failover-for-linux-5.0-rc1.patch

From 2247488626283177dd90b01482f3bd6b02ee1372 Mon Sep 17 00:00:00 2001
From: Dongli Zhang <dongli.zhang@oracle.com>
Date: Thu, 10 Jan 2019 06:00:51 +0800
Subject: [PATCH 1/1] failover for linux-5.0-rc1

Signed-off-by: Dongli Zhang <dongli.zhang0129@gmail.com>
---
 drivers/net/net_failover.c | 140 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/netdevice.h  |  24 ++++++++
 include/net/failover.h     |  28 +++++++++
 net/core/dev.c             |   3 +
 net/core/ethtool.c         |   3 +
 net/core/failover.c        |  44 ++++++++++++++
 net/ethernet/eth.c         |   3 +
 7 files changed, 245 insertions(+)

diff --git a/drivers/net/net_failover.c b/drivers/net/net_failover.c
index ed1166a..6f07a24 100644
--- a/drivers/net/net_failover.c
+++ b/drivers/net/net_failover.c
@@ -27,11 +27,40 @@
 #include <uapi/linux/if_arp.h>
 #include <net/net_failover.h>
 
+/*
+ *
+ * MAC address of Virtual Function changes unexpectedly
+ * ----------------------------------------------------
+ * If a Virtual Function's MAC address is not assigned in the host, then the VF
+ * (virtual function) driver will use a random MAC address. This random MAC
+ * address may change each time the VF driver is reloaded. You can assign a static
+ * MAC address in the host machine. This static MAC address will survive
+ * a VF driver reload.
+ */
+
+/*
+ * called by:
+ *   - drivers/net/net_failover.c|58| <<net_failover_open>> if ((primary_dev && net_failover_xmit_ready(primary_dev)) ||
+ *   - drivers/net/net_failover.c|59| <<net_failover_open>> (standby_dev && net_failover_xmit_ready(standby_dev))) {
+ *   - drivers/net/net_failover.c|113| <<net_failover_start_xmit>> if (!xmit_dev || !net_failover_xmit_ready(xmit_dev)) {
+ *   - drivers/net/net_failover.c|115| <<net_failover_start_xmit>> if (!xmit_dev || !net_failover_xmit_ready(xmit_dev))
+ *   - drivers/net/net_failover.c|370| <<nfo_ethtool_get_link_ksettings>> if (!slave_dev || !net_failover_xmit_ready(slave_dev)) {
+ *   - drivers/net/net_failover.c|372| <<nfo_ethtool_get_link_ksettings>> if (!slave_dev || !net_failover_xmit_ready(slave_dev)) {
+ *   - drivers/net/net_failover.c|718| <<net_failover_slave_link_change>> if ((primary_dev && net_failover_xmit_ready(primary_dev)) ||
+ *   - drivers/net/net_failover.c|719| <<net_failover_slave_link_change>> (standby_dev && net_failover_xmit_ready(standby_dev))) {
+ *
+ * 返回netif_running(dev) && netif_carrier_ok(dev)
+ */
 static bool net_failover_xmit_ready(struct net_device *dev)
 {
 	return netif_running(dev) && netif_carrier_ok(dev);
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_open = net_failover_open()
+ *
+ * 对net_failover_info->primary_dev和net_failover_info->standby_dev分别调用open
+ */
 static int net_failover_open(struct net_device *dev)
 {
 	struct net_failover_info *nfo_info = netdev_priv(dev);
@@ -67,6 +96,9 @@ static int net_failover_open(struct net_device *dev)
 	return err;
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_stop = net_failover_close()
+ */
 static int net_failover_close(struct net_device *dev)
 {
 	struct net_failover_info *nfo_info = netdev_priv(dev);
@@ -85,6 +117,10 @@ static int net_failover_close(struct net_device *dev)
 	return 0;
 }
 
