[deliverable/linux.git] / Documentation / networking / tc-actions-env-rules.txt


The "environmental" 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 intentionally 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 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.

3) Dropping packets you don't own is a no-no. You simply return
TC_ACT_SHOT to the caller and they will drop it.

The "environmental" 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 don't need to do anything.

Post on netdev if something is unclear.
Commit	Line	Data
d892afe2	1
25985edc	2	The "environmental" rules for authors of any new tc actions are:
d892afe2 JHS	3
	4	1) If you stealeth or borroweth any packet thou shalt be branching
	5	from the righteous path and thou shalt cloneth.
	6
d9195881 ML	7	For example if your action queues a packet to be processed later,
d9195881 ML	8	or intentionally branches by redirecting a packet, then you need to
d892afe2	9	clone the packet.
d9195881	10
d892afe2	11	There are certain fields in the skb tc_verd that need to be reset so we
d9195881 ML	12	avoid loops, etc. A few are generic enough that skb_act_clone()
d9195881 ML	13	resets them for you, so invoke skb_act_clone() rather than skb_clone().
d892afe2 JHS	14
	15	2) If you munge any packet thou shalt call pskb_expand_head in the case
	16	someone else is referencing the skb. After that you "own" the skb.
d892afe2	17
d9195881	18	3) Dropping packets you don't own is a no-no. You simply return
d892afe2 JHS	19	TC_ACT_SHOT to the caller and they will drop it.
d892afe2 JHS	20
25985edc	21	The "environmental" rules for callers of actions (qdiscs etc) are:
d892afe2	22
d9195881	23	*) Thou art responsible for freeing anything returned as being
d892afe2	24	TC_ACT_SHOT/STOLEN/QUEUED. If none of TC_ACT_SHOT/STOLEN/QUEUED is
d9195881	25	returned, then all is great and you don't need to do anything.
d892afe2 JHS	26
	27	Post on netdev if something is unclear.
	28