On Mon, 2012-08-13 at 17:27 +0200, Jiri Pirko wrote:

This lists are supposed to serve for storing pointers to all upper devices.
Eventually it will replace dev->master pointer which is used for
bonding, bridge, team but it cannot be used for vlan, macvlan where
there might be multiple "masters" present.

New upper device list resolves this limitation. Also, the information
stored in lists is used for preventing looping setups like
"bond->somethingelse->samebond"

Signed-off-by: Jiri Pirko <redacted>

[...]

This needs a better name.  It doesn't really have anything to do with
uniqueness and doesn't ensure exclusivity.  I think that it would be
fine to keep the 'master' term.

+	struct list_head list;
+	struct rcu_head rcu;
+};

[...]

+static int __netdev_upper_dev_link(struct net_device *dev,
+				   struct net_device *upper_dev, bool unique)
+{
+	struct netdev_upper *upper;
+
+	ASSERT_RTNL();
+
+	if (dev == upper_dev)
+		return -EBUSY;
+	/*
+	 * To prevent loops, check if dev is not upper device to upper_dev.
+	 */
+	if (__netdev_has_upper_dev(upper_dev, dev, true))
+		return -EBUSY;
+
+	if (__netdev_find_upper(dev, upper_dev))
+		return -EEXIST;
+
+	if (unique && netdev_unique_upper_dev_get(dev))
+		return -EBUSY;
+
+	upper = kmalloc(sizeof(*upper), GFP_KERNEL);
+	if (!upper)
+		return -ENOMEM;
+
+	upper->dev = upper_dev;
+	upper->unique = unique;
+
+	/*
+	 * Ensure that unique upper link is always the first item in the list.
+	 */
+	if (unique)
+		list_add_rcu(&upper->list, &dev->upper_dev_list);
+	else
+		list_add_tail_rcu(&upper->list, &dev->upper_dev_list);
+	dev_hold(upper_dev);

This behaviour (calling dev_hold()) matches netdev_set_master().  But
it's oddly asymmetric: generally the administrator can remove either the
upper device or the lower device (rtnl_link_ops or unbinding a physical
device) and the upper device driver must then unlink itself from the
lower device (using a notifier to catch lower device removal).

If the upper device driver fails to unlink when the upper device is
unregistered, then this extra reference causes netdev_wait_allrefs() to
hang... is that the intent?  Or should there be a more explicit counter
and check on unregistration, e.g. WARN_ON(dev->num_lower_devs != 0)?

If it fails to unlink when the lower device is removed, this warning in
rollback_registered_many() may be triggered:

		/* Notifier chain MUST detach us from master device. */
		WARN_ON(dev->master);

I think that needs to become WARN_ON(netdev_has_upper_dev(dev)).

+	return 0;
+}

[...] 

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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