In vlan_insert_tag(), we insert a 4-byte VLAN header _after_
mac header:
memmove(skb->data, skb->data + VLAN_HLEN, 2 * ETH_ALEN);
...
veth->h_vlan_proto = htons(ETH_P_8021Q);
...
veth->h_vlan_TCI = htons(vlan_tci);
so after it, we should recompute the checksum to include these 4 bytes.
skb->data still points to the mac header, therefore VLAN header is at
(2 * ETH_ALEN = 12) bytes after it, not (ETH_HLEN = 14) bytes.
This can also be observed via tcpdump:
0x0000: ffff ffff ffff 5254 005d 6f6e 8100 000a
0x0010: 0806 0001 0800 0604 0001 5254 005d 6f6e
0x0020: c0a8 026e 0000 0000 0000 c0a8 0282
Similar for __pop_vlan_tci(), the vlan header we remove is the one
overwritten in:
memmove(skb->data + VLAN_HLEN, skb->data, 2 * ETH_ALEN);
Therefore the VLAN_HLEN = 4 bytes after 2 * ETH_ALEN is the part
we want to sub from checksum.
Cc: David S. Miller <davem@davemloft.net>
Cc: Jesse Gross <jesse@nicira.com>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
7b024082b2