2) Do not forget to update netdev->trans_start to jiffies after
each new tx packet is given to the hardware.
-3) Do not forget that once you return 0 from your hard_start_xmit
+3) A hard_start_xmit method must not modify the shared parts of a
+ cloned SKB.
+
+4) Do not forget that once you return 0 from your hard_start_xmit
method, it is your driver's responsibility to free up the SKB
and in some finite amount of time.