linux-kernel - Re: [RFC PATCH net-next v2 1/1] net: Support for switch port configuration

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Message-ID: <54935E28.8050602@cumulusnetworks.com>
Date:	Thu, 18 Dec 2014 15:07:20 -0800
From:	Roopa Prabhu <roopa@...ulusnetworks.com>
To:	John Fastabend <john.r.fastabend@...el.com>
CC:	"Varlese, Marco" <marco.varlese@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Thomas Graf <tgraf@...g.ch>, Jiri Pirko <jiri@...nulli.us>,
	"sfeldma@...il.com" <sfeldma@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next v2 1/1] net: Support for switch port configuration

On 12/18/14, 11:21 AM, John Fastabend wrote:
> On 12/18/2014 10:14 AM, Roopa Prabhu wrote:
>> On 12/18/14, 10:02 AM, Varlese, Marco wrote:
>>> Removed unnecessary content for ease of reading...
>>>
>>>>>>>>> +/* Switch Port Attributes section */
>>>>>>>>> +
>>>>>>>>> +enum {
>>>>>>>>> +    IFLA_ATTR_UNSPEC,
>>>>>>>>> +    IFLA_ATTR_LEARNING,
>>>>>>>> Any reason you want learning here ?. This is covered as part  of
>>>>>>>> the bridge setlink attributes.
>>>>>>>>
>>>>>>> Yes, because the user may _not_ want to go through a bridge
>>>>>>> interface
>>>>>> necessarily.
>>>>>> But, the bridge setlink/getlink interface was changed to accommodate
>>>> 'self'
>>>>>> for exactly such cases.
>>>>>> I kind of understand your case for the other attributes (these are
>>>>>> per port settings that switch asics provide).
>>>>>>
>>>>>> However, i don't understand the reason to pull in bridge attributes here.
>>>>>>
>>>>> Maybe, I am missing something so you might help. The learning attribute -
>>>> in my case - it is like all other attributes: a port attribute (as you said, port
>>>> settings that the switch provides per port).
>>>>> So, what I was saying is "why the user shall go through a bridge to configure
>>>> the learning attribute"? From my perspective, it is as any other attribute and
>>>> as such configurable on the port.
>>>>
>>>> Thinking about this some more, i don't see why any of these attributes
>>>> (except loopback. I dont understand the loopback attribute) cant be part of
>>>> the birdge port attributes.
>>>>
>>>> With this we will end up adding l2 attributes in two places: the general link
>>>> attributes and bridge attributes.
>>>>
>>>> And since we have gone down the path of using ndo_bridge_setlink/getlink
>>>> with 'self'....we should stick to that for all l2 attributes.
>>>>
>>>> The idea of overloading ndo_bridge_set/getlink, was to have the same set of
>>>> attributes but support both cases where the user wants to go through the
>>>> bridge driver or directly to the switch port driver. So, you are not really going
>>>> through the bridge driver if you use 'self' and ndo_bridge_setlink/getlink.
>>>>
>>> Roopa, one of the comments I got from Thomas Graf on my v1 patch
>>> was that your patch and mine were supplementary ("I think Roopa's
>>> patches are supplementary. Not all switchdev users will be backed
>>> with a Linux Bridge. I therefore welcome your patches very
>>> much")... I also understood by others that the patch made sense for
>>> the same reason. I simply do not understand why these attributes
>>> (and maybe others in the future) could not be configured directly
>>> on a standard port but have to go through a bridge.
>>>
>> ok, i am very confused in that case. The whole moving of bridge
>> attributes from the bridge driver to rtnetlink.c was to make the
>> bridge attributes accessible to any driver who wants to set l2/bridge
>> attributes on their switch ports. So, its unclear to me why we are
>> doing this parallel thing again. This move to rtnetlink.c was done
>> during the recent rocker support. so, maybe scott/jiri can elaborate
>> more.
>
> Not sure if this will add to the confusion or help. But you do not
> need to have the bridge.ko loaded or netdev's attached to a bridge
> to use the setlink/getlink ndo ops and netlink messages.
>
> This was intentionally done. Its already used with NIC devices to
> configure embedded bridge settings such as VEB/VEPA.

that helps my case, thanks.
>
> I think I'm just repeating Roopa though.
>

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