netdev - Re: [PATCH net-next 6/6] netdevsim: Add simple FIB resource controller via devlink

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Date:   Mon, 9 Apr 2018 10:18:19 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        roopa@...ulusnetworks.com, shm@...ulusnetworks.com,
        jiri@...lanox.com, idosch@...lanox.com,
        jakub.kicinski@...ronome.com, andy.roulin@...il.com
Subject: Re: [PATCH net-next 6/6] netdevsim: Add simple FIB resource
 controller via devlink

Fri, Apr 06, 2018 at 11:22:29PM CEST, dsa@...ulusnetworks.com wrote:
>On 4/5/18 11:52 PM, Jiri Pirko wrote:
>> Thu, Apr 05, 2018 at 11:06:41PM CEST, dsa@...ulusnetworks.com wrote:
>>> On 4/5/18 2:10 PM, David Ahern wrote:
>>>>
>>>> The ASIC here is the kernel tables in a namespace. It does not make
>>>> sense to have 2 devlink instances for a single namespace.
>>>
>>> I put this example controller in netdevsim per a suggestion from Ido.
>>> The netdevsim seemed like a good idea given that modules intention --
>>> testing network facilities. Perhaps I should have done this as a
>>> completely standalone module ...
>>>
>>> The intention is to treat the kernel's tables *per namespace* as a
>>> standalone entity that can be managed very similar to ASIC resources.
>> 
>> So you say you want to treat a namespace as an ASIC? That sounds very
>> odd to me :/
>
>Why? The kernel has forwarding tables, acl's, etc just like the ASIC,
>and each namespace is a separate set of tables.

I don't get it. What's the point? For HW, the reason is it has limited
resources and those resources are not mapped 1:1 with kernel object.
However, for kernel, that is meaningless.


>
>If you think about it, userspace "programs" the kernel just like mlxsw
>and userspace SDKs "program" an asic.

I don't give a **** about sdks. I have no clue why you mention that here.


>
>
>>> Given that I can add a resource controller module
>>> (drivers/net/kern_res_mgr.c?) that creates a 'struct device' per network
>>> namespace with a devlink instance. In this case the device would very
>>> much be tied to the namespace 1:1.
>> 
>> That sounds more reasonable and accurate, yet still odd. You would not
>> have any netdevices there? Any ports?
>> 
>
>Sure, what ever ports are assigned to or created in the namespace.
>
>Nothing about the devlink API says it has to be a real h/w device.

Sure, it could represent something made-up, like netdevsim. However I
see a big misfit when you want to represent a namespace.


>Nothing about the devlink API says it can only be used for real h/w that
>has ports represented by netdevices that the devlink instance some how
>has "control" over.
>
>As the netdevsim demo shows, I can build an L3 resource controller for
>the kernel tables using just the devlink API and the in-kernel notifiers.