net/tls,core: export get_netdev_for_sock

* remove netdev_sk_get_lowest_dev() from net/core
* move get_netdev_for_sock() from net/tls to net/core

get_netdev_for_sock() is a utility that is used to obtain
the net_device structure from a connected socket.

Later patches will use this for nvme-tcp DDP and DDP DDGST offloads.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Ben-Ishay <benishay@nvidia.com>
Signed-off-by: Shai Malin <smalin@nvidia.com>
Signed-off-by: Aurelien Aptel <aaptel@nvidia.com>

include/linux/netdevice.h

@@ -3079,8 +3079,7 @@ int init_dummy_netdev(struct net_device *dev);
 struct net_device *netdev_get_xmit_slave(struct net_device *dev,
 					 struct sk_buff *skb,
 					 bool all_slaves);
-struct net_device *netdev_sk_get_lowest_dev(struct net_device *dev,
-					    struct sock *sk);
+struct net_device *get_netdev_for_sock(struct sock *sk);
 struct net_device *dev_get_by_index(struct net *net, int ifindex);
 struct net_device *__dev_get_by_index(struct net *net, int ifindex);
 struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);

net/core/dev.c

@@ -8152,27 +8152,27 @@ static struct net_device *netdev_sk_get_lower_dev(struct net_device *dev,
 }
 
 /**
- * netdev_sk_get_lowest_dev - Get the lowest device in chain given device and socket
- * @dev: device
+ * netdev_sk_get_lowest_dev - Get the lowest device in socket
  * @sk: the socket
  *
- * %NULL is returned if no lower device is found.
+ * Assumes that the socket is already connected.
+ * Returns the lower device or %NULL if no lower device is found.
  */
-
-struct net_device *netdev_sk_get_lowest_dev(struct net_device *dev,
-					    struct sock *sk)
+struct net_device *get_netdev_for_sock(struct sock *sk)
 {
-	struct net_device *lower;
+	struct dst_entry *dst = sk_dst_get(sk);
+	struct net_device *dev, *lower;
 
-	lower = netdev_sk_get_lower_dev(dev, sk);
-	while (lower) {
+	if (unlikely(!dst))
+		return NULL;
+	dev = dst->dev;
+	while ((lower = netdev_sk_get_lower_dev(dev, sk)))
 		dev = lower;
-		lower = netdev_sk_get_lower_dev(dev, sk);
-	}
-
+	dev_hold(dev);
+	dst_release(dst);
 	return dev;
 }
-EXPORT_SYMBOL(netdev_sk_get_lowest_dev);
+EXPORT_SYMBOL_GPL(get_netdev_for_sock);
 
 static void netdev_adjacent_add_links(struct net_device *dev)
 {

net/tls/tls_device.c

@@ -120,22 +120,6 @@ static void tls_device_queue_ctx_destruction(struct tls_context *ctx)
 		tls_device_free_ctx(ctx);
 }
 
-/* We assume that the socket is already connected */
-static struct net_device *get_netdev_for_sock(struct sock *sk)
-{
-	struct dst_entry *dst = sk_dst_get(sk);
-	struct net_device *netdev = NULL;
-
-	if (likely(dst)) {
-		netdev = netdev_sk_get_lowest_dev(dst->dev, sk);
-		dev_hold(netdev);
-	}
-
-	dst_release(dst);
-
-	return netdev;
-}
-
 static void destroy_record(struct tls_record_info *record)
 {
 	int i;