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authorJamal Hadi Salim <hadi@cyberus.ca>2007-10-26 02:49:09 -0700
committerDavid S. Miller <davem@davemloft.net>2007-10-26 02:49:09 -0700
commitd892afe2ca905ddb00a4f16927c8b465cdd31b20 (patch)
treec15295f448a19046423bbb480fcfefe319f91928 /Documentation/networking/tc-actions-env-rules.txt
parenta057ae3c104dd2c661e55d2af37e70d168c65e00 (diff)
[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>
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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.
+