Author: Jamal Hadi Salim <[EMAIL PROTECTED]>
AuthorDate: Fri Oct 26 02:49:09 2007 -0700
Committer: David S. Miller <[EMAIL PROTECTED]>
CommitDate: Fri Oct 26 02:49:09 2007 -0700
[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 <[EMAIL PROTECTED]>
Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
Documentation/networking/tc-actions-env-rules.txt | 29 +++++++++++++++++++++
1 files changed, 29 insertions(+), 0 deletions(-)
diff --git a/Documentation/networking/tc-actions-env-rules.txt
new file mode 100644
@@ -0,0 +1,29 @@
+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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