netdev - Re: [RFC net-next (resend) 2/4] net: bridge: send notification for roaming hosts

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Message-ID: <93e02466-b4a0-48fd-beb0-c93b1008ff08@lunn.ch>
Date: Fri, 8 Nov 2024 14:42:18 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Elliot Ayrey <elliot.ayrey@...iedtelesis.co.nz>
Cc: "David S . Miller" <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Roopa Prabhu <roopa@...dia.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, bridge@...ts.linux.dev
Subject: Re: [RFC net-next (resend) 2/4] net: bridge: send notification for
 roaming hosts

> This is achieved by temporarily updating the fdb entry with the new
> port, setting a new notify roaming bit, firing off a notification, and
> restoring the original port immediately afterwards. The port remains
> unchanged, respecting the sticky flag, but userspace is now notified
> of the new port the host was seen on.

This sounds a bit hacky. Could you add a new optional attribute to the
netlink message indicating the roam destination, so there is no need
to play games with the actual port?

I'm not too deep into how these all works, but i also wounder about
backwards compatibility. Old code which does not look for
FDB_NOTIFY_ROAMING_BIT is going to think it really has moved, with
your code. By using a new attribute, and not changing the port, old
code just sees a notification it is on the port it always was on,
which is less likely to cause issues?

And do we want to differentiate between it wants to roam, but the
sticky bit has stopped that, and it really has roamed?

	Andrew