bonding: add common function to check ipsec device

This patch adds a common function to check the status of IPSec devices.
This function will be useful for future implementations, such as IPSec ESN
and state offload callbacks.
Suggested-by: Nikolay Aleksandrov <razor@blackwall.org>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Jay Vosburgh <jv@jvosburgh.net>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/bonding/bond_main.c

@@ -418,6 +418,41 @@ static int bond_vlan_rx_kill_vid(struct net_device *bond_dev,
 /*---------------------------------- XFRM -----------------------------------*/
 
 #ifdef CONFIG_XFRM_OFFLOAD
+/**
+ * bond_ipsec_dev - Get active device for IPsec offload
+ * @xs: pointer to transformer state struct
+ *
+ * Context: caller must hold rcu_read_lock.
+ *
+ * Return: the device for ipsec offload, or NULL if not exist.
+ **/
+static struct net_device *bond_ipsec_dev(struct xfrm_state *xs)
+{
+	struct net_device *bond_dev = xs->xso.dev;
+	struct bonding *bond;
+	struct slave *slave;
+
+	if (!bond_dev)
+		return NULL;
+
+	bond = netdev_priv(bond_dev);
+	if (BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP)
+		return NULL;
+
+	slave = rcu_dereference(bond->curr_active_slave);
+	if (!slave)
+		return NULL;
+
+	if (!xs->xso.real_dev)
+		return NULL;
+
+	if (xs->xso.real_dev != slave->dev)
+		pr_warn_ratelimited("%s: (slave %s): not same with IPsec offload real dev %s\n",
+				    bond_dev->name, slave->dev->name, xs->xso.real_dev->name);
+
+	return slave->dev;
+}
+
 /**
  * bond_ipsec_add_sa - program device with a security association
  * @xs: pointer to transformer state struct
@@ -640,23 +675,12 @@ static void bond_ipsec_free_sa(struct xfrm_state *xs)
  **/
 static bool bond_ipsec_offload_ok(struct sk_buff *skb, struct xfrm_state *xs)
 {
-	struct net_device *bond_dev = xs->xso.dev;
 	struct net_device *real_dev;
-	struct slave *curr_active;
-	struct bonding *bond;
 	bool ok = false;
 
-	bond = netdev_priv(bond_dev);
 	rcu_read_lock();
-	curr_active = rcu_dereference(bond->curr_active_slave);
-	if (!curr_active)
-		goto out;
-	real_dev = curr_active->dev;
-
-	if (BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP)
-		goto out;
-
-	if (!xs->xso.real_dev)
+	real_dev = bond_ipsec_dev(xs);
+	if (!real_dev)
 		goto out;
 
 	if (!real_dev->xfrmdev_ops ||