Linux Virtualization - Apr 2018 - [PATCH v7 net-next 2/4] net: Introduce generic failover module

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 4/19/2018 7:44 PM, Michael S. Tsirkin wrote:
> 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.
Yes. some of the code is based on bonding/team and netvsc. i added a reference
to netvsc in the comment, will also include bonding/team driver.
>
>> +
>> +/* 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.
OK.
>
>> +	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.
Thanks for catching, I broke this when i moved the dev_open() and dev_set_mtu()
calls from register to join. I need to reset slave_dev mtu to orig_mtu on
failure.

>
>
>> +	err = dev_set_mtu(slave_dev, failover_dev->mtu);
> How do we know slave supports this MTU? same applies to
> failover_change_mtu.
The err check below should catch it and we will reset the mtu back and
fail the join/register.
>
>
>
>
>> +	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 ...
Yes. we need to update the failover_stats before the slave goes 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.
Not sure why we need to get stats from lower devs here?

>
>
>> +	}
>> +
>> +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.
ok. failover_create can copy these values from standby_dev and
we can validate that they match when primary_dev registers.
>
>> +	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?
The failover dev has no queue (IFF_NO_QUEUE) , so doesn't go through qdisc
twice.
>
>> +
>> +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?
I think it should be possible to add it be calling the lower dev ndo_xdp
routines
with proper checks. can we add this later?
>
>> +};
>> +
>> +#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.
I guess i need to add something like bond_compute_features() to handle this.
>
>> +
>> +	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.
ok. will add a function that handles these fields too.
>
>
>> +
>> +	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 Fri, Apr 20, 2018 at 08:21:00AM -0700, Samudrala, Sridhar
wrote:
> > > +	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.
> 
> Not sure why we need to get stats from lower devs here?
link down is often indication of a hardware problem.
lower dev might stop responding down the road.
> > > +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?
> 
> I think it should be possible to add it be calling the lower dev ndo_xdp
routines
> with proper checks. can we add this later?
I'd be concerned that if you don't xdp userspace will keep poking
at lower devs. Then it will stop working if you add this later.

-- 
MST