netdev - Re: [PATCH net] bridge: notify user space of fdb port change

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Date:	Wed, 14 May 2014 09:34:38 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	Jon Maxwell <jmaxwell37@...il.com>, stephen@...workplumber.org
CC:	davem@...emloft.net, vyasevic@...hat.com,
	bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jpirko@...hat.com,
	jmaxwell@...hat.com
Subject: Re: [PATCH net] bridge: notify user space of fdb port change

(2014/05/13 16:55), Jon Maxwell wrote:
> From: Jon Maxwell <jmaxwell37@...il.com>
> 
> There has been a number incidents recently where customers running KVM have 
> reported that VM hosts on different Hypervisors are unreachable. Based on 
> pcap traces we found that the bridge was broadcasting the ARP request out 
> onto the network. However some NICs have an inbuilt switch which on occasions 
> were broadcasting the VMs ARP request back through the physical NIC on the 
> Hypervisor. This resulted in the bridge changing ports and incorrectly learning
> that the VMs mac address was external. As a result the ARP reply was directed 
> back onto the external network and VM never updated it's ARP cache. This patch 
> will notify the bridge command to identify such port toggling.
> 
> Signed-off-by: Jon Maxwell <jmaxwell37@...il.com>
> ---
>  net/bridge/br_fdb.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
> index 9203d5a..37742e2 100644
> --- a/net/bridge/br_fdb.c
> +++ b/net/bridge/br_fdb.c
> @@ -507,6 +507,8 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
>  					source->dev->name);
>  		} else {
>  			/* fastpath: update of existing entry */
> +			if (source->port_no != fdb->dst->port_no)

It seems that we don't need to fetch port_no and it is enough to compare
source and fdb->dst.

> +				fdb_notify(br, fdb, RTM_NEWNEIGH);
>  			fdb->dst = source;
>  			fdb->updated = jiffies;
>  			if (unlikely(added_by_user))
> 

This notifies fdb entry before updating existing entry. Is this on purpose?
I think we should notify the updated fdb entry.
Similar code fdb_add_entry() does after updating it.

Also, isn't it better to move update of dst into "if" block?

	if (source != fdb->dst) {
		fdb->dst = source;
		modified = true;
	}
	...
	if (modified) ...

Thanks,
Toshiaki Makita
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