netdev - Re: [PATCH 2/5] net: bridge: Implement bridge flood flag

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Date:   Thu, 17 Mar 2022 12:39:12 +0100
From:   Mattias Forsblad <mattias.forsblad@...il.com>
To:     Joachim Wiberg <troglobit@...il.com>, netdev@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Tobias Waldekranz <tobias@...dekranz.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Vladimir Oltean <olteanv@...il.com>
Subject: Re: [PATCH 2/5] net: bridge: Implement bridge flood flag

On 2022-03-17 10:07, Joachim Wiberg wrote:
> On Thu, Mar 17, 2022 at 07:50, Mattias Forsblad <mattias.forsblad@...il.com> wrote:
>> This patch implements the bridge flood flags. There are three different
>> flags matching unicast, multicast and broadcast. When the corresponding
>> flag is cleared packets received on bridge ports will not be flooded
>> towards the bridge.
> 
> If I've not completely misunderstood things, I believe the flood and
> mcast_flood flags operate on unknown unicast and multicast.  With that
> in mind I think the hot path in br_input.c needs a bit more eyes.  I'll
> add my own comments below.
> 
> Happy incident I saw this patch set, I have a very similar one for these
> flags to the bridge itself, with the intent to improve handling of all
> classes of multicast to/from the bridge itself.
> 
>> [snip]
>> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
>> index e0c13fcc50ed..fcb0757bfdcc 100644
>> --- a/net/bridge/br_input.c
>> +++ b/net/bridge/br_input.c
>> @@ -109,11 +109,12 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
>>  		/* by definition the broadcast is also a multicast address */
>>  		if (is_broadcast_ether_addr(eth_hdr(skb)->h_dest)) {
>>  			pkt_type = BR_PKT_BROADCAST;
>> -			local_rcv = true;
>> +			local_rcv = true && br_opt_get(br, BROPT_BCAST_FLOOD);
> 
> Minor comment, I believe the preferred style is more like this:
> 
> 	if (br_opt_get(br, BROPT_BCAST_FLOOD))
>         	local_rcv = true;
> 
>>  		} else {
>>  			pkt_type = BR_PKT_MULTICAST;
>> -			if (br_multicast_rcv(&brmctx, &pmctx, vlan, skb, vid))
>> -				goto drop;
>> +			if (br_opt_get(br, BROPT_MCAST_FLOOD))
>> +				if (br_multicast_rcv(&brmctx, &pmctx, vlan, skb, vid))
>> +					goto drop;
> 
> Since the BROPT_MCAST_FLOOD flag should only control uknown multicast,
> we cannot bypass the call to br_multicast_rcv(), which helps with the
> classifcation.  E.g., we want IGMP/MLD reports to be forwarded to all
> router ports, while the mdb lookup (below) is what an tell us if we
> have uknown multicast and there we can check the BROPT_MCAST_FLOOD
> flag for the bridge itself.

The original flag was name was local_receive to separate it from being
mistaken for the flood unknown flags. However the comment I've got was
to align it with the existing (port) flags. These flags have nothing to do with
the port flood unknown flags. Imagine the setup below:

           vlan1
             |
            br0             br1
           /   \           /   \
         swp1 swp2       swp3 swp4

We want to have swp1/2 as member of a normal vlan filtering bridge br0 /w learning on. 
On br1 we want to just forward packets between swp3/4 and disable learning. 
Additional we don't want this traffic to impact the CPU. 
If we disable learning on swp3/4 all traffic will be unknown and if we also 
have flood unknown on the CPU-port because of requirements for br0 it will
impact the traffic to br1. Thus we want to restrict traffic between swp3/4<->CPU port
with the help of the PVT.

/Mattias