+/*
+ * called by:
+ *   - drivers/net/net_failover.c|129| <<net_failover_start_xmit>> return net_failover_drop_xmit(skb, dev);
+ */
 static netdev_tx_t net_failover_drop_xmit(struct sk_buff *skb,
 					  struct net_device *dev)
 {
@@ -93,26 +129,46 @@ static netdev_tx_t net_failover_drop_xmit(struct sk_buff *skb,
 	return NETDEV_TX_OK;
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_start_xmit = net_failover_start_xmit()
+ */
 static netdev_tx_t net_failover_start_xmit(struct sk_buff *skb,
 					   struct net_device *dev)
 {
+	/* 在net_failover_create()分配的 */
 	struct net_failover_info *nfo_info = netdev_priv(dev);
 	struct net_device *xmit_dev;
 
 	/* Try xmit via primary netdev followed by standby netdev */
 	xmit_dev = rcu_dereference_bh(nfo_info->primary_dev);
+	/*
+	 * net_failover_xmit_ready():
+	 *     返回netif_running(dev) && netif_carrier_ok(dev)
+	 */
 	if (!xmit_dev || !net_failover_xmit_ready(xmit_dev)) {
 		xmit_dev = rcu_dereference_bh(nfo_info->standby_dev);
+		/*
+		 * net_failover_xmit_ready():
+		 *     返回netif_running(dev) && netif_carrier_ok(dev)
+		 */
 		if (!xmit_dev || !net_failover_xmit_ready(xmit_dev))
 			return net_failover_drop_xmit(skb, dev);
 	}
 
+	/*
+	 * 上面先尝试net_failover_info->primary_dev
+	 * 再尝试net_failover_info->standby_dev
+	 */
+
 	skb->dev = xmit_dev;
 	skb->queue_mapping = qdisc_skb_cb(skb)->slave_dev_queue_mapping;
 
 	return dev_queue_xmit(skb);
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_select_queue = net_failover_select_queue()
+ */
 static u16 net_failover_select_queue(struct net_device *dev,
 				     struct sk_buff *skb,
 				     struct net_device *sb_dev,
@@ -180,6 +236,9 @@ static void net_failover_fold_stats(struct rtnl_link_stats64 *_res,
 	}
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_get_stats64 = net_failover_get_stats()
+ */
 static void net_failover_get_stats(struct net_device *dev,
 				   struct rtnl_link_stats64 *stats)
 {
@@ -213,6 +272,9 @@ static void net_failover_get_stats(struct net_device *dev,
 	spin_unlock(&nfo_info->stats_lock);
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_change_mtu = net_failover_change_mtu()
+ */
 static int net_failover_change_mtu(struct net_device *dev, int new_mtu)
 {
 	struct net_failover_info *nfo_info = netdev_priv(dev);
@@ -241,6 +303,9 @@ static int net_failover_change_mtu(struct net_device *dev, int new_mtu)
 	return 0;
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_set_rx_mode = net_failover_set_rx_mode()
+ */
 static void net_failover_set_rx_mode(struct net_device *dev)
 {
 	struct net_failover_info *nfo_info = netdev_priv(dev);
@@ -263,6 +328,9 @@ static void net_failover_set_rx_mode(struct net_device *dev)
 	rcu_read_unlock();
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_vlan_rx_add_vid = net_failover_vlan_rx_add_vid()
+ */
 static int net_failover_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
 					u16 vid)
 {
@@ -288,6 +356,9 @@ static int net_failover_vlan_rx_add_vid(struct net_device *dev, __be16 proto,
 	return ret;
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_vlan_rx_kill_vid = net_failover_vlan_rx_kill_vid()
+ */
 static int net_failover_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,
 					 u16 vid)
 {
@@ -305,6 +376,10 @@ static int net_failover_vlan_rx_kill_vid(struct net_device *dev, __be16 proto,
 	return 0;
 }
 
