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

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Message-Id: <DCCFAE52-F4BD-4877-A6FC-3C3AE180E871@cumulusnetworks.com>
Date:	Sat, 20 Sep 2014 10:21:10 -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>,
	David Miller <davem@...emloft.net>,
	Neil Horman <nhorman@...driver.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Thomas Graf <tgraf@...g.ch>, dborkman <dborkman@...hat.com>,
	ogerlitz <ogerlitz@...lanox.com>, jesse <jesse@...ira.com>,
	pshelar <pshelar@...ira.com>, azhou <azhou@...ira.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Vlad Yasevich <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	"John W. Linville" <linville@...driver.com>, dev@...nvswitch.org,
	jasowang@...hat.com, ebiederm@...ssion.com,
	nicolas.dichtel@...nd.com,
	Sergey Ryazanov <ryazanov.s.a@...il.com>,
	Lennert Buytenhek <buytenh@...tstofly.org>,
	Aviad Raveh <aviadr@...lanox.com>,
	Felix Fietkau <nbd@...nwrt.org>, alexei.starovoitov@...il.com,
	Neil.Jerram@...aswitch.com, ronye@...lanox.com,
	Simon Horman <simon.horman@...ronome.com>,
	Alexander H Duyck <alexander.h.duyck@...el.com>,
	Shrijeet Mukherjee <shm@...ulusnetworks.com>
Subject: Re: [patch net-next v2 8/9] switchdev: introduce Netlink API


On Sep 20, 2014, at 5:51 AM, Roopa Prabhu <roopa@...ulusnetworks.com> wrote:

> On 9/20/14, 1:10 AM, Scott Feldman wrote:
>> 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
>> 
>> 
> Keeping the goal to not change or not add a new userspace API in mind,
> I have :
>     user -> rtnetlink -> kernel -> ndo_op -> swdev driver  -> HW
> 

Then you have the same as Jiri, for the traditional L2/L3 case.

> Jiri has:
>     user -> genl (newapi) -> kernel -> swdev_* -> swdev driver -> HW

Jiri’s genl is for userspace apps that are talking rtnetlink, like OVS.  It’s not a substitute for rtnetlink, it’s an alternative.  The complete picture is:

user -> swdev genl -----
                        \
                         \
                          -------> kernel -> ndo_swdev_* -> swdev driver -> HW
                         /
                        /
user -> rtnetlink ------


-scott



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