netdev - Re: [patch net-next v2 8/9] switchdev: introduce Netlink API

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Message-Id: <DDC24110-C3F5-470F-B9BE-1D1792415D1E@cumulusnetworks.com>
Date:	Sat, 20 Sep 2014 01:10:13 -0700
From:	Scott Feldman <sfeldma@...ulusnetworks.com>
To:	Roopa Prabhu <roopa@...ulusnetworks.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>,
	netdev <netdev@...r.kernel.org>, davem@...emloft.net,
	nhorman@...driver.com, andy@...yhouse.net, tgraf@...g.ch,
	dborkman@...hat.com, ogerlitz@...lanox.com, jesse@...ira.com,
	pshelar@...ira.com, azhou@...ira.com, ben@...adent.org.uk,
	stephen@...workplumber.org, jeffrey.t.kirsher@...el.com,
	vyasevic@...hat.com, xiyou.wangcong@...il.com,
	john.r.fastabend@...el.com, edumazet@...gle.com,
	f.fainelli@...il.com, linville@...driver.com, dev@...nvswitch.org,
	jasowang@...hat.com, ebiederm@...ssion.com,
	nicolas.dichtel@...nd.com, ryazanov.s.a@...il.com,
	buytenh@...tstofly.org, aviadr@...lanox.com, nbd@...nwrt.org,
	alexei.starovoitov@...il.com, Neil.Jerram@...aswitch.com,
	ronye@...lanox.com, simon.horman@...ronome.com,
	alexander.h.duyck@...el.com,
	Shrijeet Mukherjee <shm@...ulusnetworks.com>
Subject: Re: [patch net-next v2 8/9] switchdev: introduce Netlink API


On Sep 19, 2014, at 8:41 PM, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:

> On 9/19/14, 8:49 AM, Jiri Pirko wrote:
>> Fri, Sep 19, 2014 at 05:25:48PM CEST, jhs@...atatu.com wrote:
>>> On 09/19/14 09:49, Jiri Pirko wrote:
>>>> This patch exposes switchdev API using generic Netlink.
>>>> Example userspace utility is here:
>>>> https://github.com/jpirko/switchdev
>>>> 
>>> Is this just a temporary test tool? Otherwise i dont see reason
>>> for its existence (or the API that it feeds on).
>> Please read the conversation I had with Pravin and Jesse in v1 thread.
>> Long story short they like to have the api separated from ovs datapath
>> so ovs daemon can use it to directly communicate with driver. Also John
>> Fastabend requested a way to work with driver flows without using ovs ->
>> that was the original reason I created switchdev genl api.
>> 
>> Regarding the "sw" tool, yes it is for testing purposes now. ovs daemon
>> will use directly switchdev genl api.
>> 
>> I hope I cleared this out.
> We already have all the needed rtnetlink kernel api and userspace tools around it to support all
> switching asic features. ie, the rtnetlink api is the switchdev api. We can do l2, l3, acl's with it.
> Its unclear to me why we need another new netlink api. Which will mean none of the existing tools to
> create bridges etc will work on a switchdev.
> Which seems like going in the direction exactly opposite to what we had discussed earlier.

Existing rtnetlink isn’t available to swdev without some kind of snooping the echoes from the various kernel components (bridge, fib, etc).  With swdev_flow, as Jiri has defined it, there is an additional conversion needed to bridge the gap (bad expression, I know) between rtnetlink and swdev_flow.  This conversion happens in the kernel components.  For example, the bridge module, still driven from userspace by existing rtnetlink, will formulate the necessary swdev_flow insert/remove calls to the swdev driver such that HW will offload the fwd path.

You have:
    user -> rtnetlink -> kernel -> netlink echo -> [some process] -> [some driver] -> HW

Jiri has:
    user -> rtnetlink -> kernel -> swdev_* -> swdev driver -> HW

> If a non-ovs flow interface is needed from userspace, we can extend the existing interface to include flows.
> I don't understand why we should replace the existing rtnetlink switchdev api to accommodate flows.
> 
> Thanks,
> Roopa
> 


-scott



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