+/*
+ * used by:
+ *   - drivers/net/net_failover.c|800| <<net_failover_create>> failover_dev->netdev_ops = &failover_dev_ops;
+ */
 static const struct net_device_ops failover_dev_ops = {
 	.ndo_open		= net_failover_open,
 	.ndo_stop		= net_failover_close,
@@ -322,6 +397,9 @@ static const struct net_device_ops failover_dev_ops = {
 #define FAILOVER_NAME "net_failover"
 #define FAILOVER_VERSION "0.1"
 
+/*
+ * struct ethtool_ops failover_ethtool_ops.get_drvinfo = nfo_ethtool_get_drvinfo()
+ */
 static void nfo_ethtool_get_drvinfo(struct net_device *dev,
 				    struct ethtool_drvinfo *drvinfo)
 {
@@ -329,6 +407,9 @@ static void nfo_ethtool_get_drvinfo(struct net_device *dev,
 	strlcpy(drvinfo->version, FAILOVER_VERSION, sizeof(drvinfo->version));
 }
 
+/*
+ * struct ethtool_ops failover_ethtool_ops.get_link_ksettings = nfo_ethtool_get_link_ksettings()
+ */
 static int nfo_ethtool_get_link_ksettings(struct net_device *dev,
 					  struct ethtool_link_ksettings *cmd)
 {
@@ -360,6 +441,12 @@ static const struct ethtool_ops failover_ethtool_ops = {
  * Change the associated network device from lower dev to failover dev.
  * note: already called with rcu_read_lock
  */
+/*
+ * used by:
+ *   - net/core/failover.c|66| <<failover_slave_register>> err = netdev_rx_handler_register(slave_dev, fops->slave_handle_frame,
+ * 
+ * struct failover_ops net_failover_ops.slave_handle_frame = net_failover_handle_frame()
+ */
 static rx_handler_result_t net_failover_handle_frame(struct sk_buff **pskb)
 {
 	struct sk_buff *skb = *pskb;
@@ -460,6 +547,12 @@ static void net_failover_lower_state_changed(struct net_device *slave_dev,
 	netdev_lower_state_changed(slave_dev, &info);
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|63| <<failover_slave_register>> fops->slave_pre_register(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_pre_register = net_failover_slave_pre_register()
+ */
 static int net_failover_slave_pre_register(struct net_device *slave_dev,
 					   struct net_device *failover_dev)
 {
@@ -496,6 +589,12 @@ static int net_failover_slave_pre_register(struct net_device *slave_dev,
 	return 0;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|86| <<failover_slave_register>> !fops->slave_register(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_register = net_failover_slave_register()
+ */
 static int net_failover_slave_register(struct net_device *slave_dev,
 				       struct net_device *failover_dev)
 {
@@ -575,6 +674,12 @@ static int net_failover_slave_register(struct net_device *slave_dev,
 	return err;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|119| <<failover_slave_unregister>> fops->slave_pre_unregister(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_pre_unregister = net_failover_slave_pre_unregister()
+ */
 static int net_failover_slave_pre_unregister(struct net_device *slave_dev,
 					     struct net_device *failover_dev)
 {
@@ -591,6 +696,12 @@ static int net_failover_slave_pre_unregister(struct net_device *slave_dev,
 	return 0;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|127| <<failover_slave_unregister>> !fops->slave_unregister(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_unregister = net_failover_slave_unregister()
+ */
 static int net_failover_slave_unregister(struct net_device *slave_dev,
 					 struct net_device *failover_dev)
 {
@@ -634,6 +745,12 @@ static int net_failover_slave_unregister(struct net_device *slave_dev,
 	return 0;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|153| <<failover_slave_link_change>> !fops->slave_link_change(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_link_change = net_failover_slave_link_change()
+ */
 static int net_failover_slave_link_change(struct net_device *slave_dev,
 					  struct net_device *failover_dev)
 {
@@ -663,6 +780,12 @@ static int net_failover_slave_link_change(struct net_device *slave_dev,
 	return 0;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|178| <<failover_slave_name_change>> !fops->slave_name_change(slave_dev, failover_dev))
+ *
+ * struct failover_ops net_failover_ops.slave_name_change = net_failover_slave_name_change()
+ */
 static int net_failover_slave_name_change(struct net_device *slave_dev,
 					  struct net_device *failover_dev)
 {
@@ -685,6 +808,10 @@ static int net_failover_slave_name_change(struct net_device *slave_dev,
 	return 0;
 }
 
