linux-kernel - Re: [PATCH RFC net-next 00/10] MC Flood disable and snooping

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Date: Sat, 6 Apr 2024 00:15:02 +0300
From: Vladimir Oltean <olteanv@...il.com>
To: Joseph Huang <joseph.huang.2024@...il.com>
Cc: Nikolay Aleksandrov <razor@...ckwall.org>,
	Joseph Huang <Joseph.Huang@...min.com>, netdev@...r.kernel.org,
	Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Roopa Prabhu <roopa@...dia.com>,
	Linus Lüssing <linus.luessing@...3.blue>,
	linux-kernel@...r.kernel.org, bridge@...ts.linux.dev
Subject: Re: [PATCH RFC net-next 00/10] MC Flood disable and snooping

On Fri, Apr 05, 2024 at 04:22:43PM -0400, Joseph Huang wrote:
> Like this?
> 
> bridge link set dev swp0 mcast_flood off
>   - all flooding disabled
> 
> bridge link set dev swp0 mcast_flood on
>   - all flooding enabled
> 
> bridge link set dev swp0 mcast_flood on mcast_ipv4_data_flood off
> mcast_ipv6_data_flood off
>   - IPv4 data packets flooding disabled, IPv6 data packets flooding
> disabled, everything else floods (that is to say, only allow IPv4 local
> subnet and IPv6 link-local to flood)
> 
> ?

Yeah.

> The syntax seems to be counterintuitive.
> 
> Or like this?
> 
> bridge link set dev swp0 mcast_flood on mcast_ipv4_ctrl_flood on
>   - only allow IPv4 local subnet to flood, everything else off
> 
> ?

Nope.

> So basically the question is, what should the behavior be when something is
> omitted from the command line?

The answer is always: "new options should default to behaving exactly
like before". It's not just about the command line arguments, but also
about the actual netlink attributes that iproute2 (and other tooling)
creates when communicating with the kernel. Old user space has no idea
about the existence of mcast_ipv4_ctrl_flood et. al. So, if netlink
attributes specifying their value are not sent by user space, their
value in the kernel must mimic the value of mcast_flood.