Hi,
I'm using the AF_PACKET socket with setsockopt(PACKET_AUXDATA) to get
the incoming VLAN tag. Correct me if I'm wrong, but as far as I see the
first VLAN tag is always stripped - either in hardware or in
net/core/dev.c in __netif_receive_skb_core() - and stored in
skb->vlan_tci. Therefore, it won't be in the packet data anymore.
If I use the socket with ETH_P_ALL as protocol, everything works as
expected. But if I'm using an actual protocol number, instead of the
catch all, the tp_vlan_tci field inside the auxdata will be zero. I've
traced this to commit d4b812dea4a236f729526facf97df1a9d18e191c (vlan:
mask vlan prio bits):
+ if (unlikely(vlan_tx_tag_present(skb))) {
+ if (vlan_tx_tag_get_id(skb))
+ skb->pkt_type = PACKET_OTHERHOST;
+ /* Note: we might in the future use prio bits
+ * and set skb->priority like in vlan_do_receive()
+ * For the time being, just ignore Priority Code Point
+ */
+ skb->vlan_tci = 0;
+ }
The ptype_all callbacks (which are working as expected) are before this
code and the ptype_specific callbacks (which are not working) are after
this piece of code. I don't know it this is a bug or not, I guess it is
one, at least from the AF_PACKET socket point of view. If not, how I'm
supposed to get the original VLAN tag with socket(AF_PACKET,
my_protocol)?
I also don't understand the commit (message) as the subject suggesets
only the prio bits should be masked, but with "skb->vlan_tci = 0"
everything is masked. Therefore, I've put the original (hopefully the
mail addresses are still valid) authors in CC.
Thanks,
-michael
