net: Allow devices to specify a device specific sysfs group.

This isn't beautifully abstracted, but it is simple,
simplifies uses and so far is only needed for the bonding driver.
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -900,8 +900,8 @@ struct net_device
 
 	/* class/net/name entry */
 	struct device		dev;
-	/* space for optional statistics and wireless sysfs groups */
-	const struct attribute_group *sysfs_groups[3];
+	/* space for optional device, statistics, and wireless sysfs groups */
+	const struct attribute_group *sysfs_groups[4];
 
 	/* rtnetlink link ops */
 	const struct rtnl_link_ops *rtnl_link_ops;

net/core/net-sysfs.c

@@ -544,8 +544,11 @@ int netdev_register_kobject(struct net_device *net)
 	dev_set_name(dev, "%s", net->name);
 
 #ifdef CONFIG_SYSFS
-	*groups++ = &netstat_group;
+	/* Allow for a device specific group */
+	if (*groups)
+		groups++;
 
+	*groups++ = &netstat_group;
 #ifdef CONFIG_WIRELESS_EXT_SYSFS
 	if (net->ieee80211_ptr)
 		*groups++ = &wireless_group;