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Date:   Sun, 11 Apr 2021 20:09:39 +0300
From:   Vladimir Oltean <olteanv@gmail.com>
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     Ansuel Smith <ansuelsmth@gmail.com>, netdev@vger.kernel.org,
        Marek =?utf-8?B?QmVow7pu?= <marek.behun@nic.cz>,
        David Ahern <dsahern@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, Andrew Lunn <andrew@lunn.ch>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andriin@fb.com>,
        Eric Dumazet <edumazet@google.com>,
        Wei Wang <weiwan@google.com>,
        Cong Wang <cong.wang@bytedance.com>,
        Taehee Yoo <ap420073@gmail.com>,
        =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        Di Zhu <zhudi21@huawei.com>,
        Weilong Chen <chenweilong@huawei.com>,
        Nikolay Aleksandrov <nikolay@nvidia.com>,
        Colin Ian King <colin.king@canonical.com>,
        Roopa Prabhu <roopa@cumulusnetworks.com>,
        Francis Laniel <laniel_francis@privacyrequired.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC iproute2-next] iplink: allow to change iplink value
Message-ID: <20210411170939.cxmva5vdcpqu4bmi@skbuf>
References: <20210410133454.4768-1-ansuelsmth@gmail.com>
 <20210410133454.4768-5-ansuelsmth@gmail.com>
 <20210411100411.6d16e51d@hermes.local>
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On Sun, Apr 11, 2021 at 10:04:11AM -0700, Stephen Hemminger wrote:
> On Sat, 10 Apr 2021 15:34:50 +0200
> Ansuel Smith <ansuelsmth@gmail.com> wrote:
> 
> > Allow to change the interface to which a given interface is linked to.
> > This is useful in the case of multi-CPU port DSA, for changing the CPU
> > port of a given user port.
> > 
> > Signed-off-by: Marek Beh?n <marek.behun@nic.cz>
> > Cc: David Ahern <dsahern@gmail.com>
> > Cc: Stephen Hemminger <stephen@networkplumber.org>
> 
> This may work for DSA but it won't work for all the device types vlan/macsec/... that
> now use the link attribute.  It looks like the change link handling for those
> device types just ignores the link attribute (maybe ok). But before supporting this
> as an API, it would be better if all the other drivers that use IFLA_LINK
> had error checks in their change link handling.
> 
> Please add error checks in kernel first.

Would it be better to expose this as a netlink attribute specific to
DSA, instead of iflink which as you point out has uses for other virtual
interfaces like veth, and the semantics there are not quite the same?