netdev - HW bridging support using notifiers?

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Message-ID: <542E0089.5050005@gmail.com>
Date:	Thu, 02 Oct 2014 18:48:57 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	netdev@...r.kernel.org
CC:	davem@...emloft.net, jiri@...nulli.us, stephen@...workplumber.org,
	andy@...yhouse.net, tgraf@...g.ch, nbd@...nwrt.org,
	john.r.fastabend@...el.com, edumazet@...gle.com,
	vyasevic@...hat.com, buytenh@...tstofly.org,
	sfeldma@...ulusnetworks.com
Subject: HW bridging support using notifiers?

Hi all,

I am taking a look at adding HW bridging support to DSA, in way that's
usable outside of DSA.

Lennert's approach in 2008 [1] looks conceptually good to me,as he
noted, it uses a bunch of new ndo's which is not only limiting to one
ndo implementer per struct net_device, but also is mostly consuming the
information from the bridge layer, while the ndo is an action

So here's what I am up to now:

- use the NETDEV_JOIN notifier to discover when a bridge port is added
- use the NETDEV_LEAVE notifier, still need to verify this does not
break netconsole as indicated in net/bridge/br_if.c
- use the NETDEV_CHANGEINFODATA notifier to notify about STP state changes

Now, this raises a bunch of questions:

- we would need a getter to return the stp state of a given network
device when called with NETDEV_CHANGEINFODATA, is that acceptable? This
would be the first function exported by the bridge layer to expose
internal data

NB: this also raises the question of the race condition and locking
within br_set_stp_state() and when the network devices notifier callback
runs

- or do we need a new network device notifier accepting an opaque
pointer which could provide us with the data we what, something like
this: call_netdevices_notifier_data(NETDEV_CHANGEINFODATA, dev, info),
where info would be a structure/union telling what's this data about

Let me know what you think, thanks!

[1]: http://patchwork.ozlabs.org/patch/16578/
--
Florian
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