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From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
Date:   Mon, 10 Jan 2022 11:32:16 +0800
Message-ID: <CAAd53p7egh8G=fPMcua_FTHrA3HA6Dp85FqVhvcSbuO2y8Xz9A@mail.gmail.com>
Subject: Re: [PATCH 1/3 v3] net: usb: r8152: Check used MAC passthrough address
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Andrew Lunn <andrew@lunn.ch>, Oliver Neukum <oneukum@suse.com>,
        Aaron Ma <aaron.ma@canonical.com>, henning.schild@siemens.com,
        linux-usb@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, davem@davemloft.net,
        hayeswang@realtek.com, tiwai@suse.de
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On Fri, Jan 7, 2022 at 10:31 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Fri, 7 Jan 2022 10:01:33 +0800 Kai-Heng Feng wrote:
> > > On device creation, udev can check if it now has both interfaces? If
> > > the internal interface is up, it is probably in use. Otherwise, take
> > > its MAC address and assign it to the dock interface, and give the
> > > internal interface a random MAC address, just in case.
> > >
> > > You probably need to delay NetworkManager, systemd-networkkd,
> > > /etc/network/interfaces etc, so that they don't do anything until
> > > after udevd has settled, indicating all devices have probably been
> > > found.
> >
> > I don't think it's a good idea. On my laptop,
> > systemd-udev-settle.service can add extra 5~10 seconds boot time
> > delay.
> > Furthermore, the external NIC in question is in a USB/Thunderbolt
> > dock, it can present pre-boot, or it can be hotplugged at any time.
>
> IIUC our guess is that this feature used for NAC and IEEE 802.1X.
> In that case someone is already provisioning certificates to all
> the machines, and must provide a config for all its interfaces.
> It should be pretty simple to also put the right MAC address override
> in the NetworkManager/systemd-networkd/whatever config, no?

If that's really the case, why do major OEMs came up with MAC
pass-through? Stupid may it be, I don't think it's a solution looking
for problem.

Kai-Heng