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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: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jamal Hadi Salim 2007-10-26 02:49:09 -07:00 committed by David S. Miller
parent a057ae3c10
commit d892afe2ca
1 changed files with 29 additions and 0 deletions
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29
Documentation/networking/tc-actions-env-rules.txt Normal file
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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.