Dave Johnson wrote:
+/* VLAN rx hw acceleration helper. This acts like netif_{rx,receive_skb}(). */
+static inline int __vlan_hwaccel_rx(struct sk_buff *skb,
+ struct vlan_group *grp,
+ unsigned short vlan_tag, int polling)
+{
...
+ /* Driver removed vlan tag from the packet, but we have no
+ * vlan device for this VID.
+ *
+ * This can occur for 2 reasons:
+ * 1) Have a vlan group, we want some VIDs, just not this VID.
+ * 2) Have no vlan group, but hardware limitation requires it
+ * to remove vlan tags anyway.
+ *
+ * Normally if no vlan group is configured, the underlying
+ * driver will configure the hardware to NOT strip out the
+ * vlan tag. It can then call netif_receive_skb/netif_rx
+ * with the vlan tag still intact. However some devices
+ * cannot be configured to keep the vlan tag and must not
+ * call netif_receive_skb/netif_rx with the vlan tag
+ * missing. This would allow the normal protocol handlers
+ * to process this tagged packet as if it arived without a
+ * vlan tag.
+ *
+ * We need to re-add the TAG and hand the packet off to the
+ * base device with the TAG present so any protocol handlers
+ * (PF_PACKET, etc...) will get a chance to see it.
+ */
This looks like a rather expensive operation for the unlikely case
that packets will be received by a packet socket. IMO it should only
be reconstructed if actually needed, by af_packet itself.
As we discussed some time back storing the VLAN tag in the CB on
TX clashes with other users of the CB like qdiscs, so we need a
new field in the skb for this anyway.
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