Commit d892afe2 authored by Jamal Hadi Salim's avatar Jamal Hadi Salim Committed by David S. Miller
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[NET]: Document some simple rules for actions 



This patch adds documentation on what is expected of an
action which branches away from the action-graph or when it
needs to trample on actins. It also describes what is expected of
users of such actions.

Signed-off-by: default avatarJamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a057ae3c

Documentation/networking/tc-actions-env-rules.txt

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The "enviromental" 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 intentionaly 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 so much so 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 dont own is a nono. You simply return

TC_ACT_SHOT to the caller and they will drop it.



The "enviromental" 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 dont need to do anything.



Post on netdev if something is unclear.