netdev - Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support

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Date:   Mon, 07 Dec 2020 22:56:57 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <olteanv@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, vivien.didelot@...il.com,
        j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH v3 net-next 2/4] net: dsa: Link aggregation support

On Thu, Dec 03, 2020 at 20:18, Florian Fainelli <f.fainelli@...il.com> wrote:
> On 12/3/2020 5:33 PM, Andrew Lunn wrote:
>>> Of course, neither is fully correct. There is always more to improve on
>>> the communication side of things.
>> 
>> I wonder if switchdev needs to gain an enumeration API? A way to ask
>> the underlying driver, what can you offload? The user can then get an
>> idea what is likely to be offloaded, and what not. If that API is fine
>> grain enough, it can list the different LAG algorithms supported.
>
> For stack offloads we can probably easily agree on what constitutes a
> vendor neutral offload and a name for that enumeration. For other
> features this is going to become an unmaintainable list of features and
> then we are no better than we started 6 years ago with submitting
> OpenWrt's swconfig and each switch driver advertising its features and
> configuration API via netlink.
>
> NETIF_F_SWITCHDEV_OFFLOAD would not be fine grained enough, this needs
> to be a per action selection, just like when offloading the bridge, or
> tc, you need to be able to hint the driver whether the offload is being
> requested by the user.

That makes sense. So you are talking about adding something akin to tc's
skip_hw/skip_sw to `ip link`?

> For now, I would just go with implicitly falling back to doing the LAG
> in software if the requested mode is not supported and leveraging extack
> to indicate that was the case.

Ahh, you can use extack for successful operations? I did not know that,
I think that strikes a good balance.