netdev - Re: [patch net-next 01/15] net: introduce upper device lists

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Message-ID: <20121231112212.03319226@nehalam.linuxnetplumber.net>
Date:	Mon, 31 Dec 2012 11:22:12 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jiri Pirko <jiri@...nulli.us>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
	bhutchings@...arflare.com, faisal.latif@...el.com, fbl@...hat.com,
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	fubar@...ibm.com, andy@...yhouse.net, divy@...lsio.com,
	jitendra.kalsaria@...gic.com, sony.chacko@...gic.com,
	linux-driver@...gic.com, kaber@...sh.net, ursula.braun@...ibm.com,
	blaschka@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
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	amwang@...hat.com, nhorman@...driver.com,
	john.r.fastabend@...el.com, pablo@...filter.org
Subject: Re: [patch net-next 01/15] net: introduce upper device lists

On Sun, 30 Dec 2012 12:58:08 +0100
Jiri Pirko <jiri@...nulli.us> 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.
> 
> 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 <jiri@...nulli.us>

I like the concept of knowing the topology of layered network devices.
The name "upper device lists" is a little confusing to me.
Also, the amount of additional data structures and book keeping
seems more than needed; but not sure how to reduce it down to the
least code.

For simple case of detecting loops, just using existing master
pointer is sufficient.
       ethernet --> bonding --> bridge --+
                       ^                 |
                       |                 |
                       +-----------------+
This is the simple case of detecting if singularly linked list
is a loop.

The only device where multiple upper devices is possible seems
to be macvlan. Could the special case code be limited to there?
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