+/*
+ * used by:
+ *   - drivers/net/net_failover.c|808| <<net_failover_create>> failover = failover_register(failover_dev, &net_failover_ops);
+ */
 static struct failover_ops net_failover_ops = {
 	.slave_pre_register	= net_failover_slave_pre_register,
 	.slave_register		= net_failover_slave_register,
@@ -708,8 +835,13 @@ static struct failover_ops net_failover_ops = {
  *
  * Return: pointer to failover instance
  */
+/*
+ * called by:
+ *   - drivers/net/virtio_net.c|3078| <<virtnet_probe>> vi->failover = net_failover_create(vi->dev);
+ */
 struct failover *net_failover_create(struct net_device *standby_dev)
 {
+	/* 根据目前的情况, standby_dev就是virtio_net的net_device */
 	struct device *dev = standby_dev->dev.parent;
 	struct net_device *failover_dev;
 	struct failover *failover;
@@ -724,7 +856,15 @@ struct failover *net_failover_create(struct net_device *standby_dev)
 		return ERR_PTR(-ENOMEM);
 	}
 
+	/*
+	 * failover_dev: vf的
+	 * standby_dev : virtio的
+	 */
 	dev_net_set(failover_dev, dev_net(standby_dev));
+	/*
+	 * #define SET_NETDEV_DEV(net, pdev)  ((net)->dev.parent = (pdev))
+	 * 设置failover_dev->>dev.parent = dev
+	 */
 	SET_NETDEV_DEV(failover_dev, dev);
 
 	failover_dev->netdev_ops = &failover_dev_ops;
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 1377d08..fd30457 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1542,7 +1542,20 @@ 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
+/*
+ * used by:
+ *   - include/linux/netdevice.h|4609| <<netif_is_failover>> return dev->priv_flags & IFF_FAILOVER;
+ *   - net/core/failover.c|274| <<failover_register>> dev->priv_flags |= IFF_FAILOVER;
+ *   - net/core/failover.c|305| <<failover_unregister>> failover_dev->priv_flags &= ~IFF_FAILOVER;
+ */
 #define IFF_FAILOVER			IFF_FAILOVER
+/*
+ * used by:
+ *   - include/linux/netdevice.h|4614| <<netif_is_failover_slave>> return dev->priv_flags & IFF_FAILOVER_SLAVE;
+ *   - net/core/failover.c|93| <<failover_slave_register>> slave_dev->priv_flags |= IFF_FAILOVER_SLAVE;
+ *   - net/core/failover.c|100| <<failover_slave_register>> slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+ *   - net/core/failover.c|134| <<failover_slave_unregister>> slave_dev->priv_flags &= ~IFF_FAILOVER_SLAVE;
+ */
 #define IFF_FAILOVER_SLAVE		IFF_FAILOVER_SLAVE
 
 /**
@@ -4604,11 +4617,22 @@ static inline bool netif_is_rxfh_configured(const struct net_device *dev)
 	return dev->priv_flags & IFF_RXFH_CONFIGURED;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|201| <<failover_event>> if (netif_is_failover(event_dev))
+ *   - net/core/failover.c|236| <<failover_existing_slave_register>> if (netif_is_failover(dev))
+ */
 static inline bool netif_is_failover(const struct net_device *dev)
 {
 	return dev->priv_flags & IFF_FAILOVER;
 }
 
