *failover_dev,
    61				       struct failover_ops *failover_ops)
    62	{
    63		struct failover_info *finfo;
    64		int err, orig_mtu;
    65		bool standby;
    66	
    67		if (failover_ops) {
    68			if (!failover_ops->slave_join)
    69				return -EINVAL;
    70	
    71			return failover_ops->slave_join(slave_dev, failover_dev);
    72		}
    73	
    74		if (netif_running(failover_dev)) {
    75			err = dev_open(slave_dev);
    76			if (err && (err != -EBUSY)) {
    77				netdev_err(failover_dev, "Opening slave %s failed err:%d\n",
    78					   slave_dev->name, err);
    79				goto err_dev_open;
    80			}
    81		}
    82	
    83		/* Align MTU of slave with failover dev */
    84		orig_mtu = slave_dev->mtu;
    85		err = dev_set_mtu(slave_dev, failover_dev->mtu);
    86		if (err) {
    87			netdev_err(failover_dev, "unable to change mtu of %s to %u
register failed\n",
    88				   slave_dev->name, failover_dev->mtu);
    89			goto err_set_mtu;
    90		}
    91	
    92		finfo = netdev_priv(failover_dev);
    93		standby = (slave_dev->dev.parent == failover_dev->dev.parent);
    94	
    95		dev_hold(slave_dev);
    96	
    97		if (standby) {
    98			rcu_assign_pointer(finfo->standby_dev, slave_dev);
  > 99			dev_get_stats(finfo->standby_dev, &finfo->standby_stats);
   100		} else {
   101			rcu_assign_pointer(finfo->primary_dev, slave_dev);
   102			dev_get_stats(finfo->primary_dev, &finfo->primary_stats);
   103			failover_dev->min_mtu = slave_dev->min_mtu;
   104			failover_dev->max_mtu = slave_dev->max_mtu;
   105		}
   106	
   107		netdev_info(failover_dev, "failover slave:%s joined\n",
   108			    slave_dev->name);
   109	
   110		return 0;
   111	
   112	err_set_mtu:
   113		dev_close(slave_dev);
   114	err_dev_open:
   115		return err;
   116	}
   117	

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