[Bridge] [PATCH v9 net-next 05/12] bridge: Add the ability to configure pvid

Vlad Yasevich vyasevic at redhat.com
Mon Feb 4 16:59:23 UTC 2013

On 02/03/2013 09:49 AM, Michał Mirosław wrote:
> 2013/2/2 Vlad Yasevich <vyasevic at redhat.com>:
>> On 02/01/2013 08:15 PM, Michał Mirosław wrote:
>>> 2013/2/2 Michał Mirosław <mirqus at gmail.com>:
>>>> 2013/2/1 Vlad Yasevich <vyasevic at redhat.com>:
>>>>> A user may designate a certain vlan as PVID.  This means that
>>>>> any ingress frame that does not contain a vlan tag is assigned to
>>>>> this vlan and any forwarding decisions are made with this vlan in mind.
>>>> [...]
>>>>>    struct net_port_vlans {
>>>>>           u16                             port_idx;
>>>>> +       u16                             pvid;
>>>> I'm confused about the implementation. I would expect pvid field in
>>>> net_bridge_port and adding a tag if it isn't there on ingress path.
>>>> The rest would be just like without PVIDs. But here you pvid field to
>>>> net_port_vlans, and don't do anything with it in receive nor transmit
>>>> path. Does it work? What am I missing?
>>> Found the answer in next patch (you should merge #5 and #6).
>> It was split for incremental testing.  #5 added the ability to set and
>> delete it without impacting anything.  #6 added the actual work that pvid
>> does.
>>> Still,
>>> the implementation looks overly complicated. If you force the packet
>>> to canonical form on ingress (keeping outer tag in skb->vlan_tci, and
>>> setting skb->vlan_tci = pvid if there is no tag) the code should get
>>> simpler.
>> What if there is no outer tag?  That's what the ingress code is doing.
>> If there is no outer tag, pvid is written to vlan_tci.  If there was
>> outer tag in vlan_tci, it's left alone.  This way at the end of ingress
>> vlan_tci is always set.
>> At egress, we grab that tag and compare it against pvid if any.  If it
>> matches, it's stripped.  If it doesn't, we output with the tag thus
>> adding the header.
>> The only thing I can simplify is grab the tci directly at egress, but
>> that's what the code will do anyway.
> ... br_allowed_input(..., struct sk_buff **pskb)
> {
>    *pskb = vlan_untag(*pskb);
>    skb = *pskb;
>    if (!skb)
>      return 0;
>    if (!skb->vlan_tci && (pvid & VLAN_TAG_PRESENT))
>      skb->vlan_tci = pvid;
>    return check_vlan_allowed(skb->vlan_tci);
> }

vlan_untag typically already happens for non-accelerated packets, so no 
need to call it again.  We shouldn't really be touching accelerated 
packets at ingress, because we may have to undo what we've done on 
egress.  That would be very expensive in case of flooding.

> struct sk_buff *br_handle_vlan(..., struct sk_buff *skb)
> {
>     /* we guaranteed in br_allowed_input() that all packets processed
> in bridge code
>      * will be like received with NETIF_F_HW_VLAN_RX feature enabled. */
>     if (skb->vlan_tci & (VLAN_VID_MASK|VLAN_TAG_PRESENT) == pvid)
>       skb->vlan_tci = 0;  // what about 802.1p?
>     return skb;
> }

This doesn't work for when you should be sending a tagged frame to the 
bridge device when receive was non-accelerated.  It would mean that the
802.1q header was already stripped, and you have to put it back 
correctly so that it can go through the vlan interface (think vlan on 
top of bridge).

> BTW, you implement three features: VLAN filtering, PVID handling,
> per-VLAN FDB. Yet there are 10 patches that mix and match parts of the
> implementation.

I've tried to separate them as well as I can.  I guess the only ones out
of order are 11 and 12.  12 is last on purpose since its contentious and 
can be easily dropped from the end.  I can and should move 11 in with 
main vlan filtering code.  Essentially 1-5 would be VLAN filtering, 5 & 
6 would be PVID, and the rest would FDB.

If you can see a better breakdown, I would appreciate it.


> It's really hard to review this when you have to jump
> between patches to understand whats going on. I don't know what the
> best split would be, but I got the feeling that this is not the
> presented one.
> Best Regards,
> Michał Mirosław

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