+/*
+ * called by:
+ *   - net/core/failover.c|119| <<failover_slave_unregister>> if (!netif_is_failover_slave(slave_dev))
+ *   - net/core/failover.c|150| <<failover_slave_link_change>> if (!netif_is_failover_slave(slave_dev))
+ *   - net/core/failover.c|175| <<failover_slave_name_change>> if (!netif_is_failover_slave(slave_dev))
+ */
 static inline bool netif_is_failover_slave(const struct net_device *dev)
 {
 	return dev->priv_flags & IFF_FAILOVER_SLAVE;
diff --git a/include/net/failover.h b/include/net/failover.h
index bb15438..07a7cca 100644
--- a/include/net/failover.h
+++ b/include/net/failover.h
@@ -7,18 +7,46 @@
 #include <linux/netdevice.h>
 
 struct failover_ops {
+	/*
+	 * called by:
+	 *   - net/core/failover.c|63| <<failover_slave_register>> fops->slave_pre_register(slave_dev, failover_dev))
+	 */
 	int (*slave_pre_register)(struct net_device *slave_dev,
 				  struct net_device *failover_dev);
+	/*
+	 * called by:
+	 *   - net/core/failover.c|86| <<failover_slave_register>> !fops->slave_register(slave_dev, failover_dev))
+	 */
 	int (*slave_register)(struct net_device *slave_dev,
 			      struct net_device *failover_dev);
+	/*
+	 * called by:
+	 *   - net/core/failover.c|119| <<failover_slave_unregister>> fops->slave_pre_unregister(slave_dev, failover_dev))
+	 */
 	int (*slave_pre_unregister)(struct net_device *slave_dev,
 				    struct net_device *failover_dev);
+	/*
+	 * called by:
+	 *   - net/core/failover.c|127| <<failover_slave_unregister>> !fops->slave_unregister(slave_dev, failover_dev))
+	 */
 	int (*slave_unregister)(struct net_device *slave_dev,
 				struct net_device *failover_dev);
+	/*
+	 * called by:
+	 *   - net/core/failover.c|153| <<failover_slave_link_change>> !fops->slave_link_change(slave_dev, failover_dev))
+	 */
 	int (*slave_link_change)(struct net_device *slave_dev,
 				 struct net_device *failover_dev);
+	/*
+	 * called by:
+	 *   - net/core/failover.c|178| <<failover_slave_name_change>> !fops->slave_name_change(slave_dev, failover_dev))
+	 */
 	int (*slave_name_change)(struct net_device *slave_dev,
 				 struct net_device *failover_dev);
+	/*
+	 * used by:
+	 *   - net/core/failover.c|66| <<failover_slave_register>> err = netdev_rx_handler_register(slave_dev, fops->slave_handle_frame,
+	 */
 	rx_handler_result_t (*slave_handle_frame)(struct sk_buff **pskb);
 };
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 82f2002..b789c86 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3186,6 +3186,9 @@ static netdev_features_t harmonize_features(struct sk_buff *skb,
 	return features;
 }
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_features_check = passthru_features_check()
+ */
 netdev_features_t passthru_features_check(struct sk_buff *skb,
 					  struct net_device *dev,
 					  netdev_features_t features)
diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index 158264f..5fc51fe 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -35,6 +35,9 @@
  * we can turn these into dev_() function calls.
  */
 
+/*
+ * struct ethtool_ops failover_ethtool_ops.get_link = ethtool_op_get_link()
+ */
 u32 ethtool_op_get_link(struct net_device *dev)
 {
 	return netif_carrier_ok(dev) ? 1 : 0;
diff --git a/net/core/failover.c b/net/core/failover.c
index 4a92a98..9a71ba7 100644
--- a/net/core/failover.c
+++ b/net/core/failover.c
@@ -14,9 +14,23 @@
 #include <linux/if_vlan.h>
 #include <net/failover.h>
 
+/*
+ * used by:
+ *   - net/core/failover.c|26| <<failover_get_bymac>> list_for_each_entry(failover, &failover_list, list) {
+ *   - net/core/failover.c|264| <<failover_register>> list_add_tail(&failover->list, &failover_list);
+ */
 static LIST_HEAD(failover_list);
 static DEFINE_SPINLOCK(failover_lock);
 
