On Tue, Sep 28, 2010 at 04:39:59PM +0200, Arnd Bergmann wrote:

On Tuesday 28 September 2010, Michael S. Tsirkin wrote:

quoted

quoted

quoted

+   skb_reserve(skb, NET_IP_ALIGN);
+   skb_put(skb, len);
+
+   if (skb_copy_datagram_from_iovec(skb, 0, iov, 0, len)) {
+           kfree_skb(skb);
+           return -EAGAIN;
+   }
+
+   skb->protocol = eth_type_trans(skb, mp->dev);

Why are you calling eth_type_trans() on transmit?

So that GSO can work.  BTW macvtap does:

        skb_set_network_header(skb, ETH_HLEN);
        skb_reset_mac_header(skb);
        skb->protocol = eth_hdr(skb)->h_proto;

and I think this is broken for vlans. Arnd?

Hmm, that code (besides set_network_header) was added by Sridhar
for GSO support. I believe I originally did eth_type_trans but
had to change it before that time because it broke something.
Unfortunately, my memory on that is not very good any more.

Can you be more specific what the problem is? Do you think
it breaks when a guest sends VLAN tagged frames or when macvtap
is connected to a VLAN interface that adds another tag (or
only the combination)?

	Arnd

I expect the protocol value to be wrong when guest sends vlan tagged
frames as 802.1q frames have a different format.

-- 
MST