netdev - Re: [PATCH net-next 0/9] DSA changes for multiple CPU ports (part 4)

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Date:   Sat, 3 Sep 2022 04:48:32 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <olteanv@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Colin Foster <colin.foster@...advantage.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Ansuel Smith <ansuelsmth@...il.com>,
        DENG Qingfang <dqfext@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Luiz Angelo Daros de Luca <luizluca@...il.com>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>
Subject: Re: [PATCH net-next 0/9] DSA changes for multiple CPU ports (part
 4)

On Fri, 2 Sep 2022 10:31:46 +0000
Vladimir Oltean <vladimir.oltean@....com> wrote:

> On Tue, Aug 30, 2022 at 10:59:23PM +0300, Vladimir Oltean wrote:
> > This series represents the final part of that effort. We have:
> > 
> > - the introduction of new UAPI in the form of IFLA_DSA_MASTER  
> 
> Call for opinions: when I resend this, should I keep rtnl_link_ops,
> or should I do what Marek attempted to do, and make the existing iflink
> between a user port and its master writable from user space?
> https://lore.kernel.org/netdev/20190824024251.4542-4-marek.behun@nic.cz/
> 
> I'm not sure if we have that many more use cases for rtnl_link_ops..
> at some point I was thinking we could change the way in which dsa_loop
> probes, and allow dynamic creation of such interfaces using RTM_NEWLINK;
> but looking closer at that, it's a bit more complicated, since we'd need
> to attach dsa_loop user ports to a virtual switch, and probe all ports
> at the same time rather than one by one.

My opinion is that it would be better to add new DSA specific netlink
operations instead of using the existing iflink as I did in the that
patch.

I think that DSA should have it's own IP subcommands. Using the
standard, already existing API, is not sufficient for more complex
configurations/DSA routing settings. Consider DSA where there are
multiple switches and the switches are connected via multiple ports:

+----------+   +---------------+   +---------+
|     eth0 <---> sw0p0   sw0p2 <---> sw1p0
| cpu      |   |               |   |        ....
|     eth1 <---> sw0p1   s20p3 <---> sw1p1
+----------+   +---------------+   +---------+

The routing is more complicated in this scenario. The old API is not
sufficient.

Marek