+/*
+ * called by:
+ *   - net/core/failover.c|68| <<failover_slave_register>> failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+ *   - net/core/failover.c|124| <<failover_slave_unregister>> failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+ *   - net/core/failover.c|155| <<failover_slave_link_change>> failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+ *   - net/core/failover.c|180| <<failover_slave_name_change>> failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
+ *
+ * 根据地址返回failover_list中的failover的net_device
+ */
 static struct net_device *failover_get_bymac(u8 *mac, struct failover_ops **ops)
 {
 	struct net_device *failover_dev;
@@ -43,6 +57,11 @@ static struct net_device *failover_get_bymac(u8 *mac, struct failover_ops **ops)
  * Registers a slave device to a failover instance. Only ethernet devices
  * are supported.
  */
+/*
+ * called by:
+ *   - net/core/failover.c|201| <<failover_event>> return failover_slave_register(event_dev);
+ *   - net/core/failover.c|230| <<failover_existing_slave_register>> failover_slave_register(dev);
+ */
 static int failover_slave_register(struct net_device *slave_dev)
 {
 	struct netdev_lag_upper_info lag_upper_info;
@@ -55,6 +74,13 @@ static int failover_slave_register(struct net_device *slave_dev)
 
 	ASSERT_RTNL();
 
+	/*
+	 * 根据地址返回failover_list中的failover的net_device
+	 *
+	 * fops是net_failover_ops
+	 *   .slave_pre_register     = net_failover_slave_pre_register,
+	 *   .slave_register         = net_failover_slave_register,
+	 */
 	failover_dev = failover_get_bymac(slave_dev->perm_addr, &fops);
 	if (!failover_dev)
 		goto done;
@@ -182,6 +208,9 @@ static int failover_slave_name_change(struct net_device *slave_dev)
 	return NOTIFY_DONE;
 }
 
+/*
+ * struct notifier_block failover_notifier.notifier_call = failover_event()
+ */
 static int
 failover_event(struct notifier_block *this, unsigned long event, void *ptr)
 {
@@ -211,6 +240,10 @@ static struct notifier_block failover_notifier = {
 	.notifier_call = failover_event,
 };
 
+/*
+ * called by:
+ *   - net/core/failover.c|274| <<failover_register>> failover_existing_slave_register(dev);
+ */
 static void
 failover_existing_slave_register(struct net_device *failover_dev)
 {
@@ -221,6 +254,9 @@ failover_existing_slave_register(struct net_device *failover_dev)
 	for_each_netdev(net, dev) {
 		if (netif_is_failover(dev))
 			continue;
+		/*
+		 * 调用两次还是多次????
+		 */
 		if (ether_addr_equal(failover_dev->perm_addr, dev->perm_addr))
 			failover_slave_register(dev);
 	}
@@ -239,6 +275,10 @@ failover_existing_slave_register(struct net_device *failover_dev)
  *
  * Return: pointer to failover instance
  */
+/*
+ * called only by:
+ *   - drivers/net/net_failover.c|886| <<net_failover_create>> failover = failover_register(failover_dev, &net_failover_ops);
+ */
 struct failover *failover_register(struct net_device *dev,
 				   struct failover_ops *ops)
 {
@@ -275,6 +315,10 @@ EXPORT_SYMBOL_GPL(failover_register);
  *
  * Unregisters and frees a failover instance.
  */
+/*
+ * called by only:
+ *   - drivers/net/net_failover.c|954| <<net_failover_destroy>> failover_unregister(failover);
+ */
 void failover_unregister(struct failover *failover)
 {
 	struct net_device *failover_dev;
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 4c52011..2e9ed93 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -332,6 +332,9 @@ int eth_change_mtu(struct net_device *dev, int new_mtu)
 }
 EXPORT_SYMBOL(eth_change_mtu);
 
+/*
+ * struct net_device_ops failover_dev_ops.ndo_validate_addr = eth_validate_addr()
+ */
 int eth_validate_addr(struct net_device *dev)
 {
 	if (!is_valid_ether_addr(dev->dev_addr))
-- 
2.7.4