Ingo Oeser wrote:
> On Saturday 26 May 2007, Patrick McHardy wrote:
>
>>net/8021q ignores the VLAN header overhead, so we should probably do the
>>same here for consistency. Using IS_VLAN_IP (and IS_PPPOE_IP for current
>>-rc) looks fine, additionally we should probably also check for
>>skb->nfct != NULL to make sure that at least without connection tracking
>>the bridge doesn't perform fragmentation.
>
>
> And could we separe the conditions for that into a static helper function
> explaining each of these conditions? e.g. sth. like that:
The MTU checks are self-explanatory. Just a comment above the function
stating that it tries to find out whether a packet needs to be
refragmented because it was defragmented by IPv4 connection tracking
and exceeds the MTU should be enough.
> static bool br_nf_need_fragment(struct sk_buff *skb)
> {
> /* Plain IP packet does not fit in MTU */
> if (!(skb->protocol == htons(ETH_P_IP) && skb->len > skb->dev->mtu))
> return true;
>
> /* VLAN encapsulated IP packet does not fit in MTU */
> if (IS_VLAN_IP(skb) && skb->len > skb->dev->mtu - VLAN_HLEN)
> return true;
>
> /* PPPoE encapsulated IP packet does not fit in MTU */
> if (IS_PPPOE_IP(skb) && skb->len > skb->dev->mtu - PPPOE_SES_HLEN)
> return true;
>
> return false;
> }
As I said, I don't think we should account for the VLAN header overhead,
the VLAN code itself doesn't even do it. And we should exclude packets
that don't have a connection tracking reference attached since we are
only undoing the damage connection tracking did by defragmenting it
and should avoid fragmenting other packets as good as possible.
> and then br_nf_dev_queue_xmit() becomes:
>
> static int br_nf_dev_queue_xmit(struct sk_buff *skb)
> {
> if (br_nf_need_fragment(skb) && !skb_is_gso(skb))
> return ip_fragment(skb, br_dev_queue_push_xmit);
> else
> return br_dev_queue_push_xmit(skb);
> }
>
> which is much more readable, more documented and doesn't contain a condition monster :-)
>
> @Patrick: Could you check, wether the PPPoE case is correct?
It looks OK. But there is another problem, ip_fragment doesn't care
about the PPPoE overhead and produces a packet that will be too large
after restoring the PPPoE header. A second __fake_rtable that accounts
for the PPPoE overhead could probably fix that ..
> What do you think? Should I submit a patch for that?
Sure :)
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