can: export a safe netdev_priv wrapper for candev

In net_device notifier calls, it was impossible to determine
if a CAN device is based on candev in a safe way.
This patch adds such test in order to access candev storage
from within those notifiers.

Signed-off-by: Kurt Van Dijck <redacted>

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 963e2cc..6c1e704 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c

@@ -795,6 +795,18 @@ void unregister_candev(struct net_device *dev)
 }
 EXPORT_SYMBOL_GPL(unregister_candev);
 
+/*
+ * Test if a network device is a candev based device
+ * and return the can_priv* if so.
+ */
+struct can_priv *safe_candev_priv(struct net_device *dev)
+{
+	if ((dev->type != ARPHRD_CAN) || (dev->rtnl_link_ops != &can_link_ops))
+		return NULL;

+
+	return netdev_priv(dev);
+}
+
 static __init int can_dev_init(void)
 {
 	int err;

diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 7747d9b..fb0ab65 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h

@@ -106,6 +106,9 @@ u8 can_len2dlc(u8 len);
 struct net_device *alloc_candev(int sizeof_priv, unsigned int echo_skb_max);
 void free_candev(struct net_device *dev);
 
+/* a candev safe wrapper around netdev_priv */
+struct can_priv *safe_candev_priv(struct net_device *dev);
+
 int open_candev(struct net_device *dev);
 void close_candev(struct net_device *dev);