Re: [PATCH net-next RFC v2] switchdev: bridge: drop hardware forwarded packets

[Scott Feldman <sfeldma@gmail.com>]

On Fri, Mar 20, 2015 at 9:58 AM,  <roopa@cumulusnetworks.com> wrote:
> From: Roopa Prabhu <roopa@cumulusnetworks.com>
>
> On a Linux bridge with bridge forwarding offloaded to switch ASIC,
> there is a need to not re-forward frames that have already been
> forwarded in hardware.
>
> Typically these are broadcast or multicast frames forwarded by the
> hardware to multiple destination ports including sending a copy of
> the packet to the cpu (kernel e.g. an arp broadcast).
> The bridge driver will try to forward the packet again, resulting in
> two copies of the same packet.
>
> These packets can also come up to the kernel for logging when they hit
> a LOG acl rule in hardware. In such cases, you do want the packet
> to go through the bridge netfilter hooks. Hence, this patch adds the
> required checks just before the packet is being xmited.
>
> v2:
>         - Add a new hw_fwded flag in skbuff to indicate that the packet
>         is already hardware forwarded. Switch driver will set this flag.
>         I have been trying to avoid having this flag in the skb
>         and thats why this patch has been in my tree for long. Cant think
>         of other better alternatives. Suggestions are welcome. I have put
>         this under CONFIG_NET_SWITCHDEV to minimize the impact.
>
> Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
> Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>
> ---
>  include/linux/skbuff.h  |    7 +++++--
>  net/bridge/br_forward.c |   11 +++++++++++
>  2 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index bba1330..1973b5c 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -560,8 +560,11 @@ struct sk_buff {
>                                 fclone:2,
>                                 peeked:1,
>                                 head_frag:1,
> -                               xmit_more:1;
> -       /* one bit hole */
> +                               xmit_more:1,
> +#ifdef CONFIG_NET_SWITCHDEV
> +                               hw_fwded:1;
> +#endif
> +       /* one bit hole if CONFIG_NET_SWITCHDEV not defined */

Did you want this flag not copied in __copy_skb_header()?  Seems those
flags are special cased.  There is room for a bit here:

#ifdef CONFIG_IPV6_NDISC_NODETYPE
        __u8                    ndisc_nodetype:2;
#endif
        __u8                    ipvs_property:1;
        __u8                    inner_protocol_type:1;
        __u8                    remcsum_offload:1;
        /* 3 or 5 bit hole */
         <<<<<<<<

>         kmemcheck_bitfield_end(flags1);
>
>         /* fields enclosed in headers_start/headers_end are copied
> diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
> index 3304a54..b60b96e 100644
> --- a/net/bridge/br_forward.c
> +++ b/net/bridge/br_forward.c
> @@ -37,6 +37,17 @@ static inline int should_deliver(const struct net_bridge_port *p,
>
>  int br_dev_queue_push_xmit(struct sk_buff *skb)
>  {
> +
> +#ifdef CONFIG_NET_SWITCHDEV
> +       /* If skb is already hw forwarded and the port being forwarded
> +        * to is a switch port, dont reforward
> +        */
> +       if (skb->hw_fwded && (skb->dev->features & NETIF_F_HW_SWITCH_OFFLOAD)) {

The  check for skb->dev->features & NETIF_F_HW_SWITCH_OFFLOAD is redundant.

> +               kfree_skb(skb);
> +               return 0;
> +       }
> +
> +#endif
>         if (!is_skb_forwardable(skb->dev, skb)) {
>                 kfree_skb(skb);
>         } else {
> --
> 1.7.10.4
>