From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <shemminger@vyatta.com>
Subject: Re: [patch net-next v2 01/15] net: introduce upper device
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Date: Tue, 14 Aug 2012 16:00:55 -0700
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To: Ben Hutchings <bhutchings@solarflare.com>
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On Tue, 14 Aug 2012 23:33:44 +0100
Ben Hutchings <bhutchings@solarflare.com> wrote:

> On Tue, 2012-08-14 at 17:05 +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 upper present. In case the upper link is
> > replacement for dev->master, it is marked with "master" flag.
> 
> Something I found interesting is that the dev->master pointer and now
> netdev_master_upper_dev_get{,_rcu}() are hardly used by the stackled
> drivers that set the master.  They also have to set an rx_handler on the
> lower device (which is itself mutually exclusive) which gets its own
> context pointer (rx_handler_data).
> 
> Instead, the master pointer is mostly used by device drivers to find out
> about a bridge or bonding device above *their* devices.  And that seems
> to work only for those specific device drivers, not e.g. openvswitch or
> team.  I wonder if we could find a better way to encapsulate the things
> they want do do, in a later step (not holding up this change!).

The concept is master is very useful to user level config things like
Vyatta for seeing parent/child relationship. Since is in ABI now, it
must stay.