rtnetlink: add alloc() method to rtnl_link_ops

In order to make rtnetlink ops that can create different
kinds of devices, like what we want to add to the WWAN
framework, the priv_size and setup parameters aren't quite
sufficient. Make this easier to manage by allowing ops to
allocate their own netdev via an @alloc method that gets
the tb netlink data.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/rtnetlink.h

@@ -37,6 +37,9 @@ static inline int rtnl_msg_family(const struct nlmsghdr *nlh)
  *	@maxtype: Highest device specific netlink attribute number
  *	@policy: Netlink policy for device specific attribute validation
  *	@validate: Optional validation function for netlink/changelink parameters
+ *	@alloc: netdev allocation function, can be %NULL and is then used
+ *		in place of alloc_netdev_mqs(), in this case @priv_size
+ *		and @setup are unused. Returns a netdev or ERR_PTR().
  *	@priv_size: sizeof net_device private space
  *	@setup: net_device setup function
  *	@newlink: Function for configuring and registering a new device
@@ -63,6 +66,11 @@ struct rtnl_link_ops {
 	const char		*kind;
 
 	size_t			priv_size;
+	struct net_device	*(*alloc)(struct nlattr *tb[],
+					  const char *ifname,
+					  unsigned char name_assign_type,
+					  unsigned int num_tx_queues,
+					  unsigned int num_rx_queues);
 	void			(*setup)(struct net_device *dev);
 
 	bool			netns_refund;

net/core/rtnetlink.c

@@ -376,12 +376,12 @@ int __rtnl_link_register(struct rtnl_link_ops *ops)
 	if (rtnl_link_ops_get(ops->kind))
 		return -EEXIST;
 
-	/* The check for setup is here because if ops
+	/* The check for alloc/setup is here because if ops
 	 * does not have that filled up, it is not possible
 	 * to use the ops for creating device. So do not
 	 * fill up dellink as well. That disables rtnl_dellink.
 	 */
-	if (ops->setup && !ops->dellink)
+	if ((ops->alloc || ops->setup) && !ops->dellink)
 		ops->dellink = unregister_netdevice_queue;
 
 	list_add_tail(&ops->list, &link_ops);
@@ -3165,8 +3165,17 @@ struct net_device *rtnl_create_link(struct net *net, const char *ifname,
 		return ERR_PTR(-EINVAL);
 	}
 
-	dev = alloc_netdev_mqs(ops->priv_size, ifname, name_assign_type,
-			       ops->setup, num_tx_queues, num_rx_queues);
+	if (ops->alloc) {
+		dev = ops->alloc(tb, ifname, name_assign_type,
+				 num_tx_queues, num_rx_queues);
+		if (IS_ERR(dev))
+			return dev;
+	} else {
+		dev = alloc_netdev_mqs(ops->priv_size, ifname,
+				       name_assign_type, ops->setup,
+				       num_tx_queues, num_rx_queues);
+	}
+
 	if (!dev)
 		return ERR_PTR(-ENOMEM);
 
@@ -3399,7 +3408,7 @@ static int __rtnl_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
 		return -EOPNOTSUPP;
 	}
 
-	if (!ops->setup)
+	if (!ops->alloc && !ops->setup)
 		return -EOPNOTSUPP;
 
 	if (!ifname[0]) {