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Document some simple rules for actions

PATCH Applied jamal 2 participants 2 messages Oct 21, 2007 – Oct 26, 2007

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PATCH 3/3 Document some simple rules for actions

Against net-2.6

cheers,
jamal

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From 553443b79e997afcc13f305f011b129dea9d8bde Mon Sep 17 00:00:00 2001

From: Jamal Hadi Salim <[email protected]>
Date: Sun, 21 Oct 2007 15:05:28 -0400
Subject: [PATCH 3/3] [NET_DOC] 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.

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 Documentation/networking/tc-actions-env-rules.txt |   29 +++++++++++++++++++++
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Documentation/networking/tc-actions-env-rules.txt new file +29 -0
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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.
+
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