netdev - Re: [PATCH net v2] bonding: pass link-local packets to bonding master also.

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Date:   Thu, 19 Jul 2018 18:20:20 +0200
From:   Michal Soltys <soltys@....info>
To:     Mahesh Bandewar <mahesh@...dewar.net>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Veaceslav Falico <vfalico@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     Netdev <netdev@...r.kernel.org>,
        Mahesh Bandewar <maheshb@...gle.com>
Subject: Re: [PATCH net v2] bonding: pass link-local packets to bonding master
 also.

On 07/19/2018 01:41 AM, Mahesh Bandewar wrote:
> From: Mahesh Bandewar <maheshb@...gle.com>
> 
> Commit b89f04c61efe ("bonding: deliver link-local packets with
> skb->dev set to link that packets arrived on") changed the behavior
> of how link-local-multicast packets are processed. The change in
> the behavior broke some legacy use cases where these packets are
> expected to arrive on bonding master device also.
> 
> This patch passes the packet to the stack with the link it arrived
> on as well as passes to the bonding-master device to preserve the
> legacy use case.
> 
> Fixes: b89f04c61efe ("bonding: deliver link-local packets with skb->dev set to link that packets arrived on")
> Reported-by: Michal Soltys <soltys@....info>
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
> ---
> v2: Added Fixes tag.
> v1: Initial patch.
>   drivers/net/bonding/bond_main.c | 17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 9a2ea3c1f949..1d3b7d8448f2 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -1177,9 +1177,22 @@ static rx_handler_result_t bond_handle_frame(struct sk_buff **pskb)
>   		}
>   	}
>   
> -	/* don't change skb->dev for link-local packets */
> -	if (is_link_local_ether_addr(eth_hdr(skb)->h_dest))
> +	/* Link-local multicast packets should be passed to the
> +	 * stack on the link they arrive as well as pass them to the
> +	 * bond-master device. These packets are mostly usable when
> +	 * stack receives it with the link on which they arrive
> +	 * (e.g. LLDP) but there may be some legacy behavior that
> +	 * expects these packets to appear on bonding master too.

I'd really change the comment from:

"These packets are mostly usable when stack receives it with the link on which 
they arrive (e.g. LLDP) but there may be some legacy behavior that expects 
these packets to appear on bonding master too."

to something like:

"These packets are mostly usable when stack receives it with the link on which 
they arrive, but they also must be available on aggregations. Some of the use 
cases include (but are not limited to): LLDP agents that must be able to 
operate both on enslaved interfaces as well as on bonds themselves; linux 
bridges that must be able to process/pass BPDUs from attached bonds when any 
kind of stp version is enabled on the network."

It's a bit longer, but clarifies the reasons more precisely (without going too 
deep into features like group_fwd_mask).