Re: [Bridge] RFC: [PATCH] bridge vlan integration

[Ben Greear <greearb@candelatech.com>]

Andy Gospodarek wrote:
> On 9/11/06, David Kimdon <david.kimdon@devicescape.com> wrote:
>> Hi,
>>
>> The attached patches enables the bridge to filter and forward packets
>> according to their IEEE 802.1q headers.  The goals behind this change
>> include :
>>
>> - Enable running STP on 802.1q tagged networks.  STP packets
>>   must be untagged.  It isn't obvious how else to enable STP
>>   with the current bridge and vlan code.
>> - Add native support for an untagged vlan.  Currently an untagged
>>   vlan can be implimented using ebtables or similar.
>> - On devices bridging a large number of interfaces across various
>>   vlans this significantly simplifies configuration and, depending on
>>   configuration, can improve performance.
>>
>> Comments appreciated,
>>
>> David
> 
> 
> David,
> 
> It looks like this code specifically ignores (which is OK for now) and
> clears (which is not OK) the frame's 802.1p priority.  Have you tested
> priority-tagged frames to see if they are passed correctly?  It seems
> like you should consider adding another field to the sk_buff structure
> so priority of the incoming frame can be tracked as well as add logic
> to br_vlan_output_frame and br_vlan_input_frame so the tag is saved.
> Something like this would probably be fine:
> 
> Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
> 
> --- ./include/linux/skbuff.h.gospo      2006-09-11 14:41:54.000000000 -0400
> +++ ./include/linux/skbuff.h    2006-09-11 14:43:27.000000000 -0400
> @@ -297,6 +297,7 @@ struct sk_buff {
>         __u32                   nfmark;
>  #endif /* CONFIG_NETFILTER */
>  #ifdef CONFIG_BRIDGE_VLAN
> +       unsigned int            vlan_priority;
>         unsigned int            vlan;
>  #endif

SKB bloat is not good for performance.  You can store the priority and the VID in
a single 32-bit number with room to spare...

The skb->priority is also a possible place to store the VLAN priority.

The actual VLAN code has a mapping from vlan-priority -> skb priority on ingress,
and another mapping of skb->priority -> vlan-priority on egress.  You probably
don't need to worry about this mapping for a bridge, however.

Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com