Message-ID: <20140325173927.GE8102@hmsreliant.think-freely.org>
Date:	Tue, 25 Mar 2014 13:39:27 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Jiri Pirko <jiri@...nulli.us>,
	Florian Fainelli <f.fainelli@...il.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>, andy@...yhouse.net,
	tgraf@...g.ch, dborkman@...hat.com, ogerlitz@...lanox.com,
	jesse@...ira.com, pshelar@...ira.com, azhou@...ira.com,
	Ben Hutchings <ben@...adent.org.uk>,
	Stephen Hemminger <stephen@...workplumber.org>,
	jeffrey.t.kirsher@...el.com, vyasevic <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	Lennert Buytenhek <buytenh@...tstofly.org>
Subject: Re: [patch net-next RFC 0/4] introduce infrastructure for support of
 switch chip datapath

On Mon, Mar 24, 2014 at 07:07:35PM -0400, Jamal Hadi Salim wrote:
> On 03/22/14 05:48, Jiri Pirko wrote:
> >Fri, Mar 21, 2014 at 01:04:20PM CET, jhs@...atatu.com wrote:
> 
> >Hmm. This got me thinking about netdev and switches well and perhaps the
> >switchdev api could be mostly implemented by couple of more ndos and
> >feature flags. That way we could stick to your immortal netdev :)
> >
> >
> 
> Perhaps ;->
> 
> >>
> >>In my view: that (immortal) device for L2/bridging is the bridge or
> >>maybe a more barebone version of the bridge (since it has gained a
> >>little more weight in recent times).
> >
> >Well, I do not think that bridge is ideal abstraction for modern switch
> >chips. Bridge is very limited.
> >
> 
> True - but i was more thinking of being inclusive of the smaller
> devices. They are mostly L2 only and in very limited scope. And thats
> probably 95% of the population. The things you are talking about
> are very high end and they can do more. Florian's taxanomy was useful.
> 
> >But I don't necessary think it is needed to "mask" as a bride or mimic a
> >bridge in any way. DSA does not do that either.
No, but it would be really nice if these smaller devices could take advantage of
this infrastructure.  Looking at it, I don't see why thats not possible.  The
big trick (as we've discussed in the past), is using a net_device structure to
take advantage of all the features that net_devices offer while not enabling the
device specific features that some hardware doesn't allow.

For instance the broadcom chips that live in many wireless routers would be well
served by the model jiri has here as far as Media level interface control is
concerned (i.e. ifup/down/speed/duplex/etc), but its a bit lacking in that
net_devices are assumed to support L3 protocol configuration (i.e. they can have
ip addresses assigned to them), which you can't IIRC do on these chips.

Would it be worth considering a private interface model?  That is to say:

1) Ports on a switch chip are accessed using net_device structures, but
registered to a private list contained within the switch device, rather than to
the net namespaces device list.

2) Access to the switch ports via user space is done through the master switch
interface with additional netlink attributes specifying the port on the switch
to access (or not to access the master switch device directly)


Such a model I think might fit well with Jiri's code here and provide greater
flexibility for a wider range of devices.  It would of course require
augmentation for user space, but the changes would be additive, so I think they
would be reasonable.  This would also allow the switch device to have a hook in
the control path to block or allow features that the hardware may or may not
support while still being able to use the existing net_device infrastructure to
support these operations as they are normally carried out.

Best
Neil

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