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-rw-r--r-- | Documentation/networking/tc-actions-env-rules.txt | 29 |
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diff --git a/Documentation/networking/tc-actions-env-rules.txt b/Documentation/networking/tc-actions-env-rules.txt new file mode 100644 index 000000000000..01e716d185f4 --- /dev/null +++ b/Documentation/networking/tc-actions-env-rules.txt | |||
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1 | |||
2 | The "enviromental" rules for authors of any new tc actions are: | ||
3 | |||
4 | 1) If you stealeth or borroweth any packet thou shalt be branching | ||
5 | from the righteous path and thou shalt cloneth. | ||
6 | |||
7 | For example if your action queues a packet to be processed later | ||
8 | or intentionaly branches by redirecting a packet then you need to | ||
9 | clone the packet. | ||
10 | There are certain fields in the skb tc_verd that need to be reset so we | ||
11 | avoid loops etc. A few are generic enough so much so that skb_act_clone() | ||
12 | resets them for you. So invoke skb_act_clone() rather than skb_clone() | ||
13 | |||
14 | 2) If you munge any packet thou shalt call pskb_expand_head in the case | ||
15 | someone else is referencing the skb. After that you "own" the skb. | ||
16 | You must also tell us if it is ok to munge the packet (TC_OK2MUNGE), | ||
17 | this way any action downstream can stomp on the packet. | ||
18 | |||
19 | 3) dropping packets you dont own is a nono. You simply return | ||
20 | TC_ACT_SHOT to the caller and they will drop it. | ||
21 | |||
22 | The "enviromental" rules for callers of actions (qdiscs etc) are: | ||
23 | |||
24 | *) thou art responsible for freeing anything returned as being | ||
25 | TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is | ||
26 | returned then all is great and you dont need to do anything. | ||
27 | |||
28 | Post on netdev if something is unclear. | ||
29 | |||