we used to handle the vlan tag etc insertion very very very late,

we used to handle the vlan tag etc insertion very very very late,
on al already ass embed ethernet frame, which meant:
-copy (most of) the existing ethernet header into a ether_vlan_header
on the stack
-fill the extra fields in ether_vlan_header
-set the ether type
-m_adj() to make room for the extra space ether_vlan_header needs
-m_copyback the ether_vlan_header into the mbuf
that involves moving data around, which isn't all that cheap.
cleaner & easier to have ether_output prepend the ether_vlan_header instead
of the regular ethernet header, which makes the vlan tagging essentially
free in most cases.
help & ok reyk, naddy; waste of time bikeshedding tech@