netdev - Re: [PATCH net-next 5/5] switchdev: update documentation for offload_fwd

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Date:	Thu, 9 Jul 2015 13:27:25 +0900
From:	Simon Horman <simon.horman@...ronome.com>
To:	sfeldma@...il.com
Cc:	netdev@...r.kernel.org, jiri@...nulli.us, roopa@...ulusnetworks.com
Subject: Re: [PATCH net-next 5/5] switchdev: update documentation for
 offload_fwd_mark

On Wed, Jul 08, 2015 at 04:16:43PM -0700, sfeldma@...il.com wrote:
> From: Scott Feldman <sfeldma@...il.com>
> 
> Signed-off-by: Scott Feldman <sfeldma@...il.com>
> ---
>  Documentation/networking/switchdev.txt |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/networking/switchdev.txt b/Documentation/networking/switchdev.txt
> index c5d7ade..b864e47 100644
> --- a/Documentation/networking/switchdev.txt
> +++ b/Documentation/networking/switchdev.txt
> @@ -279,8 +279,18 @@ and unknown unicast packets to all ports in domain, if allowed by port's
>  current STP state.  The switch driver, knowing which ports are within which
>  vlan L2 domain, can program the switch device for flooding.  The packet should
>  also be sent to the port netdev for processing by the bridge driver.  The
> -bridge should not reflood the packet to the same ports the device flooded.
> -XXX: the mechanism to avoid duplicate flood packets is being discuseed.
> +bridge should not reflood the packet to the same ports the device flooded,
> +otherwise there will be duplicate packets on the wire.
> +
> +To avoid duplicate packets, the device/driver can mark a packet as already

I wonder if  'should' or 'may' would be clearer than 'can'.

> +forwarded using skb->offload_fwd_mark.  The same mark is set on the device
> +ports in the domain using dev->offload_fwd_mark.  If the skb->offload_fwd_mark
> +is non-zero and matches the forwarding egress port's dev->skb_mark, the kernel
> +will drop the skb right before transmit on the egress port, with the
> +understanding that the device already forwarded the packet on same egress port.
> +The driver can use switchdev_port_fwd_mark_set() to set a globally unique mark
> +for port's dev->offload_fwd_mark, based on the port's parent ID (switch ID) and
> +a group ifindex.
>  
>  It is possible for the switch device to not handle flooding and push the
>  packets up to the bridge driver for flooding.  This is not ideal as the number
> -- 
> 1.7.10.4
> 
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