net: add support for phys_port_name

Similar to port id allow netdevices to specify port names and export
the name via sysfs. Drivers can implement the netdevice operation to
assist udev in having sane default names for the devices using the
rule:

$ cat /etc/udev/rules.d/80-net-setup-link.rules
SUBSYSTEM=="net", ACTION=="add", ATTR{phys_port_name}!="",
NAME="$attr{phys_port_name}"

Use of phys_name versus phys_id was suggested-by Jiri Pirko.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Scott Feldman <sfeldma@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 25b4b5d..6abe634 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -982,6 +982,24 @@
 	return 0;
 }
 
+static int rtnl_phys_port_name_fill(struct sk_buff *skb, struct net_device *dev)
+{
+	char name[IFNAMSIZ];
+	int err;
+
+	err = dev_get_phys_port_name(dev, name, sizeof(name));
+	if (err) {
+		if (err == -EOPNOTSUPP)
+			return 0;
+		return err;
+	}
+
+	if (nla_put(skb, IFLA_PHYS_PORT_NAME, strlen(name), name))
+		return -EMSGSIZE;
+
+	return 0;
+}
+
 static int rtnl_phys_switch_id_fill(struct sk_buff *skb, struct net_device *dev)
 {
 	int err;
@@ -1072,6 +1090,9 @@
 	if (rtnl_phys_port_id_fill(skb, dev))
 		goto nla_put_failure;
 
+	if (rtnl_phys_port_name_fill(skb, dev))
+		goto nla_put_failure;
+
 	if (rtnl_phys_switch_id_fill(skb, dev))
 		goto nla_put_failure;