The "environmental" rules for authors of any new tc actions are:

  
  1) If you stealeth or borroweth any packet thou shalt be branching
  from the righteous path and thou shalt cloneth.

  For example if your action queues a packet to be processed later,
  or intentionally branches by redirecting a packet, then you need to

  clone the packet.

  There are certain fields in the skb tc_verd that need to be reset so we

  avoid loops, etc.  A few are generic enough that skb_act_clone()
  resets them for you, so invoke skb_act_clone() rather than skb_clone().

  
  2) If you munge any packet thou shalt call pskb_expand_head in the case
  someone else is referencing the skb. After that you "own" the skb.
  You must also tell us if it is ok to munge the packet (TC_OK2MUNGE),
  this way any action downstream can stomp on the packet.

  3) Dropping packets you don't own is a no-no. You simply return

  TC_ACT_SHOT to the caller and they will drop it.

  The "environmental" rules for callers of actions (qdiscs etc) are:

  *) Thou art responsible for freeing anything returned as being

  TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is

  returned, then all is great and you don't need to do anything.

  
  Post on netdev if something is unclear.