netdev - Re: [PATCH net-next 3/9] net: dsa: allow the DSA master to be seen and changed through rtnetlink

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Date:   Wed, 31 Aug 2022 20:50:20 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        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,
        Colin Foster <colin.foster@...advantage.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Marek Behún <kabel@...nel.org>,
        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 3/9] net: dsa: allow the DSA master to be seen
 and changed through rtnetlink

On Tue, 30 Aug 2022 22:59:26 +0300 Vladimir Oltean wrote:
> Some DSA switches have multiple CPU ports, which can be used to improve
> CPU termination throughput, but DSA, through dsa_tree_setup_cpu_ports(),
> sets up only the first one, leading to suboptimal use of hardware.
> 
> The desire is to not change the default configuration but to permit the
> user to create a dynamic mapping between individual user ports and the
> CPU port that they are served by, configurable through rtnetlink. It is
> also intended to permit load balancing between CPU ports, and in that
> case, the foreseen model is for the DSA master to be a bonding interface
> whose lowers are the physical DSA masters.
> 
> To that end, we create a struct rtnl_link_ops for DSA user ports with
> the "dsa" kind. We expose the IFLA_DSA_MASTER link attribute that
> contains the ifindex of the newly desired DSA master.

net/dsa/port.c: In function ‘dsa_port_change_master’:
net/dsa/port.c:1414:13: warning: unused variable ‘port’ [-Wunused-variable]
 1414 |         int port = dp->index;
      |             ^~~~

I presume you had a look around what side effects setting rtnl_link_ops
will have? Should .netns_refund be true?